SCons 2.3.3

User Guide

Steven Knight and the SCons Development Team

Steven Knight

version 2.3.3

SCons User's Guide Copyright (c) 2004, 2005, 2006, 2007 Steven Knight

2004 - 2014


Table of Contents

Preface
1. SCons Principles
2. A Caveat About This Guide's Completeness
3. Acknowledgements
4. Contact
1. Building and Installing SCons
1.1. Installing Python
1.2. Installing SCons From Pre-Built Packages
1.2.1. Installing SCons on Red Hat (and Other RPM-based) Linux Systems
1.2.2. Installing SCons on Debian Linux Systems
1.2.3. Installing SCons on Windows Systems
1.3. Building and Installing SCons on Any System
1.3.1. Building and Installing Multiple Versions of SCons Side-by-Side
1.3.2. Installing SCons in Other Locations
1.3.3. Building and Installing SCons Without Administrative Privileges
2. Simple Builds
2.1. Building Simple C / C++ Programs
2.2. Building Object Files
2.3. Simple Java Builds
2.4. Cleaning Up After a Build
2.5. The SConstruct File
2.5.1. SConstruct Files Are Python Scripts
2.5.2. SCons Functions Are Order-Independent
2.6. Making the SCons Output Less Verbose
3. Less Simple Things to Do With Builds
3.1. Specifying the Name of the Target (Output) File
3.2. Compiling Multiple Source Files
3.3. Making a list of files with Glob
3.4. Specifying Single Files Vs. Lists of Files
3.5. Making Lists of Files Easier to Read
3.6. Keyword Arguments
3.7. Compiling Multiple Programs
3.8. Sharing Source Files Between Multiple Programs
4. Building and Linking with Libraries
4.1. Building Libraries
4.1.1. Building Libraries From Source Code or Object Files
4.1.2. Building Static Libraries Explicitly: the StaticLibrary Builder
4.1.3. Building Shared (DLL) Libraries: the SharedLibrary Builder
4.2. Linking with Libraries
4.3. Finding Libraries: the $LIBPATH Construction Variable
5. Node Objects
5.1. Builder Methods Return Lists of Target Nodes
5.2. Explicitly Creating File and Directory Nodes
5.3. Printing Node File Names
5.4. Using a Node's File Name as a String
5.5. GetBuildPath: Getting the Path From a Node or String
6. Dependencies
6.1. Deciding When an Input File Has Changed: the Decider Function
6.1.1. Using MD5 Signatures to Decide if a File Has Changed
6.1.2. Using Time Stamps to Decide If a File Has Changed
6.1.3. Deciding If a File Has Changed Using Both MD Signatures and Time Stamps
6.1.4. Writing Your Own Custom Decider Function
6.1.5. Mixing Different Ways of Deciding If a File Has Changed
6.2. Older Functions for Deciding When an Input File Has Changed
6.2.1. The SourceSignatures Function
6.2.2. The TargetSignatures Function
6.3. Implicit Dependencies: The $CPPPATH Construction Variable
6.4. Caching Implicit Dependencies
6.4.1. The --implicit-deps-changed Option
6.4.2. The --implicit-deps-unchanged Option
6.5. Explicit Dependencies: the Depends Function
6.6. Dependencies From External Files: the ParseDepends Function
6.7. Ignoring Dependencies: the Ignore Function
6.8. Order-Only Dependencies: the Requires Function
6.9. The AlwaysBuild Function
7. Environments
7.1. Using Values From the External Environment
7.2. Construction Environments
7.2.1. Creating a Construction Environment: the Environment Function
7.2.2. Fetching Values From a Construction Environment
7.2.3. Expanding Values From a Construction Environment: the subst Method
7.2.4. Handling Problems With Value Expansion
7.2.5. Controlling the Default Construction Environment: the DefaultEnvironment Function
7.2.6. Multiple Construction Environments
7.2.7. Making Copies of Construction Environments: the Clone Method
7.2.8. Replacing Values: the Replace Method
7.2.9. Setting Values Only If They're Not Already Defined: the SetDefault Method
7.2.10. Appending to the End of Values: the Append Method
7.2.11. Appending Unique Values: the AppendUnique Method
7.2.12. Appending to the Beginning of Values: the Prepend Method
7.2.13. Prepending Unique Values: the PrependUnique Method
7.3. Controlling the Execution Environment for Issued Commands
7.3.1. Propagating PATH From the External Environment
7.3.2. Adding to PATH Values in the Execution Environment
8. Automatically Putting Command-line Options into their Construction Variables
8.1. Merging Options into the Environment: the MergeFlags Function
8.2. Separating Compile Arguments into their Variables: the ParseFlags Function
8.3. Finding Installed Library Information: the ParseConfig Function
9. Controlling Build Output
9.1. Providing Build Help: the Help Function
9.2. Controlling How SCons Prints Build Commands: the $*COMSTR Variables
9.3. Providing Build Progress Output: the Progress Function
9.4. Printing Detailed Build Status: the GetBuildFailures Function
10. Controlling a Build From the Command Line
10.1. Command-Line Options
10.1.1. Not Having to Specify Command-Line Options Each Time: the SCONSFLAGS Environment Variable
10.1.2. Getting Values Set by Command-Line Options: the GetOption Function
10.1.3. Setting Values of Command-Line Options: the SetOption Function
10.1.4. Strings for Getting or Setting Values of SCons Command-Line Options
10.1.5. Adding Custom Command-Line Options: the AddOption Function
10.2. Command-Line variable=value Build Variables
10.2.1. Controlling Command-Line Build Variables
10.2.2. Providing Help for Command-Line Build Variables
10.2.3. Reading Build Variables From a File
10.2.4. Pre-Defined Build Variable Functions
10.2.5. Adding Multiple Command-Line Build Variables at Once
10.2.6. Handling Unknown Command-Line Build Variables: the UnknownVariables Function
10.3. Command-Line Targets
10.3.1. Fetching Command-Line Targets: the COMMAND_LINE_TARGETS Variable
10.3.2. Controlling the Default Targets: the Default Function
10.3.3. Fetching the List of Build Targets, Regardless of Origin: the BUILD_TARGETS Variable
11. Installing Files in Other Directories: the Install Builder
11.1. Installing Multiple Files in a Directory
11.2. Installing a File Under a Different Name
11.3. Installing Multiple Files Under Different Names
12. Platform-Independent File System Manipulation
12.1. Copying Files or Directories: The Copy Factory
12.2. Deleting Files or Directories: The Delete Factory
12.3. Moving (Renaming) Files or Directories: The Move Factory
12.4. Updating the Modification Time of a File: The Touch Factory
12.5. Creating a Directory: The Mkdir Factory
12.6. Changing File or Directory Permissions: The Chmod Factory
12.7. Executing an action immediately: the Execute Function
13. Controlling Removal of Targets
13.1. Preventing target removal during build: the Precious Function
13.2. Preventing target removal during clean: the NoClean Function
13.3. Removing additional files during clean: the Clean Function
14. Hierarchical Builds
14.1. SConscript Files
14.2. Path Names Are Relative to the SConscript Directory
14.3. Top-Level Path Names in Subsidiary SConscript Files
14.4. Absolute Path Names
14.5. Sharing Environments (and Other Variables) Between SConscript Files
14.5.1. Exporting Variables
14.5.2. Importing Variables
14.5.3. Returning Values From an SConscript File
15. Separating Source and Build Directories
15.1. Specifying a Variant Directory Tree as Part of an SConscript Call
15.2. Why SCons Duplicates Source Files in a Variant Directory Tree
15.3. Telling SCons to Not Duplicate Source Files in the Variant Directory Tree
15.4. The VariantDir Function
15.5. Using VariantDir With an SConscript File
15.6. Using Glob with VariantDir
16. Variant Builds
17. Internationalization and localization with gettext
17.1. Prerequisites
17.2. Simple project
18. Writing Your Own Builders
18.1. Writing Builders That Execute External Commands
18.2. Attaching a Builder to a Construction Environment
18.3. Letting SCons Handle The File Suffixes
18.4. Builders That Execute Python Functions
18.5. Builders That Create Actions Using a Generator
18.6. Builders That Modify the Target or Source Lists Using an Emitter
18.7. Where To Put Your Custom Builders and Tools
19. Not Writing a Builder: the Command Builder
20. Pseudo-Builders: the AddMethod function
21. Writing Scanners
21.1. A Simple Scanner Example
21.2. Adding a search path to a scanner: FindPathDirs
22. Building From Code Repositories
22.1. The Repository Method
22.2. Finding source files in repositories
22.3. Finding #include files in repositories
22.3.1. Limitations on #include files in repositories
22.4. Finding the SConstruct file in repositories
22.5. Finding derived files in repositories
22.6. Guaranteeing local copies of files
23. Multi-Platform Configuration (Autoconf Functionality)
23.1. Configure Contexts
23.2. Checking for the Existence of Header Files
23.3. Checking for the Availability of a Function
23.4. Checking for the Availability of a Library
23.5. Checking for the Availability of a typedef
23.6. Checking the size of a datatype
23.7. Adding Your Own Custom Checks
23.8. Not Configuring When Cleaning Targets
24. Caching Built Files
24.1. Specifying the Shared Cache Directory
24.2. Keeping Build Output Consistent
24.3. Not Using the Shared Cache for Specific Files
24.4. Disabling the Shared Cache
24.5. Populating a Shared Cache With Already-Built Files
24.6. Minimizing Cache Contention: the --random Option
25. Alias Targets
26. Java Builds
26.1. Building Java Class Files: the Java Builder
26.2. How SCons Handles Java Dependencies
26.3. Building Java Archive (.jar) Files: the Jar Builder
26.4. Building C Header and Stub Files: the JavaH Builder
26.5. Building RMI Stub and Skeleton Class Files: the RMIC Builder
27. Miscellaneous Functionality
27.1. Verifying the Python Version: the EnsurePythonVersion Function
27.2. Verifying the SCons Version: the EnsureSConsVersion Function
27.3. Explicitly Terminating SCons While Reading SConscript Files: the Exit Function
27.4. Searching for Files: the FindFile Function
27.5. Handling Nested Lists: the Flatten Function
27.6. Finding the Invocation Directory: the GetLaunchDir Function
28. Troubleshooting
28.1. Why is That Target Being Rebuilt? the --debug=explain Option
28.2. What's in That Construction Environment? the Dump Method
28.3. What Dependencies Does SCons Know About? the --tree Option
28.4. How is SCons Constructing the Command Lines It Executes? the --debug=presub Option
28.5. Where is SCons Searching for Libraries? the --debug=findlibs Option
28.6. Where is SCons Blowing Up? the --debug=stacktrace Option
28.7. How is SCons Making Its Decisions? the --taskmastertrace Option
28.8. Watch SCons prepare targets for building: the --debug=prepare Option
28.9. Why is a file disappearing? the --debug=duplicate Option
A. Construction Variables
B. Builders
C. Tools
D. Functions and Environment Methods
E. Handling Common Tasks

List of Examples

E.1. Wildcard globbing to create a list of filenames
E.2. Filename extension substitution
E.3. Appending a path prefix to a list of filenames
E.4. Substituting a path prefix with another one
E.5. Filtering a filename list to exclude/retain only a specific set of extensions
E.6. The "backtick function": run a shell command and capture the output
E.7. Generating source code: how code can be generated and used by SCons

Preface

Thank you for taking the time to read about SCons. SCons is a next-generation software construction tool, or make tool--that is, a software utility for building software (or other files) and keeping built software up-to-date whenever the underlying input files change.

The most distinctive thing about SCons is that its configuration files are actually scripts, written in the Python programming language. This is in contrast to most alternative build tools, which typically invent a new language to configure the build. SCons still has a learning curve, of course, because you have to know what functions to call to set up your build properly, but the underlying syntax used should be familiar to anyone who has ever looked at a Python script.

Paradoxically, using Python as the configuration file format makes SCons easier for non-programmers to learn than the cryptic languages of other build tools, which are usually invented by programmers for other programmers. This is in no small part due to the consistency and readability that are hallmarks of Python. It just so happens that making a real, live scripting language the basis for the configuration files makes it a snap for more accomplished programmers to do more complicated things with builds, as necessary.

1. SCons Principles

There are a few overriding principles we try to live up to in designing and implementing SCons:

Correctness

First and foremost, by default, SCons guarantees a correct build even if it means sacrificing performance a little. We strive to guarantee the build is correct regardless of how the software being built is structured, how it may have been written, or how unusual the tools are that build it.

Performance

Given that the build is correct, we try to make SCons build software as quickly as possible. In particular, wherever we may have needed to slow down the default SCons behavior to guarantee a correct build, we also try to make it easy to speed up SCons through optimization options that let you trade off guaranteed correctness in all end cases for a speedier build in the usual cases.

Convenience

SCons tries to do as much for you out of the box as reasonable, including detecting the right tools on your system and using them correctly to build the software.

In a nutshell, we try hard to make SCons just "do the right thing" and build software correctly, with a minimum of hassles.

2. A Caveat About This Guide's Completeness

One word of warning as you read through this Guide: Like too much Open Source software out there, the SCons documentation isn't always kept up-to-date with the available features. In other words, there's a lot that SCons can do that isn't yet covered in this User's Guide. (Come to think of it, that also describes a lot of proprietary software, doesn't it?)

Although this User's Guide isn't as complete as we'd like it to be, our development process does emphasize making sure that the SCons man page is kept up-to-date with new features. So if you're trying to figure out how to do something that SCons supports but can't find enough (or any) information here, it would be worth your while to look at the man page to see if the information is covered there. And if you do, maybe you'd even consider contributing a section to the User's Guide so the next person looking for that information won't have to go through the same thing...?

3. Acknowledgements

SCons would not exist without a lot of help from a lot of people, many of whom may not even be aware that they helped or served as inspiration. So in no particular order, and at the risk of leaving out someone:

First and foremost, SCons owes a tremendous debt to Bob Sidebotham, the original author of the classic Perl-based Cons tool which Bob first released to the world back around 1996. Bob's work on Cons classic provided the underlying architecture and model of specifying a build configuration using a real scripting language. My real-world experience working on Cons informed many of the design decisions in SCons, including the improved parallel build support, making Builder objects easily definable by users, and separating the build engine from the wrapping interface.

Greg Wilson was instrumental in getting SCons started as a real project when he initiated the Software Carpentry design competition in February 2000. Without that nudge, marrying the advantages of the Cons classic architecture with the readability of Python might have just stayed no more than a nice idea.

The entire SCons team have been absolutely wonderful to work with, and SCons would be nowhere near as useful a tool without the energy, enthusiasm and time people have contributed over the past few years. The "core team" of Chad Austin, Anthony Roach, Bill Deegan, Charles Crain, Steve Leblanc, Greg Noel, Gary Oberbrunner, Greg Spencer and Christoph Wiedemann have been great about reviewing my (and other) changes and catching problems before they get in the code base. Of particular technical note: Anthony's outstanding and innovative work on the tasking engine has given SCons a vastly superior parallel build model; Charles has been the master of the crucial Node infrastructure; Christoph's work on the Configure infrastructure has added crucial Autoconf-like functionality; and Greg has provided excellent support for Microsoft Visual Studio.

Special thanks to David Snopek for contributing his underlying "Autoscons" code that formed the basis of Christoph's work with the Configure functionality. David was extremely generous in making this code available to SCons, given that he initially released it under the GPL and SCons is released under a less-restrictive MIT-style license.

Thanks to Peter Miller for his splendid change management system, Aegis, which has provided the SCons project with a robust development methodology from day one, and which showed me how you could integrate incremental regression tests into a practical development cycle (years before eXtreme Programming arrived on the scene).

And last, thanks to Guido van Rossum for his elegant scripting language, which is the basis not only for the SCons implementation, but for the interface itself.

4. Contact

The best way to contact people involved with SCons, including the author, is through the SCons mailing lists.

If you want to ask general questions about how to use SCons send email to scons-users@scons.org.

If you want to contact the SCons development community directly, send email to scons-dev@scons.org.

If you want to receive announcements about SCons, join the low-volume announce@scons.tigris.org mailing list.

Chapter 1. Building and Installing SCons

This chapter will take you through the basic steps of installing SCons on your system, and building SCons if you don't have a pre-built package available (or simply prefer the flexibility of building it yourself). Before that, however, this chapter will also describe the basic steps involved in installing Python on your system, in case that is necessary. Fortunately, both SCons and Python are very easy to install on almost any system, and Python already comes installed on many systems.

1.1. Installing Python

Because SCons is written in Python, you must obviously have Python installed on your system to use SCons. Before you try to install Python, you should check to see if Python is already available on your system by typing python -V (capital 'V') or python --version at your system's command-line prompt.

$ python -V
Python 2.5.1
    

And on a Windows system with Python installed:

C:\>python -V
Python 2.5.1
    

If Python is not installed on your system, you will see an error message stating something like "command not found" (on UNIX or Linux) or "'python' is not recognized as an internal or external command, operable progam or batch file" (on Windows). In that case, you need to install Python before you can install SCons.

The standard location for information about downloading and installing Python is http://www.python.org/download/. See that page for information about how to download and install Python on your system.

SCons will work with any 2.x version of Python from 2.7 on; 3.0 and later are not yet supported. If you need to install Python and have a choice, we recommend using the most recent 2.x Python version available. Newer Pythons have significant improvements that help speed up the performance of SCons.

1.2. Installing SCons From Pre-Built Packages

SCons comes pre-packaged for installation on a number of systems, including Linux and Windows systems. You do not need to read this entire section, you should need to read only the section appropriate to the type of system you're running on.

1.2.1. Installing SCons on Red Hat (and Other RPM-based) Linux Systems

SCons comes in RPM (Red Hat Package Manager) format, pre-built and ready to install on Red Hat Linux, Fedora, or any other Linux distribution that uses RPM. Your distribution may already have an SCons RPM built specifically for it; many do, including SUSE, Mandrake and Fedora. You can check for the availability of an SCons RPM on your distribution's download servers, or by consulting an RPM search site like http://www.rpmfind.net/ or http://rpm.pbone.net/.

If your distribution supports installation via yum, you should be able to install SCons by running:

# yum install scons
      

If your Linux distribution does not already have a specific SCons RPM file, you can download and install from the generic RPM provided by the SCons project. This will install the SCons script(s) in /usr/bin, and the SCons library modules in /usr/lib/scons.

To install from the command line, simply download the appropriate .rpm file, and then run:

# rpm -Uvh scons-2.3.3-1.noarch.rpm
      

Or, you can use a graphical RPM package manager. See your package manager application's documention for specific instructions about how to use it to install a downloaded RPM.

1.2.2. Installing SCons on Debian Linux Systems

Debian Linux systems use a different package management format that also makes it very easy to install SCons.

If your system is connected to the Internet, you can install the latest official Debian package by running:

# apt-get install scons
      

1.2.3. Installing SCons on Windows Systems

SCons provides a Windows installer that makes installation extremely easy. Download the scons-2.3.3.win32.exe file from the SCons download page at http://www.scons.org/download.php. Then all you need to do is execute the file (usually by clicking on its icon in Windows Explorer). These will take you through a small sequence of windows that will install SCons on your system.

1.3. Building and Installing SCons on Any System

If a pre-built SCons package is not available for your system, then you can still easily build and install SCons using the native Python distutils package.

The first step is to download either the scons-2.3.3.tar.gz or scons-2.3.3.zip, which are available from the SCons download page at http://www.scons.org/download.html.

Unpack the archive you downloaded, using a utility like tar on Linux or UNIX, or WinZip on Windows. This will create a directory called scons-2.3.3, usually in your local directory. Then change your working directory to that directory and install SCons by executing the following commands:

# cd scons-2.3.3
# python setup.py install
    

This will build SCons, install the scons script in the python which is used to run the setup.py's scripts directory (/usr/local/bin or C:\Python25\Scripts), and will install the SCons build engine in the corresponding library directory for the python used (/usr/local/lib/scons or C:\Python25\scons). Because these are system directories, you may need root (on Linux or UNIX) or Administrator (on Windows) privileges to install SCons like this.

1.3.1. Building and Installing Multiple Versions of SCons Side-by-Side

The SCons setup.py script has some extensions that support easy installation of multiple versions of SCons in side-by-side locations. This makes it easier to download and experiment with different versions of SCons before moving your official build process to a new version, for example.

To install SCons in a version-specific location, add the --version-lib option when you call setup.py:

# python setup.py install --version-lib
      

This will install the SCons build engine in the /usr/lib/scons-2.3.3 or C:\Python25\scons-2.3.3 directory, for example.

If you use the --version-lib option the first time you install SCons, you do not need to specify it each time you install a new version. The SCons setup.py script will detect the version-specific directory name(s) and assume you want to install all versions in version-specific directories. You can override that assumption in the future by explicitly specifying the --standalone-lib option.

1.3.2. Installing SCons in Other Locations

You can install SCons in locations other than the default by specifying the --prefix= option:

# python setup.py install --prefix=/opt/scons
      

This would install the scons script in /opt/scons/bin and the build engine in /opt/scons/lib/scons,

Note that you can specify both the --prefix= and the --version-lib options at the same type, in which case setup.py will install the build engine in a version-specific directory relative to the specified prefix. Adding --version-lib to the above example would install the build engine in /opt/scons/lib/scons-2.3.3.

1.3.3. Building and Installing SCons Without Administrative Privileges

If you don't have the right privileges to install SCons in a system location, simply use the --prefix= option to install it in a location of your choosing. For example, to install SCons in appropriate locations relative to the user's $HOME directory, the scons script in $HOME/bin and the build engine in $HOME/lib/scons, simply type:

$ python setup.py install --prefix=$HOME
      

You may, of course, specify any other location you prefer, and may use the --version-lib option if you would like to install version-specific directories relative to the specified prefix.

This can also be used to experiment with a newer version of SCons than the one installed in your system locations. Of course, the location in which you install the newer version of the scons script ($HOME/bin in the above example) must be configured in your PATH variable before the directory containing the system-installed version of the scons script.

Chapter 2. Simple Builds

In this chapter, you will see several examples of very simple build configurations using SCons, which will demonstrate how easy it is to use SCons to build programs from several different programming languages on different types of systems.

2.1. Building Simple C / C++ Programs

Here's the famous "Hello, World!" program in C:

int
main()
{
    printf("Hello, world!\n");
}
   

And here's how to build it using SCons. Enter the following into a file named SConstruct:

Program('hello.c')
      

This minimal configuration file gives SCons two pieces of information: what you want to build (an executable program), and the input file from which you want it built (the hello.c file). Program is a builder_method, a Python call that tells SCons that you want to build an executable program.

That's it. Now run the scons command to build the program. On a POSIX-compliant system like Linux or UNIX, you'll see something like:

% scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cc -o hello.o -c hello.c
cc -o hello hello.o
scons: done building targets.

On a Windows system with the Microsoft Visual C++ compiler, you'll see something like:

C:\>scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cl /Fohello.obj /c hello.c /nologo
link /nologo /OUT:hello.exe hello.obj
embedManifestExeCheck(target, source, env)
scons: done building targets.

First, notice that you only need to specify the name of the source file, and that SCons correctly deduces the names of the object and executable files to be built from the base of the source file name.

Second, notice that the same input SConstruct file, without any changes, generates the correct output file names on both systems: hello.o and hello on POSIX systems, hello.obj and hello.exe on Windows systems. This is a simple example of how SCons makes it extremely easy to write portable software builds.

(Note that we won't provide duplicate side-by-side POSIX and Windows output for all of the examples in this guide; just keep in mind that, unless otherwise specified, any of the examples should work equally well on both types of systems.)

2.2. Building Object Files

The Program builder method is only one of many builder methods that SCons provides to build different types of files. Another is the Object builder method, which tells SCons to build an object file from the specified source file:

Object('hello.c')
      

Now when you run the scons command to build the program, it will build just the hello.o object file on a POSIX system:

% scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cc -o hello.o -c hello.c
scons: done building targets.

And just the hello.obj object file on a Windows system (with the Microsoft Visual C++ compiler):

C:\>scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cl /Fohello.obj /c hello.c /nologo
scons: done building targets.

2.3. Simple Java Builds

SCons also makes building with Java extremely easy. Unlike the Program and Object builder methods, however, the Java builder method requires that you specify the name of a destination directory in which you want the class files placed, followed by the source directory in which the .java files live:

Java('classes', 'src')
     

If the src directory contains a single hello.java file, then the output from running the scons command would look something like this (on a POSIX system):

% scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
javac -d classes -sourcepath src src/hello.java
scons: done building targets.

We'll cover Java builds in more detail, including building Java archive (.jar) and other types of file, in Chapter 26, Java Builds.

2.4. Cleaning Up After a Build

When using SCons, it is unnecessary to add special commands or target names to clean up after a build. Instead, you simply use the -c or --clean option when you invoke SCons, and SCons removes the appropriate built files. So if we build our example above and then invoke scons -c afterwards, the output on POSIX looks like:

% scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cc -o hello.o -c hello.c
cc -o hello hello.o
scons: done building targets.
% scons -c
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed hello.o
Removed hello
scons: done cleaning targets.

And the output on Windows looks like:

C:\>scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cl /Fohello.obj /c hello.c /nologo
link /nologo /OUT:hello.exe hello.obj
embedManifestExeCheck(target, source, env)
scons: done building targets.
C:\>scons -c
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed hello.obj
Removed hello.exe
scons: done cleaning targets.

Notice that SCons changes its output to tell you that it is Cleaning targets ... and done cleaning targets.

2.5. The SConstruct File

If you're used to build systems like Make you've already figured out that the SConstruct file is the SCons equivalent of a Makefile. That is, the SConstruct file is the input file that SCons reads to control the build.

2.5.1. SConstruct Files Are Python Scripts

There is, however, an important difference between an SConstruct file and a Makefile: the SConstruct file is actually a Python script. If you're not already familiar with Python, don't worry. This User's Guide will introduce you step-by-step to the relatively small amount of Python you'll need to know to be able to use SCons effectively. And Python is very easy to learn.

One aspect of using Python as the scripting language is that you can put comments in your SConstruct file using Python's commenting convention; that is, everything between a '#' and the end of the line will be ignored:

# Arrange to build the "hello" program.
Program('hello.c')    # "hello.c" is the source file.
     

You'll see throughout the remainder of this Guide that being able to use the power of a real scripting language can greatly simplify the solutions to complex requirements of real-world builds.

2.5.2. SCons Functions Are Order-Independent

One important way in which the SConstruct file is not exactly like a normal Python script, and is more like a Makefile, is that the order in which the SCons functions are called in the SConstruct file does not affect the order in which SCons actually builds the programs and object files you want it to build.[1] In other words, when you call the Program builder (or any other builder method), you're not telling SCons to build the program at the instant the builder method is called. Instead, you're telling SCons to build the program that you want, for example, a program built from a file named hello.c, and it's up to SCons to build that program (and any other files) whenever it's necessary. (We'll learn more about how SCons decides when building or rebuilding a file is necessary in Chapter 6, Dependencies, below.)

SCons reflects this distinction between calling a builder method like Program and actually building the program by printing the status messages that indicate when it's "just reading" the SConstruct file, and when it's actually building the target files. This is to make it clear when SCons is executing the Python statements that make up the SConstruct file, and when SCons is actually executing the commands or other actions to build the necessary files.

Let's clarify this with an example. Python has a print statement that prints a string of characters to the screen. If we put print statements around our calls to the Program builder method:

print "Calling Program('hello.c')"
Program('hello.c')
print "Calling Program('goodbye.c')"
Program('goodbye.c')
print "Finished calling Program()"
       

Then when we execute SCons, we see the output from the print statements in between the messages about reading the SConscript files, indicating that that is when the Python statements are being executed:

% scons
scons: Reading SConscript files ...
Calling Program('hello.c')
Calling Program('goodbye.c')
Finished calling Program()
scons: done reading SConscript files.
scons: Building targets ...
cc -o goodbye.o -c goodbye.c
cc -o goodbye goodbye.o
cc -o hello.o -c hello.c
cc -o hello hello.o
scons: done building targets.

Notice also that SCons built the goodbye program first, even though the "reading SConscript" output shows that we called Program('hello.c') first in the SConstruct file.

2.6. Making the SCons Output Less Verbose

You've already seen how SCons prints some messages about what it's doing, surrounding the actual commands used to build the software:

C:\>scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
cl /Fohello.obj /c hello.c /nologo
link /nologo /OUT:hello.exe hello.obj
embedManifestExeCheck(target, source, env)
scons: done building targets.

These messages emphasize the order in which SCons does its work: all of the configuration files (generically referred to as SConscript files) are read and executed first, and only then are the target files built. Among other benefits, these messages help to distinguish between errors that occur while the configuration files are read, and errors that occur while targets are being built.

One drawback, of course, is that these messages clutter the output. Fortunately, they're easily disabled by using the -Q option when invoking SCons:

C:\>scons -Q
cl /Fohello.obj /c hello.c /nologo
link /nologo /OUT:hello.exe hello.obj
embedManifestExeCheck(target, source, env)

Because we want this User's Guide to focus on what SCons is actually doing, we're going to use the -Q option to remove these messages from the output of all the remaining examples in this Guide.



[1] In programming parlance, the SConstruct file is declarative, meaning you tell SCons what you want done and let it figure out the order in which to do it, rather than strictly imperative, where you specify explicitly the order in which to do things.

Chapter 3. Less Simple Things to Do With Builds

In this chapter, you will see several examples of very simple build configurations using SCons, which will demonstrate how easy it is to use SCons to build programs from several different programming languages on different types of systems.

3.1. Specifying the Name of the Target (Output) File

You've seen that when you call the Program builder method, it builds the resulting program with the same base name as the source file. That is, the following call to build an executable program from the hello.c source file will build an executable program named hello on POSIX systems, and an executable program named hello.exe on Windows systems:

Program('hello.c')
    

If you want to build a program with a different name than the base of the source file name, you simply put the target file name to the left of the source file name:

Program('new_hello', 'hello.c')
       

(SCons requires the target file name first, followed by the source file name, so that the order mimics that of an assignment statement in most programming languages, including Python: "program = source files".)

Now SCons will build an executable program named new_hello when run on a POSIX system:

% scons -Q
cc -o hello.o -c hello.c
cc -o new_hello hello.o

And SCons will build an executable program named new_hello.exe when run on a Windows system:

C:\>scons -Q
cl /Fohello.obj /c hello.c /nologo
link /nologo /OUT:new_hello.exe hello.obj
embedManifestExeCheck(target, source, env)

3.2. Compiling Multiple Source Files

You've just seen how to configure SCons to compile a program from a single source file. It's more common, of course, that you'll need to build a program from many input source files, not just one. To do this, you need to put the source files in a Python list (enclosed in square brackets), like so:

Program(['prog.c', 'file1.c', 'file2.c'])
       

A build of the above example would look like:

% scons -Q
cc -o file1.o -c file1.c
cc -o file2.o -c file2.c
cc -o prog.o -c prog.c
cc -o prog prog.o file1.o file2.o

Notice that SCons deduces the output program name from the first source file specified in the list--that is, because the first source file was prog.c, SCons will name the resulting program prog (or prog.exe on a Windows system). If you want to specify a different program name, then (as we've seen in the previous section) you slide the list of source files over to the right to make room for the output program file name. (SCons puts the output file name to the left of the source file names so that the order mimics that of an assignment statement: "program = source files".) This makes our example:

Program('program', ['prog.c', 'file1.c', 'file2.c'])
       

On Linux, a build of this example would look like:

% scons -Q
cc -o file1.o -c file1.c
cc -o file2.o -c file2.c
cc -o prog.o -c prog.c
cc -o program prog.o file1.o file2.o

Or on Windows:

C:\>scons -Q
cl /Fofile1.obj /c file1.c /nologo
cl /Fofile2.obj /c file2.c /nologo
cl /Foprog.obj /c prog.c /nologo
link /nologo /OUT:program.exe prog.obj file1.obj file2.obj
embedManifestExeCheck(target, source, env)

3.3. Making a list of files with Glob

You can also use the Glob function to find all files matching a certain template, using the standard shell pattern matching characters *, ? and [abc] to match any of a, b or c. [!abc] is also supported, to match any character except a, b or c. This makes many multi-source-file builds quite easy:

Program('program', Glob('*.c'))
    

The SCons man page has more details on using Glob with variant directories (see Chapter 16, Variant Builds, below) and repositories (see Chapter 22, Building From Code Repositories, below), and returning strings rather than Nodes.

3.4. Specifying Single Files Vs. Lists of Files

We've now shown you two ways to specify the source for a program, one with a list of files:

Program('hello', ['file1.c', 'file2.c'])
    

And one with a single file:

Program('hello', 'hello.c')
    

You could actually put a single file name in a list, too, which you might prefer just for the sake of consistency:

Program('hello', ['hello.c'])
    

SCons functions will accept a single file name in either form. In fact, internally, SCons treats all input as lists of files, but allows you to omit the square brackets to cut down a little on the typing when there's only a single file name.

Important

Although SCons functions are forgiving about whether or not you use a string vs. a list for a single file name, Python itself is more strict about treating lists and strings differently. So where SCons allows either a string or list:

# The following two calls both work correctly:
Program('program1', 'program1.c')
Program('program2', ['program2.c'])
    

Trying to do "Python things" that mix strings and lists will cause errors or lead to incorrect results:

common_sources = ['file1.c', 'file2.c']

# THE FOLLOWING IS INCORRECT AND GENERATES A PYTHON ERROR
# BECAUSE IT TRIES TO ADD A STRING TO A LIST:
Program('program1', common_sources + 'program1.c')

# The following works correctly, because it's adding two
# lists together to make another list.
Program('program2', common_sources + ['program2.c'])
    

3.5. Making Lists of Files Easier to Read

One drawback to the use of a Python list for source files is that each file name must be enclosed in quotes (either single quotes or double quotes). This can get cumbersome and difficult to read when the list of file names is long. Fortunately, SCons and Python provide a number of ways to make sure that the SConstruct file stays easy to read.

To make long lists of file names easier to deal with, SCons provides a Split function that takes a quoted list of file names, with the names separated by spaces or other white-space characters, and turns it into a list of separate file names. Using the Split function turns the previous example into:

Program('program', Split('main.c file1.c file2.c'))
    

(If you're already familiar with Python, you'll have realized that this is similar to the split() method in the Python standard string module. Unlike the split() member function of strings, however, the Split function does not require a string as input and will wrap up a single non-string object in a list, or return its argument untouched if it's already a list. This comes in handy as a way to make sure arbitrary values can be passed to SCons functions without having to check the type of the variable by hand.)

Putting the call to the Split function inside the Program call can also be a little unwieldy. A more readable alternative is to assign the output from the Split call to a variable name, and then use the variable when calling the Program function:

src_files = Split('main.c file1.c file2.c')
Program('program', src_files)
    

Lastly, the Split function doesn't care how much white space separates the file names in the quoted string. This allows you to create lists of file names that span multiple lines, which often makes for easier editing:

src_files = Split("""main.c
                     file1.c
                     file2.c""")
Program('program', src_files)
    

(Note in this example that we used the Python "triple-quote" syntax, which allows a string to contain multiple lines. The three quotes can be either single or double quotes.)

3.6. Keyword Arguments

SCons also allows you to identify the output file and input source files using Python keyword arguments. The output file is known as the target, and the source file(s) are known (logically enough) as the source. The Python syntax for this is:

src_files = Split('main.c file1.c file2.c')
Program(target = 'program', source = src_files)
    

Because the keywords explicitly identify what each argument is, you can actually reverse the order if you prefer:

src_files = Split('main.c file1.c file2.c')
Program(source = src_files, target = 'program')
    

Whether or not you choose to use keyword arguments to identify the target and source files, and the order in which you specify them when using keywords, are purely personal choices; SCons functions the same regardless.

3.7. Compiling Multiple Programs

In order to compile multiple programs within the same SConstruct file, simply call the Program method multiple times, once for each program you need to build:

Program('foo.c')
Program('bar', ['bar1.c', 'bar2.c'])
       

SCons would then build the programs as follows:

% scons -Q
cc -o bar1.o -c bar1.c
cc -o bar2.o -c bar2.c
cc -o bar bar1.o bar2.o
cc -o foo.o -c foo.c
cc -o foo foo.o

Notice that SCons does not necessarily build the programs in the same order in which you specify them in the SConstruct file. SCons does, however, recognize that the individual object files must be built before the resulting program can be built. We'll discuss this in greater detail in the "Dependencies" section, below.

3.8. Sharing Source Files Between Multiple Programs

It's common to re-use code by sharing source files between multiple programs. One way to do this is to create a library from the common source files, which can then be linked into resulting programs. (Creating libraries is discussed in Chapter 4, Building and Linking with Libraries, below.)

A more straightforward, but perhaps less convenient, way to share source files between multiple programs is simply to include the common files in the lists of source files for each program:

Program(Split('foo.c common1.c common2.c'))
Program('bar', Split('bar1.c bar2.c common1.c common2.c'))
       

SCons recognizes that the object files for the common1.c and common2.c source files each need to be built only once, even though the resulting object files are each linked in to both of the resulting executable programs:

% scons -Q
cc -o bar1.o -c bar1.c
cc -o bar2.o -c bar2.c
cc -o common1.o -c common1.c
cc -o common2.o -c common2.c
cc -o bar bar1.o bar2.o common1.o common2.o
cc -o foo.o -c foo.c
cc -o foo foo.o common1.o common2.o

If two or more programs share a lot of common source files, repeating the common files in the list for each program can be a maintenance problem when you need to change the list of common files. You can simplify this by creating a separate Python list to hold the common file names, and concatenating it with other lists using the Python + operator:

common = ['common1.c', 'common2.c']
foo_files = ['foo.c'] + common
bar_files = ['bar1.c', 'bar2.c'] + common
Program('foo', foo_files)
Program('bar', bar_files)
    

This is functionally equivalent to the previous example.

Chapter 4. Building and Linking with Libraries

It's often useful to organize large software projects by collecting parts of the software into one or more libraries. SCons makes it easy to create libraries and to use them in the programs.

4.1. Building Libraries

You build your own libraries by specifying Library instead of Program:

Library('foo', ['f1.c', 'f2.c', 'f3.c'])
      

SCons uses the appropriate library prefix and suffix for your system. So on POSIX or Linux systems, the above example would build as follows (although ranlib may not be called on all systems):

% scons -Q
cc -o f1.o -c f1.c
cc -o f2.o -c f2.c
cc -o f3.o -c f3.c
ar rc libfoo.a f1.o f2.o f3.o
ranlib libfoo.a

On a Windows system, a build of the above example would look like:

C:\>scons -Q
cl /Fof1.obj /c f1.c /nologo
cl /Fof2.obj /c f2.c /nologo
cl /Fof3.obj /c f3.c /nologo
lib /nologo /OUT:foo.lib f1.obj f2.obj f3.obj

The rules for the target name of the library are similar to those for programs: if you don't explicitly specify a target library name, SCons will deduce one from the name of the first source file specified, and SCons will add an appropriate file prefix and suffix if you leave them off.

4.1.1. Building Libraries From Source Code or Object Files

The previous example shows building a library from a list of source files. You can, however, also give the Library call object files, and it will correctly realize In fact, you can arbitrarily mix source code files and object files in the source list:

Library('foo', ['f1.c', 'f2.o', 'f3.c', 'f4.o'])
        

And SCons realizes that only the source code files must be compiled into object files before creating the final library:

% scons -Q
cc -o f1.o -c f1.c
cc -o f3.o -c f3.c
ar rc libfoo.a f1.o f2.o f3.o f4.o
ranlib libfoo.a

Of course, in this example, the object files must already exist for the build to succeed. See Chapter 5, Node Objects, below, for information about how you can build object files explicitly and include the built files in a library.

4.1.2. Building Static Libraries Explicitly: the StaticLibrary Builder

The Library function builds a traditional static library. If you want to be explicit about the type of library being built, you can use the synonym StaticLibrary function instead of Library:

StaticLibrary('foo', ['f1.c', 'f2.c', 'f3.c'])
        

There is no functional difference between the StaticLibrary and Library functions.

4.1.3. Building Shared (DLL) Libraries: the SharedLibrary Builder

If you want to build a shared library (on POSIX systems) or a DLL file (on Windows systems), you use the SharedLibrary function:

SharedLibrary('foo', ['f1.c', 'f2.c', 'f3.c'])
        

The output on POSIX:

% scons -Q
cc -o f1.os -c f1.c
cc -o f2.os -c f2.c
cc -o f3.os -c f3.c
cc -o libfoo.so -shared f1.os f2.os f3.os

And the output on Windows:

C:\>scons -Q
cl /Fof1.obj /c f1.c /nologo
cl /Fof2.obj /c f2.c /nologo
cl /Fof3.obj /c f3.c /nologo
link /nologo /dll /out:foo.dll /implib:foo.lib f1.obj f2.obj f3.obj
RegServerFunc(target, source, env)
embedManifestDllCheck(target, source, env)

Notice again that SCons takes care of building the output file correctly, adding the -shared option for a POSIX compilation, and the /dll option on Windows.

4.2. Linking with Libraries

Usually, you build a library because you want to link it with one or more programs. You link libraries with a program by specifying the libraries in the $LIBS construction variable, and by specifying the directory in which the library will be found in the $LIBPATH construction variable:

Library('foo', ['f1.c', 'f2.c', 'f3.c'])
Program('prog.c', LIBS=['foo', 'bar'], LIBPATH='.')
      

Notice, of course, that you don't need to specify a library prefix (like lib) or suffix (like .a or .lib). SCons uses the correct prefix or suffix for the current system.

On a POSIX or Linux system, a build of the above example would look like:

% scons -Q
cc -o f1.o -c f1.c
cc -o f2.o -c f2.c
cc -o f3.o -c f3.c
ar rc libfoo.a f1.o f2.o f3.o
ranlib libfoo.a
cc -o prog.o -c prog.c
cc -o prog prog.o -L. -lfoo -lbar

On a Windows system, a build of the above example would look like:

C:\>scons -Q
cl /Fof1.obj /c f1.c /nologo
cl /Fof2.obj /c f2.c /nologo
cl /Fof3.obj /c f3.c /nologo
lib /nologo /OUT:foo.lib f1.obj f2.obj f3.obj
cl /Foprog.obj /c prog.c /nologo
link /nologo /OUT:prog.exe /LIBPATH:. foo.lib bar.lib prog.obj
embedManifestExeCheck(target, source, env)

As usual, notice that SCons has taken care of constructing the correct command lines to link with the specified library on each system.

Note also that, if you only have a single library to link with, you can specify the library name in single string, instead of a Python list, so that:

Program('prog.c', LIBS='foo', LIBPATH='.')
    

is equivalent to:

Program('prog.c', LIBS=['foo'], LIBPATH='.')
    

This is similar to the way that SCons handles either a string or a list to specify a single source file.

4.3. Finding Libraries: the $LIBPATH Construction Variable

By default, the linker will only look in certain system-defined directories for libraries. SCons knows how to look for libraries in directories that you specify with the $LIBPATH construction variable. $LIBPATH consists of a list of directory names, like so:

Program('prog.c', LIBS = 'm',
                  LIBPATH = ['/usr/lib', '/usr/local/lib'])
      

Using a Python list is preferred because it's portable across systems. Alternatively, you could put all of the directory names in a single string, separated by the system-specific path separator character: a colon on POSIX systems:

LIBPATH = '/usr/lib:/usr/local/lib'
    

or a semi-colon on Windows systems:

LIBPATH = 'C:\\lib;D:\\lib'
    

(Note that Python requires that the backslash separators in a Windows path name be escaped within strings.)

When the linker is executed, SCons will create appropriate flags so that the linker will look for libraries in the same directories as SCons. So on a POSIX or Linux system, a build of the above example would look like:

% scons -Q
cc -o prog.o -c prog.c
cc -o prog prog.o -L/usr/lib -L/usr/local/lib -lm

On a Windows system, a build of the above example would look like:

C:\>scons -Q
cl /Foprog.obj /c prog.c /nologo
link /nologo /OUT:prog.exe /LIBPATH:\usr\lib /LIBPATH:\usr\local\lib m.lib prog.obj
embedManifestExeCheck(target, source, env)

Note again that SCons has taken care of the system-specific details of creating the right command-line options.

Chapter 5. Node Objects

Internally, SCons represents all of the files and directories it knows about as Nodes. These internal objects (not object files) can be used in a variety of ways to make your SConscript files portable and easy to read.

5.1. Builder Methods Return Lists of Target Nodes

All builder methods return a list of Node objects that identify the target file or files that will be built. These returned Nodes can be passed as arguments to other builder methods.

For example, suppose that we want to build the two object files that make up a program with different options. This would mean calling the Object builder once for each object file, specifying the desired options:

Object('hello.c', CCFLAGS='-DHELLO')
Object('goodbye.c', CCFLAGS='-DGOODBYE')
    

One way to combine these object files into the resulting program would be to call the Program builder with the names of the object files listed as sources:

Object('hello.c', CCFLAGS='-DHELLO')
Object('goodbye.c', CCFLAGS='-DGOODBYE')
Program(['hello.o', 'goodbye.o'])
    

The problem with specifying the names as strings is that our SConstruct file is no longer portable across operating systems. It won't, for example, work on Windows because the object files there would be named hello.obj and goodbye.obj, not hello.o and goodbye.o.

A better solution is to assign the lists of targets returned by the calls to the Object builder to variables, which we can then concatenate in our call to the Program builder:

hello_list = Object('hello.c', CCFLAGS='-DHELLO')
goodbye_list = Object('goodbye.c', CCFLAGS='-DGOODBYE')
Program(hello_list + goodbye_list)
      

This makes our SConstruct file portable again, the build output on Linux looking like:

% scons -Q
cc -o goodbye.o -c -DGOODBYE goodbye.c
cc -o hello.o -c -DHELLO hello.c
cc -o hello hello.o goodbye.o

And on Windows:

C:\>scons -Q
cl /Fogoodbye.obj /c goodbye.c -DGOODBYE
cl /Fohello.obj /c hello.c -DHELLO
link /nologo /OUT:hello.exe hello.obj goodbye.obj
embedManifestExeCheck(target, source, env)

We'll see examples of using the list of nodes returned by builder methods throughout the rest of this guide.

5.2. Explicitly Creating File and Directory Nodes

It's worth mentioning here that SCons maintains a clear distinction between Nodes that represent files and Nodes that represent directories. SCons supports File and Dir functions that, respectively, return a file or directory Node:

hello_c = File('hello.c')
Program(hello_c)

classes = Dir('classes')
Java(classes, 'src')
      

Normally, you don't need to call File or Dir directly, because calling a builder method automatically treats strings as the names of files or directories, and translates them into the Node objects for you. The File and Dir functions can come in handy in situations where you need to explicitly instruct SCons about the type of Node being passed to a builder or other function, or unambiguously refer to a specific file in a directory tree.

There are also times when you may need to refer to an entry in a file system without knowing in advance whether it's a file or a directory. For those situations, SCons also supports an Entry function, which returns a Node that can represent either a file or a directory.

xyzzy = Entry('xyzzy')
    

The returned xyzzy Node will be turned into a file or directory Node the first time it is used by a builder method or other function that requires one vs. the other.

5.3. Printing Node File Names

One of the most common things you can do with a Node is use it to print the file name that the node represents. Keep in mind, though, that because the object returned by a builder call is a list of Nodes, you must use Python subscripts to fetch individual Nodes from the list. For example, the following SConstruct file:

object_list = Object('hello.c')
program_list = Program(object_list)
print "The object file is:", object_list[0]
print "The program file is:", program_list[0]
      

Would print the following file names on a POSIX system:

% scons -Q
The object file is: hello.o
The program file is: hello
cc -o hello.o -c hello.c
cc -o hello hello.o

And the following file names on a Windows system:

C:\>scons -Q
The object file is: hello.obj
The program file is: hello.exe
cl /Fohello.obj /c hello.c /nologo
link /nologo /OUT:hello.exe hello.obj
embedManifestExeCheck(target, source, env)

Note that in the above example, the object_list[0] extracts an actual Node object from the list, and the Python print statement converts the object to a string for printing.

5.4. Using a Node's File Name as a String

Printing a Node's name as described in the previous section works because the string representation of a Node object is the name of the file. If you want to do something other than print the name of the file, you can fetch it by using the builtin Python str function. For example, if you want to use the Python os.path.exists to figure out whether a file exists while the SConstruct file is being read and executed, you can fetch the string as follows:

import os.path
program_list = Program('hello.c')
program_name = str(program_list[0])
if not os.path.exists(program_name):
    print program_name, "does not exist!"
      

Which executes as follows on a POSIX system:

% scons -Q
hello does not exist!
cc -o hello.o -c hello.c
cc -o hello hello.o

5.5. GetBuildPath: Getting the Path From a Node or String

env.GetBuildPath(file_or_list) returns the path of a Node or a string representing a path. It can also take a list of Nodes and/or strings, and returns the list of paths. If passed a single Node, the result is the same as calling str(node) (see above). The string(s) can have embedded construction variables, which are expanded as usual, using the calling environment's set of variables. The paths can be files or directories, and do not have to exist.

env=Environment(VAR="value")
n=File("foo.c")
print env.GetBuildPath([n, "sub/dir/$VAR"])
      

Would print the following file names:

% scons -Q
['foo.c', 'sub/dir/value']
scons: `.' is up to date.

There is also a function version of GetBuildPath which can be called without an Environment; that uses the default SCons Environment to do substitution on any string arguments.

Chapter 6. Dependencies

So far we've seen how SCons handles one-time builds. But one of the main functions of a build tool like SCons is to rebuild only what is necessary when source files change--or, put another way, SCons should not waste time rebuilding things that don't need to be rebuilt. You can see this at work simply by re-invoking SCons after building our simple hello example:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q
scons: `.' is up to date.

The second time it is executed, SCons realizes that the hello program is up-to-date with respect to the current hello.c source file, and avoids rebuilding it. You can see this more clearly by naming the hello program explicitly on the command line:

% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.

Note that SCons reports "...is up to date" only for target files named explicitly on the command line, to avoid cluttering the output.

6.1. Deciding When an Input File Has Changed: the Decider Function

Another aspect of avoiding unnecessary rebuilds is the fundamental build tool behavior of rebuilding things when an input file changes, so that the built software is up to date. By default, SCons keeps track of this through an MD5 signature, or checksum, of the contents of each file, although you can easily configure SCons to use the modification times (or time stamps) instead. You can even specify your own Python function for deciding if an input file has changed.

6.1.1. Using MD5 Signatures to Decide if a File Has Changed

By default, SCons keeps track of whether a file has changed based on an MD5 checksum of the file's contents, not the file's modification time. This means that you may be surprised by the default SCons behavior if you are used to the Make convention of forcing a rebuild by updating the file's modification time (using the touch command, for example):

% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o
% touch hello.c
% scons -Q hello
scons: `hello' is up to date.

Even though the file's modification time has changed, SCons realizes that the contents of the hello.c file have not changed, and therefore that the hello program need not be rebuilt. This avoids unnecessary rebuilds when, for example, someone rewrites the contents of a file without making a change. But if the contents of the file really do change, then SCons detects the change and rebuilds the program as required:

% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o
%     [CHANGE THE CONTENTS OF hello.c]
% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o

Note that you can, if you wish, specify this default behavior (MD5 signatures) explicitly using the Decider function as follows:

Program('hello.c')
Decider('MD5')
      

You can also use the string 'content' as a synonym for 'MD5' when calling the Decider function.

6.1.1.1. Ramifications of Using MD5 Signatures

Using MD5 signatures to decide if an input file has changed has one surprising benefit: if a source file has been changed in such a way that the contents of the rebuilt target file(s) will be exactly the same as the last time the file was built, then any "downstream" target files that depend on the rebuilt-but-not-changed target file actually need not be rebuilt.

So if, for example, a user were to only change a comment in a hello.c file, then the rebuilt hello.o file would be exactly the same as the one previously built (assuming the compiler doesn't put any build-specific information in the object file). SCons would then realize that it would not need to rebuild the hello program as follows:

% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o
%   [CHANGE A COMMENT IN hello.c]
% scons -Q hello
cc -o hello.o -c hello.c
scons: `hello' is up to date.

In essence, SCons "short-circuits" any dependent builds when it realizes that a target file has been rebuilt to exactly the same file as the last build. This does take some extra processing time to read the contents of the target (hello.o) file, but often saves time when the rebuild that was avoided would have been time-consuming and expensive.

6.1.2. Using Time Stamps to Decide If a File Has Changed

If you prefer, you can configure SCons to use the modification time of a file, not the file contents, when deciding if a target needs to be rebuilt. SCons gives you two ways to use time stamps to decide if an input file has changed since the last time a target has been built.

The most familiar way to use time stamps is the way Make does: that is, have SCons decide that a target must be rebuilt if a source file's modification time is newer than the target file. To do this, call the Decider function as follows:

Object('hello.c')
Decider('timestamp-newer')
        

This makes SCons act like Make when a file's modification time is updated (using the touch command, for example):

% scons -Q hello.o
cc -o hello.o -c hello.c
% touch hello.c
% scons -Q hello.o
cc -o hello.o -c hello.c

And, in fact, because this behavior is the same as the behavior of Make, you can also use the string 'make' as a synonym for 'timestamp-newer' when calling the Decider function:

Object('hello.c')
Decider('make')
      

One drawback to using times stamps exactly like Make is that if an input file's modification time suddenly becomes older than a target file, the target file will not be rebuilt. This can happen if an old copy of a source file is restored from a backup archive, for example. The contents of the restored file will likely be different than they were the last time a dependent target was built, but the target won't be rebuilt because the modification time of the source file is not newer than the target.

Because SCons actually stores information about the source files' time stamps whenever a target is built, it can handle this situation by checking for an exact match of the source file time stamp, instead of just whether or not the source file is newer than the target file. To do this, specify the argument 'timestamp-match' when calling the Decider function:

Object('hello.c')
Decider('timestamp-match')
        

When configured this way, SCons will rebuild a target whenever a source file's modification time has changed. So if we use the touch -t option to change the modification time of hello.c to an old date (January 1, 1989), SCons will still rebuild the target file:

% scons -Q hello.o
cc -o hello.o -c hello.c
% touch -t 198901010000 hello.c
% scons -Q hello.o
cc -o hello.o -c hello.c

In general, the only reason to prefer timestamp-newer instead of timestamp-match, would be if you have some specific reason to require this Make-like behavior of not rebuilding a target when an otherwise-modified source file is older.

6.1.3. Deciding If a File Has Changed Using Both MD Signatures and Time Stamps

As a performance enhancement, SCons provides a way to use MD5 checksums of file contents but to read those contents only when the file's timestamp has changed. To do this, call the Decider function with 'MD5-timestamp' argument as follows:

Program('hello.c')
Decider('MD5-timestamp')
        

So configured, SCons will still behave like it does when using Decider('MD5'):

% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o
% touch hello.c
% scons -Q hello
scons: `hello' is up to date.
% edit hello.c
    [CHANGE THE CONTENTS OF hello.c]
% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o
      

However, the second call to SCons in the above output, when the build is up-to-date, will have been performed by simply looking at the modification time of the hello.c file, not by opening it and performing an MD5 checksum calcuation on its contents. This can significantly speed up many up-to-date builds.

The only drawback to using Decider('MD5-timestamp') is that SCons will not rebuild a target file if a source file was modified within one second of the last time SCons built the file. While most developers are programming, this isn't a problem in practice, since it's unlikely that someone will have built and then thought quickly enough to make a substantive change to a source file within one second. Certain build scripts or continuous integration tools may, however, rely on the ability to apply changes to files automatically and then rebuild as quickly as possible, in which case use of Decider('MD5-timestamp') may not be appropriate.

6.1.4. Writing Your Own Custom Decider Function

The different string values that we've passed to the Decider function are essentially used by SCons to pick one of several specific internal functions that implement various ways of deciding if a dependency (usually a source file) has changed since a target file has been built. As it turns out, you can also supply your own function to decide if a dependency has changed.

For example, suppose we have an input file that contains a lot of data, in some specific regular format, that is used to rebuild a lot of different target files, but each target file really only depends on one particular section of the input file. We'd like to have each target file depend on only its section of the input file. However, since the input file may contain a lot of data, we want to open the input file only if its timestamp has changed. This could be done with a custom Decider function that might look something like this:

Program('hello.c')
def decide_if_changed(dependency, target, prev_ni):
    if self.get_timestamp() != prev_ni.timestamp:
        dep = str(dependency)
        tgt = str(target)
        if specific_part_of_file_has_changed(dep, tgt):
            return True
    return False
Decider(decide_if_changed)
        

Note that in the function definition, the dependency (input file) is the first argument, and then the target. Both of these are passed to the functions as SCons Node objects, which we convert to strings using the Python str().

The third argument, prev_ni, is an object that holds the signature or timestamp information that was recorded about the dependency the last time the target was built. A prev_ni object can hold different information, depending on the type of thing that the dependency argument represents. For normal files, the prev_ni object has the following attributes:

.csig

The content signature, or MD5 checksum, of the contents of the dependency file the list time the target was built.

.size

The size in bytes of the dependency file the list time the target was built.

.timestamp

The modification time of the dependency file the list time the target was built.

Note that ignoring some of the arguments in your custom Decider function is a perfectly normal thing to do, if they don't impact the way you want to decide if the dependency file has changed.

Another thing to look out for is the fact that the three attributes above may not be present at the time of the first run. Without any prior build, no targets have been created and no .sconsign DB file exists yet. So, you should always check whether the prev_ni attribute in question is available.

We finally present a small example for a csig-based decider function. Note how the signature information for the dependency file has to get initialized via get_csig during each function call (this is mandatory!).

env = Environment()

def config_file_decider(dependency, target, prev_ni):
    import os.path

    # We always have to init the .csig value...
    dep_csig = dependency.get_csig()
    # .csig may not exist, because no target was built yet...
    if 'csig' not in dir(prev_ni):
        return True
    # Target file may not exist yet
    if not os.path.exists(str(target.abspath)):
        return True
    if dep_csig != prev_ni.csig:
        # Some change on source file => update installed one
        return True
    return False

def update_file():
    f = open("test.txt","a")
    f.write("some line\n")
    f.close()

update_file()

# Activate our own decider function
env.Decider(config_file_decider)

env.Install("install","test.txt")
      

6.1.5. Mixing Different Ways of Deciding If a File Has Changed

The previous examples have all demonstrated calling the global Decider function to configure all dependency decisions that SCons makes. Sometimes, however, you want to be able to configure different decision-making for different targets. When that's necessary, you can use the env.Decider method to affect only the configuration decisions for targets built with a specific construction environment.

For example, if we arbitrarily want to build one program using MD5 checkums and another using file modification times from the same source we might configure it this way:

env1 = Environment(CPPPATH = ['.'])
env2 = env1.Clone()
env2.Decider('timestamp-match')
env1.Program('prog-MD5', 'program1.c')
env2.Program('prog-timestamp', 'program2.c')
        

If both of the programs include the same inc.h file, then updating the modification time of inc.h (using the touch command) will cause only prog-timestamp to be rebuilt:

% scons -Q
cc -o program1.o -c -I. program1.c
cc -o prog-MD5 program1.o
cc -o program2.o -c -I. program2.c
cc -o prog-timestamp program2.o
% touch inc.h
% scons -Q
cc -o program2.o -c -I. program2.c
cc -o prog-timestamp program2.o

6.2. Older Functions for Deciding When an Input File Has Changed

SCons still supports two functions that used to be the primary methods for configuring the decision about whether or not an input file has changed. These functions have been officially deprecated as SCons version 2.0, and their use is discouraged, mainly because they rely on a somewhat confusing distinction between how source files and target files are handled. These functions are documented here mainly in case you encounter them in older SConscript files.

6.2.1. The SourceSignatures Function

The SourceSignatures function is fairly straightforward, and supports two different argument values to configure whether source file changes should be decided using MD5 signatures:

Program('hello.c')
SourceSignatures('MD5')
      

Or using time stamps:

Program('hello.c')
SourceSignatures('timestamp')
      

These are roughly equivalent to specifying Decider('MD5') or Decider('timestamp-match'), respectively, although it only affects how SCons makes decisions about dependencies on source files--that is, files that are not built from any other files.

6.2.2. The TargetSignatures Function

The TargetSignatures function specifies how SCons decides when a target file has changed when it is used as a dependency of (input to) another target--that is, the TargetSignatures function configures how the signatures of "intermediate" target files are used when deciding if a "downstream" target file must be rebuilt. [2]

The TargetSignatures function supports the same 'MD5' and 'timestamp' argument values that are supported by the SourceSignatures, with the same meanings, but applied to target files. That is, in the example:

Program('hello.c')
TargetSignatures('MD5')
      

The MD5 checksum of the hello.o target file will be used to decide if it has changed since the last time the "downstream" hello target file was built. And in the example:

Program('hello.c')
TargetSignatures('timestamp')
      

The modification time of the hello.o target file will be used to decide if it has changed since the last time the "downstream" hello target file was built.

The TargetSignatures function supports two additional argument values: 'source' and 'build'. The 'source' argument specifies that decisions involving whether target files have changed since a previous build should use the same behavior for the decisions configured for source files (using the SourceSignatures function). So in the example:

Program('hello.c')
TargetSignatures('source')
SourceSignatures('timestamp')
      

All files, both targets and sources, will use modification times when deciding if an input file has changed since the last time a target was built.

Lastly, the 'build' argument specifies that SCons should examine the build status of a target file and always rebuild a "downstream" target if the target file was itself rebuilt, without re-examining the contents or timestamp of the newly-built target file. If the target file was not rebuilt during this scons invocation, then the target file will be examined the same way as configured by the SourceSignature call to decide if it has changed.

This mimics the behavior of build signatures in earlier versions of SCons. A build signature re-combined signatures of all the input files that went into making the target file, so that the target file itself did not need to have its contents read to compute an MD5 signature. This can improve performance for some configurations, but is generally not as effective as using Decider('MD5-timestamp').

6.3. Implicit Dependencies: The $CPPPATH Construction Variable

Now suppose that our "Hello, World!" program actually has an #include line to include the hello.h file in the compilation:

#include <hello.h>
int
main()
{
    printf("Hello, %s!\n", string);
}
      

And, for completeness, the hello.h file looks like this:

#define string    "world"
      

In this case, we want SCons to recognize that, if the contents of the hello.h file change, the hello program must be recompiled. To do this, we need to modify the SConstruct file like so:

Program('hello.c', CPPPATH = '.')
      

The $CPPPATH value tells SCons to look in the current directory ('.') for any files included by C source files (.c or .h files). With this assignment in the SConstruct file:

% scons -Q hello
cc -o hello.o -c -I. hello.c
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.
%     [CHANGE THE CONTENTS OF hello.h]
% scons -Q hello
cc -o hello.o -c -I. hello.c
cc -o hello hello.o

First, notice that SCons added the -I. argument from the $CPPPATH variable so that the compilation would find the hello.h file in the local directory.

Second, realize that SCons knows that the hello program must be rebuilt because it scans the contents of the hello.c file for the #include lines that indicate another file is being included in the compilation. SCons records these as implicit dependencies of the target file, Consequently, when the hello.h file changes, SCons realizes that the hello.c file includes it, and rebuilds the resulting hello program that depends on both the hello.c and hello.h files.

Like the $LIBPATH variable, the $CPPPATH variable may be a list of directories, or a string separated by the system-specific path separation character (':' on POSIX/Linux, ';' on Windows). Either way, SCons creates the right command-line options so that the following example:

Program('hello.c', CPPPATH = ['include', '/home/project/inc'])
      

Will look like this on POSIX or Linux:

% scons -Q hello
cc -o hello.o -c -Iinclude -I/home/project/inc hello.c
cc -o hello hello.o

And like this on Windows:

C:\>scons -Q hello.exe
cl /Fohello.obj /c hello.c /nologo /Iinclude /I\home\project\inc
link /nologo /OUT:hello.exe hello.obj
embedManifestExeCheck(target, source, env)

6.4. Caching Implicit Dependencies

Scanning each file for #include lines does take some extra processing time. When you're doing a full build of a large system, the scanning time is usually a very small percentage of the overall time spent on the build. You're most likely to notice the scanning time, however, when you rebuild all or part of a large system: SCons will likely take some extra time to "think about" what must be built before it issues the first build command (or decides that everything is up to date and nothing must be rebuilt).

In practice, having SCons scan files saves time relative to the amount of potential time lost to tracking down subtle problems introduced by incorrect dependencies. Nevertheless, the "waiting time" while SCons scans files can annoy individual developers waiting for their builds to finish. Consequently, SCons lets you cache the implicit dependencies that its scanners find, for use by later builds. You can do this by specifying the --implicit-cache option on the command line:

% scons -Q --implicit-cache hello
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.

