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

<variablelist 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">
  <varlistentry id="f-Action">
    <term><function>Action</function>(<parameter>action, [output, [var, ...]] [key=value, ...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Action</methodname>(<parameter>action, [output, [var, ...]] [key=value, ...]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-AddMethod">
    <term><function>AddMethod</function>(<parameter>object, function, [name]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>AddMethod</methodname>(<parameter>function, [name]</parameter>)</term>
    <listitem><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>
More 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>
</listitem>
  </varlistentry>
  <varlistentry id="f-AddOption">
    <term><function>AddOption</function>(<parameter>arguments</parameter>)</term>
    <listitem><para>
Adds a local (project-specific) command-line option.
<parameter>arguments</parameter>
are the same as those supported by the <function>add_option</function>
method in the standard Python library module <systemitem>optparse</systemitem>,
with a few additional capabilities noted below.
See the documentation for
<systemitem>optparse</systemitem>
for a thorough discussion of its option-processing capabities.
</para>

<para>
In addition to the arguments and values supported by the
<systemitem>optparse</systemitem>
<function>add_option</function>
method, &f-AddOption;
allows setting the
<parameter>nargs</parameter>
keyword value to
a string consisting of a question mark
(<literal>'?'</literal>)
to indicate that the option argument for
that option string is optional.
If the option string is present on the
command line but has no matching option
argument, the value of the
<parameter>const</parameter>
keyword argument is produced as the value
of the option.
If the option string is omitted from
the command line, the value of the
<parameter>default</parameter>
keyword argument is produced, as usual;
if there is no
<parameter>default</parameter>
keyword argument in the &f-AddOption; call,
<constant>None</constant> is produced.
</para>

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

<para>
Once a new command-line option has been added with
&f-AddOption;,
the option value may be accessed using
&f-link-GetOption;
or
&f-link-env-GetOption;.
&f-link-SetOption; is not currently supported for
options added with &f-AddOption;.
<!-- was:
The value may also be set using
&f-SetOption;
or
&f-env.SetOption;,
if conditions in a
&SConscript;
require overriding any default value.
Note however that a
value specified on the command line will
<emphasis>always</emphasis>
override a value set by any SConscript file.
-->
</para>

<para>
Help text for an option is a combination
of the string supplied in the
<parameter>help</parameter> keyword
argument to &f-AddOption; and information
collected from the other keyword arguments.
Such help is displayed if the
<option>-h</option> command line option
is used (but not with <option>-H</option>).
Help for all local options is displayed
under the separate heading
<emphasis role="bold">Local Options</emphasis>.
The options are unsorted - they will appear
in the help text in the order in which the
&f-AddOption;
calls occur.
</para>

<para>
Example:
</para>

<example_commands>
AddOption(
    '--prefix',
    dest='prefix',
    nargs=1,
    type='string',
    action='store',
    metavar='DIR',
    help='installation prefix',
)
env = Environment(PREFIX=GetOption('prefix'))
</example_commands>

<para>For that example,
the following help text would be produced:</para>

<screen>
Local Options:
  --prefix=DIR                installation prefix
</screen>

<para>
Help text for local options may be unavailable if
the &f-link-Help; function has been called,
see the &f-Help; documentation for details.
</para>

<note>
<para>
As an artifact of the internal implementation,
the behavior of options added by &AddOption;
which take option arguments is undefined
<emphasis>if</emphasis> whitespace
(rather than an <literal>=</literal> sign) is used as
the separator on the command line.
Users should avoid such usage; it is recommended
to add a note to this effect to project documentation
if the situation is likely to arise.
In addition, if the <parameter>nargs</parameter>
keyword is used to specify more than one following
option argument (that is, with a value of <constant>2</constant>
or greater), such arguments would necessarily
be whitespace separated, triggering the issue.
Developers should not use &AddOption; this way.
Future versions of &SCons; will likely forbid such usage.
</para>
</note>

</listitem>
  </varlistentry>
  <varlistentry id="f-AddPostAction">
    <term><function>AddPostAction</function>(<parameter>target, action</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>AddPostAction</methodname>(<parameter>target, action</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-AddPreAction">
    <term><function>AddPreAction</function>(<parameter>target, action</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>AddPreAction</methodname>(<parameter>target, action</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Alias">
    <term><function>Alias</function>(<parameter>alias, [targets, [action]]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Alias</methodname>(<parameter>alias, [targets, [action]]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-AllowSubstExceptions">
    <term><function>AllowSubstExceptions</function>(<parameter>[exception, ...]</parameter>)</term>
    <listitem><para>
Specifies the exceptions that will be allowed
when expanding construction variables.
By default,
any construction variable expansions that generate a
<literal>NameError</literal>
or
<literal>IndexError</literal>
exception will expand to a
<literal>''</literal>
(an empty string) and not cause scons to fail.
All exceptions not in the specified list
will generate an error message
and terminate processing.
</para>

<para>
If
&f-AllowSubstExceptions;
is called multiple times,
each call completely overwrites the previous list
of allowed exceptions.
</para>

<para>
Example:
</para>

<example_commands>
# 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)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-AlwaysBuild">
    <term><function>AlwaysBuild</function>(<parameter>target, ...</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>AlwaysBuild</methodname>(<parameter>target, ...</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Append">
    <term><replaceable>env</replaceable>.<methodname>Append</methodname>(<parameter>key=val, [...]</parameter>)</term>
    <listitem><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 <literal>*PATH</literal>;
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 <literal>PATH</literal>),
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>

