A factory function to create an Action object for the specified action. See the manpage section "Action Objects" 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 global function form delays all variable expansion until the Action object is actually used.

Adds function to an object as a method. function will be called with an instance object as the first argument as for other methods. If name is given, it is used as the name of the new method, else the name of function is used.

When the global function AddMethod is called, the object to add the method to must be passed as the first argument; typically this will be Environment, in order to create a method which applies to all construction environments subsequently constructed. When called using the env.AddMethod form, the method is added to the specified construction environment only. Added methods propagate through env.Clone calls.

More examples:

# Function to add must accept an instance argument.
# The Python convention is to call this 'self'.
def my_method(self, arg):
    print("my_method() got", arg)

# Use the global function to add a method to the Environment class:
AddMethod(Environment, my_method)
env = Environment()
env.my_method('arg')

# Use the optional name argument to set the name of the method:
env.AddMethod(my_method, 'other_method_name')
env.other_method_name('another arg')

Adds a local (project-specific) command-line option. arguments are the same as those supported by the add_option method in the standard Python library module optparse, 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, AddOption allows setting the nargs keyword value to a string consisting of a question mark ('?') to indicate that the option argument for that option string is optional. If the option string is present on the command line but has no matching option argument, the value of the const keyword argument is produced as the value of the option. If the option string is omitted from the command line, the value of the default keyword argument is produced, as usual; if there is no default keyword argument in the AddOption call, None is produced.

optparse recognizes abbreviations of long option names, as long as they can be unambiguously resolved. For example, if add_option is called to define a --devicename option, it will recognize --device, --dev and so forth as long as there is no other option which could also match to the same abbreviation. Options added via AddOption do not support the automatic recognition of abbreviations. Instead, to allow specific abbreviations, include them as synonyms in the AddOption call itself.

Once a new command-line option has been added with AddOption, the option value may be accessed using GetOption or env.GetOption. SetOption is not currently supported for options added with AddOption.

Help text for an option is a combination of the string supplied in the help keyword argument to AddOption and information collected from the other keyword arguments. Such help is displayed if the -h command line option is used (but not with -H). Help for all local options is displayed under the separate heading Local Options. The options are unsorted - they 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'))

For that example, the following help text would be produced:

Local Options:
  --prefix=DIR                installation prefix

Help text for local options may be unavailable if the Help function has been called, see the Help documentation for details.

Arranges for the specified action to be performed after the specified target has been built. action may be an Action object, or anything that can be converted into an Action object. See the manpage section "Action Objects" for a complete explanation.

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.

foo = Program('foo.c')
# remove execute permission from binary:
AddPostAction(foo, Chmod('$TARGET', "a-x"))

Arranges for the specified action to be performed before the specified target is built. action may be an Action object, or anything that can be converted into an Action object. See the manpage section "Action Objects" for a complete explanation.

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.

Creates an alias target that can be used as a reference to zero or more other targets, specified by the optional source parameter. Aliases provide a way to give a shorter or more descriptive name to specific targets, and to group multiple targets under a single name. The alias name, or an Alias Node object, may be used as a dependency of any other target, including another alias.

alias and source may each be a string or Node object, or a list of strings or Node objects; if Nodes are used for alias they must be Alias nodes. If source is omitted, the alias is created but has no reference; if selected for building this will result in a “Nothing to be done.” message. An empty alias can be used to define the alias in a visible place in the project; it can later be appended to in a subsidiary SConscript file with the actual target(s) to refer to. The optional action parameter specifies an action or list of actions that will be executed whenever the any of the alias targets are out-of-date.

Alias can be called for an existing alias, which appends the alias and/or action arguments to the existing lists for that alias.

Returns a list of Alias Node objects representing the alias(es), which exist outside of any physical file system. The alias name space is separate from the name space for tangible targets; to avoid confusion do not reuse target names as alias names.

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")

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 '' (an empty 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)

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.

Appends value(s) intelligently to construction variables in env. The construction variables and values to add to them are passed as key=val pairs (Python keyword arguments). env.Append is designed to allow adding values without having to think about the data type of an existing construction variable. Regular Python syntax can also be used to manipulate the construction variable, but for that you may need to know the types involved, for example pure Python lets you directly "add" two lists of strings, but adding a string to a list or a list to a string requires different syntax - things Append takes care of. Some pre-defined construction variables do have type expectations based on how SCons will use them: for example $CPPDEFINES is often a string or a list of strings, but can also be a list of tuples or a dictionary; while $LIBEMITTER is expected to be a callable or list of callables, and $BUILDERS is expected to be a dictionary. Consult the documentation for the various construction variables for more details.

The following descriptions apply to both the Append and Prepend methods, as well as their Unique variants, with the differences being the insertion point of the added values and whether duplication is allowed.

val can be almost any type. If env does not have a construction variable named key, then key is simply stored with a value of val. Otherwise, val is combinined with the existing value, possibly converting into an appropriate type which can hold the expanded contents. There are a few special cases to be aware of. Normally, when two strings are combined, the result is a new string containing their concatenation (and you are responsible for supplying any needed separation); however, the contents of $CPPDEFINES will will be postprocessed by adding a prefix and/or suffix to each entry when the command line is produced, so SCons keeps them separate - appending a string will result in a separate string entry, not a combined string. For $CPPDEFINES. as well as $LIBS, and the various *PATH variables, SCons will amend the variable by supplying the compiler-specific syntax (e.g. prepending a -D or /D prefix for $CPPDEFINES), so you should omit this syntax when adding values to these variables. Examples (gcc syntax shown in the expansion of CPPDEFINES):

env = Environment(CXXFLAGS="-std=c11", CPPDEFINES="RELEASE")
print(f"CXXFLAGS = {env['CXXFLAGS']}, CPPDEFINES = {env['CPPDEFINES']}")
# notice including a leading space in CXXFLAGS addition
env.Append(CXXFLAGS=" -O", CPPDEFINES="EXTRA")
print(f"CXXFLAGS = {env['CXXFLAGS']}, CPPDEFINES = {env['CPPDEFINES']}")
print("CPPDEFINES will expand to", env.subst('$_CPPDEFFLAGS'))

$ scons -Q
CXXFLAGS = -std=c11, CPPDEFINES = RELEASE
CXXFLAGS = -std=c11 -O, CPPDEFINES = deque(['RELEASE', 'EXTRA'])
CPPDEFINES will expand to -DRELEASE -DEXTRA
scons: `.' is up to date.