If you don't want to specify --implicit-cache on the command line each time, you can make it the default behavior for your build by setting the implicit_cache option in an SConscript file:

SetOption('implicit_cache', 1)
    

SCons does not cache implicit dependencies like this by default because the --implicit-cache causes SCons to simply use the implicit dependencies stored during the last run, without any checking for whether or not those dependencies are still correct. Specifically, this means --implicit-cache instructs SCons to not rebuild "correctly" in the following cases:

  • When --implicit-cache is used, SCons will ignore any changes that may have been made to search paths (like $CPPPATH or $LIBPATH,). This can lead to SCons not rebuilding a file if a change to $CPPPATH would normally cause a different, same-named file from a different directory to be used.

  • When --implicit-cache is used, SCons will not detect if a same-named file has been added to a directory that is earlier in the search path than the directory in which the file was found last time.

6.4.1. The --implicit-deps-changed Option

When using cached implicit dependencies, sometimes you want to "start fresh" and have SCons re-scan the files for which it previously cached the dependencies. For example, if you have recently installed a new version of external code that you use for compilation, the external header files will have changed and the previously-cached implicit dependencies will be out of date. You can update them by running SCons with the --implicit-deps-changed option:

% scons -Q --implicit-deps-changed hello
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.

In this case, SCons will re-scan all of the implicit dependencies and cache updated copies of the information.

6.4.2. The --implicit-deps-unchanged Option

By default when caching dependencies, SCons notices when a file has been modified and re-scans the file for any updated implicit dependency information. Sometimes, however, you may want to force SCons to use the cached implicit dependencies, even if the source files changed. This can speed up a build for example, when you have changed your source files but know that you haven't changed any #include lines. In this case, you can use the --implicit-deps-unchanged option:

% scons -Q --implicit-deps-unchanged hello
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.

In this case, SCons will assume that the cached implicit dependencies are correct and will not bother to re-scan changed files. For typical builds after small, incremental changes to source files, the savings may not be very big, but sometimes every bit of improved performance counts.

6.5. Explicit Dependencies: the Depends Function

Sometimes a file depends on another file that is not detected by an SCons scanner. For this situation, SCons allows you to specific explicitly that one file depends on another file, and must be rebuilt whenever that file changes. This is specified using the Depends method:

hello = Program('hello.c')
Depends(hello, 'other_file')
    
% scons -Q hello
cc -c hello.c -o hello.o
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.
% edit other_file
    [CHANGE THE CONTENTS OF other_file]
% scons -Q hello
cc -c hello.c -o hello.o
cc -o hello hello.o
    

Note that the dependency (the second argument to Depends) may also be a list of Node objects (for example, as returned by a call to a Builder):

hello = Program('hello.c')
goodbye = Program('goodbye.c')
Depends(hello, goodbye)
    

in which case the dependency or dependencies will be built before the target(s):

% scons -Q hello
cc -c goodbye.c -o goodbye.o
cc -o goodbye goodbye.o
cc -c hello.c -o hello.o
cc -o hello hello.o
    

6.6. Dependencies From External Files: the ParseDepends Function

SCons has built-in scanners for a number of languages. Sometimes these scanners fail to extract certain implicit dependencies due to limitations of the scanner implementation.

The following example illustrates a case where the built-in C scanner is unable to extract the implicit dependency on a header file.

#define FOO_HEADER <foo.h>
#include FOO_HEADER

int main() {
    return FOO;
}
      
% scons -Q
cc -o hello.o -c -I. hello.c
cc -o hello hello.o
%    [CHANGE CONTENTS OF foo.h]
% scons -Q
scons: `.' is up to date.

Apparently, the scanner does not know about the header dependency. Being not a full-fledged C preprocessor, the scanner does not expand the macro.

In these cases, you may also use the compiler to extract the implicit dependencies. ParseDepends can parse the contents of the compiler output in the style of Make, and explicitly establish all of the listed dependencies.

The following example uses ParseDepends to process a compiler generated dependency file which is generated as a side effect during compilation of the object file:

obj = Object('hello.c', CCFLAGS='-MD -MF hello.d', CPPPATH='.')
SideEffect('hello.d', obj)
ParseDepends('hello.d')
Program('hello', obj)
      
% scons -Q
cc -o hello.o -c -MD -MF hello.d -I. hello.c
cc -o hello hello.o
%    [CHANGE CONTENTS OF foo.h]
% scons -Q
cc -o hello.o -c -MD -MF hello.d -I. hello.c

Parsing dependencies from a compiler-generated .d file has a chicken-and-egg problem, that causes unnecessary rebuilds:

% scons -Q
cc -o hello.o -c -MD -MF hello.d -I. hello.c
cc -o hello hello.o
% scons -Q --debug=explain
scons: rebuilding `hello.o' because `foo.h' is a new dependency
cc -o hello.o -c -MD -MF hello.d -I. hello.c
% scons -Q
scons: `.' is up to date.
    

In the first pass, the dependency file is generated while the object file is compiled. At that time, SCons does not know about the dependency on foo.h. In the second pass, the object file is regenerated because foo.h is detected as a new dependency.

ParseDepends immediately reads the specified file at invocation time and just returns if the file does not exist. A dependency file generated during the build process is not automatically parsed again. Hence, the compiler-extracted dependencies are not stored in the signature database during the same build pass. This limitation of ParseDepends leads to unnecessary recompilations. Therefore, ParseDepends should only be used if scanners are not available for the employed language or not powerful enough for the specific task.

6.7. Ignoring Dependencies: the Ignore Function

Sometimes it makes sense to not rebuild a program, even if a dependency file changes. In this case, you would tell SCons specifically to ignore a dependency as follows:

hello_obj=Object('hello.c')
hello = Program(hello_obj)
Ignore(hello_obj, 'hello.h')
      
% scons -Q hello
cc -c -o hello.o hello.c
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.
% edit hello.h
  [CHANGE THE CONTENTS OF hello.h]
% scons -Q hello
scons: `hello' is up to date.
    

Now, the above example is a little contrived, because it's hard to imagine a real-world situation where you wouldn't want to rebuild hello if the hello.h file changed. A more realistic example might be if the hello program is being built in a directory that is shared between multiple systems that have different copies of the stdio.h include file. In that case, SCons would notice the differences between the different systems' copies of stdio.h and would rebuild hello each time you change systems. You could avoid these rebuilds as follows:

hello = Program('hello.c', CPPPATH=['/usr/include'])
Ignore(hello, '/usr/include/stdio.h')
    

Ignore can also be used to prevent a generated file from being built by default. This is due to the fact that directories depend on their contents. So to ignore a generated file from the default build, you specify that the directory should ignore the generated file. Note that the file will still be built if the user specifically requests the target on scons command line, or if the file is a dependency of another file which is requested and/or is built by default.

hello_obj=Object('hello.c')
hello = Program(hello_obj)
Ignore('.',[hello,hello_obj])
      
% scons -Q
scons: `.' is up to date.
% scons -Q hello
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q hello
scons: `hello' is up to date.

6.8. Order-Only Dependencies: the Requires Function

Occasionally, it may be useful to specify that a certain file or directory must, if necessary, be built or created before some other target is built, but that changes to that file or directory do not require that the target itself be rebuilt. Such a relationship is called an order-only dependency because it only affects the order in which things must be built--the dependency before the target--but it is not a strict dependency relationship because the target should not change in response to changes in the dependent file.

For example, suppose that you want to create a file every time you run a build that identifies the time the build was performed, the version number, etc., and which is included in every program that you build. The version file's contents will change every build. If you specify a normal dependency relationship, then every program that depends on that file would be rebuilt every time you ran SCons. For example, we could use some Python code in a SConstruct file to create a new version.c file with a string containing the current date every time we run SCons, and then link a program with the resulting object file by listing version.c in the sources:

import time

version_c_text = """
char *date = "%s";
""" % time.ctime(time.time())
open('version.c', 'w').write(version_c_text)

hello = Program(['hello.c', 'version.c'])
      

If we list version.c as an actual source file, though, then the version.o file will get rebuilt every time we run SCons (because the SConstruct file itself changes the contents of version.c) and the hello executable will get re-linked every time (because the version.o file changes):

% scons -Q hello
cc -o hello.o -c hello.c
cc -o version.o -c version.c
cc -o hello hello.o version.o
% sleep 1
% scons -Q hello
cc -o version.o -c version.c
cc -o hello hello.o version.o
% sleep 1
% scons -Q hello
cc -o version.o -c version.c
cc -o hello hello.o version.o

(Note that for the above example to work, we sleep for one second in between each run, so that the SConstruct file will create a version.c file with a time string that's one second later than the previous run.)

One solution is to use the Requires function to specify that the version.o must be rebuilt before it is used by the link step, but that changes to version.o should not actually cause the hello executable to be re-linked:

import time

version_c_text = """
char *date = "%s";
""" % time.ctime(time.time())
open('version.c', 'w').write(version_c_text)

version_obj = Object('version.c')

hello = Program('hello.c',
                LINKFLAGS = str(version_obj[0]))

Requires(hello, version_obj)
      

Notice that because we can no longer list version.c as one of the sources for the hello program, we have to find some other way to get it into the link command line. For this example, we're cheating a bit and stuffing the object file name (extracted from version_obj list returned by the Object call) into the $LINKFLAGS variable, because $LINKFLAGS is already included in the $LINKCOM command line.

With these changes, we get the desired behavior of only re-linking the hello executable when the hello.c has changed, even though the version.o is rebuilt (because the SConstruct file still changes the version.c contents directly each run):

% scons -Q hello
cc -o version.o -c version.c
cc -o hello.o -c hello.c
cc -o hello version.o hello.o
% sleep 1
% scons -Q hello
cc -o version.o -c version.c
scons: `hello' is up to date.
% sleep 1
%     [CHANGE THE CONTENTS OF hello.c]
% scons -Q hello
cc -o version.o -c version.c
cc -o hello.o -c hello.c
cc -o hello version.o hello.o
% sleep 1
% scons -Q hello
cc -o version.o -c version.c
scons: `hello' is up to date.

6.9. The AlwaysBuild Function

How SCons handles dependencies can also be affected by the AlwaysBuild method. When a file is passed to the AlwaysBuild method, like so:

hello = Program('hello.c')
AlwaysBuild(hello)
      

Then the specified target file (hello in our example) will always be considered out-of-date and rebuilt whenever that target file is evaluated while walking the dependency graph:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q
cc -o hello hello.o

The AlwaysBuild function has a somewhat misleading name, because it does not actually mean the target file will be rebuilt every single time SCons is invoked. Instead, it means that the target will, in fact, be rebuilt whenever the target file is encountered while evaluating the targets specified on the command line (and their dependencies). So specifying some other target on the command line, a target that does not itself depend on the AlwaysBuild target, will still be rebuilt only if it's out-of-date with respect to its dependencies:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q hello.o
scons: `hello.o' is up to date.


[2] This easily-overlooked distinction between how SCons decides if the target itself must be rebuilt and how the target is then used to decide if a different target must be rebuilt is one of the confusing things that has led to the TargetSignatures and SourceSignatures functions being replaced by the simpler Decider function.

Chapter 7. Environments

An environment is a collection of values that can affect how a program executes. SCons distinguishes between three different types of environments that can affect the behavior of SCons itself (subject to the configuration in the SConscript files), as well as the compilers and other tools it executes:

External Environment

The external environment is the set of variables in the user's environment at the time the user runs SCons. These variables are available within the SConscript files through the Python os.environ dictionary. See Section 7.1, “Using Values From the External Environment”, below.

Construction Environment

A construction environment is a distinct object creating within a SConscript file and and which contains values that affect how SCons decides what action to use to build a target, and even to define which targets should be built from which sources. One of the most powerful features of SCons is the ability to create multiple construction environments, including the ability to clone a new, customized construction environment from an existing construction environment. See Section 7.2, “Construction Environments”, below.

Execution Environment

An execution environment is the values that SCons sets when executing an external command (such as a compiler or linker) to build one or more targets. Note that this is not the same as the external environment (see above). See Section 7.3, “Controlling the Execution Environment for Issued Commands”, below.

Unlike Make, SCons does not automatically copy or import values between different environments (with the exception of explicit clones of construction environments, which inherit values from their parent). This is a deliberate design choice to make sure that builds are, by default, repeatable regardless of the values in the user's external environment. This avoids a whole class of problems with builds where a developer's local build works because a custom variable setting causes a different compiler or build option to be used, but the checked-in change breaks the official build because it uses different environment variable settings.

Note that the SConscript writer can easily arrange for variables to be copied or imported between environments, and this is often very useful (or even downright necessary) to make it easy for developers to customize the build in appropriate ways. The point is not that copying variables between different environments is evil and must always be avoided. Instead, it should be up to the implementer of the build system to make conscious choices about how and when to import a variable from one environment to another, making informed decisions about striking the right balance between making the build repeatable on the one hand and convenient to use on the other.

7.1. Using Values From the External Environment

The external environment variable settings that the user has in force when executing SCons are available through the normal Python os.environ dictionary. This means that you must add an import os statement to any SConscript file in which you want to use values from the user's external environment.

import os
     

More usefully, you can use the os.environ dictionary in your SConscript files to initialize construction environments with values from the user's external environment. See the next section, Section 7.2, “Construction Environments”, for information on how to do this.

7.2. Construction Environments

It is rare that all of the software in a large, complicated system needs to be built the same way. For example, different source files may need different options enabled on the command line, or different executable programs need to be linked with different libraries. SCons accommodates these different build requirements by allowing you to create and configure multiple construction environments that control how the software is built. A construction environment is an object that has a number of associated construction variables, each with a name and a value. (A construction environment also has an attached set of Builder methods, about which we'll learn more later.)

7.2.1. Creating a Construction Environment: the Environment Function

A construction environment is created by the Environment method:

env = Environment()
       

By default, SCons initializes every new construction environment with a set of construction variables based on the tools that it finds on your system, plus the default set of builder methods necessary for using those tools. The construction variables are initialized with values describing the C compiler, the Fortran compiler, the linker, etc., as well as the command lines to invoke them.

When you initialize a construction environment you can set the values of the environment's construction variables to control how a program is built. For example:

 env = Environment(CC = 'gcc',
                   CCFLAGS = '-O2')

 env.Program('foo.c')
         

The construction environment in this example is still initialized with the same default construction variable values, except that the user has explicitly specified use of the GNU C compiler gcc, and further specifies that the -O2 (optimization level two) flag should be used when compiling the object file. In other words, the explicit initializations of $CC and $CCFLAGS override the default values in the newly-created construction environment. So a run from this example would look like:

% scons -Q
gcc -o foo.o -c -O2 foo.c
gcc -o foo foo.o

7.2.2. Fetching Values From a Construction Environment

You can fetch individual construction variables using the normal syntax for accessing individual named items in a Python dictionary:

env = Environment()
print "CC is:", env['CC']
        

This example SConstruct file doesn't build anything, but because it's actually a Python script, it will print the value of $CC for us:

% scons -Q
CC is: cc
scons: `.' is up to date.

A construction environment, however, is actually an object with associated methods, etc. If you want to have direct access to only the dictionary of construction variables, you can fetch this using the Dictionary method:

env = Environment(FOO = 'foo', BAR = 'bar')
dict = env.Dictionary()
for key in ['OBJSUFFIX', 'LIBSUFFIX', 'PROGSUFFIX']:
    print "key = %s, value = %s" % (key, dict[key])
         

This SConstruct file will print the specified dictionary items for us on POSIX systems as follows:

% scons -Q
key = OBJSUFFIX, value = .o
key = LIBSUFFIX, value = .a
key = PROGSUFFIX, value = 
scons: `.' is up to date.

And on Windows:

C:\>scons -Q
key = OBJSUFFIX, value = .obj
key = LIBSUFFIX, value = .lib
key = PROGSUFFIX, value = .exe
scons: `.' is up to date.

If you want to loop and print the values of all of the construction variables in a construction environment, the Python code to do that in sorted order might look something like:

env = Environment()
for item in sorted(env.Dictionary().items()):
    print "construction variable = '%s', value = '%s'" % item
      

7.2.3. Expanding Values From a Construction Environment: the subst Method

Another way to get information from a construction environment is to use the subst method on a string containing $ expansions of construction variable names. As a simple example, the example from the previous section that used env['CC'] to fetch the value of $CC could also be written as:

env = Environment()
print "CC is:", env.subst('$CC')
      

One advantage of using subst to expand strings is that construction variables in the result get re-expanded until there are no expansions left in the string. So a simple fetch of a value like $CCCOM:

env = Environment(CCFLAGS = '-DFOO')
print "CCCOM is:", env['CCCOM']
      

Will print the unexpanded value of $CCCOM, showing us the construction variables that still need to be expanded:

% scons -Q
CCCOM is: $CC $CCFLAGS $CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS -c -o $TARGET $SOURCES
scons: `.' is up to date.
      

Calling the subst method on $CCOM, however:

env = Environment(CCFLAGS = '-DFOO')
print "CCCOM is:", env.subst('$CCCOM')
      

Will recursively expand all of the construction variables prefixed with $ (dollar signs), showing us the final output:

% scons -Q
CCCOM is: gcc -DFOO -c -o
scons: `.' is up to date.
      

Note that because we're not expanding this in the context of building something there are no target or source files for $TARGET and $SOURCES to expand.

7.2.4. Handling Problems With Value Expansion

If a problem occurs when expanding a construction variable, by default it is expanded to '' (a null string), and will not cause scons to fail.

env = Environment()
print "value is:", env.subst( '->$MISSING<-' )
        
% scons -Q
value is: -><-
scons: `.' is up to date.

This default behaviour can be changed using the AllowSubstExceptions function. When a problem occurs with a variable expansion it generates an exception, and the AllowSubstExceptions function controls which of these exceptions are actually fatal and which are allowed to occur safely. By default, NameError and IndexError are the two exceptions that are allowed to occur: so instead of causing scons to fail, these are caught, the variable expanded to '' and scons execution continues. To require that all construction variable names exist, and that indexes out of range are not allowed, call AllowSubstExceptions with no extra arguments.

AllowSubstExceptions()
env = Environment()
print "value is:", env.subst( '->$MISSING<-' )
        
% scons -Q
value is:
scons: *** NameError `MISSING' trying to evaluate `$MISSING'
File "/home/my/project/SConstruct", line 3, in <module>

This can also be used to allow other exceptions that might occur, most usefully with the ${...} construction variable syntax. For example, this would allow zero-division to occur in a variable expansion in addition to the default exceptions allowed

AllowSubstExceptions(IndexError, NameError, ZeroDivisionError)
env = Environment()
print "value is:", env.subst( '->${1 / 0}<-' )
        
% scons -Q
value is: -><-
scons: `.' is up to date.

If AllowSubstExceptions is called multiple times, each call completely overwrites the previous list of allowed exceptions.

7.2.5. Controlling the Default Construction Environment: the DefaultEnvironment Function

All of the Builder functions that we've introduced so far, like Program and Library, actually use a default construction environment that contains settings for the various compilers and other tools that SCons configures by default, or otherwise knows about and has discovered on your system. The goal of the default construction environment is to make many configurations to "just work" to build software using readily available tools with a minimum of configuration changes.

You can, however, control the settings in the default construction environment by using the DefaultEnvironment function to initialize various settings:

DefaultEnvironment(CC = '/usr/local/bin/gcc')
      

When configured as above, all calls to the Program or Object Builder will build object files with the /usr/local/bin/gcc compiler.

Note that the DefaultEnvironment function returns the initialized default construction environment object, which can then be manipulated like any other construction environment. So the following would be equivalent to the previous example, setting the $CC variable to /usr/local/bin/gcc but as a separate step after the default construction environment has been initialized:

env = DefaultEnvironment()
env['CC'] = '/usr/local/bin/gcc'
      

One very common use of the DefaultEnvironment function is to speed up SCons initialization. As part of trying to make most default configurations "just work," SCons will actually search the local system for installed compilers and other utilities. This search can take time, especially on systems with slow or networked file systems. If you know which compiler(s) and/or other utilities you want to configure, you can control the search that SCons performs by specifying some specific tool modules with which to initialize the default construction environment:

env = DefaultEnvironment(tools = ['gcc', 'gnulink'],
                         CC = '/usr/local/bin/gcc')
      

So the above example would tell SCons to explicitly configure the default environment to use its normal GNU Compiler and GNU Linker settings (without having to search for them, or any other utilities for that matter), and specifically to use the compiler found at /usr/local/bin/gcc.

7.2.6. Multiple Construction Environments

The real advantage of construction environments is that you can create as many different construction environments as you need, each tailored to a different way to build some piece of software or other file. If, for example, we need to build one program with the -O2 flag and another with the -g (debug) flag, we would do this like so:

opt = Environment(CCFLAGS = '-O2')
dbg = Environment(CCFLAGS = '-g')

opt.Program('foo', 'foo.c')

dbg.Program('bar', 'bar.c')
        
% scons -Q
cc -o bar.o -c -g bar.c
cc -o bar bar.o
cc -o foo.o -c -O2 foo.c
cc -o foo foo.o

We can even use multiple construction environments to build multiple versions of a single program. If you do this by simply trying to use the Program builder with both environments, though, like this:

opt = Environment(CCFLAGS = '-O2')
dbg = Environment(CCFLAGS = '-g')

opt.Program('foo', 'foo.c')

dbg.Program('foo', 'foo.c')
        

Then SCons generates the following error:

% scons -Q

scons: *** Two environments with different actions were specified for the same target: foo.o
File "/home/my/project/SConstruct", line 6, in <module>

This is because the two Program calls have each implicitly told SCons to generate an object file named foo.o, one with a $CCFLAGS value of -O2 and one with a $CCFLAGS value of -g. SCons can't just decide that one of them should take precedence over the other, so it generates the error. To avoid this problem, we must explicitly specify that each environment compile foo.c to a separately-named object file using the Object builder, like so:

opt = Environment(CCFLAGS = '-O2')
dbg = Environment(CCFLAGS = '-g')

o = opt.Object('foo-opt', 'foo.c')
opt.Program(o)

d = dbg.Object('foo-dbg', 'foo.c')
dbg.Program(d)
        

Notice that each call to the Object builder returns a value, an internal SCons object that represents the object file that will be built. We then use that object as input to the Program builder. This avoids having to specify explicitly the object file name in multiple places, and makes for a compact, readable SConstruct file. Our SCons output then looks like:

% scons -Q
cc -o foo-dbg.o -c -g foo.c
cc -o foo-dbg foo-dbg.o
cc -o foo-opt.o -c -O2 foo.c
cc -o foo-opt foo-opt.o

7.2.7. Making Copies of Construction Environments: the Clone Method

Sometimes you want more than one construction environment to share the same values for one or more variables. Rather than always having to repeat all of the common variables when you create each construction environment, you can use the Clone method to create a copy of a construction environment.

Like the Environment call that creates a construction environment, the Clone method takes construction variable assignments, which will override the values in the copied construction environment. For example, suppose we want to use gcc to create three versions of a program, one optimized, one debug, and one with neither. We could do this by creating a "base" construction environment that sets $CC to gcc, and then creating two copies, one which sets $CCFLAGS for optimization and the other which sets $CCFLAGS for debugging:

env = Environment(CC = 'gcc')
opt = env.Clone(CCFLAGS = '-O2')
dbg = env.Clone(CCFLAGS = '-g')

env.Program('foo', 'foo.c')

o = opt.Object('foo-opt', 'foo.c')
opt.Program(o)

d = dbg.Object('foo-dbg', 'foo.c')
dbg.Program(d)
        

Then our output would look like:

% scons -Q
gcc -o foo.o -c foo.c
gcc -o foo foo.o
gcc -o foo-dbg.o -c -g foo.c
gcc -o foo-dbg foo-dbg.o
gcc -o foo-opt.o -c -O2 foo.c
gcc -o foo-opt foo-opt.o

7.2.8. Replacing Values: the Replace Method

You can replace existing construction variable values using the Replace method:

env = Environment(CCFLAGS = '-DDEFINE1')
env.Replace(CCFLAGS = '-DDEFINE2')
env.Program('foo.c')
        

The replacing value (-DDEFINE2 in the above example) completely replaces the value in the construction environment:

% scons -Q
cc -o foo.o -c -DDEFINE2 foo.c
cc -o foo foo.o

You can safely call Replace for construction variables that don't exist in the construction environment:

env = Environment()
env.Replace(NEW_VARIABLE = 'xyzzy')
print "NEW_VARIABLE =", env['NEW_VARIABLE']
        

In this case, the construction variable simply gets added to the construction environment:

% scons -Q
NEW_VARIABLE = xyzzy
scons: `.' is up to date.

Because the variables aren't expanded until the construction environment is actually used to build the targets, and because SCons function and method calls are order-independent, the last replacement "wins" and is used to build all targets, regardless of the order in which the calls to Replace() are interspersed with calls to builder methods:

env = Environment(CCFLAGS = '-DDEFINE1')
print "CCFLAGS =", env['CCFLAGS']
env.Program('foo.c')

env.Replace(CCFLAGS = '-DDEFINE2')
print "CCFLAGS =", env['CCFLAGS']
env.Program('bar.c')
        

The timing of when the replacement actually occurs relative to when the targets get built becomes apparent if we run scons without the -Q option:

% scons
scons: Reading SConscript files ...
CCFLAGS = -DDEFINE1
CCFLAGS = -DDEFINE2
scons: done reading SConscript files.
scons: Building targets ...
cc -o bar.o -c -DDEFINE2 bar.c
cc -o bar bar.o
cc -o foo.o -c -DDEFINE2 foo.c
cc -o foo foo.o
scons: done building targets.

Because the replacement occurs while the SConscript files are being read, the $CCFLAGS variable has already been set to -DDEFINE2 by the time the foo.o target is built, even though the call to the Replace method does not occur until later in the SConscript file.

7.2.9. Setting Values Only If They're Not Already Defined: the SetDefault Method

Sometimes it's useful to be able to specify that a construction variable should be set to a value only if the construction environment does not already have that variable defined You can do this with the SetDefault method, which behaves similarly to the set_default method of Python dictionary objects:

env.SetDefault(SPECIAL_FLAG = '-extra-option')
      

This is especially useful when writing your own Tool modules to apply variables to construction environments.

7.2.10. Appending to the End of Values: the Append Method

You can append a value to an existing construction variable using the Append method:

env = Environment(CCFLAGS = ['-DMY_VALUE'])
env.Append(CCFLAGS = ['-DLAST'])
env.Program('foo.c')
        

SCons then supplies both the -DMY_VALUE and -DLAST flags when compiling the object file:

% scons -Q
cc -o foo.o -c -DMY_VALUE -DLAST foo.c
cc -o foo foo.o

If the construction variable doesn't already exist, the Append method will create it:

env = Environment()
env.Append(NEW_VARIABLE = 'added')
print "NEW_VARIABLE =", env['NEW_VARIABLE']
        

Which yields:

% scons -Q
NEW_VARIABLE = added
scons: `.' is up to date.

Note that the Append function tries to be "smart" about how the new value is appended to the old value. If both are strings, the previous and new strings are simply concatenated. Similarly, if both are lists, the lists are concatenated. If, however, one is a string and the other is a list, the string is added as a new element to the list.

7.2.11. Appending Unique Values: the AppendUnique Method

Some times it's useful to add a new value only if the existing construction variable doesn't already contain the value. This can be done using the AppendUnique method:

env.AppendUnique(CCFLAGS=['-g'])
      

In the above example, the -g would be added only if the $CCFLAGS variable does not already contain a -g value.

7.2.12. Appending to the Beginning of Values: the Prepend Method

You can append a value to the beginning of an existing construction variable using the Prepend method:

env = Environment(CCFLAGS = ['-DMY_VALUE'])
env.Prepend(CCFLAGS = ['-DFIRST'])
env.Program('foo.c')
        

SCons then supplies both the -DFIRST and -DMY_VALUE flags when compiling the object file:

% scons -Q
cc -o foo.o -c -DFIRST -DMY_VALUE foo.c
cc -o foo foo.o

If the construction variable doesn't already exist, the Prepend method will create it:

env = Environment()
env.Prepend(NEW_VARIABLE = 'added')
print "NEW_VARIABLE =", env['NEW_VARIABLE']
        

Which yields:

% scons -Q
NEW_VARIABLE = added
scons: `.' is up to date.

Like the Append function, the Prepend function tries to be "smart" about how the new value is appended to the old value. If both are strings, the previous and new strings are simply concatenated. Similarly, if both are lists, the lists are concatenated. If, however, one is a string and the other is a list, the string is added as a new element to the list.

7.2.13. Prepending Unique Values: the PrependUnique Method

Some times it's useful to add a new value to the beginning of a construction variable only if the existing value doesn't already contain the to-be-added value. This can be done using the PrependUnique method:

env.PrependUnique(CCFLAGS=['-g'])
      

In the above example, the -g would be added only if the $CCFLAGS variable does not already contain a -g value.

7.3. Controlling the Execution Environment for Issued Commands

When SCons builds a target file, it does not execute the commands with the same external environment that you used to execute SCons. Instead, it uses the dictionary stored in the $ENV construction variable as the external environment for executing commands.

The most important ramification of this behavior is that the PATH environment variable, which controls where the operating system will look for commands and utilities, is not the same as in the external environment from which you called SCons. This means that SCons will not, by default, necessarily find all of the tools that you can execute from the command line.

The default value of the PATH environment variable on a POSIX system is /usr/local/bin:/bin:/usr/bin. The default value of the PATH environment variable on a Windows system comes from the Windows registry value for the command interpreter. If you want to execute any commands--compilers, linkers, etc.--that are not in these default locations, you need to set the PATH value in the $ENV dictionary in your construction environment.

The simplest way to do this is to initialize explicitly the value when you create the construction environment; this is one way to do that:

path = ['/usr/local/bin', '/bin', '/usr/bin']
env = Environment(ENV = {'PATH' : path})
    

Assign a dictionary to the $ENV construction variable in this way completely resets the external environment so that the only variable that will be set when external commands are executed will be the PATH value. If you want to use the rest of the values in $ENV and only set the value of PATH, the most straightforward way is probably:

env['ENV']['PATH'] = ['/usr/local/bin', '/bin', '/usr/bin']
    

Note that SCons does allow you to define the directories in the PATH in a string, separated by the pathname-separator character for your system (':' on POSIX systems, ';' on Windows):

env['ENV']['PATH'] = '/usr/local/bin:/bin:/usr/bin'
    

But doing so makes your SConscript file less portable, (although in this case that may not be a huge concern since the directories you list are likley system-specific, anyway).

7.3.1. Propagating PATH From the External Environment

You may want to propagate the external PATH to the execution environment for commands. You do this by initializing the PATH variable with the PATH value from the os.environ dictionary, which is Python's way of letting you get at the external environment:

import os
env = Environment(ENV = {'PATH' : os.environ['PATH']})
      

Alternatively, you may find it easier to just propagate the entire external environment to the execution environment for commands. This is simpler to code than explicity selecting the PATH value:

import os
env = Environment(ENV = os.environ)
      

Either of these will guarantee that SCons will be able to execute any command that you can execute from the command line. The drawback is that the build can behave differently if it's run by people with different PATH values in their environment--for example, if both the /bin and /usr/local/bin directories have different cc commands, then which one will be used to compile programs will depend on which directory is listed first in the user's PATH variable.

7.3.2. Adding to PATH Values in the Execution Environment

One of the most common requirements for manipulating a variable in the execution environment is to add one or more custom directories to a search like the $PATH variable on Linux or POSIX systems, or the %PATH% variable on Windows, so that a locally-installed compiler or other utility can be found when SCons tries to execute it to update a target. SCons provides PrependENVPath and AppendENVPath functions to make adding things to execution variables convenient. You call these functions by specifying the variable to which you want the value added, and then value itself. So to add some /usr/local directories to the $PATH and $LIB variables, you might:

env = Environment(ENV = os.environ)
env.PrependENVPath('PATH', '/usr/local/bin')
env.AppendENVPath('LIB', '/usr/local/lib')
      

Note that the added values are strings, and if you want to add multiple directories to a variable like $PATH, you must include the path separate character (: on Linux or POSIX, ; on Windows) in the string.

Chapter 8. Automatically Putting Command-line Options into their Construction Variables

This chapter describes the MergeFlags, ParseFlags, and ParseConfig methods of a construction environment.

8.1. Merging Options into the Environment: the MergeFlags Function

SCons construction environments have a MergeFlags method that merges a dictionary of values into the construction environment. MergeFlags treats each value in the dictionary as a list of options such as one might pass to a command (such as a compiler or linker). MergeFlags will not duplicate an option if it already exists in the construction environment variable.

MergeFlags tries to be intelligent about merging options. When merging options to any variable whose name ends in PATH, MergeFlags keeps the leftmost occurrence of the option, because in typical lists of directory paths, the first occurrence "wins." When merging options to any other variable name, MergeFlags keeps the rightmost occurrence of the option, because in a list of typical command-line options, the last occurrence "wins."

env = Environment()
env.Append(CCFLAGS = '-option -O3 -O1')
flags = { 'CCFLAGS' : '-whatever -O3' }
env.MergeFlags(flags)
print env['CCFLAGS']
   
% scons -Q
['-option', '-O1', '-whatever', '-O3']
scons: `.' is up to date.

Note that the default value for $CCFLAGS is an internal SCons object which automatically converts the options we specified as a string into a list.

env = Environment()
env.Append(CPPPATH = ['/include', '/usr/local/include', '/usr/include'])
flags = { 'CPPPATH' : ['/usr/opt/include', '/usr/local/include'] }
env.MergeFlags(flags)
print env['CPPPATH']
   
% scons -Q
['/include', '/usr/local/include', '/usr/include', '/usr/opt/include']
scons: `.' is up to date.

Note that the default value for $CPPPATH is a normal Python list, so we must specify its values as a list in the dictionary we pass to the MergeFlags function.

If MergeFlags is passed anything other than a dictionary, it calls the ParseFlags method to convert it into a dictionary.

env = Environment()
env.Append(CCFLAGS = '-option -O3 -O1')
env.Append(CPPPATH = ['/include', '/usr/local/include', '/usr/include'])
env.MergeFlags('-whatever -I/usr/opt/include -O3 -I/usr/local/include')
print env['CCFLAGS']
print env['CPPPATH']
   
% scons -Q
['-option', '-O1', '-whatever', '-O3']
['/include', '/usr/local/include', '/usr/include', '/usr/opt/include']
scons: `.' is up to date.

In the combined example above, ParseFlags has sorted the options into their corresponding variables and returned a dictionary for MergeFlags to apply to the construction variables in the specified construction environment.

8.2. Separating Compile Arguments into their Variables: the ParseFlags Function

SCons has a bewildering array of construction variables for different types of options when building programs. Sometimes you may not know exactly which variable should be used for a particular option.

SCons construction environments have a ParseFlags method that takes a set of typical command-line options and distrbutes them into the appropriate construction variables. Historically, it was created to support the ParseConfig method, so it focuses on options used by the GNU Compiler Collection (GCC) for the C and C++ toolchains.

ParseFlags returns a dictionary containing the options distributed into their respective construction variables. Normally, this dictionary would be passed to MergeFlags to merge the options into a construction environment, but the dictionary can be edited if desired to provide additional functionality. (Note that if the flags are not going to be edited, calling MergeFlags with the options directly will avoid an additional step.)

env = Environment()
d = env.ParseFlags("-I/opt/include -L/opt/lib -lfoo")
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')
   
% scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cc -o f1.o -c -I/opt/include f1.c
cc -o f1 f1.o -L/opt/lib -lfoo

Note that if the options are limited to generic types like those above, they will be correctly translated for other platform types:

C:\>scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cl /Fof1.obj /c f1.c /nologo /I\opt\include
link /nologo /OUT:f1.exe /LIBPATH:\opt\lib foo.lib f1.obj
embedManifestExeCheck(target, source, env)

Since the assumption is that the flags are used for the GCC toolchain, unrecognized flags are placed in $CCFLAGS so they will be used for both C and C++ compiles:

env = Environment()
d = env.ParseFlags("-whatever")
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')
   
% scons -Q
CCFLAGS -whatever
cc -o f1.o -c -whatever f1.c
cc -o f1 f1.o

ParseFlags will also accept a (recursive) list of strings as input; the list is flattened before the strings are processed:

env = Environment()
d = env.ParseFlags(["-I/opt/include", ["-L/opt/lib", "-lfoo"]])
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')
   
% scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cc -o f1.o -c -I/opt/include f1.c
cc -o f1 f1.o -L/opt/lib -lfoo

If a string begins with a "!" (an exclamation mark, often called a bang), the string is passed to the shell for execution. The output of the command is then parsed:

env = Environment()
d = env.ParseFlags(["!echo -I/opt/include", "!echo -L/opt/lib", "-lfoo"])
for k,v in sorted(d.items()):
    if v:
        print k, v
env.MergeFlags(d)
env.Program('f1.c')
   
% scons -Q
CPPPATH ['/opt/include']
LIBPATH ['/opt/lib']
LIBS ['foo']
cc -o f1.o -c -I/opt/include f1.c
cc -o f1 f1.o -L/opt/lib -lfoo

ParseFlags is regularly updated for new options; consult the man page for details about those currently recognized.

8.3. Finding Installed Library Information: the ParseConfig Function

Configuring the right options to build programs to work with libraries--especially shared libraries--that are available on POSIX systems can be very complicated. To help this situation, various utilies with names that end in config return the command-line options for the GNU Compiler Collection (GCC) that are needed to use these libraries; for example, the command-line options to use a library named lib would be found by calling a utility named lib-config.

A more recent convention is that these options are available from the generic pkg-config program, which has common framework, error handling, and the like, so that all the package creator has to do is provide the set of strings for his particular package.

SCons construction environments have a ParseConfig method that executes a *config utility (either pkg-config or a more specific utility) and configures the appropriate construction variables in the environment based on the command-line options returned by the specified command.

env = Environment()
env['CPPPATH'] = ['/lib/compat']
env.ParseConfig("pkg-config x11 --cflags --libs")
print env['CPPPATH']
   

SCons will execute the specified command string, parse the resultant flags, and add the flags to the appropriate environment variables.

% scons -Q
['/lib/compat', '/usr/X11/include']
scons: `.' is up to date.
 

In the example above, SCons has added the include directory to CPPPATH. (Depending upon what other flags are emitted by the pkg-config command, other variables may have been extended as well.)

Note that the options are merged with existing options using the MergeFlags method, so that each option only occurs once in the construction variable:

env = Environment()
env.ParseConfig("pkg-config x11 --cflags --libs")
env.ParseConfig("pkg-config x11 --cflags --libs")
print env['CPPPATH']
   
% scons -Q
['/usr/X11/include']
scons: `.' is up to date.
 

Chapter 9. Controlling Build Output

A key aspect of creating a usable build configuration is providing good output from the build so its users can readily understand what the build is doing and get information about how to control the build. SCons provides several ways of controlling output from the build configuration to help make the build more useful and understandable.

9.1. Providing Build Help: the Help Function

It's often very useful to be able to give users some help that describes the specific targets, build options, etc., that can be used for your build. SCons provides the Help function to allow you to specify this help text:

Help("""
Type: 'scons program' to build the production program,
      'scons debug' to build the debug version.
""")
       

(Note the above use of the Python triple-quote syntax, which comes in very handy for specifying multi-line strings like help text.)

When the SConstruct or SConscript files contain such a call to the Help function, the specified help text will be displayed in response to the SCons -h option:

% scons -h
scons: Reading SConscript files ...
scons: done reading SConscript files.

Type: 'scons program' to build the production program,
      'scons debug' to build the debug version.

Use scons -H for help about command-line options.

The SConscript files may contain multiple calls to the Help function, in which case the specified text(s) will be concatenated when displayed. This allows you to split up the help text across multiple SConscript files. In this situation, the order in which the SConscript files are called will determine the order in which the Help functions are called, which will determine the order in which the various bits of text will get concatenated.

Another use would be to make the help text conditional on some variable. For example, suppose you only want to display a line about building a Windows-only version of a program when actually run on Windows. The following SConstruct file:

env = Environment()

Help("\nType: 'scons program' to build the production program.\n")

if env['PLATFORM'] == 'win32':
    Help("\nType: 'scons windebug' to build the Windows debug version.\n")
       

Will display the complete help text on Windows:

C:\>scons -h
scons: Reading SConscript files ...
scons: done reading SConscript files.

Type: 'scons program' to build the production program.

Type: 'scons windebug' to build the Windows debug version.

Use scons -H for help about command-line options.

But only show the relevant option on a Linux or UNIX system:

% scons -h
scons: Reading SConscript files ...
scons: done reading SConscript files.

Type: 'scons program' to build the production program.

Use scons -H for help about command-line options.

If there is no Help text in the SConstruct or SConscript files, SCons will revert to displaying its standard list that describes the SCons command-line options. This list is also always displayed whenever the -H option is used.

9.2. Controlling How SCons Prints Build Commands: the $*COMSTR Variables

Sometimes the commands executed to compile object files or link programs (or build other targets) can get very long, long enough to make it difficult for users to distinguish error messages or other important build output from the commands themselves. All of the default $*COM variables that specify the command lines used to build various types of target files have a corresponding $*COMSTR variable that can be set to an alternative string that will be displayed when the target is built.

For example, suppose you want to have SCons display a "Compiling" message whenever it's compiling an object file, and a "Linking" when it's linking an executable. You could write a SConstruct file that looks like:

env = Environment(CCCOMSTR = "Compiling $TARGET",
                  LINKCOMSTR = "Linking $TARGET")
env.Program('foo.c')
       

Which would then yield the output:

% scons -Q
Compiling foo.o
Linking foo
    

SCons performs complete variable substitution on $*COMSTR variables, so they have access to all of the standard variables like $TARGET $SOURCES, etc., as well as any construction variables that happen to be configured in the construction environment used to build a specific target.

Of course, sometimes it's still important to be able to see the exact command that SCons will execute to build a target. For example, you may simply need to verify that SCons is configured to supply the right options to the compiler, or a developer may want to cut-and-paste a compile command to add a few options for a custom test.

One common way to give users control over whether or not SCons should print the actual command line or a short, configured summary is to add support for a VERBOSE command-line variable to your SConstruct file. A simple configuration for this might look like:

env = Environment()
if ARGUMENTS.get('VERBOSE') != "1':
    env['CCCOMSTR'] = "Compiling $TARGET"
    env['LINKCOMSTR'] = "Linking $TARGET"
env.Program('foo.c')
       

By only setting the appropriate $*COMSTR variables if the user specifies VERBOSE=1 on the command line, the user has control over how SCons displays these particular command lines:

% scons -Q
Compiling foo.o
Linking foo
% scons -Q -c
Removed foo.o
Removed foo
% scons -Q VERBOSE=1
cc -o foo.o -c foo.c
cc -o foo foo.o
    

9.3. Providing Build Progress Output: the Progress Function

Another aspect of providing good build output is to give the user feedback about what SCons is doing even when nothing is being built at the moment. This can be especially true for large builds when most of the targets are already up-to-date. Because SCons can take a long time making absolutely sure that every target is, in fact, up-to-date with respect to a lot of dependency files, it can be easy for users to mistakenly conclude that SCons is hung or that there is some other problem with the build.

One way to deal with this perception is to configure SCons to print something to let the user know what it's "thinking about." The Progress function allows you to specify a string that will be printed for every file that SCons is "considering" while it is traversing the dependency graph to decide what targets are or are not up-to-date.

Progress('Evaluating $TARGET\n')
Program('f1.c')
Program('f2.c')
      

Note that the Progress function does not arrange for a newline to be printed automatically at the end of the string (as does the Python print statement), and we must specify the \n that we want printed at the end of the configured string. This configuration, then, will have SCons print that it is Evaluating each file that it encounters in turn as it traverses the dependency graph:

% scons -Q
Evaluating SConstruct
Evaluating f1.c
Evaluating f1.o
cc -o f1.o -c f1.c
Evaluating f1
cc -o f1 f1.o
Evaluating f2.c
Evaluating f2.o
cc -o f2.o -c f2.c
Evaluating f2
cc -o f2 f2.o
Evaluating .

Of course, normally you don't want to add all of these additional lines to your build output, as that can make it difficult for the user to find errors or other important messages. A more useful way to display this progress might be to have the file names printed directly to the user's screen, not to the same standard output stream where build output is printed, and to use a carriage return character (\r) so that each file name gets re-printed on the same line. Such a configuration would look like:

Progress('$TARGET\r',
         file=open('/dev/tty', 'w'),
         overwrite=True)
Program('f1.c')
Program('f2.c')
    

Note that we also specified the overwrite=True argument to the Progress function, which causes SCons to "wipe out" the previous string with space characters before printing the next Progress string. Without the overwrite=True argument, a shorter file name would not overwrite all of the charactes in a longer file name that precedes it, making it difficult to tell what the actual file name is on the output. Also note that we opened up the /dev/tty file for direct access (on POSIX) to the user's screen. On Windows, the equivalent would be to open the con: file name.

Also, it's important to know that although you can use $TARGET to substitute the name of the node in the string, the Progress function does not perform general variable substitution (because there's not necessarily a construction environment involved in evaluating a node like a source file, for example).

You can also specify a list of strings to the Progress function, in which case SCons will display each string in turn. This can be used to implement a "spinner" by having SCons cycle through a sequence of strings:

Progress(['-\r', '\\\r', '|\r', '/\r'], interval=5)
Program('f1.c')
Program('f2.c')
    

Note that here we have also used the interval= keyword argument to have SCons only print a new "spinner" string once every five evaluated nodes. Using an interval= count, even with strings that use $TARGET like our examples above, can be a good way to lessen the work that SCons expends printing Progress strings, while still giving the user feedback that indicates SCons is still working on evaluating the build.

Lastly, you can have direct control over how to print each evaluated node by passing a Python function (or other Python callable) to the Progress function. Your function will be called for each evaluated node, allowing you to implement more sophisticated logic like adding a counter:

screen = open('/dev/tty', 'w')
count = 0
def progress_function(node)
    count += 1
    screen.write('Node %4d: %s\r' % (count, node))

Progress(progress_function)
      

Of course, if you choose, you could completely ignore the node argument to the function, and just print a count, or anything else you wish.

(Note that there's an obvious follow-on question here: how would you find the total number of nodes that will be evaluated so you can tell the user how close the build is to finishing? Unfortunately, in the general case, there isn't a good way to do that, short of having SCons evaluate its dependency graph twice, first to count the total and the second time to actually build the targets. This would be necessary because you can't know in advance which target(s) the user actually requested to be built. The entire build may consist of thousands of Nodes, for example, but maybe the user specifically requested that only a single object file be built.)

9.4. Printing Detailed Build Status: the GetBuildFailures Function

SCons, like most build tools, returns zero status to the shell on success and nonzero status on failure. Sometimes it's useful to give more information about the build status at the end of the run, for instance to print an informative message, send an email, or page the poor slob who broke the build.

SCons provides a GetBuildFailures method that you can use in a python atexit function to get a list of objects describing the actions that failed while attempting to build targets. There can be more than one if you're using -j. Here's a simple example:

import atexit

def print_build_failures():
    from SCons.Script import GetBuildFailures
    for bf in GetBuildFailures():
        print "%s failed: %s" % (bf.node, bf.errstr)
atexit.register(print_build_failures)
      

The atexit.register call registers print_build_failures as an atexit callback, to be called before SCons exits. When that function is called, it calls GetBuildFailures to fetch the list of failed objects. See the man page for the detailed contents of the returned objects; some of the more useful attributes are .node, .errstr, .filename, and .command. The filename is not necessarily the same file as the node; the node is the target that was being built when the error occurred, while the filenameis the file or dir that actually caused the error. Note: only call GetBuildFailures at the end of the build; calling it at any other time is undefined.

Here is a more complete example showing how to turn each element of GetBuildFailures into a string:

# Make the build fail if we pass fail=1 on the command line
if ARGUMENTS.get('fail', 0):
    Command('target', 'source', ['/bin/false'])

def bf_to_str(bf):
    """Convert an element of GetBuildFailures() to a string
    in a useful way."""
    import SCons.Errors
    if bf is None: # unknown targets product None in list
        return '(unknown tgt)'
    elif isinstance(bf, SCons.Errors.StopError):
        return str(bf)
    elif bf.node:
        return str(bf.node) + ': ' + bf.errstr
    elif bf.filename:
        return bf.filename + ': ' + bf.errstr
    return 'unknown failure: ' + bf.errstr
import atexit

def build_status():
    """Convert the build status to a 2-tuple, (status, msg)."""
    from SCons.Script import GetBuildFailures
    bf = GetBuildFailures()
    if bf:
        # bf is normally a list of build failures; if an element is None,
        # it's because of a target that scons doesn't know anything about.
        status = 'failed'
        failures_message = "\n".join(["Failed building %s" % bf_to_str(x)
                           for x in bf if x is not None])
    else:
        # if bf is None, the build completed successfully.
        status = 'ok'
        failures_message = ''
    return (status, failures_message)

def display_build_status():
    """Display the build status.  Called by atexit.
    Here you could do all kinds of complicated things."""
    status, failures_message = build_status()
    if status == 'failed':
       print "FAILED!!!!"  # could display alert, ring bell, etc.
    elif status == 'ok':
       print "Build succeeded."
    print failures_message

atexit.register(display_build_status)
      

When this runs, you'll see the appropriate output:

% scons -Q
scons: `.' is up to date.
Build succeeded.
% scons -Q fail=1
scons: *** [target] Source `source' not found, needed by target `target'.
FAILED!!!!
Failed building target: Source `source' not found, needed by target `target'.

Chapter 10. Controlling a Build From the Command Line

SCons provides a number of ways for the writer of the SConscript files to give the users who will run SCons a great deal of control over the build execution. The arguments that the user can specify on the command line are broken down into three types:

Options

Command-line options always begin with one or two - (hyphen) characters. SCons provides ways for you to examine and set options values from within your SConscript files, as well as the ability to define your own custom options. See Section 10.1, “Command-Line Options”, below.

Variables

Any command-line argument containing an = (equal sign) is considered a variable setting with the form variable=value. SCons provides direct access to all of the command-line variable settings, the ability to apply command-line variable settings to construction environments, and functions for configuring specific types of variables (Boolean values, path names, etc.) with automatic validation of the user's specified values. See Section 10.2, “Command-Line variable=value Build Variables”, below.

Targets

Any command-line argument that is not an option or a variable setting (does not begin with a hyphen and does not contain an equal sign) is considered a target that the user (presumably) wants SCons to build. A list of Node objects representing the target or targets to build. SCons provides access to the list of specified targets, as well as ways to set the default list of targets from within the SConscript files. See Section 10.3, “Command-Line Targets”, below.

10.1. Command-Line Options

SCons has many command-line options that control its behavior. A SCons command-line option always begins with one or two - (hyphen) characters.

10.1.1. Not Having to Specify Command-Line Options Each Time: the SCONSFLAGS Environment Variable

Users may find themselves supplying the same command-line options every time they run SCons. For example, you might find it saves time to specify a value of -j 2 to have SCons run up to two build commands in parallel. To avoid having to type -j 2 by hand every time, you can set the external environment variable SCONSFLAGS to a string containing command-line options that you want SCons to use.

If, for example, you're using a POSIX shell that's compatible with the Bourne shell, and you always want SCons to use the -Q option, you can set the SCONSFLAGS environment as follows:

% scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
    ... [build output] ...
scons: done building targets.
% export SCONSFLAGS="-Q"
% scons
    ... [build output] ...

Users of csh-style shells on POSIX systems can set the SCONSFLAGS environment as follows:

$ setenv SCONSFLAGS "-Q"
      

Windows users may typically want to set the SCONSFLAGS in the appropriate tab of the System Properties window.

10.1.2. Getting Values Set by Command-Line Options: the GetOption Function

SCons provides the GetOption function to get the values set by the various command-line options. One common use of this is to check whether or not the -h or --help option has been specified. Normally, SCons does not print its help text until after it has read all of the SConscript files, because it's possible that help text has been added by some subsidiary SConscript file deep in the source tree hierarchy. Of course, reading all of the SConscript files takes extra time.

If you know that your configuration does not define any additional help text in subsidiary SConscript files, you can speed up the command-line help available to users by using the GetOption function to load the subsidiary SConscript files only if the the user has not specified the -h or --help option, like so:

if not GetOption('help'):
    SConscript('src/SConscript', export='env')
      

In general, the string that you pass to the GetOption function to fetch the value of a command-line option setting is the same as the "most common" long option name (beginning with two hyphen characters), although there are some exceptions. The list of SCons command-line options and the GetOption strings for fetching them, are available in the Section 10.1.4, “Strings for Getting or Setting Values of SCons Command-Line Options” section, below.

10.1.3. Setting Values of Command-Line Options: the SetOption Function

You can also set the values of SCons command-line options from within the SConscript files by using the SetOption function. The strings that you use to set the values of SCons command-line options are available in the Section 10.1.4, “Strings for Getting or Setting Values of SCons Command-Line Options” section, below.

One use of the SetOption function is to specify a value for the -j or --jobs option, so that users get the improved performance of a parallel build without having to specify the option by hand. A complicating factor is that a good value for the -j option is somewhat system-dependent. One rough guideline is that the more processors your system has, the higher you want to set the -j value, in order to take advantage of the number of CPUs.

For example, suppose the administrators of your development systems have standardized on setting a NUM_CPU environment variable to the number of processors on each system. A little bit of Python code to access the environment variable and the SetOption function provide the right level of flexibility:

import os
num_cpu = int(os.environ.get('NUM_CPU', 2))
SetOption('num_jobs', num_cpu)
print "running with -j", GetOption('num_jobs')
        

The above snippet of code sets the value of the --jobs option to the value specified in the $NUM_CPU environment variable. (This is one of the exception cases where the string is spelled differently from the from command-line option. The string for fetching or setting the --jobs value is num_jobs for historical reasons.) The code in this example prints the num_jobs value for illustrative purposes. It uses a default value of 2 to provide some minimal parallelism even on single-processor systems:

% scons -Q
running with -j 2
scons: `.' is up to date.

But if the $NUM_CPU environment variable is set, then we use that for the default number of jobs:

% export NUM_CPU="4"
% scons -Q
running with -j 4
scons: `.' is up to date.

But any explicit -j or --jobs value the user specifies an the command line is used first, regardless of whether or not the $NUM_CPU environment variable is set:

% scons -Q -j 7
running with -j 7
scons: `.' is up to date.
% export NUM_CPU="4"
% scons -Q -j 3
running with -j 3
scons: `.' is up to date.

10.1.4. Strings for Getting or Setting Values of SCons Command-Line Options

The strings that you can pass to the GetOption and SetOption functions usually correspond to the first long-form option name (beginning with two hyphen characters: --), after replacing any remaining hyphen characters with underscores.

The full list of strings and the variables they correspond to is as follows:

String for GetOption and SetOptionCommand-Line Option(s)
cache_debug--cache-debug
cache_disable--cache-disable
cache_force--cache-force
cache_show--cache-show
clean-c, --clean, --remove
config--config
directory-C, --directory
diskcheck--diskcheck
duplicate--duplicate
file-f, --file, --makefile , --sconstruct
help-h, --help
ignore_errors--ignore-errors
implicit_cache--implicit-cache
implicit_deps_changed--implicit-deps-changed
implicit_deps_unchanged--implicit-deps-unchanged
interactive--interact, --interactive
keep_going-k, --keep-going
max_drift--max-drift
no_exec-n, --no-exec, --just-print, --dry-run, --recon
no_site_dir--no-site-dir
num_jobs-j, --jobs
profile_file--profile
question-q, --question
random--random
repository-Y, --repository, --srcdir
silent-s, --silent, --quiet
site_dir--site-dir
stack_size--stack-size
taskmastertrace_file--taskmastertrace
warn--warn --warning

10.1.5. Adding Custom Command-Line Options: the AddOption Function

SCons also allows you to define your own command-line options with the AddOption function. The AddOption function takes the same arguments as the optparse.add_option function from the standard Python library. [3] Once you have added a custom command-line option with the AddOption function, the value of the option (if any) is immediately available using the standard GetOption function. (The value can also be set using SetOption, although that's not very useful in practice because a default value can be specified in directly in the AddOption call.)

One useful example of using this functionality is to provide a --prefix for users:

AddOption('--prefix',
          dest='prefix',
          type='string',
          nargs=1,
          action='store',
          metavar='DIR',
          help='installation prefix')

env = Environment(PREFIX = GetOption('prefix'))

installed_foo = env.Install('$PREFIX/usr/bin', 'foo.in')
Default(installed_foo)
        

The above code uses the GetOption function to set the $PREFIX construction variable to any value that the user specifies with a command-line option of --prefix. Because $PREFIX will expand to a null string if it's not initialized, running SCons without the option of --prefix will install the file in the /usr/bin/ directory:

% scons -Q -n
Install file: "foo.in" as "/usr/bin/foo.in"

But specifying --prefix=/tmp/install on the command line causes the file to be installed in the /tmp/install/usr/bin/ directory:

% scons -Q -n --prefix=/tmp/install
Install file: "foo.in" as "/tmp/install/usr/bin/foo.in"

10.2. Command-Line variable=value Build Variables

You may want to control various aspects of your build by allowing the user to specify variable=value values on the command line. For example, suppose you want users to be able to build a debug version of a program by running SCons as follows:

% scons -Q debug=1
    

SCons provides an ARGUMENTS dictionary that stores all of the variable=value assignments from the command line. This allows you to modify aspects of your build in response to specifications on the command line. (Note that unless you want to require that users always specify a variable, you probably want to use the Python ARGUMENTS.get() function, which allows you to specify a default value to be used if there is no specification on the command line.)

The following code sets the $CCFLAGS construction variable in response to the debug flag being set in the ARGUMENTS dictionary:

env = Environment()
debug = ARGUMENTS.get('debug', 0)
if int(debug):
    env.Append(CCFLAGS = '-g')
env.Program('prog.c')
       

This results in the -g compiler option being used when debug=1 is used on the command line:

% scons -Q debug=0
cc -o prog.o -c prog.c
cc -o prog prog.o
% scons -Q debug=0
scons: `.' is up to date.
% scons -Q debug=1
cc -o prog.o -c -g prog.c
cc -o prog prog.o
% scons -Q debug=1
scons: `.' is up to date.

Notice that SCons keeps track of the last values used to build the object files, and as a result correctly rebuilds the object and executable files only when the value of the debug argument has changed.

The ARGUMENTS dictionary has two minor drawbacks. First, because it is a dictionary, it can only store one value for each specified keyword, and thus only "remembers" the last setting for each keyword on the command line. This makes the ARGUMENTS dictionary inappropriate if users should be able to specify multiple values on the command line for a given keyword. Second, it does not preserve the order in which the variable settings were specified, which is a problem if you want the configuration to behave differently in response to the order in which the build variable settings were specified on the command line.

To accomodate these requirements, SCons provides an ARGLIST variable that gives you direct access to variable=value settings on the command line, in the exact order they were specified, and without removing any duplicate settings. Each element in the ARGLIST variable is itself a two-element list containing the keyword and the value of the setting, and you must loop through, or otherwise select from, the elements of ARGLIST to process the specific settings you want in whatever way is appropriate for your configuration. For example, the following code to let the user add to the CPPDEFINES construction variable by specifying multiple define= settings on the command line:

cppdefines = []
for key, value in ARGLIST:
    if key == 'define':
        cppdefines.append(value)
env = Environment(CPPDEFINES = cppdefines)
env.Object('prog.c')
       

Yields the following output:

% scons -Q define=FOO
cc -o prog.o -c -DFOO prog.c
% scons -Q define=FOO define=BAR
cc -o prog.o -c -DFOO -DBAR prog.c

Note that the ARGLIST and ARGUMENTS variables do not interfere with each other, but merely provide slightly different views into how the user specified variable=value settings on the command line. You can use both variables in the same SCons configuration. In general, the ARGUMENTS dictionary is more convenient to use, (since you can just fetch variable settings through a dictionary access), and the ARGLIST list is more flexible (since you can examine the specific order in which the user's command-line variabe settings).

10.2.1. Controlling Command-Line Build Variables

Being able to use a command-line build variable like debug=1 is handy, but it can be a chore to write specific Python code to recognize each such variable, check for errors and provide appropriate messages, and apply the values to a construction variable. To help with this, SCons supports a class to define such build variables easily, and a mechanism to apply the build variables to a construction environment. This allows you to control how the build variables affect construction environments.

For example, suppose that you want users to set a RELEASE construction variable on the command line whenever the time comes to build a program for release, and that the value of this variable should be added to the command line with the appropriate -D option (or other command line option) to pass the value to the C compiler. Here's how you might do that by setting the appropriate value in a dictionary for the $CPPDEFINES construction variable:

vars = Variables(None, ARGUMENTS)
vars.Add('RELEASE', 'Set to 1 to build for release', 0)
env = Environment(variables = vars,
                  CPPDEFINES={'RELEASE_BUILD' : '${RELEASE}'})
env.Program(['foo.c', 'bar.c'])
        

This SConstruct file first creates a Variables object which uses the values from the command-line options dictionary ARGUMENTS (the vars = Variables(None, ARGUMENTS) call). It then uses the object's Add method to indicate that the RELEASE variable can be set on the command line, and that its default value will be 0 (the third argument to the Add method). The second argument is a line of help text; we'll learn how to use it in the next section.

We then pass the created Variables object as a variables keyword argument to the Environment call used to create the construction environment. This then allows a user to set the RELEASE build variable on the command line and have the variable show up in the command line used to build each object from a C source file:

% scons -Q RELEASE=1
cc -o bar.o -c -DRELEASE_BUILD=1 bar.c
cc -o foo.o -c -DRELEASE_BUILD=1 foo.c
cc -o foo foo.o bar.o

NOTE: Before SCons release 0.98.1, these build variables were known as "command-line build options." The class was actually named the Options class, and in the sections below, the various functions were named BoolOption, EnumOption, ListOption, PathOption, PackageOption and AddOptions. These older names still work, and you may encounter them in older SConscript files, but they have been officially deprecated as of SCons version 2.0.

10.2.2. Providing Help for Command-Line Build Variables

To make command-line build variables most useful, you ideally want to provide some help text that will describe the available variables when the user runs scons -h. You could write this text by hand, but SCons provides an easier way. Variables objects support a GenerateHelpText method that will, as its name suggests, generate text that describes the various variables that have been added to it. You then pass the output from this method to the Help function:

vars = Variables(None, ARGUMENTS)
vars.Add('RELEASE', 'Set to 1 to build for release', 0)
env = Environment(variables = vars)
Help(vars.GenerateHelpText(env))
        

SCons will now display some useful text when the -h option is used:

% scons -Q -h

RELEASE: Set to 1 to build for release
    default: 0
    actual: 0

Use scons -H for help about command-line options.

Notice that the help output shows the default value, and the current actual value of the build variable.

10.2.3. Reading Build Variables From a File

Giving the user a way to specify the value of a build variable on the command line is useful, but can still be tedious if users must specify the variable every time they run SCons. We can let users provide customized build variable settings in a local file by providing a file name when we create the Variables object:

vars = Variables('custom.py')
vars.Add('RELEASE', 'Set to 1 to build for release', 0)
env = Environment(variables = vars,
                  CPPDEFINES={'RELEASE_BUILD' : '${RELEASE}'})
env.Program(['foo.c', 'bar.c'])
Help(vars.GenerateHelpText(env))
        

This then allows the user to control the RELEASE variable by setting it in the custom.py file:

RELEASE = 1
        

Note that this file is actually executed like a Python script. Now when we run SCons:

% scons -Q
cc -o bar.o -c -DRELEASE_BUILD=1 bar.c
cc -o foo.o -c -DRELEASE_BUILD=1 foo.c
cc -o foo foo.o bar.o

And if we change the contents of custom.py to:

RELEASE = 0
        

The object files are rebuilt appropriately with the new variable:

% scons -Q
cc -o bar.o -c -DRELEASE_BUILD=0 bar.c
cc -o foo.o -c -DRELEASE_BUILD=0 foo.c
cc -o foo foo.o bar.o

Finally, you can combine both methods with:

vars = Variables('custom.py', ARGUMENTS)
      

where values in the option file custom.py get overwritten by the ones specified on the command line.

10.2.4. Pre-Defined Build Variable Functions

SCons provides a number of functions that provide ready-made behaviors for various types of command-line build variables.

10.2.4.1. True/False Values: the BoolVariable Build Variable Function

It's often handy to be able to specify a variable that controls a simple Boolean variable with a true or false value. It would be even more handy to accomodate users who have different preferences for how to represent true or false values. The BoolVariable function makes it easy to accomodate these common representations of true or false.