</listitem>
  </varlistentry>
  <varlistentry id="f-AppendENVPath">
    <term><replaceable>env</replaceable>.<methodname>AppendENVPath</methodname>(<parameter>name, newpath, [envname, sep, delete_existing=False]</parameter>)</term>
    <listitem><para>
Append path elements specified by <parameter>newpath</parameter>
to the given search path string or list <parameter>name</parameter>
in mapping <parameter>envname</parameter> in the &consenv;.
Supplying <parameter>envname</parameter> is optional:
the default is the execution environment &cv-link-ENV;.
Optional <parameter>sep</parameter> is used as the search path separator,
the default is the platform's separator (<systemitem>os.pathsep</systemitem>).
A path element will only appear once.
Any duplicates in <parameter>newpath</parameter> are dropped,
keeping the last appearing (to preserve path order).
If <parameter>delete_existing</parameter>
is <constant>False</constant> (the default)
any addition duplicating an existing path element is ignored;
if <parameter>delete_existing</parameter>
is <constant>True</constant> the existing value will
be dropped and the path element will be added at the end.
To help maintain uniqueness all paths are normalized (using
<systemitem>os.path.normpath</systemitem>
and
<systemitem>os.path.normcase</systemitem>).
</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>

<para>
See also &f-link-env-PrependENVPath;.
</para>

</listitem>
  </varlistentry>
  <varlistentry id="f-AppendUnique">
    <term><replaceable>env</replaceable>.<methodname>AppendUnique</methodname>(<parameter>key=val, [...], delete_existing=False</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Builder">
    <term><function>Builder</function>(<parameter>action, [arguments]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Builder</methodname>(<parameter>action, [arguments]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-CacheDir">
    <term><function>CacheDir</function>(<parameter>cache_dir, custom_class=None</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>CacheDir</methodname>(<parameter>cache_dir, custom_class=None</parameter>)</term>
    <listitem><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 &buildsig; 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 &buildsig;, 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>

<para>
Note that (at this time) &SCons; provides no facilities
for managing the derived-file cache. It is up to the developer
to arrange for cache pruning, expiry, etc. if needed.
</para>

</listitem>
  </varlistentry>
  <varlistentry id="f-Clean">
    <term><function>Clean</function>(<parameter>targets, files_or_dirs</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Clean</methodname>(<parameter>targets, files_or_dirs</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Clone">
    <term><replaceable>env</replaceable>.<methodname>Clone</methodname>(<parameter>[key=val, ...]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Command">
    <term><function>Command</function>(<parameter>target, source, action, [key=val, ...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Command</methodname>(<parameter>target, source, action, [key=val, ...]</parameter>)</term>
    <listitem><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 &gt; $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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Configure">
    <term><function>Configure</function>(<parameter>env, [custom_tests, conf_dir, log_file, config_h]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Configure</methodname>(<parameter>[custom_tests, conf_dir, log_file, config_h]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Decider">
    <term><function>Decider</function>(<parameter>function</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Decider</methodname>(<parameter>function</parameter>)</term>
    <listitem><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 &contentsig;.
</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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Default">
    <term><function>Default</function>(<parameter>target[, ...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Default</methodname>(<parameter>target[, ...]</parameter>)</term>
    <listitem><para>
Specify default targets to the &SCons; target selection mechanism.
Any call to &f-Default; will cause &SCons; to use the
defined default target list instead of
its built-in algorithm for determining default targets
(see the manpage section "Target Selection").
</para>

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

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

<para>
The current list of targets added using
&f-Default; is available in the
&DEFAULT_TARGETS; list (see below).
</para>

<para>
Examples:
</para>

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

</listitem>
  </varlistentry>
  <varlistentry id="f-DefaultEnvironment">
    <term><function>DefaultEnvironment</function>(<parameter>[**kwargs]</parameter>)</term>
    <listitem><para>
Instantiates and returns the default &consenv; object.
The &defenv; is used internally by SCons
in order to execute many of the global functions in this list
(that is, those not called as methods of a specific &consenv;).
It is not mandatory to call &f-DefaultEnvironment;:
the &defenv; will be instantiated automatically when the
build phase begins if the function has not been called,
however calling it explicitly gives the opportunity to
affect and examine the contents of the &defenv;.
</para>
<para>
The &defenv; is a singleton, so the keyword
arguments affect it only on the first call, on subsequent
calls the already-constructed object is returned and
any keyword arguments are silently ignored.
The &defenv; can be modified after instantiation
in the same way as any &consenv;.
Modifying the &defenv; has no effect on the &consenv;
constructed by an &f-link-Environment; or &f-link-Clone; call.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Depends">
    <term><function>Depends</function>(<parameter>target, dependency</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Depends</methodname>(<parameter>target, dependency</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Detect">
    <term><replaceable>env</replaceable>.<methodname>Detect</methodname>(<parameter>progs</parameter>)</term>
    <listitem><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 in the execution environment
(<varname>env</varname><literal>['ENV']['PATH']</literal>).
On Windows systems, additionally applies the filename suffixes found in
the execution environment
(<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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Dictionary">
    <term><replaceable>env</replaceable>.<methodname>Dictionary</methodname>(<parameter>[vars]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Dir">
    <term><function>Dir</function>(<parameter>name, [directory]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Dir</methodname>(<parameter>name, [directory]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Dump">
    <term><replaceable>env</replaceable>.<methodname>Dump</methodname>(<parameter>[key], [format]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-EnsurePythonVersion">
    <term><function>EnsurePythonVersion</function>(<parameter>major, minor</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>EnsurePythonVersion</methodname>(<parameter>major, minor</parameter>)</term>
    <listitem><para>
Ensure that the Python version is at least
<varname>major</varname>.<varname>minor</varname>.
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.
</para>

<para>
Example:
</para>

<example_commands>
EnsurePythonVersion(2,2)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-EnsureSConsVersion">
    <term><function>EnsureSConsVersion</function>(<parameter>major, minor, [revision]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>EnsureSConsVersion</methodname>(<parameter>major, minor, [revision]</parameter>)</term>
    <listitem><para>
Ensure that the SCons version is at least
<varname>major.minor</varname>,
or
<varname>major.minor.revision</varname>.
if
<varname>revision</varname>
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.
</para>

<para>
Examples:
</para>

<example_commands>
EnsureSConsVersion(0,14)

