path: root/SCons/Environment.xml

<?xml version="1.0"?>
<!--
Copyright The SCons Foundation

This file is processed by the bin/SConsDoc.py module.
See its __doc__ string for a discussion of the format.
-->

<!DOCTYPE sconsdoc [
<!ENTITY % scons SYSTEM '../doc/scons.mod'>
%scons;
<!ENTITY % builders-mod SYSTEM '../doc/generated/builders.mod'>
%builders-mod;
<!ENTITY % functions-mod SYSTEM '../doc/generated/functions.mod'>
%functions-mod;
<!ENTITY % tools-mod SYSTEM '../doc/generated/tools.mod'>
%tools-mod;
<!ENTITY % variables-mod SYSTEM '../doc/generated/variables.mod'>
%variables-mod;
]>

<sconsdoc xmlns="http://www.scons.org/dbxsd/v1.0"
          xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
          xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">


<!-- Construction variables -->

<cvar name="BUILDERS">
<summary>
<para>
A dictionary mapping the names of the builders
available through the &consenv; to underlying Builder objects.
Custom builders need to be added to this to make them available.
</para>

<para>
A platform-dependent default list of builders such as
&b-link-Program;, &b-link-Library; etc. is used to
populate this &consvar; when the &consenv; is initialized
via the presence/absence of the tools those builders depend on.
&cv-BUILDERS; can be examined to learn which builders will
actually be available at run-time.
</para>

<para>
Note that if you initialize this &consvar; through
assignment when the &consenv; is created,
that value for &cv-BUILDERS; will override any defaults:
</para>

<example_commands>
bld = Builder(action='foobuild &lt; $SOURCE > $TARGET')
env = Environment(BUILDERS={'NewBuilder': bld})
</example_commands>

<para>
To instead use a new Builder object in addition to the default Builders,
add your new Builder object like this:
</para>

<example_commands>
env = Environment()
env.Append(BUILDERS={'NewBuilder': bld})
</example_commands>

<para>
or this:
</para>

<example_commands>
env = Environment()
env['BUILDERS']['NewBuilder'] = bld
</example_commands>
</summary>
</cvar>

<cvar name="ENV">
<summary>
<para>
A dictionary of environment variables
to use when invoking commands. When
&cv-ENV; is used in a command all list
values will be joined using the path separator and any other non-string
values will simply be coerced to a string.
Note that, by default,
&scons;
does
<emphasis>not</emphasis>
propagate the environment in effect when you
execute
&scons;
to the commands used to build target files.
This is so that builds will be guaranteed
repeatable regardless of the environment
variables set at the time
&scons;
is invoked.
</para>

<para>
If you want to propagate your
environment variables
to the commands executed
to build target files,
you must do so explicitly:
</para>

<example_commands>
import os
env = Environment(ENV=os.environ.copy())
</example_commands>

<para>
Note that you can choose only to propagate
certain environment variables.
A common example is
the system
<envar>PATH</envar>
environment variable,
so that
&scons;
uses the same utilities
as the invoking shell (or other process):
</para>

<example_commands>
import os
env = Environment(ENV={'PATH': os.environ['PATH']})
</example_commands>
</summary>
</cvar>

<cvar name="SCANNERS">
<summary>
<para>
A list of the available implicit dependency scanners.
New file scanners may be added by
appending to this list,
although the more flexible approach
is to associate scanners
with a specific Builder.
See the manpage sections "Builder Objects"
and "Scanner Objects"
for more information.
</para>
</summary>
</cvar>

<cvar name="CHANGED_SOURCES">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="CHANGED_TARGETS">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="SOURCE">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="SOURCES">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="TARGET">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="TARGETS">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="UNCHANGED_SOURCES">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="UNCHANGED_TARGETS">
<summary>
<para>
A reserved variable name
that may not be set or used in a construction environment.
(See the manpage section "Variable Substitution"
for more information).
</para>
</summary>
</cvar>

<cvar name="TOOLS">
<summary>
<para>
A list of the names of the Tool specifications
that are part of this construction environment.
</para>
</summary>
</cvar>

<cvar name="CACHEDIR_CLASS">
    <summary>
        <para>
The class type that SCons should use when instantiating a
new &f-link-CacheDir; for the given environment. It must be
a subclass of the SCons.CacheDir.CacheDir class.
        </para>
    </summary>
</cvar>

<!-- Functions /  Construction environment methods -->

<scons_function name="Action">
<arguments>
(action, [output, [var, ...]] [key=value, ...])
</arguments>
<summary>
<para>
A factory function to create an Action object for
the specified
<parameter>action</parameter>.
See the manpage section "Action Objects"
for a complete explanation of the arguments and behavior.
</para>

<para>
Note that the &f-env-Action;
form of the invocation will expand
construction variables in any argument strings,
including the
<parameter>action</parameter>
argument, at the time it is called
using the construction variables in the
<replaceable>env</replaceable>
construction environment through which
&f-env-Action; was called.
The &f-Action; global function
form delays all variable expansion
until the Action object is actually used.
</para>
</summary>
</scons_function>

<scons_function name="AddMethod">
<arguments signature="global">
(object, function, [name])
</arguments>
<arguments signature="env">
(function, [name])
</arguments>
<summary>
<para>
Adds <parameter>function</parameter> to an object as a method.
<parameter>function</parameter> will be called with an instance
object as the first argument as for other methods.
If <parameter>name</parameter> is given, it is used as
the name of the new method, else the name of
<parameter>function</parameter> is used.
</para>
<para>
When the global function &f-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 &consenvs;
subsequently constructed.
When called using the &f-env-AddMethod; form,
the method is added to the specified &consenv; only.
Added methods propagate through &f-env-Clone; calls.
</para>

<para>
Examples:
</para>

<example_commands>
# 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')
</example_commands>
</summary>
</scons_function>

<scons_function name="AddPostAction">
<arguments>
(target, action)
</arguments>
<summary>
<para>
Arranges for the specified
<parameter>action</parameter>
to be performed
after the specified
<parameter>target</parameter>
has been built.
The specified action(s) 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.
</para>

<para>
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.
</para>
</summary>
</scons_function>

<scons_function name="AddPreAction">
<arguments>
(target, action)
</arguments>
<summary>
<para>
Arranges for the specified
<parameter>action</parameter>
to be performed
before the specified
<parameter>target</parameter>
is built.
The specified action(s) 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.
</para>

<para>
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.
</para>

<para>
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
<filename>.c</filename>
file via an intermediate object file:
</para>

<example_commands>
foo = Program('foo.c')
AddPreAction(foo, 'pre_action')
</example_commands>

<para>
The specified
<literal>pre_action</literal>
would be executed before
&scons;
calls the link command that actually
generates the executable program binary
<filename>foo</filename>,
not before compiling the
<filename>foo.c</filename>
file into an object file.
</para>
</summary>
</scons_function>

<scons_function name="Alias">
<arguments>
(alias, [targets, [action]])
</arguments>
<summary>
<para>
Creates one or more phony targets that
expand to one or more other targets.
An optional
<parameter>action</parameter>
(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.
&f-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.
Aliases are global even if set through
the construction environment method.
</para>