Because $CPPDEFINES is intended for command-line specification of C/C++ preprocessor macros, additional syntax is accepted when adding to it. The preprocessor accepts arguments to predefine a macro name by itself (-DFOO for most compilers, /DFOO for Microsoft C++), which gives it an implicit value of 1, or can be given with a replacement value (-DBAR=TEXT). SCons follows these rules when adding to $CPPDEFINES:

Examples:

env = Environment(CPPDEFINES="FOO")
print("CPPDEFINES =", env['CPPDEFINES'])
env.Append(CPPDEFINES="BAR=1")
print("CPPDEFINES =", env['CPPDEFINES'])
env.Append(CPPDEFINES=[("OTHER", 2)])
print("CPPDEFINES =", env['CPPDEFINES'])
env.Append(CPPDEFINES={"EXTRA": "arg"})
print("CPPDEFINES =", env['CPPDEFINES'])
print("CPPDEFINES will expand to", env.subst('$_CPPDEFFLAGS'))

$ scons -Q
CPPDEFINES = FOO
CPPDEFINES = deque(['FOO', 'BAR=1'])
CPPDEFINES = deque(['FOO', 'BAR=1', ('OTHER', 2)])
CPPDEFINES = deque(['FOO', 'BAR=1', ('OTHER', 2), ('EXTRA', 'arg')])
CPPDEFINES will expand to -DFOO -DBAR=1 -DOTHER=2 -DEXTRA=arg
scons: `.' is up to date.

Examples of adding multiple macros:

env = Environment()
env.Append(CPPDEFINES=[("ONE", 1), "TWO", ("THREE", )])
print("CPPDEFINES =", env['CPPDEFINES'])
env.Append(CPPDEFINES={"FOUR": 4, "FIVE": None})
print("CPPDEFINES =", env['CPPDEFINES'])
print("CPPDEFINES will expand to", env.subst('$_CPPDEFFLAGS'))

$ scons -Q
CPPDEFINES = [('ONE', 1), 'TWO', ('THREE',)]
CPPDEFINES = deque([('ONE', 1), 'TWO', ('THREE',), ('FOUR', 4), ('FIVE', None)])
CPPDEFINES will expand to -DONE=1 -DTWO -DTHREE -DFOUR=4 -DFIVE
scons: `.' is up to date.

Changed in version 4.5: clarifined the use of tuples vs. other types, handling is now consistent across the four functions.

env = Environment()
env.Append(CPPDEFINES=("MACRO1", "MACRO2"))
print("CPPDEFINES =", env['CPPDEFINES'])
env.Append(CPPDEFINES=[("MACRO3", "MACRO4")])
print("CPPDEFINES =", env['CPPDEFINES'])
print("CPPDEFINES will expand to", env.subst('$_CPPDEFFLAGS'))

$ scons -Q
CPPDEFINES = ('MACRO1', 'MACRO2')
CPPDEFINES = deque(['MACRO1', 'MACRO2', ('MACRO3', 'MACRO4')])
CPPDEFINES will expand to -DMACRO1 -DMACRO2 -DMACRO3=MACRO4
scons: `.' is up to date.

See $CPPDEFINES for more details.

Appending a string val to a dictonary-typed construction variable enters val as the key in the dictionary, and None as its value. Using a tuple type to supply a key-value pair only works for the special case of $CPPDEFINES described above.

Although most combinations of types work without needing to know the details, some combinations do not make sense and Python raises an exception.

When using env.Append to modify construction variables which are path specifications (conventionally, the names of such end in PATH), it is recommended to add the values as a list of strings, even if you are only adding a single string. The same goes for adding library names to $LIBS.

env.Append(CPPPATH=["#/include"])

See also env.AppendUnique, env.Prepend and env.PrependUnique.

Append path elements specified by newpath to the given search path string or list name in mapping envname in the construction environment. Supplying envname is optional: the default is the execution environment $ENV. Optional sep is used as the search path separator, the default is the platform's separator (os.pathsep). A path element will only appear once. Any duplicates in newpath are dropped, keeping the last appearing (to preserve path order). If delete_existing is False (the default) any addition duplicating an existing path element is ignored; if delete_existing is True the existing value will be dropped and the path element will be added at the end. To help maintain uniqueness all paths are normalized (using os.path.normpath and os.path.normcase).

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

See also env.PrependENVPath.

Append values to construction variables in the current construction environment, maintaining uniqueness. Works like env.Append, except that values that would become duplicates are not added. If delete_existing is set to a true value, then for any duplicate, the existing instance of val is first removed, then val is appended, having the effect of moving it to the end.

Example:

env.AppendUnique(CCFLAGS='-g', FOO=['foo.yyy'])

See also env.Append, env.Prepend and env.PrependUnique.

Creates a Builder object for the specified action. See the manpage section "Builder Objects" 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.

Direct scons to maintain a derived-file cache in cache_dir. The derived files in the cache will be shared among all the builds specifying the same cache_dir. Specifying a cache_dir of None disables derived file caching.

Calling the environment method env.CacheDir limits the effect to targets built through the specified construction environment. Calling the global function CacheDir sets a global default that will be used by all targets built through construction environments that do not set up environment-specific caching by calling env.CacheDir.

Caching behavior can be configured by passing a specialized cache class as the optional custom_class parameter. This class must be a subclass of SCons.CacheDir.CacheDir. SCons will internally invoke the custom class for performing caching operations. If the parameter is omitted or set to None, SCons will use the default SCons.CacheDir.CacheDir class.

When derived-file caching 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 file with matching build signature exists (indicating the input file(s) and build action(s) were identical to those for the current target), and if so, will retrieve the file from the cache. scons will report Retrieved `file' from cache instead of the normal build message. If the derived file is not present in the cache, scons will build it and then place a copy of the built file in the cache, identified by its build signature, for future use.

The Retrieved `file' from cache messages are useful for human consumption, but less useful when comparing log files between scons runs which will show differences that are noisy and not actually significant. To disable, use the --cache-show option. With this option, scons changes printing to always show the action that would have been used to build the file without caching.

Derived-file caching may be disabled for any invocation of scons by giving the --cache-disable command line option; cache updating may be disabled, leaving cache fetching enabled, by giving the --cache-readonly option.