EnsureSConsVersion(0,96,90)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-Environment">
    <term><function>Environment</function>(<parameter>[key=value, ...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Environment</methodname>(<parameter>[key=value, ...]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Execute">
    <term><function>Execute</function>(<parameter>action, [actionargs ...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Execute</methodname>(<parameter>action, [actionargs ...]</parameter>)</term>
    <listitem><para>
Executes an Action.
<parameter>action</parameter>
may be an Action object
or it may be a command-line string,
list of commands,
or executable &Python; function,
each of which will first be converted
into an Action object
and then executed.
Any additional arguments to &f-Execute;
are passed on to the &f-link-Action; factory function
which actually creates the Action object
(see the manpage section <link linkend="action_objects">Action Objects</link>
for a description). Example:
</para>

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

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

<para>
&f-Execute; returns the exit value of the command
or return value of the &Python; function.
&scons;
prints an error message if the executed
<parameter>action</parameter>
fails (exits with or returns a non-zero value),
however it does
<emphasis>not</emphasis>,
automatically terminate the build for such a failure.
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>
if Execute("mkdir sub/dir/ectory"):
    # The mkdir failed, don't try to build.
    Exit(1)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-Exit">
    <term><function>Exit</function>(<parameter>[value]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Exit</methodname>(<parameter>[value]</parameter>)</term>
    <listitem><para>
This tells
&scons;
to exit immediately
with the specified
<varname>value</varname>.
A default exit value of
<literal>0</literal>
(zero)
is used if no value is specified.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Export">
    <term><function>Export</function>(<parameter>[vars...], [key=value...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Export</methodname>(<parameter>[vars...], [key=value...]</parameter>)</term>
    <listitem><para>
Exports variables from the current
SConscript file to a global collection where they can be
imported by other SConscript files.
<parameter>vars</parameter> may be one or more
strings representing variable names to be exported.
If a string contains whitespace, it is split into
separate strings, as if multiple string arguments
had been given.  A <parameter>vars</parameter> argument
may also be a dictionary, which can be used to map variables
to different names when exported.
Keyword arguments can be used to provide names and their values.
</para>

<para>
&f-Export; calls are cumulative. Specifying a previously
exported variable will overwrite the earlier value.
Both local variables and global variables can be exported.
</para>

<para>
Examples:
</para>

<example_commands>
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})
</example_commands>

<para>
Note that the
&f-link-SConscript;
function supports an &exports;
argument that allows exporting a variable or
set of variables to a specific SConscript file or files.
See the description below.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-File">
    <term><function>File</function>(<parameter>name, [directory]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>File</methodname>(<parameter>name, [directory]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-FindFile">
    <term><function>FindFile</function>(<parameter>file, dirs</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>FindFile</methodname>(<parameter>file, dirs</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-FindInstalledFiles">
    <term><function>FindInstalledFiles</function>()</term>
    <term><replaceable>env</replaceable>.<methodname>FindInstalledFiles</methodname>()</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-FindPathDirs">
    <term><function>FindPathDirs</function>(<parameter>variable</parameter>)</term>
    <listitem><para>
Returns a function
(actually a callable Python object)
intended to be used as the
<varname>path_function</varname>
of a Scanner object.
The returned object will look up the specified
<varname>variable</varname>
in a construction environment
and treat the construction variable's value as a list of
directory paths that should be searched
(like
&cv-link-CPPPATH;,
&cv-link-LIBPATH;,
etc.).
</para>

<para>
Note that use of
&f-FindPathDirs;
is generally preferable to
writing your own
<varname>path_function</varname>
for the following reasons:
1) The returned list will contain all appropriate directories
found in source trees
(when
&f-link-VariantDir;
is used)
or in code repositories
(when
&f-Repository;
or the
<option>-Y</option>
option are used).
2) scons will identify expansions of
<varname>variable</varname>
that evaluate to the same list of directories as,
in fact, the same list,
and avoid re-scanning the directories for files,
when possible.
</para>

<para>
Example:
</para>

<example_commands>
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'))
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-FindSourceFiles">
    <term><function>FindSourceFiles</function>(<parameter>node='"."'</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>FindSourceFiles</methodname>(<parameter>node='"."'</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Flatten">
    <term><function>Flatten</function>(<parameter>sequence</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Flatten</methodname>(<parameter>sequence</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-GetBuildFailures">
    <term><function>GetBuildFailures</function>()</term>
    <listitem><para>
Returns a list of exceptions for the
actions that failed while
attempting to build targets.
Each element in the returned list is a
<classname>BuildError</classname>
object
with the following attributes
that record various aspects
of the build failure:
</para>

<para>
<literal>.node</literal>
The node that was being built
when the build failure occurred.
</para>

<para>
<literal>.status</literal>
The numeric exit status
returned by the command or Python function
that failed when trying to build the
specified Node.
</para>

<para>
<literal>.errstr</literal>
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.)
</para>

<para>
<literal>.filename</literal>
The name of the file or
directory that actually caused the failure.
This may be different from the
<literal>.node</literal>
attribute.
For example,
if an attempt to build a target named
<filename>sub/dir/target</filename>
fails because the
<filename>sub/dir</filename>
directory could not be created,
then the
<literal>.node</literal>
attribute will be
<filename>sub/dir/target</filename>
but the
<literal>.filename</literal>
attribute will be
<filename>sub/dir</filename>.
</para>

<para>
<literal>.executor</literal>
The SCons Executor object
for the target Node
being built.
This can be used to retrieve
the construction environment used
for the failed action.
</para>

<para>
<literal>.action</literal>
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.
</para>

<para>
<literal>.command</literal>
The actual expanded command that was executed and failed,
after expansion of
&cv-link-TARGET;,
&cv-link-SOURCE;,
and other construction variables.
</para>

<para>
Note that the
&f-GetBuildFailures;
function
will always return an empty list
until any build failure has occurred,
which means that
&f-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
<function>atexit.register</function>()
function.
Example:
</para>