<para>
Examples:
</para>

<example_commands>
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")
</example_commands>
</summary>
</scons_function>

<scons_function name="AlwaysBuild">
<arguments>
(target, ...)
</arguments>
<summary>
<para>
Marks each given
<parameter>target</parameter>
so that it is always assumed to be out of date,
and will always be rebuilt if needed.
Note, however, that
&f-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
<emphasis>always</emphasis>
be built if so specified.
Multiple targets can be passed in to a single call to
&f-AlwaysBuild;.
</para>
</summary>
</scons_function>

<scons_function name="Append">
<arguments signature="env">
(key=val, [...])
</arguments>
<summary>
<para>
Intelligently append values to &consvars; in the &consenv;
named by <varname>env</varname>.
The &consvars; and values to add to them are passed as
<parameter>key=val</parameter> pairs (&Python; keyword arguments).
&f-env-Append; is designed to allow adding values
without normally having to know the data type of an existing &consvar;.
Regular &Python; syntax can also be used to manipulate the &consvar;,
but for that you must know the type of the &consvar;:
for example, different &Python; syntax is needed to combine
a list of values with a single string value, or vice versa.
Some pre-defined &consvars; do have type expectations
based on how &SCons; will use them,
for example &cv-link-CPPDEFINES; is normally a string or a list of strings,
but can be a string,
a list of strings,
a list of tuples,
or a dictionary, while &cv-link-LIBEMITTER;
would expect a callable or list of callables,
and &cv-link-BUILDERS; would expect a mapping type.
Consult the documentation for the various &consvars; for more details.
</para>

<para>
The following descriptions apply to both the append
and prepend functions, the only difference being
the insertion point of the added values.
</para>
<para>
If <varname>env</varname>.  does not have a &consvar;
indicated by <parameter>key</parameter>,
<parameter>val</parameter>
is added to the environment under that key as-is.
</para>

<para>
<parameter>val</parameter> can be almost any type,
and &SCons; will combine it with an existing value into an appropriate type,
but there are a few special cases to be aware of.
When two strings are combined,
the result is normally a new string,
with the caller responsible for supplying any needed separation.
The exception to this is the &consvar; &cv-link-CPPDEFINES;,
in which each item will be postprocessed by adding a prefix
and/or suffix,
so the contents are treated as a list of strings, that is,
adding a string will result in a separate string entry,
not a combined string. For &cv-CPPDEFINES; as well as
for &cv-link-LIBS;, and the various <varname>*PATH</varname>
variables, &SCons; will supply the compiler-specific
syntax (e.g. adding a <literal>-D</literal> or <literal>/D</literal>
prefix for &cv-CPPDEFINES;), so this syntax should be omitted when
adding values to these variables.
Example (gcc syntax shown in the expansion of &CPPDEFINES;):
</para>

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

<screen>
$ scons -Q
CXXFLAGS=-std=c11, CPPDEFINES=RELEASE
CXXFLAGS=-std=c11 -O, CPPDEFINES=['RELEASE', 'EXTRA']
CPPDEFINES will expand to -DRELEASE -DEXTRA
scons: `.' is up to date.
</screen>

<para>
Because &cv-link-CPPDEFINES; is intended to
describe C/C++ pre-processor macro definitions,
it accepts additional syntax.
Preprocessor macros can be valued, or un-valued, as in
<computeroutput>-DBAR=1</computeroutput> or
<computeroutput>-DFOO</computeroutput>.
The macro can be be supplied as a complete string including the value,
or as a tuple (or list) of macro, value, or as a dictionary.
Example (again gcc syntax in the expanded defines):
</para>

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

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

<para>
Adding a string <parameter>val</parameter>
to a dictonary &consvar; will enter
<parameter>val</parameter> as the key in the dict,
and <literal>None</literal> as its value.
Using a tuple type to supply a key + value only works
for the special case of &cv-link-CPPDEFINES;
described above.
</para>

<para>
Although most combinations of types work without
needing to know the details, some combinations
do not make sense and a &Python; exception will be raised.
</para>

<para>
When using &f-env-Append; to modify &consvars;
which are path specifications (conventionally,
the names of such end in <varname>PATH</varname>),
it is recommended to add the values as a list of strings,
even if there is only a single string to add.
The same goes for adding library names to &cv-LIBS;.
</para>

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

<para>
See also &f-link-env-AppendUnique;,
&f-link-env-Prepend; and &f-link-env-PrependUnique;.
</para>

</summary>
</scons_function>

<scons_function name="AppendENVPath">
<arguments signature="env">
(name, newpath, [envname, sep, delete_existing=False])
</arguments>
<summary>
<para>
Append new path elements to the given path in the
specified external environment (&cv-link-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
<function>os.path.normpath</function>
and
<function>os.path.normcase</function>).
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.
</para>

<para>
If
<parameter>delete_existing</parameter>
is <constant>False</constant>, then adding a path that already exists
will not move it to the end; it will stay where it is in the list.
</para>

<para>
Example:
</para>

<example_commands>
print('before:', env['ENV']['INCLUDE'])
include_path = '/foo/bar:/foo'
env.AppendENVPath('INCLUDE', include_path)
print('after:', env['ENV']['INCLUDE'])
</example_commands>

<para>Yields:</para>
<screen>
before: /foo:/biz
after: /biz:/foo/bar:/foo
</screen>
</summary>
</scons_function>

<scons_function name="AppendUnique">
<arguments signature="env">
(key=val, [...], delete_existing=False)
</arguments>
<summary>
<para>
Append values to &consvars; in the current &consenv;,
maintaining uniqueness.
Works like &f-link-env-Append; (see for details),
except that values already present in the &consvar;
will not be added again.
If <parameter>delete_existing</parameter>
is <constant>True</constant>,
the existing matching value is first removed,
and the requested value is added,
having the effect of moving such values to the end.
</para>

<para>
Example:
</para>

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

<para>
See also &f-link-env-Append;,
&f-link-env-Prepend;
and &f-link-env-PrependUnique;.
</para>
</summary>
</scons_function>

<scons_function name="Builder">
<arguments>
(action, [arguments])
</arguments>
<summary>
<para>
Creates a Builder object for
the specified
<parameter>action</parameter>.
See the manpage section "Builder Objects"
for a complete explanation of the arguments and behavior.
</para>

<para>
Note that the
<function>env.Builder</function>()
form of the invocation will expand
construction variables in any arguments strings,
including the
<parameter>action</parameter>
argument,
at the time it is called
using the construction variables in the
<varname>env</varname>
construction environment through which
&f-env-Builder; was called.
The
&f-Builder;
form delays all variable expansion
until after the Builder object is actually called.
</para>
</summary>
</scons_function>

<scons_function name="CacheDir">
<arguments>
(cache_dir, custom_class=None)
</arguments>
<summary>
<para>
Direct
&scons;
to maintain a derived-file cache in
<parameter>cache_dir</parameter>.
The derived files in the cache will be shared
among all the builds specifying the same
<parameter>cache_dir</parameter>.
Specifying a
<parameter>cache_dir</parameter>
of
<constant>None</constant>
disables derived file caching.
</para>