If the --cache-force option is used, scons will place a copy of all derived files into the cache, even if they already existed and were not built by this invocation. This is useful to populate a cache the first time a cache_dir is used for a build, or to bring a cache up to date after a build with cache updating disabled (--cache-disable or --cache-readonly) has been done.

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.

Note that (at this time) SCons provides no facilities for managing the derived-file cache. It is up to the developer to arrange for cache pruning, expiry, access control, etc. if needed.

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))

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 to allow merging command-line style arguments into the appropriate construction variables (see env.MergeFlags).

# create an environment for compiling programs that use wxWidgets
wx_env = env.Clone(parse_flags='!wx-config --cflags --cxxflags')

Executes a specific action (or list of actions) to build a target file or files from a source file or files. This is more convenient than defining a separate Builder object for a single special-case build.

The Command function accepts source_scanner, target_scanner, source_factory, and target_factory keyword arguments. These arguments can be used to specify a Scanner object that will be used to apply a custom scanner for a source or target. For example, 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. The *_factory arguments take a factory function that Command will use to turn any sources or targets specified as strings into SCons Nodes. See the manpage section "Builder Objects" for more information about how these arguments work in a Builder.

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 the manpage section "Action Objects" 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(
    target='foo.out',
    source='foo.in',
    action="$FOO_BUILD < $SOURCES > $TARGET"
)

env.Command(
    target='bar.out',
    source='bar.in',
    action=["rm -f $TARGET", "$BAR_BUILD < $SOURCES > $TARGET"],
    ENV={'PATH': '/usr/local/bin/'},
)


import os
def rename(env, target, source):
    os.rename('.tmp', str(target[0]))


env.Command(
    target='baz.out',
    source='baz.in',
    action=["$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 entries they are. If necessary, you can explicitly specify that targets or source nodes should be treated as directories 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.

Creates a Configure object for integrated functionality similar to GNU autoconf. See the manpage section "Configure Contexts" for a complete explanation of the arguments and behavior.

Allows setting options for SCons debug options. Currently the only supported value is json which sets the path to the json file created when --debug=json is set.

DebugOptions(json='#/build/output/scons_stats.json')

Specifies that all up-to-date decisions for targets built through this construction environment will be handled by the specified function. function can be the name of a function or one of the following strings that specify the predefined decision function that will be applied:

Examples:

# Use exact timestamp matches by default.
Decider('timestamp-match')

# Use hash 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 a Python function you supply. Such a function must accept the following four arguments:

The function should return a value which evaluates True if the dependency has "changed" since the last time the target was built (indicating that the target should be rebuilt), and a value which evaluates False 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, repo_node=None):
    return not os.path.exists(str(target))

env.Decider(my_decider)

Specify default targets to the SCons target selection mechanism. Any call to Default will cause SCons to use the defined default target list instead of its built-in algorithm for determining default targets (see the manpage section "Target Selection").

target may be one or more strings, a list of strings, a NodeList as returned by a Builder, or None. A string target may be the name of a file or directory, or a target previously defined by a call to Alias (defining the alias later will still create the alias, but it will not be recognized as a default). Calls to Default are additive. A target of None will clear any existing default target list; subsequent calls to Default will add to the (now empty) default target list like normal.

Both forms of this call affect the same global list of default targets; the construction environment method applies construction variable expansion to the targets.

The current list of targets added using Default is available in the DEFAULT_TARGETS list (see below).

Examples:

Default('foo', 'bar', 'baz')
env.Default(['a', 'b', 'c'])
hello = env.Program('hello', 'hello.c')
env.Default(hello)

Instantiates and returns the global construction environment object. This environment is used internally by SCons when it executes many of the global functions listed in this section (that is, those not called as methods of a specific construction environment). The default environment is a singleton: the keyword arguments are used only on the first call; on subsequent calls the already-constructed object is returned and any keyword arguments are silently ignored. The default environment can still be modified after instantiation in the same way as any other construction environment. The default environment is independent: modifying it has no effect on any other construction environment constructed by an Environment or Clone call.

It is not mandatory to call DefaultEnvironment: the default environment is instantiated automatically when the build phase begins if this function has not been called; however calling it explicitly gives the opportunity to affect and examine the contents of the default environment. Instantiation happens even if no build instructions appar to use it, as there are internal uses. If there are no uses in the project SConscript files, a small performance gain may be seen by calling DefaultEnvironment with an empty tools list, thus avoiding that part of the initialization cost. This is mainly of interest in testing when scons is launched repeatedly in a short time period:

DefaultEnvironment(tools=[])

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)

Find an executable from one or more choices: progs may be a string or a list of strings. Returns the first value from progs that was found, or None. Executable is searched by checking the paths in the execution environment (env['ENV']['PATH']). On Windows systems, additionally applies the filename suffixes found in the execution environment (env['ENV']['PATHEXT']) but will not include any such extension in the return value. env.Detect is a wrapper around env.WhereIs.

Returns a dictionary object containing the construction variables in the construction environment. If there are any arguments specified, the values of the specified construction variables are returned as a string (if one argument) or as a list of strings.

Example:

cvars = env.Dictionary()
cc_values = env.Dictionary('CC', 'CCFLAGS', 'CCCOM')

Returns Directory Node(s). A Directory Node is an object that represents a directory. name can be a relative or absolute path or a list of such paths. 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 single pathname, the corresponding node is returned. If name is a list, SCons returns a list of 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 manpage section "File and Directory Nodes" for more information.

Serializes construction variables to a string. The method supports the following formats specified by format:

If key is None (the default) the entire dictionary of construction variables is serialized. If supplied, it is taken as the name of a construction variable whose value is serialized.

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': [],
  ...

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)

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)

Return a new construction environment initialized with the specified key=value pairs. The keyword arguments parse_flags, platform, toolpath, tools and variables are also specially recognized. See the manpage section "Construction Environments" for more details.

Executes an Action. action may be an Action object or it may be a command-line string, list of commands, or executable Python function, each of which will first be converted into an Action object and then executed. Any additional arguments to Execute are passed on to the Action factory function which actually creates the Action object (see the manpage section Action Objects for a description). Example:

Execute(Copy('file.out', 'file.in'))

Execute performs its action immediately, as part of the SConscript-reading phase. There are no sources or targets declared in an Execute call, so any objects it manipulates will not be tracked as part of the SCons dependency graph. In the example above, neither file.out nor file.in will be tracked objects.