The BoolVariable function takes three arguments: the name of the build variable, the default value of the build variable, and the help string for the variable. It then returns appropriate information for passing to the Add method of a Variables object, like so:

vars = Variables('custom.py')
vars.Add(BoolVariable('RELEASE', 'Set to build for release', 0))
env = Environment(variables = vars,
                  CPPDEFINES={'RELEASE_BUILD' : '${RELEASE}'})
env.Program('foo.c')
          

With this build variable, the RELEASE variable can now be enabled by setting it to the value yes or t:

% scons -Q RELEASE=yes foo.o
cc -o foo.o -c -DRELEASE_BUILD=True foo.c
% scons -Q RELEASE=t foo.o
cc -o foo.o -c -DRELEASE_BUILD=True foo.c

Other values that equate to true include y, 1, on and all.

Conversely, RELEASE may now be given a false value by setting it to no or f:

% scons -Q RELEASE=no foo.o
cc -o foo.o -c -DRELEASE_BUILD=False foo.c
% scons -Q RELEASE=f foo.o
cc -o foo.o -c -DRELEASE_BUILD=False foo.c

Other values that equate to false include n, 0, off and none.

Lastly, if a user tries to specify any other value, SCons supplies an appropriate error message:

% scons -Q RELEASE=bad_value foo.o

scons: *** Error converting option: RELEASE
Invalid value for boolean option: bad_value
File "/home/my/project/SConstruct", line 4, in <module>

10.2.4.2. Single Value From a List: the EnumVariable Build Variable Function

Suppose that we want a user to be able to set a COLOR variable that selects a background color to be displayed by an application, but that we want to restrict the choices to a specific set of allowed colors. This can be set up quite easily using the EnumVariable, which takes a list of allowed_values in addition to the variable name, default value, and help text arguments:

vars = Variables('custom.py')
vars.Add(EnumVariable('COLOR', 'Set background color', 'red',
                    allowed_values=('red', 'green', 'blue')))
env = Environment(variables = vars,
                  CPPDEFINES={'COLOR' : '"${COLOR}"'})
env.Program('foo.c')
          

The user can now explicity set the COLOR build variable to any of the specified allowed values:

% scons -Q COLOR=red foo.o
cc -o foo.o -c -DCOLOR="red" foo.c
% scons -Q COLOR=blue foo.o
cc -o foo.o -c -DCOLOR="blue" foo.c
% scons -Q COLOR=green foo.o
cc -o foo.o -c -DCOLOR="green" foo.c

But, almost more importantly, an attempt to set COLOR to a value that's not in the list generates an error message:

% scons -Q COLOR=magenta foo.o

scons: *** Invalid value for option COLOR: magenta.  Valid values are: ('red', 'green', 'blue')
File "/home/my/project/SConstruct", line 5, in <module>

The EnumVariable function also supports a way to map alternate names to allowed values. Suppose, for example, that we want to allow the user to use the word navy as a synonym for blue. We do this by adding a map dictionary that will map its key values to the desired legal value:

vars = Variables('custom.py')
vars.Add(EnumVariable('COLOR', 'Set background color', 'red',
                    allowed_values=('red', 'green', 'blue'),
                    map={'navy':'blue'}))
env = Environment(variables = vars,
                  CPPDEFINES={'COLOR' : '"${COLOR}"'})
env.Program('foo.c')
          

As desired, the user can then use navy on the command line, and SCons will translate it into blue when it comes time to use the COLOR variable to build a target:

% scons -Q COLOR=navy foo.o
cc -o foo.o -c -DCOLOR="blue" foo.c

By default, when using the EnumVariable function, arguments that differ from the legal values only in case are treated as illegal values:

% scons -Q COLOR=Red foo.o

scons: *** Invalid value for option COLOR: Red.  Valid values are: ('red', 'green', 'blue')
File "/home/my/project/SConstruct", line 5, in <module>
% scons -Q COLOR=BLUE foo.o

scons: *** Invalid value for option COLOR: BLUE.  Valid values are: ('red', 'green', 'blue')
File "/home/my/project/SConstruct", line 5, in <module>
% scons -Q COLOR=nAvY foo.o

scons: *** Invalid value for option COLOR: nAvY.  Valid values are: ('red', 'green', 'blue')
File "/home/my/project/SConstruct", line 5, in <module>

The EnumVariable function can take an additional ignorecase keyword argument that, when set to 1, tells SCons to allow case differences when the values are specified:

vars = Variables('custom.py')
vars.Add(EnumVariable('COLOR', 'Set background color', 'red',
                    allowed_values=('red', 'green', 'blue'),
                    map={'navy':'blue'},
                    ignorecase=1))
env = Environment(variables = vars,
                  CPPDEFINES={'COLOR' : '"${COLOR}"'})
env.Program('foo.c')
          

Which yields the output:

% scons -Q COLOR=Red foo.o
cc -o foo.o -c -DCOLOR="Red" foo.c
% scons -Q COLOR=BLUE foo.o
cc -o foo.o -c -DCOLOR="BLUE" foo.c
% scons -Q COLOR=nAvY foo.o
cc -o foo.o -c -DCOLOR="blue" foo.c
% scons -Q COLOR=green foo.o
cc -o foo.o -c -DCOLOR="green" foo.c

Notice that an ignorecase value of 1 preserves the case-spelling that the user supplied. If you want SCons to translate the names into lower-case, regardless of the case used by the user, specify an ignorecase value of 2:

vars = Variables('custom.py')
vars.Add(EnumVariable('COLOR', 'Set background color', 'red',
                    allowed_values=('red', 'green', 'blue'),
                    map={'navy':'blue'},
                    ignorecase=2))
env = Environment(variables = vars,
                  CPPDEFINES={'COLOR' : '"${COLOR}"'})
env.Program('foo.c')
          

Now SCons will use values of red, green or blue regardless of how the user spells those values on the command line:

% scons -Q COLOR=Red foo.o
cc -o foo.o -c -DCOLOR="red" foo.c
% scons -Q COLOR=nAvY foo.o
cc -o foo.o -c -DCOLOR="blue" foo.c
% scons -Q COLOR=GREEN foo.o
cc -o foo.o -c -DCOLOR="green" foo.c

10.2.4.3. Multiple Values From a List: the ListVariable Build Variable Function

Another way in which you might want to allow users to control a build variable is to specify a list of one or more legal values. SCons supports this through the ListVariable function. If, for example, we want a user to be able to set a COLORS variable to one or more of the legal list of values:

vars = Variables('custom.py')
vars.Add(ListVariable('COLORS', 'List of colors', 0,
                    ['red', 'green', 'blue']))
env = Environment(variables = vars,
                  CPPDEFINES={'COLORS' : '"${COLORS}"'})
env.Program('foo.c')
          

A user can now specify a comma-separated list of legal values, which will get translated into a space-separated list for passing to the any build commands:

% scons -Q COLORS=red,blue foo.o
cc -o foo.o -c -DCOLORS="red blue" foo.c
% scons -Q COLORS=blue,green,red foo.o
cc -o foo.o -c -DCOLORS="blue green red" foo.c

In addition, the ListVariable function allows the user to specify explicit keywords of all or none to select all of the legal values, or none of them, respectively:

% scons -Q COLORS=all foo.o
cc -o foo.o -c -DCOLORS="red green blue" foo.c
% scons -Q COLORS=none foo.o
cc -o foo.o -c -DCOLORS="" foo.c

And, of course, an illegal value still generates an error message:

% scons -Q COLORS=magenta foo.o

scons: *** Error converting option: COLORS
Invalid value(s) for option: magenta
File "/home/my/project/SConstruct", line 5, in <module>

10.2.4.4. Path Names: the PathVariable Build Variable Function

SCons supports a PathVariable function to make it easy to create a build variable to control an expected path name. If, for example, you need to define a variable in the preprocessor that controls the location of a configuration file:

vars = Variables('custom.py')
vars.Add(PathVariable('CONFIG',
                    'Path to configuration file',
                    '/etc/my_config'))
env = Environment(variables = vars,
                  CPPDEFINES={'CONFIG_FILE' : '"$CONFIG"'})
env.Program('foo.c')
          

This then allows the user to override the CONFIG build variable on the command line as necessary:

% scons -Q foo.o
cc -o foo.o -c -DCONFIG_FILE="/etc/my_config" foo.c
% scons -Q CONFIG=/usr/local/etc/other_config foo.o
scons: `foo.o' is up to date.

By default, PathVariable checks to make sure that the specified path exists and generates an error if it doesn't:

% scons -Q CONFIG=/does/not/exist foo.o

scons: *** Path for option CONFIG does not exist: /does/not/exist
File "/home/my/project/SConstruct", line 6, in <module>

PathVariable provides a number of methods that you can use to change this behavior. If you want to ensure that any specified paths are, in fact, files and not directories, use the PathVariable.PathIsFile method:

vars = Variables('custom.py')
vars.Add(PathVariable('CONFIG',
                    'Path to configuration file',
                    '/etc/my_config',
                    PathVariable.PathIsFile))
env = Environment(variables = vars,
                  CPPDEFINES={'CONFIG_FILE' : '"$CONFIG"'})
env.Program('foo.c')
          

Conversely, to ensure that any specified paths are directories and not files, use the PathVariable.PathIsDir method:

vars = Variables('custom.py')
vars.Add(PathVariable('DBDIR',
                    'Path to database directory',
                    '/var/my_dbdir',
                    PathVariable.PathIsDir))
env = Environment(variables = vars,
                  CPPDEFINES={'DBDIR' : '"$DBDIR"'})
env.Program('foo.c')
          

If you want to make sure that any specified paths are directories, and you would like the directory created if it doesn't already exist, use the PathVariable.PathIsDirCreate method:

vars = Variables('custom.py')
vars.Add(PathVariable('DBDIR',
                    'Path to database directory',
                    '/var/my_dbdir',
                    PathVariable.PathIsDirCreate))
env = Environment(variables = vars,
                  CPPDEFINES={'DBDIR' : '"$DBDIR"'})
env.Program('foo.c')
          

Lastly, if you don't care whether the path exists, is a file, or a directory, use the PathVariable.PathAccept method to accept any path that the user supplies:

vars = Variables('custom.py')
vars.Add(PathVariable('OUTPUT',
                    'Path to output file or directory',
                    None,
                    PathVariable.PathAccept))
env = Environment(variables = vars,
                  CPPDEFINES={'OUTPUT' : '"$OUTPUT"'})
env.Program('foo.c')
          

10.2.4.5. Enabled/Disabled Path Names: the PackageVariable Build Variable Function

Sometimes you want to give users even more control over a path name variable, allowing them to explicitly enable or disable the path name by using yes or no keywords, in addition to allow them to supply an explicit path name. SCons supports the PackageVariable function to support this:

vars = Variables('custom.py')
vars.Add(PackageVariable('PACKAGE',
                       'Location package',
                       '/opt/location'))
env = Environment(variables = vars,
                  CPPDEFINES={'PACKAGE' : '"$PACKAGE"'})
env.Program('foo.c')
          

When the SConscript file uses the PackageVariable funciton, user can now still use the default or supply an overriding path name, but can now explicitly set the specified variable to a value that indicates the package should be enabled (in which case the default should be used) or disabled:

% scons -Q foo.o
cc -o foo.o -c -DPACKAGE="/opt/location" foo.c
% scons -Q PACKAGE=/usr/local/location foo.o
cc -o foo.o -c -DPACKAGE="/usr/local/location" foo.c
% scons -Q PACKAGE=yes foo.o
cc -o foo.o -c -DPACKAGE="True" foo.c
% scons -Q PACKAGE=no foo.o
cc -o foo.o -c -DPACKAGE="False" foo.c

10.2.5. Adding Multiple Command-Line Build Variables at Once

Lastly, SCons provides a way to add multiple build variables to a Variables object at once. Instead of having to call the Add method multiple times, you can call the AddVariables method with a list of build variables to be added to the object. Each build variable is specified as either a tuple of arguments, just like you'd pass to the Add method itself, or as a call to one of the pre-defined functions for pre-packaged command-line build variables. in any order:

vars = Variables()
vars.AddVariables(
    ('RELEASE', 'Set to 1 to build for release', 0),
    ('CONFIG', 'Configuration file', '/etc/my_config'),
    BoolVariable('warnings', 'compilation with -Wall and similiar', 1),
    EnumVariable('debug', 'debug output and symbols', 'no',
               allowed_values=('yes', 'no', 'full'),
               map={}, ignorecase=0),  # case sensitive
    ListVariable('shared',
               'libraries to build as shared libraries',
               'all',
               names = list_of_libs),
    PackageVariable('x11',
                  'use X11 installed here (yes = search some places)',
                  'yes'),
    PathVariable('qtdir', 'where the root of Qt is installed', qtdir),
)
        

10.2.6. Handling Unknown Command-Line Build Variables: the UnknownVariables Function

Users may, of course, occasionally misspell variable names in their command-line settings. SCons does not generate an error or warning for any unknown variables the users specifies on the command line. (This is in no small part because you may be processing the arguments directly using the ARGUMENTS dictionary, and therefore SCons can't know in the general case whether a given "misspelled" variable is really unknown and a potential problem, or something that your SConscript file will handle directly with some Python code.)

If, however, you're using a Variables object to define a specific set of command-line build variables that you expect users to be able to set, you may want to provide an error message or warning of your own if the user supplies a variable setting that is not among the defined list of variable names known to the Variables object. You can do this by calling the UnknownVariables method of the Variables object:

vars = Variables(None)
vars.Add('RELEASE', 'Set to 1 to build for release', 0)
env = Environment(variables = vars,
                  CPPDEFINES={'RELEASE_BUILD' : '${RELEASE}'})
unknown = vars.UnknownVariables()
if unknown:
    print "Unknown variables:", unknown.keys()
    Exit(1)
env.Program('foo.c')
        

The UnknownVariables method returns a dictionary containing the keywords and values of any variables the user specified on the command line that are not among the variables known to the Variables object (from having been specified using the Variables object'sAdd method). In the examble above, we check for whether the dictionary returned by the UnknownVariables is non-empty, and if so print the Python list containing the names of the unknwown variables and then call the Exit function to terminate SCons:

% scons -Q NOT_KNOWN=foo
Unknown variables: ['NOT_KNOWN']

Of course, you can process the items in the dictionary returned by the UnknownVariables function in any way appropriate to your build configuration, including just printing a warning message but not exiting, logging an error somewhere, etc.

Note that you must delay the call of UnknownVariables until after you have applied the Variables object to a construction environment with the variables= keyword argument of an Environment call.

10.3. Command-Line Targets

10.3.1. Fetching Command-Line Targets: the COMMAND_LINE_TARGETS Variable

SCons supports a COMMAND_LINE_TARGETS variable that lets you fetch the list of targets that the user specified on the command line. You can use the targets to manipulate the build in any way you wish. As a simple example, suppose that you want to print a reminder to the user whenever a specific program is built. You can do this by checking for the target in the COMMAND_LINE_TARGETS list:

if 'bar' in COMMAND_LINE_TARGETS:
    print "Don't forget to copy `bar' to the archive!"
Default(Program('foo.c'))
Program('bar.c')
        

Then, running SCons with the default target works as it always does, but explicity specifying the bar target on the command line generates the warning message:

% scons -Q
cc -o foo.o -c foo.c
cc -o foo foo.o
% scons -Q bar
Don't forget to copy `bar' to the archive!
cc -o bar.o -c bar.c
cc -o bar bar.o

Another practical use for the COMMAND_LINE_TARGETS variable might be to speed up a build by only reading certain subsidiary SConscript files if a specific target is requested.

10.3.2. Controlling the Default Targets: the Default Function

One of the most basic things you can control is which targets SCons will build by default--that is, when there are no targets specified on the command line. As mentioned previously, SCons will normally build every target in or below the current directory by default--that is, when you don't explicitly specify one or more targets on the command line. Sometimes, however, you may want to specify explicitly that only certain programs, or programs in certain directories, should be built by default. You do this with the Default function:

env = Environment()
hello = env.Program('hello.c')
env.Program('goodbye.c')
Default(hello)
         

This SConstruct file knows how to build two programs, hello and goodbye, but only builds the hello program by default:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q
scons: `hello' is up to date.
% scons -Q goodbye
cc -o goodbye.o -c goodbye.c
cc -o goodbye goodbye.o

Note that, even when you use the Default function in your SConstruct file, you can still explicitly specify the current directory (.) on the command line to tell SCons to build everything in (or below) the current directory:

% scons -Q .
cc -o goodbye.o -c goodbye.c
cc -o goodbye goodbye.o
cc -o hello.o -c hello.c
cc -o hello hello.o

You can also call the Default function more than once, in which case each call adds to the list of targets to be built by default:

env = Environment()
prog1 = env.Program('prog1.c')
Default(prog1)
prog2 = env.Program('prog2.c')
prog3 = env.Program('prog3.c')
Default(prog3)
         

Or you can specify more than one target in a single call to the Default function:

env = Environment()
prog1 = env.Program('prog1.c')
prog2 = env.Program('prog2.c')
prog3 = env.Program('prog3.c')
Default(prog1, prog3)
      

Either of these last two examples will build only the prog1 and prog3 programs by default:

% scons -Q
cc -o prog1.o -c prog1.c
cc -o prog1 prog1.o
cc -o prog3.o -c prog3.c
cc -o prog3 prog3.o
% scons -Q .
cc -o prog2.o -c prog2.c
cc -o prog2 prog2.o

You can list a directory as an argument to Default:

env = Environment()
env.Program(['prog1/main.c', 'prog1/foo.c'])
env.Program(['prog2/main.c', 'prog2/bar.c'])
Default('prog1')
         

In which case only the target(s) in that directory will be built by default:

% scons -Q
cc -o prog1/foo.o -c prog1/foo.c
cc -o prog1/main.o -c prog1/main.c
cc -o prog1/main prog1/main.o prog1/foo.o
% scons -Q
scons: `prog1' is up to date.
% scons -Q .
cc -o prog2/bar.o -c prog2/bar.c
cc -o prog2/main.o -c prog2/main.c
cc -o prog2/main prog2/main.o prog2/bar.o

Lastly, if for some reason you don't want any targets built by default, you can use the Python None variable:

env = Environment()
prog1 = env.Program('prog1.c')
prog2 = env.Program('prog2.c')
Default(None)
         

Which would produce build output like:

% scons -Q
scons: *** No targets specified and no Default() targets found.  Stop.
Found nothing to build
% scons -Q .
cc -o prog1.o -c prog1.c
cc -o prog1 prog1.o
cc -o prog2.o -c prog2.c
cc -o prog2 prog2.o

10.3.2.1. Fetching the List of Default Targets: the DEFAULT_TARGETS Variable

SCons supports a DEFAULT_TARGETS variable that lets you get at the current list of default targets. The DEFAULT_TARGETS variable has two important differences from the COMMAND_LINE_TARGETS variable. First, the DEFAULT_TARGETS variable is a list of internal SCons nodes, so you need to convert the list elements to strings if you want to print them or look for a specific target name. Fortunately, you can do this easily by using the Python map function to run the list through str:

prog1 = Program('prog1.c')
Default(prog1)
print "DEFAULT_TARGETS is", map(str, DEFAULT_TARGETS)
           

(Keep in mind that all of the manipulation of the DEFAULT_TARGETS list takes place during the first phase when SCons is reading up the SConscript files, which is obvious if we leave off the -Q flag when we run SCons:)

% scons
scons: Reading SConscript files ...
DEFAULT_TARGETS is ['prog1']
scons: done reading SConscript files.
scons: Building targets ...
cc -o prog1.o -c prog1.c
cc -o prog1 prog1.o
scons: done building targets.

Second, the contents of the DEFAULT_TARGETS list change in response to calls to the Default function, as you can see from the following SConstruct file:

prog1 = Program('prog1.c')
Default(prog1)
print "DEFAULT_TARGETS is now", map(str, DEFAULT_TARGETS)
prog2 = Program('prog2.c')
Default(prog2)
print "DEFAULT_TARGETS is now", map(str, DEFAULT_TARGETS)
           

Which yields the output:

% scons
scons: Reading SConscript files ...
DEFAULT_TARGETS is now ['prog1']
DEFAULT_TARGETS is now ['prog1', 'prog2']
scons: done reading SConscript files.
scons: Building targets ...
cc -o prog1.o -c prog1.c
cc -o prog1 prog1.o
cc -o prog2.o -c prog2.c
cc -o prog2 prog2.o
scons: done building targets.

In practice, this simply means that you need to pay attention to the order in which you call the Default function and refer to the DEFAULT_TARGETS list, to make sure that you don't examine the list before you've added the default targets you expect to find in it.

10.3.3. Fetching the List of Build Targets, Regardless of Origin: the BUILD_TARGETS Variable

We've already been introduced to the COMMAND_LINE_TARGETS variable, which contains a list of targets specified on the command line, and the DEFAULT_TARGETS variable, which contains a list of targets specified via calls to the Default method or function. Sometimes, however, you want a list of whatever targets SCons will try to build, regardless of whether the targets came from the command line or a Default call. You could code this up by hand, as follows:

if COMMAND_LINE_TARGETS:
    targets = COMMAND_LINE_TARGETS
else:
    targets = DEFAULT_TARGETS
      

SCons, however, provides a convenient BUILD_TARGETS variable that eliminates the need for this by-hand manipulation. Essentially, the BUILD_TARGETS variable contains a list of the command-line targets, if any were specified, and if no command-line targets were specified, it contains a list of the targets specified via the Default method or function.

Because BUILD_TARGETS may contain a list of SCons nodes, you must convert the list elements to strings if you want to print them or look for a specific target name, just like the DEFAULT_TARGETS list:

prog1 = Program('prog1.c')
Program('prog2.c')
Default(prog1)
print "BUILD_TARGETS is", map(str, BUILD_TARGETS)
        

Notice how the value of BUILD_TARGETS changes depending on whether a target is specified on the command line:

% scons -Q
BUILD_TARGETS is ['prog1']
cc -o prog1.o -c prog1.c
cc -o prog1 prog1.o
% scons -Q prog2
BUILD_TARGETS is ['prog2']
cc -o prog2.o -c prog2.c
cc -o prog2 prog2.o
% scons -Q -c .
BUILD_TARGETS is ['.']
Removed prog1.o
Removed prog1
Removed prog2.o
Removed prog2


[3] The AddOption function is, in fact, implemented using a subclass of the optparse.OptionParser.

Chapter 11. Installing Files in Other Directories: the Install Builder

Once a program is built, it is often appropriate to install it in another directory for public use. You use the Install method to arrange for a program, or any other file, to be copied into a destination directory:

env = Environment()
hello = env.Program('hello.c')
env.Install('/usr/bin', hello)
     

Note, however, that installing a file is still considered a type of file "build." This is important when you remember that the default behavior of SCons is to build files in or below the current directory. If, as in the example above, you are installing files in a directory outside of the top-level SConstruct file's directory tree, you must specify that directory (or a higher directory, such as /) for it to install anything there:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q /usr/bin
Install file: "hello" as "/usr/bin/hello"

It can, however, be cumbersome to remember (and type) the specific destination directory in which the program (or any other file) should be installed. This is an area where the Alias function comes in handy, allowing you, for example, to create a pseudo-target named install that can expand to the specified destination directory:

env = Environment()
hello = env.Program('hello.c')
env.Install('/usr/bin', hello)
env.Alias('install', '/usr/bin')
    

This then yields the more natural ability to install the program in its destination as follows:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q install
Install file: "hello" as "/usr/bin/hello"

11.1. Installing Multiple Files in a Directory

You can install multiple files into a directory simply by calling the Install function multiple times:

env = Environment()
hello = env.Program('hello.c')
goodbye = env.Program('goodbye.c')
env.Install('/usr/bin', hello)
env.Install('/usr/bin', goodbye)
env.Alias('install', '/usr/bin')
      

Or, more succinctly, listing the multiple input files in a list (just like you can do with any other builder):

env = Environment()
hello = env.Program('hello.c')
goodbye = env.Program('goodbye.c')
env.Install('/usr/bin', [hello, goodbye])
env.Alias('install', '/usr/bin')
    

Either of these two examples yields:

% scons -Q install
cc -o goodbye.o -c goodbye.c
cc -o goodbye goodbye.o
Install file: "goodbye" as "/usr/bin/goodbye"
cc -o hello.o -c hello.c
cc -o hello hello.o
Install file: "hello" as "/usr/bin/hello"

11.2. Installing a File Under a Different Name

The Install method preserves the name of the file when it is copied into the destination directory. If you need to change the name of the file when you copy it, use the InstallAs function:

env = Environment()
hello = env.Program('hello.c')
env.InstallAs('/usr/bin/hello-new', hello)
env.Alias('install', '/usr/bin')
      

This installs the hello program with the name hello-new as follows:

% scons -Q install
cc -o hello.o -c hello.c
cc -o hello hello.o
Install file: "hello" as "/usr/bin/hello-new"

11.3. Installing Multiple Files Under Different Names

Lastly, if you have multiple files that all need to be installed with different file names, you can either call the InstallAs function multiple times, or as a shorthand, you can supply same-length lists for both the target and source arguments:

env = Environment()
hello = env.Program('hello.c')
goodbye = env.Program('goodbye.c')
env.InstallAs(['/usr/bin/hello-new',
               '/usr/bin/goodbye-new'],
               [hello, goodbye])
env.Alias('install', '/usr/bin')
      

In this case, the InstallAs function loops through both lists simultaneously, and copies each source file into its corresponding target file name:

% scons -Q install
cc -o goodbye.o -c goodbye.c
cc -o goodbye goodbye.o
Install file: "goodbye" as "/usr/bin/goodbye-new"
cc -o hello.o -c hello.c
cc -o hello hello.o
Install file: "hello" as "/usr/bin/hello-new"

Chapter 12. Platform-Independent File System Manipulation

SCons provides a number of platform-independent functions, called factories, that perform common file system manipulations like copying, moving or deleting files and directories, or making directories. These functions are factories because they don't perform the action at the time they're called, they each return an Action object that can be executed at the appropriate time.

12.1. Copying Files or Directories: The Copy Factory

Suppose you want to arrange to make a copy of a file, and don't have a suitable pre-existing builder. [4] One way would be to use the Copy action factory in conjunction with the Command builder:

Command("file.out", "file.in", Copy("$TARGET", "$SOURCE"))
      

Notice that the action returned by the Copy factory will expand the $TARGET and $SOURCE strings at the time file.out is built, and that the order of the arguments is the same as that of a builder itself--that is, target first, followed by source:

% scons -Q
Copy("file.out", "file.in")

You can, of course, name a file explicitly instead of using $TARGET or $SOURCE:

Command("file.out", [], Copy("$TARGET", "file.in"))
      

Which executes as:

% scons -Q
Copy("file.out", "file.in")

The usefulness of the Copy factory becomes more apparent when you use it in a list of actions passed to the Command builder. For example, suppose you needed to run a file through a utility that only modifies files in-place, and can't "pipe" input to output. One solution is to copy the source file to a temporary file name, run the utility, and then copy the modified temporary file to the target, which the Copy factory makes extremely easy:

Command("file.out", "file.in",
        [
          Copy("tempfile", "$SOURCE"),
          "modify tempfile",
          Copy("$TARGET", "tempfile"),
        ])
      

The output then looks like:

% scons -Q
Copy("tempfile", "file.in")
modify tempfile
Copy("file.out", "tempfile")

The Copy factory has a third optional argument which controls how symlinks are copied.

# Symbolic link shallow copied as a new symbolic link:
Command("LinkIn", "LinkOut", Copy("$TARGET", "$SOURCE"[, True]))

# Symbolic link target copied as a file or directory:
Command("LinkIn", "FileOrDirectoryOut", Copy("$TARGET", "$SOURCE", False))
      

12.2. Deleting Files or Directories: The Delete Factory

If you need to delete a file, then the Delete factory can be used in much the same way as the Copy factory. For example, if we want to make sure that the temporary file in our last example doesn't exist before we copy to it, we could add Delete to the beginning of the command list:

Command("file.out", "file.in",
        [
          Delete("tempfile"),
          Copy("tempfile", "$SOURCE"),
          "modify tempfile",
          Copy("$TARGET", "tempfile"),
        ])
      

Which then executes as follows:

% scons -Q
Delete("tempfile")
Copy("tempfile", "file.in")
modify tempfile
Copy("file.out", "tempfile")

Of course, like all of these Action factories, the Delete factory also expands $TARGET and $SOURCE variables appropriately. For example:

Command("file.out", "file.in",
        [
          Delete("$TARGET"),
          Copy("$TARGET", "$SOURCE")
        ])
      

Executes as:

% scons -Q
Delete("file.out")
Copy("file.out", "file.in")

Note, however, that you typically don't need to call the Delete factory explicitly in this way; by default, SCons deletes its target(s) for you before executing any action.

One word of caution about using the Delete factory: it has the same variable expansions available as any other factory, including the $SOURCE variable. Specifying Delete("$SOURCE") is not something you usually want to do!

12.3. Moving (Renaming) Files or Directories: The Move Factory

The Move factory allows you to rename a file or directory. For example, if we don't want to copy the temporary file, we could use:

Command("file.out", "file.in",
        [
          Copy("tempfile", "$SOURCE"),
          "modify tempfile",
          Move("$TARGET", "tempfile"),
        ])
      

Which would execute as:

% scons -Q
Copy("tempfile", "file.in")
modify tempfile
Move("file.out", "tempfile")

12.4. Updating the Modification Time of a File: The Touch Factory

If you just need to update the recorded modification time for a file, use the Touch factory:

Command("file.out", "file.in",
        [
          Copy("$TARGET", "$SOURCE"),
          Touch("$TARGET"),
        ])
      

Which executes as:

% scons -Q
Copy("file.out", "file.in")
Touch("file.out")

12.5. Creating a Directory: The Mkdir Factory

If you need to create a directory, use the Mkdir factory. For example, if we need to process a file in a temporary directory in which the processing tool will create other files that we don't care about, you could use:

Command("file.out", "file.in",
        [
          Delete("tempdir"),
          Mkdir("tempdir"),
          Copy("tempdir/${SOURCE.file}", "$SOURCE"),
          "process tempdir",
          Move("$TARGET", "tempdir/output_file"),
          Delete("tempdir"),
        ])
      

Which executes as:

% scons -Q
Delete("tempdir")
Mkdir("tempdir")
Copy("tempdir/file.in", "file.in")
process tempdir
Move("file.out", "tempdir/output_file")
scons: *** [file.out] tempdir/output_file: No such file or directory

12.6. Changing File or Directory Permissions: The Chmod Factory

To change permissions on a file or directory, use the Chmod factory. The permission argument uses POSIX-style permission bits and should typically be expressed as an octal, not decimal, number:

Command("file.out", "file.in",
        [
          Copy("$TARGET", "$SOURCE"),
          Chmod("$TARGET", 0755),
        ])
      

Which executes:

% scons -Q
Copy("file.out", "file.in")
Chmod("file.out", 0755)

12.7. Executing an action immediately: the Execute Function

We've been showing you how to use Action factories in the Command function. You can also execute an Action returned by a factory (or actually, any Action) at the time the SConscript file is read by using the Execute function. For example, if we need to make sure that a directory exists before we build any targets,

Execute(Mkdir('/tmp/my_temp_directory'))
      

Notice that this will create the directory while the SConscript file is being read:

% scons
scons: Reading SConscript files ...
Mkdir("/tmp/my_temp_directory")
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.

If you're familiar with Python, you may wonder why you would want to use this instead of just calling the native Python os.mkdir() function. The advantage here is that the Mkdir action will behave appropriately if the user specifies the SCons -n or -q options--that is, it will print the action but not actually make the directory when -n is specified, or make the directory but not print the action when -q is specified.

The Execute function returns the exit status or return value of the underlying action being executed. It will also print an error message if the action fails and returns a non-zero value. SCons will not, however, actually stop the build if the action fails. If you want the build to stop in response to a failure in an action called by Execute, you must do so by explicitly checking the return value and calling the Exit function (or a Python equivalent):

if Execute(Mkdir('/tmp/my_temp_directory')):
    # A problem occurred while making the temp directory.
    Exit(1)
    


[4] Unfortunately, in the early days of SCons design, we used the name Copy for the function that returns a copy of the environment, otherwise that would be the logical choice for a Builder that copies a file or directory tree to a target location.

Chapter 13. Controlling Removal of Targets

There are two occasions when SCons will, by default, remove target files. The first is when SCons determines that an target file needs to be rebuilt and removes the existing version of the target before executing The second is when SCons is invoked with the -c option to "clean" a tree of its built targets. These behaviours can be suppressed with the Precious and NoClean functions, respectively.

13.1. Preventing target removal during build: the Precious Function

By default, SCons removes targets before building them. Sometimes, however, this is not what you want. For example, you may want to update a library incrementally, not by having it deleted and then rebuilt from all of the constituent object files. In such cases, you can use the Precious method to prevent SCons from removing the target before it is built:

  env = Environment(RANLIBCOM='')
  lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
  env.Precious(lib)
      

Although the output doesn't look any different, SCons does not, in fact, delete the target library before rebuilding it:

% scons -Q
cc -o f1.o -c f1.c
cc -o f2.o -c f2.c
cc -o f3.o -c f3.c
ar rc libfoo.a f1.o f2.o f3.o

SCons will, however, still delete files marked as Precious when the -c option is used.

13.2. Preventing target removal during clean: the NoClean Function

By default, SCons removes all built targets when invoked with the -c option to clean a source tree of built targets. Sometimes, however, this is not what you want. For example, you may want to remove only intermediate generated files (such as object files), but leave the final targets (the libraries) untouched. In such cases, you can use the NoClean method to prevent SCons from removing a target during a clean:

env = Environment(RANLIBCOM='')
lib = env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
env.NoClean(lib)
      

Notice that the libfoo.a is not listed as a removed file:

% scons -Q
cc -o f1.o -c f1.c
cc -o f2.o -c f2.c
cc -o f3.o -c f3.c
ar rc libfoo.a f1.o f2.o f3.o
% scons -c
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Cleaning targets ...
Removed f1.o
Removed f2.o
Removed f3.o
scons: done cleaning targets.

13.3. Removing additional files during clean: the Clean Function

There may be additional files that you want removed when the -c option is used, but which SCons doesn't know about because they're not normal target files. For example, perhaps a command you invoke creates a log file as part of building the target file you want. You would like the log file cleaned, but you don't want to have to teach SCons that the command "builds" two files.

You can use the Clean function to arrange for additional files to be removed when the -c option is used. Notice, however, that the Clean function takes two arguments, and the second argument is the name of the additional file you want cleaned (foo.log in this example):

t = Command('foo.out', 'foo.in', 'build -o $TARGET $SOURCE')
Clean(t, 'foo.log')
      

The first argument is the target with which you want the cleaning of this additional file associated. In the above example, we've used the return value from the Command function, which represents the foo.out target. Now whenever the foo.out target is cleaned by the -c option, the foo.log file will be removed as well:

% scons -Q
build -o foo.out foo.in
% scons -Q -c
Removed foo.out
Removed foo.log

Chapter 14. Hierarchical Builds

The source code for large software projects rarely stays in a single directory, but is nearly always divided into a hierarchy of directories. Organizing a large software build using SCons involves creating a hierarchy of build scripts using the SConscript function.

14.1. SConscript Files

As we've already seen, the build script at the top of the tree is called SConstruct. The top-level SConstruct file can use the SConscript function to include other subsidiary scripts in the build. These subsidiary scripts can, in turn, use the SConscript function to include still other scripts in the build. By convention, these subsidiary scripts are usually named SConscript. For example, a top-level SConstruct file might arrange for four subsidiary scripts to be included in the build as follows:

SConscript(['drivers/display/SConscript',
            'drivers/mouse/SConscript',
            'parser/SConscript',
            'utilities/SConscript'])
    

In this case, the SConstruct file lists all of the SConscript files in the build explicitly. (Note, however, that not every directory in the tree necessarily has an SConscript file.) Alternatively, the drivers subdirectory might contain an intermediate SConscript file, in which case the SConscript call in the top-level SConstruct file would look like:

SConscript(['drivers/SConscript',
            'parser/SConscript',
            'utilities/SConscript'])
    

And the subsidiary SConscript file in the drivers subdirectory would look like:

SConscript(['display/SConscript',
            'mouse/SConscript'])
    

Whether you list all of the SConscript files in the top-level SConstruct file, or place a subsidiary SConscript file in intervening directories, or use some mix of the two schemes, is up to you and the needs of your software.

14.2. Path Names Are Relative to the SConscript Directory

Subsidiary SConscript files make it easy to create a build hierarchy because all of the file and directory names in a subsidiary SConscript files are interpreted relative to the directory in which the SConscript file lives. Typically, this allows the SConscript file containing the instructions to build a target file to live in the same directory as the source files from which the target will be built, making it easy to update how the software is built whenever files are added or deleted (or other changes are made).

For example, suppose we want to build two programs prog1 and prog2 in two separate directories with the same names as the programs. One typical way to do this would be with a top-level SConstruct file like this:

SConscript(['prog1/SConscript',
            'prog2/SConscript'])
      

And subsidiary SConscript files that look like this:

env = Environment()
env.Program('prog1', ['main.c', 'foo1.c', 'foo2.c'])
      

And this:

env = Environment()
env.Program('prog2', ['main.c', 'bar1.c', 'bar2.c'])
      

Then, when we run SCons in the top-level directory, our build looks like:

% scons -Q
cc -o prog1/foo1.o -c prog1/foo1.c
cc -o prog1/foo2.o -c prog1/foo2.c
cc -o prog1/main.o -c prog1/main.c
cc -o prog1/prog1 prog1/main.o prog1/foo1.o prog1/foo2.o
cc -o prog2/bar1.o -c prog2/bar1.c
cc -o prog2/bar2.o -c prog2/bar2.c
cc -o prog2/main.o -c prog2/main.c
cc -o prog2/prog2 prog2/main.o prog2/bar1.o prog2/bar2.o

Notice the following: First, you can have files with the same names in multiple directories, like main.c in the above example. Second, unlike standard recursive use of Make, SCons stays in the top-level directory (where the SConstruct file lives) and issues commands that use the path names from the top-level directory to the target and source files within the hierarchy.

14.3. Top-Level Path Names in Subsidiary SConscript Files

If you need to use a file from another directory, it's sometimes more convenient to specify the path to a file in another directory from the top-level SConstruct directory, even when you're using that file in a subsidiary SConscript file in a subdirectory. You can tell SCons to interpret a path name as relative to the top-level SConstruct directory, not the local directory of the SConscript file, by appending a # (hash mark) to the beginning of the path name:

env = Environment()
env.Program('prog', ['main.c', '#lib/foo1.c', 'foo2.c'])
       

In this example, the lib directory is directly underneath the top-level SConstruct directory. If the above SConscript file is in a subdirectory named src/prog, the output would look like:

% scons -Q
cc -o lib/foo1.o -c lib/foo1.c
cc -o src/prog/foo2.o -c src/prog/foo2.c
cc -o src/prog/main.o -c src/prog/main.c
cc -o src/prog/prog src/prog/main.o lib/foo1.o src/prog/foo2.o

(Notice that the lib/foo1.o object file is built in the same directory as its source file. See Chapter 15, Separating Source and Build Directories, below, for information about how to build the object file in a different subdirectory.)

14.4. Absolute Path Names

Of course, you can always specify an absolute path name for a file--for example:

env = Environment()
env.Program('prog', ['main.c', '/usr/joe/lib/foo1.c', 'foo2.c'])
       

Which, when executed, would yield:

% scons -Q
cc -o src/prog/foo2.o -c src/prog/foo2.c
cc -o src/prog/main.o -c src/prog/main.c
cc -o /usr/joe/lib/foo1.o -c /usr/joe/lib/foo1.c
cc -o src/prog/prog src/prog/main.o /usr/joe/lib/foo1.o src/prog/foo2.o

(As was the case with top-relative path names, notice that the /usr/joe/lib/foo1.o object file is built in the same directory as its source file. See Chapter 15, Separating Source and Build Directories, below, for information about how to build the object file in a different subdirectory.)

14.5. Sharing Environments (and Other Variables) Between SConscript Files

In the previous example, each of the subsidiary SConscript files created its own construction environment by calling Environment separately. This obviously works fine, but if each program must be built with the same construction variables, it's cumbersome and error-prone to initialize separate construction environments in the same way over and over in each subsidiary SConscript file.

SCons supports the ability to export variables from a parent SConscript file to its subsidiary SConscript files, which allows you to share common initialized values throughout your build hierarchy.

14.5.1. Exporting Variables

There are two ways to export a variable, such as a construction environment, from an SConscript file, so that it may be used by other SConscript files. First, you can call the Export function with a list of variables, or a string of white-space separated variable names. Each call to Export adds one or more variables to a global list of variables that are available for import by other SConscript files.

env = Environment()
Export('env')
      

You may export more than one variable name at a time:

env = Environment()
debug = ARGUMENTS['debug']
Export('env', 'debug')
      

Because white space is not legal in Python variable names, the Export function will even automatically split a string into separate names for you:

Export('env debug')
      

Second, you can specify a list of variables to export as a second argument to the SConscript function call:

SConscript('src/SConscript', 'env')
      

Or as the exports keyword argument:

SConscript('src/SConscript', exports='env')
      

These calls export the specified variables to only the listed SConscript files. You may, however, specify more than one SConscript file in a list:

SConscript(['src1/SConscript',
            'src2/SConscript'], exports='env')
      

This is functionally equivalent to calling the SConscript function multiple times with the same exports argument, one per SConscript file.

14.5.2. Importing Variables

Once a variable has been exported from a calling SConscript file, it may be used in other SConscript files by calling the Import function:

Import('env')
env.Program('prog', ['prog.c'])
      

The Import call makes the env construction environment available to the SConscript file, after which the variable can be used to build programs, libraries, etc.

Like the Export function, the Import function can be used with multiple variable names:

Import('env', 'debug')
env = env.Clone(DEBUG = debug)
env.Program('prog', ['prog.c'])
      

And the Import function will similarly split a string along white-space into separate variable names:

Import('env debug')
env = env.Clone(DEBUG = debug)
env.Program('prog', ['prog.c'])
      

Lastly, as a special case, you may import all of the variables that have been exported by supplying an asterisk to the Import function:

Import('*')
env = env.Clone(DEBUG = debug)
env.Program('prog', ['prog.c'])
      

If you're dealing with a lot of SConscript files, this can be a lot simpler than keeping arbitrary lists of imported variables in each file.

14.5.3. Returning Values From an SConscript File

Sometimes, you would like to be able to use information from a subsidiary SConscript file in some way. For example, suppose that you want to create one library from source files scattered throughout a number of subsidiary SConscript files. You can do this by using the Return function to return values from the subsidiary SConscript files to the calling file.

If, for example, we have two subdirectories foo and bar that should each contribute a source file to a Library, what we'd like to be able to do is collect the object files from the subsidiary SConscript calls like this:

env = Environment()
Export('env')
objs = []
for subdir in ['foo', 'bar']:
    o = SConscript('%s/SConscript' % subdir)
    objs.append(o)
env.Library('prog', objs)
        

We can do this by using the Return function in the foo/SConscript file like this:

Import('env')
obj = env.Object('foo.c')
Return('obj')
        

(The corresponding bar/SConscript file should be pretty obvious.) Then when we run SCons, the object files from the subsidiary subdirectories are all correctly archived in the desired library:

% scons -Q
cc -o bar/bar.o -c bar/bar.c
cc -o foo/foo.o -c foo/foo.c
ar rc libprog.a foo/foo.o bar/bar.o
ranlib libprog.a

Chapter 15. Separating Source and Build Directories

It's often useful to keep any built files completely separate from the source files. In SCons, this is usually done by creating one or more separate variant directory trees that are used to hold the built objects files, libraries, and executable programs, etc. for a specific flavor, or variant, of build. SCons provides two ways to do this, one through the SConscript function that we've already seen, and the second through a more flexible VariantDir function.

One historical note: the VariantDir function used to be called BuildDir. That name is still supported but has been deprecated because the SCons functionality differs from the model of a "build directory" implemented by other build systems like the GNU Autotools.

15.1. Specifying a Variant Directory Tree as Part of an SConscript Call

The most straightforward way to establish a variant directory tree uses the fact that the usual way to set up a build hierarchy is to have an SConscript file in the source subdirectory. If you then pass a variant_dir argument to the SConscript function call:

SConscript('src/SConscript', variant_dir='build')
      

SCons will then build all of the files in the build subdirectory:

% ls src
SConscript  hello.c
% scons -Q
cc -o build/hello.o -c build/hello.c
cc -o build/hello build/hello.o
% ls build
SConscript  hello  hello.c  hello.o

But wait a minute--what's going on here? SCons created the object file build/hello.o in the build subdirectory, as expected. But even though our hello.c file lives in the src subdirectory, SCons has actually compiled a build/hello.c file to create the object file.

What's happened is that SCons has duplicated the hello.c file from the src subdirectory to the build subdirectory, and built the program from there. The next section explains why SCons does this.

15.2. Why SCons Duplicates Source Files in a Variant Directory Tree

SCons duplicates source files in variant directory trees because it's the most straightforward way to guarantee a correct build regardless of include-file directory paths, relative references between files, or tool support for putting files in different locations, and the SCons philosophy is to, by default, guarantee a correct build in all cases.

The most direct reason to duplicate source files in variant directories is simply that some tools (mostly older versions) are written to only build their output files in the same directory as the source files. In this case, the choices are either to build the output file in the source directory and move it to the variant directory, or to duplicate the source files in the variant directory.

Additionally, relative references between files can cause problems if we don't just duplicate the hierarchy of source files in the variant directory. You can see this at work in use of the C preprocessor #include mechanism with double quotes, not angle brackets:

#include "file.h"
    

The de facto standard behavior for most C compilers in this case is to first look in the same directory as the source file that contains the #include line, then to look in the directories in the preprocessor search path. Add to this that the SCons implementation of support for code repositories (described below) means not all of the files will be found in the same directory hierarchy, and the simplest way to make sure that the right include file is found is to duplicate the source files into the variant directory, which provides a correct build regardless of the original location(s) of the source files.

Although source-file duplication guarantees a correct build even in these end-cases, it can usually be safely disabled. The next section describes how you can disable the duplication of source files in the variant directory.

15.3. Telling SCons to Not Duplicate Source Files in the Variant Directory Tree

In most cases and with most tool sets, SCons can place its target files in a build subdirectory without duplicating the source files and everything will work just fine. You can disable the default SCons behavior by specifying duplicate=0 when you call the SConscript function:

SConscript('src/SConscript', variant_dir='build', duplicate=0)
    

When this flag is specified, SCons uses the variant directory like most people expect--that is, the output files are placed in the variant directory while the source files stay in the source directory:

% ls src
SConscript
hello.c
% scons -Q
cc -c src/hello.c -o build/hello.o
cc -o build/hello build/hello.o
% ls build
hello
hello.o
    

15.4. The VariantDir Function

Use the VariantDir function to establish that target files should be built in a separate directory from the source files:

VariantDir('build', 'src')
env = Environment()
env.Program('build/hello.c')
      

Note that when you're not using an SConscript file in the src subdirectory, you must actually specify that the program must be built from the build/hello.c file that SCons will duplicate in the build subdirectory.

When using the VariantDir function directly, SCons still duplicates the source files in the variant directory by default:

% ls src
hello.c
% scons -Q
cc -o build/hello.o -c build/hello.c
cc -o build/hello build/hello.o
% ls build
hello  hello.c  hello.o

You can specify the same duplicate=0 argument that you can specify for an SConscript call:

VariantDir('build', 'src', duplicate=0)
env = Environment()
env.Program('build/hello.c')
      

In which case SCons will disable duplication of the source files:

% ls src
hello.c
% scons -Q
cc -o build/hello.o -c src/hello.c
cc -o build/hello build/hello.o
% ls build
hello  hello.o

15.5. Using VariantDir With an SConscript File

Even when using the VariantDir function, it's much more natural to use it with a subsidiary SConscript file. For example, if the src/SConscript looks like this:

env = Environment()
env.Program('hello.c')
      

Then our SConstruct file could look like:

VariantDir('build', 'src')
SConscript('build/SConscript')
      

Yielding the following output:

% ls src
SConscript  hello.c
% scons -Q
cc -o build/hello.o -c build/hello.c
cc -o build/hello build/hello.o
% ls build
SConscript  hello  hello.c  hello.o

Notice that this is completely equivalent to the use of SConscript that we learned about in the previous section.

15.6. Using Glob with VariantDir

The Glob file name pattern matching function works just as usual when using VariantDir. For example, if the src/SConscript looks like this:

env = Environment()
env.Program('hello', Glob('*.c'))
      

Then with the same SConstruct file as in the previous section, and source files f1.c and f2.c in src, we would see the following output:

% ls src
SConscript  f1.c  f2.c  f2.h
% scons -Q
cc -o build/f1.o -c build/f1.c
cc -o build/f2.o -c build/f2.c
cc -o build/hello build/f1.o build/f2.o
% ls build
SConscript  f1.c  f1.o  f2.c  f2.h  f2.o  hello

The Glob function returns Nodes in the build/ tree, as you'd expect.

Chapter 16. Variant Builds

The variant_dir keyword argument of the SConscript function provides everything we need to show how easy it is to create variant builds using SCons. Suppose, for example, that we want to build a program for both Windows and Linux platforms, but that we want to build it in a shared directory with separate side-by-side build directories for the Windows and Linux versions of the program.

platform = ARGUMENTS.get('OS', Platform())

include = "#export/$PLATFORM/include"
lib = "#export/$PLATFORM/lib"
bin = "#export/$PLATFORM/bin"

env = Environment(PLATFORM = platform,
                  BINDIR = bin,
                  INCDIR = include,
                  LIBDIR = lib,
                  CPPPATH = [include],
                  LIBPATH = [lib],
                  LIBS = 'world')

Export('env')

env.SConscript('src/SConscript', variant_dir='build/$PLATFORM')
    

This SConstruct file, when run on a Linux system, yields:

% scons -Q OS=linux
Install file: "build/linux/world/world.h" as "export/linux/include/world.h"
cc -o build/linux/hello/hello.o -c -Iexport/linux/include build/linux/hello/hello.c
cc -o build/linux/world/world.o -c -Iexport/linux/include build/linux/world/world.c
ar rc build/linux/world/libworld.a build/linux/world/world.o
ranlib build/linux/world/libworld.a
Install file: "build/linux/world/libworld.a" as "export/linux/lib/libworld.a"
cc -o build/linux/hello/hello build/linux/hello/hello.o -Lexport/linux/lib -lworld
Install file: "build/linux/hello/hello" as "export/linux/bin/hello"

The same SConstruct file on Windows would build:

C:\>scons -Q OS=windows
Install file: "build/windows/world/world.h" as "export/windows/include/world.h"
cl /Fobuild\windows\hello\hello.obj /c build\windows\hello\hello.c /nologo /Iexport\windows\include
cl /Fobuild\windows\world\world.obj /c build\windows\world\world.c /nologo /Iexport\windows\include
lib /nologo /OUT:build\windows\world\world.lib build\windows\world\world.obj
Install file: "build/windows/world/world.lib" as "export/windows/lib/world.lib"
link /nologo /OUT:build\windows\hello\hello.exe /LIBPATH:export\windows\lib world.lib build\windows\hello\hello.obj
embedManifestExeCheck(target, source, env)
Install file: "build/windows/hello/hello.exe" as "export/windows/bin/hello.exe"

Chapter 17. Internationalization and localization with gettext

The gettext toolset supports internationalization and localization of SCons-based projects. Builders provided by gettext automatize generation and updates of translation files. You can manage translations and translation templates similarly to how it's done with autotools.

17.1. Prerequisites

To follow examples provided in this chapter set up your operating system to support two or more languages. In following examples we use locales en_US, de_DE, and pl_PL.

Ensure, that you have GNU gettext utilities installed on your system.

To edit translation files you may wish to install poedit editor.

17.2. Simple project

Let's start with a very simple project, the "Hello world" program for example

/* hello.c */
#include <stdio.h>
int main(int argc, char* argv[])
{
  printf("Hello world\n");
  return 0;
}
    

Prepare a SConstruct to compile the program as usual.

# SConstruct
env = Environment()
hello = Program(["hello.c"])
    

Now we'll convert the project to a multi-lingual one. If you don't already have GNU gettext utilities installed, install them from your preffered package repository, or download from http://ftp.gnu.org/gnu/gettext/. For the purpose of this example, you should have following three locales installed on your system: en_US, de_DE and pl_PL. On debian, for example, you may enable certain locales through dpkg-reconfigure locales.

First prepare the hello.c program for internationalization. Change the previous code so it reads as follows:

/* hello.c */
#include <stdio.h>
#include <libintl.h>
#include <locale.h>
int main(int argc, char* argv[])
{
  bindtextdomain("hello", "locale");
  setlocale(LC_ALL, "");
  textdomain("hello");
  printf(gettext("Hello world\n"));
  return 0;
}
    

Detailed recipes for such conversion can be found at http://www.gnu.org/software/gettext/manual/gettext.html#Sources. The gettext("...") has two purposes. First, it marks messages for the xgettext(1) program, which we will use to extract from the sources the messages for localization. Second, it calls the gettext library internals to translate the message at runtime.

Now we shall instruct SCons how to generate and maintain translation files. For that, use the Translate builder and MOFiles builder. The first one takes source files, extracts internationalized messages from them, creates so-called POT file (translation template), and then creates PO translation files, one for each requested language. Later, during the development lifecycle, the builder keeps all these files up-to date. The MOFiles builder compiles the PO files to binary form. Then install the MO files under directory called locale.

The completed SConstruct is as follows:

# SConstruct
env = Environment( tools = ['default', 'gettext'] )
hello = env.Program(["hello.c"])
env['XGETTEXTFLAGS'] = [
  '--package-name=%s' % 'hello',
  '--package-version=%s' % '1.0',
]
po = env.Translate(["pl","en", "de"], ["hello.c"], POAUTOINIT = 1)
mo = env.MOFiles(po)
InstallAs(["locale/en/LC_MESSAGES/hello.mo"], ["en.mo"])
InstallAs(["locale/pl/LC_MESSAGES/hello.mo"], ["pl.mo"])
InstallAs(["locale/de/LC_MESSAGES/hello.mo"], ["de.mo"])
    

Generate the translation files with scons po-update. You should see the output from SCons simillar to this:

user@host:$ scons po-update
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
Entering '/home/ptomulik/projects/tmp'
xgettext --package-name=hello --package-version=1.0 -o - hello.c
Leaving '/home/ptomulik/projects/tmp'
Writting 'messages.pot' (new file)
msginit --no-translator -l pl -i messages.pot -o pl.po
Created pl.po.
msginit --no-translator -l en -i messages.pot -o en.po
Created en.po.
msginit --no-translator -l de -i messages.pot -o de.po
Created de.po.
scons: done building targets.
    

If everything is right, you should see following new files.

user@host:$ ls *.po*
de.po  en.po  messages.pot  pl.po
    

Open en.po in poedit and provide the English translation to message "Hello world\n". Do the same for de.po (deutsch) and pl.po (polish). Let the translations be, for example:

  • en: "Welcome to beautiful world!\n"

  • de: "Hallo Welt!\n"

  • pl: "Witaj swiecie!\n"

Now compile the project by executing scons. The output should be similar to this:

user@host:$ scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
msgfmt -c -o de.mo de.po
msgfmt -c -o en.mo en.po
gcc -o hello.o -c hello.c
gcc -o hello hello.o
Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo"
Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo"
msgfmt -c -o pl.mo pl.po
Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
scons: done building targets.
    

SCons automatically compiled the PO files to binary format MO, and the InstallAs lines installed these files under locale folder.

Your program should be now ready. You may try it as follows (linux):

user@host:$ LANG=en_US.UTF-8 ./hello
Welcome to beautiful world
    

user@host:$ LANG=de_DE.UTF-8 ./hello
Hallo Welt
    

user@host:$ LANG=pl_PL.UTF-8 ./hello
Witaj swiecie
    

To demonstrate the further life of translation files, let's change Polish translation (poedit pl.po) to "Witaj drogi swiecie\n". Run scons to see how scons reacts to this

user@host:$scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
msgfmt -c -o pl.mo pl.po
Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
scons: done building targets.
    

Now, open hello.c and add another one printf line with new message.

/* hello.c */
#include <stdio.h>
#include <libintl.h>
#include <locale.h>
int main(int argc, char* argv[])
{
  bindtextdomain("hello", "locale");
  setlocale(LC_ALL, "");
  textdomain("hello");
  printf(gettext("Hello world\n"));
  printf(gettext("and good bye\n"));
  return 0;
}
    

Compile project with scons. This time, the msgmerge(1) program is used by SCons to update PO file. The output from compilation is like:

user@host:$scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
Entering '/home/ptomulik/projects/tmp'
xgettext --package-name=hello --package-version=1.0 -o - hello.c
Leaving '/home/ptomulik/projects/tmp'
Writting 'messages.pot' (messages in file were outdated)
msgmerge --update de.po messages.pot
... done.
msgfmt -c -o de.mo de.po
msgmerge --update en.po messages.pot
... done.
msgfmt -c -o en.mo en.po
gcc -o hello.o -c hello.c
gcc -o hello hello.o
Install file: "de.mo" as "locale/de/LC_MESSAGES/hello.mo"
Install file: "en.mo" as "locale/en/LC_MESSAGES/hello.mo"
msgmerge --update pl.po messages.pot
... done.
msgfmt -c -o pl.mo pl.po
Install file: "pl.mo" as "locale/pl/LC_MESSAGES/hello.mo"
scons: done building targets.
    

The next example demonstrates what happens if we change the source code in such way that the internationalized messages do not change. The answer is that none of translation files (POT, PO) are touched (i.e. no content changes, no creation/modification time changed and so on). Let's append another line to the program (after the last printf), so its code becomes:

/* hello.c */
#include <stdio.h>
#include <libintl.h>
#include <locale.h>
int main(int argc, char* argv[])
{
  bindtextdomain("hello", "locale");
  setlocale(LC_ALL, "");
  textdomain("hello");
  printf(gettext("Hello world\n"));
  printf(gettext("and good bye\n"));
  printf("----------------\n");
  return a;
}
    

Compile the project. You'll see on your screen

user@host:$scons
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets ...
Entering '/home/ptomulik/projects/tmp'
xgettext --package-name=hello --package-version=1.0 -o - hello.c
Leaving '/home/ptomulik/projects/tmp'
Not writting 'messages.pot' (messages in file found to be up-to-date)
gcc -o hello.o -c hello.c
gcc -o hello hello.o
scons: done building targets.
    

As you see, the internationalized messages ditn't change, so the POT and the rest of translation files have not even been touched.

Chapter 18. Writing Your Own Builders

Although SCons provides many useful methods for building common software products (programs, libraries, documents, etc.), you frequently want to be able to build some other type of file not supported directly by SCons. Fortunately, SCons makes it very easy to define your own Builder objects for any custom file types you want to build. (In fact, the SCons interfaces for creating Builder objects are flexible enough and easy enough to use that all of the the SCons built-in Builder objects are created using the mechanisms described in this section.)

18.1. Writing Builders That Execute External Commands

The simplest Builder to create is one that executes an external command. For example, if we want to build an output file by running the contents of the input file through a command named foobuild, creating that Builder might look like:

bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
    

All the above line does is create a free-standing Builder object. The next section will show us how to actually use it.

18.2. Attaching a Builder to a Construction Environment

A Builder object isn't useful until it's attached to a construction environment so that we can call it to arrange for files to be built. This is done through the $BUILDERS construction variable in an environment. The $BUILDERS variable is a Python dictionary that maps the names by which you want to call various Builder objects to the objects themselves. For example, if we want to call the Builder we just defined by the name Foo, our SConstruct file might look like:

bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env = Environment(BUILDERS = {'Foo' : bld})
    

With the Builder attached to our construction environment with the name Foo, we can now actually call it like so:

env.Foo('file.foo', 'file.input')
    

Then when we run SCons it looks like:

% scons -Q
foobuild < file.input > file.foo

Note, however, that the default $BUILDERS variable in a construction environment comes with a default set of Builder objects already defined: Program, Library, etc. And when we explicitly set the $BUILDERS variable when we create the construction environment, the default Builders are no longer part of the environment:

bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
       
% scons -Q
AttributeError: 'SConsEnvironment' object has no attribute 'Program':
  File "/home/my/project/SConstruct", line 4:
    env.Program('hello.c')

To be able to use both our own defined Builder objects and the default Builder objects in the same construction environment, you can either add to the $BUILDERS variable using the Append function:

env = Environment()
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env.Append(BUILDERS = {'Foo' : bld})
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
    

Or you can explicitly set the appropriately-named key in the $BUILDERS dictionary:

env = Environment()
bld = Builder(action = 'foobuild < $SOURCE > $TARGET')
env['BUILDERS']['Foo'] = bld
env.Foo('file.foo', 'file.input')
env.Program('hello.c')
    

Either way, the same construction environment can then use both the newly-defined Foo Builder and the default Program Builder:

% scons -Q
foobuild < file.input > file.foo
cc -o hello.o -c hello.c
cc -o hello hello.o

18.3. Letting SCons Handle The File Suffixes

By supplying additional information when you create a Builder, you can let SCons add appropriate file suffixes to the target and/or the source file. For example, rather than having to specify explicitly that you want the Foo Builder to build the file.foo target file from the file.input source file, you can give the .foo and .input suffixes to the Builder, making for more compact and readable calls to the Foo Builder:

bld = Builder(action = 'foobuild < $SOURCE > $TARGET',
              suffix = '.foo',
              src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file1')
env.Foo('file2')
    
% scons -Q
foobuild < file1.input > file1.foo
foobuild < file2.input > file2.foo

You can also supply a prefix keyword argument if it's appropriate to have SCons append a prefix to the beginning of target file names.

18.4. Builders That Execute Python Functions

In SCons, you don't have to call an external command to build a file. You can, instead, define a Python function that a Builder object can invoke to build your target file (or files). Such a builder function definition looks like:

def build_function(target, source, env):
    # Code to build "target" from "source"
    return None
    

The arguments of a builder function are:

target

A list of Node objects representing the target or targets to be built by this builder function. The file names of these target(s) may be extracted using the Python str function.

source

A list of Node objects representing the sources to be used by this builder function to build the targets. The file names of these source(s) may be extracted using the Python str function.

env

The construction environment used for building the target(s). The builder function may use any of the environment's construction variables in any way to affect how it builds the targets.

The builder function must return a 0 or None value if the target(s) are built successfully. The builder function may raise an exception or return any non-zero value to indicate that the build is unsuccessful,

Once you've defined the Python function that will build your target file, defining a Builder object for it is as simple as specifying the name of the function, instead of an external command, as the Builder's action argument:

def build_function(target, source, env):
    # Code to build "target" from "source"
    return None
bld = Builder(action = build_function,
              suffix = '.foo',
              src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file')
       

And notice that the output changes slightly, reflecting the fact that a Python function, not an external command, is now called to build the target file:

% scons -Q
build_function(["file.foo"], ["file.input"])

18.5. Builders That Create Actions Using a Generator

SCons Builder objects can create an action "on the fly" by using a function called a generator. This provides a great deal of flexibility to construct just the right list of commands to build your target. A generator looks like:

def generate_actions(source, target, env, for_signature):
    return 'foobuild < %s > %s' % (target[0], source[0])
    

The arguments of a generator are:

source

A list of Node objects representing the sources to be built by the command or other action generated by this function. The file names of these source(s) may be extracted using the Python str function.

target

A list of Node objects representing the target or targets to be built by the command or other action generated by this function. The file names of these target(s) may be extracted using the Python str function.

env

The construction environment used for building the target(s). The generator may use any of the environment's construction variables in any way to determine what command or other action to return.

for_signature

A flag that specifies whether the generator is being called to contribute to a build signature, as opposed to actually executing the command.

The generator must return a command string or other action that will be used to build the specified target(s) from the specified source(s).

Once you've defined a generator, you create a Builder to use it by specifying the generator keyword argument instead of action.

def generate_actions(source, target, env, for_signature):
    return 'foobuild < %s > %s' % (source[0], target[0])
bld = Builder(generator = generate_actions,
              suffix = '.foo',
              src_suffix = '.input')
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file')
    
% scons -Q
foobuild < file.input > file.foo

Note that it's illegal to specify both an action and a generator for a Builder.

18.6. Builders That Modify the Target or Source Lists Using an Emitter

SCons supports the ability for a Builder to modify the lists of target(s) from the specified source(s). You do this by defining an emitter function that takes as its arguments the list of the targets passed to the builder, the list of the sources passed to the builder, and the construction environment. The emitter function should return the modified lists of targets that should be built and sources from which the targets will be built.