<para>
When specifying a
<parameter>custom_class</parameter> which should be a class type which is a subclass of
<classname>SCons.CacheDir.CacheDir</classname>, SCons will
internally invoke this class to use for performing caching operations.
This argument is optional and if left to default <constant>None</constant>, will use the
default <classname>SCons.CacheDir.CacheDir</classname> class.
</para>

<para>
Calling the environment method
&f-link-env-CacheDir;
limits the effect to targets built
through the specified construction environment.
Calling the global function
&f-link-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 &f-env-CacheDir;.
</para>

<para>
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
<computeroutput>Retrieved `file' from cache</computeroutput>
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.
</para>

<para>
The
<computeroutput>Retrieved `file' from cache</computeroutput>
messages are useful for human consumption,
but less so when comparing log files between
&scons; runs which will show differences that are
noisy and not actually significant.
To disable,
use the <option>--cache-show</option> option.
With this option, &scons;
will print the action that would
have been used to build the file without
considering cache retrieval.
</para>

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

<para>
If the
<option>--cache-force</option>
option is used,
&scons;
will place a copy of
<emphasis>all</emphasis>
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 a
<parameter>cache_dir</parameter>
is used for a build,
or to bring a cache up to date after
a build with cache updating disabled
(<option>--cache-disable</option>
or <option>--cache-readonly</option>)
has been done.
</para>

<para>
The
&f-link-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.
</para>
</summary>
</scons_function>

<scons_function name="Clean">
<arguments>
(targets, files_or_dirs)
</arguments>
<summary>
<para>
This specifies a list of files or directories which should be removed
whenever the targets are specified with the
<option>-c</option>
command line option.
The specified targets may be a list
or an individual target.
Multiple calls to
&f-Clean;
are legal,
and create new targets or add files and directories to the
clean list for the specified targets.
</para>

<para>
Multiple files or directories should be specified
either as separate arguments to the
&f-Clean;
method, or as a list.
&f-Clean;
will also accept the return value of any of the construction environment
Builder methods.
Examples:
</para>

<para>
The related
&f-link-NoClean;
function overrides calling
&f-Clean;
for the same target,
and any targets passed to both functions will
<emphasis>not</emphasis>
be removed by the
<option>-c</option>
option.
</para>

<para>
Examples:
</para>

<example_commands>
Clean('foo', ['bar', 'baz'])
Clean('dist', env.Program('hello', 'hello.c'))
Clean(['foo', 'bar'], 'something_else_to_clean')
</example_commands>

<para>
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.
</para>
<example_commands>
Clean(docdir, os.path.join(docdir, projectname))
</example_commands>
</summary>
</scons_function>

<scons_function name="Clone">
<arguments signature="env">
([key=val, ...])
</arguments>
<summary>
<para>
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.
</para>

<para>
Example:
</para>

<example_commands>
env2 = env.Clone()
env3 = env.Clone(CCFLAGS='-g')
</example_commands>

<para>
Additionally, a list of tools and a toolpath may be specified, as in
the &f-link-Environment; constructor:
</para>

<example_commands>
def MyTool(env):
    env['FOO'] = 'bar'

env4 = env.Clone(tools=['msvc', MyTool])
</example_commands>

<para>
The
<parameter>parse_flags</parameter>
keyword argument is also recognized to allow merging command-line
style arguments into the appropriate construction
variables (see &f-link-env-MergeFlags;).
</para>

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

<builder name="Command">
<summary>
<para>
The &b-Command; "Builder" is actually
a function that looks like a Builder,
but takes a required third argument, which is the
action to take to construct the target
from the source, used for "one-off" builds
where a full builder is not needed.
Thus it does not follow the builder
calling rules described at the start of this section.
See instead the &f-link-Command; function description
for the calling syntax and details.
</para>
</summary>
</builder>

<scons_function name="Command">
<arguments>
(target, source, action, [key=val, ...])
</arguments>
<summary>
<para>
Executes a specific <parameter>action</parameter>
(or list of actions)
to build a <parameter>target</parameter> file or files
from a <parameter>source</parameter> file or files.
This is more convenient
than defining a separate Builder object
for a single special-case build.
</para>

<para>
The
&Command; function accepts
<parameter>source_scanner</parameter>,
<parameter>target_scanner</parameter>,
<parameter>source_factory</parameter>, and
<parameter>target_factory</parameter>
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
<literal>DirScanner</literal>
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 <parameter>*_factory</parameter> 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.
</para>

<para>
Any other keyword arguments specified override any
same-named existing construction variables.
</para>

<para>
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
(<literal>@</literal>)
to suppress printing the command in question,
or by a hyphen
(<literal>-</literal>)
to ignore the exit status of the external command.
</para>

<para>
Examples:
</para>

<example_commands>
env.Command(
    target='foo.out',
    source='foo.in',
    action="$FOO_BUILD &lt; $SOURCES &gt; $TARGET"
)

env.Command(
    target='bar.out',
    source='bar.in',
    action=["rm -f $TARGET", "$BAR_BUILD &lt; $SOURCES &gt; $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 &lt; $SOURCES &gt; .tmp", rename],
)
</example_commands>

<para>
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
&f-link-Dir;
or
&f-link-env-Dir;
functions.
</para>

<para>
Examples:
</para>

<example_commands>
env.Command('ddd.list', Dir('ddd'), 'ls -l $SOURCE > $TARGET')

env['DISTDIR'] = 'destination/directory'
env.Command(env.Dir('$DISTDIR')), None, make_distdir)
</example_commands>

<para>
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.
</para>
</summary>
</scons_function>

<scons_function name="Configure">
<arguments signature="global">
(env, [custom_tests, conf_dir, log_file, config_h])
</arguments>
<arguments signature="env">
([custom_tests, conf_dir, log_file, config_h])
</arguments>
<summary>
<para>
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.
</para>
</summary>
</scons_function>

<scons_function name="Decider">
<arguments>
(function)
</arguments>
<summary>
<para>
Specifies that all up-to-date decisions for
targets built through this construction environment
will be handled by the specified
<parameter>function</parameter>.
<parameter>function</parameter> can be the name of
a function or one of the following strings
that specify the predefined decision function
that will be applied:
</para>

<para>
<variablelist>
<varlistentry>
<term><literal>"timestamp-newer"</literal></term>
<listitem>
<para>
Specifies that a target shall be considered out of date and rebuilt
if the dependency's timestamp is newer than the target file's timestamp.
This is the behavior of the classic Make utility,
and
<literal>make</literal>
can be used a synonym for
<literal>timestamp-newer</literal>.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>"timestamp-match"</literal></term>
<listitem>
<para>
Specifies that a target shall be considered out of date and rebuilt
if the dependency's timestamp is different than the
timestamp recorded the last time the target was built.
This provides behavior very similar to the classic Make utility
(in particular, files are not opened up so that their
contents can be checksummed)
except that the target will also be rebuilt if a
dependency file has been restored to a version with an
<emphasis>earlier</emphasis>
timestamp, such as can happen when restoring files from backup archives.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>"content"</literal></term>
<listitem>
<para>
Specifies that a target shall be considered out of date and rebuilt
if the dependency's content has changed since the last time
the target was built,
as determined be performing an checksum
on the dependency's contents
and comparing it to the checksum recorded the
last time the target was built.
<literal>MD5</literal>
can be used as a synonym for
<literal>content</literal>, but it is deprecated.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>"content-timestamp"</literal></term>
<listitem>
<para>
Specifies that a target shall be considered out of date and rebuilt
if the dependency's content has changed since the last time
the target was built,
except that dependencies with a timestamp that matches
the last time the target was rebuilt will be
assumed to be up-to-date and
<emphasis>not</emphasis>
rebuilt.
This provides behavior very similar
to the
<literal>content</literal>
behavior of always checksumming file contents,
with an optimization of not checking
the contents of files whose timestamps haven't changed.
The drawback is that SCons will
<emphasis>not</emphasis>
detect if a file's content has changed
but its timestamp is the same,
as might happen in an automated script
that runs a build,
updates a file,
and runs the build again,
all within a single second.
<literal>MD5-timestamp</literal>
can be used as a synonym for
<literal>content-timestamp</literal>, but it is deprecated.
</para>
</listitem>
</varlistentry>
</variablelist>
</para>