<example_commands>
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)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-GetBuildPath">
    <term><function>GetBuildPath</function>(<parameter>file, [...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>GetBuildPath</methodname>(<parameter>file, [...]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-GetLaunchDir">
    <term><function>GetLaunchDir</function>()</term>
    <term><replaceable>env</replaceable>.<methodname>GetLaunchDir</methodname>()</term>
    <listitem><para>
Returns the absolute path name of the directory from which
&scons;
was initially invoked.
This can be useful when using the
<option>-u</option>,
<option>-U</option>
or
<option>-D</option>
options, which internally
change to the directory in which the
&SConstruct;
file is found.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-GetOption">
    <term><function>GetOption</function>(<parameter>name</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>GetOption</methodname>(<parameter>name</parameter>)</term>
    <listitem><para>
This function provides a way to query the value of
options which can be set via the command line or using the
&f-link-SetOption; function.
</para>
<para>
<parameter>name</parameter> can be an entry from the following table,
which shows the corresponding command line arguments
that could affect the value.
<parameter>name</parameter> can be also be the destination
variable name from a project-specific option added using the
&f-link-AddOption; function, as long as the addition
happens prior to the &f-GetOption; call in the SConscript files.
</para>

<informaltable rowsep="1" colsep="1" frame="topbot">
<tgroup cols="3">
<thead>
<row>
  <entry align="left">Query name</entry>
  <entry align="left">Command-line options</entry>
  <entry align="left">Notes</entry>
</row>
</thead>

<tbody>
<row>
  <entry><varname>cache_debug</varname></entry>
  <entry><option>--cache-debug</option></entry>
</row>
<row>
  <entry><varname>cache_disable</varname></entry>
  <entry>
      <option>--cache-disable</option>,
      <option>--no-cache</option>
  </entry>
</row>
<row>
  <entry><varname>cache_force</varname></entry>
  <entry>
      <option>--cache-force</option>,
      <option>--cache-populate</option>
  </entry>
</row>
<row>
  <entry><varname>cache_readonly</varname></entry>
  <entry><option>--cache-readonly</option></entry>
</row>
<row>
  <entry><varname>cache_show</varname></entry>
  <entry><option>--cache-show</option></entry>
</row>
<row>
  <entry><varname>clean</varname></entry>
  <entry>
      <option>-c</option>,
      <option>--clean</option>,
      <option>--remove</option>
  </entry>
</row>
<row>
  <entry><varname>climb_up</varname></entry>
  <entry>
      <option>-D</option>
      <option>-U</option>
      <option>-u</option>
      <option>--up</option>
      <option>--search_up</option>
  </entry>
</row>
<row>
  <entry><varname>config</varname></entry>
  <entry><option>--config</option></entry>
</row>
<row>
  <entry><varname>debug</varname></entry>
  <entry><option>--debug</option></entry>
</row>
<row>
  <entry><varname>directory</varname></entry>
  <entry><option>-C</option>, <option>--directory</option></entry>
</row>
<row>
  <entry><varname>diskcheck</varname></entry>
  <entry><option>--diskcheck</option></entry>
</row>
<row>
  <entry><varname>duplicate</varname></entry>
  <entry><option>--duplicate</option></entry>
</row>
<row>
  <entry><varname>enable_virtualenv</varname></entry>
  <entry><option>--enable-virtualenv</option></entry>
</row>
<row>
  <entry><varname>experimental</varname></entry>
  <entry><option>--experimental</option></entry>
  <entry><emphasis>since 4.2</emphasis></entry>
</row>
<row>
  <entry><varname>file</varname></entry>
  <entry>
      <option>-f</option>,
      <option>--file</option>,
      <option>--makefile</option>,
      <option>--sconstruct</option>
  </entry>
</row>
<row>
  <entry><varname>hash_format</varname></entry>
  <entry><option>--hash-format</option></entry>
  <entry><emphasis>since 4.2</emphasis></entry>
</row>
<row>
  <entry><varname>help</varname></entry>
  <entry><option>-h</option>, <option>--help</option></entry>
</row>
<row>
  <entry><varname>ignore_errors</varname></entry>
  <entry><option>-i</option>, <option>--ignore-errors</option></entry>
</row>
<row>
  <entry><varname>ignore_virtualenv</varname></entry>
  <entry><option>--ignore-virtualenv</option></entry>
</row>
<row>
  <entry><varname>implicit_cache</varname></entry>
  <entry><option>--implicit-cache</option></entry>
</row>
<row>
  <entry><varname>implicit_deps_changed</varname></entry>
  <entry><option>--implicit-deps-changed</option></entry>
</row>
<row>
  <entry><varname>implicit_deps_unchanged</varname></entry>
  <entry><option>--implicit-deps-unchanged</option></entry>
</row>
<row>
  <entry><varname>include_dir</varname></entry>
  <entry><option>-I</option>, <option>--include-dir</option></entry>
</row>
<row>
  <entry><varname>install_sandbox</varname></entry>
  <entry><option>--install-sandbox</option></entry>
  <entry>Available only if the &t-link-install; tool has been called</entry>
</row>
<row>
  <entry><varname>keep_going</varname></entry>
  <entry><option>-k</option>, <option>--keep-going</option></entry>
</row>
<row>
  <entry><varname>max_drift</varname></entry>
  <entry><option>--max-drift</option></entry>
</row>
<row>
  <entry><varname>md5_chunksize</varname></entry>
  <entry>
      <option>--hash-chunksize</option>,
      <option>--md5-chunksize</option>
  </entry>
  <entry><emphasis><option>--hash-chunksize</option> since 4.2</emphasis></entry>
</row>
<row>
  <entry><varname>no_exec</varname></entry>
  <entry>
      <option>-n</option>,
      <option>--no-exec</option>,
      <option>--just-print</option>,
      <option>--dry-run</option>,
      <option>--recon</option>
  </entry>
</row>
<row>
  <entry><varname>no_progress</varname></entry>
  <entry><option>-Q</option></entry>
</row>
<row>
  <entry><varname>num_jobs</varname></entry>
  <entry><option>-j</option>, <option>--jobs</option></entry>
</row>
<row>
  <entry><varname>package_type</varname></entry>
  <entry><option>--package-type</option></entry>
  <entry>Available only if the &t-link-packaging; tool has been called</entry>
</row>
<row>
  <entry><varname>profile_file</varname></entry>
  <entry><option>--profile</option></entry>
</row>
<row>
  <entry><varname>question</varname></entry>
  <entry><option>-q</option>, <option>--question</option></entry>
</row>
<row>
  <entry><varname>random</varname></entry>
  <entry><option>--random</option></entry>
</row>
<row>
  <entry><varname>repository</varname></entry>
  <entry>
      <option>-Y</option>,
      <option>--repository</option>,
      <option>--srcdir</option>
  </entry>
</row>
<row>
  <entry><varname>silent</varname></entry>
  <entry>
      <option>-s</option>,
      <option>--silent</option>,
      <option>--quiet</option>
  </entry>
</row>
<row>
  <entry><varname>site_dir</varname></entry>
  <entry><option>--site-dir</option>, <option>--no-site-dir</option></entry>
</row>
<row>
  <entry><varname>stack_size</varname></entry>
  <entry><option>--stack-size</option></entry>
</row>
<row>
  <entry><varname>taskmastertrace_file</varname></entry>
  <entry><option>--taskmastertrace</option></entry>
</row>
<row>
  <entry><varname>tree_printers</varname></entry>
  <entry><option>--tree</option></entry>
</row>
<row>
  <entry><varname>warn</varname></entry>
  <entry><option>--warn</option>, <option>--warning</option></entry>
</row>