For example, suppose you want to define a Builder that always calls a foobuild program, and you want to automatically add a new target file named new_target and a new source file named new_source whenever it's called. The SConstruct file might look like this:

def modify_targets(target, source, env):
    target.append('new_target')
    source.append('new_source')
    return target, source
bld = Builder(action = 'foobuild $TARGETS - $SOURCES',
              suffix = '.foo',
              src_suffix = '.input',
              emitter = modify_targets)
env = Environment(BUILDERS = {'Foo' : bld})
env.Foo('file')
    

And would yield the following output:

% scons -Q
foobuild file.foo new_target - file.input new_source

One very flexible thing that you can do is use a construction variable to specify different emitter functions for different construction variable. To do this, specify a string containing a construction variable expansion as the emitter when you call the Builder function, and set that construction variable to the desired emitter function in different construction environments:

bld = Builder(action = 'my_command $SOURCES > $TARGET',
              suffix = '.foo',
              src_suffix = '.input',
              emitter = '$MY_EMITTER')
def modify1(target, source, env):
    return target, source + ['modify1.in']
def modify2(target, source, env):
    return target, source + ['modify2.in']
env1 = Environment(BUILDERS = {'Foo' : bld},
                   MY_EMITTER = modify1)
env2 = Environment(BUILDERS = {'Foo' : bld},
                   MY_EMITTER = modify2)
env1.Foo('file1')
env2.Foo('file2')
import os
env1['ENV']['PATH'] = env2['ENV']['PATH'] + os.pathsep + os.getcwd()
env2['ENV']['PATH'] = env2['ENV']['PATH'] + os.pathsep + os.getcwd()
        
bld = Builder(action = 'my_command $SOURCES > $TARGET',
              suffix = '.foo',
              src_suffix = '.input',
              emitter = '$MY_EMITTER')
def modify1(target, source, env):
    return target, source + ['modify1.in']
def modify2(target, source, env):
    return target, source + ['modify2.in']
env1 = Environment(BUILDERS = {'Foo' : bld},
                   MY_EMITTER = modify1)
env2 = Environment(BUILDERS = {'Foo' : bld},
                   MY_EMITTER = modify2)
env1.Foo('file1')
env2.Foo('file2')
    

In this example, the modify1.in and modify2.in files get added to the source lists of the different commands:

% scons -Q
my_command file1.input modify1.in > file1.foo
my_command file2.input modify2.in > file2.foo

18.7. Where To Put Your Custom Builders and Tools

The site_scons directories give you a place to put Python modules and packages that you can import into your SConscript files (site_scons), add-on tools that can integrate into SCons (site_scons/site_tools), and a site_scons/site_init.py file that gets read before any SConstruct or SConscript file, allowing you to change SCons's default behavior.

Each system type (Windows, Mac, Linux, etc.) searches a canonical set of directories for site_scons; see the man page for details. The top-level SConstruct's site_scons dir is always searched last, and its dir is placed first in the tool path so it overrides all others.

If you get a tool from somewhere (the SCons wiki or a third party, for instance) and you'd like to use it in your project, a site_scons dir is the simplest place to put it. Tools come in two flavors; either a Python function that operates on an Environment or a Python module or package containing two functions, exists() and generate().

A single-function Tool can just be included in your site_scons/site_init.py file where it will be parsed and made available for use. For instance, you could have a site_scons/site_init.py file like this:

def TOOL_ADD_HEADER(env):
   """A Tool to add a header from $HEADER to the source file"""
   add_header = Builder(action=['echo "$HEADER" > $TARGET',
                                'cat $SOURCE >> $TARGET'])
   env.Append(BUILDERS = {'AddHeader' : add_header})
   env['HEADER'] = '' # set default value
      

and a SConstruct like this:

# Use TOOL_ADD_HEADER from site_scons/site_init.py
env=Environment(tools=['default', TOOL_ADD_HEADER], HEADER="=====")
env.AddHeader('tgt', 'src')
    

The TOOL_ADD_HEADER tool method will be called to add the AddHeader tool to the environment.

A more full-fledged tool with exists() and generate() methods can be installed either as a module in the file site_scons/site_tools/toolname.py or as a package in the directory site_scons/site_tools/toolname. In the case of using a package, the exists() and generate() are in the file site_scons/site_tools/toolname/__init__.py. (In all the above case toolname is replaced by the name of the tool.) Since site_scons/site_tools is automatically added to the head of the tool search path, any tool found there will be available to all environments. Furthermore, a tool found there will override a built-in tool of the same name, so if you need to change the behavior of a built-in tool, site_scons gives you the hook you need.

Many people have a library of utility Python functions they'd like to include in SConscripts; just put that module in site_scons/my_utils.py or any valid Python module name of your choice. For instance you can do something like this in site_scons/my_utils.py to add build_id and MakeWorkDir functions:

from SCons.Script import *   # for Execute and Mkdir
def build_id():
   """Return a build ID (stub version)"""
   return "100"
def MakeWorkDir(workdir):
   """Create the specified dir immediately"""
   Execute(Mkdir(workdir))
      

And then in your SConscript or any sub-SConscript anywhere in your build, you can import my_utils and use it:

import my_utils
print "build_id=" + my_utils.build_id()
my_utils.MakeWorkDir('/tmp/work')
    

Note that although you can put this library in site_scons/site_init.py, it is no better there than site_scons/my_utils.py since you still have to import that module into your SConscript. Also note that in order to refer to objects in the SCons namespace such as Environment or Mkdir or Execute in any file other than a SConstruct or SConscript you always need to do

from SCons.Script import *
    

This is true in modules in site_scons such as site_scons/site_init.py as well.

You can use any of the user- or machine-wide site dirs such as ~/.scons/site_scons instead of ./site_scons, or use the --site-dir option to point to your own dir. site_init.py and site_tools will be located under that dir. To avoid using a site_scons dir at all, even if it exists, use the --no-site-dir option.

Chapter 19. Not Writing a Builder: the Command Builder

Creating a Builder and attaching it to a construction environment allows for a lot of flexibility when you want to re-use actions to build multiple files of the same type. This can, however, be cumbersome if you only need to execute one specific command to build a single file (or group of files). For these situations, SCons supports a Command Builder that arranges for a specific action to be executed to build a specific file or files. This looks a lot like the other builders (like Program, Object, etc.), but takes as an additional argument the command to be executed to build the file:

env = Environment()
env.Command('foo.out', 'foo.in', "sed 's/x/y/' < $SOURCE > $TARGET")
     

When executed, SCons runs the specified command, substituting $SOURCE and $TARGET as expected:

% scons -Q
sed 's/x/y/' < foo.in > foo.out

This is often more convenient than creating a Builder object and adding it to the $BUILDERS variable of a construction environment

Note that the action you specify to the Command Builder can be any legal SCons Action, such as a Python function:

env = Environment()
def build(target, source, env):
    # Whatever it takes to build
    return None
env.Command('foo.out', 'foo.in', build)
     

Which executes as follows:

% scons -Q
build(["foo.out"], ["foo.in"])

Note that $SOURCE and $TARGET are expanded in the source and target as well as of SCons 1.1, so you can write:

env.Command('${SOURCE.basename}.out', 'foo.in', build)
     

which does the same thing as the previous example, but allows you to avoid repeating yourself.

Chapter 20. Pseudo-Builders: the AddMethod function

The AddMethod function is used to add a method to an environment. It's typically used to add a "pseudo-builder," a function that looks like a Builder but wraps up calls to multiple other Builders or otherwise processes its arguments before calling one or more Builders. In the following example, we want to install the program into the standard /usr/bin directory hierarchy, but also copy it into a local install/bin directory from which a package might be built:

def install_in_bin_dirs(env, source):
    """Install source in both bin dirs"""
    i1 = env.Install("$BIN", source)
    i2 = env.Install("$LOCALBIN", source)
    return [i1[0], i2[0]] # Return a list, like a normal builder
env = Environment(BIN='/usr/bin', LOCALBIN='#install/bin')
env.AddMethod(install_in_bin_dirs, "InstallInBinDirs")
env.InstallInBinDirs(Program('hello.c')) # installs hello in both bin dirs     
     

This produces the following:

% scons -Q /
cc -o hello.o -c hello.c
cc -o hello hello.o
Install file: "hello" as "/usr/bin/hello"
Install file: "hello" as "install/bin/hello"

As mentioned, a pseudo-builder also provides more flexibility in parsing arguments than you can get with a Builder. The next example shows a pseudo-builder with a named argument that modifies the filename, and a separate argument for the resource file (rather than having the builder figure it out by file extension). This example also demonstrates using the global AddMethod function to add a method to the global Environment class, so it will be used in all subsequently created environments.

def BuildTestProg(env, testfile, resourcefile, testdir="tests"):
    """Build the test program;
    prepends "test_" to src and target,
    and puts target into testdir."""
    srcfile = "test_%s.c" % testfile
    target = "%s/test_%s" % (testdir, testfile)
    if env['PLATFORM'] == 'win32':
        resfile = env.RES(resourcefile)
        p = env.Program(target, [srcfile, resfile])
    else:
        p = env.Program(target, srcfile)
    return p
AddMethod(Environment, BuildTestProg)

env = Environment()
env.BuildTestProg('stuff', resourcefile='res.rc')
     

This produces the following on Linux:

% scons -Q
cc -o test_stuff.o -c test_stuff.c
cc -o tests/test_stuff test_stuff.o

And the following on Windows:

C:\>scons -Q
rc /fores.res res.rc
cl /Fotest_stuff.obj /c test_stuff.c /nologo
link /nologo /OUT:tests\test_stuff.exe test_stuff.obj res.res
embedManifestExeCheck(target, source, env)

Using AddMethod is better than just adding an instance method to a construction environment because it gets called as a proper method, and because AddMethod provides for copying the method to any clones of the construction environment instance.

Chapter 21. Writing Scanners

SCons has built-in scanners that know how to look in C, Fortran and IDL source files for information about other files that targets built from those files depend on--for example, in the case of files that use the C preprocessor, the .h files that are specified using #include lines in the source. You can use the same mechanisms that SCons uses to create its built-in scanners to write scanners of your own for file types that SCons does not know how to scan "out of the box."

21.1. A Simple Scanner Example

Suppose, for example, that we want to create a simple scanner for .foo files. A .foo file contains some text that will be processed, and can include other files on lines that begin with include followed by a file name:

include filename.foo
    

Scanning a file will be handled by a Python function that you must supply. Here is a function that will use the Python re module to scan for the include lines in our example:

import re

include_re = re.compile(r'^include\s+(\S+)$', re.M)

def kfile_scan(node, env, path, arg):
    contents = node.get_text_contents()
    return env.File(include_re.findall(contents))
    

It is important to note that you have to return a list of File nodes from the scanner function, simple strings for the file names won't do. As in the examples we are showing here, you can use the File function of your current Environment in order to create nodes on the fly from a sequence of file names with relative paths.

The scanner function must accept the four specified arguments and return a list of implicit dependencies. Presumably, these would be dependencies found from examining the contents of the file, although the function can perform any manipulation at all to generate the list of dependencies.

node

An SCons node object representing the file being scanned. The path name to the file can be used by converting the node to a string using the str() function, or an internal SCons get_text_contents() object method can be used to fetch the contents.

env

The construction environment in effect for this scan. The scanner function may choose to use construction variables from this environment to affect its behavior.

path

A list of directories that form the search path for included files for this scanner. This is how SCons handles the $CPPPATH and $LIBPATH variables.

arg

An optional argument that you can choose to have passed to this scanner function by various scanner instances.

A Scanner object is created using the Scanner function, which typically takes an skeys argument to associate the type of file suffix with this scanner. The Scanner object must then be associated with the $SCANNERS construction variable of a construction environment, typically by using the Append method:

kscan = Scanner(function = kfile_scan,
                skeys = ['.k'])
env.Append(SCANNERS = kscan)
    

When we put it all together, it looks like:

  import re

  include_re = re.compile(r'^include\s+(\S+)$', re.M)

  def kfile_scan(node, env, path):
      contents = node.get_text_contents()
      includes = include_re.findall(contents)
      return env.File(includes)

  kscan = Scanner(function = kfile_scan,
                  skeys = ['.k'])

  env = Environment(ENV = {'PATH' : '/usr/local/bin'})
  env.Append(SCANNERS = kscan)

  env.Command('foo', 'foo.k', 'kprocess < $SOURCES > $TARGET')
      

21.2. Adding a search path to a scanner: FindPathDirs

Many scanners need to search for included files or dependencies using a path variable; this is how $CPPPATH and $LIBPATH work. The path to search is passed to your scanner as the path argument. Path variables may be lists of nodes, semicolon-separated strings, or even contain SCons variables which need to be expanded. Fortunately, SCons provides the FindPathDirs function which itself returns a function to expand a given path (given as a SCons construction variable name) to a list of paths at the time the scanner is called. Deferring evaluation until that point allows, for instance, the path to contain $TARGET references which differ for each file scanned.

Using FindPathDirs is quite easy. Continuing the above example, using KPATH as the construction variable with the search path (analogous to $CPPPATH), we just modify the Scanner constructor call to include a path keyword arg:

kscan = Scanner(function = kfile_scan,
                skeys = ['.k'],
                path=FindPathDirs('KPATH'))
      

FindPathDirs returns a callable object that, when called, will essentially expand the elements in env['KPATH'] and tell the scanner to search in those dirs. It will also properly add related repository and variant dirs to the search list. As a side note, the returned method stores the path in an efficient way so lookups are fast even when variable substitutions may be needed. This is important since many files get scanned in a typical build.

Chapter 22. Building From Code Repositories

Often, a software project will have one or more central repositories, directory trees that contain source code, or derived files, or both. You can eliminate additional unnecessary rebuilds of files by having SCons use files from one or more code repositories to build files in your local build tree.

22.1. The Repository Method

It's often useful to allow multiple programmers working on a project to build software from source files and/or derived files that are stored in a centrally-accessible repository, a directory copy of the source code tree. (Note that this is not the sort of repository maintained by a source code management system like BitKeeper, CVS, or Subversion.) You use the Repository method to tell SCons to search one or more central code repositories (in order) for any source files and derived files that are not present in the local build tree:

env = Environment()
env.Program('hello.c')
Repository('/usr/repository1', '/usr/repository2')
      

Multiple calls to the Repository method will simply add repositories to the global list that SCons maintains, with the exception that SCons will automatically eliminate the current directory and any non-existent directories from the list.

22.2. Finding source files in repositories

The above example specifies that SCons will first search for files under the /usr/repository1 tree and next under the /usr/repository2 tree. SCons expects that any files it searches for will be found in the same position relative to the top-level directory. In the above example, if the hello.c file is not found in the local build tree, SCons will search first for a /usr/repository1/hello.c file and then for a /usr/repository2/hello.c file to use in its place.

So given the SConstruct file above, if the hello.c file exists in the local build directory, SCons will rebuild the hello program as normal:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o

If, however, there is no local hello.c file, but one exists in /usr/repository1, SCons will recompile the hello program from the source file it finds in the repository:

% scons -Q
cc -o hello.o -c /usr/repository1/hello.c
cc -o hello hello.o

And similarly, if there is no local hello.c file and no /usr/repository1/hello.c, but one exists in /usr/repository2:

% scons -Q
cc -o hello.o -c /usr/repository2/hello.c
cc -o hello hello.o

22.3. Finding #include files in repositories

We've already seen that SCons will scan the contents of a source file for #include file names and realize that targets built from that source file also depend on the #include file(s). For each directory in the $CPPPATH list, SCons will actually search the corresponding directories in any repository trees and establish the correct dependencies on any #include files that it finds in repository directory.

Unless the C compiler also knows about these directories in the repository trees, though, it will be unable to find the #include files. If, for example, the hello.c file in our previous example includes the hello.h in its current directory, and the hello.h only exists in the repository:

% scons -Q
cc -o hello.o -c hello.c
hello.c:1: hello.h: No such file or directory
    

In order to inform the C compiler about the repositories, SCons will add appropriate -I flags to the compilation commands for each directory in the $CPPPATH list. So if we add the current directory to the construction environment $CPPPATH like so:

env = Environment(CPPPATH = ['.'])
env.Program('hello.c')
Repository('/usr/repository1')
      

Then re-executing SCons yields:

% scons -Q
cc -o hello.o -c -I. -I/usr/repository1 hello.c
cc -o hello hello.o

The order of the -I options replicates, for the C preprocessor, the same repository-directory search path that SCons uses for its own dependency analysis. If there are multiple repositories and multiple $CPPPATH directories, SCons will add the repository directories to the beginning of each $CPPPATH directory, rapidly multiplying the number of -I flags. If, for example, the $CPPPATH contains three directories (and shorter repository path names!):

env = Environment(CPPPATH = ['dir1', 'dir2', 'dir3'])
env.Program('hello.c')
Repository('/r1', '/r2')
      

Then we'll end up with nine -I options on the command line, three (for each of the $CPPPATH directories) times three (for the local directory plus the two repositories):

% scons -Q
cc -o hello.o -c -Idir1 -I/r1/dir1 -I/r2/dir1 -Idir2 -I/r1/dir2 -I/r2/dir2 -Idir3 -I/r1/dir3 -I/r2/dir3 hello.c
cc -o hello hello.o

22.3.1. Limitations on #include files in repositories

SCons relies on the C compiler's -I options to control the order in which the preprocessor will search the repository directories for #include files. This causes a problem, however, with how the C preprocessor handles #include lines with the file name included in double-quotes.

As we've seen, SCons will compile the hello.c file from the repository if it doesn't exist in the local directory. If, however, the hello.c file in the repository contains a #include line with the file name in double quotes:

#include "hello.h"
int
main(int argc, char *argv[])
{
    printf(HELLO_MESSAGE);
    return (0);
}
      

Then the C preprocessor will always use a hello.h file from the repository directory first, even if there is a hello.h file in the local directory, despite the fact that the command line specifies -I as the first option:

% scons -Q
cc -o hello.o -c -I. -I/usr/repository1 /usr/repository1/hello.c
cc -o hello hello.o

This behavior of the C preprocessor--always search for a #include file in double-quotes first in the same directory as the source file, and only then search the -I--can not, in general, be changed. In other words, it's a limitation that must be lived with if you want to use code repositories in this way. There are three ways you can possibly work around this C preprocessor behavior:

  1. Some modern versions of C compilers do have an option to disable or control this behavior. If so, add that option to $CFLAGS (or $CXXFLAGS or both) in your construction environment(s). Make sure the option is used for all construction environments that use C preprocessing!

  2. Change all occurrences of #include "file.h" to #include &lt;file.h&gt;. Use of #include with angle brackets does not have the same behavior--the -I directories are searched first for #include files--which gives SCons direct control over the list of directories the C preprocessor will search.

  3. Require that everyone working with compilation from repositories check out and work on entire directories of files, not individual files. (If you use local wrapper scripts around your source code control system's command, you could add logic to enforce this restriction there.

22.4. Finding the SConstruct file in repositories

SCons will also search in repositories for the SConstruct file and any specified SConscript files. This poses a problem, though: how can SCons search a repository tree for an SConstruct file if the SConstruct file itself contains the information about the pathname of the repository? To solve this problem, SCons allows you to specify repository directories on the command line using the -Y option:

% scons -Q -Y /usr/repository1 -Y /usr/repository2
    

When looking for source or derived files, SCons will first search the repositories specified on the command line, and then search the repositories specified in the SConstruct or SConscript files.

22.5. Finding derived files in repositories

If a repository contains not only source files, but also derived files (such as object files, libraries, or executables), SCons will perform its normal MD5 signature calculation to decide if a derived file in a repository is up-to-date, or the derived file must be rebuilt in the local build directory. For the SCons signature calculation to work correctly, a repository tree must contain the .sconsign files that SCons uses to keep track of signature information.

Usually, this would be done by a build integrator who would run SCons in the repository to create all of its derived files and .sconsign files, or who would run SCons in a separate build directory and copy the resulting tree to the desired repository:

% cd /usr/repository1
% scons -Q
cc -o file1.o -c file1.c
cc -o file2.o -c file2.c
cc -o hello.o -c hello.c
cc -o hello hello.o file1.o file2.o

(Note that this is safe even if the SConstruct file lists /usr/repository1 as a repository, because SCons will remove the current build directory from its repository list for that invocation.)

Now, with the repository populated, we only need to create the one local source file we're interested in working with at the moment, and use the -Y option to tell SCons to fetch any other files it needs from the repository:

% cd $HOME/build
% edit hello.c
% scons -Q -Y /usr/repository1
cc -c -o hello.o hello.c
cc -o hello hello.o /usr/repository1/file1.o /usr/repository1/file2.o
    

Notice that SCons realizes that it does not need to rebuild local copies file1.o and file2.o files, but instead uses the already-compiled files from the repository.

22.6. Guaranteeing local copies of files

If the repository tree contains the complete results of a build, and we try to build from the repository without any files in our local tree, something moderately surprising happens:

% mkdir $HOME/build2
% cd $HOME/build2
% scons -Q -Y /usr/all/repository hello
scons: `hello' is up-to-date.
    

Why does SCons say that the hello program is up-to-date when there is no hello program in the local build directory? Because the repository (not the local directory) contains the up-to-date hello program, and SCons correctly determines that nothing needs to be done to rebuild that up-to-date copy of the file.

There are, however, many times when you want to ensure that a local copy of a file always exists. A packaging or testing script, for example, may assume that certain generated files exist locally. To tell SCons to make a copy of any up-to-date repository file in the local build directory, use the Local function:

env = Environment()
hello = env.Program('hello.c')
Local(hello)
      

If we then run the same command, SCons will make a local copy of the program from the repository copy, and tell you that it is doing so:

% scons -Y /usr/all/repository hello
Local copy of hello from /usr/all/repository/hello
scons: `hello' is up-to-date.
    

(Notice that, because the act of making the local copy is not considered a "build" of the hello file, SCons still reports that it is up-to-date.)

Chapter 23. Multi-Platform Configuration (Autoconf Functionality)

SCons has integrated support for multi-platform build configuration similar to that offered by GNU Autoconf, such as figuring out what libraries or header files are available on the local system. This section describes how to use this SCons feature.

Note

This chapter is still under development, so not everything is explained as well as it should be. See the SCons man page for additional information.

23.1. Configure Contexts

The basic framework for multi-platform build configuration in SCons is to attach a configure context to a construction environment by calling the Configure function, perform a number of checks for libraries, functions, header files, etc., and to then call the configure context's Finish method to finish off the configuration:

env = Environment()
conf = Configure(env)
# Checks for libraries, header files, etc. go here!
env = conf.Finish()
    

SCons provides a number of basic checks, as well as a mechanism for adding your own custom checks.

Note that SCons uses its own dependency mechanism to determine when a check needs to be run--that is, SCons does not run the checks every time it is invoked, but caches the values returned by previous checks and uses the cached values unless something has changed. This saves a tremendous amount of developer time while working on cross-platform build issues.

The next sections describe the basic checks that SCons supports, as well as how to add your own custom checks.

23.2. Checking for the Existence of Header Files

Testing the existence of a header file requires knowing what language the header file is. A configure context has a CheckCHeader method that checks for the existence of a C header file:

env = Environment()
conf = Configure(env)
if not conf.CheckCHeader('math.h'):
    print 'Math.h must be installed!'
    Exit(1)
if conf.CheckCHeader('foo.h'):
    conf.env.Append('-DHAS_FOO_H')
env = conf.Finish()
    

Note that you can choose to terminate the build if a given header file doesn't exist, or you can modify the construction environment based on the existence of a header file.

If you need to check for the existence a C++ header file, use the CheckCXXHeader method:

env = Environment()
conf = Configure(env)
if not conf.CheckCXXHeader('vector.h'):
    print 'vector.h must be installed!'
    Exit(1)
env = conf.Finish()
    

23.3. Checking for the Availability of a Function

Check for the availability of a specific function using the CheckFunc method:

env = Environment()
conf = Configure(env)
if not conf.CheckFunc('strcpy'):
    print 'Did not find strcpy(), using local version'
    conf.env.Append(CPPDEFINES = '-Dstrcpy=my_local_strcpy')
env = conf.Finish()
    

23.4. Checking for the Availability of a Library

Check for the availability of a library using the CheckLib method. You only specify the basename of the library, you don't need to add a lib prefix or a .a or .lib suffix:

env = Environment()
conf = Configure(env)
if not conf.CheckLib('m'):
    print 'Did not find libm.a or m.lib, exiting!'
    Exit(1)
env = conf.Finish()
    

Because the ability to use a library successfully often depends on having access to a header file that describes the library's interface, you can check for a library and a header file at the same time by using the CheckLibWithHeader method:

env = Environment()
conf = Configure(env)
if not conf.CheckLibWithHeader('m', 'math.h', 'c'):
    print 'Did not find libm.a or m.lib, exiting!'
    Exit(1)
env = conf.Finish()
    

This is essentially shorthand for separate calls to the CheckHeader and CheckLib functions.

23.5. Checking for the Availability of a typedef

Check for the availability of a typedef by using the CheckType method:

env = Environment()
conf = Configure(env)
if not conf.CheckType('off_t'):
    print 'Did not find off_t typedef, assuming int'
    conf.env.Append(CCFLAGS = '-Doff_t=int')
env = conf.Finish()
    

You can also add a string that will be placed at the beginning of the test file that will be used to check for the typedef. This provide a way to specify files that must be included to find the typedef:

env = Environment()
conf = Configure(env)
if not conf.CheckType('off_t', '#include &lt;sys/types.h&gt;\n'):
    print 'Did not find off_t typedef, assuming int'
    conf.env.Append(CCFLAGS = '-Doff_t=int')
env = conf.Finish()
    

23.6. Checking the size of a datatype

Check the size of a datatype by using the CheckTypeSize method:

env = Environment()
conf = Configure(env)
int_size = conf.CheckTypeSize('unsigned int')
print 'sizeof unsigned int is', int_size
env = conf.Finish()
    
% scons -Q
sizeof unsigned int is 4
scons: `.' is up to date.
    

23.7. Adding Your Own Custom Checks

A custom check is a Python function that checks for a certain condition to exist on the running system, usually using methods that SCons supplies to take care of the details of checking whether a compilation succeeds, a link succeeds, a program is runnable, etc. A simple custom check for the existence of a specific library might look as follows:

mylib_test_source_file = """
#include &lt;mylib.h&gt;
int main(int argc, char **argv)
{
    MyLibrary mylib(argc, argv);
    return 0;
}
"""

def CheckMyLibrary(context):
    context.Message('Checking for MyLibrary...')
    result = context.TryLink(mylib_test_source_file, '.c')
    context.Result(result)
    return result
    

The Message and Result methods should typically begin and end a custom check to let the user know what's going on: the Message call prints the specified message (with no trailing newline) and the Result call prints yes if the check succeeds and no if it doesn't. The TryLink method actually tests for whether the specified program text will successfully link.

(Note that a custom check can modify its check based on any arguments you choose to pass it, or by using or modifying the configure context environment in the context.env attribute.)

This custom check function is then attached to the configure context by passing a dictionary to the Configure call that maps a name of the check to the underlying function:

env = Environment()
conf = Configure(env, custom_tests = {'CheckMyLibrary' : CheckMyLibrary})
    

You'll typically want to make the check and the function name the same, as we've done here, to avoid potential confusion.

We can then put these pieces together and actually call the CheckMyLibrary check as follows:

mylib_test_source_file = """
#include &lt;mylib.h&gt;
int main(int argc, char **argv)
{
    MyLibrary mylib(argc, argv);
    return 0;
}
"""

def CheckMyLibrary(context):
    context.Message('Checking for MyLibrary... ')
    result = context.TryLink(mylib_test_source_file, '.c')
    context.Result(result)
    return result

env = Environment()
conf = Configure(env, custom_tests = {'CheckMyLibrary' : CheckMyLibrary})
if not conf.CheckMyLibrary():
    print 'MyLibrary is not installed!'
    Exit(1)
env = conf.Finish()

# We would then add actual calls like Program() to build
# something using the "env" construction environment.
    

If MyLibrary is not installed on the system, the output will look like:

% scons
scons: Reading SConscript file ...
Checking for MyLibrary... failed
MyLibrary is not installed!
    

If MyLibrary is installed, the output will look like:

% scons
scons: Reading SConscript file ...
Checking for MyLibrary... failed
scons: done reading SConscript
scons: Building targets ...
    .
    .
    .
    

23.8. Not Configuring When Cleaning Targets

Using multi-platform configuration as described in the previous sections will run the configuration commands even when invoking scons -c to clean targets:

% scons -Q -c
Checking for MyLibrary... yes
Removed foo.o
Removed foo
    

Although running the platform checks when removing targets doesn't hurt anything, it's usually unnecessary. You can avoid this by using the GetOption method to check whether the -c (clean) option has been invoked on the command line:

env = Environment()
if not env.GetOption('clean'):
    conf = Configure(env, custom_tests = {'CheckMyLibrary' : CheckMyLibrary})
    if not conf.CheckMyLibrary():
        print 'MyLibrary is not installed!'
        Exit(1)
    env = conf.Finish()
    
% scons -Q -c
Removed foo.o
Removed foo
    

Chapter 24. Caching Built Files

On multi-developer software projects, you can sometimes speed up every developer's builds a lot by allowing them to share the derived files that they build. SCons makes this easy, as well as reliable.

24.1. Specifying the Shared Cache Directory

To enable sharing of derived files, use the CacheDir function in any SConscript file:

CacheDir('/usr/local/build_cache')
       

Note that the directory you specify must already exist and be readable and writable by all developers who will be sharing derived files. It should also be in some central location that all builds will be able to access. In environments where developers are using separate systems (like individual workstations) for builds, this directory would typically be on a shared or NFS-mounted file system.

Here's what happens: When a build has a CacheDir specified, every time a file is built, it is stored in the shared cache directory along with its MD5 build signature. [5] On subsequent builds, before an action is invoked to build a file, SCons will check the shared cache directory to see if a file with the exact same build signature already exists. If so, the derived file will not be built locally, but will be copied into the local build directory from the shared cache directory, like so:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q -c
Removed hello.o
Removed hello
% scons -Q
Retrieved `hello.o' from cache
Retrieved `hello' from cache

Note that the CacheDir feature still calculates MD5 build sigantures for the shared cache file names even if you configure SCons to use timestamps to decide if files are up to date. (See the Chapter 6, Dependencies chapter for information about the Decider function.) Consequently, using CacheDir may reduce or eliminate any potential performance improvements from using timestamps for up-to-date decisions.

24.2. Keeping Build Output Consistent

One potential drawback to using a shared cache is that the output printed by SCons can be inconsistent from invocation to invocation, because any given file may be rebuilt one time and retrieved from the shared cache the next time. This can make analyzing build output more difficult, especially for automated scripts that expect consistent output each time.

If, however, you use the --cache-show option, SCons will print the command line that it would have executed to build the file, even when it is retrieving the file from the shared cache. This makes the build output consistent every time the build is run:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q -c
Removed hello.o
Removed hello
% scons -Q --cache-show
cc -o hello.o -c hello.c
cc -o hello hello.o

The trade-off, of course, is that you no longer know whether or not SCons has retrieved a derived file from cache or has rebuilt it locally.

24.3. Not Using the Shared Cache for Specific Files

You may want to disable caching for certain specific files in your configuration. For example, if you only want to put executable files in a central cache, but not the intermediate object files, you can use the NoCache function to specify that the object files should not be cached:

env = Environment()
obj = env.Object('hello.c')
env.Program('hello.c')
CacheDir('cache')
NoCache('hello.o')
       

Then when you run scons after cleaning the built targets, it will recompile the object file locally (since it doesn't exist in the shared cache directory), but still realize that the shared cache directory contains an up-to-date executable program that can be retrieved instead of re-linking:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q -c
Removed hello.o
Removed hello
% scons -Q
cc -o hello.o -c hello.c
Retrieved `hello' from cache
    

24.4. Disabling the Shared Cache

Retrieving an already-built file from the shared cache is usually a significant time-savings over rebuilding the file, but how much of a savings (or even whether it saves time at all) can depend a great deal on your system or network configuration. For example, retrieving cached files from a busy server over a busy network might end up being slower than rebuilding the files locally.

In these cases, you can specify the --cache-disable command-line option to tell SCons to not retrieve already-built files from the shared cache directory:

% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q -c
Removed hello.o
Removed hello
% scons -Q
Retrieved `hello.o' from cache
Retrieved `hello' from cache
% scons -Q -c
Removed hello.o
Removed hello
% scons -Q --cache-disable
cc -o hello.o -c hello.c
cc -o hello hello.o

24.5. Populating a Shared Cache With Already-Built Files

Sometimes, you may have one or more derived files already built in your local build tree that you wish to make available to other people doing builds. For example, you may find it more effective to perform integration builds with the cache disabled (per the previous section) and only populate the shared cache directory with the built files after the integration build has completed successfully. This way, the cache will only get filled up with derived files that are part of a complete, successful build not with files that might be later overwritten while you debug integration problems.

In this case, you can use the the --cache-force option to tell SCons to put all derived files in the cache, even if the files already exist in your local tree from having been built by a previous invocation:

% scons -Q --cache-disable
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q -c
Removed hello.o
Removed hello
% scons -Q --cache-disable
cc -o hello.o -c hello.c
cc -o hello hello.o
% scons -Q --cache-force
scons: `.' is up to date.
% scons -Q
scons: `.' is up to date.

Notice how the above sample run demonstrates that the --cache-disable option avoids putting the built hello.o and hello files in the cache, but after using the --cache-force option, the files have been put in the cache for the next invocation to retrieve.

24.6. Minimizing Cache Contention: the --random Option

If you allow multiple builds to update the shared cache directory simultaneously, two builds that occur at the same time can sometimes start "racing" with one another to build the same files in the same order. If, for example, you are linking multiple files into an executable program:

Program('prog',
        ['f1.c', 'f2.c', 'f3.c', 'f4.c', 'f5.c'])
       

SCons will normally build the input object files on which the program depends in their normal, sorted order:

% scons -Q
cc -o f1.o -c f1.c
cc -o f3.o -c f3.c
cc -o f4.o -c f4.c
cc -o f2.o -c f2.c
cc -o f5.o -c f5.c
cc -o prog f1.o f2.o f3.o f4.o f5.o

But if two such builds take place simultaneously, they may each look in the cache at nearly the same time and both decide that f1.o must be rebuilt and pushed into the shared cache directory, then both decide that f2.o must be rebuilt (and pushed into the shared cache directory), then both decide that f3.o must be rebuilt... This won't cause any actual build problems--both builds will succeed, generate correct output files, and populate the cache--but it does represent wasted effort.

To alleviate such contention for the cache, you can use the --random command-line option to tell SCons to build dependencies in a random order:

  % scons -Q --random
  cc -o f3.o -c f3.c
  cc -o f1.o -c f1.c
  cc -o f5.o -c f5.c
  cc -o f2.o -c f2.c
  cc -o f4.o -c f4.c
  cc -o prog f1.o f2.o f3.o f4.o f5.o
    

Multiple builds using the --random option will usually build their dependencies in different, random orders, which minimizes the chances for a lot of contention for same-named files in the shared cache directory. Multiple simultaneous builds might still race to try to build the same target file on occasion, but long sequences of inefficient contention should be rare.

Note, of course, the --random option will cause the output that SCons prints to be inconsistent from invocation to invocation, which may be an issue when trying to compare output from different build runs.

If you want to make sure dependencies will be built in a random order without having to specify the --random on very command line, you can use the SetOption function to set the random option within any SConscript file:

SetOption('random', 1)
Program('prog',
        ['f1.c', 'f2.c', 'f3.c', 'f4.c', 'f5.c'])
       


[5] Actually, the MD5 signature is used as the name of the file in the shared cache directory in which the contents are stored.

Chapter 25. Alias Targets

We've already seen how you can use the Alias function to create a target named install:

env = Environment()
hello = env.Program('hello.c')
env.Install('/usr/bin', hello)
env.Alias('install', '/usr/bin')
     

You can then use this alias on the command line to tell SCons more naturally that you want to install files:

% scons -Q install
cc -o hello.o -c hello.c
cc -o hello hello.o
Install file: "hello" as "/usr/bin/hello"

Like other Builder methods, though, the Alias method returns an object representing the alias being built. You can then use this object as input to anothother Builder. This is especially useful if you use such an object as input to another call to the Alias Builder, allowing you to create a hierarchy of nested aliases:

env = Environment()
p = env.Program('foo.c')
l = env.Library('bar.c')
env.Install('/usr/bin', p)
env.Install('/usr/lib', l)
ib = env.Alias('install-bin', '/usr/bin')
il = env.Alias('install-lib', '/usr/lib')
env.Alias('install', [ib, il])
     

This example defines separate install, install-bin, and install-lib aliases, allowing you finer control over what gets installed:

% scons -Q install-bin
cc -o foo.o -c foo.c
cc -o foo foo.o
Install file: "foo" as "/usr/bin/foo"
% scons -Q install-lib
cc -o bar.o -c bar.c
ar rc libbar.a bar.o
ranlib libbar.a
Install file: "libbar.a" as "/usr/lib/libbar.a"
% scons -Q -c /
Removed foo.o
Removed foo
Removed /usr/bin/foo
Removed bar.o
Removed libbar.a
Removed /usr/lib/libbar.a
% scons -Q install
cc -o foo.o -c foo.c
cc -o foo foo.o
Install file: "foo" as "/usr/bin/foo"
cc -o bar.o -c bar.c
ar rc libbar.a bar.o
ranlib libbar.a
Install file: "libbar.a" as "/usr/lib/libbar.a"

Chapter 26. Java Builds

So far, we've been using examples of building C and C++ programs to demonstrate the features of SCons. SCons also supports building Java programs, but Java builds are handled slightly differently, which reflects the ways in which the Java compiler and tools build programs differently than other languages' tool chains.

26.1. Building Java Class Files: the Java Builder

The basic activity when programming in Java, of course, is to take one or more .java files containing Java source code and to call the Java compiler to turn them into one or more .class files. In SCons, you do this by giving the Java Builder a target directory in which to put the .class files, and a source directory that contains the .java files:

Java('classes', 'src')
      

If the src directory contains three .java source files, then running SCons might look like this:

% scons -Q
javac -d classes -sourcepath src src/Example1.java src/Example2.java src/Example3.java

SCons will actually search the src directory tree for all of the .java files. The Java compiler will then create the necessary class files in the classes subdirectory, based on the class names found in the .java files.

26.2. How SCons Handles Java Dependencies

In addition to searching the source directory for .java files, SCons actually runs the .java files through a stripped-down Java parser that figures out what classes are defined. In other words, SCons knows, without you having to tell it, what .class files will be produced by the javac call. So our one-liner example from the preceding section:

Java('classes', 'src')
      

Will not only tell you reliably that the .class files in the classes subdirectory are up-to-date:

% scons -Q
javac -d classes -sourcepath src src/Example1.java src/Example2.java src/Example3.java
% scons -Q classes
scons: `classes' is up to date.

But it will also remove all of the generated .class files, even for inner classes, without you having to specify them manually. For example, if our Example1.java and Example3.java files both define additional classes, and the class defined in Example2.java has an inner class, running scons -c will clean up all of those .class files as well:

% scons -Q
javac -d classes -sourcepath src src/Example1.java src/Example2.java src/Example3.java
% scons -Q -c classes
Removed classes/Example1.class
Removed classes/AdditionalClass1.class
Removed classes/Example2$Inner2.class
Removed classes/Example2.class
Removed classes/Example3.class
Removed classes/AdditionalClass3.class

To ensure correct handling of .class dependencies in all cases, you need to tell SCons which Java version is being used. This is needed because Java 1.5 changed the .class file names for nested anonymous inner classes. Use the JAVAVERSION construction variable to specify the version in use. With Java 1.6, the one-liner example can then be defined like this:

Java('classes', 'src', JAVAVERSION='1.6')
    

See JAVAVERSION in the man page for more information.

26.3. Building Java Archive (.jar) Files: the Jar Builder

After building the class files, it's common to collect them into a Java archive (.jar) file, which you do by calling the Jar Builder method. If you want to just collect all of the class files within a subdirectory, you can just specify that subdirectory as the Jar source:

Java(target = 'classes', source = 'src')
Jar(target = 'test.jar', source = 'classes')
      

SCons will then pass that directory to the jar command, which will collect all of the underlying .class files:

% scons -Q
javac -d classes -sourcepath src src/Example1.java src/Example2.java src/Example3.java
jar cf test.jar classes

If you want to keep all of the .class files for multiple programs in one location, and only archive some of them in each .jar file, you can pass the Jar builder a list of files as its source. It's extremely simple to create multiple .jar files this way, using the lists of target class files created by calls to the Java builder as sources to the various Jar calls:

prog1_class_files = Java(target = 'classes', source = 'prog1')
prog2_class_files = Java(target = 'classes', source = 'prog2')
Jar(target = 'prog1.jar', source = prog1_class_files)
Jar(target = 'prog2.jar', source = prog2_class_files)
      

This will then create prog1.jar and prog2.jar next to the subdirectories that contain their .java files:

% scons -Q
javac -d classes -sourcepath prog1 prog1/Example1.java prog1/Example2.java
javac -d classes -sourcepath prog2 prog2/Example3.java prog2/Example4.java
jar cf prog1.jar -C classes Example1.class -C classes Example2.class
jar cf prog2.jar -C classes Example3.class -C classes Example4.class

26.4. Building C Header and Stub Files: the JavaH Builder

You can generate C header and source files for implementing native methods, by using the JavaH Builder. There are several ways of using the JavaH Builder. One typical invocation might look like:

classes = Java(target = 'classes', source = 'src/pkg/sub')
JavaH(target = 'native', source = classes)
      

The source is a list of class files generated by the call to the Java Builder, and the target is the output directory in which we want the C header files placed. The target gets converted into the -d when SCons runs javah:

% scons -Q
javac -d classes -sourcepath src/pkg/sub src/pkg/sub/Example1.java src/pkg/sub/Example2.java src/pkg/sub/Example3.java
javah -d native -classpath classes pkg.sub.Example1 pkg.sub.Example2 pkg.sub.Example3

In this case, the call to javah will generate the header files native/pkg_sub_Example1.h, native/pkg_sub_Example2.h and native/pkg_sub_Example3.h. Notice that SCons remembered that the class files were generated with a target directory of classes, and that it then specified that target directory as the -classpath option to the call to javah.

Although it's more convenient to use the list of class files returned by the Java Builder as the source of a call to the JavaH Builder, you can specify the list of class files by hand, if you prefer. If you do, you need to set the $JAVACLASSDIR construction variable when calling JavaH:

Java(target = 'classes', source = 'src/pkg/sub')
class_file_list = ['classes/pkg/sub/Example1.class',
                   'classes/pkg/sub/Example2.class',
                   'classes/pkg/sub/Example3.class']
JavaH(target = 'native', source = class_file_list, JAVACLASSDIR = 'classes')
      

The $JAVACLASSDIR value then gets converted into the -classpath when SCons runs javah:

% scons -Q
javac -d classes -sourcepath src/pkg/sub src/pkg/sub/Example1.java src/pkg/sub/Example2.java src/pkg/sub/Example3.java
javah -d native -classpath classes pkg.sub.Example1 pkg.sub.Example2 pkg.sub.Example3

Lastly, if you don't want a separate header file generated for each source file, you can specify an explicit File Node as the target of the JavaH Builder:

classes = Java(target = 'classes', source = 'src/pkg/sub')
JavaH(target = File('native.h'), source = classes)
      

Because SCons assumes by default that the target of the JavaH builder is a directory, you need to use the File function to make sure that SCons doesn't create a directory named native.h. When a file is used, though, SCons correctly converts the file name into the javah -o option:

% scons -Q
javac -d classes -sourcepath src/pkg/sub src/pkg/sub/Example1.java src/pkg/sub/Example2.java src/pkg/sub/Example3.java
javah -o native.h -classpath classes pkg.sub.Example1 pkg.sub.Example2 pkg.sub.Example3

26.5. Building RMI Stub and Skeleton Class Files: the RMIC Builder

You can generate Remote Method Invocation stubs by using the RMIC Builder. The source is a list of directories, typically returned by a call to the Java Builder, and the target is an output directory where the _Stub.class and _Skel.class files will be placed:

classes = Java(target = 'classes', source = 'src/pkg/sub')
RMIC(target = 'outdir', source = classes)
      

As it did with the JavaH Builder, SCons remembers the class directory and passes it as the -classpath option to rmic:

% scons -Q
javac -d classes -sourcepath src/pkg/sub src/pkg/sub/Example1.java src/pkg/sub/Example2.java
rmic -d outdir -classpath classes pkg.sub.Example1 pkg.sub.Example2

This example would generate the files outdir/pkg/sub/Example1_Skel.class, outdir/pkg/sub/Example1_Stub.class, outdir/pkg/sub/Example2_Skel.class and outdir/pkg/sub/Example2_Stub.class.

Chapter 27. Miscellaneous Functionality

SCons supports a lot of additional functionality that doesn't readily fit into the other chapters.

27.1. Verifying the Python Version: the EnsurePythonVersion Function

Although the SCons code itself will run on any 2.x Python version 2.7 or later, you are perfectly free to make use of Python syntax and modules from later versions when writing your SConscript files or your own local modules. If you do this, it's usually helpful to configure SCons to exit gracefully with an error message if it's being run with a version of Python that simply won't work with your code. This is especially true if you're going to use SCons to build source code that you plan to distribute publicly, where you can't be sure of the Python version that an anonymous remote user might use to try to build your software.

SCons provides an EnsurePythonVersion function for this. You simply pass it the major and minor versions numbers of the version of Python you require:

EnsurePythonVersion(2, 5)
    

And then SCons will exit with the following error message when a user runs it with an unsupported earlier version of Python:

% scons -Q
Python 2.5 or greater required, but you have Python 2.3.6
    

27.2. Verifying the SCons Version: the EnsureSConsVersion Function

You may, of course, write your SConscript files to use features that were only added in recent versions of SCons. When you publicly distribute software that is built using SCons, it's helpful to have SCons verify the version being used and exit gracefully with an error message if the user's version of SCons won't work with your SConscript files. SCons provides an EnsureSConsVersion function that verifies the version of SCons in the same the EnsurePythonVersion function verifies the version of Python, by passing in the major and minor versions numbers of the version of SCons you require:

EnsureSConsVersion(1, 0)
    

And then SCons will exit with the following error message when a user runs it with an unsupported earlier version of SCons:

% scons -Q
SCons 1.0 or greater required, but you have SCons 0.98.5
    

27.3. Explicitly Terminating SCons While Reading SConscript Files: the Exit Function

SCons supports an Exit function which can be used to terminate SCons while reading the SConscript files, usually because you've detected a condition under which it doesn't make sense to proceed:

if ARGUMENTS.get('FUTURE'):
    print "The FUTURE option is not supported yet!"
    Exit(2)
env = Environment()
env.Program('hello.c')
      
% scons -Q FUTURE=1
The FUTURE option is not supported yet!
% scons -Q
cc -o hello.o -c hello.c
cc -o hello hello.o

The Exit function takes as an argument the (numeric) exit status that you want SCons to exit with. If you don't specify a value, the default is to exit with 0, which indicates successful execution.

Note that the Exit function is equivalent to calling the Python sys.exit function (which the it actually calls), but because Exit is a SCons function, you don't have to import the Python sys module to use it.

27.4. Searching for Files: the FindFile Function

The FindFile function searches for a file in a list of directories. If there is only one directory, it can be given as a simple string. The function returns a File node if a matching file exists, or None if no file is found. (See the documentation for the Glob function for an alternative way of searching for entries in a directory.)

# one directory
print FindFile('missing', '.')
t = FindFile('exists', '.')
print t.__class__, t
      
% scons -Q
None
<class 'SCons.Node.FS.File'> exists
scons: `.' is up to date.
# several directories
includes = [ '.', 'include', 'src/include']
headers = [ 'nonesuch.h', 'config.h', 'private.h', 'dist.h']
for hdr in headers:
    print '%-12s' % ('%s:' % hdr), FindFile(hdr, includes)
      
% scons -Q
nonesuch.h:  None
config.h:    config.h
private.h:   src/include/private.h
dist.h:      include/dist.h
scons: `.' is up to date.

If the file exists in more than one directory, only the first occurrence is returned.

print FindFile('multiple', ['sub1', 'sub2', 'sub3'])
print FindFile('multiple', ['sub2', 'sub3', 'sub1'])
print FindFile('multiple', ['sub3', 'sub1', 'sub2'])
      
% scons -Q
sub1/multiple
sub2/multiple
sub3/multiple
scons: `.' is up to date.

In addition to existing files, FindFile will also find derived files (that is, non-leaf files) that haven't been built yet. (Leaf files should already exist, or the build will fail!)

# Neither file exists, so build will fail
Command('derived', 'leaf', 'cat >$TARGET $SOURCE')
print FindFile('leaf', '.')
print FindFile('derived', '.')
      
% scons -Q
leaf
derived
cat > derived leaf
# Only 'leaf' exists
Command('derived', 'leaf', 'cat >$TARGET $SOURCE')
print FindFile('leaf', '.')
print FindFile('derived', '.')
      
% scons -Q
leaf
derived
cat > derived leaf

If a source file exists, FindFile will correctly return the name in the build directory.

# Only 'src/leaf' exists
VariantDir('build', 'src')
print FindFile('leaf', 'build')
      
% scons -Q
build/leaf
scons: `.' is up to date.

27.5. Handling Nested Lists: the Flatten Function

SCons supports a Flatten function which takes an input Python sequence (list or tuple) and returns a flattened list containing just the individual elements of the sequence. This can be handy when trying to examine a list composed of the lists returned by calls to various Builders. For example, you might collect object files built in different ways into one call to the Program Builder by just enclosing them in a list, as follows:

objects = [
    Object('prog1.c'),
    Object('prog2.c', CCFLAGS='-DFOO'),
]
Program(objects)
      

Because the Builder calls in SCons flatten their input lists, this works just fine to build the program:

% scons -Q
cc -o prog1.o -c prog1.c
cc -o prog2.o -c -DFOO prog2.c
cc -o prog1 prog1.o prog2.o

But if you were debugging your build and wanted to print the absolute path of each object file in the objects list, you might try the following simple approach, trying to print each Node's abspath attribute:

objects = [
    Object('prog1.c'),
    Object('prog2.c', CCFLAGS='-DFOO'),
]
Program(objects)

for object_file in objects:
    print object_file.abspath
      

This does not work as expected because each call to str is operating an embedded list returned by each Object call, not on the underlying Nodes within those lists:

% scons -Q
AttributeError: 'NodeList' object has no attribute 'abspath':
  File "/home/my/project/SConstruct", line 8:
    print object_file.abspath

The solution is to use the Flatten function so that you can pass each Node to the str separately:

objects = [
    Object('prog1.c'),
    Object('prog2.c', CCFLAGS='-DFOO'),
]
Program(objects)

for object_file in Flatten(objects):
    print object_file.abspath
      
% scons -Q
/home/me/project/prog1.o
/home/me/project/prog2.o
cc -o prog1.o -c prog1.c
cc -o prog2.o -c -DFOO prog2.c
cc -o prog1 prog1.o prog2.o
    

27.6. Finding the Invocation Directory: the GetLaunchDir Function

If you need to find the directory from which the user invoked the scons command, you can use the GetLaunchDir function:

env = Environment(
    LAUNCHDIR = GetLaunchDir(),
)
env.Command('directory_build_info',
            '$LAUNCHDIR/build_info'
            Copy('$TARGET', '$SOURCE'))
    

Because SCons is usually invoked from the top-level directory in which the SConstruct file lives, the Python os.getcwd() is often equivalent. However, the SCons -u, -U and -D command-line options, when invoked from a subdirectory, will cause SCons to change to the directory in which the SConstruct file is found. When those options are used, GetLaunchDir will still return the path to the user's invoking subdirectory, allowing the SConscript configuration to still get at configuration (or other) files from the originating directory.

Chapter 28. Troubleshooting

The experience of configuring any software build tool to build a large code base usually, at some point, involves trying to figure out why the tool is behaving a certain way, and how to get it to behave the way you want. SCons is no different. This appendix contains a number of different ways in which you can get some additional insight into SCons' behavior.

Note that we're always interested in trying to improve how you can troubleshoot configuration problems. If you run into a problem that has you scratching your head, and which there just doesn't seem to be a good way to debug, odds are pretty good that someone else will run into the same problem, too. If so, please let the SCons development team know (preferably by filing a bug report or feature request at our project pages at tigris.org) so that we can use your feedback to try to come up with a better way to help you, and others, get the necessary insight into SCons behavior to help identify and fix configuration issues.

28.1. Why is That Target Being Rebuilt? the --debug=explain Option

Let's look at a simple example of a misconfigured build that causes a target to be rebuilt every time SCons is run:

# Intentionally misspell the output file name in the
# command used to create the file:
Command('file.out', 'file.in', 'cp $SOURCE file.oout')
      

(Note to Windows users: The POSIX cp command copies the first file named on the command line to the second file. In our example, it copies the file.in file to the file.out file.)

Now if we run SCons multiple times on this example, we see that it re-runs the cp command every time:

% scons -Q
cp file.in file.oout
% scons -Q
cp file.in file.oout
% scons -Q
cp file.in file.oout

In this example, the underlying cause is obvious: we've intentionally misspelled the output file name in the cp command, so the command doesn't actually build the file.out file that we've told SCons to expect. But if the problem weren't obvious, it would be helpful to specify the --debug=explain option on the command line to have SCons tell us very specifically why it's decided to rebuild the target:

% scons -Q --debug=explain
scons: building `file.out' because it doesn't exist
cp file.in file.oout

If this had been a more complicated example involving a lot of build output, having SCons tell us that it's trying to rebuild the target file because it doesn't exist would be an important clue that something was wrong with the command that we invoked to build it.

Note that you can also use --warn=target-not-built which checks whether or not expected targets exist after a build rule is executed.

% scons -Q --warn=target-not-built
cp file.in file.oout

scons: warning: Cannot find target file.out after building
File "/home/garyo/src/scons-scons/src/script/scons.py", line 199, in <module>

The --debug=explain option also comes in handy to help figure out what input file changed. Given a simple configuration that builds a program from three source files, changing one of the source files and rebuilding with the --debug=explain option shows very specifically why SCons rebuilds the files that it does:

% scons -Q
cc -o file1.o -c file1.c
cc -o file2.o -c file2.c
cc -o file3.o -c file3.c
cc -o prog file1.o file2.o file3.o
%     [CHANGE THE CONTENTS OF file2.c]
% scons -Q --debug=explain
scons: rebuilding `file2.o' because `file2.c' changed
cc -o file2.o -c file2.c
scons: rebuilding `prog' because `file2.o' changed
cc -o prog file1.o file2.o file3.o

This becomes even more helpful in identifying when a file is rebuilt due to a change in an implicit dependency, such as an incuded .h file. If the file1.c and file3.c files in our example both included a hello.h file, then changing that included file and re-running SCons with the --debug=explain option will pinpoint that it's the change to the included file that starts the chain of rebuilds:

% scons -Q
cc -o file1.o -c -I. file1.c
cc -o file2.o -c -I. file2.c
cc -o file3.o -c -I. file3.c
cc -o prog file1.o file2.o file3.o
%     [CHANGE THE CONTENTS OF hello.h]
% scons -Q --debug=explain
scons: rebuilding `file1.o' because `hello.h' changed
cc -o file1.o -c -I. file1.c
scons: rebuilding `file3.o' because `hello.h' changed
cc -o file3.o -c -I. file3.c
scons: rebuilding `prog' because:
           `file1.o' changed
           `file3.o' changed
cc -o prog file1.o file2.o file3.o

(Note that the --debug=explain option will only tell you why SCons decided to rebuild necessary targets. It does not tell you what files it examined when deciding not to rebuild a target file, which is often a more valuable question to answer.)

28.2. What's in That Construction Environment? the Dump Method

When you create a construction environment, SCons populates it with construction variables that are set up for various compilers, linkers and utilities that it finds on your system. Although this is usually helpful and what you want, it might be frustrating if SCons doesn't set certain variables that you expect to be set. In situations like this, it's sometimes helpful to use the construction environment Dump method to print all or some of the construction variables. Note that the Dump method returns the representation of the variables in the environment for you to print (or otherwise manipulate):

env = Environment()
print env.Dump()
      

On a POSIX system with gcc installed, this might generate:

% scons
scons: Reading SConscript files ...
{ 'BUILDERS': {'_InternalInstall': <function InstallBuilderWrapper at 0x700000&gt;, '_InternalInstallVersionedLib': <function InstallVersionedBuilderWrapper at 0x700000&gt;, '_InternalInstallAs': <function InstallAsBuilderWrapper at 0x700000&gt;},
  'CONFIGUREDIR': '#/.sconf_temp',
  'CONFIGURELOG': '#/config.log',
  'CPPSUFFIXES': [ '.c',
                   '.C',
                   '.cxx',
                   '.cpp',
                   '.c++',
                   '.cc',
                   '.h',
                   '.H',
                   '.hxx',
                   '.hpp',
                   '.hh',
                   '.F',
                   '.fpp',
                   '.FPP',
                   '.m',
                   '.mm',
                   '.S',
                   '.spp',
                   '.SPP',
                   '.sx'],
  'DSUFFIXES': ['.d'],
  'Dir': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'Dirs': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'ENV': { 'PATH': '/usr/local/bin:/opt/bin:/bin:/usr/bin'},
  'ESCAPE': <function escape at 0x700000&gt;,
  'File': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'HOST_ARCH': None,
  'HOST_OS': None,
  'IDLSUFFIXES': ['.idl', '.IDL'],
  'INSTALL': <function copyFunc at 0x700000&gt;,
  'INSTALLVERSIONEDLIB': <function copyFuncVersionedLib at 0x700000&gt;,
  'LIBPREFIX': 'lib',
  'LIBPREFIXES': ['$LIBPREFIX'],
  'LIBSUFFIX': '.a',
  'LIBSUFFIXES': ['$LIBSUFFIX', '$SHLIBSUFFIX'],
  'MAXLINELENGTH': 128072,
  'OBJPREFIX': '',
  'OBJSUFFIX': '.o',
  'PLATFORM': 'posix',
  'PROGPREFIX': '',
  'PROGSUFFIX': '',
  'PSPAWN': <function piped_env_spawn at 0x700000&gt;,
  'RDirs': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'SCANNERS': [],
  'SHELL': 'sh',
  'SHLIBPREFIX': '$LIBPREFIX',
  'SHLIBSUFFIX': '.so',
  'SHOBJPREFIX': '$OBJPREFIX',
  'SHOBJSUFFIX': '$OBJSUFFIX',
  'SPAWN': <function subprocess_spawn at 0x700000&gt;,
  'TARGET_ARCH': None,
  'TARGET_OS': None,
  'TEMPFILE': <class 'SCons.Platform.TempFileMunge'>,
  'TEMPFILEPREFIX': '@',
  'TOOLS': ['install', 'install'],
  '_CPPDEFFLAGS': '${_defines(CPPDEFPREFIX, CPPDEFINES, CPPDEFSUFFIX, __env__)}',
  '_CPPINCFLAGS': '$( ${_concat(INCPREFIX, CPPPATH, INCSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
  '_LIBDIRFLAGS': '$( ${_concat(LIBDIRPREFIX, LIBPATH, LIBDIRSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
  '_LIBFLAGS': '${_concat(LIBLINKPREFIX, LIBS, LIBLINKSUFFIX, __env__)}',
  '__DRPATH': '$_DRPATH',
  '__RPATH': '$_RPATH',
  '_concat': <function _concat at 0x700000&gt;,
  '_defines': <function _defines at 0x700000&gt;,
  '_stripixes': <function _stripixes at 0x700000&gt;}
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.

On a Windows system with Visual C++ the output might look like:

C:\>scons
scons: Reading SConscript files ...
{ 'BUILDERS': {'_InternalInstallVersionedLib': <function InstallVersionedBuilderWrapper at 0x700000&gt;, '_InternalInstall': <function InstallBuilderWrapper at 0x700000&gt;, 'Object': <SCons.Builder.CompositeBuilder object at 0x700000&gt;, 'PCH': <SCons.Builder.BuilderBase object at 0x700000&gt;, 'RES': <SCons.Builder.BuilderBase object at 0x700000&gt;, 'SharedObject': <SCons.Builder.CompositeBuilder object at 0x700000&gt;, 'StaticObject': <SCons.Builder.CompositeBuilder object at 0x700000&gt;, '_InternalInstallAs': <function InstallAsBuilderWrapper at 0x700000&gt;},
  'CC': 'cl',
  'CCCOM': <SCons.Action.FunctionAction object at 0x700000&gt;,
  'CCFLAGS': ['/nologo'],
  'CCPCHFLAGS': ['${(PCH and "/Yu%s \\"/Fp%s\\""%(PCHSTOP or "",File(PCH))) or ""}'],
  'CCPDBFLAGS': ['${(PDB and "/Z7") or ""}'],
  'CFILESUFFIX': '.c',
  'CFLAGS': [],
  'CONFIGUREDIR': '#/.sconf_temp',
  'CONFIGURELOG': '#/config.log',
  'CPPDEFPREFIX': '/D',
  'CPPDEFSUFFIX': '',
  'CPPSUFFIXES': [ '.c',
                   '.C',
                   '.cxx',
                   '.cpp',
                   '.c++',
                   '.cc',
                   '.h',
                   '.H',
                   '.hxx',
                   '.hpp',
                   '.hh',
                   '.F',
                   '.fpp',
                   '.FPP',
                   '.m',
                   '.mm',
                   '.S',
                   '.spp',
                   '.SPP',
                   '.sx'],
  'CXX': '$CC',
  'CXXCOM': '${TEMPFILE("$CXX $_MSVC_OUTPUT_FLAG /c $CHANGED_SOURCES $CXXFLAGS $CCFLAGS $_CCCOMCOM")}',
  'CXXFILESUFFIX': '.cc',
  'CXXFLAGS': ['$(', '/TP', '$)'],
  'DSUFFIXES': ['.d'],
  'Dir': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'Dirs': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'ENV': { 'PATH': 'C:\\WINDOWS\\System32',
           'PATHEXT': '.COM;.EXE;.BAT;.CMD',
           'SystemRoot': 'C:\\WINDOWS'},
  'ESCAPE': <function escape at 0x700000&gt;,
  'File': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'HOST_ARCH': '',
  'HOST_OS': 'win32',
  'IDLSUFFIXES': ['.idl', '.IDL'],
  'INCPREFIX': '/I',
  'INCSUFFIX': '',
  'INSTALL': <function copyFunc at 0x700000&gt;,
  'INSTALLVERSIONEDLIB': <function copyFuncVersionedLib at 0x700000&gt;,
  'LIBPREFIX': '',
  'LIBPREFIXES': ['$LIBPREFIX'],
  'LIBSUFFIX': '.lib',
  'LIBSUFFIXES': ['$LIBSUFFIX'],
  'MAXLINELENGTH': 2048,
  'MSVC_SETUP_RUN': True,
  'OBJPREFIX': '',
  'OBJSUFFIX': '.obj',
  'PCHCOM': '$CXX /Fo${TARGETS[1]} $CXXFLAGS $CCFLAGS $CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS /c $SOURCES /Yc$PCHSTOP /Fp${TARGETS[0]} $CCPDBFLAGS $PCHPDBFLAGS',
  'PCHPDBFLAGS': ['${(PDB and "/Yd") or ""}'],
  'PLATFORM': 'win32',
  'PROGPREFIX': '',
  'PROGSUFFIX': '.exe',
  'PSPAWN': <function piped_spawn at 0x700000&gt;,
  'RC': 'rc',
  'RCCOM': <SCons.Action.FunctionAction object at 0x700000&gt;,
  'RCFLAGS': [],
  'RCSUFFIXES': ['.rc', '.rc2'],
  'RDirs': <SCons.Defaults.Variable_Method_Caller object at 0x700000&gt;,
  'SCANNERS': [],
  'SHCC': '$CC',
  'SHCCCOM': <SCons.Action.FunctionAction object at 0x700000&gt;,
  'SHCCFLAGS': ['$CCFLAGS'],
  'SHCFLAGS': ['$CFLAGS'],
  'SHCXX': '$CXX',
  'SHCXXCOM': '${TEMPFILE("$SHCXX $_MSVC_OUTPUT_FLAG /c $CHANGED_SOURCES $SHCXXFLAGS $SHCCFLAGS $_CCCOMCOM")}',
  'SHCXXFLAGS': ['$CXXFLAGS'],
  'SHELL': None,
  'SHLIBPREFIX': '',
  'SHLIBSUFFIX': '.dll',
  'SHOBJPREFIX': '$OBJPREFIX',
  'SHOBJSUFFIX': '$OBJSUFFIX',
  'SPAWN': <function spawn at 0x700000&gt;,
  'STATIC_AND_SHARED_OBJECTS_ARE_THE_SAME': 1,
  'TARGET_ARCH': None,
  'TARGET_OS': None,
  'TEMPFILE': <class 'SCons.Platform.TempFileMunge'>,
  'TEMPFILEPREFIX': '@',
  'TOOLS': ['msvc', 'install', 'install'],
  '_CCCOMCOM': '$CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS $CCPCHFLAGS $CCPDBFLAGS',
  '_CPPDEFFLAGS': '${_defines(CPPDEFPREFIX, CPPDEFINES, CPPDEFSUFFIX, __env__)}',
  '_CPPINCFLAGS': '$( ${_concat(INCPREFIX, CPPPATH, INCSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
  '_LIBDIRFLAGS': '$( ${_concat(LIBDIRPREFIX, LIBPATH, LIBDIRSUFFIX, __env__, RDirs, TARGET, SOURCE)} $)',
  '_LIBFLAGS': '${_concat(LIBLINKPREFIX, LIBS, LIBLINKSUFFIX, __env__)}',
  '_MSVC_OUTPUT_FLAG': <function msvc_output_flag at 0x700000&gt;,
  '_concat': <function _concat at 0x700000&gt;,
  '_defines': <function _defines at 0x700000&gt;,
  '_stripixes': <function _stripixes at 0x700000&gt;}
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.