<para>
Examples:
</para>

<example_commands>
# 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')
</example_commands>

<para>
In addition to the above already-available functions, the
<parameter>function</parameter>
argument may be a &Python; function you supply.
Such a function must accept the following four arguments:
</para>

<para>
<variablelist>
<varlistentry>
<term><parameter>dependency</parameter></term>
<listitem>
<para>
The Node (file) which
should cause the
<parameter>target</parameter>
to be rebuilt
if it has "changed" since the last tme
<parameter>target</parameter>
was built.
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>target</parameter></term>
<listitem>
<para>
The Node (file) being built.
In the normal case,
this is what should get rebuilt
if the
<parameter>dependency</parameter>
has "changed."
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><parameter>prev_ni</parameter></term>
<listitem>
<para>
Stored information about the state of the
<parameter>dependency</parameter>
the last time the
<parameter>target</parameter>
was built.
This can be consulted to match various
file characteristics
such as the timestamp,
size, or content signature.
</para>
</listitem>
</varlistentry>
    <varlistentry>
<term><parameter>repo_node</parameter></term>
<listitem>
<para>
If set, use this Node instead of the one specified by
<parameter>dependency</parameter>
to determine if the dependency has changed.
This argument is optional so should be written
as a default argument (typically it would be
written as <parameter>repo_node=None</parameter>).
A caller will normally only set this if the
target only exists in a Repository.
</para>
</listitem>
</varlistentry>

</variablelist>
</para>

<para>
The
<parameter>function</parameter>
should return a value which evaluates
<constant>True</constant>
if the
<parameter>dependency</parameter>
has "changed" since the last time
the
<parameter>target</parameter>
was built
(indicating that the target
<emphasis>should</emphasis>
be rebuilt),
and a value which evaluates
<constant>False</constant>
otherwise
(indicating that the target should
<emphasis>not</emphasis>
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.
</para>

<para>
Example:
</para>

<example_commands>
def my_decider(dependency, target, prev_ni, repo_node=None):
    return not os.path.exists(str(target))

env.Decider(my_decider)
</example_commands>
</summary>
</scons_function>

<scons_function name="Depends">
<arguments>
(target, dependency)
</arguments>
<summary>
<para>
Specifies an explicit dependency;
the
<parameter>target</parameter>
will be rebuilt
whenever the
<parameter>dependency</parameter>
has changed.
Both the specified
<parameter>target</parameter>
and
<parameter>dependency</parameter>
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.
</para>

<para>
Example:
</para>

<example_commands>
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)
</example_commands>
</summary>
</scons_function>

<scons_function name="Detect">
<arguments signature="env">
(progs)
</arguments>
<summary>
<para>
Find an executable from one or more choices:
<parameter>progs</parameter> may be a string or a list of strings.
Returns the first value from <parameter>progs</parameter>
that was found, or <constant>None</constant>.
Executable is searched by checking the paths specified
by <varname>env</varname><literal>['ENV']['PATH']</literal>.
On Windows systems, additionally applies the filename suffixes found in
<varname>env</varname><literal>['ENV']['PATHEXT']</literal>
but will not include any such extension in the return value.
&f-env-Detect; is a wrapper around &f-link-env-WhereIs;.
</para>
</summary>
</scons_function>

<scons_function name="Dictionary">
<arguments signature="env">
([vars])
</arguments>
<summary>
<para>
Returns a dictionary object
containing the &consvars; in the &consenv;.
If there are any arguments specified,
the values of the specified &consvars;
are returned as a string (if one
argument) or as a list of strings.
</para>

<para>
Example:
</para>

<example_commands>
cvars = env.Dictionary()
cc_values = env.Dictionary('CC', 'CCFLAGS', 'CCCOM')
</example_commands>
</summary>
</scons_function>

<scons_function name="Dir">
<arguments>
(name, [directory])
</arguments>
<summary>
<para>
Returns Directory Node(s).
A Directory Node is an object that represents a directory.
<parameter>name</parameter>
can be a relative or absolute path or a list of such paths.
<parameter>directory</parameter>
is an optional directory that will be used as the parent directory.
If no
<parameter>directory</parameter>
is specified, the current script's directory is used as the parent.
</para>

<para>
If
<parameter>name</parameter>
is a single pathname, the corresponding node is returned.
If
<parameter>name</parameter>
is a list, SCons returns a list of nodes.
Construction variables are expanded in
<parameter>name</parameter>.
</para>

<para>
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.
</para>
</summary>
</scons_function>

<scons_function name="Dump">
<arguments signature="env">
([key], [format])
</arguments>
<summary>
<para>
Serializes &consvars; to a string.
The method supports the following formats specified by
<parameter>format</parameter>:
<variablelist>
<varlistentry>
<term><literal>pretty</literal></term>
<listitem>
<para>
Returns a pretty printed representation of the environment (if
<parameter>format</parameter>
is not specified, this is the default).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>json</literal></term>
<listitem>
<para>
Returns a JSON-formatted string representation of the environment.
</para>
</listitem>
</varlistentry>
</variablelist>

If <varname>key</varname> is
<constant>None</constant> (the default) the entire
dictionary of &consvars; is serialized.
If supplied, it is taken as the name of a &consvar;
whose value is serialized.
</para>

<para>
This SConstruct:
</para>

<example_commands>
env=Environment()
print(env.Dump('CCCOM'))
</example_commands>

<para>
will print:
</para>

<example_commands>
'$CC -c -o $TARGET $CCFLAGS $CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS $SOURCES'
</example_commands>

<para>
While this SConstruct:
</para>

<example_commands>
env = Environment()
print(env.Dump())
</example_commands>

<para>
will print:
</para>
<example_commands>
{ 'AR': 'ar',
  'ARCOM': '$AR $ARFLAGS $TARGET $SOURCES\n$RANLIB $RANLIBFLAGS $TARGET',
  'ARFLAGS': ['r'],
  'AS': 'as',
  'ASCOM': '$AS $ASFLAGS -o $TARGET $SOURCES',
  'ASFLAGS': [],
  ...
</example_commands>
</summary>
</scons_function>