</tbody>
</tgroup>
</informaltable>

<para>
See the documentation for the
corresponding command line option for information about each specific
option.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Glob">
    <term><function>Glob</function>(<parameter>pattern, [ondisk, source, strings, exclude]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Glob</methodname>(<parameter>pattern, [ondisk, source, strings, exclude]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Help">
    <term><function>Help</function>(<parameter>text, append=False</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Help</methodname>(<parameter>text, append=False</parameter>)</term>
    <listitem><para>
Specifies a local help message to be printed if the
<option>-h</option>
argument is given to
&scons;.
Subsequent calls to
&f-Help;
append <parameter>text</parameter> to the previously
defined local help text.
</para>
<para>
For the first call to &f-Help; only,
if <parameter>append</parameter> is <constant>False</constant>
(the default)
any local help message generated through
&f-link-AddOption; calls is replaced.
If <parameter>append</parameter> is <constant>True</constant>,
<parameter>text</parameter> is appended to
the existing help text.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Ignore">
    <term><function>Ignore</function>(<parameter>target, dependency</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Ignore</methodname>(<parameter>target, dependency</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Import">
    <term><function>Import</function>(<parameter>vars...</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Import</methodname>(<parameter>vars...</parameter>)</term>
    <listitem><para>
Imports variables into the current SConscript file.
<parameter>vars</parameter>
must be strings representing names of variables
which have been previously exported either by the
&f-link-Export; function or by the
&exports; argument to
&f-link-SConscript;.
Variables exported by
&f-SConscript;
take precedence.
Multiple variable names can be passed to
&f-Import;
as separate arguments or as words in a space-separated string.
The wildcard <literal>"*"</literal> can be used to import all
available variables.
</para>

<para>
Examples:
</para>

<example_commands>
Import("env")
Import("env", "variable")
Import(["env", "variable"])
Import("*")
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-Literal">
    <term><function>Literal</function>(<parameter>string</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Literal</methodname>(<parameter>string</parameter>)</term>
    <listitem><para>
The specified
<parameter>string</parameter>
will be preserved as-is
and not have construction variables expanded.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Local">
    <term><function>Local</function>(<parameter>targets</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Local</methodname>(<parameter>targets</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-MergeFlags">
    <term><replaceable>env</replaceable>.<methodname>MergeFlags</methodname>(<parameter>arg, [unique]</parameter>)</term>
    <listitem><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>
If <literal>unique</literal> is true (the default),
duplicate values are not stored.
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.
If <literal>unique</literal> is false,
values are added even if they are duplicates.
</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>
</listitem>
  </varlistentry>
  <varlistentry id="f-NoCache">
    <term><function>NoCache</function>(<parameter>target, ...</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>NoCache</methodname>(<parameter>target, ...</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-NoClean">
    <term><function>NoClean</function>(<parameter>target, ...</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>NoClean</methodname>(<parameter>target, ...</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-ParseConfig">
    <term><replaceable>env</replaceable>.<methodname>ParseConfig</methodname>(<parameter>command, [function, unique]</parameter>)</term>
    <listitem><para>
Updates the current &consenv; with the values extracted
from the output of running external <parameter>command</parameter>,
by passing it to a helper <parameter>function</parameter>.
<parameter>command</parameter> may be a string
or a list of strings representing the command and
its arguments.
If <parameter>function</parameter>
is omitted or <constant>None</constant>,
&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>
<parameter>command</parameter> is executed using the
SCons execution environment (that is, the &consvar;
&cv-link-ENV; in the current &consenv;).
If <parameter>command</parameter> needs additional information
to operate properly, that needs to be set in the execution environment.
For example, <command>pkg-config</command>
may need a custom value set in the <envar>PKG_CONFIG_PATH</envar>
environment variable.
</para>

<para>
&f-env-MergeFlags; needs to understand
the output produced by <parameter>command</parameter>
in order to distribute it to appropriate &consvars;.
&f-env-MergeFlags; uses a separate function to
do that processing -
see &f-link-env-ParseFlags; for the details, including a
a table of options and corresponding construction variables.
To provide alternative processing of the output of
<parameter>command</parameter>,
you can suppply a custom
<parameter>function</parameter>,
which must accept three arguments:
the &consenv; to modify,
a string argument containing the output from running
<parameter>command</parameter>,
and the optional
<parameter>unique</parameter> flag.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-ParseDepends">
    <term><function>ParseDepends</function>(<parameter>filename, [must_exist, only_one]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>ParseDepends</methodname>(<parameter>filename, [must_exist, only_one]</parameter>)</term>
    <listitem><para>
Parses the contents of <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 <parameter>filename</parameter>
does not exist.
The optional
<parameter>must_exist</parameter>
argument may be set to <constant>True</constant>
to have &SCons;
raise an exception if the file does not exist,
or is otherwise inaccessible.
</para>

