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.

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')

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'))

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.

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.

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")

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)

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 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'])

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

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'])

Deprecated synonyms for VariantDir and env.VariantDir(). The build_dir argument becomes the variant_dir argument of VariantDir or env.VariantDir().

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.

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.

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. 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.)

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.

A now-deprecated synonym for env.Clone().

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:

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:

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, repo_node=None):
    return not os.path.exists(str(target))

env.Decider(my_decider)

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. As noted above, both forms of this call affect the same global list of default targets; the construction environment method applies construction variable expansion to the 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.

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.

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)

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')

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.

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': [],
  ...

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.

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)

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

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.

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.

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.

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:

See the documentation for the corresponding command line object for information about each specific option.

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.)

The exclude argument may be set to a pattern or a list of patterns (following the same Unix shell semantics) which must be filtered out of returned elements. Elements matching a least one pattern of this list will be excluded.

Examples:

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

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. With append set to False, any Help text generated with AddOption is clobbered. If append is True, the AddOption help is prepended to the help string, thus preserving the -h message.

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')

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("*")

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 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'])

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'))

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.

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.

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
-isystem            CCFLAGS
-iquote             CCFLAGS
-idirafter          CCFLAGS
-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')

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.

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.

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'])

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

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'])

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)

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.

This returns a Directory Node similar to Dir. The python module / package is looked up and if located the directory is returned for the location. modulename Is a named python package / module to lookup the directory for it's location.

If modulename is a list, SCons returns a list of Dir nodes. Construction variables are expanded in modulename.

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 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')

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')

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

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')

The optional must_exist argument, if true, causes an exception to be raised if a requested SConscript file is not found. The current default is false, causing only a warning to be omitted, but this behavior is deprecated. For scripts which truly intend to be optional, transition to explicty supplying must_exist=False to the call.

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)

By default, scons changes its working directory to the directory in which each subsidiary SConscript file lives. This behavior may be disabled by specifying either:

SConscriptChdir(0)
env.SConscriptChdir(0)

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:

env = Environment()
SConscriptChdir(0)
SConscript('foo/SConscript')	# will not chdir to foo
env.SConscriptChdir(1)
SConscript('bar/SConscript')	# will chdir to bar

This tells scons to store all file signatures in the specified database file. If the file name is omitted, .sconsign is used by default. (The actual file name(s) stored on disk may have an appropriated suffix appended by the dbm_module.) If file is not an absolute path name, the file is placed in the same directory as the top-level SConstruct file.

If file is None, then scons will store file signatures in a separate .sconsign file in each directory, not in one global database file. (This was the default behavior prior to SCons 0.96.91 and 0.97.)

The optional dbm_module argument can be used to specify which Python database module The default is to use a custom SCons.dblite module that uses pickled Python data structures, and which works on all Python versions.

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.
SConsignFile("etc/scons-signatures")

# Stores signatures in the specified absolute file name.
SConsignFile("/home/me/SCons/signatures")

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

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'

This function provides a way to set a select subset of the scons command line options from a SConscript file. The options supported are:

See the documentation for the corresponding command line object for information about each specific option.

Example:

SetOption('max_drift', 1)

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 and its associate factory functions are deprecated. There is no replacement. The intended use was to keep a local tree in sync with an archive, but in actuality the function only causes the archive to be fetched on the first run. Synchronizing with the archive is best done external to SCons.

Arrange for non-existent source files to be fetched from a source code management system using the specified builder. The specified entries may be a Node, string or list of both, and may represent either individual source files or directories in which source files can be found.

For any non-existent source files, scons will search up the directory tree and use the first SourceCode builder it finds. The specified builder may be None, in which case scons will not use a builder to fetch source files for the specified entries, even if a SourceCode builder has been specified for a directory higher up the tree.

scons will, by default, fetch files from SCCS or RCS subdirectories without explicit configuration. This takes some extra processing time to search for the necessary source code management files on disk. You can avoid these extra searches and speed up your build a little by disabling these searches as follows:

env.SourceCode('.', None)

Note that if the specified builder is one you create by hand, it must have an associated construction environment to use when fetching a source file.

scons provides a set of canned factory functions that return appropriate Builders for various popular source code management systems. Canonical examples of invocation include:

env.SourceCode('.', env.BitKeeper('/usr/local/BKsources'))
env.SourceCode('src', env.CVS('/usr/local/CVSROOT'))
env.SourceCode('/', env.RCS())
env.SourceCode(['f1.c', 'f2.c'], env.SCCS())
env.SourceCode('no_source.c', None)

Note: Although it is not yet officially deprecated, use of this function is discouraged. See the Decider function for a more flexible and straightforward way to configure SCons' decision-making.

The SourceSignatures function tells scons how to decide if a source file (a file that is not built from any other files) has changed since the last time it was used to build a particular target file. Legal values are MD5 or timestamp.

If the environment method is used, the specified type of source signature is only used when deciding whether targets built with that environment are up-to-date or must be rebuilt. If the global function is used, the specified type of source signature becomes the default used for all decisions about whether targets are up-to-date.

MD5 means scons decides that a source file has changed if the MD5 checksum of its contents has changed since the last time it was used to rebuild a particular target file.

timestamp means scons decides that a source file has changed if its timestamp (modification time) has changed since the last time it was used to rebuild a particular target file. (Note that although this is similar to the behavior of Make, by default it will also rebuild if the dependency is older than the last time it was used to rebuild the target file.)

There is no different between the two behaviors for Python Value node objects.

MD5 signatures take longer to compute, but are more accurate than timestamp signatures. The default value is MD5.