<scons_function name="Environment">
<arguments>
([key=value, ...])
</arguments>
<summary>
<para>
Return a new construction environment
initialized with the specified
<parameter>key</parameter>=<replaceable>value</replaceable>
pairs.
The keyword arguments
<parameter>parse_flags</parameter>,
<parameter>platform</parameter>,
<parameter>toolpath</parameter>,
<parameter>tools</parameter>
and <parameter>variables</parameter>
are also specially recognized.
See the manpage section "Construction Environments" for more details.
</para>
</summary>
</scons_function>

<scons_function name="Execute">
<arguments>
(action, [strfunction, varlist])
</arguments>
<summary>
<para>
Executes an Action object.
The specified
<parameter>action</parameter>
may be an Action object
(see manpage section "Action Objects"
for an explanation of 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.
Any additional arguments to &f-Execute;
(<parameter>strfunction</parameter>, <parameter>varlist</parameter>)
are passed on to the &f-link-Action; factory function
which actually creates the Action object.
The exit value of the command
or return value of the &Python; function
will be returned.
</para>

<para>
Note that
&scons;
will print an error message if the executed
<parameter>action</parameter>
fails--that is,
exits with or returns a non-zero value.
&scons;
will
<emphasis>not</emphasis>,
however,
automatically terminate the build
if the specified
<parameter>action</parameter>
fails.
If you want the build to stop in response to a failed
&f-Execute;
call,
you must explicitly check for a non-zero return value:
</para>

<example_commands>
Execute(Copy('file.out', 'file.in'))

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

<scons_function name="File">
<arguments>
(name, [directory])
</arguments>
<summary>
<para>
Returns File Node(s).
A File Node is an object that represents a file.
<parameter>name</parameter>
can be a relative or absolute path or a list of such paths.
<parameter>directory</parameter>
is an optional directory that will be used as the parent directory.
If no
<parameter>directory</parameter>
is specified, the current script's directory is used as the parent.
</para>

<para>
If
<parameter>name</parameter>
is a single pathname, the corresponding node is returned.
If
<parameter>name</parameter>
is a list, SCons returns a list of nodes.
Construction variables are expanded in
<parameter>name</parameter>.
</para>

<para>
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.
</para>
</summary>
</scons_function>

<scons_function name="FindFile">
<arguments>
(file, dirs)
</arguments>
<summary>
<para>
Search for
<parameter>file</parameter>
in the path specified by
<parameter>dirs</parameter>.
<parameter>dirs</parameter>
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.
</para>

<para>
Example:
</para>

<example_commands>
foo = env.FindFile('foo', ['dir1', 'dir2'])
</example_commands>
</summary>
</scons_function>

<scons_function name="FindInstalledFiles">
<arguments>
()
</arguments>
<summary>
<para>
Returns the list of targets set up by the
&b-link-Install;
or
&b-link-InstallAs;
builders.
</para>

<para>
This function serves as a convenient method to select the contents of
a binary package.
</para>

<para>
Example:
</para>

<example_commands>
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()
</example_commands>
</summary>
</scons_function>

<scons_function name="FindSourceFiles">
<arguments>
(node='"."')
</arguments>
<summary>
<para>
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
<parameter>node</parameter>
which defaults to the '"."'-node. It will then return all leaves of
<parameter>node</parameter>.
These are all children which have no further children.
</para>

<para>
This function is a convenient method to select the contents of a Source
Package.
</para>

<para>
Example:
</para>

<example_commands>
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')
</example_commands>

<para>
As you can see build support files (SConstruct in the above example)
will also be returned by this function.
</para>
</summary>
</scons_function>

<scons_function name="Flatten">
<arguments>
(sequence)
</arguments>
<summary>
<para>
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.
</para>

<para>
Examples:
</para>

<example_commands>
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))
</example_commands>
</summary>
</scons_function>

<scons_function name="GetBuildPath">
<arguments>
(file, [...])
</arguments>
<summary>
<para>
Returns the
&scons;
path name (or names) for the specified
<parameter>file</parameter>
(or files).
The specified
<parameter>file</parameter>
or files
may be
&scons;
Nodes or strings representing path names.
</para>
</summary>
</scons_function>

<scons_function name="Glob">
<arguments>
(pattern, [ondisk, source, strings, exclude])
</arguments>
<summary>
<para>
Returns Nodes (or strings) that match the specified
<parameter>pattern</parameter>,
relative to the directory of the current
&SConscript;
file.
The evironment method form (&f-env-Glob;)
performs string substition on
<parameter>pattern</parameter>
and returns whatever matches
the resulting expanded pattern.
</para>

<para>
The specified
<parameter>pattern</parameter>
uses Unix shell style metacharacters for matching:
</para>

<example_commands>
  *       matches everything
  ?       matches any single character
  [seq]   matches any character in seq
  [!seq]  matches any char not in seq
</example_commands>

<para>
If the first character of a filename is a dot,
it must be matched explicitly.
Character matches do
<emphasis>not</emphasis>
span directory separators.
</para>

<para>
The
&f-Glob;
knows about
repositories
(see the
&f-link-Repository;
function)
and source directories
(see the
&f-link-VariantDir;
function)
and
returns a Node (or string, if so configured)
in the local (SConscript) directory
if a matching Node is found
anywhere in a corresponding
repository or source directory.
</para>

<para>
The
<parameter>ondisk</parameter>
argument may be set to a value which evaluates
<constant>False</constant>
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.
</para>

<para>
The
<parameter>source</parameter>
argument may be set to a value which evaluates
<constant>True</constant>
to specify that,
when the local directory is a
&f-VariantDir;,
the returned Nodes should be from the
corresponding source directory,
not the local directory.
</para>

<para>
The
<parameter>strings</parameter>
argument may be set to a value which evaluates
<constant>True</constant>
to have the
&f-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.)
</para>

<para>
The
<parameter>exclude</parameter>
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.
</para>

<para>
Examples:
</para>

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

<!--
<scons_function name="GlobalBuilders">
<arguments signature="global">
(flag)
</arguments>
<summary>
<para>
When
<parameter>flag</parameter>
is non-zero,
adds the names of the default builders
(Program, Library, etc.)
to the global name space
so they can be called without an explicit construction environment.
(This is the default.)
When
<parameter>flag</parameter>
is zero,
the names of the default builders are removed
from the global name space
so that an explicit construction environment is required
to call all builders.
</para>
</summary>
</scons_function>
-->

<scons_function name="Ignore">
<arguments>
(target, dependency)
</arguments>
<summary>
<para>
The specified dependency file(s)
will be ignored when deciding if
the target file(s) need to be rebuilt.
</para>

<para>
You can also use
&f-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.
</para>

<para>
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.
</para>

<para>
Examples:
</para>

<example_commands>
env.Ignore('foo', 'foo.c')
env.Ignore('bar', ['bar1.h', 'bar2.h'])
env.Ignore('.', 'foobar.obj')
env.Ignore('bar', 'bar/foobar.obj')
</example_commands>
</summary>
</scons_function>

<scons_function name="Literal">
<arguments>
(string)
</arguments>
<summary>
<para>
The specified
<parameter>string</parameter>
will be preserved as-is
and not have construction variables expanded.
</para>
</summary>
</scons_function>

<scons_function name="Local">
<arguments>
(targets)
</arguments>
<summary>
<para>
The specified
<parameter>targets</parameter>
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.
</para>
</summary>
</scons_function>