Execute returns the exit value of the command or return value of the Python function. scons prints an error message if the executed action fails (exits with or returns a non-zero value), however it does not, automatically terminate the build for such a failure. If you want the build to stop in response to a failed Execute call, you must explicitly check for a non-zero return value:

if Execute("mkdir sub/dir/ectory"):
    # The mkdir failed, don't try to build.
    Exit(1)

This tells scons to exit immediately with the specified value. A default exit value of 0 (zero) is used if no value is specified.

Exports variables for sharing with other SConscript files. The variables are added to a global collection where they can be imported by other SConscript files. vars may be one or more strings, or a list of strings. If any string contains whitespace, it is split automatically into individual strings. Each string must match the name of a variable that is in scope during evaluation of the current SConscript file, or an exception is raised.

A vars argument may also be a dictionary or individual keyword arguments; in accordance with Python syntax rules, keyword arguments must come after any non-keyword arguments. The dictionary/keyword form can be used to map the local name of a variable to a different name to be used for imports. See the Examples for an illustration of the syntax.

Export calls are cumulative. Specifying a previously exported variable will replace the previous value in the collection. Both local variables and global variables can be exported.

To use an exported variable, an SConscript must call Import to bring it into its own scope. Importing creates an additional reference to the object that was originally exported, so if that object is mutable, changes made will be visible to other users of that object.

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 also supports an exports argument that allows exporting one or more variables to the SConscript files invoked by that call (only). See the description of that function for details.

Returns File Node(s). A File Node is an object that represents a file. name can be a relative or absolute path or a list of such paths. 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 single pathname, the corresponding node is returned. If name is a list, SCons returns a list of 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 manpage section "File and Directory Nodes" for more information.

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'])

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()

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'))

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.

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))

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)

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.

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.

Query the value of settable options which may have been set on the command line, or by using the SetOption function. The value of the option is returned in a type matching how the option was declared - see the documentation for the corresponding command line option for information about each specific option.

name can be an entry from the following table, which shows the corresponding command line arguments that could affect the value. name can be also be the destination variable name from a project-specific option added using the AddOption function, as long as that addition has been processed prior to the GetOption call in the SConscript files.

Returns a possibly empty list of Nodes (or strings) that match pathname specification pattern. pattern can be absolute, top-relative, or (most commonly) relative to the directory of the current SConscript file. Glob matches both files stored on disk and Nodes which SCons already knows about, even if any corresponding file is not currently stored on disk. The evironment method form (env.Glob) performs string substition on pattern and returns whatever matches the resulting expanded pattern. The results are sorted, unlike for the similar Python glob.glob function, to ensure build order will be stable.

pattern can contain POSIX-style shell metacharacters for matching:

For a literal match, wrap the metacharacter in brackets to escape the normal behavior. For example, '[?]' matches the character '?'.

Filenames starting with a dot are specially handled - they can only be matched by patterns that start with a dot (or have a dot immediately following a pathname separator character, or slash), they are not not matched by the metacharacters. Metacharacter matches also do not span directory separators.

Glob understands repositories (see the Repository function) and source directories (see the VariantDir function) and returns a Node (or string, if so configured) match in the local (SConscript) directory if a matching Node is found anywhere in a corresponding repository or source directory.

If the optional ondisk argument evaluates false, the search for matches on disk is disabled, and only matches from already-configured File or Dir Nodes are returned. The default is to return Nodes for matches on disk as well.

If the optional source argument evaluates true, and the local directory is a variant directory, then Glob returnes Nodes from the corresponding source directory, rather than the local directory.

If the optional strings argument evaluates true, Glob returns matches as strings, rather than Nodes. The returned strings will be relative to the local (SConscript) directory. (Note that while this may make it easier to perform arbitrary manipulation of file names, it loses the context SCons would have in the Node, so if the returned strings are passed to a different SConscript file, any Node translation there will be relative to that SConscript directory, not to the original SConscript directory.)

The optional exclude argument may be set to a pattern or a list of patterns descibing files or directories to filter out of the match list. Elements matching a least one specified pattern will be excluded. These patterns use the same syntax as for pattern.

Examples:

Program("foo", Glob("*.c"))
Zip("/tmp/everything", Glob(".??*") + Glob("*"))
sources = Glob("*.cpp", exclude=["os_*_specific_*.cpp"]) \
    + Glob("os_%s_specific_*.cpp" % currentOS)

Adds text to the help message shown when scons is called with the -h or --help argument.

On the first call to Help, if append is False (the default), any existing help text is discarded. The default help text is the help for the scons command itself plus help collected from any project-local AddOption calls. This is the help printed if Help has never been called. If append is True, text is appended to the existing help text. If local_only is also True (the default is False), the project-local help from AddOption calls is preserved in the help message but the scons command help is not.

Subsequent calls to Help ignore the keyword arguments append and local_only and always append to the existing help text.

Changed in 4.6.0: added local_only.

Ignores dependency when deciding if target needs to be rebuilt. target and dependency can each be a single filename or Node or a list of filenames or Nodes.

Ignore can also be used to remove a target from the default build by specifying the directory the target will be built in as target and the file you want to skip selecting for building as dependency. Note that this only removes the target from the default target selection algorithm: if it is a dependency of another object being built SCons still builds it normally. 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')

Imports variables into the scope of the current SConscript file. vars must be strings representing names of variables which have been previously exported either by the Export function or by the exports argument to the SConscript function. Variables exported by the SConscript call take precedence. Multiple variable names can be passed to Import as separate arguments, as a list of strings, or as words in a space-separated string. The wildcard "*" can be used to import all available variables.

If the imported variable is mutable, changes made locally will be reflected in the object the variable is bound to. This allows subsidiary SConscript files to contribute to building up, for example, a construction environment.

Examples:

Import("env")
Import("env", "variable")
Import(["env", "variable"])
Import("*")

The specified string will be preserved as-is and not have construction variables expanded.

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.

Merges values from arg into construction variables in env. If arg is a dictionary, each key-value pair represents a construction variable name and the corresponding flags to merge. If arg is not a dictionary, MergeFlags attempts to convert it to one before the values are merged. env.ParseFlags is used for this, so values to be converted are subject to the same limitations: ParseFlags has knowledge of which construction variables certain flags should go to, but not all; and only for GCC and compatible compiler chains. arg must be a single object, so to pass multiple strings, enclose them in a list.