The construction environments in these examples have actually been restricted to just gcc and Visual C++, respectively. In a real-life situation, the construction environments will likely contain a great many more variables. Also note that we've massaged the example output above to make the memory address of all objects a constant 0x700000. In reality, you would see a different hexadecimal number for each object.

To make it easier to see just what you're interested in, the Dump method allows you to specify a specific constrcution variable that you want to disply. For example, it's not unusual to want to verify the external environment used to execute build commands, to make sure that the PATH and other environment variables are set up the way they should be. You can do this as follows:

env = Environment()
print env.Dump('ENV')
      

Which might display the following when executed on a POSIX system:

% scons
scons: Reading SConscript files ...
{ 'PATH': '/usr/local/bin:/opt/bin:/bin:/usr/bin'}
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.

And the following when executed on a Windows system:

C:\>scons
scons: Reading SConscript files ...
{ 'PATH': 'C:\\WINDOWS\\System32',
  'PATHEXT': '.COM;.EXE;.BAT;.CMD',
  'SystemRoot': 'C:\\WINDOWS'}
scons: done reading SConscript files.
scons: Building targets ...
scons: `.' is up to date.
scons: done building targets.

28.3. What Dependencies Does SCons Know About? the --tree Option

Sometimes the best way to try to figure out what SCons is doing is simply to take a look at the dependency graph that it constructs based on your SConscript files. The --tree option will display all or part of the SCons dependency graph in an "ASCII art" graphical format that shows the dependency hierarchy.

For example, given the following input SConstruct file:

env = Environment(CPPPATH = ['.'])
env.Program('prog', ['f1.c', 'f2.c', 'f3.c'])
      

Running SCons with the --tree=all option yields:

% scons -Q --tree=all
cc -o f1.o -c -I. f1.c
cc -o f2.o -c -I. f2.c
cc -o f3.o -c -I. f3.c
cc -o prog f1.o f2.o f3.o
+-.
  +-SConstruct
  +-f1.c
  +-f1.o
  | +-f1.c
  | +-inc.h
  +-f2.c
  +-f2.o
  | +-f2.c
  | +-inc.h
  +-f3.c
  +-f3.o
  | +-f3.c
  | +-inc.h
  +-inc.h
  +-prog
    +-f1.o
    | +-f1.c
    | +-inc.h
    +-f2.o
    | +-f2.c
    | +-inc.h
    +-f3.o
      +-f3.c
      +-inc.h

The tree will also be printed when the -n (no execute) option is used, which allows you to examine the dependency graph for a configuration without actually rebuilding anything in the tree.

The --tree option only prints the dependency graph for the specified targets (or the default target(s) if none are specified on the command line). So if you specify a target like f2.o on the command line, the --tree option will only print the dependency graph for that file:

% scons -Q --tree=all f2.o
cc -o f2.o -c -I. f2.c
+-f2.o
  +-f2.c
  +-inc.h

This is, of course, useful for restricting the output from a very large build configuration to just a portion in which you're interested. Multiple targets are fine, in which case a tree will be printed for each specified target:

% scons -Q --tree=all f1.o f3.o
cc -o f1.o -c -I. f1.c
+-f1.o
  +-f1.c
  +-inc.h
cc -o f3.o -c -I. f3.c
+-f3.o
  +-f3.c
  +-inc.h

The status argument may be used to tell SCons to print status information about each file in the dependency graph:

% scons -Q --tree=status
cc -o f1.o -c -I. f1.c
cc -o f2.o -c -I. f2.c
cc -o f3.o -c -I. f3.c
cc -o prog f1.o f2.o f3.o
 E         = exists
  R        = exists in repository only
   b       = implicit builder
   B       = explicit builder
    S      = side effect
     P     = precious
      A    = always build
       C   = current
        N  = no clean
         H = no cache

[E b      ]+-.
[E     C  ]  +-SConstruct
[E     C  ]  +-f1.c
[E B   C  ]  +-f1.o
[E     C  ]  | +-f1.c
[E     C  ]  | +-inc.h
[E     C  ]  +-f2.c
[E B   C  ]  +-f2.o
[E     C  ]  | +-f2.c
[E     C  ]  | +-inc.h
[E     C  ]  +-f3.c
[E B   C  ]  +-f3.o
[E     C  ]  | +-f3.c
[E     C  ]  | +-inc.h
[E     C  ]  +-inc.h
[E B   C  ]  +-prog
[E B   C  ]    +-f1.o
[E     C  ]    | +-f1.c
[E     C  ]    | +-inc.h
[E B   C  ]    +-f2.o
[E     C  ]    | +-f2.c
[E     C  ]    | +-inc.h
[E B   C  ]    +-f3.o
[E     C  ]      +-f3.c
[E     C  ]      +-inc.h

Note that --tree=all,status is equivalent; the all is assumed if only status is present. As an alternative to all, you can specify --tree=derived to have SCons only print derived targets in the tree output, skipping source files (like .c and .h files):

% scons -Q --tree=derived
cc -o f1.o -c -I. f1.c
cc -o f2.o -c -I. f2.c
cc -o f3.o -c -I. f3.c
cc -o prog f1.o f2.o f3.o
+-.
  +-f1.o
  +-f2.o
  +-f3.o
  +-prog
    +-f1.o
    +-f2.o
    +-f3.o

You can use the status modifier with derived as well:

% scons -Q --tree=derived,status
cc -o f1.o -c -I. f1.c
cc -o f2.o -c -I. f2.c
cc -o f3.o -c -I. f3.c
cc -o prog f1.o f2.o f3.o
 E         = exists
  R        = exists in repository only
   b       = implicit builder
   B       = explicit builder
    S      = side effect
     P     = precious
      A    = always build
       C   = current
        N  = no clean
         H = no cache

[E b      ]+-.
[E B   C  ]  +-f1.o
[E B   C  ]  +-f2.o
[E B   C  ]  +-f3.o
[E B   C  ]  +-prog
[E B   C  ]    +-f1.o
[E B   C  ]    +-f2.o
[E B   C  ]    +-f3.o

Note that the order of the --tree= arguments doesn't matter; --tree=status,derived is completely equivalent.

The default behavior of the --tree option is to repeat all of the dependencies each time the library dependency (or any other dependency file) is encountered in the tree. If certain target files share other target files, such as two programs that use the same library:

env = Environment(CPPPATH = ['.'],
                  LIBS = ['foo'],
                  LIBPATH = ['.'])
env.Library('foo', ['f1.c', 'f2.c', 'f3.c'])
env.Program('prog1.c')
env.Program('prog2.c')
      

Then there can be a lot of repetition in the --tree= output:

% scons -Q --tree=all
cc -o f1.o -c -I. f1.c
cc -o f2.o -c -I. f2.c
cc -o f3.o -c -I. f3.c
ar rc libfoo.a f1.o f2.o f3.o
ranlib libfoo.a
cc -o prog1.o -c -I. prog1.c
cc -o prog1 prog1.o -L. -lfoo
cc -o prog2.o -c -I. prog2.c
cc -o prog2 prog2.o -L. -lfoo
+-.
  +-SConstruct
  +-f1.c
  +-f1.o
  | +-f1.c
  | +-inc.h
  +-f2.c
  +-f2.o
  | +-f2.c
  | +-inc.h
  +-f3.c
  +-f3.o
  | +-f3.c
  | +-inc.h
  +-inc.h
  +-libfoo.a
  | +-f1.o
  | | +-f1.c
  | | +-inc.h
  | +-f2.o
  | | +-f2.c
  | | +-inc.h
  | +-f3.o
  |   +-f3.c
  |   +-inc.h
  +-prog1
  | +-prog1.o
  | | +-prog1.c
  | | +-inc.h
  | +-libfoo.a
  |   +-f1.o
  |   | +-f1.c
  |   | +-inc.h
  |   +-f2.o
  |   | +-f2.c
  |   | +-inc.h
  |   +-f3.o
  |     +-f3.c
  |     +-inc.h
  +-prog1.c
  +-prog1.o
  | +-prog1.c
  | +-inc.h
  +-prog2
  | +-prog2.o
  | | +-prog2.c
  | | +-inc.h
  | +-libfoo.a
  |   +-f1.o
  |   | +-f1.c
  |   | +-inc.h
  |   +-f2.o
  |   | +-f2.c
  |   | +-inc.h
  |   +-f3.o
  |     +-f3.c
  |     +-inc.h
  +-prog2.c
  +-prog2.o
    +-prog2.c
    +-inc.h

In a large configuration with many internal libraries and include files, this can very quickly lead to huge output trees. To help make this more manageable, a prune modifier may be added to the option list, in which case SCons will print the name of a target that has already been visited during the tree-printing in [square brackets] as an indication that the dependencies of the target file may be found by looking farther up the tree:

% scons -Q --tree=prune
cc -o f1.o -c -I. f1.c
cc -o f2.o -c -I. f2.c
cc -o f3.o -c -I. f3.c
ar rc libfoo.a f1.o f2.o f3.o
ranlib libfoo.a
cc -o prog1.o -c -I. prog1.c
cc -o prog1 prog1.o -L. -lfoo
cc -o prog2.o -c -I. prog2.c
cc -o prog2 prog2.o -L. -lfoo
+-.
  +-SConstruct
  +-f1.c
  +-f1.o
  | +-f1.c
  | +-inc.h
  +-f2.c
  +-f2.o
  | +-f2.c
  | +-inc.h
  +-f3.c
  +-f3.o
  | +-f3.c
  | +-inc.h
  +-inc.h
  +-libfoo.a
  | +-[f1.o]
  | +-[f2.o]
  | +-[f3.o]
  +-prog1
  | +-prog1.o
  | | +-prog1.c
  | | +-inc.h
  | +-[libfoo.a]
  +-prog1.c
  +-[prog1.o]
  +-prog2
  | +-prog2.o
  | | +-prog2.c
  | | +-inc.h
  | +-[libfoo.a]
  +-prog2.c
  +-[prog2.o]

Like the status keyword, the prune argument by itself is equivalent to --tree=all,prune.

28.4. How is SCons Constructing the Command Lines It Executes? the --debug=presub Option

Sometimes it's useful to look at the pre-substitution string that SCons uses to generate the command lines it executes. This can be done with the --debug=presub option:

% scons -Q --debug=presub
Building prog.o with action:
  $CC -o $TARGET -c $CFLAGS $CCFLAGS $_CCOMCOM $SOURCES
cc -o prog.o -c -I. prog.c
Building prog with action:
  $SMART_LINKCOM
cc -o prog prog.o
    

28.5. Where is SCons Searching for Libraries? the --debug=findlibs Option

To get some insight into what library names SCons is searching for, and in which directories it is searching, Use the --debug=findlibs option. Given the following input SConstruct file:

env = Environment(LIBPATH = ['libs1', 'libs2'])
env.Program('prog.c', LIBS=['foo', 'bar'])
      

And the libraries libfoo.a and libbar.a in libs1 and libs2, respectively, use of the --debug=findlibs option yields:

% scons -Q --debug=findlibs
  findlibs: looking for 'libfoo.a' in 'libs1' ...
  findlibs: ... FOUND 'libfoo.a' in 'libs1'
  findlibs: looking for 'libfoo.so' in 'libs1' ...
  findlibs: looking for 'libfoo.so' in 'libs2' ...
  findlibs: looking for 'libbar.a' in 'libs1' ...
  findlibs: looking for 'libbar.a' in 'libs2' ...
  findlibs: ... FOUND 'libbar.a' in 'libs2'
  findlibs: looking for 'libbar.so' in 'libs1' ...
  findlibs: looking for 'libbar.so' in 'libs2' ...
cc -o prog.o -c prog.c
cc -o prog prog.o -Llibs1 -Llibs2 -lfoo -lbar

28.6. Where is SCons Blowing Up? the --debug=stacktrace Option

In general, SCons tries to keep its error messages short and informative. That means we usually try to avoid showing the stack traces that are familiar to experienced Python programmers, since they usually contain much more information than is useful to most people.

For example, the following SConstruct file:

Program('prog.c')
      

Generates the following error if the prog.c file does not exist:

% scons -Q
scons: *** [prog.o] Source `prog.c' not found, needed by target `prog.o'.

In this case, the error is pretty obvious. But if it weren't, and you wanted to try to get more information about the error, the --debug=stacktrace option would show you exactly where in the SCons source code the problem occurs:

% scons -Q --debug=stacktrace
scons: *** [prog.o] Source `prog.c' not found, needed by target `prog.o'.
scons: internal stack trace:
  File "bootstrap/src/engine/SCons/Job.py", line 199, in start
    task.prepare()
  File "bootstrap/src/engine/SCons/Script/Main.py", line 173, in prepare
    return SCons.Taskmaster.OutOfDateTask.prepare(self)
  File "bootstrap/src/engine/SCons/Taskmaster.py", line 191, in prepare
    executor.prepare()
  File "bootstrap/src/engine/SCons/Executor.py", line 396, in prepare
    raise SCons.Errors.StopError(msg % (s, self.batches[0].targets[0]))

Of course, if you do need to dive into the SCons source code, we'd like to know if, or how, the error messages or troubleshooting options could have been improved to avoid that. Not everyone has the necessary time or Python skill to dive into the source code, and we'd like to improve SCons for those people as well...

28.7. How is SCons Making Its Decisions? the --taskmastertrace Option

The internal SCons subsystem that handles walking the dependency graph and controls the decision-making about what to rebuild is the Taskmaster. SCons supports a --taskmastertrace option that tells the Taskmaster to print information about the children (dependencies) of the various Nodes on its walk down the graph, which specific dependent Nodes are being evaluated, and in what order.

The --taskmastertrace option takes as an argument the name of a file in which to put the trace output, with - (a single hyphen) indicating that the trace messages should be printed to the standard output:

env = Environment(CPPPATH = ['.'])
env.Program('prog.c')
      
% scons -Q --taskmastertrace=- prog

Taskmaster: Looking for a node to evaluate
Taskmaster:     Considering node <no_state   0   'prog'> and its children:
Taskmaster:        <no_state   0   'prog.o'>
Taskmaster:      adjusted ref count: <pending    1   'prog'>, child 'prog.o'
Taskmaster:     Considering node <no_state   0   'prog.o'> and its children:
Taskmaster:        <no_state   0   'prog.c'>
Taskmaster:        <no_state   0   'inc.h'>
Taskmaster:      adjusted ref count: <pending    1   'prog.o'>, child 'prog.c'
Taskmaster:      adjusted ref count: <pending    2   'prog.o'>, child 'inc.h'
Taskmaster:     Considering node <no_state   0   'prog.c'> and its children:
Taskmaster: Evaluating <pending    0   'prog.c'>

Task.make_ready_current(): node <pending    0   'prog.c'>
Task.prepare():      node <up_to_date 0   'prog.c'>
Task.executed_with_callbacks(): node <up_to_date 0   'prog.c'>
Task.postprocess():  node <up_to_date 0   'prog.c'>
Task.postprocess():  removing <up_to_date 0   'prog.c'>
Task.postprocess():  adjusted parent ref count <pending    1   'prog.o'>

Taskmaster: Looking for a node to evaluate
Taskmaster:     Considering node <no_state   0   'inc.h'> and its children:
Taskmaster: Evaluating <pending    0   'inc.h'>

Task.make_ready_current(): node <pending    0   'inc.h'>
Task.prepare():      node <up_to_date 0   'inc.h'>
Task.executed_with_callbacks(): node <up_to_date 0   'inc.h'>
Task.postprocess():  node <up_to_date 0   'inc.h'>
Task.postprocess():  removing <up_to_date 0   'inc.h'>
Task.postprocess():  adjusted parent ref count <pending    0   'prog.o'>

Taskmaster: Looking for a node to evaluate
Taskmaster:     Considering node <pending    0   'prog.o'> and its children:
Taskmaster:        <up_to_date 0   'prog.c'>
Taskmaster:        <up_to_date 0   'inc.h'>
Taskmaster: Evaluating <pending    0   'prog.o'>

Task.make_ready_current(): node <pending    0   'prog.o'>
Task.prepare():      node <executing  0   'prog.o'>
Task.execute():      node <executing  0   'prog.o'>
cc -o prog.o -c -I. prog.c
Task.executed_with_callbacks(): node <executing  0   'prog.o'>
Task.postprocess():  node <executed   0   'prog.o'>
Task.postprocess():  removing <executed   0   'prog.o'>
Task.postprocess():  adjusted parent ref count <pending    0   'prog'>

Taskmaster: Looking for a node to evaluate
Taskmaster:     Considering node <pending    0   'prog'> and its children:
Taskmaster:        <executed   0   'prog.o'>
Taskmaster: Evaluating <pending    0   'prog'>

Task.make_ready_current(): node <pending    0   'prog'>
Task.prepare():      node <executing  0   'prog'>
Task.execute():      node <executing  0   'prog'>
cc -o prog prog.o
Task.executed_with_callbacks(): node <executing  0   'prog'>
Task.postprocess():  node <executed   0   'prog'>

Taskmaster: Looking for a node to evaluate
Taskmaster: No candidate anymore.

The --taskmastertrace option doesn't provide information about the actual calculations involved in deciding if a file is up-to-date, but it does show all of the dependencies it knows about for each Node, and the order in which those dependencies are evaluated. This can be useful as an alternate way to determine whether or not your SCons configuration, or the implicit dependency scan, has actually identified all the correct dependencies you want it to.

28.8. Watch SCons prepare targets for building: the --debug=prepare Option

Sometimes SCons doesn't build the target you want and it's difficult to figure out why. You can use the --debug=prepare option to see all the targets SCons is considering, whether they are already up-to-date or not. The message is printed before SCons decides whether to build the target.

28.9. Why is a file disappearing? the --debug=duplicate Option

When using the Duplicate option to create variant dirs, sometimes you may find files not getting copied to where you expect (or not at all), or files mysteriously disappearing. These are usually because of a misconfiguration of some kind in the SConstruct/SConscript, but they can be tricky to debug. The --debug=duplicate option shows each time a variant file is unlinked and relinked from its source (or copied, depending on settings), and also shows a message for removing "stale" variant-dir files that no longer have a corresponding source file. It also prints a line for each target that's removed just before building, since that can also be mistaken for the same thing.

Appendix A. Construction Variables

This appendix contains descriptions of all of the construction variables that are potentially available "out of the box" in this version of SCons. Whether or not setting a construction variable in a construction environment will actually have an effect depends on whether any of the Tools and/or Builders that use the variable have been included in the construction environment.

In this appendix, we have appended the initial $ (dollar sign) to the beginning of each variable name when it appears in the text, but left off the dollar sign in the left-hand column where the name appears for each entry.

AR

The static library archiver.

ARCHITECTURE

Specifies the system architecture for which the package is being built. The default is the system architecture of the machine on which SCons is running. This is used to fill in the Architecture: field in an Ipkg control file, and as part of the name of a generated RPM file.

ARCOM

The command line used to generate a static library from object files.

ARCOMSTR

The string displayed when an object file is generated from an assembly-language source file. If this is not set, then $ARCOM (the command line) is displayed.

env = Environment(ARCOMSTR = "Archiving $TARGET")
ARFLAGS

General options passed to the static library archiver.

AS

The assembler.

ASCOM

The command line used to generate an object file from an assembly-language source file.

ASCOMSTR

The string displayed when an object file is generated from an assembly-language source file. If this is not set, then $ASCOM (the command line) is displayed.

env = Environment(ASCOMSTR = "Assembling $TARGET")
ASFLAGS

General options passed to the assembler.

ASPPCOM

The command line used to assemble an assembly-language source file into an object file after first running the file through the C preprocessor. Any options specified in the $ASFLAGS and $CPPFLAGS construction variables are included on this command line.

ASPPCOMSTR

The string displayed when an object file is generated from an assembly-language source file after first running the file through the C preprocessor. If this is not set, then $ASPPCOM (the command line) is displayed.

env = Environment(ASPPCOMSTR = "Assembling $TARGET")
ASPPFLAGS

General options when an assembling an assembly-language source file into an object file after first running the file through the C preprocessor. The default is to use the value of $ASFLAGS.

BIBTEX

The bibliography generator for the TeX formatter and typesetter and the LaTeX structured formatter and typesetter.

BIBTEXCOM

The command line used to call the bibliography generator for the TeX formatter and typesetter and the LaTeX structured formatter and typesetter.

BIBTEXCOMSTR

The string displayed when generating a bibliography for TeX or LaTeX. If this is not set, then $BIBTEXCOM (the command line) is displayed.

env = Environment(BIBTEXCOMSTR = "Generating bibliography $TARGET")
BIBTEXFLAGS

General options passed to the bibliography generator for the TeX formatter and typesetter and the LaTeX structured formatter and typesetter.

BITKEEPER

The BitKeeper executable.

BITKEEPERCOM

The command line for fetching source files using BitKeeper.

BITKEEPERCOMSTR

The string displayed when fetching a source file using BitKeeper. If this is not set, then $BITKEEPERCOM (the command line) is displayed.

BITKEEPERGET

The command ($BITKEEPER) and subcommand for fetching source files using BitKeeper.

BITKEEPERGETFLAGS

Options that are passed to the BitKeeper get subcommand.

BUILDERS

A dictionary mapping the names of the builders available through this environment to underlying Builder objects. Builders named Alias, CFile, CXXFile, DVI, Library, Object, PDF, PostScript, and Program are available by default. If you initialize this variable when an Environment is created:

env = Environment(BUILDERS = {'NewBuilder' : foo})

the default Builders will no longer be available. To use a new Builder object in addition to the default Builders, add your new Builder object like this:

env = Environment()
env.Append(BUILDERS = {'NewBuilder' : foo})

or this:

env = Environment()
env['BUILDERS]['NewBuilder'] = foo
CC

The C compiler.

CCCOM

The command line used to compile a C source file to a (static) object file. Any options specified in the $CFLAGS, $CCFLAGS and $CPPFLAGS construction variables are included on this command line.

CCCOMSTR

The string displayed when a C source file is compiled to a (static) object file. If this is not set, then $CCCOM (the command line) is displayed.

env = Environment(CCCOMSTR = "Compiling static object $TARGET")
CCFLAGS

General options that are passed to the C and C++ compilers.

CCPCHFLAGS

Options added to the compiler command line to support building with precompiled headers. The default value expands expands to the appropriate Microsoft Visual C++ command-line options when the $PCH construction variable is set.

CCPDBFLAGS

Options added to the compiler command line to support storing debugging information in a Microsoft Visual C++ PDB file. The default value expands expands to appropriate Microsoft Visual C++ command-line options when the $PDB construction variable is set.

The Visual C++ compiler option that SCons uses by default to generate PDB information is /Z7. This works correctly with parallel (-j) builds because it embeds the debug information in the intermediate object files, as opposed to sharing a single PDB file between multiple object files. This is also the only way to get debug information embedded into a static library. Using the /Zi instead may yield improved link-time performance, although parallel builds will no longer work.

You can generate PDB files with the /Zi switch by overriding the default $CCPDBFLAGS variable as follows:

env['CCPDBFLAGS'] = ['${(PDB and "/Zi /Fd%s" % File(PDB)) or ""}']

An alternative would be to use the /Zi to put the debugging information in a separate .pdb file for each object file by overriding the $CCPDBFLAGS variable as follows:

env['CCPDBFLAGS'] = '/Zi /Fd${TARGET}.pdb'
CCVERSION

The version number of the C compiler. This may or may not be set, depending on the specific C compiler being used.

CFILESUFFIX

The suffix for C source files. This is used by the internal CFile builder when generating C files from Lex (.l) or YACC (.y) input files. The default suffix, of course, is .c (lower case). On case-insensitive systems (like Windows), SCons also treats .C (upper case) files as C files.

CFLAGS

General options that are passed to the C compiler (C only; not C++).

CHANGE_SPECFILE

A hook for modifying the file that controls the packaging build (the .spec for RPM, the control for Ipkg, the .wxs for MSI). If set, the function will be called after the SCons template for the file has been written. XXX

CHANGED_SOURCES

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

CHANGED_TARGETS

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

CHANGELOG

The name of a file containing the change log text to be included in the package. This is included as the %changelog section of the RPM .spec file.

_concat

A function used to produce variables like $_CPPINCFLAGS. It takes four or five arguments: a prefix to concatenate onto each element, a list of elements, a suffix to concatenate onto each element, an environment for variable interpolation, and an optional function that will be called to transform the list before concatenation.

env['_CPPINCFLAGS'] = '$( ${_concat(INCPREFIX, CPPPATH, INCSUFFIX, __env__, RDirs)} $)',
CONFIGUREDIR

The name of the directory in which Configure context test files are written. The default is .sconf_temp in the top-level directory containing the SConstruct file.

CONFIGURELOG

The name of the Configure context log file. The default is config.log in the top-level directory containing the SConstruct file.

_CPPDEFFLAGS

An automatically-generated construction variable containing the C preprocessor command-line options to define values. The value of $_CPPDEFFLAGS is created by appending $CPPDEFPREFIX and $CPPDEFSUFFIX to the beginning and end of each definition in $CPPDEFINES.

CPPDEFINES

A platform independent specification of C preprocessor definitions. The definitions will be added to command lines through the automatically-generated $_CPPDEFFLAGS construction variable (see above), which is constructed according to the type of value of $CPPDEFINES:

If $CPPDEFINES is a string, the values of the $CPPDEFPREFIX and $CPPDEFSUFFIX construction variables will be added to the beginning and end.

# Will add -Dxyz to POSIX compiler command lines,
# and /Dxyz to Microsoft Visual C++ command lines.
env = Environment(CPPDEFINES='xyz')

If $CPPDEFINES is a list, the values of the $CPPDEFPREFIX and $CPPDEFSUFFIX construction variables will be appended to the beginning and end of each element in the list. If any element is a list or tuple, then the first item is the name being defined and the second item is its value:

# Will add -DB=2 -DA to POSIX compiler command lines,
# and /DB=2 /DA to Microsoft Visual C++ command lines.
env = Environment(CPPDEFINES=[('B', 2), 'A'])

If $CPPDEFINES is a dictionary, the values of the $CPPDEFPREFIX and $CPPDEFSUFFIX construction variables will be appended to the beginning and end of each item from the dictionary. The key of each dictionary item is a name being defined to the dictionary item's corresponding value; if the value is None, then the name is defined without an explicit value. Note that the resulting flags are sorted by keyword to ensure that the order of the options on the command line is consistent each time scons is run.

# Will add -DA -DB=2 to POSIX compiler command lines,
# and /DA /DB=2 to Microsoft Visual C++ command lines.
env = Environment(CPPDEFINES={'B':2, 'A':None})
CPPDEFPREFIX

The prefix used to specify preprocessor definitions on the C compiler command line. This will be appended to the beginning of each definition in the $CPPDEFINES construction variable when the $_CPPDEFFLAGS variable is automatically generated.

CPPDEFSUFFIX

The suffix used to specify preprocessor definitions on the C compiler command line. This will be appended to the end of each definition in the $CPPDEFINES construction variable when the $_CPPDEFFLAGS variable is automatically generated.

CPPFLAGS

User-specified C preprocessor options. These will be included in any command that uses the C preprocessor, including not just compilation of C and C++ source files via the $CCCOM, $SHCCCOM, $CXXCOM and $SHCXXCOM command lines, but also the $FORTRANPPCOM, $SHFORTRANPPCOM, $F77PPCOM and $SHF77PPCOM command lines used to compile a Fortran source file, and the $ASPPCOM command line used to assemble an assembly language source file, after first running each file through the C preprocessor. Note that this variable does not contain -I (or similar) include search path options that scons generates automatically from $CPPPATH. See $_CPPINCFLAGS, below, for the variable that expands to those options.

_CPPINCFLAGS

An automatically-generated construction variable containing the C preprocessor command-line options for specifying directories to be searched for include files. The value of $_CPPINCFLAGS is created by appending $INCPREFIX and $INCSUFFIX to the beginning and end of each directory in $CPPPATH.

CPPPATH

The list of directories that the C preprocessor will search for include directories. The C/C++ implicit dependency scanner will search these directories for include files. Don't explicitly put include directory arguments in CCFLAGS or CXXFLAGS because the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in CPPPATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #:

env = Environment(CPPPATH='#/include')

The directory look-up can also be forced using the Dir() function:

include = Dir('include')
env = Environment(CPPPATH=include)

The directory list will be added to command lines through the automatically-generated $_CPPINCFLAGS construction variable, which is constructed by appending the values of the $INCPREFIX and $INCSUFFIX construction variables to the beginning and end of each directory in $CPPPATH. Any command lines you define that need the CPPPATH directory list should include $_CPPINCFLAGS:

env = Environment(CCCOM="my_compiler $_CPPINCFLAGS -c -o $TARGET $SOURCE")
CPPSUFFIXES

The list of suffixes of files that will be scanned for C preprocessor implicit dependencies (#include lines). The default list is:

[".c", ".C", ".cxx", ".cpp", ".c++", ".cc",
 ".h", ".H", ".hxx", ".hpp", ".hh",
 ".F", ".fpp", ".FPP",
 ".m", ".mm",
 ".S", ".spp", ".SPP"]
CVS

The CVS executable.

CVSCOFLAGS

Options that are passed to the CVS checkout subcommand.

CVSCOM

The command line used to fetch source files from a CVS repository.

CVSCOMSTR

The string displayed when fetching a source file from a CVS repository. If this is not set, then $CVSCOM (the command line) is displayed.

CVSFLAGS

General options that are passed to CVS. By default, this is set to -d $CVSREPOSITORY to specify from where the files must be fetched.

CVSREPOSITORY

The path to the CVS repository. This is referenced in the default $CVSFLAGS value.

CXX

The C++ compiler.

CXXCOM

The command line used to compile a C++ source file to an object file. Any options specified in the $CXXFLAGS and $CPPFLAGS construction variables are included on this command line.

CXXCOMSTR

The string displayed when a C++ source file is compiled to a (static) object file. If this is not set, then $CXXCOM (the command line) is displayed.

env = Environment(CXXCOMSTR = "Compiling static object $TARGET")
CXXFILESUFFIX

The suffix for C++ source files. This is used by the internal CXXFile builder when generating C++ files from Lex (.ll) or YACC (.yy) input files. The default suffix is .cc. SCons also treats files with the suffixes .cpp, .cxx, .c++, and .C++ as C++ files, and files with .mm suffixes as Objective C++ files. On case-sensitive systems (Linux, UNIX, and other POSIX-alikes), SCons also treats .C (upper case) files as C++ files.

CXXFLAGS

General options that are passed to the C++ compiler. By default, this includes the value of $CCFLAGS, so that setting $CCFLAGS affects both C and C++ compilation. If you want to add C++-specific flags, you must set or override the value of $CXXFLAGS.

CXXVERSION

The version number of the C++ compiler. This may or may not be set, depending on the specific C++ compiler being used.

DC

DC.

DCOM

DCOM.

DDEBUG

DDEBUG.

_DDEBUGFLAGS

_DDEBUGFLAGS.

DDEBUGPREFIX

DDEBUGPREFIX.

DDEBUGSUFFIX

DDEBUGSUFFIX.

DESCRIPTION

A long description of the project being packaged. This is included in the relevant section of the file that controls the packaging build.

DESCRIPTION_lang

A language-specific long description for the specified lang. This is used to populate a %description -l section of an RPM .spec file.

DFILESUFFIX

DFILESUFFIX.

DFLAGPREFIX

DFLAGPREFIX.

_DFLAGS

_DFLAGS.

DFLAGS

DFLAGS.

DFLAGSUFFIX

DFLAGSUFFIX.

_DINCFLAGS

_DINCFLAGS.

DINCPREFIX

DINCPREFIX.

DINCSUFFIX

DINCSUFFIX.

Dir

A function that converts a string into a Dir instance relative to the target being built.

A function that converts a string into a Dir instance relative to the target being built.

Dirs

A function that converts a list of strings into a list of Dir instances relative to the target being built.

DLIB

DLIB.

DLIBCOM

DLIBCOM.

_DLIBDIRFLAGS

_DLIBDIRFLAGS.

DLIBDIRPREFIX

DLIBDIRPREFIX.

DLIBDIRSUFFIX

DLIBDIRSUFFIX.

DLIBFLAGPREFIX

DLIBFLAGPREFIX.

_DLIBFLAGS

_DLIBFLAGS.

DLIBFLAGSUFFIX

DLIBFLAGSUFFIX.

DLIBLINKPREFIX

DLIBLINKPREFIX.

DLIBLINKSUFFIX

DLIBLINKSUFFIX.

DLINK

DLINK.

DLINKCOM

DLINKCOM.

DLINKFLAGPREFIX

DLINKFLAGPREFIX.

DLINKFLAGS

DLINKFLAGS.

DLINKFLAGSUFFIX

DLINKFLAGSUFFIX.

DOCBOOK_DEFAULT_XSL_EPUB

The default XSLT file for the DocbookEpub builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_DEFAULT_XSL_HTML

The default XSLT file for the DocbookHtml builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_DEFAULT_XSL_HTMLCHUNKED

The default XSLT file for the DocbookHtmlChunked builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_DEFAULT_XSL_HTMLHELP

The default XSLT file for the DocbookHtmlhelp builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_DEFAULT_XSL_MAN

The default XSLT file for the DocbookMan builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_DEFAULT_XSL_PDF

The default XSLT file for the DocbookPdf builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_DEFAULT_XSL_SLIDESHTML

The default XSLT file for the DocbookSlidesHtml builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_DEFAULT_XSL_SLIDESPDF

The default XSLT file for the DocbookSlidesPdf builder within the current environment, if no other XSLT gets specified via keyword.

DOCBOOK_FOP

The path to the PDF renderer fop or xep, if one of them is installed (fop gets checked first).

DOCBOOK_FOPCOM

The full command-line for the PDF renderer fop or xep.

DOCBOOK_FOPCOMSTR

The string displayed when a renderer like fop or xep is used to create PDF output from an XML file.

DOCBOOK_FOPFLAGS

Additonal command-line flags for the PDF renderer fop or xep.

DOCBOOK_XMLLINT

The path to the external executable xmllint, if it's installed. Note, that this is only used as last fallback for resolving XIncludes, if no libxml2 or lxml Python binding can be imported in the current system.

DOCBOOK_XMLLINTCOM

The full command-line for the external executable xmllint.

DOCBOOK_XMLLINTCOMSTR

The string displayed when xmllint is used to resolve XIncludes for a given XML file.

DOCBOOK_XMLLINTFLAGS

Additonal command-line flags for the external executable xmllint.

DOCBOOK_XSLTPROC

The path to the external executable xsltproc (or saxon, xalan), if one of them is installed. Note, that this is only used as last fallback for XSL transformations, if no libxml2 or lxml Python binding can be imported in the current system.

DOCBOOK_XSLTPROCCOM

The full command-line for the external executable xsltproc (or saxon, xalan).

DOCBOOK_XSLTPROCCOMSTR

The string displayed when xsltproc is used to transform an XML file via a given XSLT stylesheet.

DOCBOOK_XSLTPROCFLAGS

Additonal command-line flags for the external executable xsltproc (or saxon, xalan).

DOCBOOK_XSLTPROCPARAMS

Additonal parameters that are not intended for the XSLT processor executable, but the XSL processing itself. By default, they get appended at the end of the command line for saxon and saxon-xslt, respectively.

DPATH

DPATH.

DSUFFIXES

The list of suffixes of files that will be scanned for imported D package files. The default list is:

['.d']
_DVERFLAGS

_DVERFLAGS.

DVERPREFIX

DVERPREFIX.

DVERSIONS

DVERSIONS.

DVERSUFFIX

DVERSUFFIX.

DVIPDF

The TeX DVI file to PDF file converter.

DVIPDFCOM

The command line used to convert TeX DVI files into a PDF file.

DVIPDFCOMSTR

The string displayed when a TeX DVI file is converted into a PDF file. If this is not set, then $DVIPDFCOM (the command line) is displayed.

DVIPDFFLAGS

General options passed to the TeX DVI file to PDF file converter.

DVIPS

The TeX DVI file to PostScript converter.

DVIPSFLAGS

General options passed to the TeX DVI file to PostScript converter.

ENV

A dictionary of environment variables to use when invoking commands. When $ENV is used in a command all list values will be joined using the path separator and any other non-string values will simply be coerced to a string. Note that, by default, scons does not propagate the environment in force when you execute scons to the commands used to build target files. This is so that builds will be guaranteed repeatable regardless of the environment variables set at the time scons is invoked.

If you want to propagate your environment variables to the commands executed to build target files, you must do so explicitly:

import os
env = Environment(ENV = os.environ)

Note that you can choose only to propagate certain environment variables. A common example is the system PATH environment variable, so that scons uses the same utilities as the invoking shell (or other process):

import os
env = Environment(ENV = {'PATH' : os.environ['PATH']})
ESCAPE

A function that will be called to escape shell special characters in command lines. The function should take one argument: the command line string to escape; and should return the escaped command line.

F03

The Fortran 03 compiler. You should normally set the $FORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $F03 if you need to use a specific compiler or compiler version for Fortran 03 files.

F03COM

The command line used to compile a Fortran 03 source file to an object file. You only need to set $F03COM if you need to use a specific command line for Fortran 03 files. You should normally set the $FORTRANCOM variable, which specifies the default command line for all Fortran versions.

F03COMSTR

The string displayed when a Fortran 03 source file is compiled to an object file. If this is not set, then $F03COM or $FORTRANCOM (the command line) is displayed.

F03FILESUFFIXES

The list of file extensions for which the F03 dialect will be used. By default, this is ['.f03']

F03FLAGS

General user-specified options that are passed to the Fortran 03 compiler. Note that this variable does not contain -I (or similar) include search path options that scons generates automatically from $F03PATH. See $_F03INCFLAGS below, for the variable that expands to those options. You only need to set $F03FLAGS if you need to define specific user options for Fortran 03 files. You should normally set the $FORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

_F03INCFLAGS

An automatically-generated construction variable containing the Fortran 03 compiler command-line options for specifying directories to be searched for include files. The value of $_F03INCFLAGS is created by appending $INCPREFIX and $INCSUFFIX to the beginning and end of each directory in $F03PATH.

F03PATH

The list of directories that the Fortran 03 compiler will search for include directories. The implicit dependency scanner will search these directories for include files. Don't explicitly put include directory arguments in $F03FLAGS because the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in $F03PATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #: You only need to set $F03PATH if you need to define a specific include path for Fortran 03 files. You should normally set the $FORTRANPATH variable, which specifies the include path for the default Fortran compiler for all Fortran versions.

env = Environment(F03PATH='#/include')

The directory look-up can also be forced using the Dir() function:

include = Dir('include')
env = Environment(F03PATH=include)

The directory list will be added to command lines through the automatically-generated $_F03INCFLAGS construction variable, which is constructed by appending the values of the $INCPREFIX and $INCSUFFIX construction variables to the beginning and end of each directory in $F03PATH. Any command lines you define that need the F03PATH directory list should include $_F03INCFLAGS:

env = Environment(F03COM="my_compiler $_F03INCFLAGS -c -o $TARGET $SOURCE")
F03PPCOM

The command line used to compile a Fortran 03 source file to an object file after first running the file through the C preprocessor. Any options specified in the $F03FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $F03PPCOM if you need to use a specific C-preprocessor command line for Fortran 03 files. You should normally set the $FORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

F03PPCOMSTR

The string displayed when a Fortran 03 source file is compiled to an object file after first running the file through the C preprocessor. If this is not set, then $F03PPCOM or $FORTRANPPCOM (the command line) is displayed.

F03PPFILESUFFIXES

The list of file extensions for which the compilation + preprocessor pass for F03 dialect will be used. By default, this is empty

F77

The Fortran 77 compiler. You should normally set the $FORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $F77 if you need to use a specific compiler or compiler version for Fortran 77 files.

F77COM

The command line used to compile a Fortran 77 source file to an object file. You only need to set $F77COM if you need to use a specific command line for Fortran 77 files. You should normally set the $FORTRANCOM variable, which specifies the default command line for all Fortran versions.

F77COMSTR

The string displayed when a Fortran 77 source file is compiled to an object file. If this is not set, then $F77COM or $FORTRANCOM (the command line) is displayed.

F77FILESUFFIXES

The list of file extensions for which the F77 dialect will be used. By default, this is ['.f77']

F77FLAGS

General user-specified options that are passed to the Fortran 77 compiler. Note that this variable does not contain -I (or similar) include search path options that scons generates automatically from $F77PATH. See $_F77INCFLAGS below, for the variable that expands to those options. You only need to set $F77FLAGS if you need to define specific user options for Fortran 77 files. You should normally set the $FORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

_F77INCFLAGS

An automatically-generated construction variable containing the Fortran 77 compiler command-line options for specifying directories to be searched for include files. The value of $_F77INCFLAGS is created by appending $INCPREFIX and $INCSUFFIX to the beginning and end of each directory in $F77PATH.

F77PATH

The list of directories that the Fortran 77 compiler will search for include directories. The implicit dependency scanner will search these directories for include files. Don't explicitly put include directory arguments in $F77FLAGS because the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in $F77PATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #: You only need to set $F77PATH if you need to define a specific include path for Fortran 77 files. You should normally set the $FORTRANPATH variable, which specifies the include path for the default Fortran compiler for all Fortran versions.

env = Environment(F77PATH='#/include')

The directory look-up can also be forced using the Dir() function:

include = Dir('include')
env = Environment(F77PATH=include)

The directory list will be added to command lines through the automatically-generated $_F77INCFLAGS construction variable, which is constructed by appending the values of the $INCPREFIX and $INCSUFFIX construction variables to the beginning and end of each directory in $F77PATH. Any command lines you define that need the F77PATH directory list should include $_F77INCFLAGS:

env = Environment(F77COM="my_compiler $_F77INCFLAGS -c -o $TARGET $SOURCE")
F77PPCOM

The command line used to compile a Fortran 77 source file to an object file after first running the file through the C preprocessor. Any options specified in the $F77FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $F77PPCOM if you need to use a specific C-preprocessor command line for Fortran 77 files. You should normally set the $FORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

F77PPCOMSTR

The string displayed when a Fortran 77 source file is compiled to an object file after first running the file through the C preprocessor. If this is not set, then $F77PPCOM or $FORTRANPPCOM (the command line) is displayed.

F77PPFILESUFFIXES

The list of file extensions for which the compilation + preprocessor pass for F77 dialect will be used. By default, this is empty

F90

The Fortran 90 compiler. You should normally set the $FORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $F90 if you need to use a specific compiler or compiler version for Fortran 90 files.

F90COM

The command line used to compile a Fortran 90 source file to an object file. You only need to set $F90COM if you need to use a specific command line for Fortran 90 files. You should normally set the $FORTRANCOM variable, which specifies the default command line for all Fortran versions.

F90COMSTR

The string displayed when a Fortran 90 source file is compiled to an object file. If this is not set, then $F90COM or $FORTRANCOM (the command line) is displayed.

F90FILESUFFIXES

The list of file extensions for which the F90 dialect will be used. By default, this is ['.f90']

F90FLAGS

General user-specified options that are passed to the Fortran 90 compiler. Note that this variable does not contain -I (or similar) include search path options that scons generates automatically from $F90PATH. See $_F90INCFLAGS below, for the variable that expands to those options. You only need to set $F90FLAGS if you need to define specific user options for Fortran 90 files. You should normally set the $FORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

_F90INCFLAGS

An automatically-generated construction variable containing the Fortran 90 compiler command-line options for specifying directories to be searched for include files. The value of $_F90INCFLAGS is created by appending $INCPREFIX and $INCSUFFIX to the beginning and end of each directory in $F90PATH.

F90PATH

The list of directories that the Fortran 90 compiler will search for include directories. The implicit dependency scanner will search these directories for include files. Don't explicitly put include directory arguments in $F90FLAGS because the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in $F90PATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #: You only need to set $F90PATH if you need to define a specific include path for Fortran 90 files. You should normally set the $FORTRANPATH variable, which specifies the include path for the default Fortran compiler for all Fortran versions.

env = Environment(F90PATH='#/include')

The directory look-up can also be forced using the Dir() function:

include = Dir('include')
env = Environment(F90PATH=include)

The directory list will be added to command lines through the automatically-generated $_F90INCFLAGS construction variable, which is constructed by appending the values of the $INCPREFIX and $INCSUFFIX construction variables to the beginning and end of each directory in $F90PATH. Any command lines you define that need the F90PATH directory list should include $_F90INCFLAGS:

env = Environment(F90COM="my_compiler $_F90INCFLAGS -c -o $TARGET $SOURCE")
F90PPCOM

The command line used to compile a Fortran 90 source file to an object file after first running the file through the C preprocessor. Any options specified in the $F90FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $F90PPCOM if you need to use a specific C-preprocessor command line for Fortran 90 files. You should normally set the $FORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

F90PPCOMSTR

The string displayed when a Fortran 90 source file is compiled after first running the file through the C preprocessor. If this is not set, then $F90PPCOM or $FORTRANPPCOM (the command line) is displayed.

F90PPFILESUFFIXES

The list of file extensions for which the compilation + preprocessor pass for F90 dialect will be used. By default, this is empty

F95

The Fortran 95 compiler. You should normally set the $FORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $F95 if you need to use a specific compiler or compiler version for Fortran 95 files.

F95COM

The command line used to compile a Fortran 95 source file to an object file. You only need to set $F95COM if you need to use a specific command line for Fortran 95 files. You should normally set the $FORTRANCOM variable, which specifies the default command line for all Fortran versions.

F95COMSTR

The string displayed when a Fortran 95 source file is compiled to an object file. If this is not set, then $F95COM or $FORTRANCOM (the command line) is displayed.

F95FILESUFFIXES

The list of file extensions for which the F95 dialect will be used. By default, this is ['.f95']

F95FLAGS

General user-specified options that are passed to the Fortran 95 compiler. Note that this variable does not contain -I (or similar) include search path options that scons generates automatically from $F95PATH. See $_F95INCFLAGS below, for the variable that expands to those options. You only need to set $F95FLAGS if you need to define specific user options for Fortran 95 files. You should normally set the $FORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

_F95INCFLAGS

An automatically-generated construction variable containing the Fortran 95 compiler command-line options for specifying directories to be searched for include files. The value of $_F95INCFLAGS is created by appending $INCPREFIX and $INCSUFFIX to the beginning and end of each directory in $F95PATH.

F95PATH

The list of directories that the Fortran 95 compiler will search for include directories. The implicit dependency scanner will search these directories for include files. Don't explicitly put include directory arguments in $F95FLAGS because the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in $F95PATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #: You only need to set $F95PATH if you need to define a specific include path for Fortran 95 files. You should normally set the $FORTRANPATH variable, which specifies the include path for the default Fortran compiler for all Fortran versions.

env = Environment(F95PATH='#/include')

The directory look-up can also be forced using the Dir() function:

include = Dir('include')
env = Environment(F95PATH=include)

The directory list will be added to command lines through the automatically-generated $_F95INCFLAGS construction variable, which is constructed by appending the values of the $INCPREFIX and $INCSUFFIX construction variables to the beginning and end of each directory in $F95PATH. Any command lines you define that need the F95PATH directory list should include $_F95INCFLAGS:

env = Environment(F95COM="my_compiler $_F95INCFLAGS -c -o $TARGET $SOURCE")
F95PPCOM

The command line used to compile a Fortran 95 source file to an object file after first running the file through the C preprocessor. Any options specified in the $F95FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $F95PPCOM if you need to use a specific C-preprocessor command line for Fortran 95 files. You should normally set the $FORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

F95PPCOMSTR

The string displayed when a Fortran 95 source file is compiled to an object file after first running the file through the C preprocessor. If this is not set, then $F95PPCOM or $FORTRANPPCOM (the command line) is displayed.

F95PPFILESUFFIXES

The list of file extensions for which the compilation + preprocessor pass for F95 dialect will be used. By default, this is empty

File

A function that converts a string into a File instance relative to the target being built.

A function that converts a string into a File instance relative to the target being built.

FORTRAN

The default Fortran compiler for all versions of Fortran.

FORTRANCOM

The command line used to compile a Fortran source file to an object file. By default, any options specified in the $FORTRANFLAGS, $CPPFLAGS, $_CPPDEFFLAGS, $_FORTRANMODFLAG, and $_FORTRANINCFLAGS construction variables are included on this command line.

FORTRANCOMSTR

The string displayed when a Fortran source file is compiled to an object file. If this is not set, then $FORTRANCOM (the command line) is displayed.

FORTRANFILESUFFIXES

The list of file extensions for which the FORTRAN dialect will be used. By default, this is ['.f', '.for', '.ftn']

FORTRANFLAGS

General user-specified options that are passed to the Fortran compiler. Note that this variable does not contain -I (or similar) include or module search path options that scons generates automatically from $FORTRANPATH. See $_FORTRANINCFLAGS and $_FORTRANMODFLAG, below, for the variables that expand those options.

_FORTRANINCFLAGS

An automatically-generated construction variable containing the Fortran compiler command-line options for specifying directories to be searched for include files and module files. The value of $_FORTRANINCFLAGS is created by prepending/appending $INCPREFIX and $INCSUFFIX to the beginning and end of each directory in $FORTRANPATH.

FORTRANMODDIR

Directory location where the Fortran compiler should place any module files it generates. This variable is empty, by default. Some Fortran compilers will internally append this directory in the search path for module files, as well.

FORTRANMODDIRPREFIX

The prefix used to specify a module directory on the Fortran compiler command line. This will be appended to the beginning of the directory in the $FORTRANMODDIR construction variables when the $_FORTRANMODFLAG variables is automatically generated.

FORTRANMODDIRSUFFIX

The suffix used to specify a module directory on the Fortran compiler command line. This will be appended to the beginning of the directory in the $FORTRANMODDIR construction variables when the $_FORTRANMODFLAG variables is automatically generated.

_FORTRANMODFLAG

An automatically-generated construction variable containing the Fortran compiler command-line option for specifying the directory location where the Fortran compiler should place any module files that happen to get generated during compilation. The value of $_FORTRANMODFLAG is created by prepending/appending $FORTRANMODDIRPREFIX and $FORTRANMODDIRSUFFIX to the beginning and end of the directory in $FORTRANMODDIR.

FORTRANMODPREFIX

The module file prefix used by the Fortran compiler. SCons assumes that the Fortran compiler follows the quasi-standard naming convention for module files of module_name.mod. As a result, this variable is left empty, by default. For situations in which the compiler does not necessarily follow the normal convention, the user may use this variable. Its value will be appended to every module file name as scons attempts to resolve dependencies.

FORTRANMODSUFFIX

The module file suffix used by the Fortran compiler. SCons assumes that the Fortran compiler follows the quasi-standard naming convention for module files of module_name.mod. As a result, this variable is set to ".mod", by default. For situations in which the compiler does not necessarily follow the normal convention, the user may use this variable. Its value will be appended to every module file name as scons attempts to resolve dependencies.

FORTRANPATH

The list of directories that the Fortran compiler will search for include files and (for some compilers) module files. The Fortran implicit dependency scanner will search these directories for include files (but not module files since they are autogenerated and, as such, may not actually exist at the time the scan takes place). Don't explicitly put include directory arguments in FORTRANFLAGS because the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in FORTRANPATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #:

env = Environment(FORTRANPATH='#/include')

The directory look-up can also be forced using the Dir() function:

include = Dir('include')
env = Environment(FORTRANPATH=include)

The directory list will be added to command lines through the automatically-generated $_FORTRANINCFLAGS construction variable, which is constructed by appending the values of the $INCPREFIX and $INCSUFFIX construction variables to the beginning and end of each directory in $FORTRANPATH. Any command lines you define that need the FORTRANPATH directory list should include $_FORTRANINCFLAGS:

env = Environment(FORTRANCOM="my_compiler $_FORTRANINCFLAGS -c -o $TARGET $SOURCE")
FORTRANPPCOM

The command line used to compile a Fortran source file to an object file after first running the file through the C preprocessor. By default, any options specified in the $FORTRANFLAGS, $CPPFLAGS, $_CPPDEFFLAGS, $_FORTRANMODFLAG, and $_FORTRANINCFLAGS construction variables are included on this command line.

FORTRANPPCOMSTR

The string displayed when a Fortran source file is compiled to an object file after first running the file through the C preprocessor. If this is not set, then $FORTRANPPCOM (the command line) is displayed.

FORTRANPPFILESUFFIXES

The list of file extensions for which the compilation + preprocessor pass for FORTRAN dialect will be used. By default, this is ['.fpp', '.FPP']

FORTRANSUFFIXES

The list of suffixes of files that will be scanned for Fortran implicit dependencies (INCLUDE lines and USE statements). The default list is:

[".f", ".F", ".for", ".FOR", ".ftn", ".FTN", ".fpp", ".FPP",
".f77", ".F77", ".f90", ".F90", ".f95", ".F95"]
FRAMEWORKPATH

On Mac OS X with gcc, a list containing the paths to search for frameworks. Used by the compiler to find framework-style includes like #include <Fmwk/Header.h>. Used by the linker to find user-specified frameworks when linking (see $FRAMEWORKS). For example:

 env.AppendUnique(FRAMEWORKPATH='#myframeworkdir')

will add

  ... -Fmyframeworkdir

to the compiler and linker command lines.

_FRAMEWORKPATH

On Mac OS X with gcc, an automatically-generated construction variable containing the linker command-line options corresponding to $FRAMEWORKPATH.

FRAMEWORKPATHPREFIX

On Mac OS X with gcc, the prefix to be used for the FRAMEWORKPATH entries. (see $FRAMEWORKPATH). The default value is -F.

FRAMEWORKPREFIX

On Mac OS X with gcc, the prefix to be used for linking in frameworks (see $FRAMEWORKS). The default value is -framework.

_FRAMEWORKS

On Mac OS X with gcc, an automatically-generated construction variable containing the linker command-line options for linking with FRAMEWORKS.

FRAMEWORKS

On Mac OS X with gcc, a list of the framework names to be linked into a program or shared library or bundle. The default value is the empty list. For example:

 env.AppendUnique(FRAMEWORKS=Split('System Cocoa SystemConfiguration'))
FRAMEWORKSFLAGS

On Mac OS X with gcc, general user-supplied frameworks options to be added at the end of a command line building a loadable module. (This has been largely superseded by the $FRAMEWORKPATH, $FRAMEWORKPATHPREFIX, $FRAMEWORKPREFIX and $FRAMEWORKS variables described above.)

GS

The Ghostscript program used, e.g. to convert PostScript to PDF files.

GSCOM

The full Ghostscript command line used for the conversion process. Its default value is $GS $GSFLAGS -sOutputFile=$TARGET $SOURCES.

GSCOMSTR

The string displayed when Ghostscript is called for the conversion process. If this is not set (the default), then $GSCOM (the command line) is displayed.

GSFLAGS

General options passed to the Ghostscript program, when converting PostScript to PDF files for example. Its default value is -dNOPAUSE -dBATCH -sDEVICE=pdfwrite

HOST_ARCH

The name of the host hardware architecture used to create the Environment. If a platform is specified when creating the Environment, then that Platform's logic will handle setting this value. This value is immutable, and should not be changed by the user after the Environment is initialized. Currently only set for Win32.

Sets the host architecture for Visual Studio compiler. If not set, default to the detected host architecture: note that this may depend on the python you are using. This variable must be passed as an argument to the Environment() constructor; setting it later has no effect.

Valid values are the same as for $TARGET_ARCH.

This is currently only used on Windows, but in the future it will be used on other OSes as well.

HOST_OS

The name of the host operating system used to create the Environment. If a platform is specified when creating the Environment, then that Platform's logic will handle setting this value. This value is immutable, and should not be changed by the user after the Environment is initialized. Currently only set for Win32.

IDLSUFFIXES

The list of suffixes of files that will be scanned for IDL implicit dependencies (#include or import lines). The default list is:

[".idl", ".IDL"]
IMPLICIT_COMMAND_DEPENDENCIES

Controls whether or not SCons will add implicit dependencies for the commands executed to build targets.

By default, SCons will add to each target an implicit dependency on the command represented by the first argument on any command line it executes. The specific file for the dependency is found by searching the PATH variable in the ENV environment used to execute the command.

If the construction variable $IMPLICIT_COMMAND_DEPENDENCIES is set to a false value (None, False, 0, etc.), then the implicit dependency will not be added to the targets built with that construction environment.

env = Environment(IMPLICIT_COMMAND_DEPENDENCIES = 0)
INCPREFIX

The prefix used to specify an include directory on the C compiler command line. This will be appended to the beginning of each directory in the $CPPPATH and $FORTRANPATH construction variables when the $_CPPINCFLAGS and $_FORTRANINCFLAGS variables are automatically generated.

INCSUFFIX

The suffix used to specify an include directory on the C compiler command line. This will be appended to the end of each directory in the $CPPPATH and $FORTRANPATH construction variables when the $_CPPINCFLAGS and $_FORTRANINCFLAGS variables are automatically generated.

INSTALL

A function to be called to install a file into a destination file name. The default function copies the file into the destination (and sets the destination file's mode and permission bits to match the source file's). The function takes the following arguments:

def install(dest, source, env):

dest is the path name of the destination file. source is the path name of the source file. env is the construction environment (a dictionary of construction values) in force for this file installation.

INSTALLSTR

The string displayed when a file is installed into a destination file name. The default is:

Install file: "$SOURCE" as "$TARGET"
INTEL_C_COMPILER_VERSION

Set by the "intelc" Tool to the major version number of the Intel C compiler selected for use.

JAR

The Java archive tool.

The Java archive tool.

JARCHDIR

The directory to which the Java archive tool should change (using the -C option).

The directory to which the Java archive tool should change (using the -C option).

JARCOM

The command line used to call the Java archive tool.

The command line used to call the Java archive tool.

JARCOMSTR

The string displayed when the Java archive tool is called If this is not set, then $JARCOM (the command line) is displayed.

env = Environment(JARCOMSTR = "JARchiving $SOURCES into $TARGET")

The string displayed when the Java archive tool is called If this is not set, then $JARCOM (the command line) is displayed.

env = Environment(JARCOMSTR = "JARchiving $SOURCES into $TARGET")
JARFLAGS

General options passed to the Java archive tool. By default this is set to cf to create the necessary jar file.

General options passed to the Java archive tool. By default this is set to cf to create the necessary jar file.

JARSUFFIX

The suffix for Java archives: .jar by default.

The suffix for Java archives: .jar by default.

JAVABOOTCLASSPATH

Specifies the list of directories that will be added to the javac command line via the -bootclasspath option. The individual directory names will be separated by the operating system's path separate character (: on UNIX/Linux/POSIX, ; on Windows).

JAVAC

The Java compiler.

JAVACCOM

The command line used to compile a directory tree containing Java source files to corresponding Java class files. Any options specified in the $JAVACFLAGS construction variable are included on this command line.

JAVACCOMSTR

The string displayed when compiling a directory tree of Java source files to corresponding Java class files. If this is not set, then $JAVACCOM (the command line) is displayed.

env = Environment(JAVACCOMSTR = "Compiling class files $TARGETS from $SOURCES")
JAVACFLAGS

General options that are passed to the Java compiler.

JAVACLASSDIR

The directory in which Java class files may be found. This is stripped from the beginning of any Java .class file names supplied to the JavaH builder.

JAVACLASSPATH

Specifies the list of directories that will be searched for Java .class file. The directories in this list will be added to the javac and javah command lines via the -classpath option. The individual directory names will be separated by the operating system's path separate character (: on UNIX/Linux/POSIX, ; on Windows).

Note that this currently just adds the specified directory via the -classpath option. SCons does not currently search the $JAVACLASSPATH directories for dependency .class files.

JAVACLASSSUFFIX

The suffix for Java class files; .class by default.

JAVAH

The Java generator for C header and stub files.

JAVAHCOM

The command line used to generate C header and stub files from Java classes. Any options specified in the $JAVAHFLAGS construction variable are included on this command line.

JAVAHCOMSTR

The string displayed when C header and stub files are generated from Java classes. If this is not set, then $JAVAHCOM (the command line) is displayed.

env = Environment(JAVAHCOMSTR = "Generating header/stub file(s) $TARGETS from $SOURCES")
JAVAHFLAGS

General options passed to the C header and stub file generator for Java classes.

JAVASOURCEPATH

Specifies the list of directories that will be searched for input .java file. The directories in this list will be added to the javac command line via the -sourcepath option. The individual directory names will be separated by the operating system's path separate character (: on UNIX/Linux/POSIX, ; on Windows).

Note that this currently just adds the specified directory via the -sourcepath option. SCons does not currently search the $JAVASOURCEPATH directories for dependency .java files.

JAVASUFFIX

The suffix for Java files; .java by default.

JAVAVERSION

Specifies the Java version being used by the Java builder. This is not currently used to select one version of the Java compiler vs. another. Instead, you should set this to specify the version of Java supported by your javac compiler. The default is 1.4.

This is sometimes necessary because Java 1.5 changed the file names that are created for nested anonymous inner classes, which can cause a mismatch with the files that SCons expects will be generated by the javac compiler. Setting $JAVAVERSION to 1.5 (or 1.6, as appropriate) can make SCons realize that a Java 1.5 or 1.6 build is actually up to date.

LATEX

The LaTeX structured formatter and typesetter.

LATEXCOM

The command line used to call the LaTeX structured formatter and typesetter.

LATEXCOMSTR

The string displayed when calling the LaTeX structured formatter and typesetter. If this is not set, then $LATEXCOM (the command line) is displayed.

env = Environment(LATEXCOMSTR = "Building $TARGET from LaTeX input $SOURCES")
LATEXFLAGS

General options passed to the LaTeX structured formatter and typesetter.

LATEXRETRIES

The maximum number of times that LaTeX will be re-run if the .log generated by the $LATEXCOM command indicates that there are undefined references. The default is to try to resolve undefined references by re-running LaTeX up to three times.

LATEXSUFFIXES

The list of suffixes of files that will be scanned for LaTeX implicit dependencies (\include or \import files). The default list is:

[".tex", ".ltx", ".latex"]
LDMODULE

The linker for building loadable modules. By default, this is the same as $SHLINK.

LDMODULECOM

The command line for building loadable modules. On Mac OS X, this uses the $LDMODULE, $LDMODULEFLAGS and $FRAMEWORKSFLAGS variables. On other systems, this is the same as $SHLINK.

LDMODULECOMSTR

The string displayed when building loadable modules. If this is not set, then $LDMODULECOM (the command line) is displayed.

LDMODULEFLAGS

General user options passed to the linker for building loadable modules.

LDMODULEPREFIX

The prefix used for loadable module file names. On Mac OS X, this is null; on other systems, this is the same as $SHLIBPREFIX.

LDMODULESUFFIX

The suffix used for loadable module file names. On Mac OS X, this is null; on other systems, this is the same as $SHLIBSUFFIX.

LEX

The lexical analyzer generator.

LEXCOM

The command line used to call the lexical analyzer generator to generate a source file.

LEXCOMSTR

The string displayed when generating a source file using the lexical analyzer generator. If this is not set, then $LEXCOM (the command line) is displayed.

env = Environment(LEXCOMSTR = "Lex'ing $TARGET from $SOURCES")
LEXFLAGS

General options passed to the lexical analyzer generator.