<!--
<scons_function name="MergeShellPaths">
<arguments signature="env">
( arg ", [" prepend ])
</arguments>
<summary>
<para>
Merges the elements of the specified
<parameter>arg</parameter>,
which must be a dictionary, to the construction
environment's copy of the shell environment
in env['ENV'].
(This is the environment which is passed
to subshells spawned by SCons.)
Note that
<parameter>arg</parameter>
must be a single value,
so multiple strings must
be passed in as a list,
not as separate arguments to
&f-MergeShellPaths;.
</para>

<para>
New values are prepended to the environment variable by default,
unless prepend=0 is specified.
Duplicate values are always eliminated,
since this function calls
&f-link-AppendENVPath;
or
&f-link-PrependENVPath;
depending on the
<parameter>prepend</parameter>
argument.  See those functions for more details.
</para>

<para>
Examples:
</para>

<example_commands>
# Prepend a path to the shell PATH.
env.MergeShellPaths({'PATH': '/usr/local/bin'})
# Append two dirs to the shell INCLUDE.
env.MergeShellPaths({'INCLUDE': ['c:/inc1', 'c:/inc2']}, prepend=0)
</example_commands>
</summary>
</scons_function>
-->

<scons_function name="MergeFlags">
<arguments signature="env">
(arg, [unique])
</arguments>
<summary>
<para>
Merges values from
<parameter>arg</parameter>
into &consvars; in the current &consenv;.
If
<parameter>arg</parameter>
is not a dictionary,
it is converted to one by calling
&f-link-env-ParseFlags;
on the argument
before the values are merged.
Note that
<parameter>arg</parameter>
must be a single value,
so multiple strings must
be passed in as a list,
not as separate arguments to
&f-env-MergeFlags;.
</para>

<para>
By default,
duplicate values are eliminated;
you can, however, specify
<literal>unique=False</literal>
to allow duplicate
values to be added.
When eliminating duplicate values,
any &consvars; that end with
the string
<literal>PATH</literal>
keep the left-most unique value.
All other &consvars; keep
the right-most unique value.
</para>

<para>
Examples:
</para>

<example_commands>
# 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'])
</example_commands>
</summary>
</scons_function>

<scons_function name="NoCache">
<arguments>
(target, ...)
</arguments>
<summary>
<para>
Specifies a list of files which should
<emphasis>not</emphasis>
be cached whenever the
&f-link-CacheDir;
method has been activated.
The specified targets may be a list
or an individual target.
</para>

<para>
Multiple files should be specified
either as separate arguments to the
&f-NoCache;
method, or as a list.
&f-NoCache;
will also accept the return value of any of the construction environment
Builder methods.
</para>

<para>
Calling
&f-NoCache;
on directories and other non-File Node types has no effect because
only File Nodes are cached.
</para>

<para>
Examples:
</para>

<example_commands>
NoCache('foo.elf')
NoCache(env.Program('hello', 'hello.c'))
</example_commands>
</summary>
</scons_function>

<scons_function name="NoClean">
<arguments>
(target, ...)
</arguments>
<summary>
<para>
Specifies a list of files or directories which should
<emphasis>not</emphasis>
be removed whenever the targets (or their dependencies)
are specified with the
<option>-c</option>
command line option.
The specified targets may be a list
or an individual target.
Multiple calls to
&f-NoClean;
are legal,
and prevent each specified target
from being removed by calls to the
<option>-c</option>
option.
</para>

<para>
Multiple files or directories should be specified
either as separate arguments to the
&f-NoClean;
method, or as a list.
&f-NoClean;
will also accept the return value of any of the construction environment
Builder methods.
</para>

<para>
Calling
&f-NoClean;
for a target overrides calling
&f-link-Clean;
for the same target,
and any targets passed to both functions will
<emphasis>not</emphasis>
be removed by the
<option>-c</option>
option.
</para>

<para>
Examples:
</para>

<example_commands>
NoClean('foo.elf')
NoClean(env.Program('hello', 'hello.c'))
</example_commands>
</summary>
</scons_function>

<scons_function name="ParseConfig">
<arguments signature="env">
(command, [function, unique])
</arguments>
<summary>
<para>
Updates the current &consenv; with the values extracted
from the output from running external <parameter>command</parameter>,
by calling a helper function <parameter>function</parameter>
which understands
the output of <parameter>command</parameter>.
<parameter>command</parameter> may be a string
or a list of strings representing the command and
its arguments.
If <parameter>function</parameter>
is not given,
&f-link-env-MergeFlags; is used.
By default,
duplicate values are not
added to any construction variables;
you can specify
<parameter>unique=False</parameter>
to allow duplicate values to be added.
</para>

<para>
If &f-env-MergeFlags; is used,
it expects a response in the style of a
<command>*-config</command>
command typical of the POSIX programming environment
(for example,
<application>gtk-config</application>)
and adds the options
to the appropriate construction variables.
Interpreted options
and the construction variables they affect
are as specified for the
&f-link-env-ParseFlags;
method (which
&f-env-MergeFlags; calls).
See that method's description
for a table of options and corresponding construction variables.
</para>

<para>
If &f-env-MergeFlags; cannot interpret the results of
<parameter>command</parameter>,
you can suppply a custom
<parameter>function</parameter> to do so.
<parameter>function</parameter>
must accept three arguments:
the &consenv; to modify, the string returned
by running <parameter>command</parameter>,
and the optional
<parameter>unique</parameter> flag.
</para>
</summary>
</scons_function>

<scons_function name="ParseDepends">
<arguments>
(filename, [must_exist, only_one])
</arguments>
<summary>
<para>
Parses the contents of the specified
<parameter>filename</parameter>
as a list of dependencies in the style of
&Make;
or
<application>mkdep</application>,
and explicitly establishes all of the listed dependencies.
</para>

<para>
By default,
it is not an error
if the specified
<parameter>filename</parameter>
does not exist.
The optional
<parameter>must_exist</parameter>
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.
</para>

<para>
The optional
<parameter>only_one</parameter>
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
<literal>gcc -M</literal>
flag,
which should typically only
write dependency information for
one output file into a corresponding
<filename>.d</filename>
file.
</para>

<para>
The
<parameter>filename</parameter>
and all of the files listed therein
will be interpreted relative to
the directory of the
&SConscript;
file which calls the
&f-ParseDepends;
function.
</para>
</summary>
</scons_function>

<scons_function name="ParseFlags">
<arguments signature="env">
(flags, ...)
</arguments>
<summary>
<para>
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
&f-link-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
&f-env-MergeFlags;
will call this method if its argument is not a dictionary,
so it is usually not necessary to call
&f-env-ParseFlags;
directly unless you want to manipulate the values.)
</para>

<para>
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.
</para>

<para>
Flag values are translated accordig to the prefix found,
and added to the following construction variables:
</para>

<example_commands>
-arch                   CCFLAGS, LINKFLAGS
-D                      CPPDEFINES
-framework              FRAMEWORKS
-frameworkdir=          FRAMEWORKPATH
-fmerge-all-constants   CCFLAGS, LINKFLAGS
-fopenmp                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
</example_commands>