If unique is true (the default), duplicate values are not retained. In case of duplication, any construction variable names that end in PATH keep the left-most value so the path searcb order is not altered. All other construction variables keep the right-most value. If unique is false, values are appended even if they are duplicates.

Examples:

# Add an optimization flag to $CCFLAGS.
env.MergeFlags({'CCFLAGS': '-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
# for two distinct packages and merge into the construction variables.
env.MergeFlags(
    [
        '-O3',
        '!pkg-config gtk+-2.0 --cflags --libs',
        '!pkg-config libpng12 --cflags --libs',
    ]
)

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'))

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'))

Updates the current construction environment with the values extracted from the output of running external command, by passing it to a helper function. command may be a string or a list of strings representing the command and its arguments. If function is omitted or None, env.MergeFlags is used. By default, duplicate values are not added to any construction variables; you can specify unique=False to allow duplicate values to be added.

command is executed using the SCons execution environment (that is, the construction variable $ENV in the current construction environment). If command needs additional information to operate properly, that needs to be set in the execution environment. For example, pkg-config may need a custom value set in the PKG_CONFIG_PATH environment variable.

env.MergeFlags needs to understand the output produced by command in order to distribute it to appropriate construction variables. env.MergeFlags uses a separate function to do that processing - see env.ParseFlags for the details, including a a table of options and corresponding construction variables. To provide alternative processing of the output of command, you can suppply a custom function, which must accept three arguments: the construction environment to modify, a string argument containing the output from running command, and the optional unique flag.

Parses the contents of 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 filename does not exist. The optional must_exist argument may be set to True to have SCons raise an exception if the file does not exist, or is otherwise inaccessible.

The optional only_one argument may be set to True to have SCons raise an exception 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.

filename and all of the files listed therein will be interpreted relative to the directory of the SConscript file which calls the ParseDepends function.

Parses one or more strings containing typical command-line flags for GCC-style tool chains and returns a dictionary with the flag values separated into the appropriate SCons construction variables. 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. This can be used to call a *-config command typical of the POSIX programming environment (for example, pkg-config). Note that such a command is executed using the SCons execution environment; if the command needs additional information, that information needs to be explicitly provided. See ParseConfig for more details.

Flag values are translated according to the prefix found, and added to the following construction variables:

-arch                   CCFLAGS, LINKFLAGS
-D                      CPPDEFINES
-framework              FRAMEWORKS
-frameworkdir=          FRAMEWORKPATH
-fmerge-all-constants   CCFLAGS, LINKFLAGS
-fopenmp                CCFLAGS, LINKFLAGS
-fsanitize              CCFLAGS, LINKFLAGS
-include                CCFLAGS
-imacros                CCFLAGS
-isysroot               CCFLAGS, LINKFLAGS
-isystem                CCFLAGS
-iquote                 CCFLAGS
-idirafter              CCFLAGS
-I                      CPPPATH
-l                      LIBS
-L                      LIBPATH
-mno-cygwin             CCFLAGS, LINKFLAGS
-mwindows               LINKFLAGS
-openmp                 CCFLAGS, 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')

When called as a global function, returns a callable platform object selected by plat (defaults to the detected platform for the current system) that can be used to initialize a construction environment by passing it as the platform keyword argument to the Environment function.

Example:

env = Environment(platform=Platform('win32'))

When called as a method of an environment, calls the platform object indicated by plat to update that environment.

env.Platform('posix')

See the manpage section "Construction Environments" for more details.

Marks 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 a single call, and may be strings and/or nodes. Returns a list of the affected target nodes.

Prepend values to construction variables in the current construction environment, Works like env.Append (see for details), except that values are added to the front, rather than the end, of any existing value of the construction variable

Example:

env.Prepend(CCFLAGS='-g ', FOO=['foo.yyy'])

See also env.Append, env.AppendUnique and env.PrependUnique.

Prepend path elements specified by newpath to the given search path string or list name in mapping envname in the construction environment. Supplying envname is optional: the default is the execution environment $ENV. Optional sep is used as the search path separator, the default is the platform's separator (os.pathsep). A path element will only appear once. Any duplicates in newpath are dropped, keeping the first appearing (to preserve path order). If delete_existing is False any addition duplicating an existing path element is ignored; if delete_existing is True (the default) the existing value will be dropped and the path element will be inserted at the beginning. To help maintain uniqueness all paths are normalized (using os.path.normpath and os.path.normcase).

Example:

print('before:', env['ENV']['INCLUDE'])
include_path = '/foo/bar:/foo'
env.PrependENVPath('INCLUDE', include_path)
print('after:', env['ENV']['INCLUDE'])

Yields:

before: /biz:/foo
after: /foo/bar:/foo:/biz

See also env.AppendENVPath.

Prepend values to construction variables in the current construction environment, maintaining uniqueness. Works like env.Append, except that values are added to the front, rather than the end, of the construction variable, and values that would become duplicates are not added. If delete_existing is set to a true value, then for any duplicate, the existing instance of val is first removed, then val is inserted, having the effect of moving it to the front.

Example:

env.PrependUnique(CCFLAGS='-g', FOO=['foo.yyy'])

See also env.Append, env.AppendUnique and env.Prepend.

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 (default 1). 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 **kwargs as arguments to your function or method signatures. 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, **kwargs):
    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 to Progress is a string or list of strings, it is taken as text to be displayed every interval evaluated Nodes. If the first argument is a list of strings, then each string in the list will be displayed in rotating fashion every interval evaluated Nodes.

The default is to print the string on standard output. An alternate output stream may be specified with the file keyword argument, which the caller must pass already opened.

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 carriage return) (\r) to cause each line to overwritten by the next line, and the overwrite keyword argument (default False) to make sure the previously-printed file name is overwritten with blank spaces:

import sys
Progress('$TARGET\r', overwrite=True)

A list of strings can be used to implement a "spinner" on the user's screen as follows, changing every five evaluated Nodes:

Progress(['-\r', '\\\r', '|\r', '/\r'], interval=5)

Marks target as a pseudo target, not representing the production of any physical target file. If any pseudo target does exist, SCons will abort the build with an error. Multiple targets can be passed in a single call, and may be strings and/or Nodes. Returns a list of the affected target nodes.

Pseudo may be useful in conjuction with a builder call (such as Command) which does not create a physical target, and the behavior if the target accidentally existed would be incorrect. This is similar in concept to the GNU make .PHONY target. SCons also provides a powerful target alias capability (see Alias) which may provide more flexibility in many situations when defining target names that are not directly built.