_LIBDIRFLAGS

An automatically-generated construction variable containing the linker command-line options for specifying directories to be searched for library. The value of $_LIBDIRFLAGS is created by appending $LIBDIRPREFIX and $LIBDIRSUFFIX to the beginning and end of each directory in $LIBPATH.

LIBDIRPREFIX

The prefix used to specify a library directory on the linker command line. This will be appended to the beginning of each directory in the $LIBPATH construction variable when the $_LIBDIRFLAGS variable is automatically generated.

LIBDIRSUFFIX

The suffix used to specify a library directory on the linker command line. This will be appended to the end of each directory in the $LIBPATH construction variable when the $_LIBDIRFLAGS variable is automatically generated.

LIBEMITTER

TODO

_LIBFLAGS

An automatically-generated construction variable containing the linker command-line options for specifying libraries to be linked with the resulting target. The value of $_LIBFLAGS is created by appending $LIBLINKPREFIX and $LIBLINKSUFFIX to the beginning and end of each filename in $LIBS.

LIBLINKPREFIX

The prefix used to specify a library to link on the linker command line. This will be appended to the beginning of each library in the $LIBS construction variable when the $_LIBFLAGS variable is automatically generated.

LIBLINKSUFFIX

The suffix used to specify a library to link on the linker command line. This will be appended to the end of each library in the $LIBS construction variable when the $_LIBFLAGS variable is automatically generated.

LIBPATH

The list of directories that will be searched for libraries. The implicit dependency scanner will search these directories for include files. Don't explicitly put include directory arguments in $LINKFLAGS or $SHLINKFLAGS because the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in LIBPATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #:

env = Environment(LIBPATH='#/libs')

The directory look-up can also be forced using the Dir() function:

libs = Dir('libs')
env = Environment(LIBPATH=libs)

The directory list will be added to command lines through the automatically-generated $_LIBDIRFLAGS construction variable, which is constructed by appending the values of the $LIBDIRPREFIX and $LIBDIRSUFFIX construction variables to the beginning and end of each directory in $LIBPATH. Any command lines you define that need the LIBPATH directory list should include $_LIBDIRFLAGS:

env = Environment(LINKCOM="my_linker $_LIBDIRFLAGS $_LIBFLAGS -o $TARGET $SOURCE")
LIBPREFIX

The prefix used for (static) library file names. A default value is set for each platform (posix, win32, os2, etc.), but the value is overridden by individual tools (ar, mslib, sgiar, sunar, tlib, etc.) to reflect the names of the libraries they create.

LIBPREFIXES

A list of all legal prefixes for library file names. When searching for library dependencies, SCons will look for files with these prefixes, the base library name, and suffixes in the $LIBSUFFIXES list.

LIBS

A list of one or more libraries that will be linked with any executable programs created by this environment.

The library list will be added to command lines through the automatically-generated $_LIBFLAGS construction variable, which is constructed by appending the values of the $LIBLINKPREFIX and $LIBLINKSUFFIX construction variables to the beginning and end of each filename in $LIBS. Any command lines you define that need the LIBS library list should include $_LIBFLAGS:

env = Environment(LINKCOM="my_linker $_LIBDIRFLAGS $_LIBFLAGS -o $TARGET $SOURCE")

If you add a File object to the $LIBS list, the name of that file will be added to $_LIBFLAGS, and thus the link line, as is, without $LIBLINKPREFIX or $LIBLINKSUFFIX. For example:

env.Append(LIBS=File('/tmp/mylib.so'))

In all cases, scons will add dependencies from the executable program to all the libraries in this list.

LIBSUFFIX

The suffix used for (static) library file names. A default value is set for each platform (posix, win32, os2, etc.), but the value is overridden by individual tools (ar, mslib, sgiar, sunar, tlib, etc.) to reflect the names of the libraries they create.

LIBSUFFIXES

A list of all legal suffixes for library file names. When searching for library dependencies, SCons will look for files with prefixes, in the $LIBPREFIXES list, the base library name, and these suffixes.

LICENSE

The abbreviated name of the license under which this project is released (gpl, lpgl, bsd etc.). See http://www.opensource.org/licenses/alphabetical for a list of license names.

LINESEPARATOR

The separator used by the Substfile and Textfile builders. This value is used between sources when constructing the target. It defaults to the current system line separator.

LINGUAS_FILE

The $LINGUAS_FILE defines file(s) containing list of additional linguas to be processed by POInit, POUpdate or MOFiles builders. It also affects Translate builder. If the variable contains a string, it defines name of the list file. The $LINGUAS_FILE may be a list of file names as well. If $LINGUAS_FILE is set to True (or non-zero numeric value), the list will be read from default file named LINGUAS.

LINK

The linker.

LINKCOM

The command line used to link object files into an executable.

LINKCOMSTR

The string displayed when object files are linked into an executable. If this is not set, then $LINKCOM (the command line) is displayed.

env = Environment(LINKCOMSTR = "Linking $TARGET")
LINKFLAGS

General user options passed to the linker. Note that this variable should not contain -l (or similar) options for linking with the libraries listed in $LIBS, nor -L (or similar) library search path options that scons generates automatically from $LIBPATH. See $_LIBFLAGS above, for the variable that expands to library-link options, and $_LIBDIRFLAGS above, for the variable that expands to library search path options.

M4

The M4 macro preprocessor.

M4COM

The command line used to pass files through the M4 macro preprocessor.

M4COMSTR

The string displayed when a file is passed through the M4 macro preprocessor. If this is not set, then $M4COM (the command line) is displayed.

M4FLAGS

General options passed to the M4 macro preprocessor.

MAKEINDEX

The makeindex generator for the TeX formatter and typesetter and the LaTeX structured formatter and typesetter.

MAKEINDEXCOM

The command line used to call the makeindex generator for the TeX formatter and typesetter and the LaTeX structured formatter and typesetter.

MAKEINDEXCOMSTR

The string displayed when calling the makeindex generator for the TeX formatter and typesetter and the LaTeX structured formatter and typesetter. If this is not set, then $MAKEINDEXCOM (the command line) is displayed.

MAKEINDEXFLAGS

General options passed to the makeindex generator for the TeX formatter and typesetter and the LaTeX structured formatter and typesetter.

MAXLINELENGTH

The maximum number of characters allowed on an external command line. On Win32 systems, link lines longer than this many characters are linked via a temporary file name.

MIDL

The Microsoft IDL compiler.

MIDLCOM

The command line used to pass files to the Microsoft IDL compiler.

MIDLCOMSTR

The string displayed when the Microsoft IDL copmiler is called. If this is not set, then $MIDLCOM (the command line) is displayed.

MIDLFLAGS

General options passed to the Microsoft IDL compiler.

MOSUFFIX

Suffix used for MO files (default: '.mo'). See msgfmt tool and MOFiles builder.

MSGFMT

Absolute path to msgfmt(1) binary, found by Detect(). See msgfmt tool and MOFiles builder.

MSGFMTCOM

Complete command line to run msgfmt(1) program. See msgfmt tool and MOFiles builder.

MSGFMTCOMSTR

String to display when msgfmt(1) is invoked (default: '', which means ``print $MSGFMTCOM''). See msgfmt tool and MOFiles builder.

MSGFMTFLAGS

Additional flags to msgfmt(1). See msgfmt tool and MOFiles builder.

MSGINIT

Path to msginit(1) program (found via Detect()). See msginit tool and POInit builder.

MSGINITCOM

Complete command line to run msginit(1) program. See msginit tool and POInit builder.

MSGINITCOMSTR

String to display when msginit(1) is invoked (default: '', which means ``print $MSGINITCOM''). See msginit tool and POInit builder.

MSGINITFLAGS

List of additional flags to msginit(1) (default: []). See msginit tool and POInit builder.

_MSGINITLOCALE

Internal ``macro''. Computes locale (language) name based on target filename (default: '${TARGET.filebase}' ).

See msginit tool and POInit builder.

MSGMERGE

Absolute path to msgmerge(1) binary as found by Detect(). See msgmerge tool and POUpdate builder.

MSGMERGECOM

Complete command line to run msgmerge(1) command. See msgmerge tool and POUpdate builder.

MSGMERGECOMSTR

String to be displayed when msgmerge(1) is invoked (default: '', which means ``print $MSGMERGECOM''). See msgmerge tool and POUpdate builder.

MSGMERGEFLAGS

Additional flags to msgmerge(1) command. See msgmerge tool and POUpdate builder.

MSSDK_DIR

The directory containing the Microsoft SDK (either Platform SDK or Windows SDK) to be used for compilation.

MSSDK_VERSION

The version string of the Microsoft SDK (either Platform SDK or Windows SDK) to be used for compilation. Supported versions include 6.1, 6.0A, 6.0, 2003R2 and 2003R1.

MSVC_BATCH

When set to any true value, specifies that SCons should batch compilation of object files when calling the Microsoft Visual C/C++ compiler. All compilations of source files from the same source directory that generate target files in a same output directory and were configured in SCons using the same construction environment will be built in a single call to the compiler. Only source files that have changed since their object files were built will be passed to each compiler invocation (via the $CHANGED_SOURCES construction variable). Any compilations where the object (target) file base name (minus the .obj) does not match the source file base name will be compiled separately.

MSVC_USE_SCRIPT

Use a batch script to set up Microsoft Visual Studio compiler

$MSVC_USE_SCRIPT overrides $MSVC_VERSION and $TARGET_ARCH. If set to the name of a Visual Studio .bat file (e.g. vcvars.bat), SCons will run that bat file and extract the relevant variables from the result (typically %INCLUDE%, %LIB%, and %PATH%). Setting MSVC_USE_SCRIPT to None bypasses the Visual Studio autodetection entirely; use this if you are running SCons in a Visual Studio cmd window and importing the shell's environment variables.

MSVC_VERSION

Sets the preferred version of Microsoft Visual C/C++ to use.

If $MSVC_VERSION is not set, SCons will (by default) select the latest version of Visual C/C++ installed on your system. If the specified version isn't installed, tool initialization will fail. This variable must be passed as an argument to the Environment() constructor; setting it later has no effect.

Valid values for Windows are 12.0, 12.0Exp, 11.0, 11.0Exp, 10.0, 10.0Exp, 9.0, 9.0Exp, 8.0, 8.0Exp, 7.1, 7.0, and 6.0. Versions ending in Exp refer to "Express" or "Express for Desktop" editions.

MSVS

When the Microsoft Visual Studio tools are initialized, they set up this dictionary with the following keys:

VERSION: the version of MSVS being used (can be set via $MSVS_VERSION)

VERSIONS: the available versions of MSVS installed

VCINSTALLDIR: installed directory of Visual C++

VSINSTALLDIR: installed directory of Visual Studio

FRAMEWORKDIR: installed directory of the .NET framework

FRAMEWORKVERSIONS: list of installed versions of the .NET framework, sorted latest to oldest.

FRAMEWORKVERSION: latest installed version of the .NET framework

FRAMEWORKSDKDIR: installed location of the .NET SDK.

PLATFORMSDKDIR: installed location of the Platform SDK.

PLATFORMSDK_MODULES: dictionary of installed Platform SDK modules, where the dictionary keys are keywords for the various modules, and the values are 2-tuples where the first is the release date, and the second is the version number.

If a value isn't set, it wasn't available in the registry.

MSVS_ARCH

Sets the architecture for which the generated project(s) should build.

The default value is x86. amd64 is also supported by SCons for some Visual Studio versions. Trying to set $MSVS_ARCH to an architecture that's not supported for a given Visual Studio version will generate an error.

MSVS_PROJECT_GUID

The string placed in a generated Microsoft Visual Studio project file as the value of the ProjectGUID attribute. There is no default value. If not defined, a new GUID is generated.

MSVS_SCC_AUX_PATH

The path name placed in a generated Microsoft Visual Studio project file as the value of the SccAuxPath attribute if the MSVS_SCC_PROVIDER construction variable is also set. There is no default value.

MSVS_SCC_CONNECTION_ROOT

The root path of projects in your SCC workspace, i.e the path under which all project and solution files will be generated. It is used as a reference path from which the relative paths of the generated Microsoft Visual Studio project and solution files are computed. The relative project file path is placed as the value of the SccLocalPath attribute of the project file and as the values of the SccProjectFilePathRelativizedFromConnection[i] (where [i] ranges from 0 to the number of projects in the solution) attributes of the GlobalSection(SourceCodeControl) section of the Microsoft Visual Studio solution file. Similarly the relative solution file path is placed as the values of the SccLocalPath[i] (where [i] ranges from 0 to the number of projects in the solution) attributes of the GlobalSection(SourceCodeControl) section of the Microsoft Visual Studio solution file. This is used only if the MSVS_SCC_PROVIDER construction variable is also set. The default value is the current working directory.

MSVS_SCC_PROJECT_NAME

The project name placed in a generated Microsoft Visual Studio project file as the value of the SccProjectName attribute if the MSVS_SCC_PROVIDER construction variable is also set. In this case the string is also placed in the SccProjectName0 attribute of the GlobalSection(SourceCodeControl) section of the Microsoft Visual Studio solution file. There is no default value.

MSVS_SCC_PROVIDER

The string placed in a generated Microsoft Visual Studio project file as the value of the SccProvider attribute. The string is also placed in the SccProvider0 attribute of the GlobalSection(SourceCodeControl) section of the Microsoft Visual Studio solution file. There is no default value.

MSVS_VERSION

Sets the preferred version of Microsoft Visual Studio to use.

If $MSVS_VERSION is not set, SCons will (by default) select the latest version of Visual Studio installed on your system. So, if you have version 6 and version 7 (MSVS .NET) installed, it will prefer version 7. You can override this by specifying the MSVS_VERSION variable in the Environment initialization, setting it to the appropriate version ('6.0' or '7.0', for example). If the specified version isn't installed, tool initialization will fail.

This is obsolete: use $MSVC_VERSION instead. If $MSVS_VERSION is set and $MSVC_VERSION is not, $MSVC_VERSION will be set automatically to $MSVS_VERSION. If both are set to different values, scons will raise an error.

MSVSBUILDCOM

The build command line placed in a generated Microsoft Visual Studio project file. The default is to have Visual Studio invoke SCons with any specified build targets.

MSVSCLEANCOM

The clean command line placed in a generated Microsoft Visual Studio project file. The default is to have Visual Studio invoke SCons with the -c option to remove any specified targets.

MSVSENCODING

The encoding string placed in a generated Microsoft Visual Studio project file. The default is encoding Windows-1252.

MSVSPROJECTCOM

The action used to generate Microsoft Visual Studio project files.

MSVSPROJECTSUFFIX

The suffix used for Microsoft Visual Studio project (DSP) files. The default value is .vcproj when using Visual Studio version 7.x (.NET) or later version, and .dsp when using earlier versions of Visual Studio.

MSVSREBUILDCOM

The rebuild command line placed in a generated Microsoft Visual Studio project file. The default is to have Visual Studio invoke SCons with any specified rebuild targets.

MSVSSCONS

The SCons used in generated Microsoft Visual Studio project files. The default is the version of SCons being used to generate the project file.

MSVSSCONSCOM

The default SCons command used in generated Microsoft Visual Studio project files.

MSVSSCONSCRIPT

The sconscript file (that is, SConstruct or SConscript file) that will be invoked by Visual Studio project files (through the $MSVSSCONSCOM variable). The default is the same sconscript file that contains the call to MSVSProject to build the project file.

MSVSSCONSFLAGS

The SCons flags used in generated Microsoft Visual Studio project files.

MSVSSOLUTIONCOM

The action used to generate Microsoft Visual Studio solution files.

MSVSSOLUTIONSUFFIX

The suffix used for Microsoft Visual Studio solution (DSW) files. The default value is .sln when using Visual Studio version 7.x (.NET), and .dsw when using earlier versions of Visual Studio.

MT

The program used on Windows systems to embed manifests into DLLs and EXEs. See also $WINDOWS_EMBED_MANIFEST.

MTEXECOM

The Windows command line used to embed manifests into executables. See also $MTSHLIBCOM.

MTFLAGS

Flags passed to the $MT manifest embedding program (Windows only).

MTSHLIBCOM

The Windows command line used to embed manifests into shared libraries (DLLs). See also $MTEXECOM.

MWCW_VERSION

The version number of the MetroWerks CodeWarrior C compiler to be used.

MWCW_VERSIONS

A list of installed versions of the MetroWerks CodeWarrior C compiler on this system.

NAME

Specfies the name of the project to package.

no_import_lib

When set to non-zero, suppresses creation of a corresponding Windows static import lib by the SharedLibrary builder when used with MinGW, Microsoft Visual Studio or Metrowerks. This also suppresses creation of an export (.exp) file when using Microsoft Visual Studio.

OBJPREFIX

The prefix used for (static) object file names.

OBJSUFFIX

The suffix used for (static) object file names.

P4

The Perforce executable.

P4COM

The command line used to fetch source files from Perforce.

P4COMSTR

The string displayed when fetching a source file from Perforce. If this is not set, then $P4COM (the command line) is displayed.

P4FLAGS

General options that are passed to Perforce.

PACKAGEROOT

Specifies the directory where all files in resulting archive will be placed if applicable. The default value is "$NAME-$VERSION".

PACKAGETYPE

Selects the package type to build. Currently these are available:

* msi - Microsoft Installer * rpm - Redhat Package Manger * ipkg - Itsy Package Management System * tarbz2 - compressed tar * targz - compressed tar * zip - zip file * src_tarbz2 - compressed tar source * src_targz - compressed tar source * src_zip - zip file source

This may be overridden with the "package_type" command line option.

PACKAGEVERSION

The version of the package (not the underlying project). This is currently only used by the rpm packager and should reflect changes in the packaging, not the underlying project code itself.

PCH

The Microsoft Visual C++ precompiled header that will be used when compiling object files. This variable is ignored by tools other than Microsoft Visual C++. When this variable is defined SCons will add options to the compiler command line to cause it to use the precompiled header, and will also set up the dependencies for the PCH file. Example:

env['PCH'] = 'StdAfx.pch'
PCHCOM

The command line used by the PCH builder to generated a precompiled header.

PCHCOMSTR

The string displayed when generating a precompiled header. If this is not set, then $PCHCOM (the command line) is displayed.

PCHPDBFLAGS

A construction variable that, when expanded, adds the /yD flag to the command line only if the $PDB construction variable is set.

PCHSTOP

This variable specifies how much of a source file is precompiled. This variable is ignored by tools other than Microsoft Visual C++, or when the PCH variable is not being used. When this variable is define it must be a string that is the name of the header that is included at the end of the precompiled portion of the source files, or the empty string if the "#pragma hrdstop" construct is being used:

env['PCHSTOP'] = 'StdAfx.h'
PDB

The Microsoft Visual C++ PDB file that will store debugging information for object files, shared libraries, and programs. This variable is ignored by tools other than Microsoft Visual C++. When this variable is defined SCons will add options to the compiler and linker command line to cause them to generate external debugging information, and will also set up the dependencies for the PDB file. Example:

env['PDB'] = 'hello.pdb'

The Visual C++ compiler switch that SCons uses by default to generate PDB information is /Z7. This works correctly with parallel (-j) builds because it embeds the debug information in the intermediate object files, as opposed to sharing a single PDB file between multiple object files. This is also the only way to get debug information embedded into a static library. Using the /Zi instead may yield improved link-time performance, although parallel builds will no longer work. You can generate PDB files with the /Zi switch by overriding the default $CCPDBFLAGS variable; see the entry for that variable for specific examples.

PDFCOM

A deprecated synonym for $DVIPDFCOM.

PDFLATEX

The pdflatex utility.

PDFLATEXCOM

The command line used to call the pdflatex utility.

PDFLATEXCOMSTR

The string displayed when calling the pdflatex utility. If this is not set, then $PDFLATEXCOM (the command line) is displayed.

env = Environment(PDFLATEX;COMSTR = "Building $TARGET from LaTeX input $SOURCES")
PDFLATEXFLAGS

General options passed to the pdflatex utility.

PDFPREFIX

The prefix used for PDF file names.

PDFSUFFIX

The suffix used for PDF file names.

PDFTEX

The pdftex utility.

PDFTEXCOM

The command line used to call the pdftex utility.

PDFTEXCOMSTR

The string displayed when calling the pdftex utility. If this is not set, then $PDFTEXCOM (the command line) is displayed.

env = Environment(PDFTEXCOMSTR = "Building $TARGET from TeX input $SOURCES")
PDFTEXFLAGS

General options passed to the pdftex utility.

PKGCHK

On Solaris systems, the package-checking program that will be used (along with $PKGINFO) to look for installed versions of the Sun PRO C++ compiler. The default is /usr/sbin/pgkchk.

PKGINFO

On Solaris systems, the package information program that will be used (along with $PKGCHK) to look for installed versions of the Sun PRO C++ compiler. The default is pkginfo.

PLATFORM

The name of the platform used to create the Environment. If no platform is specified when the Environment is created, scons autodetects the platform.

env = Environment(tools = [])
if env['PLATFORM'] == 'cygwin':
    Tool('mingw')(env)
else:
    Tool('msvc')(env)
POAUTOINIT

The $POAUTOINIT variable, if set to True (on non-zero numeric value), let the msginit tool to automatically initialize missing PO files with msginit(1). This applies to both, POInit and POUpdate builders (and others that use any of them).

POCREATE_ALIAS

Common alias for all PO files created with POInit builder (default: 'po-create'). See msginit tool and POInit builder.

POSUFFIX

Suffix used for PO files (default: '.po') See msginit tool and POInit builder.

POTDOMAIN

The $POTDOMAIN defines default domain, used to generate POT filename as $POTDOMAIN.pot when no POT file name is provided by the user. This applies to POTUpdate, POInit and POUpdate builders (and builders, that use them, e.g. Translate). Normally (if $POTDOMAIN is not defined), the builders use messages.pot as default POT file name.

POTSUFFIX

Suffix used for PO Template files (default: '.pot'). See xgettext tool and POTUpdate builder.

POTUPDATE_ALIAS

Name of the common phony target for all PO Templates created with POUpdate (default: 'pot-update'). See xgettext tool and POTUpdate builder.

POUPDATE_ALIAS

Common alias for all PO files being defined with POUpdate builder (default: 'po-update'). See msgmerge tool and POUpdate builder.

PRINT_CMD_LINE_FUNC

A Python function used to print the command lines as they are executed (assuming command printing is not disabled by the -q or -s options or their equivalents). The function should take four arguments: s, the command being executed (a string), target, the target being built (file node, list, or string name(s)), source, the source(s) used (file node, list, or string name(s)), and env, the environment being used.

The function must do the printing itself. The default implementation, used if this variable is not set or is None, is:

def print_cmd_line(s, target, source, env):
  sys.stdout.write(s + "\n")

Here's an example of a more interesting function:

def print_cmd_line(s, target, source, env):
   sys.stdout.write("Building %s -> %s...\n" %
    (' and '.join([str(x) for x in source]),
     ' and '.join([str(x) for x in target])))
env=Environment(PRINT_CMD_LINE_FUNC=print_cmd_line)
env.Program('foo', 'foo.c')

This just prints "Building targetname from sourcename..." instead of the actual commands. Such a function could also log the actual commands to a log file, for example.

PROGEMITTER

TODO

PROGPREFIX

The prefix used for executable file names.

PROGSUFFIX

The suffix used for executable file names.

PSCOM

The command line used to convert TeX DVI files into a PostScript file.

PSCOMSTR

The string displayed when a TeX DVI file is converted into a PostScript file. If this is not set, then $PSCOM (the command line) is displayed.

PSPREFIX

The prefix used for PostScript file names.

PSSUFFIX

The prefix used for PostScript file names.

QT_AUTOSCAN

Turn off scanning for mocable files. Use the Moc Builder to explicitly specify files to run moc on.

QT_BINPATH

The path where the qt binaries are installed. The default value is '$QTDIR/bin'.

QT_CPPPATH

The path where the qt header files are installed. The default value is '$QTDIR/include'. Note: If you set this variable to None, the tool won't change the $CPPPATH construction variable.

QT_DEBUG

Prints lots of debugging information while scanning for moc files.

QT_LIB

Default value is 'qt'. You may want to set this to 'qt-mt'. Note: If you set this variable to None, the tool won't change the $LIBS variable.

QT_LIBPATH

The path where the qt libraries are installed. The default value is '$QTDIR/lib'. Note: If you set this variable to None, the tool won't change the $LIBPATH construction variable.

QT_MOC

Default value is '$QT_BINPATH/moc'.

QT_MOCCXXPREFIX

Default value is ''. Prefix for moc output files, when source is a cxx file.

QT_MOCCXXSUFFIX

Default value is '.moc'. Suffix for moc output files, when source is a cxx file.

QT_MOCFROMCXXCOM

Command to generate a moc file from a cpp file.

QT_MOCFROMCXXCOMSTR

The string displayed when generating a moc file from a cpp file. If this is not set, then $QT_MOCFROMCXXCOM (the command line) is displayed.

QT_MOCFROMCXXFLAGS

Default value is '-i'. These flags are passed to moc, when moccing a C++ file.

QT_MOCFROMHCOM

Command to generate a moc file from a header.

QT_MOCFROMHCOMSTR

The string displayed when generating a moc file from a cpp file. If this is not set, then $QT_MOCFROMHCOM (the command line) is displayed.

QT_MOCFROMHFLAGS

Default value is ''. These flags are passed to moc, when moccing a header file.

QT_MOCHPREFIX

Default value is 'moc_'. Prefix for moc output files, when source is a header.

QT_MOCHSUFFIX

Default value is '$CXXFILESUFFIX'. Suffix for moc output files, when source is a header.

QT_UIC

Default value is '$QT_BINPATH/uic'.

QT_UICCOM

Command to generate header files from .ui files.

QT_UICCOMSTR

The string displayed when generating header files from .ui files. If this is not set, then $QT_UICCOM (the command line) is displayed.

QT_UICDECLFLAGS

Default value is ''. These flags are passed to uic, when creating a a h file from a .ui file.

QT_UICDECLPREFIX

Default value is ''. Prefix for uic generated header files.

QT_UICDECLSUFFIX

Default value is '.h'. Suffix for uic generated header files.

QT_UICIMPLFLAGS

Default value is ''. These flags are passed to uic, when creating a cxx file from a .ui file.

QT_UICIMPLPREFIX

Default value is 'uic_'. Prefix for uic generated implementation files.

QT_UICIMPLSUFFIX

Default value is '$CXXFILESUFFIX'. Suffix for uic generated implementation files.

QT_UISUFFIX

Default value is '.ui'. Suffix of designer input files.

QTDIR

The qt tool tries to take this from os.environ. It also initializes all QT_* construction variables listed below. (Note that all paths are constructed with python's os.path.join() method, but are listed here with the '/' separator for easier reading.) In addition, the construction environment variables $CPPPATH, $LIBPATH and $LIBS may be modified and the variables $PROGEMITTER, $SHLIBEMITTER and $LIBEMITTER are modified. Because the build-performance is affected when using this tool, you have to explicitly specify it at Environment creation:

Environment(tools=['default','qt'])

The qt tool supports the following operations:

Automatic moc file generation from header files. You do not have to specify moc files explicitly, the tool does it for you. However, there are a few preconditions to do so: Your header file must have the same filebase as your implementation file and must stay in the same directory. It must have one of the suffixes .h, .hpp, .H, .hxx, .hh. You can turn off automatic moc file generation by setting QT_AUTOSCAN to 0. See also the corresponding Moc() builder method.

Automatic moc file generation from cxx files. As stated in the qt documentation, include the moc file at the end of the cxx file. Note that you have to include the file, which is generated by the transformation ${QT_MOCCXXPREFIX}<basename>${QT_MOCCXXSUFFIX}, by default <basename>.moc. A warning is generated after building the moc file, if you do not include the correct file. If you are using VariantDir, you may need to specify duplicate=1. You can turn off automatic moc file generation by setting QT_AUTOSCAN to 0. See also the corresponding Moc builder method.

Automatic handling of .ui files. The implementation files generated from .ui files are handled much the same as yacc or lex files. Each .ui file given as a source of Program, Library or SharedLibrary will generate three files, the declaration file, the implementation file and a moc file. Because there are also generated headers, you may need to specify duplicate=1 in calls to VariantDir. See also the corresponding Uic builder method.

RANLIB

The archive indexer.

RANLIBCOM

The command line used to index a static library archive.

RANLIBCOMSTR

The string displayed when a static library archive is indexed. If this is not set, then $RANLIBCOM (the command line) is displayed.

env = Environment(RANLIBCOMSTR = "Indexing $TARGET")
RANLIBFLAGS

General options passed to the archive indexer.

RC

The resource compiler used to build a Microsoft Visual C++ resource file.

RCCOM

The command line used to build a Microsoft Visual C++ resource file.

RCCOMSTR

The string displayed when invoking the resource compiler to build a Microsoft Visual C++ resource file. If this is not set, then $RCCOM (the command line) is displayed.

RCFLAGS

The flags passed to the resource compiler by the RES builder.

RCINCFLAGS

An automatically-generated construction variable containing the command-line options for specifying directories to be searched by the resource compiler. The value of $RCINCFLAGS is created by appending $RCINCPREFIX and $RCINCSUFFIX to the beginning and end of each directory in $CPPPATH.

RCINCPREFIX

The prefix (flag) used to specify an include directory on the resource compiler command line. This will be appended to the beginning of each directory in the $CPPPATH construction variable when the $RCINCFLAGS variable is expanded.

RCINCSUFFIX

The suffix used to specify an include directory on the resource compiler command line. This will be appended to the end of each directory in the $CPPPATH construction variable when the $RCINCFLAGS variable is expanded.

RCS

The RCS executable. Note that this variable is not actually used for the command to fetch source files from RCS; see the $RCS_CO construction variable, below.

RCS_CO

The RCS "checkout" executable, used to fetch source files from RCS.

RCS_COCOM

The command line used to fetch (checkout) source files from RCS.

RCS_COCOMSTR

The string displayed when fetching a source file from RCS. If this is not set, then $RCS_COCOM (the command line) is displayed.

RCS_COFLAGS

Options that are passed to the $RCS_CO command.

RDirs

A function that converts a string into a list of Dir instances by searching the repositories.

REGSVR

The program used on Windows systems to register a newly-built DLL library whenever the SharedLibrary builder is passed a keyword argument of register=1.

REGSVRCOM

The command line used on Windows systems to register a newly-built DLL library whenever the SharedLibrary builder is passed a keyword argument of register=1.

REGSVRCOMSTR

The string displayed when registering a newly-built DLL file. If this is not set, then $REGSVRCOM (the command line) is displayed.

REGSVRFLAGS

Flags passed to the DLL registration program on Windows systems when a newly-built DLL library is registered. By default, this includes the /s that prevents dialog boxes from popping up and requiring user attention.

RMIC

The Java RMI stub compiler.

RMICCOM

The command line used to compile stub and skeleton class files from Java classes that contain RMI implementations. Any options specified in the $RMICFLAGS construction variable are included on this command line.

RMICCOMSTR

The string displayed when compiling stub and skeleton class files from Java classes that contain RMI implementations. If this is not set, then $RMICCOM (the command line) is displayed.

env = Environment(RMICCOMSTR = "Generating stub/skeleton class files $TARGETS from $SOURCES")
RMICFLAGS

General options passed to the Java RMI stub compiler.

_RPATH

An automatically-generated construction variable containing the rpath flags to be used when linking a program with shared libraries. The value of $_RPATH is created by appending $RPATHPREFIX and $RPATHSUFFIX to the beginning and end of each directory in $RPATH.

RPATH

A list of paths to search for shared libraries when running programs. Currently only used in the GNU (gnulink), IRIX (sgilink) and Sun (sunlink) linkers. Ignored on platforms and toolchains that don't support it. Note that the paths added to RPATH are not transformed by scons in any way: if you want an absolute path, you must make it absolute yourself.

RPATHPREFIX

The prefix used to specify a directory to be searched for shared libraries when running programs. This will be appended to the beginning of each directory in the $RPATH construction variable when the $_RPATH variable is automatically generated.

RPATHSUFFIX

The suffix used to specify a directory to be searched for shared libraries when running programs. This will be appended to the end of each directory in the $RPATH construction variable when the $_RPATH variable is automatically generated.

RPCGEN

The RPC protocol compiler.

RPCGENCLIENTFLAGS

Options passed to the RPC protocol compiler when generating client side stubs. These are in addition to any flags specified in the $RPCGENFLAGS construction variable.

RPCGENFLAGS

General options passed to the RPC protocol compiler.

RPCGENHEADERFLAGS

Options passed to the RPC protocol compiler when generating a header file. These are in addition to any flags specified in the $RPCGENFLAGS construction variable.

RPCGENSERVICEFLAGS

Options passed to the RPC protocol compiler when generating server side stubs. These are in addition to any flags specified in the $RPCGENFLAGS construction variable.

RPCGENXDRFLAGS

Options passed to the RPC protocol compiler when generating XDR routines. These are in addition to any flags specified in the $RPCGENFLAGS construction variable.

SCANNERS

A list of the available implicit dependency scanners. New file scanners may be added by appending to this list, although the more flexible approach is to associate scanners with a specific Builder. See the sections "Builder Objects" and "Scanner Objects," below, for more information.

SCCS

The SCCS executable.

SCCSCOM

The command line used to fetch source files from SCCS.

SCCSCOMSTR

The string displayed when fetching a source file from a CVS repository. If this is not set, then $SCCSCOM (the command line) is displayed.

SCCSFLAGS

General options that are passed to SCCS.

SCCSGETFLAGS

Options that are passed specifically to the SCCS "get" subcommand. This can be set, for example, to -e to check out editable files from SCCS.

SCONS_HOME

The (optional) path to the SCons library directory, initialized from the external environment. If set, this is used to construct a shorter and more efficient search path in the $MSVSSCONS command line executed from Microsoft Visual Studio project files.

SHCC

The C compiler used for generating shared-library objects.

SHCCCOM

The command line used to compile a C source file to a shared-library object file. Any options specified in the $SHCFLAGS, $SHCCFLAGS and $CPPFLAGS construction variables are included on this command line.

SHCCCOMSTR

The string displayed when a C source file is compiled to a shared object file. If this is not set, then $SHCCCOM (the command line) is displayed.

env = Environment(SHCCCOMSTR = "Compiling shared object $TARGET")
SHCCFLAGS

Options that are passed to the C and C++ compilers to generate shared-library objects.

SHCFLAGS

Options that are passed to the C compiler (only; not C++) to generate shared-library objects.

SHCXX

The C++ compiler used for generating shared-library objects.

SHCXXCOM

The command line used to compile a C++ source file to a shared-library object file. Any options specified in the $SHCXXFLAGS and $CPPFLAGS construction variables are included on this command line.

SHCXXCOMSTR

The string displayed when a C++ source file is compiled to a shared object file. If this is not set, then $SHCXXCOM (the command line) is displayed.

env = Environment(SHCXXCOMSTR = "Compiling shared object $TARGET")
SHCXXFLAGS

Options that are passed to the C++ compiler to generate shared-library objects.

SHDC

SHDC.

SHDCOM

SHDCOM.

SHDLINK

SHDLINK.

SHDLINKCOM

SHDLINKCOM.

SHDLINKFLAGS

SHDLINKFLAGS.

SHELL

A string naming the shell program that will be passed to the $SPAWN function. See the $SPAWN construction variable for more information.

SHF03

The Fortran 03 compiler used for generating shared-library objects. You should normally set the $SHFORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $SHF03 if you need to use a specific compiler or compiler version for Fortran 03 files.

SHF03COM

The command line used to compile a Fortran 03 source file to a shared-library object file. You only need to set $SHF03COM if you need to use a specific command line for Fortran 03 files. You should normally set the $SHFORTRANCOM variable, which specifies the default command line for all Fortran versions.

SHF03COMSTR

The string displayed when a Fortran 03 source file is compiled to a shared-library object file. If this is not set, then $SHF03COM or $SHFORTRANCOM (the command line) is displayed.

SHF03FLAGS

Options that are passed to the Fortran 03 compiler to generated shared-library objects. You only need to set $SHF03FLAGS if you need to define specific user options for Fortran 03 files. You should normally set the $SHFORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

SHF03PPCOM

The command line used to compile a Fortran 03 source file to a shared-library object file after first running the file through the C preprocessor. Any options specified in the $SHF03FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $SHF03PPCOM if you need to use a specific C-preprocessor command line for Fortran 03 files. You should normally set the $SHFORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

SHF03PPCOMSTR

The string displayed when a Fortran 03 source file is compiled to a shared-library object file after first running the file through the C preprocessor. If this is not set, then $SHF03PPCOM or $SHFORTRANPPCOM (the command line) is displayed.

SHF77

The Fortran 77 compiler used for generating shared-library objects. You should normally set the $SHFORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $SHF77 if you need to use a specific compiler or compiler version for Fortran 77 files.

SHF77COM

The command line used to compile a Fortran 77 source file to a shared-library object file. You only need to set $SHF77COM if you need to use a specific command line for Fortran 77 files. You should normally set the $SHFORTRANCOM variable, which specifies the default command line for all Fortran versions.

SHF77COMSTR

The string displayed when a Fortran 77 source file is compiled to a shared-library object file. If this is not set, then $SHF77COM or $SHFORTRANCOM (the command line) is displayed.

SHF77FLAGS

Options that are passed to the Fortran 77 compiler to generated shared-library objects. You only need to set $SHF77FLAGS if you need to define specific user options for Fortran 77 files. You should normally set the $SHFORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

SHF77PPCOM

The command line used to compile a Fortran 77 source file to a shared-library object file after first running the file through the C preprocessor. Any options specified in the $SHF77FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $SHF77PPCOM if you need to use a specific C-preprocessor command line for Fortran 77 files. You should normally set the $SHFORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

SHF77PPCOMSTR

The string displayed when a Fortran 77 source file is compiled to a shared-library object file after first running the file through the C preprocessor. If this is not set, then $SHF77PPCOM or $SHFORTRANPPCOM (the command line) is displayed.

SHF90

The Fortran 90 compiler used for generating shared-library objects. You should normally set the $SHFORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $SHF90 if you need to use a specific compiler or compiler version for Fortran 90 files.

SHF90COM

The command line used to compile a Fortran 90 source file to a shared-library object file. You only need to set $SHF90COM if you need to use a specific command line for Fortran 90 files. You should normally set the $SHFORTRANCOM variable, which specifies the default command line for all Fortran versions.

SHF90COMSTR

The string displayed when a Fortran 90 source file is compiled to a shared-library object file. If this is not set, then $SHF90COM or $SHFORTRANCOM (the command line) is displayed.

SHF90FLAGS

Options that are passed to the Fortran 90 compiler to generated shared-library objects. You only need to set $SHF90FLAGS if you need to define specific user options for Fortran 90 files. You should normally set the $SHFORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

SHF90PPCOM

The command line used to compile a Fortran 90 source file to a shared-library object file after first running the file through the C preprocessor. Any options specified in the $SHF90FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $SHF90PPCOM if you need to use a specific C-preprocessor command line for Fortran 90 files. You should normally set the $SHFORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

SHF90PPCOMSTR

The string displayed when a Fortran 90 source file is compiled to a shared-library object file after first running the file through the C preprocessor. If this is not set, then $SHF90PPCOM or $SHFORTRANPPCOM (the command line) is displayed.

SHF95

The Fortran 95 compiler used for generating shared-library objects. You should normally set the $SHFORTRAN variable, which specifies the default Fortran compiler for all Fortran versions. You only need to set $SHF95 if you need to use a specific compiler or compiler version for Fortran 95 files.

SHF95COM

The command line used to compile a Fortran 95 source file to a shared-library object file. You only need to set $SHF95COM if you need to use a specific command line for Fortran 95 files. You should normally set the $SHFORTRANCOM variable, which specifies the default command line for all Fortran versions.

SHF95COMSTR

The string displayed when a Fortran 95 source file is compiled to a shared-library object file. If this is not set, then $SHF95COM or $SHFORTRANCOM (the command line) is displayed.

SHF95FLAGS

Options that are passed to the Fortran 95 compiler to generated shared-library objects. You only need to set $SHF95FLAGS if you need to define specific user options for Fortran 95 files. You should normally set the $SHFORTRANFLAGS variable, which specifies the user-specified options passed to the default Fortran compiler for all Fortran versions.

SHF95PPCOM

The command line used to compile a Fortran 95 source file to a shared-library object file after first running the file through the C preprocessor. Any options specified in the $SHF95FLAGS and $CPPFLAGS construction variables are included on this command line. You only need to set $SHF95PPCOM if you need to use a specific C-preprocessor command line for Fortran 95 files. You should normally set the $SHFORTRANPPCOM variable, which specifies the default C-preprocessor command line for all Fortran versions.

SHF95PPCOMSTR

The string displayed when a Fortran 95 source file is compiled to a shared-library object file after first running the file through the C preprocessor. If this is not set, then $SHF95PPCOM or $SHFORTRANPPCOM (the command line) is displayed.

SHFORTRAN

The default Fortran compiler used for generating shared-library objects.

SHFORTRANCOM

The command line used to compile a Fortran source file to a shared-library object file.

SHFORTRANCOMSTR

The string displayed when a Fortran source file is compiled to a shared-library object file. If this is not set, then $SHFORTRANCOM (the command line) is displayed.

SHFORTRANFLAGS

Options that are passed to the Fortran compiler to generate shared-library objects.

SHFORTRANPPCOM

The command line used to compile a Fortran source file to a shared-library object file after first running the file through the C preprocessor. Any options specified in the $SHFORTRANFLAGS and $CPPFLAGS construction variables are included on this command line.

SHFORTRANPPCOMSTR

The string displayed when a Fortran source file is compiled to a shared-library object file after first running the file through the C preprocessor. If this is not set, then $SHFORTRANPPCOM (the command line) is displayed.

SHLIBEMITTER

TODO

SHLIBPREFIX

The prefix used for shared library file names.

SHLIBSUFFIX

The suffix used for shared library file names.

SHLIBVERSION

When this construction variable is defined, a versioned shared library is created. This modifies the $SHLINKFLAGS as required, adds the version number to the library name, and creates the symlinks that are needed. $SHLIBVERSION needs to be of the form X.Y.Z, where X and Y are numbers, and Z is a number but can also contain letters to designate alpha, beta, or release candidate patch levels.

SHLINK

The linker for programs that use shared libraries.

SHLINKCOM

The command line used to link programs using shared libraries.

SHLINKCOMSTR

The string displayed when programs using shared libraries are linked. If this is not set, then $SHLINKCOM (the command line) is displayed.

env = Environment(SHLINKCOMSTR = "Linking shared $TARGET")
SHLINKFLAGS

General user options passed to the linker for programs using shared libraries. Note that this variable should not contain -l (or similar) options for linking with the libraries listed in $LIBS, nor -L (or similar) include search path options that scons generates automatically from $LIBPATH. See $_LIBFLAGS above, for the variable that expands to library-link options, and $_LIBDIRFLAGS above, for the variable that expands to library search path options.

SHOBJPREFIX

The prefix used for shared object file names.

SHOBJSUFFIX

The suffix used for shared object file names.

SOURCE

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

SOURCE_URL

The URL (web address) of the location from which the project was retrieved. This is used to fill in the Source: field in the controlling information for Ipkg and RPM packages.

SOURCES

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

SPAWN

A command interpreter function that will be called to execute command line strings. The function must expect the following arguments:

def spawn(shell, escape, cmd, args, env):

sh is a string naming the shell program to use. escape is a function that can be called to escape shell special characters in the command line. cmd is the path to the command to be executed. args is the arguments to the command. env is a dictionary of the environment variables in which the command should be executed.

STATIC_AND_SHARED_OBJECTS_ARE_THE_SAME

When this variable is true, static objects and shared objects are assumed to be the same; that is, SCons does not check for linking static objects into a shared library.

SUBST_DICT

The dictionary used by the Substfile or Textfile builders for substitution values. It can be anything acceptable to the dict() constructor, so in addition to a dictionary, lists of tuples are also acceptable.

SUBSTFILEPREFIX

The prefix used for Substfile file names, the null string by default.

SUBSTFILESUFFIX

The suffix used for Substfile file names, the null string by default.

SUMMARY

A short summary of what the project is about. This is used to fill in the Summary: field in the controlling information for Ipkg and RPM packages, and as the Description: field in MSI packages.

SWIG

The scripting language wrapper and interface generator.

SWIGCFILESUFFIX

The suffix that will be used for intermediate C source files generated by the scripting language wrapper and interface generator. The default value is _wrap$CFILESUFFIX. By default, this value is used whenever the -c++ option is not specified as part of the $SWIGFLAGS construction variable.

SWIGCOM

The command line used to call the scripting language wrapper and interface generator.

SWIGCOMSTR

The string displayed when calling the scripting language wrapper and interface generator. If this is not set, then $SWIGCOM (the command line) is displayed.

SWIGCXXFILESUFFIX

The suffix that will be used for intermediate C++ source files generated by the scripting language wrapper and interface generator. The default value is _wrap$CFILESUFFIX. By default, this value is used whenever the -c++ option is specified as part of the $SWIGFLAGS construction variable.

SWIGDIRECTORSUFFIX

The suffix that will be used for intermediate C++ header files generated by the scripting language wrapper and interface generator. These are only generated for C++ code when the SWIG 'directors' feature is turned on. The default value is _wrap.h.

SWIGFLAGS

General options passed to the scripting language wrapper and interface generator. This is where you should set -python, -perl5, -tcl, or whatever other options you want to specify to SWIG. If you set the -c++ option in this variable, scons will, by default, generate a C++ intermediate source file with the extension that is specified as the $CXXFILESUFFIX variable.

_SWIGINCFLAGS

An automatically-generated construction variable containing the SWIG command-line options for specifying directories to be searched for included files. The value of $_SWIGINCFLAGS is created by appending $SWIGINCPREFIX and $SWIGINCSUFFIX to the beginning and end of each directory in $SWIGPATH.

SWIGINCPREFIX

The prefix used to specify an include directory on the SWIG command line. This will be appended to the beginning of each directory in the $SWIGPATH construction variable when the $_SWIGINCFLAGS variable is automatically generated.

SWIGINCSUFFIX

The suffix used to specify an include directory on the SWIG command line. This will be appended to the end of each directory in the $SWIGPATH construction variable when the $_SWIGINCFLAGS variable is automatically generated.

SWIGOUTDIR

Specifies the output directory in which the scripting language wrapper and interface generator should place generated language-specific files. This will be used by SCons to identify the files that will be generated by the swig call, and translated into the swig -outdir option on the command line.

SWIGPATH

The list of directories that the scripting language wrapper and interface generate will search for included files. The SWIG implicit dependency scanner will search these directories for include files. The default is to use the same path specified as $CPPPATH.

Don't explicitly put include directory arguments in SWIGFLAGS; the result will be non-portable and the directories will not be searched by the dependency scanner. Note: directory names in SWIGPATH will be looked-up relative to the SConscript directory when they are used in a command. To force scons to look-up a directory relative to the root of the source tree use #:

env = Environment(SWIGPATH='#/include')

The directory look-up can also be forced using the Dir() function:

include = Dir('include')
env = Environment(SWIGPATH=include)

The directory list will be added to command lines through the automatically-generated $_SWIGINCFLAGS construction variable, which is constructed by appending the values of the $SWIGINCPREFIX and $SWIGINCSUFFIX construction variables to the beginning and end of each directory in $SWIGPATH. Any command lines you define that need the SWIGPATH directory list should include $_SWIGINCFLAGS:

env = Environment(SWIGCOM="my_swig -o $TARGET $_SWIGINCFLAGS $SORUCES")
SWIGVERSION

The version number of the SWIG tool.

TAR

The tar archiver.

TARCOM

The command line used to call the tar archiver.

TARCOMSTR

The string displayed when archiving files using the tar archiver. If this is not set, then $TARCOM (the command line) is displayed.

env = Environment(TARCOMSTR = "Archiving $TARGET")
TARFLAGS

General options passed to the tar archiver.

TARGET

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

TARGET_ARCH

The name of the target hardware architecture for the compiled objects created by this Environment. This defaults to the value of HOST_ARCH, and the user can override it. Currently only set for Win32.

Sets the target architecture for Visual Studio compiler (i.e. the arch of the binaries generated by the compiler). If not set, default to $HOST_ARCH, or, if that is unset, to the architecture of the running machine's OS (note that the python build or architecture has no effect). This variable must be passed as an argument to the Environment() constructor; setting it later has no effect. This is currently only used on Windows, but in the future it will be used on other OSes as well.

Valid values for Windows are x86, i386 (for 32 bits); amd64, emt64, x86_64 (for 64 bits); and ia64 (Itanium). For example, if you want to compile 64-bit binaries, you would set TARGET_ARCH='x86_64' in your SCons environment.

TARGET_OS

The name of the target operating system for the compiled objects created by this Environment. This defaults to the value of HOST_OS, and the user can override it. Currently only set for Win32.

TARGETS

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

TARSUFFIX

The suffix used for tar file names.

TEMPFILEPREFIX

The prefix for a temporary file used to execute lines longer than $MAXLINELENGTH. The default is '@'. This may be set for toolchains that use other values, such as '-@' for the diab compiler or '-via' for ARM toolchain.

TEX

The TeX formatter and typesetter.

TEXCOM

The command line used to call the TeX formatter and typesetter.

TEXCOMSTR

The string displayed when calling the TeX formatter and typesetter. If this is not set, then $TEXCOM (the command line) is displayed.

env = Environment(TEXCOMSTR = "Building $TARGET from TeX input $SOURCES")
TEXFLAGS

General options passed to the TeX formatter and typesetter.

TEXINPUTS

List of directories that the LaTeX program will search for include directories. The LaTeX implicit dependency scanner will search these directories for \include and \import files.

TEXTFILEPREFIX

The prefix used for Textfile file names, the null string by default.

TEXTFILESUFFIX

The suffix used for Textfile file names; .txt by default.

TOOLS

A list of the names of the Tool specifications that are part of this construction environment.

UNCHANGED_SOURCES

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

UNCHANGED_TARGETS

A reserved variable name that may not be set or used in a construction environment. (See "Variable Substitution," below.)

VENDOR

The person or organization who supply the packaged software. This is used to fill in the Vendor: field in the controlling information for RPM packages, and the Manufacturer: field in the controlling information for MSI packages.

VERSION

The version of the project, specified as a string.

WIN32_INSERT_DEF

A deprecated synonym for $WINDOWS_INSERT_DEF.

WIN32DEFPREFIX

A deprecated synonym for $WINDOWSDEFPREFIX.

WIN32DEFSUFFIX

A deprecated synonym for $WINDOWSDEFSUFFIX.

WIN32EXPPREFIX

A deprecated synonym for $WINDOWSEXPSUFFIX.

WIN32EXPSUFFIX

A deprecated synonym for $WINDOWSEXPSUFFIX.

WINDOWS_EMBED_MANIFEST

Set this variable to True or 1 to embed the compiler-generated manifest (normally ${TARGET}.manifest) into all Windows exes and DLLs built with this environment, as a resource during their link step. This is done using $MT and $MTEXECOM and $MTSHLIBCOM.

WINDOWS_INSERT_DEF

When this is set to true, a library build of a Windows shared library (.dll file) will also build a corresponding .def file at the same time, if a .def file is not already listed as a build target. The default is 0 (do not build a .def file).

WINDOWS_INSERT_MANIFEST

When this is set to true, scons will be aware of the .manifest files generated by Microsoft Visua C/C++ 8.

WINDOWSDEFPREFIX

The prefix used for Windows .def file names.

WINDOWSDEFSUFFIX

The suffix used for Windows .def file names.

WINDOWSEXPPREFIX

The prefix used for Windows .exp file names.

WINDOWSEXPSUFFIX

The suffix used for Windows .exp file names.

WINDOWSPROGMANIFESTPREFIX

The prefix used for executable program .manifest files generated by Microsoft Visual C/C++.

WINDOWSPROGMANIFESTSUFFIX

The suffix used for executable program .manifest files generated by Microsoft Visual C/C++.

WINDOWSSHLIBMANIFESTPREFIX

The prefix used for shared library .manifest files generated by Microsoft Visual C/C++.

WINDOWSSHLIBMANIFESTSUFFIX

The suffix used for shared library .manifest files generated by Microsoft Visual C/C++.

X_IPK_DEPENDS

This is used to fill in the Depends: field in the controlling information for Ipkg packages.

X_IPK_DESCRIPTION

This is used to fill in the Description: field in the controlling information for Ipkg packages. The default value is $SUMMARY\n$DESCRIPTION

X_IPK_MAINTAINER

This is used to fill in the Maintainer: field in the controlling information for Ipkg packages.

X_IPK_PRIORITY

This is used to fill in the Priority: field in the controlling information for Ipkg packages.

X_IPK_SECTION

This is used to fill in the Section: field in the controlling information for Ipkg packages.

X_MSI_LANGUAGE

This is used to fill in the Language: attribute in the controlling information for MSI packages.

X_MSI_LICENSE_TEXT

The text of the software license in RTF format. Carriage return characters will be replaced with the RTF equivalent \\par.

X_MSI_UPGRADE_CODE

TODO

X_RPM_AUTOREQPROV

This is used to fill in the AutoReqProv: field in the RPM .spec file.

X_RPM_BUILD

internal, but overridable

X_RPM_BUILDREQUIRES

This is used to fill in the BuildRequires: field in the RPM .spec file.

X_RPM_BUILDROOT

internal, but overridable

X_RPM_CLEAN

internal, but overridable

X_RPM_CONFLICTS

This is used to fill in the Conflicts: field in the RPM .spec file.

X_RPM_DEFATTR

This value is used as the default attributes for the files in the RPM package. The default value is (-,root,root).

X_RPM_DISTRIBUTION

This is used to fill in the Distribution: field in the RPM .spec file.

X_RPM_EPOCH

This is used to fill in the Epoch: field in the controlling information for RPM packages.

X_RPM_EXCLUDEARCH

This is used to fill in the ExcludeArch: field in the RPM .spec file.

X_RPM_EXLUSIVEARCH

This is used to fill in the ExclusiveArch: field in the RPM .spec file.

X_RPM_GROUP

This is used to fill in the Group: field in the RPM .spec file.

X_RPM_GROUP_lang

This is used to fill in the Group(lang): field in the RPM .spec file. Note that lang is not literal and should be replaced by the appropriate language code.

X_RPM_ICON

This is used to fill in the Icon: field in the RPM .spec file.

X_RPM_INSTALL

internal, but overridable

X_RPM_PACKAGER

This is used to fill in the Packager: field in the RPM .spec file.

X_RPM_POSTINSTALL

This is used to fill in the %post: section in the RPM .spec file.

X_RPM_POSTUNINSTALL

This is used to fill in the %postun: section in the RPM .spec file.

X_RPM_PREFIX

This is used to fill in the Prefix: field in the RPM .spec file.

X_RPM_PREINSTALL

This is used to fill in the %pre: section in the RPM .spec file.

X_RPM_PREP

internal, but overridable

X_RPM_PREUNINSTALL

This is used to fill in the %preun: section in the RPM .spec file.

X_RPM_PROVIDES

This is used to fill in the Provides: field in the RPM .spec file.

X_RPM_REQUIRES

This is used to fill in the Requires: field in the RPM .spec file.

X_RPM_SERIAL

This is used to fill in the Serial: field in the RPM .spec file.

X_RPM_URL

This is used to fill in the Url: field in the RPM .spec file.

XGETTEXT

Path to xgettext(1) program (found via Detect()). See xgettext tool and POTUpdate builder.

XGETTEXTCOM

Complete xgettext command line. See xgettext tool and POTUpdate builder.

XGETTEXTCOMSTR

A string that is shown when xgettext(1) command is invoked (default: '', which means "print $XGETTEXTCOM"). See xgettext tool and POTUpdate builder.

_XGETTEXTDOMAIN

Internal "macro". Generates xgettext domain name form source and target (default: '${TARGET.filebase}').

XGETTEXTFLAGS

Additional flags to xgettext(1). See xgettext tool and POTUpdate builder.

XGETTEXTFROM

Name of file containing list of xgettext(1)'s source files. Autotools' users know this as POTFILES.in so they will in most cases set XGETTEXTFROM="POTFILES.in" here. The $XGETTEXTFROM files have same syntax and semantics as the well known GNU POTFILES.in. See xgettext tool and POTUpdate builder.

_XGETTEXTFROMFLAGS

Internal "macro". Genrates list of -D<dir> flags from the $XGETTEXTPATH list.

XGETTEXTFROMPREFIX

This flag is used to add single $XGETTEXTFROM file to xgettext(1)'s commandline (default: '-f').

XGETTEXTFROMSUFFIX

(default: '')

XGETTEXTPATH

List of directories, there xgettext(1) will look for source files (default: []).

Note

This variable works only together with $XGETTEXTFROM

See also xgettext tool and POTUpdate builder.

_XGETTEXTPATHFLAGS

Internal "macro". Generates list of -f<file> flags from $XGETTEXTFROM.

XGETTEXTPATHPREFIX

This flag is used to add single search path to xgettext(1)'s commandline (default: '-D').

XGETTEXTPATHSUFFIX

(default: '')

YACC

The parser generator.

YACCCOM

The command line used to call the parser generator to generate a source file.

YACCCOMSTR

The string displayed when generating a source file using the parser generator. If this is not set, then $YACCCOM (the command line) is displayed.

env = Environment(YACCCOMSTR = "Yacc'ing $TARGET from $SOURCES")
YACCFLAGS

General options passed to the parser generator. If $YACCFLAGS contains a -d option, SCons assumes that the call will also create a .h file (if the yacc source file ends in a .y suffix) or a .hpp file (if the yacc source file ends in a .yy suffix)

YACCHFILESUFFIX

The suffix of the C header file generated by the parser generator when the -d option is used. Note that setting this variable does not cause the parser generator to generate a header file with the specified suffix, it exists to allow you to specify what suffix the parser generator will use of its own accord. The default value is .h.

YACCHXXFILESUFFIX

The suffix of the C++ header file generated by the parser generator when the -d option is used. Note that setting this variable does not cause the parser generator to generate a header file with the specified suffix, it exists to allow you to specify what suffix the parser generator will use of its own accord. The default value is .hpp, except on Mac OS X, where the default is ${TARGET.suffix}.h. because the default bison parser generator just appends .h to the name of the generated C++ file.

YACCVCGFILESUFFIX

The suffix of the file containing the VCG grammar automaton definition when the --graph= option is used. Note that setting this variable does not cause the parser generator to generate a VCG file with the specified suffix, it exists to allow you to specify what suffix the parser generator will use of its own accord. The default value is .vcg.

ZIP

The zip compression and file packaging utility.

ZIPCOM

The command line used to call the zip utility, or the internal Python function used to create a zip archive.

ZIPCOMPRESSION

The compression flag from the Python zipfile module used by the internal Python function to control whether the zip archive is compressed or not. The default value is zipfile.ZIP_DEFLATED, which creates a compressed zip archive. This value has no effect if the zipfile module is unavailable.

ZIPCOMSTR

The string displayed when archiving files using the zip utility. If this is not set, then $ZIPCOM (the command line or internal Python function) is displayed.

env = Environment(ZIPCOMSTR = "Zipping $TARGET")
ZIPFLAGS

General options passed to the zip utility.

ZIPROOT

An optional zip root directory (default empty). The filenames stored in the zip file will be relative to this directory, if given. Otherwise the filenames are relative to the current directory of the command. For instance:

env = Environment()
env.Zip('foo.zip', 'subdir1/subdir2/file1', ZIPROOT='subdir1')

will produce a zip file foo.zip containing a file with the name subdir2/file1 rather than subdir1/subdir2/file1.

ZIPSUFFIX

The suffix used for zip file names.

Appendix B. Builders

This appendix contains descriptions of all of the Builders that are potentially available "out of the box" in this version of SCons.

CFile() , env.CFile()

Builds a C source file given a lex (.l) or yacc (.y) input file. The suffix specified by the $CFILESUFFIX construction variable (.c by default) is automatically added to the target if it is not already present. Example:

# builds foo.c
env.CFile(target = 'foo.c', source = 'foo.l')
# builds bar.c
env.CFile(target = 'bar', source = 'bar.y')
Command() , env.Command()

The Command "Builder" is actually implemented as a function that looks like a Builder, but actually takes an additional argument of the action from which the Builder should be made. See the Command function description for the calling syntax and details.

CXXFile() , env.CXXFile()

Builds a C++ source file given a lex (.ll) or yacc (.yy) input file. The suffix specified by the $CXXFILESUFFIX construction variable (.cc by default) is automatically added to the target if it is not already present. Example:

# builds foo.cc
env.CXXFile(target = 'foo.cc', source = 'foo.ll')
# builds bar.cc
env.CXXFile(target = 'bar', source = 'bar.yy')
DocbookEpub() , env.DocbookEpub()

A pseudo-Builder, providing a Docbook toolchain for EPUB output.

env = Environment(tools=['docbook'])
env.DocbookEpub('manual.epub', 'manual.xml')

or simply

env = Environment(tools=['docbook'])
env.DocbookEpub('manual')
DocbookHtml() , env.DocbookHtml()

A pseudo-Builder, providing a Docbook toolchain for HTML output.

env = Environment(tools=['docbook'])
env.DocbookHtml('manual.html', 'manual.xml')

or simply

env = Environment(tools=['docbook'])
env.DocbookHtml('manual')
DocbookHtmlChunked() , env.DocbookHtmlChunked()

A pseudo-Builder, providing a Docbook toolchain for chunked HTML output. It supports the base.dir parameter. The chunkfast.xsl file (requires "EXSLT") is used as the default stylesheet. Basic syntax:

env = Environment(tools=['docbook'])
env.DocbookHtmlChunked('manual')

where manual.xml is the input file.

If you use the root.filename parameter in your own stylesheets you have to specify the new target name. This ensures that the dependencies get correct, especially for the cleanup via scons -c:

env = Environment(tools=['docbook'])
env.DocbookHtmlChunked('mymanual.html', 'manual', xsl='htmlchunk.xsl')

Some basic support for the base.dir is provided. You can add the base_dir keyword to your Builder call, and the given prefix gets prepended to all the created filenames:

env = Environment(tools=['docbook'])
env.DocbookHtmlChunked('manual', xsl='htmlchunk.xsl', base_dir='output/')

Make sure that you don't forget the trailing slash for the base folder, else your files get renamed only!

DocbookHtmlhelp() , env.DocbookHtmlhelp()

A pseudo-Builder, providing a Docbook toolchain for HTMLHELP output. Its basic syntax is:

env = Environment(tools=['docbook'])
env.DocbookHtmlhelp('manual')

where manual.xml is the input file.

If you use the root.filename parameter in your own stylesheets you have to specify the new target name. This ensures that the dependencies get correct, especially for the cleanup via scons -c:

env = Environment(tools=['docbook'])
env.DocbookHtmlhelp('mymanual.html', 'manual', xsl='htmlhelp.xsl')

Some basic support for the base.dir parameter is provided. You can add the base_dir keyword to your Builder call, and the given prefix gets prepended to all the created filenames:

env = Environment(tools=['docbook'])
env.DocbookHtmlhelp('manual', xsl='htmlhelp.xsl', base_dir='output/')

Make sure that you don't forget the trailing slash for the base folder, else your files get renamed only!

DocbookMan() , env.DocbookMan()

A pseudo-Builder, providing a Docbook toolchain for Man page output. Its basic syntax is:

env = Environment(tools=['docbook'])
env.DocbookMan('manual')

where manual.xml is the input file. Note, that you can specify a target name, but the actual output names are automatically set from the refname entries in your XML source.

DocbookPdf() , env.DocbookPdf()

A pseudo-Builder, providing a Docbook toolchain for PDF output.

env = Environment(tools=['docbook'])
env.DocbookPdf('manual.pdf', 'manual.xml')

or simply

env = Environment(tools=['docbook'])
env.DocbookPdf('manual')
DocbookSlidesHtml() , env.DocbookSlidesHtml()

A pseudo-Builder, providing a Docbook toolchain for HTML slides output.

env = Environment(tools=['docbook'])
env.DocbookSlidesHtml('manual')

If you use the titlefoil.html parameter in your own stylesheets you have to give the new target name. This ensures that the dependencies get correct, especially for the cleanup via scons -c:

env = Environment(tools=['docbook'])
env.DocbookSlidesHtml('mymanual.html','manual', xsl='slideshtml.xsl')

Some basic support for the base.dir parameter is provided. You can add the base_dir keyword to your Builder call, and the given prefix gets prepended to all the created filenames:

env = Environment(tools=['docbook'])
env.DocbookSlidesHtml('manual', xsl='slideshtml.xsl', base_dir='output/')

Make sure that you don't forget the trailing slash for the base folder, else your files get renamed only!