<para>
Any other strings not associated with options
are assumed to be the names of libraries
and added to the
&cv-LIBS;
construction variable.
</para>

<para>
Examples (all of which produce the same result):
</para>

<example_commands>
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')
</example_commands>
</summary>
</scons_function>

<scons_function name="Platform">
<arguments signature="global">
(plat)
</arguments>
<arguments signature="env">
(plat)
</arguments>
<summary>
<para>
When called as a global function,
returns a callable platform object
selected by <parameter>plat</parameter>
(defaults to the detected platform for the
current system)
that can be used to initialize
a construction environment by passing it as the
<parameter>platform</parameter> keyword argument to the
&f-link-Environment; function.
</para>

<para>
Example:
</para>

<example_commands>
env = Environment(platform=Platform('win32'))
</example_commands>

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

<example_commands>
env.Platform('posix')
</example_commands>

<para>
See the manpage section "Construction Environments" for more details.
</para>
</summary>
</scons_function>

<scons_function name="Prepend">
<arguments signature="env">
(key=val, [...])
</arguments>
<summary>
<para>
Prepend values to &consvars; in the current &consenv;,
Works like &f-link-env-Append; (see for details),
except that values are added to the front,
rather than the end, of any existing value of the &consvar;
</para>

<para>
Example:
</para>

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

<para>
See also &f-link-env-Append;,
&f-link-env-AppendUnique;
and &f-link-env-PrependUnique;.
</para>
</summary>
</scons_function>

<scons_function name="PrependENVPath">
<arguments signature="env">
(name, newpath, [envname, sep, delete_existing])
</arguments>
<summary>
<para>
Prepend new path elements to the given path in the
specified external environment (&cv-link-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
<systemitem>os.path.normpath</systemitem>
and
<systemitem>os.path.normcase</systemitem>).
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.
</para>

<para>
If
<parameter>delete_existing</parameter>
is <constant>False</constant>,
then adding a path that already exists
will not move it to the beginning;
it will stay where it is in the list.
</para>

<para>
Example:
</para>

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

<para>Yields:</para>

<screen>
before: /biz:/foo
after: /foo/bar:/foo:/biz
</screen>
</summary>
</scons_function>

<scons_function name="PrependUnique">
<arguments signature="env">
(key=val, delete_existing=False, [...])
</arguments>
<summary>
<para>
Prepend values to &consvars; in the current &consenv;,
maintaining uniqueness.
Works like &f-link-env-Append; (see for details),
except that values are added to the front,
rather than the end, of any existing value of the the &consvar;,
and values already present in the &consvar;
will not be added again.
If <parameter>delete_existing</parameter>
is <constant>True</constant>,
the existing matching value is first removed,
and the requested value is inserted,
having the effect of moving such values to the front.
</para>

<para>
Example:
</para>

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

<para>
See also &f-link-env-Append;,
&f-link-env-AppendUnique;
and &f-link-env-Prepend;.
</para>
</summary>
</scons_function>

<scons_function name="PyPackageDir">
<arguments>
(modulename)
</arguments>
<summary>
<para>
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.
<parameter>modulename</parameter>
Is a named python package / module to
lookup the directory for it's location.
</para>
<para>
If
<parameter>modulename</parameter>
is a list, SCons returns a list of Dir nodes.
Construction variables are expanded in
<parameter>modulename</parameter>.
</para>
</summary>
</scons_function>

<scons_function name="Replace">
<arguments signature="env">
(key=val, [...])
</arguments>
<summary>
<para>
Replaces construction variables in the Environment
with the specified keyword arguments.
</para>

<para>
Example:
</para>

<example_commands>
env.Replace(CCFLAGS='-g', FOO='foo.xxx')
</example_commands>
</summary>
</scons_function>

<scons_function name="Repository">
<arguments>
(directory)
</arguments>
<summary>
<para>
Specifies that
<parameter>directory</parameter>
is a repository to be searched for files.
Multiple calls to
&f-Repository;
are legal,
and each one adds to the list of
repositories that will be searched.
</para>

<para>
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.
</para>

<para>
Note that if an up-to-date derived file
already exists in a repository,
&scons;
will
<emphasis>not</emphasis>
make a copy in the local directory tree.
In order to guarantee that a local copy
will be made,
use the
&f-link-Local;
method.
</para>
</summary>
</scons_function>

<scons_function name="Requires">
<arguments>
(target, prerequisite)
</arguments>
<summary>
<para>
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,
<emphasis>before</emphasis>
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.
</para>

<para>
Example:
</para>

<example_commands>
env.Requires('foo', 'file-that-must-be-built-before-foo')
</example_commands>
</summary>
</scons_function>

<scons_function name="Scanner">
<arguments>
(function, [name, argument, skeys, path_function, node_class, node_factory, scan_check, recursive])
</arguments>
<summary>
<para>
Creates a Scanner object for
the specified
<parameter>function</parameter>.
See manpage section "Scanner Objects"
for a complete explanation of the arguments and behavior.
</para>
</summary>
</scons_function>

<scons_function name="SConscriptChdir">
<arguments>
(value)
</arguments>
<summary>
<para>
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:
</para>

<example_commands>
SConscriptChdir(0)
env.SConscriptChdir(0)
</example_commands>

<para>
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.
</para>

<para>
Example:
</para>

<example_commands>
env = Environment()
SConscriptChdir(0)
SConscript('foo/SConscript')	# will not chdir to foo
env.SConscriptChdir(1)
SConscript('bar/SConscript')	# will chdir to bar
</example_commands>
</summary>
</scons_function>

<scons_function name="SConsignFile">
<arguments>
([name, dbm_module])
</arguments>
<summary>
<para>
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.
</para>
<para>
The optional <parameter>name</parameter> 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
<filename>.sconsign</filename>.
The actual database file(s) stored on disk
may have an appropriate suffix appended
by the chosen
<parameter>dbm_module</parameter>
</para>
<para>
The optional <parameter>dbm_module</parameter>
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
<systemitem>SCons.dblite</systemitem>
module that uses pickled
&Python; data structures,
which works on all &Python; versions.
See documentation of the &Python;
<systemitem>dbm</systemitem> module
for other available types.
</para>
<para>
If called with no arguments,
the database will default to
<filename>.sconsign.dblite</filename>
in the top directory of the project,
which is also the default if
if &f-SConsignFile; is not called.
</para>
<para>
The setting is global, so the only difference
between the global function and the environment method form
is variable expansion on <parameter>name</parameter>.
There should only be one active call to this
function/method in a given build setup.
</para>
<para>
If
<parameter>name</parameter>
is set to
<constant>None</constant>,
&scons;
will store file signatures
in a separate
<filename>.sconsign</filename>
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.
</para>

<para>
Examples:
</para>

<example_commands>
# 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)
</example_commands>
</summary>
</scons_function>

<scons_function name="SetDefault">
<arguments signature="env">
(key=val, [...])
</arguments>
<summary>
<para>
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:
</para>

<example_commands>
env.SetDefault(FOO='foo')
if 'FOO' not in env:
    env['FOO'] = 'foo'
</example_commands>
</summary>
</scons_function>