Finds the location of modulename, which can be a string or a sequence of strings, each representing the name of a Python module. Construction variables are expanded in modulename. Returns a Directory Node (see Dir), or a list of Directory Nodes if modulename is a sequence. None is returned for any module not found.

When a Tool module which is installed as a Python module is used, you need to specify a toolpath argument to Tool, Environment or Clone, as tools outside the standard project locations (site_scons/site_tools) will not be found otherwise. Using PyPackageDir allows this path to be discovered at runtime instead of hardcoding the path.

Example:

env = Environment(
    tools=["default", "ExampleTool"],
    toolpath=[PyPackageDir("example_tool")]
)

Replaces construction variables in the Environment with the specified keyword arguments.

Example:

env.Replace(CCFLAGS='-g', FOO='foo.xxx')

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.

Specifies an order-only relationship between target and prerequisite. The prerequisites 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. target and prerequisite may each be a string or Node, or a list of strings or Nodes. If there are multiple target values, the prerequisite(s) are added to each one. Returns a list of the affected target nodes.

Example:

env.Requires('foo', 'file-that-must-be-built-before-foo')

Return to the calling SConscript, optionally returning the values of variables named in vars. Multiple strings contaning variable names may be passed to Return. A string containing white space is split into individual variable names. Returns the value if one variable is specified, else returns a tuple of values. Returns an empty tuple if vars is omitted.

By default Return stops processing the current SConscript and returns immediately. 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 was called.

Examples:

# Returns no values (evaluates False)
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')

Creates a Scanner object for the specified function. See manpage section "Scanner Objects" for a complete explanation of the arguments and behavior.

Executes subsidiary SConscript (build configuration) file(s). There are two ways to call the SConscript function.

The first calling style is to supply one or more SConscript file names as the first positional argument, which can be a string or a list of strings. If there is a second positional argument, it is treated as if the exports keyword argument had been given (see below). Examples:

SConscript('SConscript')  # run SConscript in the current directory
SConscript('src/SConscript')  # run SConscript in the src directory
SConscript(['src/SConscript', 'doc/SConscript'])
SConscript(Split('src/SConscript doc/SConscript'))
config = SConscript('MyConfig.py')

The second calling style is to omit the positional argument naming the script and instead specify directory names using the dirs keyword argument. The value can be a string or list of strings. In this case, scons will execute a subsidiary configuration file named SConscript (by default) in each of the specified directories. You may specify a name other than SConscript by supplying an optional name=scriptname 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 keyword argument specifies variables to make available for use by the called SConscripts, which are evaluated in an isolated context and otherwise do not have access to local variables from the calling SConscript. The value may be a string or list of strings representing variable names, or a dictionary mapping local names to the names they can be imported by. For the first (scriptnames) calling style, a second positional argument will also be interpreted as exports; the second (directory) calling style accepts no positional arguments and must use the keyword form. These variables are locally exported only to the called SConscript file(s), and take precedence over any same-named variables in the global pool managed by the Export function. The subsidiary SConscript files must use the Import function to import the variables into their local scope. 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 function, but in effect only within the scope of the SConscript call. The variant_dir argument is interpreted relative to the directory of the calling SConscript file. The source directory is the directory in which the called SConscript file resides and the SConscript file is evaluated as if it were in the variant_dir directory. Thus:

SConscript('src/SConscript', variant_dir='build')

is equivalent to:

VariantDir('build', 'src')
SConscript('build/SConscript')

If the sources are in the same directory as the SConstruct,

SConscript('SConscript', variant_dir='build')

is equivalent to:

VariantDir('build', '.')
SConscript('build/SConscript')

The optional duplicate argument is interpreted as for VariantDir. If the variant_dir argument is omitted, the duplicate argument is ignored. See the description of VariantDir for additional details and restrictions.

If the optional must_exist is True (the default), an exception is raised if a requested SConscript file is not found. To allow missing scripts to be silently ignored (the default behavior prior to SCons version 3.1), pass must_exist=False in the SConscript call.

Changed in 4.6.0: must_exist now defaults to True.

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)

SConscript returns the values of any variables named by the executed SConscript file(s) in arguments to the Return function. If a single SConscript call causes multiple scripts to be executed, the return value is a tuple containing the returns of each of the scripts. If an executed script does not explicitly call Return, it returns None.

By default, scons changes its working directory to the directory in which each subsidiary SConscript file lives while reading and processing that script. This behavior may be disabled by specifying an argument which evaluates false, in which case scons will stay in the top-level directory while reading all SConscript files. (This may be necessary when building from repositories, when all the directories in which SConscript files may be found don't necessarily exist locally.) You may enable and disable this ability by calling SConscriptChdir multiple times.

Example:

SConscriptChdir(False)
SConscript('foo/SConscript')	# will not chdir to foo
SConscriptChdir(True)
SConscript('bar/SConscript')	# will chdir to bar

Specify where to store the SCons file signature database, and which database format to use. This may be useful to specify alternate database files and/or file locations for different types of builds.

The optional name argument is the base name of the database file(s). If not an absolute path name, these are placed relative to the directory containing the top-level SConstruct file. The default is .sconsign. The actual database file(s) stored on disk may have an appropriate suffix appended by the chosen dbm_module

The optional dbm_module argument specifies which Python database module to use for reading/writing the file. The module must be imported first; then the imported module name is passed as the argument. The default is a custom SCons.dblite module that uses pickled Python data structures, which works on all Python versions. See documentation of the Python dbm module for other available types.

If called with no arguments, the database will default to .sconsign.dblite in the top directory of the project, which is also the default if if SConsignFile is not called.

The setting is global, so the only difference between the global function and the environment method form is variable expansion on name. There should only be one active call to this function/method in a given build setup.

If name is set to None, scons will store file signatures in a separate .sconsign file in each directory, not in a single combined database file. This is a backwards-compatibility meaure to support what was the default behavior prior to SCons 0.97 (i.e. before 2008). Use of this mode is discouraged and may be deprecated in a future SCons release.