DocbookSlidesPdf() , env.DocbookSlidesPdf()

A pseudo-Builder, providing a Docbook toolchain for PDF slides output.

env = Environment(tools=['docbook'])
env.DocbookSlidesPdf('manual.pdf', 'manual.xml')

or simply

env = Environment(tools=['docbook'])
env.DocbookSlidesPdf('manual')
DocbookXInclude() , env.DocbookXInclude()

A pseudo-Builder, for resolving XIncludes in a separate processing step.

env = Environment(tools=['docbook'])
env.DocbookXInclude('manual_xincluded.xml', 'manual.xml')
DocbookXslt() , env.DocbookXslt()

A pseudo-Builder, applying a given XSL transformation to the input file.

env = Environment(tools=['docbook'])
env.DocbookXslt('manual_transformed.xml', 'manual.xml', xsl='transform.xslt')

Note, that this builder requires the xsl parameter to be set.

DVI() , env.DVI()

Builds a .dvi file from a .tex, .ltx or .latex input file. If the source file suffix is .tex, scons will examine the contents of the file; if the string \documentclass or \documentstyle is found, the file is assumed to be a LaTeX file and the target is built by invoking the $LATEXCOM command line; otherwise, the $TEXCOM command line is used. If the file is a LaTeX file, the DVI builder method will also examine the contents of the .aux file and invoke the $BIBTEX command line if the string bibdata is found, start $MAKEINDEX to generate an index if a .ind file is found and will examine the contents .log file and re-run the $LATEXCOM command if the log file says it is necessary.

The suffix .dvi (hard-coded within TeX itself) is automatically added to the target if it is not already present. Examples:

# builds from aaa.tex
env.DVI(target = 'aaa.dvi', source = 'aaa.tex')
# builds bbb.dvi
env.DVI(target = 'bbb', source = 'bbb.ltx')
# builds from ccc.latex
env.DVI(target = 'ccc.dvi', source = 'ccc.latex')
Gs() , env.Gs()

A Builder for explicitly calling the gs executable. Depending on the underlying OS, the different names gs, gsos2 and gswin32c are tried.

env = Environment(tools=['gs'])
env.Gs('cover.jpg','scons-scons.pdf',
       GSFLAGS='-dNOPAUSE -dBATCH -sDEVICE=jpeg -dFirstPage=1 -dLastPage=1 -q') 
       )
Install() , env.Install()

Installs one or more source files or directories in the specified target, which must be a directory. The names of the specified source files or directories remain the same within the destination directory. The sources may be given as a string or as a node returned by a builder.

env.Install('/usr/local/bin', source = ['foo', 'bar'])
InstallAs() , env.InstallAs()

Installs one or more source files or directories to specific names, allowing changing a file or directory name as part of the installation. It is an error if the target and source arguments list different numbers of files or directories.

InstallVersionedLib() , env.InstallVersionedLib()

Installs a versioned shared library. The $SHLIBVERSION construction variable should be defined in the environment to confirm the version number in the library name. The symlinks appropriate to the architecture will be generated.

env.InstallAs(target = '/usr/local/bin/foo',
              source = 'foo_debug')
env.InstallAs(target = ['../lib/libfoo.a', '../lib/libbar.a'],
              source = ['libFOO.a', 'libBAR.a'])
Jar() , env.Jar()

Builds a Java archive (.jar) file from the specified list of sources. Any directories in the source list will be searched for .class files). Any .java files in the source list will be compiled to .class files by calling the Java Builder.

If the $JARCHDIR value is set, the jar command will change to the specified directory using the -C option. If $JARCHDIR is not set explicitly, SCons will use the top of any subdirectory tree in which Java .class were built by the Java Builder.

If the contents any of the source files begin with the string Manifest-Version, the file is assumed to be a manifest and is passed to the jar command with the m option set.

env.Jar(target = 'foo.jar', source = 'classes')

env.Jar(target = 'bar.jar',
        source = ['bar1.java', 'bar2.java'])
Java() , env.Java()

Builds one or more Java class files. The sources may be any combination of explicit .java files, or directory trees which will be scanned for .java files.

SCons will parse each source .java file to find the classes (including inner classes) defined within that file, and from that figure out the target .class files that will be created. The class files will be placed underneath the specified target directory.

SCons will also search each Java file for the Java package name, which it assumes can be found on a line beginning with the string package in the first column; the resulting .class files will be placed in a directory reflecting the specified package name. For example, the file Foo.java defining a single public Foo class and containing a package name of sub.dir will generate a corresponding sub/dir/Foo.class class file.

Examples:

env.Java(target = 'classes', source = 'src')
env.Java(target = 'classes', source = ['src1', 'src2'])
env.Java(target = 'classes', source = ['File1.java', 'File2.java'])

Java source files can use the native encoding for the underlying OS. Since SCons compiles in simple ASCII mode by default, the compiler will generate warnings about unmappable characters, which may lead to errors as the file is processed further. In this case, the user must specify the LANG environment variable to tell the compiler what encoding is used. For portibility, it's best if the encoding is hard-coded so that the compile will work if it is done on a system with a different encoding.

env = Environment()
env['ENV']['LANG'] = 'en_GB.UTF-8'
JavaH() , env.JavaH()

Builds C header and source files for implementing Java native methods. The target can be either a directory in which the header files will be written, or a header file name which will contain all of the definitions. The source can be the names of .class files, the names of .java files to be compiled into .class files by calling the Java builder method, or the objects returned from the Java builder method.

If the construction variable $JAVACLASSDIR is set, either in the environment or in the call to the JavaH builder method itself, then the value of the variable will be stripped from the beginning of any .class file names.

Examples:

# builds java_native.h
classes = env.Java(target = 'classdir', source = 'src')
env.JavaH(target = 'java_native.h', source = classes)

# builds include/package_foo.h and include/package_bar.h
env.JavaH(target = 'include',
          source = ['package/foo.class', 'package/bar.class'])

# builds export/foo.h and export/bar.h
env.JavaH(target = 'export',
          source = ['classes/foo.class', 'classes/bar.class'],
          JAVACLASSDIR = 'classes')
Library() , env.Library()

A synonym for the StaticLibrary builder method.

LoadableModule() , env.LoadableModule()

On most systems, this is the same as SharedLibrary. On Mac OS X (Darwin) platforms, this creates a loadable module bundle.

M4() , env.M4()

Builds an output file from an M4 input file. This uses a default $M4FLAGS value of -E, which considers all warnings to be fatal and stops on the first warning when using the GNU version of m4. Example:

env.M4(target = 'foo.c', source = 'foo.c.m4')
Moc() , env.Moc()

Builds an output file from a moc input file. Moc input files are either header files or cxx files. This builder is only available after using the tool 'qt'. See the $QTDIR variable for more information. Example:

env.Moc('foo.h') # generates moc_foo.cc
env.Moc('foo.cpp') # generates foo.moc
MOFiles() , env.MOFiles()

This builder belongs to msgfmt tool. The builder compiles PO files to MO files.

Example 1. Create pl.mo and en.mo by compiling pl.po and en.po:

  # ...
  env.MOFiles(['pl', 'en'])

Example 2. Compile files for languages defined in LINGUAS file:

  # ...
  env.MOFiles(LINGUAS_FILE = 1)

Example 3. Create pl.mo and en.mo by compiling pl.po and en.po plus files for languages defined in LINGUAS file:

  # ...
  env.MOFiles(['pl', 'en'], LINGUAS_FILE = 1)

Example 4. Compile files for languages defined in LINGUAS file (another version):

  # ...
  env['LINGUAS_FILE'] = 1
  env.MOFiles()
MSVSProject() , env.MSVSProject()

Builds a Microsoft Visual Studio project file, and by default builds a solution file as well.

This builds a Visual Studio project file, based on the version of Visual Studio that is configured (either the latest installed version, or the version specified by $MSVS_VERSION in the Environment constructor). For Visual Studio 6, it will generate a .dsp file. For Visual Studio 7 (.NET) and later versions, it will generate a .vcproj file.

By default, this also generates a solution file for the specified project, a .dsw file for Visual Studio 6 or a .sln file for Visual Studio 7 (.NET). This behavior may be disabled by specifying auto_build_solution=0 when you call MSVSProject, in which case you presumably want to build the solution file(s) by calling the MSVSSolution Builder (see below).

The MSVSProject builder takes several lists of filenames to be placed into the project file. These are currently limited to srcs, incs, localincs, resources, and misc. These are pretty self-explanatory, but it should be noted that these lists are added to the $SOURCES construction variable as strings, NOT as SCons File Nodes. This is because they represent file names to be added to the project file, not the source files used to build the project file.

The above filename lists are all optional, although at least one must be specified for the resulting project file to be non-empty.

In addition to the above lists of values, the following values may be specified:

target: The name of the target .dsp or .vcproj file. The correct suffix for the version of Visual Studio must be used, but the $MSVSPROJECTSUFFIX construction variable will be defined to the correct value (see example below).

variant: The name of this particular variant. For Visual Studio 7 projects, this can also be a list of variant names. These are typically things like "Debug" or "Release", but really can be anything you want. For Visual Studio 7 projects, they may also specify a target platform separated from the variant name by a | (vertical pipe) character: Debug|Xbox. The default target platform is Win32. Multiple calls to MSVSProject with different variants are allowed; all variants will be added to the project file with their appropriate build targets and sources.

buildtarget: An optional string, node, or list of strings or nodes (one per build variant), to tell the Visual Studio debugger what output target to use in what build variant. The number of buildtarget entries must match the number of variant entries.

runfile: The name of the file that Visual Studio 7 and later will run and debug. This appears as the value of the Output field in the resutling Visual Studio project file. If this is not specified, the default is the same as the specified buildtarget value.

Note that because SCons always executes its build commands from the directory in which the SConstruct file is located, if you generate a project file in a different directory than the SConstruct directory, users will not be able to double-click on the file name in compilation error messages displayed in the Visual Studio console output window. This can be remedied by adding the Visual C/C++ /FC compiler option to the $CCFLAGS variable so that the compiler will print the full path name of any files that cause compilation errors.

Example usage:

barsrcs = ['bar.cpp'],
barincs = ['bar.h'],
barlocalincs = ['StdAfx.h']
barresources = ['bar.rc','resource.h']
barmisc = ['bar_readme.txt']

dll = env.SharedLibrary(target = 'bar.dll',
                        source = barsrcs)

env.MSVSProject(target = 'Bar' + env['MSVSPROJECTSUFFIX'],
                srcs = barsrcs,
                incs = barincs,
                localincs = barlocalincs,
                resources = barresources,
                misc = barmisc,
                buildtarget = dll,
                variant = 'Release')
MSVSSolution() , env.MSVSSolution()

Builds a Microsoft Visual Studio solution file.

This builds a Visual Studio solution file, based on the version of Visual Studio that is configured (either the latest installed version, or the version specified by $MSVS_VERSION in the construction environment). For Visual Studio 6, it will generate a .dsw file. For Visual Studio 7 (.NET), it will generate a .sln file.

The following values must be specified:

target: The name of the target .dsw or .sln file. The correct suffix for the version of Visual Studio must be used, but the value $MSVSSOLUTIONSUFFIX will be defined to the correct value (see example below).

variant: The name of this particular variant, or a list of variant names (the latter is only supported for MSVS 7 solutions). These are typically things like "Debug" or "Release", but really can be anything you want. For MSVS 7 they may also specify target platform, like this "Debug|Xbox". Default platform is Win32.

projects: A list of project file names, or Project nodes returned by calls to the MSVSProject Builder, to be placed into the solution file. It should be noted that these file names are NOT added to the $SOURCES environment variable in form of files, but rather as strings. This is because they represent file names to be added to the solution file, not the source files used to build the solution file.

Example Usage:

env.MSVSSolution(target = 'Bar' + env['MSVSSOLUTIONSUFFIX'],
                 projects = ['bar' + env['MSVSPROJECTSUFFIX']],
                 variant = 'Release')
Object() , env.Object()

A synonym for the StaticObject builder method.

Package() , env.Package()

Builds a Binary Package of the given source files.

env.Package(source = FindInstalledFiles())

Builds software distribution packages. Packages consist of files to install and packaging information. The former may be specified with the source parameter and may be left out, in which case the FindInstalledFiles function will collect all files that have an Install or InstallAs Builder attached. If the target is not specified it will be deduced from additional information given to this Builder.

The packaging information is specified with the help of construction variables documented below. This information is called a tag to stress that some of them can also be attached to files with the Tag function. The mandatory ones will complain if they were not specified. They vary depending on chosen target packager.

The target packager may be selected with the "PACKAGETYPE" command line option or with the $PACKAGETYPE construction variable. Currently the following packagers available:

* msi - Microsoft Installer * rpm - Redhat Package Manger * ipkg - Itsy Package Management System * tarbz2 - compressed tar * targz - compressed tar * zip - zip file * src_tarbz2 - compressed tar source * src_targz - compressed tar source * src_zip - zip file source

An updated list is always available under the "package_type" option when running "scons --help" on a project that has packaging activated.

env = Environment(tools=['default', 'packaging'])
env.Install('/bin/', 'my_program')
env.Package( NAME           = 'foo',
             VERSION        = '1.2.3',
             PACKAGEVERSION = 0,
             PACKAGETYPE    = 'rpm',
             LICENSE        = 'gpl',
             SUMMARY        = 'balalalalal',
             DESCRIPTION    = 'this should be really really long',
             X_RPM_GROUP    = 'Application/fu',
             SOURCE_URL     = 'http://foo.org/foo-1.2.3.tar.gz'
        )
PCH() , env.PCH()

Builds a Microsoft Visual C++ precompiled header. Calling this builder method returns a list of two targets: the PCH as the first element, and the object file as the second element. Normally the object file is ignored. This builder method is only provided when Microsoft Visual C++ is being used as the compiler. The PCH builder method is generally used in conjuction with the PCH construction variable to force object files to use the precompiled header:

env['PCH'] = env.PCH('StdAfx.cpp')[0]
PDF() , env.PDF()

Builds a .pdf file from a .dvi input file (or, by extension, a .tex, .ltx, or .latex input file). The suffix specified by the $PDFSUFFIX construction variable (.pdf by default) is added automatically to the target if it is not already present. Example:

# builds from aaa.tex
env.PDF(target = 'aaa.pdf', source = 'aaa.tex')
# builds bbb.pdf from bbb.dvi
env.PDF(target = 'bbb', source = 'bbb.dvi')
POInit() , env.POInit()

This builder belongs to msginit tool. The builder initializes missing PO file(s) if $POAUTOINIT is set. If $POAUTOINIT is not set (default), POInit prints instruction for user (that is supposed to be a translator), telling how the PO file should be initialized. In normal projects you should not use POInit and use POUpdate instead. POUpdate chooses intelligently between msgmerge(1) and msginit(1). POInit always uses msginit(1) and should be regarded as builder for special purposes or for temporary use (e.g. for quick, one time initialization of a bunch of PO files) or for tests.

Target nodes defined through POInit are not built by default (they're Ignored from '.' node) but are added to special Alias ('po-create' by default). The alias name may be changed through the $POCREATE_ALIAS construction variable. All PO files defined through POInit may be easily initialized by scons po-create.

Example 1. Initialize en.po and pl.po from messages.pot:

  # ...
  env.POInit(['en', 'pl']) # messages.pot --> [en.po, pl.po] 

Example 2. Initialize en.po and pl.po from foo.pot:

  # ...
  env.POInit(['en', 'pl'], ['foo']) # foo.pot --> [en.po, pl.po] 

Example 3. Initialize en.po and pl.po from foo.pot but using $POTDOMAIN construction variable:

  # ...
  env.POInit(['en', 'pl'], POTDOMAIN='foo') # foo.pot --> [en.po, pl.po] 

Example 4. Initialize PO files for languages defined in LINGUAS file. The files will be initialized from template messages.pot:

  # ...
  env.POInit(LINGUAS_FILE = 1) # needs 'LINGUAS' file

Example 5. Initialize en.po and pl.pl PO files plus files for languages defined in LINGUAS file. The files will be initialized from template messages.pot:

  # ...
  env.POInit(['en', 'pl'], LINGUAS_FILE = 1)

Example 6. You may preconfigure your environment first, and then initialize PO files:

  # ...
  env['POAUTOINIT'] = 1
  env['LINGUAS_FILE'] = 1
  env['POTDOMAIN'] = 'foo'
  env.POInit()

which has same efect as:

  # ...
  env.POInit(POAUTOINIT = 1, LINGUAS_FILE = 1, POTDOMAIN = 'foo')
PostScript() , env.PostScript()

Builds a .ps file from a .dvi input file (or, by extension, a .tex, .ltx, or .latex input file). The suffix specified by the $PSSUFFIX construction variable (.ps by default) is added automatically to the target if it is not already present. Example:

# builds from aaa.tex
env.PostScript(target = 'aaa.ps', source = 'aaa.tex')
# builds bbb.ps from bbb.dvi
env.PostScript(target = 'bbb', source = 'bbb.dvi')
POTUpdate() , env.POTUpdate()

The builder belongs to xgettext tool. The builder updates target POT file if exists or creates one if it doesn't. The node is not built by default (i.e. it is Ignored from '.'), but only on demand (i.e. when given POT file is required or when special alias is invoked). This builder adds its targe node (messages.pot, say) to a special alias (pot-update by default, see $POTUPDATE_ALIAS) so you can update/create them easily with scons pot-update. The file is not written until there is no real change in internationalized messages (or in comments that enter POT file).

Note

You may see xgettext(1) being invoked by the xgettext tool even if there is no real change in internationalized messages (so the POT file is not being updated). This happens every time a source file has changed. In such case we invoke xgettext(1) and compare its output with the content of POT file to decide whether the file should be updated or not.

Example 1. Let's create po/ directory and place following SConstruct script there:

  # SConstruct in 'po/' subdir
  env = Environment( tools = ['default', 'xgettext'] )
  env.POTUpdate(['foo'], ['../a.cpp', '../b.cpp'])
  env.POTUpdate(['bar'], ['../c.cpp', '../d.cpp'])

Then invoke scons few times:

  user@host:$ scons             # Does not create foo.pot nor bar.pot
  user@host:$ scons foo.pot     # Updates or creates foo.pot
  user@host:$ scons pot-update  # Updates or creates foo.pot and bar.pot
  user@host:$ scons -c          # Does not clean foo.pot nor bar.pot.

the results shall be as the comments above say.

Example 2. The POTUpdate builder may be used with no target specified, in which case default target messages.pot will be used. The default target may also be overriden by setting $POTDOMAIN construction variable or providing it as an override to POTUpdate builder:

    
  # SConstruct script
  env = Environment( tools = ['default', 'xgettext'] )
  env['POTDOMAIN'] = "foo"
  env.POTUpdate(source = ["a.cpp", "b.cpp"]) # Creates foo.pot ...
  env.POTUpdate(POTDOMAIN = "bar", source = ["c.cpp", "d.cpp"]) # and bar.pot

Example 3. The sources may be specified within separate file, for example POTFILES.in:

      
  # POTFILES.in in 'po/' subdirectory
  ../a.cpp
  ../b.cpp
  # end of file

The name of the file (POTFILES.in) containing the list of sources is provided via $XGETTEXTFROM:

      
  # SConstruct file in 'po/' subdirectory
  env = Environment( tools = ['default', 'xgettext'] )
  env.POTUpdate(XGETTEXTFROM = 'POTFILES.in')

Example 4. You may use $XGETTEXTPATH to define source search path. Assume, for example, that you have files a.cpp, b.cpp, po/SConstruct, po/POTFILES.in. Then your POT-related files could look as below:

  # POTFILES.in in 'po/' subdirectory
  a.cpp
  b.cpp
  # end of file
  # SConstruct file in 'po/' subdirectory
  env = Environment( tools = ['default', 'xgettext'] )
  env.POTUpdate(XGETTEXTFROM = 'POTFILES.in', XGETTEXTPATH='../')

Example 5. Multiple search directories may be defined within a list, i.e. XGETTEXTPATH = ['dir1', 'dir2', ...]. The order in the list determines the search order of source files. The path to the first file found is used.

Let's create 0/1/po/SConstruct script:

  # SConstruct file in '0/1/po/' subdirectory
  env = Environment( tools = ['default', 'xgettext'] )
  env.POTUpdate(XGETTEXTFROM = 'POTFILES.in', XGETTEXTPATH=['../', '../../'])

and 0/1/po/POTFILES.in:

  # POTFILES.in in '0/1/po/' subdirectory
  a.cpp
  # end of file

Write two *.cpp files, the first one is 0/a.cpp:

  /* 0/a.cpp */
  gettext("Hello from ../../a.cpp")

and the second is 0/1/a.cpp:

  /* 0/1/a.cpp */
  gettext("Hello from ../a.cpp")

then run scons. You'll obtain 0/1/po/messages.pot with the message "Hello from ../a.cpp". When you reverse order in $XGETTEXTFOM, i.e. when you write SConscript as

  # SConstruct file in '0/1/po/' subdirectory
  env = Environment( tools = ['default', 'xgettext'] )
  env.POTUpdate(XGETTEXTFROM = 'POTFILES.in', XGETTEXTPATH=['../../', '../'])

then the messages.pot will contain msgid "Hello from ../../a.cpp" line and not msgid "Hello from ../a.cpp".

POUpdate() , env.POUpdate()

The builder belongs to msgmerge tool. The builder updates PO files with msgmerge(1), or initializes missing PO files as described in documentation of msginit tool and POInit builder (see also $POAUTOINIT). Note, that POUpdate does not add its targets to po-create alias as POInit does.

Target nodes defined through POUpdate are not built by default (they're Ignored from '.' node). Instead, they are added automatically to special Alias ('po-update' by default). The alias name may be changed through the $POUPDATE_ALIAS construction variable. You can easilly update PO files in your project by scons po-update.

Example 1. Update en.po and pl.po from messages.pot template (see also $POTDOMAIN), assuming that the later one exists or there is rule to build it (see POTUpdate):

  # ...
  env.POUpdate(['en','pl']) # messages.pot --> [en.po, pl.po]

Example 2. Update en.po and pl.po from foo.pot template:

  # ...
  env.POUpdate(['en', 'pl'], ['foo']) # foo.pot -->  [en.po, pl.pl]

Example 3. Update en.po and pl.po from foo.pot (another version):

  # ...
  env.POUpdate(['en', 'pl'], POTDOMAIN='foo') # foo.pot -- > [en.po, pl.pl]

Example 4. Update files for languages defined in LINGUAS file. The files are updated from messages.pot template:

  # ...
  env.POUpdate(LINGUAS_FILE = 1) # needs 'LINGUAS' file

Example 5. Same as above, but update from foo.pot template:

  # ...
  env.POUpdate(LINGUAS_FILE = 1, source = ['foo'])

Example 6. Update en.po and pl.po plus files for languages defined in LINGUAS file. The files are updated from messages.pot template:

  # produce 'en.po', 'pl.po' + files defined in 'LINGUAS':
  env.POUpdate(['en', 'pl' ], LINGUAS_FILE = 1) 

Example 7. Use $POAUTOINIT to automatically initialize PO file if it doesn't exist:

  # ...
  env.POUpdate(LINGUAS_FILE = 1, POAUTOINIT = 1)

Example 8. Update PO files for languages defined in LINGUAS file. The files are updated from foo.pot template. All necessary settings are pre-configured via environment.

  # ...
  env['POAUTOINIT'] = 1
  env['LINGUAS_FILE'] = 1
  env['POTDOMAIN'] = 'foo'
  env.POUpdate()
Program() , env.Program()

Builds an executable given one or more object files or C, C++, D, or Fortran source files. If any C, C++, D or Fortran source files are specified, then they will be automatically compiled to object files using the Object builder method; see that builder method's description for a list of legal source file suffixes and how they are interpreted. The target executable file prefix (specified by the $PROGPREFIX construction variable; nothing by default) and suffix (specified by the $PROGSUFFIX construction variable; by default, .exe on Windows systems, nothing on POSIX systems) are automatically added to the target if not already present. Example:

env.Program(target = 'foo', source = ['foo.o', 'bar.c', 'baz.f'])
RES() , env.RES()

Builds a Microsoft Visual C++ resource file. This builder method is only provided when Microsoft Visual C++ or MinGW is being used as the compiler. The .res (or .o for MinGW) suffix is added to the target name if no other suffix is given. The source file is scanned for implicit dependencies as though it were a C file. Example:

env.RES('resource.rc')
RMIC() , env.RMIC()

Builds stub and skeleton class files for remote objects from Java .class files. The target is a directory relative to which the stub and skeleton class files will be written. The source can be the names of .class files, or the objects return from the Java builder method.

If the construction variable $JAVACLASSDIR is set, either in the environment or in the call to the RMIC builder method itself, then the value of the variable will be stripped from the beginning of any .class file names.

classes = env.Java(target = 'classdir', source = 'src')
env.RMIC(target = 'outdir1', source = classes)

env.RMIC(target = 'outdir2',
         source = ['package/foo.class', 'package/bar.class'])

env.RMIC(target = 'outdir3',
         source = ['classes/foo.class', 'classes/bar.class'],
         JAVACLASSDIR = 'classes')
RPCGenClient() , env.RPCGenClient()

Generates an RPC client stub (_clnt.c) file from a specified RPC (.x) source file. Because rpcgen only builds output files in the local directory, the command will be executed in the source file's directory by default.

# Builds src/rpcif_clnt.c
env.RPCGenClient('src/rpcif.x')
RPCGenHeader() , env.RPCGenHeader()

Generates an RPC header (.h) file from a specified RPC (.x) source file. Because rpcgen only builds output files in the local directory, the command will be executed in the source file's directory by default.

# Builds src/rpcif.h
env.RPCGenHeader('src/rpcif.x')
RPCGenService() , env.RPCGenService()

Generates an RPC server-skeleton (_svc.c) file from a specified RPC (.x) source file. Because rpcgen only builds output files in the local directory, the command will be executed in the source file's directory by default.

# Builds src/rpcif_svc.c
env.RPCGenClient('src/rpcif.x')
RPCGenXDR() , env.RPCGenXDR()

Generates an RPC XDR routine (_xdr.c) file from a specified RPC (.x) source file. Because rpcgen only builds output files in the local directory, the command will be executed in the source file's directory by default.

# Builds src/rpcif_xdr.c
env.RPCGenClient('src/rpcif.x')
SharedLibrary() , env.SharedLibrary()

Builds a shared library (.so on a POSIX system, .dll on Windows) given one or more object files or C, C++, D or Fortran source files. If any source files are given, then they will be automatically compiled to object files. The static library prefix and suffix (if any) are automatically added to the target. The target library file prefix (specified by the $SHLIBPREFIX construction variable; by default, lib on POSIX systems, nothing on Windows systems) and suffix (specified by the $SHLIBSUFFIX construction variable; by default, .dll on Windows systems, .so on POSIX systems) are automatically added to the target if not already present. Example:

env.SharedLibrary(target = 'bar', source = ['bar.c', 'foo.o'])

On Windows systems, the SharedLibrary builder method will always build an import (.lib) library in addition to the shared (.dll) library, adding a .lib library with the same basename if there is not already a .lib file explicitly listed in the targets.

On Cygwin systems, the SharedLibrary builder method will always build an import (.dll.a) library in addition to the shared (.dll) library, adding a .dll.a library with the same basename if there is not already a .dll.a file explicitly listed in the targets.

Any object files listed in the source must have been built for a shared library (that is, using the SharedObject builder method). scons will raise an error if there is any mismatch.

On some platforms, there is a distinction between a shared library (loaded automatically by the system to resolve external references) and a loadable module (explicitly loaded by user action). For maximum portability, use the LoadableModule builder for the latter.

When the $SHLIBVERSION construction variable is defined a versioned shared library is created. This modifies the $SHLINKFLAGS as required, adds the version number to the library name, and creates the symlinks that are needed. $SHLIBVERSION needs to be of the form X.Y.Z, where X and Y are numbers, and Z is a number but can also contain letters to designate alpha, beta, or release candidate patch levels.

This builder may create multiple links to the library. On a POSIX system, for the shared library libbar.so.2.3.1, the links created would be libbar.so and libbar.so.2; on a Darwin (OSX) system the library would be libbar.2.3.1.dylib and the link would be libbar.dylib.

On Windows systems, specifying register=1 will cause the .dll to be registered after it is built using REGSVR32. The command that is run ("regsvr32" by default) is determined by $REGSVR construction variable, and the flags passed are determined by $REGSVRFLAGS. By default, $REGSVRFLAGS includes the /s option, to prevent dialogs from popping up and requiring user attention when it is run. If you change $REGSVRFLAGS, be sure to include the /s option. For example,

env.SharedLibrary(target = 'bar',
                  source = ['bar.cxx', 'foo.obj'],
                  register=1)

will register bar.dll as a COM object when it is done linking it.

SharedObject() , env.SharedObject()

Builds an object file for inclusion in a shared library. Source files must have one of the same set of extensions specified above for the StaticObject builder method. On some platforms building a shared object requires additional compiler option (e.g. -fPIC for gcc) in addition to those needed to build a normal (static) object, but on some platforms there is no difference between a shared object and a normal (static) one. When there is a difference, SCons will only allow shared objects to be linked into a shared library, and will use a different suffix for shared objects. On platforms where there is no difference, SCons will allow both normal (static) and shared objects to be linked into a shared library, and will use the same suffix for shared and normal (static) objects. The target object file prefix (specified by the $SHOBJPREFIX construction variable; by default, the same as $OBJPREFIX) and suffix (specified by the $SHOBJSUFFIX construction variable) are automatically added to the target if not already present. Examples:

env.SharedObject(target = 'ddd', source = 'ddd.c')
env.SharedObject(target = 'eee.o', source = 'eee.cpp')
env.SharedObject(target = 'fff.obj', source = 'fff.for')

Note that the source files will be scanned according to the suffix mappings in the SourceFileScanner object. See the section "Scanner Objects," below, for more information.

StaticLibrary() , env.StaticLibrary()

Builds a static library given one or more object files or C, C++, D or Fortran source files. If any source files are given, then they will be automatically compiled to object files. The static library prefix and suffix (if any) are automatically added to the target. The target library file prefix (specified by the $LIBPREFIX construction variable; by default, lib on POSIX systems, nothing on Windows systems) and suffix (specified by the $LIBSUFFIX construction variable; by default, .lib on Windows systems, .a on POSIX systems) are automatically added to the target if not already present. Example:

env.StaticLibrary(target = 'bar', source = ['bar.c', 'foo.o'])

Any object files listed in the source must have been built for a static library (that is, using the StaticObject builder method). scons will raise an error if there is any mismatch.

StaticObject() , env.StaticObject()

Builds a static object file from one or more C, C++, D, or Fortran source files. Source files must have one of the following extensions:

  .asm    assembly language file
  .ASM    assembly language file
  .c      C file
  .C      Windows:  C file
          POSIX:  C++ file
  .cc     C++ file
  .cpp    C++ file
  .cxx    C++ file
  .cxx    C++ file
  .c++    C++ file
  .C++    C++ file
  .d      D file
  .f      Fortran file
  .F      Windows:  Fortran file
          POSIX:  Fortran file + C pre-processor
  .for    Fortran file
  .FOR    Fortran file
  .fpp    Fortran file + C pre-processor
  .FPP    Fortran file + C pre-processor
  .m      Object C file
  .mm     Object C++ file
  .s      assembly language file
  .S      Windows:  assembly language file
          ARM: CodeSourcery Sourcery Lite
  .sx     assembly language file + C pre-processor
          POSIX:  assembly language file + C pre-processor
  .spp    assembly language file + C pre-processor
  .SPP    assembly language file + C pre-processor

The target object file prefix (specified by the $OBJPREFIX construction variable; nothing by default) and suffix (specified by the $OBJSUFFIX construction variable; .obj on Windows systems, .o on POSIX systems) are automatically added to the target if not already present. Examples:

env.StaticObject(target = 'aaa', source = 'aaa.c')
env.StaticObject(target = 'bbb.o', source = 'bbb.c++')
env.StaticObject(target = 'ccc.obj', source = 'ccc.f')

Note that the source files will be scanned according to the suffix mappings in SourceFileScanner object. See the section "Scanner Objects," below, for more information.

Substfile() , env.Substfile()

The Substfile builder creates a single text file from another file or set of files by concatenating them with $LINESEPARATOR and replacing text using the $SUBST_DICT construction variable. Nested lists of source files are flattened. See also Textfile.

If a single source file is present with an .in suffix, the suffix is stripped and the remainder is used as the default target name.

The prefix and suffix specified by the $SUBSTFILEPREFIX and $SUBSTFILESUFFIX construction variables (the null string by default in both cases) are automatically added to the target if they are not already present.

If a construction variable named $SUBST_DICT is present, it may be either a Python dictionary or a sequence of (key,value) tuples. If it is a dictionary it is converted into a list of tuples in an arbitrary order, so if one key is a prefix of another key or if one substitution could be further expanded by another subsitition, it is unpredictable whether the expansion will occur.

Any occurrences of a key in the source are replaced by the corresponding value, which may be a Python callable function or a string. If the value is a callable, it is called with no arguments to get a string. Strings are subst-expanded and the result replaces the key.

env = Environment(tools = ['default', 'textfile'])

env['prefix'] = '/usr/bin'
script_dict = {'@prefix@': '/bin', @exec_prefix@: '$prefix'}
env.Substfile('script.in', SUBST_DICT = script_dict)

conf_dict = {'%VERSION%': '1.2.3', '%BASE%': 'MyProg'}
env.Substfile('config.h.in', conf_dict, SUBST_DICT = conf_dict)

# UNPREDICTABLE - one key is a prefix of another
bad_foo = {'$foo': '$foo', '$foobar': '$foobar'}
env.Substfile('foo.in', SUBST_DICT = bad_foo)

# PREDICTABLE - keys are applied longest first
good_foo = [('$foobar', '$foobar'), ('$foo', '$foo')]
env.Substfile('foo.in', SUBST_DICT = good_foo)

# UNPREDICTABLE - one substitution could be futher expanded
bad_bar = {'@bar@': '@soap@', '@soap@': 'lye'}
env.Substfile('bar.in', SUBST_DICT = bad_bar)

# PREDICTABLE - substitutions are expanded in order
good_bar = (('@bar@', '@soap@'), ('@soap@', 'lye'))
env.Substfile('bar.in', SUBST_DICT = good_bar)

# the SUBST_DICT may be in common (and not an override)
substutions = {}
subst = Environment(tools = ['textfile'], SUBST_DICT = substitutions)
substitutions['@foo@'] = 'foo'
subst['SUBST_DICT']['@bar@'] = 'bar'
subst.Substfile('pgm1.c', [Value('#include "@foo@.h"'),
                           Value('#include "@bar@.h"'),
                           "common.in",
                           "pgm1.in"
                          ])
subst.Substfile('pgm2.c', [Value('#include "@foo@.h"'),
                           Value('#include "@bar@.h"'),
                           "common.in",
                           "pgm2.in"
                          ])

Tar() , env.Tar()

Builds a tar archive of the specified files and/or directories. Unlike most builder methods, the Tar builder method may be called multiple times for a given target; each additional call adds to the list of entries that will be built into the archive. Any source directories will be scanned for changes to any on-disk files, regardless of whether or not scons knows about them from other Builder or function calls.

env.Tar('src.tar', 'src')

# Create the stuff.tar file.
env.Tar('stuff', ['subdir1', 'subdir2'])
# Also add "another" to the stuff.tar file.
env.Tar('stuff', 'another')

# Set TARFLAGS to create a gzip-filtered archive.
env = Environment(TARFLAGS = '-c -z')
env.Tar('foo.tar.gz', 'foo')

# Also set the suffix to .tgz.
env = Environment(TARFLAGS = '-c -z',
                  TARSUFFIX = '.tgz')
env.Tar('foo')
Textfile() , env.Textfile()

The Textfile builder generates a single text file. The source strings constitute the lines; nested lists of sources are flattened. $LINESEPARATOR is used to separate the strings.

If present, the $SUBST_DICT construction variable is used to modify the strings before they are written; see the Substfile description for details.

The prefix and suffix specified by the $TEXTFILEPREFIX and $TEXTFILESUFFIX construction variables (the null string and .txt by default, respectively) are automatically added to the target if they are not already present. Examples:

# builds/writes foo.txt
env.Textfile(target = 'foo.txt', source = ['Goethe', 42, 'Schiller'])

# builds/writes bar.txt
env.Textfile(target = 'bar',
             source = ['lalala', 'tanteratei'],
             LINESEPARATOR='|*')

# nested lists are flattened automatically
env.Textfile(target = 'blob',
             source = ['lalala', ['Goethe', 42 'Schiller'], 'tanteratei'])

# files may be used as input by wraping them in File()
env.Textfile(target = 'concat',  # concatenate files with a marker between
             source = [File('concat1'), File('concat2')],
             LINESEPARATOR = '====================\n')

Results are:
foo.txt
  ....8<----
  Goethe
  42
  Schiller
  ....8<---- (no linefeed at the end)

bar.txt:
  ....8<----
  lalala|*tanteratei
  ....8<---- (no linefeed at the end)

blob.txt
  ....8<----
  lalala
  Goethe
  42
  Schiller
  tanteratei
  ....8<---- (no linefeed at the end)
Translate() , env.Translate()

This pseudo-builder belongs to gettext toolset. The builder extracts internationalized messages from source files, updates POT template (if necessary) and then updates PO translations (if necessary). If $POAUTOINIT is set, missing PO files will be automatically created (i.e. without translator person intervention). The variables $LINGUAS_FILE and $POTDOMAIN are taken into acount too. All other construction variables used by POTUpdate, and POUpdate work here too.

Example 1. The simplest way is to specify input files and output languages inline in a SCons script when invoking Translate

# SConscript in 'po/' directory
env = Environment( tools = ["default", "gettext"] )
env['POAUTOINIT'] = 1
env.Translate(['en','pl'], ['../a.cpp','../b.cpp']) 

Example 2. If you wish, you may also stick to conventional style known from autotools, i.e. using POTFILES.in and LINGUAS files

# LINGUAS
en pl 
#end
# POTFILES.in
a.cpp
b.cpp
# end
# SConscript
env = Environment( tools = ["default", "gettext"] )
env['POAUTOINIT'] = 1
env['XGETTEXTPATH'] = ['../']
env.Translate(LINGUAS_FILE = 1, XGETTEXTFROM = 'POTFILES.in') 

The last approach is perhaps the recommended one. It allows easily split internationalization/localization onto separate SCons scripts, where a script in source tree is responsible for translations (from sources to PO files) and script(s) under variant directories are responsible for compilation of PO to MO files to and for installation of MO files. The "gluing factor" synchronizing these two scripts is then the content of LINGUAS file. Note, that the updated POT and PO files are usually going to be committed back to the repository, so they must be updated within the source directory (and not in variant directories). Additionaly, the file listing of po/ directory contains LINGUAS file, so the source tree looks familiar to translators, and they may work with the project in their usual way.

Example 3. Let's prepare a development tree as below

 project/
  + SConstruct
  + build/        
  + src/
      + po/
          + SConscript
          + SConscript.i18n
          + POTFILES.in
          + LINGUAS

with build being variant directory. Write the top-level SConstruct script as follows

  # SConstruct
  env = Environment( tools = ["default", "gettext"] )
  VariantDir('build', 'src', duplicate = 0)
  env['POAUTOINIT'] = 1
  SConscript('src/po/SConscript.i18n', exports = 'env')
  SConscript('build/po/SConscript', exports = 'env')

the src/po/SConscript.i18n as

  # src/po/SConscript.i18n
  Import('env')
  env.Translate(LINGUAS_FILE=1, XGETTEXTFROM='POTFILES.in', XGETTEXTPATH=['../'])

and the src/po/SConscript

  # src/po/SConscript
  Import('env')
  env.MOFiles(LINGUAS_FILE = 1)

Such setup produces POT and PO files under source tree in src/po/ and binary MO files under variant tree in build/po/. This way the POT and PO files are separated from other output files, which must not be committed back to source repositories (e.g. MO files).

Note

In above example, the PO files are not updated, nor created automatically when you issue scons '.' command. The files must be updated (created) by hand via scons po-update and then MO files can be compiled by running scons '.'.

TypeLibrary() , env.TypeLibrary()

Builds a Windows type library (.tlb) file from an input IDL file (.idl). In addition, it will build the associated inteface stub and proxy source files, naming them according to the base name of the .idl file. For example,

env.TypeLibrary(source="foo.idl")

Will create foo.tlb, foo.h, foo_i.c, foo_p.c and foo_data.c files.

Uic() , env.Uic()

Builds a header file, an implementation file and a moc file from an ui file. and returns the corresponding nodes in the above order. This builder is only available after using the tool 'qt'. Note: you can specify .ui files directly as source files to the Program, Library and SharedLibrary builders without using this builder. Using this builder lets you override the standard naming conventions (be careful: prefixes are always prepended to names of built files; if you don't want prefixes, you may set them to ``). See the $QTDIR variable for more information. Example:

env.Uic('foo.ui') # -> ['foo.h', 'uic_foo.cc', 'moc_foo.cc']
env.Uic(target = Split('include/foo.h gen/uicfoo.cc gen/mocfoo.cc'),
        source = 'foo.ui') # -> ['include/foo.h', 'gen/uicfoo.cc', 'gen/mocfoo.cc']
Zip() , env.Zip()

Builds a zip archive of the specified files and/or directories. Unlike most builder methods, the Zip builder method may be called multiple times for a given target; each additional call adds to the list of entries that will be built into the archive. Any source directories will be scanned for changes to any on-disk files, regardless of whether or not scons knows about them from other Builder or function calls.

env.Zip('src.zip', 'src')

# Create the stuff.zip file.
env.Zip('stuff', ['subdir1', 'subdir2'])
# Also add "another" to the stuff.tar file.
env.Zip('stuff', 'another')

Appendix C. Tools

This appendix contains descriptions of all of the Tools modules that are available "out of the box" in this version of SCons.

386asm

Sets construction variables for the 386ASM assembler for the Phar Lap ETS embedded operating system.

Sets: $AS, $ASCOM, $ASFLAGS, $ASPPCOM, $ASPPFLAGS.

Uses: $CC, $CPPFLAGS, $_CPPDEFFLAGS, $_CPPINCFLAGS.

aixc++

Sets construction variables for the IMB xlc / Visual Age C++ compiler.

Sets: $CXX, $CXXVERSION, $SHCXX, $SHOBJSUFFIX.

aixcc

Sets construction variables for the IBM xlc / Visual Age C compiler.

Sets: $CC, $CCVERSION, $SHCC.

aixf77

Sets construction variables for the IBM Visual Age f77 Fortran compiler.

Sets: $F77, $SHF77.

aixlink

Sets construction variables for the IBM Visual Age linker.

Sets: $LINKFLAGS, $SHLIBSUFFIX, $SHLINKFLAGS.

applelink

Sets construction variables for the Apple linker (similar to the GNU linker).

Sets: $FRAMEWORKPATHPREFIX, $LDMODULECOM, $LDMODULEFLAGS, $LDMODULEPREFIX, $LDMODULESUFFIX, $LINKCOM, $SHLINKCOM, $SHLINKFLAGS, $_FRAMEWORKPATH, $_FRAMEWORKS.

Uses: $FRAMEWORKSFLAGS.

ar

Sets construction variables for the ar library archiver.

Sets: $AR, $ARCOM, $ARFLAGS, $LIBPREFIX, $LIBSUFFIX, $RANLIB, $RANLIBCOM, $RANLIBFLAGS.

as

Sets construction variables for the as assembler.

Sets: $AS, $ASCOM, $ASFLAGS, $ASPPCOM, $ASPPFLAGS.

Uses: $CC, $CPPFLAGS, $_CPPDEFFLAGS, $_CPPINCFLAGS.

bcc32

Sets construction variables for the bcc32 compiler.

Sets: $CC, $CCCOM, $CCFLAGS, $CFILESUFFIX, $CFLAGS, $CPPDEFPREFIX, $CPPDEFSUFFIX, $INCPREFIX, $INCSUFFIX, $SHCC, $SHCCCOM, $SHCCFLAGS, $SHCFLAGS, $SHOBJSUFFIX.

Uses: $_CPPDEFFLAGS, $_CPPINCFLAGS.

BitKeeper

Sets construction variables for the BitKeeper source code control system.

Sets: $BITKEEPER, $BITKEEPERCOM, $BITKEEPERGET, $BITKEEPERGETFLAGS.

Uses: $BITKEEPERCOMSTR.

cc

Sets construction variables for generic POSIX C copmilers.

Sets: $CC, $CCCOM, $CCFLAGS, $CFILESUFFIX, $CFLAGS, $CPPDEFPREFIX, $CPPDEFSUFFIX, $FRAMEWORKPATH, $FRAMEWORKS, $INCPREFIX, $INCSUFFIX, $SHCC, $SHCCCOM, $SHCCFLAGS, $SHCFLAGS, $SHOBJSUFFIX.

Uses: $PLATFORM.

cvf

Sets construction variables for the Compaq Visual Fortran compiler.

Sets: $FORTRAN, $FORTRANCOM, $FORTRANMODDIR, $FORTRANMODDIRPREFIX, $FORTRANMODDIRSUFFIX, $FORTRANPPCOM, $OBJSUFFIX, $SHFORTRANCOM, $SHFORTRANPPCOM.

Uses: $CPPFLAGS, $FORTRANFLAGS, $SHFORTRANFLAGS, $_CPPDEFFLAGS, $_FORTRANINCFLAGS, $_FORTRANMODFLAG.

CVS

Sets construction variables for the CVS source code management system.

Sets: $CVS, $CVSCOFLAGS, $CVSCOM, $CVSFLAGS.

Uses: $CVSCOMSTR.

cXX

Sets construction variables for generic POSIX C++ compilers.

Sets: $CPPDEFPREFIX, $CPPDEFSUFFIX, $CXX, $CXXCOM, $CXXFILESUFFIX, $CXXFLAGS, $INCPREFIX, $INCSUFFIX, $OBJSUFFIX, $SHCXX, $SHCXXCOM, $SHCXXFLAGS, $SHOBJSUFFIX.

Uses: $CXXCOMSTR.

default

Sets variables by calling a default list of Tool modules for the platform on which SCons is running.

dmd

Sets construction variables for D language compiler DMD.

Sets: $DC, $DCOM, $DDEBUG, $DDEBUGPREFIX, $DDEBUGSUFFIX, $DFILESUFFIX, $DFLAGPREFIX, $DFLAGS, $DFLAGSUFFIX, $DINCPREFIX, $DINCSUFFIX, $DLIB, $DLIBCOM, $DLIBDIRPREFIX, $DLIBDIRSUFFIX, $DLIBFLAGPREFIX, $DLIBFLAGSUFFIX, $DLIBLINKPREFIX, $DLIBLINKSUFFIX, $DLINK, $DLINKCOM, $DLINKFLAGS, $DPATH, $DVERPREFIX, $DVERSIONS, $DVERSUFFIX, $RPATHPREFIX, $RPATHSUFFIX, $SHDC, $SHDCOM, $SHDLINK, $SHDLINKCOM, $SHDLINKFLAGS, $_DDEBUGFLAGS, $_DFLAGS, $_DINCFLAGS, $_DLIBDIRFLAGS, $_DLIBFLAGS, $_DLIBFLAGS, $_DVERFLAGS, $_RPATH.

docbook

This tool tries to make working with Docbook in SCons a little easier. It provides several toolchains for creating different output formats, like HTML or PDF. Contained in the package is a distribution of the Docbook XSL stylesheets as of version 1.76.1. As long as you don't specify your own stylesheets for customization, these official versions are picked as default...which should reduce the inevitable setup hassles for you.

Implicit dependencies to images and XIncludes are detected automatically if you meet the HTML requirements. The additional stylesheet utils/xmldepend.xsl by Paul DuBois is used for this purpose.

Note, that there is no support for XML catalog resolving offered! This tool calls the XSLT processors and PDF renderers with the stylesheets you specified, that's it. The rest lies in your hands and you still have to know what you're doing when resolving names via a catalog.

For activating the tool "docbook", you have to add its name to the Environment constructor, like this

env = Environment(tools=['docbook'])

On its startup, the Docbook tool tries to find a required xsltproc processor, and a PDF renderer, e.g. fop. So make sure that these are added to your system's environment PATH and can be called directly, without specifying their full path.

For the most basic processing of Docbook to HTML, you need to have installed

  • the Python lxml binding to libxml2, or

  • the direct Python bindings for libxml2/libxslt, or

  • a standalone XSLT processor, currently detected are xsltproc, saxon, saxon-xslt and xalan.

Rendering to PDF requires you to have one of the applications fop or xep installed.

Creating a HTML or PDF document is very simple and straightforward. Say

env = Environment(tools=['docbook'])
env.DocbookHtml('manual.html', 'manual.xml')
env.DocbookPdf('manual.pdf', 'manual.xml')

to get both outputs from your XML source manual.xml. As a shortcut, you can give the stem of the filenames alone, like this:

env = Environment(tools=['docbook'])
env.DocbookHtml('manual')
env.DocbookPdf('manual')

and get the same result. Target and source lists are also supported:

env = Environment(tools=['docbook'])
env.DocbookHtml(['manual.html','reference.html'], ['manual.xml','reference.xml'])

or even

env = Environment(tools=['docbook'])
env.DocbookHtml(['manual','reference'])

Important

Whenever you leave out the list of sources, you may not specify a file extension! The Tool uses the given names as file stems, and adds the suffixes for target and source files accordingly.

The rules given above are valid for the Builders DocbookHtml, DocbookPdf, DocbookEpub, DocbookSlidesPdf and DocbookXInclude. For the DocbookMan transformation you can specify a target name, but the actual output names are automatically set from the refname entries in your XML source.

The Builders DocbookHtmlChunked, DocbookHtmlhelp and DocbookSlidesHtml are special, in that:

  1. they create a large set of files, where the exact names and their number depend on the content of the source file, and

  2. the main target is always named index.html, i.e. the output name for the XSL transformation is not picked up by the stylesheets.

As a result, there is simply no use in specifying a target HTML name. So the basic syntax for these builders is always:

env = Environment(tools=['docbook'])
env.DocbookHtmlhelp('manual')

If you want to use a specific XSL file, you can set the additional xsl parameter to your Builder call as follows:

env.DocbookHtml('other.html', 'manual.xml', xsl='html.xsl')

Since this may get tedious if you always use the same local naming for your customized XSL files, e.g. html.xsl for HTML and pdf.xsl for PDF output, a set of variables for setting the default XSL name is provided. These are:

DOCBOOK_DEFAULT_XSL_HTML        
DOCBOOK_DEFAULT_XSL_HTMLCHUNKED        
DOCBOOK_DEFAULT_XSL_HTMLHELP        
DOCBOOK_DEFAULT_XSL_PDF        
DOCBOOK_DEFAULT_XSL_EPUB        
DOCBOOK_DEFAULT_XSL_MAN        
DOCBOOK_DEFAULT_XSL_SLIDESPDF        
DOCBOOK_DEFAULT_XSL_SLIDESHTML        

and you can set them when constructing your environment:

env = Environment(tools=['docbook'],
                  DOCBOOK_DEFAULT_XSL_HTML='html.xsl',
                  DOCBOOK_DEFAULT_XSL_PDF='pdf.xsl')
env.DocbookHtml('manual') # now uses html.xsl

Sets: $DOCBOOK_DEFAULT_XSL_EPUB, $DOCBOOK_DEFAULT_XSL_HTML, $DOCBOOK_DEFAULT_XSL_HTMLCHUNKED, $DOCBOOK_DEFAULT_XSL_HTMLHELP, $DOCBOOK_DEFAULT_XSL_MAN, $DOCBOOK_DEFAULT_XSL_PDF, $DOCBOOK_DEFAULT_XSL_SLIDESHTML, $DOCBOOK_DEFAULT_XSL_SLIDESPDF, $DOCBOOK_FOP, $DOCBOOK_FOPCOM, $DOCBOOK_FOPFLAGS, $DOCBOOK_XMLLINT, $DOCBOOK_XMLLINTCOM, $DOCBOOK_XMLLINTFLAGS, $DOCBOOK_XSLTPROC, $DOCBOOK_XSLTPROCCOM, $DOCBOOK_XSLTPROCFLAGS, $DOCBOOK_XSLTPROCPARAMS.

Uses: $DOCBOOK_FOPCOMSTR, $DOCBOOK_XMLLINTCOMSTR, $DOCBOOK_XSLTPROCCOMSTR.

dvi

Attaches the DVI builder to the construction environment.

dvipdf

Sets construction variables for the dvipdf utility.

Sets: $DVIPDF, $DVIPDFCOM, $DVIPDFFLAGS.

Uses: $DVIPDFCOMSTR.

dvips

Sets construction variables for the dvips utility.

Sets: $DVIPS, $DVIPSFLAGS, $PSCOM, $PSPREFIX, $PSSUFFIX.

Uses: $PSCOMSTR.

f03

Set construction variables for generic POSIX Fortran 03 compilers.

Sets: $F03, $F03COM, $F03FLAGS, $F03PPCOM, $SHF03, $SHF03COM, $SHF03FLAGS, $SHF03PPCOM, $_F03INCFLAGS.

Uses: $F03COMSTR, $F03PPCOMSTR, $SHF03COMSTR, $SHF03PPCOMSTR.

f77

Set construction variables for generic POSIX Fortran 77 compilers.

Sets: $F77, $F77COM, $F77FILESUFFIXES, $F77FLAGS, $F77PPCOM, $F77PPFILESUFFIXES, $FORTRAN, $FORTRANCOM, $FORTRANFLAGS, $SHF77, $SHF77COM, $SHF77FLAGS, $SHF77PPCOM, $SHFORTRAN, $SHFORTRANCOM, $SHFORTRANFLAGS, $SHFORTRANPPCOM, $_F77INCFLAGS.

Uses: $F77COMSTR, $F77PPCOMSTR, $FORTRANCOMSTR, $FORTRANPPCOMSTR, $SHF77COMSTR, $SHF77PPCOMSTR, $SHFORTRANCOMSTR, $SHFORTRANPPCOMSTR.

f90

Set construction variables for generic POSIX Fortran 90 compilers.

Sets: $F90, $F90COM, $F90FLAGS, $F90PPCOM, $SHF90, $SHF90COM, $SHF90FLAGS, $SHF90PPCOM, $_F90INCFLAGS.

Uses: $F90COMSTR, $F90PPCOMSTR, $SHF90COMSTR, $SHF90PPCOMSTR.

f95

Set construction variables for generic POSIX Fortran 95 compilers.

Sets: $F95, $F95COM, $F95FLAGS, $F95PPCOM, $SHF95, $SHF95COM, $SHF95FLAGS, $SHF95PPCOM, $_F95INCFLAGS.

Uses: $F95COMSTR, $F95PPCOMSTR, $SHF95COMSTR, $SHF95PPCOMSTR.

fortran

Set construction variables for generic POSIX Fortran compilers.

Sets: $FORTRAN, $FORTRANCOM, $FORTRANFLAGS, $SHFORTRAN, $SHFORTRANCOM, $SHFORTRANFLAGS, $SHFORTRANPPCOM.

Uses: $FORTRANCOMSTR, $FORTRANPPCOMSTR, $SHFORTRANCOMSTR, $SHFORTRANPPCOMSTR.

g++

Set construction variables for the gXX C++ compiler.

Sets: $CXX, $CXXVERSION, $SHCXXFLAGS, $SHOBJSUFFIX.

g77

Set construction variables for the g77 Fortran compiler. Calls the f77 Tool module to set variables.

gas

Sets construction variables for the gas assembler. Calls the as module.

Sets: $AS.

gcc

Set construction variables for the gcc C compiler.

Sets: $CC, $CCVERSION, $SHCCFLAGS.

gdc

Sets construction variables for the D language compiler GDC.

Sets: $DC, $DCOM, $DDEBUG, $DDEBUGPREFIX, $DDEBUGSUFFIX, $DFILESUFFIX, $DFLAGPREFIX, $DFLAGS, $DFLAGSUFFIX, $DINCPREFIX, $DINCSUFFIX, $DLIB, $DLIBCOM, $DLIBFLAGPREFIX, $DLIBFLAGSUFFIX, $DLINK, $DLINKCOM, $DLINKFLAGPREFIX, $DLINKFLAGS, $DLINKFLAGSUFFIX, $DPATH, $DVERPREFIX, $DVERSIONS, $DVERSUFFIX, $RPATHPREFIX, $RPATHSUFFIX, $SHDC, $SHDCOM, $SHDLINK, $SHDLINKCOM, $SHDLINKFLAGS, $_DDEBUGFLAGS, $_DFLAGS, $_DINCFLAGS, $_DLIBFLAGS, $_DVERFLAGS, $_RPATH.

gettext

This is actually a toolset, which supports internationalization and localization of sofware being constructed with SCons. The toolset loads following tools:

  • xgettext - to extract internationalized messages from source code to POT file(s),

  • msginit - may be optionally used to initialize PO files,

  • msgmerge - to update PO files, that already contain translated messages,

  • msgfmt - to compile textual PO file to binary installable MO file.

When you enable gettext, it internally loads all abovementioned tools, so you're encouraged to see their individual documentation.

Each of the above tools provides its own builder(s) which may be used to perform particular activities related to software internationalization. You may be however interested in top-level builder Translate described few paragraphs later.

To use gettext tools add 'gettext' tool to your environment:

  env = Environment( tools = ['default', 'gettext'] )
gfortran

Sets construction variables for the GNU F95/F2003 GNU compiler.

Sets: $F77, $F90, $F95, $FORTRAN, $SHF77, $SHF77FLAGS, $SHF90, $SHF90FLAGS, $SHF95, $SHF95FLAGS, $SHFORTRAN, $SHFORTRANFLAGS.

gnulink

Set construction variables for GNU linker/loader.

Sets: $RPATHPREFIX, $RPATHSUFFIX, $SHLINKFLAGS.

gs

This Tool sets the required construction variables for working with the Ghostscript command. It also registers an appropriate Action with the PDF Builder (PDF), such that the conversion from PS/EPS to PDF happens automatically for the TeX/LaTeX toolchain. Finally, it adds an explicit Ghostscript Builder (Gs) to the environment.

Sets: $GS, $GSCOM, $GSFLAGS.

Uses: $GSCOMSTR.

hpc++

Set construction variables for the compilers aCC on HP/UX systems.

hpcc

Set construction variables for the aCC on HP/UX systems. Calls the cXX tool for additional variables.

Sets: $CXX, $CXXVERSION, $SHCXXFLAGS.

hplink

Sets construction variables for the linker on HP/UX systems.

Sets: $LINKFLAGS, $SHLIBSUFFIX, $SHLINKFLAGS.

icc

Sets construction variables for the icc compiler on OS/2 systems.

Sets: $CC, $CCCOM, $CFILESUFFIX, $CPPDEFPREFIX, $CPPDEFSUFFIX, $CXXCOM, $CXXFILESUFFIX, $INCPREFIX, $INCSUFFIX.

Uses: $CCFLAGS, $CFLAGS, $CPPFLAGS, $_CPPDEFFLAGS, $_CPPINCFLAGS.

icl

Sets construction variables for the Intel C/C++ compiler. Calls the intelc Tool module to set its variables.

ifl

Sets construction variables for the Intel Fortran compiler.

Sets: $FORTRAN, $FORTRANCOM, $FORTRANPPCOM, $SHFORTRANCOM, $SHFORTRANPPCOM.

Uses: $CPPFLAGS, $FORTRANFLAGS, $_CPPDEFFLAGS, $_FORTRANINCFLAGS.

ifort

Sets construction variables for newer versions of the Intel Fortran compiler for Linux.

Sets: $F77, $F90, $F95, $FORTRAN, $SHF77, $SHF77FLAGS, $SHF90, $SHF90FLAGS, $SHF95, $SHF95FLAGS, $SHFORTRAN, $SHFORTRANFLAGS.

ilink

Sets construction variables for the ilink linker on OS/2 systems.

Sets: $LIBDIRPREFIX, $LIBDIRSUFFIX, $LIBLINKPREFIX, $LIBLINKSUFFIX, $LINK, $LINKCOM, $LINKFLAGS.

ilink32

Sets construction variables for the Borland ilink32 linker.

Sets: $LIBDIRPREFIX, $LIBDIRSUFFIX, $LIBLINKPREFIX, $LIBLINKSUFFIX, $LINK, $LINKCOM, $LINKFLAGS.

install

Sets construction variables for file and directory installation.

Sets: $INSTALL, $INSTALLSTR.

intelc

Sets construction variables for the Intel C/C++ compiler (Linux and Windows, version 7 and later). Calls the gcc or msvc (on Linux and Windows, respectively) to set underlying variables.

Sets: $AR, $CC, $CXX, $INTEL_C_COMPILER_VERSION, $LINK.

jar

Sets construction variables for the jar utility.

Sets: $JAR, $JARCOM, $JARFLAGS, $JARSUFFIX.

Uses: $JARCOMSTR.

javac

Sets construction variables for the javac compiler.

Sets: $JAVABOOTCLASSPATH, $JAVAC, $JAVACCOM, $JAVACFLAGS, $JAVACLASSPATH, $JAVACLASSSUFFIX, $JAVASOURCEPATH, $JAVASUFFIX.

Uses: $JAVACCOMSTR.

javah

Sets construction variables for the javah tool.

Sets: $JAVACLASSSUFFIX, $JAVAH, $JAVAHCOM, $JAVAHFLAGS.

Uses: $JAVACLASSPATH, $JAVAHCOMSTR.

latex

Sets construction variables for the latex utility.

Sets: $LATEX, $LATEXCOM, $LATEXFLAGS.

Uses: $LATEXCOMSTR.

ldc

Sets construction variables for the D language compiler LDC2.

Sets: $DC, $DCOM, $DDEBUG, $DDEBUGPREFIX, $DDEBUGSUFFIX, $DFILESUFFIX, $DFLAGPREFIX, $DFLAGS, $DFLAGSUFFIX, $DINCPREFIX, $DINCSUFFIX, $DLIB, $DLIBCOM, $DLIBDIRPREFIX, $DLIBDIRSUFFIX, $DLIBFLAGPREFIX, $DLIBFLAGSUFFIX, $DLIBLINKPREFIX, $DLIBLINKSUFFIX, $DLINK, $DLINKCOM, $DLINKFLAGPREFIX, $DLINKFLAGS, $DLINKFLAGSUFFIX, $DPATH, $DVERPREFIX, $DVERSIONS, $DVERSUFFIX, $RPATHPREFIX, $RPATHSUFFIX, $SHDC, $SHDCOM, $SHDLINK, $SHDLINKCOM, $SHDLINKFLAGS, $_DDEBUGFLAGS, $_DFLAGS, $_DINCFLAGS, $_DLIBDIRFLAGS, $_DLIBFLAGS, $_DLIBFLAGS, $_DVERFLAGS, $_RPATH.

lex

Sets construction variables for the lex lexical analyser.

Sets: $LEX, $LEXCOM, $LEXFLAGS.

Uses: $LEXCOMSTR.

link

Sets construction variables for generic POSIX linkers.

Sets: $LDMODULE, $LDMODULECOM, $LDMODULEFLAGS, $LDMODULEPREFIX, $LDMODULESUFFIX, $LIBDIRPREFIX, $LIBDIRSUFFIX, $LIBLINKPREFIX, $LIBLINKSUFFIX, $LINK, $LINKCOM, $LINKFLAGS, $SHLIBSUFFIX, $SHLINK, $SHLINKCOM, $SHLINKFLAGS.

Uses: $LDMODULECOMSTR, $LINKCOMSTR, $SHLINKCOMSTR.

linkloc

Sets construction variables for the LinkLoc linker for the Phar Lap ETS embedded operating system.

Sets: $LIBDIRPREFIX, $LIBDIRSUFFIX, $LIBLINKPREFIX, $LIBLINKSUFFIX, $LINK, $LINKCOM, $LINKFLAGS, $SHLINK, $SHLINKCOM, $SHLINKFLAGS.

Uses: $LINKCOMSTR, $SHLINKCOMSTR.

m4

Sets construction variables for the m4 macro processor.

Sets: $M4, $M4COM, $M4FLAGS.

Uses: $M4COMSTR.

masm

Sets construction variables for the Microsoft assembler.

Sets: $AS, $ASCOM, $ASFLAGS, $ASPPCOM, $ASPPFLAGS.

Uses: $ASCOMSTR, $ASPPCOMSTR, $CPPFLAGS, $_CPPDEFFLAGS, $_CPPINCFLAGS.

midl

Sets construction variables for the Microsoft IDL compiler.