<para>
The optional
<parameter>only_one</parameter>
argument may be set to <constant>True</constant>
to have &SCons; raise an exception
if the file contains dependency
information for more than one target.
This can provide a small sanity check
for files intended to be generated
by, for example, the
<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>
<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>
</listitem>
  </varlistentry>
  <varlistentry id="f-ParseFlags">
    <term><replaceable>env</replaceable>.<methodname>ParseFlags</methodname>(<parameter>flags, ...</parameter>)</term>
    <listitem><para>
Parses one or more strings containing
typical command-line flags for GCC-style tool chains
and returns a dictionary with the flag values
separated into the appropriate SCons construction variables.
Intended as a companion to the
&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 (<literal>!</literal>),
the rest of the string is executed as a command,
and the output from the command is
parsed as GCC tool chain command-line flags
and added to the resulting dictionary.
This can be used to call a <filename>*-config</filename>
command typical of the POSIX programming environment
(for example,
<command>pkg-config</command>).
Note that such a command is executed using the
SCons execution environment;
if the command needs additional information,
that information needs to be explicitly provided.
See &f-link-ParseConfig; for more details.
</para>

<para>
Flag values are translated according 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
-fsanitize              CCFLAGS, LINKFLAGS
-include                CCFLAGS
-imacros                CCFLAGS
-isysroot               CCFLAGS, LINKFLAGS
-isystem                CCFLAGS
-iquote                 CCFLAGS
-idirafter              CCFLAGS
-I                      CPPPATH
-l                      LIBS
-L                      LIBPATH
-mno-cygwin             CCFLAGS, LINKFLAGS
-mwindows               LINKFLAGS
-openmp                 CCFLAGS, LINKFLAGS
-pthread                CCFLAGS, LINKFLAGS
-std=                   CFLAGS
-Wa,                    ASFLAGS, CCFLAGS
-Wl,-rpath=             RPATH
-Wl,-R,                 RPATH
-Wl,-R                  RPATH
-Wl,                    LINKFLAGS
-Wp,                    CPPFLAGS
-                       CCFLAGS
+                       CCFLAGS, LINKFLAGS
</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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Platform">
    <term><function>Platform</function>(<parameter>plat</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Platform</methodname>(<parameter>plat</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Precious">
    <term><function>Precious</function>(<parameter>target, ...</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Precious</methodname>(<parameter>target, ...</parameter>)</term>
    <listitem><para>
Marks each given
<varname>target</varname>
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
&f-Precious;.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Prepend">
    <term><replaceable>env</replaceable>.<methodname>Prepend</methodname>(<parameter>key=val, [...]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-PrependENVPath">
    <term><replaceable>env</replaceable>.<methodname>PrependENVPath</methodname>(<parameter>name, newpath, [envname, sep, delete_existing=True]</parameter>)</term>
    <listitem><para>
Prepend path elements specified by <parameter>newpath</parameter>
to the given search path string or list <parameter>name</parameter>
in mapping <parameter>envname</parameter> in the &consenv;.
Supplying <parameter>envname</parameter> is optional:
the default is the execution environment &cv-link-ENV;.
Optional <parameter>sep</parameter> is used as the search path separator,
the default is the platform's separator (<systemitem>os.pathsep</systemitem>).
A path element will only appear once.
Any duplicates in <parameter>newpath</parameter> are dropped,
keeping the first appearing (to preserve path order).
If <parameter>delete_existing</parameter>
is <constant>False</constant>
any addition duplicating an existing path element is ignored;
if <parameter>delete_existing</parameter>
is <constant>True</constant> (the default) the existing value will
be dropped and the path element will be inserted at the beginning.
To help maintain uniqueness all paths are normalized (using
<systemitem>os.path.normpath</systemitem>
and
<systemitem>os.path.normcase</systemitem>).
</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>

<para>
See also &f-link-env-AppendENVPath;.
</para>

</listitem>
  </varlistentry>
  <varlistentry id="f-PrependUnique">
    <term><replaceable>env</replaceable>.<methodname>PrependUnique</methodname>(<parameter>key=val, delete_existing=False, [...]</parameter>)</term>
    <listitem><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 &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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Progress">
    <term><function>Progress</function>(<parameter>callable, [interval]</parameter>)</term>
    <term><function>Progress</function>(<parameter>string, [interval, file, overwrite]</parameter>)</term>
    <term><function>Progress</function>(<parameter>list_of_strings, [interval, file, overwrite]</parameter>)</term>
    <listitem><para>
Allows SCons to show progress made during the build
by displaying a string or calling a function while
evaluating Nodes (e.g. files).
</para>

<para>
If the first specified argument is a Python callable
(a function or an object that has a
<methodname>__call__</methodname> method),
the function will be called
once every
<varname>interval</varname>
times a Node is evaluated (default <constant>1</constant>).
The callable will be passed the evaluated Node
as its only argument.
(For future compatibility,
it's a good idea to also add
<parameter>*args</parameter>
and
<parameter>**kwargs</parameter>
as arguments to your function or method signatures.
This will prevent the code from breaking
if &SCons; ever changes the interface
to call the function with additional arguments in the future.)
</para>

<para>
An example of a simple custom progress function
that prints a string containing the Node name
every 10 Nodes:
</para>

<example_commands>
def my_progress_function(node, *args, **kwargs):
    print('Evaluating node %s!' % node)
Progress(my_progress_function, interval=10)
</example_commands>

<para>
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
<literal>\r</literal>
(a carriage return)
at the end so that the string
will overwrite itself on a display:
</para>

<example_commands>
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)
</example_commands>

<para>
If the first argument to
&f-Progress; is a string or list of strings,
it is taken as text to be displayed every
<varname>interval</varname>
evaluated Nodes.
If the first argument is a list of strings,
then each string in the list will be displayed
in rotating fashion every
<varname>interval</varname>
evaluated Nodes.
</para>

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

<para>
The following will print a series of dots
on the error output,
one dot for every 100 evaluated Nodes:
</para>