Examples:

# Explicitly stores signatures in ".sconsign.dblite"
# in the top-level SConstruct directory (the default behavior).
SConsignFile()

# Stores signatures in the file "etc/scons-signatures"
# relative to the top-level SConstruct directory.
# SCons will add a database suffix to this name.
SConsignFile("etc/scons-signatures")

# Stores signatures in the specified absolute file name.
# SCons will add a database suffix to this name.
SConsignFile("/home/me/SCons/signatures")

# Stores signatures in a separate .sconsign file
# in each directory.
SConsignFile(None)

# Stores signatures in a GNU dbm format .sconsign file
import dbm.gnu
SConsignFile(dbm_module=dbm.gnu)

Sets construction variables to default values specified with the keyword arguments if (and only if) the variables are not already set. The following statements are equivalent:

env.SetDefault(FOO='foo')
if 'FOO' not in env:
    env['FOO'] = 'foo'

Sets scons option variable name to value. These options are all also settable via command-line options but the variable name may differ from the command-line option name - see the table for correspondences. A value set via command-line option will take precedence over one set with SetOption, which allows setting a project default in the scripts and temporarily overriding it via command line. SetOption calls can also be placed in the site_init.py file.

See the documentation in the manpage for the corresponding command line option for information about each specific option. The value parameter is mandatory, for option values which are boolean in nature (that is, the command line option does not take an argument) use a value which evaluates to true (e.g. True, 1) or false (e.g. False, 0).

Options which affect the reading and processing of SConscript files are not settable using SetOption since those files must be read in order to find the SetOption call in the first place.

The settable variables with their associated command-line options are:

Example:

SetOption('max_drift', 0)

Declares side_effect as a side effect of building target. Both side_effect and target can be a list, a file name, or a node. A side effect is a target file that is created or updated as a side effect of building other targets. For example, a Windows PDB file is created as a side effect of building the .obj files for a static library, and various log files are created updated as side effects of various TeX commands. If a target is a side effect of multiple build commands, scons will ensure that only one set of commands is executed at a time. Consequently, you only need to use this method for side-effect targets that are built as a result of multiple build commands.

Because multiple build commands may update the same side effect file, by default the side_effect target is not automatically removed when the target is removed by the -c option. (Note, however, that the side_effect might be removed as part of cleaning the directory in which it lives.) If you want to make sure the side_effect is cleaned whenever a specific target is cleaned, you must specify this explicitly with the Clean or env.Clean function.

This function returns the list of side effect Node objects that were successfully added. If the list of side effects contained any side effects that had already been added, they are not added and included in the returned list.

If arg is a string, splits on whitespace and returns a list of strings without whitespace. This mode is the most common case, and can be used to split a list of filenames (for example) rather than having to type them as a list of individually quoted words. If arg is a list or tuple returns the list or tuple unchanged. If arg is any other type of object, returns a list containing just the object. These non-string cases do not actually do any spliting, but allow an argument variable to be passed to Split without having to first check its type.

Example:

files = Split("f1.c f2.c f3.c")
files = env.Split("f4.c f5.c f6.c")
files = Split("""
    f7.c
    f8.c
    f9.c
""")

Performs construction variable interpolation (substitution) on input, which can be a string or a sequence. Substitutable elements take the form ${expression}, although if there is no ambiguity in recognizing the element, the braces can be omitted. A literal $ can be entered by using $$.

By default, leading or trailing white space will be removed from the result, and all sequences of white space will be compressed to a single space character. Additionally, any $( and $) character sequences will be stripped from the returned string, The optional raw argument may be set to 1 if you want to preserve white space and $(-$) sequences. The raw argument may be set to 2 if you want to additionally discard all characters between any $( and $) pairs (as is done for signature calculation).

If input is a sequence (list or tuple), the individual elements of the sequence will be expanded, and the results will be returned as a list.

The optional target and source keyword arguments must be set to lists of target and source nodes, respectively, if you want the $TARGET, $TARGETS, $SOURCE and $SOURCES to be available for expansion. This is usually necessary if you are calling env.subst from within a Python function used as an SCons action.

Returned string values or sequence elements are converted to their string representation by default. The optional conv argument may specify a conversion function that will be used in place of the default. For example, if you want Python objects (including SCons Nodes) to be returned as Python objects, you can use a Python lambda expression to pass in an unnamed function that simply returns its unconverted argument.

Example:

print(env.subst("The C compiler is: $CC"))

def compile(target, source, env):
    sourceDir = env.subst(
        "${SOURCE.srcdir}",
        target=target,
        source=source
    )

source_nodes = env.subst('$EXPAND_TO_NODELIST', conv=lambda x: x)

Annotates file or directory Nodes with information about how the Package Builder should package those files or directories. All Node-level tags are optional.

Examples:

# makes sure the built library will be installed with 644 file access mode
Tag(Library('lib.c'), UNIX_ATTR="0o644")

# marks file2.txt to be a documentation file
Tag('file2.txt', DOC)

Locates the tool specification module name and returns a callable tool object for that tool. The tool module is searched for in standard locations and in any paths specified by the optional toolpath parameter. The standard locations are SCons' own internal path for tools plus the toolpath, if any (see the Tools section in the manual page for more details). Any additional keyword arguments kwargs are passed to the tool module's generate function during tool object construction.

When called, the tool object updates a construction environment with construction variables and arranges any other initialization needed to use the mechanisms that tool describes.

When the env.Tool form is used, the tool object is automatically called to update env and the value of tool is appended to the $TOOLS construction variable in that environment.

Changed in version 4.2: env.Tool now returns the tool object, previously it did not return (i.e. returned None).

Examples:

env.Tool('gcc')
env.Tool('opengl', toolpath=['build/tools'])

When the global function Tool form is used, the tool object is constructed but not called, as it lacks the context of an environment to update. The tool object can be passed to an Environment or Clone call as part of the tools keyword argument, in which case the tool is applied to the environment being constructed, or it can be called directly, in which case a construction environment to update must be passed as the argument. Either approach will also update the $TOOLS construction variable.

Examples:

env = Environment(tools=[Tool('msvc')])

env = Environment()
msvctool = Tool('msvc')
msvctool(env)  # adds 'msvc' to the TOOLS variable
gltool = Tool('opengl', toolpath = ['tools'])
gltool(env)  # adds 'opengl' to the TOOLS variable

Check that all the options specified on the command line are either SCons built-in options or defined via calls to AddOption. SCons will eventually fail on unknown options anyway, but calling this function allows the build to "fail fast" before executing expensive logic later in the build.

This function should only be called after the last AddOption call in your SConscript logic. Be aware that some tools call AddOption, if you are getting error messages for arguments that they add, you will need to ensure that those tools are loaded before calling ValidateOptions.