Sets: $MIDL, $MIDLCOM, $MIDLFLAGS.

Uses: $MIDLCOMSTR.

mingw

Sets construction variables for MinGW (Minimal Gnu on Windows).

Sets: $AS, $CC, $CXX, $LDMODULECOM, $LIBPREFIX, $LIBSUFFIX, $OBJSUFFIX, $RC, $RCCOM, $RCFLAGS, $RCINCFLAGS, $RCINCPREFIX, $RCINCSUFFIX, $SHCCFLAGS, $SHCXXFLAGS, $SHLINKCOM, $SHLINKFLAGS, $SHOBJSUFFIX, $WINDOWSDEFPREFIX, $WINDOWSDEFSUFFIX.

Uses: $RCCOMSTR, $SHLINKCOMSTR.

msgfmt

This scons tool is a part of scons gettext toolset. It provides scons interface to msgfmt(1) command, which generates binary message catalog (MO) from a textual translation description (PO).

Sets: $MOSUFFIX, $MSGFMT, $MSGFMTCOM, $MSGFMTCOMSTR, $MSGFMTFLAGS, $POSUFFIX.

Uses: $LINGUAS_FILE.

msginit

This scons tool is a part of scons gettext toolset. It provides scons interface to msginit(1) program, which creates new PO file, initializing the meta information with values from user's environment (or options).

Sets: $MSGINIT, $MSGINITCOM, $MSGINITCOMSTR, $MSGINITFLAGS, $POAUTOINIT, $POCREATE_ALIAS, $POSUFFIX, $POTSUFFIX, $_MSGINITLOCALE.

Uses: $LINGUAS_FILE, $POAUTOINIT, $POTDOMAIN.

msgmerge

This scons tool is a part of scons gettext toolset. It provides scons interface to msgmerge(1) command, which merges two Uniform style .po files together.

Sets: $MSGMERGE, $MSGMERGECOM, $MSGMERGECOMSTR, $MSGMERGEFLAGS, $POSUFFIX, $POTSUFFIX, $POUPDATE_ALIAS.

Uses: $LINGUAS_FILE, $POAUTOINIT, $POTDOMAIN.

mslib

Sets construction variables for the Microsoft mslib library archiver.

Sets: $AR, $ARCOM, $ARFLAGS, $LIBPREFIX, $LIBSUFFIX.

Uses: $ARCOMSTR.

mslink

Sets construction variables for the Microsoft linker.

Sets: $LDMODULE, $LDMODULECOM, $LDMODULEFLAGS, $LDMODULEPREFIX, $LDMODULESUFFIX, $LIBDIRPREFIX, $LIBDIRSUFFIX, $LIBLINKPREFIX, $LIBLINKSUFFIX, $LINK, $LINKCOM, $LINKFLAGS, $REGSVR, $REGSVRCOM, $REGSVRFLAGS, $SHLINK, $SHLINKCOM, $SHLINKFLAGS, $WIN32DEFPREFIX, $WIN32DEFSUFFIX, $WIN32EXPPREFIX, $WIN32EXPSUFFIX, $WINDOWSDEFPREFIX, $WINDOWSDEFSUFFIX, $WINDOWSEXPPREFIX, $WINDOWSEXPSUFFIX, $WINDOWSPROGMANIFESTPREFIX, $WINDOWSPROGMANIFESTSUFFIX, $WINDOWSSHLIBMANIFESTPREFIX, $WINDOWSSHLIBMANIFESTSUFFIX, $WINDOWS_INSERT_DEF.

Uses: $LDMODULECOMSTR, $LINKCOMSTR, $REGSVRCOMSTR, $SHLINKCOMSTR.

mssdk

Sets variables for Microsoft Platform SDK and/or Windows SDK. Note that unlike most other Tool modules, mssdk does not set construction variables, but sets the environment variables in the environment SCons uses to execute the Microsoft toolchain: %INCLUDE%, %LIB%, %LIBPATH% and %PATH%.

Uses: $MSSDK_DIR, $MSSDK_VERSION, $MSVS_VERSION.

msvc

Sets construction variables for the Microsoft Visual C/C++ compiler.

Sets: $BUILDERS, $CC, $CCCOM, $CCFLAGS, $CCPCHFLAGS, $CCPDBFLAGS, $CFILESUFFIX, $CFLAGS, $CPPDEFPREFIX, $CPPDEFSUFFIX, $CXX, $CXXCOM, $CXXFILESUFFIX, $CXXFLAGS, $INCPREFIX, $INCSUFFIX, $OBJPREFIX, $OBJSUFFIX, $PCHCOM, $PCHPDBFLAGS, $RC, $RCCOM, $RCFLAGS, $SHCC, $SHCCCOM, $SHCCFLAGS, $SHCFLAGS, $SHCXX, $SHCXXCOM, $SHCXXFLAGS, $SHOBJPREFIX, $SHOBJSUFFIX.

Uses: $CCCOMSTR, $CXXCOMSTR, $PCH, $PCHSTOP, $PDB, $SHCCCOMSTR, $SHCXXCOMSTR.

msvs

Sets construction variables for Microsoft Visual Studio.

Sets: $MSVSBUILDCOM, $MSVSCLEANCOM, $MSVSENCODING, $MSVSPROJECTCOM, $MSVSREBUILDCOM, $MSVSSCONS, $MSVSSCONSCOM, $MSVSSCONSCRIPT, $MSVSSCONSFLAGS, $MSVSSOLUTIONCOM.

mwcc

Sets construction variables for the Metrowerks CodeWarrior compiler.

Sets: $CC, $CCCOM, $CFILESUFFIX, $CPPDEFPREFIX, $CPPDEFSUFFIX, $CXX, $CXXCOM, $CXXFILESUFFIX, $INCPREFIX, $INCSUFFIX, $MWCW_VERSION, $MWCW_VERSIONS, $SHCC, $SHCCCOM, $SHCCFLAGS, $SHCFLAGS, $SHCXX, $SHCXXCOM, $SHCXXFLAGS.

Uses: $CCCOMSTR, $CXXCOMSTR, $SHCCCOMSTR, $SHCXXCOMSTR.

mwld

Sets construction variables for the Metrowerks CodeWarrior linker.

Sets: $AR, $ARCOM, $LIBDIRPREFIX, $LIBDIRSUFFIX, $LIBLINKPREFIX, $LIBLINKSUFFIX, $LINK, $LINKCOM, $SHLINK, $SHLINKCOM, $SHLINKFLAGS.

nasm

Sets construction variables for the nasm Netwide Assembler.

Sets: $AS, $ASCOM, $ASFLAGS, $ASPPCOM, $ASPPFLAGS.

Uses: $ASCOMSTR, $ASPPCOMSTR.

Packaging

Sets construction variables for the Package Builder.

packaging

A framework for building binary and source packages.

pdf

Sets construction variables for the Portable Document Format builder.

Sets: $PDFPREFIX, $PDFSUFFIX.

pdflatex

Sets construction variables for the pdflatex utility.

Sets: $LATEXRETRIES, $PDFLATEX, $PDFLATEXCOM, $PDFLATEXFLAGS.

Uses: $PDFLATEXCOMSTR.

pdftex

Sets construction variables for the pdftex utility.

Sets: $LATEXRETRIES, $PDFLATEX, $PDFLATEXCOM, $PDFLATEXFLAGS, $PDFTEX, $PDFTEXCOM, $PDFTEXFLAGS.

Uses: $PDFLATEXCOMSTR, $PDFTEXCOMSTR.

Perforce

Sets construction variables for interacting with the Perforce source code management system.

Sets: $P4, $P4COM, $P4FLAGS.

Uses: $P4COMSTR.

qt

Sets construction variables for building Qt applications.

Sets: $QTDIR, $QT_AUTOSCAN, $QT_BINPATH, $QT_CPPPATH, $QT_LIB, $QT_LIBPATH, $QT_MOC, $QT_MOCCXXPREFIX, $QT_MOCCXXSUFFIX, $QT_MOCFROMCXXCOM, $QT_MOCFROMCXXFLAGS, $QT_MOCFROMHCOM, $QT_MOCFROMHFLAGS, $QT_MOCHPREFIX, $QT_MOCHSUFFIX, $QT_UIC, $QT_UICCOM, $QT_UICDECLFLAGS, $QT_UICDECLPREFIX, $QT_UICDECLSUFFIX, $QT_UICIMPLFLAGS, $QT_UICIMPLPREFIX, $QT_UICIMPLSUFFIX, $QT_UISUFFIX.

RCS

Sets construction variables for the interaction with the Revision Control System.

Sets: $RCS, $RCS_CO, $RCS_COCOM, $RCS_COFLAGS.

Uses: $RCS_COCOMSTR.

rmic

Sets construction variables for the rmic utility.

Sets: $JAVACLASSSUFFIX, $RMIC, $RMICCOM, $RMICFLAGS.

Uses: $RMICCOMSTR.

rpcgen

Sets construction variables for building with RPCGEN.

Sets: $RPCGEN, $RPCGENCLIENTFLAGS, $RPCGENFLAGS, $RPCGENHEADERFLAGS, $RPCGENSERVICEFLAGS, $RPCGENXDRFLAGS.

SCCS

Sets construction variables for interacting with the Source Code Control System.

Sets: $SCCS, $SCCSCOM, $SCCSFLAGS, $SCCSGETFLAGS.

Uses: $SCCSCOMSTR.

sgiar

Sets construction variables for the SGI library archiver.

Sets: $AR, $ARCOMSTR, $ARFLAGS, $LIBPREFIX, $LIBSUFFIX, $SHLINK, $SHLINKFLAGS.

Uses: $ARCOMSTR, $SHLINKCOMSTR.

sgic++

Sets construction variables for the SGI C++ compiler.

Sets: $CXX, $CXXFLAGS, $SHCXX, $SHOBJSUFFIX.

sgicc

Sets construction variables for the SGI C compiler.

Sets: $CXX, $SHOBJSUFFIX.

sgilink

Sets construction variables for the SGI linker.

Sets: $LINK, $RPATHPREFIX, $RPATHSUFFIX, $SHLINKFLAGS.

sunar

Sets construction variables for the Sun library archiver.

Sets: $AR, $ARCOM, $ARFLAGS, $LIBPREFIX, $LIBSUFFIX, $SHLINK, $SHLINKCOM, $SHLINKFLAGS.

Uses: $ARCOMSTR, $SHLINKCOMSTR.

sunc++

Sets construction variables for the Sun C++ compiler.

Sets: $CXX, $CXXVERSION, $SHCXX, $SHCXXFLAGS, $SHOBJPREFIX, $SHOBJSUFFIX.

suncc

Sets construction variables for the Sun C compiler.

Sets: $CXX, $SHCCFLAGS, $SHOBJPREFIX, $SHOBJSUFFIX.

sunf77

Set construction variables for the Sun f77 Fortran compiler.

Sets: $F77, $FORTRAN, $SHF77, $SHF77FLAGS, $SHFORTRAN, $SHFORTRANFLAGS.

sunf90

Set construction variables for the Sun f90 Fortran compiler.

Sets: $F90, $FORTRAN, $SHF90, $SHF90FLAGS, $SHFORTRAN, $SHFORTRANFLAGS.

sunf95

Set construction variables for the Sun f95 Fortran compiler.

Sets: $F95, $FORTRAN, $SHF95, $SHF95FLAGS, $SHFORTRAN, $SHFORTRANFLAGS.

sunlink

Sets construction variables for the Sun linker.

Sets: $RPATHPREFIX, $RPATHSUFFIX, $SHLINKFLAGS.

swig

Sets construction variables for the SWIG interface generator.

Sets: $SWIG, $SWIGCFILESUFFIX, $SWIGCOM, $SWIGCXXFILESUFFIX, $SWIGDIRECTORSUFFIX, $SWIGFLAGS, $SWIGINCPREFIX, $SWIGINCSUFFIX, $SWIGPATH, $SWIGVERSION, $_SWIGINCFLAGS.

Uses: $SWIGCOMSTR.

tar

Sets construction variables for the tar archiver.

Sets: $TAR, $TARCOM, $TARFLAGS, $TARSUFFIX.

Uses: $TARCOMSTR.

tex

Sets construction variables for the TeX formatter and typesetter.

Sets: $BIBTEX, $BIBTEXCOM, $BIBTEXFLAGS, $LATEX, $LATEXCOM, $LATEXFLAGS, $MAKEINDEX, $MAKEINDEXCOM, $MAKEINDEXFLAGS, $TEX, $TEXCOM, $TEXFLAGS.

Uses: $BIBTEXCOMSTR, $LATEXCOMSTR, $MAKEINDEXCOMSTR, $TEXCOMSTR.

textfile

Set construction variables for the Textfile and Substfile builders.

Sets: $LINESEPARATOR, $SUBSTFILEPREFIX, $SUBSTFILESUFFIX, $TEXTFILEPREFIX, $TEXTFILESUFFIX.

Uses: $SUBST_DICT.

tlib

Sets construction variables for the Borlan tib library archiver.

Sets: $AR, $ARCOM, $ARFLAGS, $LIBPREFIX, $LIBSUFFIX.

Uses: $ARCOMSTR.

xgettext

This scons tool is a part of scons gettext toolset. It provides scons interface to xgettext(1) program, which extracts internationalized messages from source code. The tool provides POTUpdate builder to make PO Template files.

Sets: $POTSUFFIX, $POTUPDATE_ALIAS, $XGETTEXTCOM, $XGETTEXTCOMSTR, $XGETTEXTFLAGS, $XGETTEXTFROM, $XGETTEXTFROMPREFIX, $XGETTEXTFROMSUFFIX, $XGETTEXTPATH, $XGETTEXTPATHPREFIX, $XGETTEXTPATHSUFFIX, $_XGETTEXTDOMAIN, $_XGETTEXTFROMFLAGS, $_XGETTEXTPATHFLAGS.

Uses: $POTDOMAIN.

yacc

Sets construction variables for the yacc parse generator.

Sets: $YACC, $YACCCOM, $YACCFLAGS, $YACCHFILESUFFIX, $YACCHXXFILESUFFIX, $YACCVCGFILESUFFIX.

Uses: $YACCCOMSTR.

zip

Sets construction variables for the zip archiver.

Sets: $ZIP, $ZIPCOM, $ZIPCOMPRESSION, $ZIPFLAGS, $ZIPSUFFIX.

Uses: $ZIPCOMSTR.

Appendix D. Functions and Environment Methods

This appendix contains descriptions of all of the function and construction environment methods in this version of SCons

Action(action, [cmd/str/fun, [var, ...]] [option=value, ...]) , env.Action(action, [cmd/str/fun, [var, ...]] [option=value, ...])

Creates an Action object for the specified action. See the section "Action Objects," below, for a complete explanation of the arguments and behavior.

Note that the env.Action() form of the invocation will expand construction variables in any argument strings, including the action argument, at the time it is called using the construction variables in the env construction environment through which env.Action() was called. The Action() form delays all variable expansion until the Action object is actually used.

AddMethod(object, function, [name]) , env.AddMethod(function, [name])

When called with the AddMethod() form, adds the specified function to the specified object as the specified method name. When called with the env.AddMethod() form, adds the specified function to the construction environment env as the specified method name. In both cases, if name is omitted or None, the name of the specified function itself is used for the method name.

Examples:

# Note that the first argument to the function to
# be attached as a method must be the object through
# which the method will be called; the Python
# convention is to call it 'self'.
def my_method(self, arg):
    print "my_method() got", arg

# Use the global AddMethod() function to add a method
# to the Environment class.  This
AddMethod(Environment, my_method)
env = Environment()
env.my_method('arg')

# Add the function as a method, using the function
# name for the method call.
env = Environment()
env.AddMethod(my_method, 'other_method_name')
env.other_method_name('another arg')
AddOption(arguments)

This function adds a new command-line option to be recognized. The specified arguments are the same as supported by the standard Python optparse.add_option() method (with a few additional capabilities noted below); see the documentation for optparse for a thorough discussion of its option-processing capabities.

In addition to the arguments and values supported by the optparse.add_option() method, the SCons AddOption function allows you to set the nargs keyword value to '?' (a string with just the question mark) to indicate that the specified long option(s) take(s) an optional argument. When nargs = '?' is passed to the AddOption function, the const keyword argument may be used to supply the "default" value that should be used when the option is specified on the command line without an explicit argument.

If no default= keyword argument is supplied when calling AddOption, the option will have a default value of None.

Once a new command-line option has been added with AddOption, the option value may be accessed using GetOption or env.GetOption(). The value may also be set, using SetOption or env.SetOption(), if conditions in a SConscript require overriding any default value. Note, however, that a value specified on the command line will always override a value set by any SConscript file.

Any specified help= strings for the new option(s) will be displayed by the -H or -h options (the latter only if no other help text is specified in the SConscript files). The help text for the local options specified by AddOption will appear below the SCons options themselves, under a separate Local Options heading. The options will appear in the help text in the order in which the AddOption calls occur.

Example:

AddOption('--prefix',
          dest='prefix',
          nargs=1, type='string',
          action='store',
          metavar='DIR',
          help='installation prefix')
env = Environment(PREFIX = GetOption('prefix'))
AddPostAction(target, action) , env.AddPostAction(target, action)

Arranges for the specified action to be performed after the specified target has been built. The specified action(s) may be an Action object, or anything that can be converted into an Action object (see below).

When multiple targets are supplied, the action may be called multiple times, once after each action that generates one or more targets in the list.

AddPreAction(target, action) , env.AddPreAction(target, action)

Arranges for the specified action to be performed before the specified target is built. The specified action(s) may be an Action object, or anything that can be converted into an Action object (see below).

When multiple targets are specified, the action(s) may be called multiple times, once before each action that generates one or more targets in the list.

Note that if any of the targets are built in multiple steps, the action will be invoked just before the "final" action that specifically generates the specified target(s). For example, when building an executable program from a specified source .c file via an intermediate object file:

foo = Program('foo.c')
AddPreAction(foo, 'pre_action')

The specified pre_action would be executed before scons calls the link command that actually generates the executable program binary foo, not before compiling the foo.c file into an object file.

Alias(alias, [targets, [action]]) , env.Alias(alias, [targets, [action]])

Creates one or more phony targets that expand to one or more other targets. An optional action (command) or list of actions can be specified that will be executed whenever the any of the alias targets are out-of-date. Returns the Node object representing the alias, which exists outside of any file system. This Node object, or the alias name, may be used as a dependency of any other target, including another alias. Alias can be called multiple times for the same alias to add additional targets to the alias, or additional actions to the list for this alias.

Examples:

Alias('install')
Alias('install', '/usr/bin')
Alias(['install', 'install-lib'], '/usr/local/lib')

env.Alias('install', ['/usr/local/bin', '/usr/local/lib'])
env.Alias('install', ['/usr/local/man'])

env.Alias('update', ['file1', 'file2'], "update_database $SOURCES")
AllowSubstExceptions([exception, ...])

Specifies the exceptions that will be allowed when expanding construction variables. By default, any construction variable expansions that generate a NameError or IndexError exception will expand to a '' (a null string) and not cause scons to fail. All exceptions not in the specified list will generate an error message and terminate processing.

If AllowSubstExceptions is called multiple times, each call completely overwrites the previous list of allowed exceptions.

Example:

# Requires that all construction variable names exist.
# (You may wish to do this if you want to enforce strictly
# that all construction variables must be defined before use.)
AllowSubstExceptions()

# Also allow a string containing a zero-division expansion
# like '${1 / 0}' to evalute to ''.
AllowSubstExceptions(IndexError, NameError, ZeroDivisionError)
AlwaysBuild(target, ...) , env.AlwaysBuild(target, ...)

Marks each given target so that it is always assumed to be out of date, and will always be rebuilt if needed. Note, however, that AlwaysBuild does not add its target(s) to the default target list, so the targets will only be built if they are specified on the command line, or are a dependent of a target specified on the command line--but they will always be built if so specified. Multiple targets can be passed in to a single call to AlwaysBuild.

env.Append(key=val, [...])

Appends the specified keyword arguments to the end of construction variables in the environment. If the Environment does not have the specified construction variable, it is simply added to the environment. If the values of the construction variable and the keyword argument are the same type, then the two values will be simply added together. Otherwise, the construction variable and the value of the keyword argument are both coerced to lists, and the lists are added together. (See also the Prepend method, below.)

Example:

env.Append(CCFLAGS = ' -g', FOO = ['foo.yyy'])
env.AppendENVPath(name, newpath, [envname, sep, delete_existing])

This appends new path elements to the given path in the specified external environment (ENV by default). This will only add any particular path once (leaving the last one it encounters and ignoring the rest, to preserve path order), and to help assure this, will normalize all paths (using os.path.normpath and os.path.normcase). This can also handle the case where the given old path variable is a list instead of a string, in which case a list will be returned instead of a string.

If delete_existing is 0, then adding a path that already exists will not move it to the end; it will stay where it is in the list.

Example:

print 'before:',env['ENV']['INCLUDE']
include_path = '/foo/bar:/foo'
env.AppendENVPath('INCLUDE', include_path)
print 'after:',env['ENV']['INCLUDE']

yields:
before: /foo:/biz
after: /biz:/foo/bar:/foo
env.AppendUnique(key=val, [...], delete_existing=0)

Appends the specified keyword arguments to the end of construction variables in the environment. If the Environment does not have the specified construction variable, it is simply added to the environment. If the construction variable being appended to is a list, then any value(s) that already exist in the construction variable will not be added again to the list. However, if delete_existing is 1, existing matching values are removed first, so existing values in the arg list move to the end of the list.

Example:

env.AppendUnique(CCFLAGS = '-g', FOO = ['foo.yyy'])
env.BitKeeper()

A factory function that returns a Builder object to be used to fetch source files using BitKeeper. The returned Builder is intended to be passed to the SourceCode function.

This function is deprecated. For details, see the entry for the SourceCode function.

Example:

env.SourceCode('.', env.BitKeeper())
BuildDir(build_dir, src_dir, [duplicate]) , env.BuildDir(build_dir, src_dir, [duplicate])

Deprecated synonyms for VariantDir and env.VariantDir(). The build_dir argument becomes the variant_dir argument of VariantDir or env.VariantDir().

Builder(action, [arguments]) , env.Builder(action, [arguments])

Creates a Builder object for the specified action. See the section "Builder Objects," below, for a complete explanation of the arguments and behavior.

Note that the env.Builder() form of the invocation will expand construction variables in any arguments strings, including the action argument, at the time it is called using the construction variables in the env construction environment through which env.Builder() was called. The Builder form delays all variable expansion until after the Builder object is actually called.

CacheDir(cache_dir) , env.CacheDir(cache_dir)

Specifies that scons will maintain a cache of derived files in cache_dir. The derived files in the cache will be shared among all the builds using the same CacheDir call. Specifying a cache_dir of None disables derived file caching.

Calling env.CacheDir() will only affect targets built through the specified construction environment. Calling CacheDir sets a global default that will be used by all targets built through construction environments that do not have an env.CacheDir() specified.

When a CacheDir() is being used and scons finds a derived file that needs to be rebuilt, it will first look in the cache to see if a derived file has already been built from identical input files and an identical build action (as incorporated into the MD5 build signature). If so, scons will retrieve the file from the cache. If the derived file is not present in the cache, scons will rebuild it and then place a copy of the built file in the cache (identified by its MD5 build signature), so that it may be retrieved by other builds that need to build the same derived file from identical inputs.

Use of a specified CacheDir may be disabled for any invocation by using the --cache-disable option.

If the --cache-force option is used, scons will place a copy of all derived files in the cache, even if they already existed and were not built by this invocation. This is useful to populate a cache the first time CacheDir is added to a build, or after using the --cache-disable option.

When using CacheDir, scons will report, "Retrieved `file' from cache," unless the --cache-show option is being used. When the --cache-show option is used, scons will print the action that would have been used to build the file, without any indication that the file was actually retrieved from the cache. This is useful to generate build logs that are equivalent regardless of whether a given derived file has been built in-place or retrieved from the cache.

The NoCache method can be used to disable caching of specific files. This can be useful if inputs and/or outputs of some tool are impossible to predict or prohibitively large.

Clean(targets, files_or_dirs) , env.Clean(targets, files_or_dirs)

This specifies a list of files or directories which should be removed whenever the targets are specified with the -c command line option. The specified targets may be a list or an individual target. Multiple calls to Clean are legal, and create new targets or add files and directories to the clean list for the specified targets.

Multiple files or directories should be specified either as separate arguments to the Clean method, or as a list. Clean will also accept the return value of any of the construction environment Builder methods. Examples:

The related NoClean function overrides calling Clean for the same target, and any targets passed to both functions will not be removed by the -c option.

Examples:

Clean('foo', ['bar', 'baz'])
Clean('dist', env.Program('hello', 'hello.c'))
Clean(['foo', 'bar'], 'something_else_to_clean')

In this example, installing the project creates a subdirectory for the documentation. This statement causes the subdirectory to be removed if the project is deinstalled.

Clean(docdir, os.path.join(docdir, projectname))
env.Clone([key=val, ...])

Returns a separate copy of a construction environment. If there are any keyword arguments specified, they are added to the returned copy, overwriting any existing values for the keywords.

Example:

env2 = env.Clone()
env3 = env.Clone(CCFLAGS = '-g')

Additionally, a list of tools and a toolpath may be specified, as in the Environment constructor:

def MyTool(env): env['FOO'] = 'bar'
env4 = env.Clone(tools = ['msvc', MyTool])

The parse_flags keyword argument is also recognized:

# create an environment for compiling programs that use wxWidgets
wx_env = env.Clone(parse_flags = '!wx-config --cflags --cxxflags')
Command(target, source, action, [key=val, ...]) , env.Command(target, source, action, [key=val, ...])

Executes a specific action (or list of actions) to build a target file or files. This is more convenient than defining a separate Builder object for a single special-case build.

As a special case, the source_scanner keyword argument can be used to specify a Scanner object that will be used to scan the sources. (The global DirScanner object can be used if any of the sources will be directories that must be scanned on-disk for changes to files that aren't already specified in other Builder of function calls.)

Any other keyword arguments specified override any same-named existing construction variables.

An action can be an external command, specified as a string, or a callable Python object; see "Action Objects," below, for more complete information. Also note that a string specifying an external command may be preceded by an @ (at-sign) to suppress printing the command in question, or by a - (hyphen) to ignore the exit status of the external command.

Examples:

env.Command('foo.out', 'foo.in',
            "$FOO_BUILD < $SOURCES > $TARGET")

env.Command('bar.out', 'bar.in',
            ["rm -f $TARGET",
             "$BAR_BUILD < $SOURCES > $TARGET"],
            ENV = {'PATH' : '/usr/local/bin/'})

def rename(env, target, source):
    import os
    os.rename('.tmp', str(target[0]))

env.Command('baz.out', 'baz.in',
            ["$BAZ_BUILD < $SOURCES > .tmp",
	     rename ])

Note that the Command function will usually assume, by default, that the specified targets and/or sources are Files, if no other part of the configuration identifies what type of entry it is. If necessary, you can explicitly specify that targets or source nodes should be treated as directoriese by using the Dir or env.Dir() functions.

Examples:

env.Command('ddd.list', Dir('ddd'), 'ls -l $SOURCE > $TARGET')

env['DISTDIR'] = 'destination/directory'
env.Command(env.Dir('$DISTDIR')), None, make_distdir)

(Also note that SCons will usually automatically create any directory necessary to hold a target file, so you normally don't need to create directories by hand.)

Configure(env, [custom_tests, conf_dir, log_file, config_h]) , env.Configure([custom_tests, conf_dir, log_file, config_h])

Creates a Configure object for integrated functionality similar to GNU autoconf. See the section "Configure Contexts," below, for a complete explanation of the arguments and behavior.

env.Copy([key=val, ...])

A now-deprecated synonym for env.Clone().

env.CVS(repository, module)

A factory function that returns a Builder object to be used to fetch source files from the specified CVS repository. The returned Builder is intended to be passed to the SourceCode function.

This function is deprecated. For details, see the entry for the SourceCode function.

The optional specified module will be added to the beginning of all repository path names; this can be used, in essence, to strip initial directory names from the repository path names, so that you only have to replicate part of the repository directory hierarchy in your local build directory.

Examples:

# Will fetch foo/bar/src.c
# from /usr/local/CVSROOT/foo/bar/src.c.
env.SourceCode('.', env.CVS('/usr/local/CVSROOT'))

# Will fetch bar/src.c
# from /usr/local/CVSROOT/foo/bar/src.c.
env.SourceCode('.', env.CVS('/usr/local/CVSROOT', 'foo'))

# Will fetch src.c
# from /usr/local/CVSROOT/foo/bar/src.c.
env.SourceCode('.', env.CVS('/usr/local/CVSROOT', 'foo/bar'))
Decider(function) , env.Decider(function)

Specifies that all up-to-date decisions for targets built through this construction environment will be handled by the specified function. The function can be one of the following strings that specify the type of decision function to be performed:

timestamp-newer

Specifies that a target shall be considered out of date and rebuilt if the dependency's timestamp is newer than the target file's timestamp. This is the behavior of the classic Make utility, and make can be used a synonym for timestamp-newer.

timestamp-match

Specifies that a target shall be considered out of date and rebuilt if the dependency's timestamp is different than the timestamp recorded the last time the target was built. This provides behavior very similar to the classic Make utility (in particular, files are not opened up so that their contents can be checksummed) except that the target will also be rebuilt if a dependency file has been restored to a version with an earlier timestamp, such as can happen when restoring files from backup archives.

MD5

Specifies that a target shall be considered out of date and rebuilt if the dependency's content has changed sine the last time the target was built, as determined be performing an MD5 checksum on the dependency's contents and comparing it to the checksum recorded the last time the target was built. content can be used as a synonym for MD5.

MD5-timestamp

Specifies that a target shall be considered out of date and rebuilt if the dependency's content has changed sine the last time the target was built, except that dependencies with a timestamp that matches the last time the target was rebuilt will be assumed to be up-to-date and not rebuilt. This provides behavior very similar to the MD5 behavior of always checksumming file contents, with an optimization of not checking the contents of files whose timestamps haven't changed. The drawback is that SCons will not detect if a file's content has changed but its timestamp is the same, as might happen in an automated script that runs a build, updates a file, and runs the build again, all within a single second.

Examples:

# Use exact timestamp matches by default.
Decider('timestamp-match')

# Use MD5 content signatures for any targets built
# with the attached construction environment.
env.Decider('content')

In addition to the above already-available functions, the function argument may be an actual Python function that takes the following three arguments:

dependency

The Node (file) which should cause the target to be rebuilt if it has "changed" since the last tme target was built.

target

The Node (file) being built. In the normal case, this is what should get rebuilt if the dependency has "changed."

prev_ni

Stored information about the state of the dependency the last time the target was built. This can be consulted to match various file characteristics such as the timestamp, size, or content signature.

The function should return a True (non-zero) value if the dependency has "changed" since the last time the target was built (indicating that the target should be rebuilt), and False (zero) otherwise (indicating that the target should not be rebuilt). Note that the decision can be made using whatever criteria are appopriate. Ignoring some or all of the function arguments is perfectly normal.

Example:

def my_decider(dependency, target, prev_ni):
    return not os.path.exists(str(target))

env.Decider(my_decider)
Default(targets) , env.Default(targets)

This specifies a list of default targets, which will be built by scons if no explicit targets are given on the command line. Multiple calls to Default are legal, and add to the list of default targets.

Multiple targets should be specified as separate arguments to the Default method, or as a list. Default will also accept the Node returned by any of a construction environment's builder methods.

Examples:

Default('foo', 'bar', 'baz')
env.Default(['a', 'b', 'c'])
hello = env.Program('hello', 'hello.c')
env.Default(hello)

An argument to Default of None will clear all default targets. Later calls to Default will add to the (now empty) default-target list like normal.

The current list of targets added using the Default function or method is available in the DEFAULT_TARGETS list; see below.

DefaultEnvironment([args])

Creates and returns a default construction environment object. This construction environment is used internally by SCons in order to execute many of the global functions in this list, and to fetch source files transparently from source code management systems.

Depends(target, dependency) , env.Depends(target, dependency)

Specifies an explicit dependency; the target will be rebuilt whenever the dependency has changed. Both the specified target and dependency can be a string (usually the path name of a file or directory) or Node objects, or a list of strings or Node objects (such as returned by a Builder call). This should only be necessary for cases where the dependency is not caught by a Scanner for the file.

Example:

env.Depends('foo', 'other-input-file-for-foo')

mylib = env.Library('mylib.c')
installed_lib = env.Install('lib', mylib)
bar = env.Program('bar.c')

# Arrange for the library to be copied into the installation
# directory before trying to build the "bar" program.
# (Note that this is for example only.  A "real" library
# dependency would normally be configured through the $LIBS
# and $LIBPATH variables, not using an env.Depends() call.)

env.Depends(bar, installed_lib)
env.Dictionary([vars])

Returns a dictionary object containing copies of all of the construction variables in the environment. If there are any variable names specified, only the specified construction variables are returned in the dictionary.

Example:

dict = env.Dictionary()
cc_dict = env.Dictionary('CC', 'CCFLAGS', 'CCCOM')
Dir(name, [directory]) , env.Dir(name, [directory])

This returns a Directory Node, an object that represents the specified directory name. name can be a relative or absolute path. directory is an optional directory that will be used as the parent directory. If no directory is specified, the current script's directory is used as the parent.

If name is a list, SCons returns a list of Dir nodes. Construction variables are expanded in name.

Directory Nodes can be used anywhere you would supply a string as a directory name to a Builder method or function. Directory Nodes have attributes and methods that are useful in many situations; see "File and Directory Nodes," below.

env.Dump([key])

Returns a pretty printable representation of the environment. key, if not None, should be a string containing the name of the variable of interest.

This SConstruct:

env=Environment()
print env.Dump('CCCOM')

will print:

'$CC -c -o $TARGET $CCFLAGS $CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS $SOURCES'

While this SConstruct:

env=Environment()
print env.Dump()

will print:

{ 'AR': 'ar',
  'ARCOM': '$AR $ARFLAGS $TARGET $SOURCES\n$RANLIB $RANLIBFLAGS $TARGET',
  'ARFLAGS': ['r'],
  'AS': 'as',
  'ASCOM': '$AS $ASFLAGS -o $TARGET $SOURCES',
  'ASFLAGS': [],
  ...
EnsurePythonVersion(major, minor) , env.EnsurePythonVersion(major, minor)

Ensure that the Python version is at least major.minor. This function will print out an error message and exit SCons with a non-zero exit code if the actual Python version is not late enough.

Example:

EnsurePythonVersion(2,2)
EnsureSConsVersion(major, minor, [revision]) , env.EnsureSConsVersion(major, minor, [revision])

Ensure that the SCons version is at least major.minor, or major.minor.revision. if revision is specified. This function will print out an error message and exit SCons with a non-zero exit code if the actual SCons version is not late enough.

Examples:

EnsureSConsVersion(0,14)

EnsureSConsVersion(0,96,90)
Environment([key=value, ...]) , env.Environment([key=value, ...])

Return a new construction environment initialized with the specified key=value pairs.

Execute(action, [strfunction, varlist]) , env.Execute(action, [strfunction, varlist])

Executes an Action object. The specified action may be an Action object (see the section "Action Objects," below, for a complete explanation of the arguments and behavior), or it may be a command-line string, list of commands, or executable Python function, each of which will be converted into an Action object and then executed. The exit value of the command or return value of the Python function will be returned.

Note that scons will print an error message if the executed action fails--that is, exits with or returns a non-zero value. scons will not, however, automatically terminate the build if the specified action fails. If you want the build to stop in response to a failed Execute call, you must explicitly check for a non-zero return value:

Execute(Copy('file.out', 'file.in'))

if Execute("mkdir sub/dir/ectory"):
    # The mkdir failed, don't try to build.
    Exit(1)
Exit([value]) , env.Exit([value])

This tells scons to exit immediately with the specified value. A default exit value of 0 (zero) is used if no value is specified.

Export(vars) , env.Export(vars)

This tells scons to export a list of variables from the current SConscript file to all other SConscript files. The exported variables are kept in a global collection, so subsequent calls to Export will over-write previous exports that have the same name. Multiple variable names can be passed to Export as separate arguments or as a list. Keyword arguments can be used to provide names and their values. A dictionary can be used to map variables to a different name when exported. Both local variables and global variables can be exported.

Examples:

env = Environment()
# Make env available for all SConscript files to Import().
Export("env")

package = 'my_name'
# Make env and package available for all SConscript files:.
Export("env", "package")

# Make env and package available for all SConscript files:
Export(["env", "package"])

# Make env available using the name debug:
Export(debug = env)

# Make env available using the name debug:
Export({"debug":env})

Note that the SConscript function supports an exports argument that makes it easier to to export a variable or set of variables to a single SConscript file. See the description of the SConscript function, below.

File(name, [directory]) , env.File(name, [directory])

This returns a File Node, an object that represents the specified file name. name can be a relative or absolute path. directory is an optional directory that will be used as the parent directory.

If name is a list, SCons returns a list of File nodes. Construction variables are expanded in name.

File Nodes can be used anywhere you would supply a string as a file name to a Builder method or function. File Nodes have attributes and methods that are useful in many situations; see "File and Directory Nodes," below.

FindFile(file, dirs) , env.FindFile(file, dirs)

Search for file in the path specified by dirs. dirs may be a list of directory names or a single directory name. In addition to searching for files that exist in the filesystem, this function also searches for derived files that have not yet been built.

Example:

foo = env.FindFile('foo', ['dir1', 'dir2'])
FindInstalledFiles() , env.FindInstalledFiles()

Returns the list of targets set up by the Install or InstallAs builders.

This function serves as a convenient method to select the contents of a binary package.

Example:

Install( '/bin', [ 'executable_a', 'executable_b' ] )

# will return the file node list
# [ '/bin/executable_a', '/bin/executable_b' ]
FindInstalledFiles()

Install( '/lib', [ 'some_library' ] )

# will return the file node list
# [ '/bin/executable_a', '/bin/executable_b', '/lib/some_library' ]
FindInstalledFiles()
FindPathDirs(variable)

Returns a function (actually a callable Python object) intended to be used as the path_function of a Scanner object. The returned object will look up the specified variable in a construction environment and treat the construction variable's value as a list of directory paths that should be searched (like $CPPPATH, $LIBPATH, etc.).

Note that use of FindPathDirs is generally preferable to writing your own path_function for the following reasons: 1) The returned list will contain all appropriate directories found in source trees (when VariantDir is used) or in code repositories (when Repository or the -Y option are used). 2) scons will identify expansions of variable that evaluate to the same list of directories as, in fact, the same list, and avoid re-scanning the directories for files, when possible.

Example:

def my_scan(node, env, path, arg):
    # Code to scan file contents goes here...
    return include_files

scanner = Scanner(name = 'myscanner',
                  function = my_scan,
                  path_function = FindPathDirs('MYPATH'))
FindSourceFiles(node='"."') , env.FindSourceFiles(node='"."')

Returns the list of nodes which serve as the source of the built files. It does so by inspecting the dependency tree starting at the optional argument node which defaults to the '"."'-node. It will then return all leaves of node. These are all children which have no further children.

This function is a convenient method to select the contents of a Source Package.

Example:

Program( 'src/main_a.c' )
Program( 'src/main_b.c' )
Program( 'main_c.c' )

# returns ['main_c.c', 'src/main_a.c', 'SConstruct', 'src/main_b.c']
FindSourceFiles()

# returns ['src/main_b.c', 'src/main_a.c' ]
FindSourceFiles( 'src' )

As you can see build support files (SConstruct in the above example) will also be returned by this function.

Flatten(sequence) , env.Flatten(sequence)

Takes a sequence (that is, a Python list or tuple) that may contain nested sequences and returns a flattened list containing all of the individual elements in any sequence. This can be helpful for collecting the lists returned by calls to Builders; other Builders will automatically flatten lists specified as input, but direct Python manipulation of these lists does not.

Examples:

foo = Object('foo.c')
bar = Object('bar.c')

# Because `foo' and `bar' are lists returned by the Object() Builder,
# `objects' will be a list containing nested lists:
objects = ['f1.o', foo, 'f2.o', bar, 'f3.o']

# Passing such a list to another Builder is all right because
# the Builder will flatten the list automatically:
Program(source = objects)

# If you need to manipulate the list directly using Python, you need to
# call Flatten() yourself, or otherwise handle nested lists:
for object in Flatten(objects):
    print str(object)
GetBuildFailures()

Returns a list of exceptions for the actions that failed while attempting to build targets. Each element in the returned list is a BuildError object with the following attributes that record various aspects of the build failure:

.node The node that was being built when the build failure occurred.

.status The numeric exit status returned by the command or Python function that failed when trying to build the specified Node.

.errstr The SCons error string describing the build failure. (This is often a generic message like "Error 2" to indicate that an executed command exited with a status of 2.)

.filename The name of the file or directory that actually caused the failure. This may be different from the .node attribute. For example, if an attempt to build a target named sub/dir/target fails because the sub/dir directory could not be created, then the .node attribute will be sub/dir/target but the .filename attribute will be sub/dir.

.executor The SCons Executor object for the target Node being built. This can be used to retrieve the construction environment used for the failed action.

.action The actual SCons Action object that failed. This will be one specific action out of the possible list of actions that would have been executed to build the target.

.command The actual expanded command that was executed and failed, after expansion of $TARGET, $SOURCE, and other construction variables.

Note that the GetBuildFailures function will always return an empty list until any build failure has occurred, which means that GetBuildFailures will always return an empty list while the SConscript files are being read. Its primary intended use is for functions that will be executed before SCons exits by passing them to the standard Python atexit.register() function. Example:

import atexit

def print_build_failures():
    from SCons.Script import GetBuildFailures
    for bf in GetBuildFailures():
        print "%s failed: %s" % (bf.node, bf.errstr)

atexit.register(print_build_failures)
GetBuildPath(file, [...]) , env.GetBuildPath(file, [...])

Returns the scons path name (or names) for the specified file (or files). The specified file or files may be scons Nodes or strings representing path names.

GetLaunchDir() , env.GetLaunchDir()

Returns the absolute path name of the directory from which scons was initially invoked. This can be useful when using the -u, -U or -D options, which internally change to the directory in which the SConstruct file is found.

GetOption(name) , env.GetOption(name)

This function provides a way to query the value of SCons options set on scons command line (or set using the SetOption function). The options supported are:

cache_debug

which corresponds to --cache-debug;

cache_disable

which corresponds to --cache-disable;

cache_force

which corresponds to --cache-force;

cache_show

which corresponds to --cache-show;

clean

which corresponds to -c, --clean and --remove;

config

which corresponds to --config;

directory

which corresponds to -C and --directory;

diskcheck

which corresponds to --diskcheck

duplicate

which corresponds to --duplicate;

file

which corresponds to -f, --file, --makefile and --sconstruct;

help

which corresponds to -h and --help;

ignore_errors

which corresponds to --ignore-errors;

implicit_cache

which corresponds to --implicit-cache;

implicit_deps_changed

which corresponds to --implicit-deps-changed;

implicit_deps_unchanged

which corresponds to --implicit-deps-unchanged;

interactive

which corresponds to --interact and --interactive;

keep_going

which corresponds to -k and --keep-going;

max_drift

which corresponds to --max-drift;

no_exec

which corresponds to -n, --no-exec, --just-print, --dry-run and --recon;

no_site_dir

which corresponds to --no-site-dir;

num_jobs

which corresponds to -j and --jobs;

profile_file

which corresponds to --profile;

question

which corresponds to -q and --question;

random

which corresponds to --random;

repository

which corresponds to -Y, --repository and --srcdir;

silent

which corresponds to -s, --silent and --quiet;

site_dir

which corresponds to --site-dir;

stack_size

which corresponds to --stack-size;

taskmastertrace_file

which corresponds to --taskmastertrace; and

warn

which corresponds to --warn and --warning.

See the documentation for the corresponding command line object for information about each specific option.

Glob(pattern, [ondisk, source, strings]) , env.Glob(pattern, [ondisk, source, strings])

Returns Nodes (or strings) that match the specified pattern, relative to the directory of the current SConscript file. The env.Glob() form performs string substition on pattern and returns whatever matches the resulting expanded pattern.

The specified pattern uses Unix shell style metacharacters for matching:

  *       matches everything
  ?       matches any single character
  [seq]   matches any character in seq
  [!seq]  matches any char not in seq

If the first character of a filename is a dot, it must be matched explicitly. Character matches do not span directory separators.

The Glob knows about repositories (see the Repository function) and source directories (see the VariantDir function) and returns a Node (or string, if so configured) in the local (SConscript) directory if matching Node is found anywhere in a corresponding repository or source directory.

The ondisk argument may be set to False (or any other non-true value) to disable the search for matches on disk, thereby only returning matches among already-configured File or Dir Nodes. The default behavior is to return corresponding Nodes for any on-disk matches found.

The source argument may be set to True (or any equivalent value) to specify that, when the local directory is a VariantDir, the returned Nodes should be from the corresponding source directory, not the local directory.

The strings argument may be set to True (or any equivalent value) to have the Glob function return strings, not Nodes, that represent the matched files or directories. The returned strings will be relative to the local (SConscript) directory. (Note that This may make it easier to perform arbitrary manipulation of file names, but if the returned strings are passed to a different SConscript file, any Node translation will be relative to the other SConscript directory, not the original SConscript directory.)

Examples:

Program('foo', Glob('*.c'))
Zip('/tmp/everything', Glob('.??*') + Glob('*'))
Help(text) , env.Help(text)

This specifies help text to be printed if the -h argument is given to scons. If Help is called multiple times, the text is appended together in the order that Help is called.

Ignore(target, dependency) , env.Ignore(target, dependency)

The specified dependency file(s) will be ignored when deciding if the target file(s) need to be rebuilt.

You can also use Ignore to remove a target from the default build. In order to do this you must specify the directory the target will be built in as the target, and the file you want to skip building as the dependency.

Note that this will only remove the dependencies listed from the files built by default. It will still be built if that dependency is needed by another object being built. See the third and forth examples below.

Examples:

env.Ignore('foo', 'foo.c')
env.Ignore('bar', ['bar1.h', 'bar2.h'])
env.Ignore('.','foobar.obj')
env.Ignore('bar','bar/foobar.obj')
Import(vars) , env.Import(vars)

This tells scons to import a list of variables into the current SConscript file. This will import variables that were exported with Export or in the exports argument to SConscript. Variables exported by SConscript have precedence. Multiple variable names can be passed to Import as separate arguments or as a list. The variable "*" can be used to import all variables.

Examples:

Import("env")
Import("env", "variable")
Import(["env", "variable"])
Import("*")
Literal(string) , env.Literal(string)

The specified string will be preserved as-is and not have construction variables expanded.

Local(targets) , env.Local(targets)

The specified targets will have copies made in the local tree, even if an already up-to-date copy exists in a repository. Returns a list of the target Node or Nodes.

env.MergeFlags(arg, [unique])

Merges the specified arg values to the construction environment's construction variables. If the arg argument is not a dictionary, it is converted to one by calling env.ParseFlags on the argument before the values are merged. Note that arg must be a single value, so multiple strings must be passed in as a list, not as separate arguments to env.MergeFlags.

By default, duplicate values are eliminated; you can, however, specify unique=0 to allow duplicate values to be added. When eliminating duplicate values, any construction variables that end with the string PATH keep the left-most unique value. All other construction variables keep the right-most unique value.

Examples:

# Add an optimization flag to $CCFLAGS.
env.MergeFlags('-O3')

# Combine the flags returned from running pkg-config with an optimization
# flag and merge the result into the construction variables.
env.MergeFlags(['!pkg-config gtk+-2.0 --cflags', '-O3'])

# Combine an optimization flag with the flags returned from running pkg-config
# twice and merge the result into the construction variables.
env.MergeFlags(['-O3',
               '!pkg-config gtk+-2.0 --cflags --libs',
               '!pkg-config libpng12 --cflags --libs'])
NoCache(target, ...) , env.NoCache(target, ...)

Specifies a list of files which should not be cached whenever the CacheDir method has been activated. The specified targets may be a list or an individual target.

Multiple files should be specified either as separate arguments to the NoCache method, or as a list. NoCache will also accept the return value of any of the construction environment Builder methods.

Calling NoCache on directories and other non-File Node types has no effect because only File Nodes are cached.

Examples:

NoCache('foo.elf')
NoCache(env.Program('hello', 'hello.c'))
NoClean(target, ...) , env.NoClean(target, ...)

Specifies a list of files or directories which should not be removed whenever the targets (or their dependencies) are specified with the -c command line option. The specified targets may be a list or an individual target. Multiple calls to NoClean are legal, and prevent each specified target from being removed by calls to the -c option.

Multiple files or directories should be specified either as separate arguments to the NoClean method, or as a list. NoClean will also accept the return value of any of the construction environment Builder methods.

Calling NoClean for a target overrides calling Clean for the same target, and any targets passed to both functions will not be removed by the -c option.

Examples:

NoClean('foo.elf')
NoClean(env.Program('hello', 'hello.c'))
env.ParseConfig(command, [function, unique])

Calls the specified function to modify the environment as specified by the output of command. The default function is env.MergeFlags, which expects the output of a typical *-config command (for example, gtk-config) and adds the options to the appropriate construction variables. By default, duplicate values are not added to any construction variables; you can specify unique=0 to allow duplicate values to be added.

Interpreted options and the construction variables they affect are as specified for the env.ParseFlags method (which this method calls). See that method's description, below, for a table of options and construction variables.

ParseDepends(filename, [must_exist, only_one]) , env.ParseDepends(filename, [must_exist, only_one])

Parses the contents of the specified filename as a list of dependencies in the style of Make or mkdep, and explicitly establishes all of the listed dependencies.

By default, it is not an error if the specified filename does not exist. The optional must_exist argument may be set to a non-zero value to have scons throw an exception and generate an error if the file does not exist, or is otherwise inaccessible.

The optional only_one argument may be set to a non-zero value to have scons thrown an exception and generate an error if the file contains dependency information for more than one target. This can provide a small sanity check for files intended to be generated by, for example, the gcc -M flag, which should typically only write dependency information for one output file into a corresponding .d file.

The filename and all of the files listed therein will be interpreted relative to the directory of the SConscript file which calls the ParseDepends function.

env.ParseFlags(flags, ...)

Parses one or more strings containing typical command-line flags for GCC tool chains and returns a dictionary with the flag values separated into the appropriate SCons construction variables. This is intended as a companion to the env.MergeFlags method, but allows for the values in the returned dictionary to be modified, if necessary, before merging them into the construction environment. (Note that env.MergeFlags will call this method if its argument is not a dictionary, so it is usually not necessary to call env.ParseFlags directly unless you want to manipulate the values.)

If the first character in any string is an exclamation mark (!), the rest of the string is executed as a command, and the output from the command is parsed as GCC tool chain command-line flags and added to the resulting dictionary.

Flag values are translated accordig to the prefix found, and added to the following construction variables:

-arch               CCFLAGS, LINKFLAGS
-D                  CPPDEFINES
-framework          FRAMEWORKS
-frameworkdir=      FRAMEWORKPATH
-include            CCFLAGS
-isysroot           CCFLAGS, LINKFLAGS
-I                  CPPPATH
-l                  LIBS
-L                  LIBPATH
-mno-cygwin         CCFLAGS, LINKFLAGS
-mwindows           LINKFLAGS
-pthread            CCFLAGS, LINKFLAGS
-std=               CFLAGS
-Wa,                ASFLAGS, CCFLAGS
-Wl,-rpath=         RPATH
-Wl,-R,             RPATH
-Wl,-R              RPATH
-Wl,                LINKFLAGS
-Wp,                CPPFLAGS
-                   CCFLAGS
+                   CCFLAGS, LINKFLAGS

Any other strings not associated with options are assumed to be the names of libraries and added to the $LIBS construction variable.

Examples (all of which produce the same result):

dict = env.ParseFlags('-O2 -Dfoo -Dbar=1')
dict = env.ParseFlags('-O2', '-Dfoo', '-Dbar=1')
dict = env.ParseFlags(['-O2', '-Dfoo -Dbar=1'])
dict = env.ParseFlags('-O2', '!echo -Dfoo -Dbar=1')
env.Perforce()

A factory function that returns a Builder object to be used to fetch source files from the Perforce source code management system. The returned Builder is intended to be passed to the SourceCode function.

This function is deprecated. For details, see the entry for the SourceCode function.

Example:

env.SourceCode('.', env.Perforce())

Perforce uses a number of external environment variables for its operation. Consequently, this function adds the following variables from the user's external environment to the construction environment's ENV dictionary: P4CHARSET, P4CLIENT, P4LANGUAGE, P4PASSWD, P4PORT, P4USER, SystemRoot, USER, and USERNAME.

Platform(string)

The Platform form returns a callable object that can be used to initialize a construction environment using the platform keyword of the Environment function.

Example:

env = Environment(platform = Platform('win32'))

The env.Platform form applies the callable object for the specified platform string to the environment through which the method was called.

env.Platform('posix')

Note that the win32 platform adds the SystemDrive and SystemRoot variables from the user's external environment to the construction environment's $ENV dictionary. This is so that any executed commands that use sockets to connect with other systems (such as fetching source files from external CVS repository specifications like :pserver:anonymous@cvs.sourceforge.net:/cvsroot/scons) will work on Windows systems.

Precious(target, ...) , env.Precious(target, ...)

Marks each given target as precious so it is not deleted before it is rebuilt. Normally scons deletes a target before building it. Multiple targets can be passed in to a single call to Precious.

env.Prepend(key=val, [...])

Appends the specified keyword arguments to the beginning of construction variables in the environment. If the Environment does not have the specified construction variable, it is simply added to the environment. If the values of the construction variable and the keyword argument are the same type, then the two values will be simply added together. Otherwise, the construction variable and the value of the keyword argument are both coerced to lists, and the lists are added together. (See also the Append method, above.)

Example:

env.Prepend(CCFLAGS = '-g ', FOO = ['foo.yyy'])
env.PrependENVPath(name, newpath, [envname, sep, delete_existing])

This appends new path elements to the given path in the specified external environment ($ENV by default). This will only add any particular path once (leaving the first one it encounters and ignoring the rest, to preserve path order), and to help assure this, will normalize all paths (using os.path.normpath and os.path.normcase). This can also handle the case where the given old path variable is a list instead of a string, in which case a list will be returned instead of a string.

If delete_existing is 0, then adding a path that already exists will not move it to the beginning; it will stay where it is in the list.

Example:

print 'before:',env['ENV']['INCLUDE']
include_path = '/foo/bar:/foo'
env.PrependENVPath('INCLUDE', include_path)
print 'after:',env['ENV']['INCLUDE']

The above example will print:

before: /biz:/foo
after: /foo/bar:/foo:/biz
env.PrependUnique(key=val, delete_existing=0, [...])

Appends the specified keyword arguments to the beginning of construction variables in the environment. If the Environment does not have the specified construction variable, it is simply added to the environment. If the construction variable being appended to is a list, then any value(s) that already exist in the construction variable will not be added again to the list. However, if delete_existing is 1, existing matching values are removed first, so existing values in the arg list move to the front of the list.

Example:

env.PrependUnique(CCFLAGS = '-g', FOO = ['foo.yyy'])
Progress(callable, [interval]) , Progress(string, [interval, file, overwrite]) , Progress(list_of_strings, [interval, file, overwrite])

Allows SCons to show progress made during the build by displaying a string or calling a function while evaluating Nodes (e.g. files).

If the first specified argument is a Python callable (a function or an object that has a __call__() method), the function will be called once every interval times a Node is evaluated. The callable will be passed the evaluated Node as its only argument. (For future compatibility, it's a good idea to also add *args and **kw as arguments to your function or method. This will prevent the code from breaking if SCons ever changes the interface to call the function with additional arguments in the future.)

An example of a simple custom progress function that prints a string containing the Node name every 10 Nodes:

def my_progress_function(node, *args, **kw):
    print 'Evaluating node %s!' % node
Progress(my_progress_function, interval=10)

A more complicated example of a custom progress display object that prints a string containing a count every 100 evaluated Nodes. Note the use of \r (a carriage return) at the end so that the string will overwrite itself on a display:

import sys
class ProgressCounter(object):
    count = 0
    def __call__(self, node, *args, **kw):
        self.count += 100
        sys.stderr.write('Evaluated %s nodes\r' % self.count)
Progress(ProgressCounter(), interval=100)

If the first argument Progress is a string, the string will be displayed every interval evaluated Nodes. The default is to print the string on standard output; an alternate output stream may be specified with the file= argument. The following will print a series of dots on the error output, one dot for every 100 evaluated Nodes:

import sys
Progress('.', interval=100, file=sys.stderr)

If the string contains the verbatim substring $TARGET, it will be replaced with the Node. Note that, for performance reasons, this is not a regular SCons variable substition, so you can not use other variables or use curly braces. The following example will print the name of every evaluated Node, using a \r (carriage return) to cause each line to overwritten by the next line, and the overwrite= keyword argument to make sure the previously-printed file name is overwritten with blank spaces:

import sys
Progress('$TARGET\r', overwrite=True)

If the first argument to Progress is a list of strings, then each string in the list will be displayed in rotating fashion every interval evaluated Nodes. This can be used to implement a "spinner" on the user's screen as follows:

Progress(['-\r', '\\\r', '|\r', '/\r'], interval=5)
Pseudo(target, ...) , env.Pseudo(target, ...)

This indicates that each given target should not be created by the build rule, and if the target is created, an error will be generated. This is similar to the gnu make .PHONY target. However, in the vast majority of cases, an Alias is more appropriate. Multiple targets can be passed in to a single call to Pseudo.

env.RCS()

A factory function that returns a Builder object to be used to fetch source files from RCS. The returned Builder is intended to be passed to the SourceCode function:

This function is deprecated. For details, see the entry for the SourceCode function.

Examples:

env.SourceCode('.', env.RCS())

Note that scons will fetch source files from RCS subdirectories automatically, so configuring RCS as demonstrated in the above example should only be necessary if you are fetching from RCS,v files in the same directory as the source files, or if you need to explicitly specify RCS for a specific subdirectory.

env.Replace(key=val, [...])

Replaces construction variables in the Environment with the specified keyword arguments.

Example:

env.Replace(CCFLAGS = '-g', FOO = 'foo.xxx')
Repository(directory) , env.Repository(directory)

Specifies that directory is a repository to be searched for files. Multiple calls to Repository are legal, and each one adds to the list of repositories that will be searched.

To scons, a repository is a copy of the source tree, from the top-level directory on down, which may contain both source files and derived files that can be used to build targets in the local source tree. The canonical example would be an official source tree maintained by an integrator. If the repository contains derived files, then the derived files should have been built using scons, so that the repository contains the necessary signature information to allow scons to figure out when it is appropriate to use the repository copy of a derived file, instead of building one locally.

Note that if an up-to-date derived file already exists in a repository, scons will not make a copy in the local directory tree. In order to guarantee that a local copy will be made, use the Local method.

Requires(target, prerequisite) , env.Requires(target, prerequisite)

Specifies an order-only relationship between the specified target file(s) and the specified prerequisite file(s). The prerequisite file(s) will be (re)built, if necessary, before the target file(s), but the target file(s) do not actually depend on the prerequisites and will not be rebuilt simply because the prerequisite file(s) change.

Example:

env.Requires('foo', 'file-that-must-be-built-before-foo')
Return([vars..., stop=])

By default, this stops processing the current SConscript file and returns to the calling SConscript file the values of the variables named in the vars string arguments. Multiple strings contaning variable names may be passed to Return. Any strings that contain white space

The optional stop= keyword argument may be set to a false value to continue processing the rest of the SConscript file after the Return call. This was the default behavior prior to SCons 0.98. However, the values returned are still the values of the variables in the named vars at the point Return is called.

Examples:

# Returns without returning a value.
Return()

# Returns the value of the 'foo' Python variable.
Return("foo")

# Returns the values of the Python variables 'foo' and 'bar'.
Return("foo", "bar")

# Returns the values of Python variables 'val1' and 'val2'.
Return('val1 val2')
Scanner(function, [argument, keys, path_function, node_class, node_factory, scan_check, recursive]) , env.Scanner(function, [argument, keys, path_function, node_class, node_factory, scan_check, recursive])

Creates a Scanner object for the specified function. See the section "Scanner Objects," below, for a complete explanation of the arguments and behavior.

env.SCCS()

A factory function that returns a Builder object to be used to fetch source files from SCCS. The returned Builder is intended to be passed to the SourceCode function.

Example:

env.SourceCode('.', env.SCCS())

Note that scons will fetch source files from SCCS subdirectories automatically, so configuring SCCS as demonstrated in the above example should only be necessary if you are fetching from s.SCCS files in the same directory as the source files, or if you need to explicitly specify SCCS for a specific subdirectory.

SConscript(scripts, [exports, variant_dir, duplicate]) , env.SConscript(scripts, [exports, variant_dir, duplicate]) , SConscript(dirs=subdirs, [name=script, exports, variant_dir, duplicate]) , env.SConscript(dirs=subdirs, [name=script, exports, variant_dir, duplicate])

This tells scons to execute one or more subsidiary SConscript (configuration) files. Any variables returned by a called script using Return will be returned by the call to SConscript. There are two ways to call the SConscript function.

The first way you can call SConscript is to explicitly specify one or more scripts as the first argument. A single script may be specified as a string; multiple scripts must be specified as a list (either explicitly or as created by a function like Split). Examples:

SConscript('SConscript')      # run SConscript in the current directory
SConscript('src/SConscript')  # run SConscript in the src directory
SConscript(['src/SConscript', 'doc/SConscript'])
config = SConscript('MyConfig.py')

The second way you can call SConscript is to specify a list of (sub)directory names as a dirs=subdirs keyword argument. In this case, scons will, by default, execute a subsidiary configuration file named SConscript in each of the specified directories. You may specify a name other than SConscript by supplying an optional name=script keyword argument. The first three examples below have the same effect as the first three examples above:

SConscript(dirs='.')      # run SConscript in the current directory
SConscript(dirs='src')    # run SConscript in the src directory
SConscript(dirs=['src', 'doc'])
SConscript(dirs=['sub1', 'sub2'], name='MySConscript')

The optional exports argument provides a list of variable names or a dictionary of named values to export to the script(s). These variables are locally exported only to the specified script(s), and do not affect the global pool of variables used by the Export function. The subsidiary script(s) must use the Import function to import the variables. Examples:

foo = SConscript('sub/SConscript', exports='env')
SConscript('dir/SConscript', exports=['env', 'variable'])
SConscript(dirs='subdir', exports='env variable')
SConscript(dirs=['one', 'two', 'three'], exports='shared_info')

If the optional variant_dir argument is present, it causes an effect equivalent to the VariantDir method described below. (If variant_dir is not present, the duplicate argument is ignored.) The variant_dir argument is interpreted relative to the directory of the calling SConscript file. See the description of the VariantDir function below for additional details and restrictions.

If variant_dir is present, the source directory is the directory in which the SConscript file resides and the SConscript file is evaluated as if it were in the variant_dir directory:

SConscript('src/SConscript', variant_dir = 'build')

is equivalent to

VariantDir('build', 'src')
SConscript('build/SConscript')

This later paradigm is often used when the sources are in the same directory as the SConstruct:

SConscript('SConscript', variant_dir = 'build')

is equivalent to

VariantDir('build', '.')
SConscript('build/SConscript')

Here are some composite examples:

# collect the configuration information and use it to build src and doc
shared_info = SConscript('MyConfig.py')
SConscript('src/SConscript', exports='shared_info')
SConscript('doc/SConscript', exports='shared_info')
# build debugging and production versions.  SConscript
# can use Dir('.').path to determine variant.
SConscript('SConscript', variant_dir='debug', duplicate=0)
SConscript('SConscript', variant_dir='prod', duplicate=0)
# build debugging and production versions.  SConscript
# is passed flags to use.
opts = { 'CPPDEFINES' : ['DEBUG'], 'CCFLAGS' : '-pgdb' }
SConscript('SConscript', variant_dir='debug', duplicate=0, exports=opts)
opts = { 'CPPDEFINES' : ['NODEBUG'], 'CCFLAGS' : '-O' }
SConscript('SConscript', variant_dir='prod', duplicate=0, exports=opts)
# build common documentation and compile for different architectures
SConscript('doc/SConscript', variant_dir='build/doc', duplicate=0)
SConscript('src/SConscript', variant_dir='build/x86', duplicate=0)
SConscript('src/SConscript', variant_dir='build/ppc', duplicate=0)
SConscriptChdir(value) , env.SConscriptChdir(value)

By default, scons changes its working directory to