<example_commands>
import sys
Progress('.', interval=100, file=sys.stderr)
</example_commands>

<para>
If the string contains the verbatim substring
<literal>$TARGET;</literal>,
it will be replaced with the Node.
Note that, for performance reasons, this is
<emphasis>not</emphasis>
a regular SCons variable substition,
so you can not use other variables
or use curly braces.
The following example will print the name of
every evaluated Node,
using a carriage return)
(<literal>\r</literal>)
to cause each line to overwritten by the next line,
and the
<parameter>overwrite</parameter>
keyword argument (default <literal>False</literal>)
to make sure the previously-printed
file name is overwritten with blank spaces:
</para>

<example_commands>
import sys
Progress('$TARGET\r', overwrite=True)
</example_commands>

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

<example_commands>
Progress(['-\r', '\\\r', '|\r', '/\r'], interval=5)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-Pseudo">
    <term><function>Pseudo</function>(<parameter>target, ...</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Pseudo</methodname>(<parameter>target, ...</parameter>)</term>
    <listitem><para>
This indicates that each given
<varname>target</varname>
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
&f-Alias;
is more appropriate.

Multiple targets can be passed in to a single call to
&f-Pseudo;.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-PyPackageDir">
    <term><function>PyPackageDir</function>(<parameter>modulename</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>PyPackageDir</methodname>(<parameter>modulename</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Replace">
    <term><replaceable>env</replaceable>.<methodname>Replace</methodname>(<parameter>key=val, [...]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Repository">
    <term><function>Repository</function>(<parameter>directory</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Repository</methodname>(<parameter>directory</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Requires">
    <term><function>Requires</function>(<parameter>target, prerequisite</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Requires</methodname>(<parameter>target, prerequisite</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Return">
    <term><function>Return</function>(<parameter>[vars..., stop=True]</parameter>)</term>
    <listitem><para>
Return to the calling SConscript, optionally
returning the values of variables named in
<varname>vars</varname>.
Multiple strings contaning variable names may be passed to
&f-Return;. A string containing white space
is split into individual variable names.
Returns the value if one variable is specified,
else returns a tuple of values.
Returns an empty tuple if <parameter>vars</parameter>
is omitted.
</para>

<para>
By default &Return; stops processing the current SConscript
and returns immediately.
The optional
<literal>stop</literal>
keyword argument
may be set to a false value
to continue processing the rest of the SConscript
file after the
&f-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
<varname>vars</varname>
at the point
&f-Return;
was called.
</para>

<para>
Examples:
</para>

<example_commands>
# Returns no values (evaluates False)
Return()

# Returns the value of the 'foo' Python variable.
Return("foo")

# Returns the values of the Python variables 'foo' and 'bar'.
Return("foo", "bar")

# Returns the values of Python variables 'val1' and 'val2'.
Return('val1 val2')
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-Scanner">
    <term><function>Scanner</function>(<parameter>function, [name, argument, skeys, path_function, node_class, node_factory, scan_check, recursive]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Scanner</methodname>(<parameter>function, [name, argument, skeys, path_function, node_class, node_factory, scan_check, recursive]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-SConscript">
    <term><function>SConscript</function>(<parameter>scripts, [exports, variant_dir, duplicate, must_exist]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>SConscript</methodname>(<parameter>scripts, [exports, variant_dir, duplicate, must_exist]</parameter>)</term>
    <term><function>SConscript</function>(<parameter>dirs=subdirs, [name=scriptname, exports, variant_dir, duplicate, must_exist]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>SConscript</methodname>(<parameter>dirs=subdirs, [name=scriptname, exports, variant_dir, duplicate, must_exist]</parameter>)</term>
    <listitem><para>
Executes one or more subsidiary SConscript (configuration) files.
There are two ways to call the
&f-SConscript; function.
</para>

<para>
The first calling style is to supply
one or more SConscript file names
as the first (positional) argument.
A single script may be specified as a string;
multiple scripts must be specified as a list of strings
(either explicitly or as created by
a function like
&f-link-Split;).
Examples:
</para>
<example_commands>
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')
</example_commands>

<para>
The other calling style is to omit the positional argument naming
scripts and instead specify a list of directory names using the
<varname>dirs</varname> keyword argument.
In this case,
&scons;
will
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
<varname>name</varname>=<replaceable>scriptname</replaceable>
keyword argument.
The first three examples below have the same effect
as the first three examples above:
</para>
<example_commands>
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')
</example_commands>

<para>
The optional
<varname>exports</varname>
keyword argument provides a string or list of strings representing
variable names, or a dictionary of named values, to export.
For the first calling style only, a second positional argument
will be interpreted as <varname>exports</varname>; the
second calling style must use the keyword argument form
for <varname>exports</varname>.
These variables are locally exported only to the called
SConscript file(s)
and do not affect the global pool of variables managed by the
&f-link-Export;
function.
<!-- If multiple dirs are provided, each script gets a fresh export. -->
The subsidiary SConscript files
must use the
&f-link-Import;
function to import the variables.
Examples:
</para>
<example_commands>
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')
</example_commands>

<para>
If the optional
<varname>variant_dir</varname>
argument is present, it causes an effect equivalent to the
&f-link-VariantDir; function,
but in effect only within the scope of the &f-SConscript; call.
The <varname>variant_dir</varname>
argument is interpreted relative to the directory of the
<emphasis>calling</emphasis> SConscript file.
The source directory is the directory in which the
<emphasis>called</emphasis> SConscript
file resides and the SConscript
file is evaluated as if it were in the
<varname>variant_dir</varname>
directory. Thus:
</para>
<example_commands>
SConscript('src/SConscript', variant_dir='build')
</example_commands>

<para>
is equivalent to:
</para>

<example_commands>
VariantDir('build', 'src')
SConscript('build/SConscript')
</example_commands>

<para>
If the sources are in the same directory as the
&SConstruct;,
</para>

<example_commands>
SConscript('SConscript', variant_dir='build')
</example_commands>

<para>
is equivalent to:
</para>

<example_commands>
VariantDir('build', '.')
SConscript('build/SConscript')
</example_commands>