Note that the default TargetSignatures setting (see below) is to use this SourceSignatures setting for any target files that are used to build other target files. Consequently, changing the value of SourceSignatures will, by default, affect the up-to-date decision for all files in the build (or all files built with a specific construction environment when env.SourceSignatures is used).

Returns a list of file names or other objects. If arg is a string, it will be split on strings of white-space characters within the string, making it easier to write long lists of file names. If arg is already a list, the list will be returned untouched. If arg is any other type of object, it will be returned as a list containing just the object.

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 on the specified string or sequence argument input.

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 strip all characters between any $( and $) pairs (as is done for signature calculation).

If the 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 the Python Λ idiom 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 tags are optional.

Examples:

# makes sure the built library will be installed with 0644 file
# access mode
Tag( Library( 'lib.c' ), UNIX_ATTR="0644" )

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

Note: Although it is not yet officially deprecated, use of this function is discouraged. See the Decider function for a more flexible and straightforward way to configure SCons' decision-making.

The TargetSignatures function tells scons how to decide if a target file (a file that is built from any other files) has changed since the last time it was used to build some other target file. Legal values are "build"; "content" (or its synonym "MD5"); "timestamp"; or "source".

If the environment method is used, the specified type of target signature is only used for targets built with that environment. If the global function is used, the specified type of signature becomes the default used for all target files that don't have an explicit target signature type specified for their environments.

"content" (or its synonym "MD5") means scons decides that a target file has changed if the MD5 checksum of its contents has changed since the last time it was used to rebuild some other target file. This means scons will open up MD5 sum the contents of target files after they're built, and may decide that it does not need to rebuild "downstream" target files if a file was rebuilt with exactly the same contents as the last time.

"timestamp" means scons decides that a target file has changed if its timestamp (modification time) has changed since the last time it was used to rebuild some other target file. (Note that although this is similar to the behavior of Make, by default it will also rebuild if the dependency is older than the last time it was used to rebuild the target file.)

"source" means scons decides that a target file has changed as specified by the corresponding SourceSignatures setting ("MD5" or "timestamp"). This means that scons will treat all input files to a target the same way, regardless of whether they are source files or have been built from other files.

"build" means scons decides that a target file has changed if it has been rebuilt in this invocation or if its content or timestamp have changed as specified by the corresponding SourceSignatures setting. This "propagates" the status of a rebuilt file so that other "downstream" target files will always be rebuilt, even if the contents or the timestamp have not changed.

"build" signatures are fastest because "content" (or "MD5") signatures take longer to compute, but are more accurate than "timestamp" signatures, and can prevent unnecessary "downstream" rebuilds when a target file is rebuilt to the exact same contents as the previous build. The "source" setting provides the most consistent behavior when other target files may be rebuilt from both source and target input files. The default value is "source".

Because the default setting is "source", using SourceSignatures is generally preferable to TargetSignatures, so that the up-to-date decision will be consistent for all files (or all files built with a specific construction environment). Use of TargetSignatures provides specific control for how built target files affect their "downstream" dependencies.

The Tool form of the function returns a callable object that can be used to initialize a construction environment using the tools keyword of the Environment() method. The object may be called with a construction environment as an argument, in which case the object will add the necessary variables to the construction environment and the name of the tool will be added to the $TOOLS construction variable.

Additional keyword arguments are passed to the tool's generate() method.

Examples:

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

env = Environment()
t = Tool('msvc')
t(env)  # adds 'msvc' to the TOOLS variable
u = Tool('opengl', toolpath = ['tools'])
u(env)  # adds 'opengl' to the TOOLS variable

The env.Tool form of the function applies the callable object for the specified tool string to the environment through which the method was called.

Additional keyword arguments are passed to the tool's generate() method.

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

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.

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.
    f = open(str(target[0]), 'wb')
    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 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))

Use the VariantDir function to create a copy of your sources in another location: if a name under variant_dir is not found but exists under src_dir, the file or directory is copied to variant_dir. Target files can be built in a different directory than the original sources by simply refering to the sources (and targets) within the variant tree.

VariantDir can be called multiple times with the same src_dir to set up multiple builds with different options (variants). The src_dir location must be in or underneath the SConstruct file's directory, and variant_dir may not be underneath src_dir.

The default behavior is for scons to physically duplicate the source files in the variant tree. Thus, a build performed in the variant tree is guaranteed to be identical to a build performed in the source tree even if intermediate source files are generated during the build, or preprocessors or other scanners search for included files relative to the source file, or individual compilers or other invoked tools are hard-coded to put derived files in the same directory as source files.

If possible on the platform, the duplication is performed by linking rather than copying; see also the --duplicate command-line option. Moreover, only the files needed for the build are duplicated; files and directories that are not used are not present in variant_dir.

Duplicating the source tree may be disabled by setting the duplicate argument to 0 (zero). 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 always more efficient than duplicate=1, and is usually safe for most builds (but see above for cases that may cause problems).

Note that VariantDir works most naturally with a subsidiary SConscript file. However, you would then call the subsidiary SConscript file not in the source directory, but in the variant_dir, regardless of the value of duplicate. This is how you tell scons which variant of a source tree to build:

# run src/SConscript in two variant directories
VariantDir('build/variant1', 'src')
SConscript('build/variant1/SConscript')
VariantDir('build/variant2', 'src')
SConscript('build/variant2/SConscript')

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

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 name to the program if it is found, and returning None if not. Searches the specified path, the value of the calling environment's PATH (env['ENV']['PATH']), or the user's current external PATH (os.environ['PATH']) by default. On Windows systems, searches for executable programs with any of the file extensions listed in the specified pathext, the calling environment's PATHEXT (env['ENV']['PATHEXT']) or the user's current PATHEXT (os.environ['PATHEXT']) by default. Will not select any path name or names in the specified reject list, if any.