<scons_function name="SideEffect">
<arguments>
(side_effect, target)
</arguments>
<summary>
<para>
Declares
<parameter>side_effect</parameter>
as a side effect of building
<parameter>target</parameter>.
Both
<parameter>side_effect</parameter>
and
<parameter>target</parameter>
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.
</para>

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

<para>
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.
</para>
</summary>
</scons_function>

<scons_function name="Split">
<arguments>(arg)</arguments>
<summary>
<para>
If <parameter>arg</parameter> 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 <parameter>arg</parameter> is a list or tuple
returns the list or tuple unchanged.
If <parameter>arg</parameter> 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
&f-Split; without having to first check its type.
</para>

<para>
Example:
</para>

<example_commands>
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
""")
</example_commands>
</summary>
</scons_function>

<scons_function name="subst">
<arguments signature="env">
(input, [raw, target, source, conv])
</arguments>
<summary>
<para>
Performs construction variable interpolation
on <parameter>input</parameter>,
which can be a string or a sequence.
</para>

<para>
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
<literal>$(</literal>
and
<literal>$)</literal>
character sequences will be stripped from the returned string,
The optional
<parameter>raw</parameter>
argument may be set to
<literal>1</literal>
if you want to preserve white space and
<literal>$(</literal>-<literal>$)</literal>
sequences.
The
<parameter>raw</parameter>
argument may be set to
<literal>2</literal>
if you want to additionally discard
all characters between any
<literal>$(</literal>
and
<literal>$)</literal>
pairs
(as is done for signature calculation).
</para>

<para>
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.
</para>

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

<para>
Returned string values or sequence elements
are converted to their string representation by default.
The optional
<parameter>conv</parameter>
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.
</para>

<para>
Example:
</para>

<example_commands>
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)
</example_commands>
</summary>
</scons_function>

<scons_function name="Tool">
<arguments>
(name, [toolpath, **kwargs])
</arguments>
<summary>

<para>
Locates the tool specification module <parameter>name</parameter>
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
<parameter>toolpath</parameter> parameter.
The standard locations are &SCons;' own internal
path for tools plus the toolpath, if any (see the
<emphasis role="bold">Tools</emphasis> section in the manual page
for more details).
Any additional keyword arguments
<parameter>kwargs</parameter> are passed
to the tool module's <function>generate</function> function
during tool object construction.
</para>

<para>
When called, the tool object
updates a &consenv; with &consvars; and arranges
any other initialization
needed to use the mechanisms that tool describes.
</para>

<para>
When the &f-env-Tool; form is used,
the tool object is automatically called to update <varname>env</varname>
and the value of <parameter>tool</parameter> is
appended to the &cv-link-TOOLS;
&consvar; in that environment.
</para>

<para>
Examples:
</para>

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

<para>
When the global function &f-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
&f-link-Environment; or &f-link-Clone; call
as part of the <parameter>tools</parameter> keyword argument,
in which case the tool is applied to the environment being constructed,
or it can be called directly,
in which case a &consenv; to update must be
passed as the argument.
Either approach will also update the
&cv-TOOLS; &consvar;.
</para>

<para>
Examples:
</para>

<example_commands>
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
</example_commands>

<para>
<emphasis>Changed in &SCons; 4.2: &f-env-Tool; now returns
the tool object, previously it did not return
(i.e. returned <constant>None</constant>).</emphasis>
</para>
</summary>
</scons_function>

<scons_function name="Value">
<arguments>
(value, [built_value], [name])
</arguments>
<summary>
<para>
Returns a Node object representing the specified &Python; value.  Value
Nodes can be used as dependencies of targets.  If the result of
calling
<function>str</function>(<parameter>value</parameter>)
changes between SCons runs, any targets depending on
<function>Value</function>(<parameter>value</parameter>)
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.
<parameter>name</parameter> can be provided as an alternative name
for the resulting <literal>Value</literal> node; this is advised
if the <parameter>value</parameter> parameter can't be converted to
a string.
</para>

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

<para>
Examples:
</para>

<example_commands>
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 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))
</example_commands>
</summary>
</scons_function>

<scons_function name="VariantDir">
<arguments>
(variant_dir, src_dir, [duplicate])
</arguments>
<summary>
<para>
Sets up an alternate build location.
When building in the <parameter>variant_dir</parameter>,
&SCons; backfills as needed with files from <parameter>src_dir</parameter>
to create a complete build directory.
&f-VariantDir;
can be called multiple times with the same
<parameter>src_dir</parameter>
to set up multiple builds with different options
(<emphasis>variants</emphasis>).
</para>

<para>
The
<parameter>variant</parameter>
location must be in or underneath the project top directory,
and <parameter>src_dir</parameter>
may not be underneath
<parameter>variant_dir</parameter>.
</para>

<para>
By default, &SCons;
physically duplicates the source files and SConscript files
as needed into 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 if preprocessors or other scanners search for included files
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 <parameter>variant_dir</parameter>.
</para>

<para>
If possible on the platform,
the duplication is performed by linking rather than copying.
This behavior is affected by the
<option>--duplicate</option>
command-line option.
</para>

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

<para>
&f-VariantDir;
works most naturally with used with a subsidiary SConscript file.
The subsidiary SConscript file is called as if it
were in
<parameter>variant_dir</parameter>,
regardless of the value of
<parameter>duplicate</parameter>.
This is how you tell
&scons;
which variant of a source tree to build:
</para>

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

<para>
See also the
&f-link-SConscript;
function, described above,
for another way to specify a variant directory
in conjunction with calling a subsidiary SConscript file.
</para>

<para>
Examples:
</para>

<example_commands>
# 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)
</example_commands>
</summary>
</scons_function>

<scons_function name="WhereIs">
<arguments>
(program, [path, pathext, reject])
</arguments>
<summary>
<para>
Searches for the specified executable
<parameter>program</parameter>,
returning the full path to the program
or <constant>None</constant>.
</para>
<para>
When called as a &consenv; method,
searches the paths in the
<parameter>path</parameter> keyword argument,
or if <constant>None</constant> (the default)
the paths listed in the &consenv;
(<varname>env</varname><literal>['ENV']['PATH']</literal>).
The external environment's path list
(<literal>os.environ['PATH']</literal>)
is used as a fallback if the key
<varname>env</varname><literal>['ENV']['PATH']</literal>
does not exist.
</para>
<para>
On Windows systems, searches for executable
programs with any of the file extensions listed in the
<parameter>pathext</parameter> keyword argument,
or if <constant>None</constant> (the default)
the pathname extensions listed in the &consenv;
(<varname>env</varname><literal>['ENV']['PATHEXT']</literal>).
The external environment's pathname extensions list
(<literal>os.environ['PATHEXT']</literal>)
is used as a fallback if the key
<varname>env</varname><literal>['ENV']['PATHEXT']</literal>
does not exist.
</para>
<para>
When called as a global function, uses the external
environment's path
<literal>os.environ['PATH']</literal>
and path extensions
<literal>os.environ['PATHEXT']</literal>,
respectively, if
<parameter>path</parameter> and
<parameter>pathext</parameter> are
<constant>None</constant>.
</para>
<para>
Will not select any
path name or names
in the optional
<parameter>reject</parameter>
list.
</para>

</summary>
</scons_function>

</sconsdoc>