If there are any unknown command line options, ValidateOptions prints an error message and exits with an error exit status. If the optional throw_exception argument is True (default is False), a SConsBadOptionError is raised, giving an opportunity for the SConscript logic to catch that exception and handle invalid options appropriately. Note that this exception name needs to be imported (see the example below).

A common build problem is typos (or thinkos) - a user enters an option that is just a little off the expected value, or perhaps a different word with a similar meaning. It may be useful to abort the build before going too far down the wrong path. For example:

$ scons --compilers=mingw  # the correct flag is --compiler
      

Here SCons could go off and run a bunch of configure steps with the default value of --compiler, since the incorrect command line did not actually supply a value to it, costing developer time to track down why the configure logic made the "wrong" choices. This example shows catching this:

from SCons.Script.SConsOptions import SConsBadOptionError

AddOption(
    '--compiler',
    dest='compiler',
    action='store',
    default='gcc',
    type='string',
)

# ... other SConscript logic ...

try:
    ValidateOptions(throw_exception=True)
except SConsBadOptionError as e:
    print(f"ValidateOptions detects a fail: ", e.opt_str)
    Exit(3)
      

New in version 4.5.0

Returns a Node object representing the specified Python value. Value Nodes can be used as dependencies of targets. If the result of calling str(value) changes between SCons runs, any targets depending on Value(value) will be rebuilt. (This is true even when using timestamps to decide if files are up-to-date.) When using timestamp source signatures, Value Nodes' timestamps are equal to the system time when the Node is created.

The returned Value Node object has a write() method that can be used to "build" a Value Node by setting a new value. The optional built_value argument can be specified when the Value Node is created to indicate the Node should already be considered "built." There is a corresponding read() method that will return the built value of the Node.

The optional name parameter can be provided as an alternative name for the resulting Value node; this is advised if the value parameter cannot be converted to a string.

Changed in version 4.0: the name parameter was added.

Examples:

env = Environment()

def create(target, source, env):
    # A function that will write a 'prefix=$SOURCE'
    # string into the file name specified as the
    # $TARGET.
    with open(str(target[0]), 'wb') as f:
        f.write('prefix=' + source[0].get_contents())

# Fetch the prefix= argument, if any, from the command
# line, and use /usr/local as the default.
prefix = ARGUMENTS.get('prefix', '/usr/local')

# Attach a .Config() builder for the above function action
# to the construction environment.
env['BUILDERS']['Config'] = Builder(action=create)
env.Config(target='package-config', source=Value(prefix))

def build_value(target, source, env):
    # A function that "builds" a Python Value by updating
    # the Python value with the contents of the file
    # specified as the source of the Builder call ($SOURCE).
    target[0].write(source[0].get_contents())

output = env.Value('before')
input = env.Value('after')

# Attach a .UpdateValue() builder for the above function
# action to the construction environment.
env['BUILDERS']['UpdateValue'] = Builder(action=build_value)
env.UpdateValue(target=Value(output), source=Value(input))

Sets up a mapping to define a variant build directory in variant_dir. src_dir may not be underneath variant_dir. A VariantDir mapping is global, even if called using the env.VariantDir form. VariantDir can be called multiple times with the same src_dir to set up multiple variant builds with different options.

Note if variant_dir is not under the project top directory, target selection rules will not pick targets in the variant directory unless they are explicitly specified.

When files in variant_dir are referenced, SCons backfills as needed with files from src_dir to create a complete build directory. By default, SCons physically duplicates the source files, SConscript files, and directory structure as needed into the variant directory. Thus, a build performed in the variant directory is guaranteed to be identical to a build performed in the source directory even if intermediate source files are generated during the build, or if preprocessors or other scanners search for included files using paths relative to the source file, or if individual compilers or other invoked tools are hard-coded to put derived files in the same directory as source files. Only the files SCons calculates are needed for the build are duplicated into variant_dir. If possible on the platform, the duplication is performed by linking rather than copying. This behavior is affected by the --duplicate command-line option.

Duplicating the source files may be disabled by setting the duplicate argument to False. This will cause SCons to invoke Builders using the path names of source files in src_dir and the path names of derived files within variant_dir. This is more efficient than duplicating, and is safe for most builds; revert to duplicate=True if it causes problems.

VariantDir works most naturally when used with a subsidiary SConscript file. The subsidiary SConscript file must be called as if it were in variant_dir, regardless of the value of duplicate. When calling an SConscript file, you can use the exports keyword argument to pass parameters (individually or as an appropriately set up environment) so the SConscript can pick up the right settings for that variant build. The SConscript must Import these to use them. Example:

env1 = Environment(...settings for variant1...)
env2 = Environment(...settings for variant2...)

# run src/SConscript in two variant directories
VariantDir('build/variant1', 'src')
SConscript('build/variant1/SConscript', exports={"env": env1})
VariantDir('build/variant2', 'src')
SConscript('build/variant2/SConscript', exports={"env": env2})

See also the SConscript function for another way to specify a variant directory in conjunction with calling a subsidiary SConscript file.

More examples:

# use names in the build directory, not the source directory
VariantDir('build', 'src', duplicate=0)
Program('build/prog', 'build/source.c')

# this builds both the source and docs in a separate subtree
VariantDir('build', '.', duplicate=0)
SConscript(dirs=['build/src','build/doc'])

# same as previous example, but only uses SConscript
SConscript(dirs='src', variant_dir='build/src', duplicate=0)
SConscript(dirs='doc', variant_dir='build/doc', duplicate=0)

Searches for the specified executable program, returning the full path to the program or None.

When called as a construction environment method, searches the paths in the path keyword argument, or if None (the default) the paths listed in the construction environment (env['ENV']['PATH']). The external environment's path list (os.environ['PATH']) is used as a fallback if the key env['ENV']['PATH'] does not exist.

On Windows systems, searches for executable programs with any of the file extensions listed in the pathext keyword argument, or if None (the default) the pathname extensions listed in the construction environment (env['ENV']['PATHEXT']). The external environment's pathname extensions list (os.environ['PATHEXT']) is used as a fallback if the key env['ENV']['PATHEXT'] does not exist.

When called as a global function, uses the external environment's path os.environ['PATH'] and path extensions os.environ['PATHEXT'], respectively, if path and pathext are None.

Will not select any path name or names in the optional reject list.