<para>
The optional
<varname>duplicate</varname> argument is
interpreted as for &f-link-VariantDir;.
If the <varname>variant_dir</varname> argument
is omitted, the <varname>duplicate</varname> argument is ignored.
See the description of
&f-link-VariantDir;
for additional details and restrictions.
</para>

<para>
<!--
If
<varname>variant_dir</varname>
and"
<varname>src_dir</varname>
are both present,
xxxxx everything is in a state of confusion.
</para>
<example_commands>
SConscript(dirs = 'src', variant_dir = 'build', src_dir = '.')
runs src/SConscript in build/src, but
SConscript(dirs = 'lib', variant_dir = 'build', src_dir = 'src')
runs lib/SConscript (in lib!).  However,
SConscript(dirs = 'src', variant_dir = 'build', src_dir = 'src')
runs src/SConscript in build.  Moreover,
SConscript(dirs = 'src/lib', variant_dir = 'build', src_dir = 'src')
runs src/lib/SConscript in build/lib.  Moreover,
SConscript(dirs = 'build/src/lib', variant_dir = 'build', src_dir = 'src')
can't find build/src/lib/SConscript, even though it ought to exist.
</example_commands>
<para>
is equivalent to
</para>
<example_commands>
????????????????
</example_commands>
<para>
and what about this alternative?
TODO??? SConscript('build/SConscript', src_dir='src')
-->
</para>

<para>
If the optional
<varname>must_exist</varname>
is <constant>True</constant>,
causes an exception to be raised if a requested
SConscript file is not found. The current default is
<constant>False</constant>,
causing only a warning to be emitted, but this default is deprecated
(<emphasis>since 3.1</emphasis>).
For scripts which truly intend to be optional, transition to
explicitly supplying
<literal>must_exist=False</literal> to the &f-SConscript; call.
</para>

<para>
Here are some composite examples:
</para>

<example_commands>
# 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')
</example_commands>

<example_commands>
# 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)
</example_commands>

<example_commands>
# 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)
</example_commands>

<example_commands>
# 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)
</example_commands>

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

</listitem>
  </varlistentry>
  <varlistentry id="f-SConscriptChdir">
    <term><function>SConscriptChdir</function>(<parameter>value</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>SConscriptChdir</methodname>(<parameter>value</parameter>)</term>
    <listitem><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
&f-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>
</listitem>
  </varlistentry>
  <varlistentry id="f-SConsignFile">
    <term><function>SConsignFile</function>(<parameter>[name, dbm_module]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>SConsignFile</methodname>(<parameter>[name, dbm_module]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-SetDefault">
    <term><replaceable>env</replaceable>.<methodname>SetDefault</methodname>(<parameter>key=val, [...]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-SetOption">
    <term><function>SetOption</function>(<parameter>name, value</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>SetOption</methodname>(<parameter>name, value</parameter>)</term>
    <listitem><para>
Sets &scons; option variable <parameter>name</parameter>
to <parameter>value</parameter>.
These options are all also settable via
command-line options but the variable name
may differ from the command-line option name - 
see the table for correspondences.
A value set via command-line option will take
precedence over one set with &f-SetOption;, which
allows setting a project default in the scripts and
temporarily overriding it via command line.
&f-SetOption; calls can also be placed in the
<filename>site_init.py</filename> file.
</para>

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

<para>
Options which affect the reading and processing of SConscript files
are not settable using &f-SetOption; since those files must
be read in order to find the &f-SetOption; call in the first place.
</para>

<para>
The settable variables with their associated command-line options are:
</para>

<informaltable rowsep="1" colsep="1" frame="topbot">
<tgroup cols="3">
<thead>
<row>
  <entry align="left">Settable name</entry>
  <entry align="left">Command-line options</entry>
  <entry align="left">Notes</entry>
</row>
</thead>

<tbody>
<row>
  <entry><varname>clean</varname></entry>
  <entry>
    <option>-c</option>,
    <option>--clean</option>,
    <option>--remove</option>
  </entry>
</row>

<row>
  <entry><varname>diskcheck</varname></entry>
  <entry><option>--diskcheck</option></entry>
</row>

<row>
  <entry><varname>duplicate</varname></entry>
  <entry><option>--duplicate</option></entry>
</row>

<row>
  <entry><varname>experimental</varname></entry>
  <entry><option>--experimental</option></entry>
  <entry><emphasis>since 4.2</emphasis></entry>
</row>

<row>
  <entry><varname>hash_chunksize</varname></entry>
  <entry><option>--hash-chunksize</option></entry>
  <entry>
    Actually sets <varname>md5_chunksize</varname>.
    <emphasis>since 4.2</emphasis>
  </entry>
</row>

<row>
  <entry><varname>hash_format</varname></entry>
  <entry><option>--hash-format</option></entry>
  <entry><emphasis>since 4.2</emphasis></entry>
</row>

<row>
  <entry><varname>help</varname></entry>
  <entry><option>-h</option>, <option>--help</option></entry>
</row>

<row>
  <entry><varname>implicit_cache</varname></entry>
  <entry><option>--implicit-cache</option></entry>
</row>

<row>
  <entry><varname>implicit_deps_changed</varname></entry>
  <entry><option>--implicit-deps-changed</option></entry>
  <entry>
    Also sets <varname>implicit_cache</varname>.
    <emphasis>(settable since 4.2)</emphasis>
  </entry>
</row>

<row>
  <entry><varname>implicit_deps_unchanged</varname></entry>
  <entry><option>--implicit-deps-unchanged</option></entry>
  <entry>
    Also sets <varname>implicit_cache</varname>.
    <emphasis>(settable since 4.2)</emphasis>
  </entry>
</row>

<row>
  <entry><varname>max_drift</varname></entry>
  <entry><option>--max-drift</option></entry>
</row>

<row>
  <entry><varname>md5_chunksize</varname></entry>
  <entry><option>--md5-chunksize</option></entry>
</row>

<row>
  <entry><varname>no_exec</varname></entry>
  <entry>
    <option>-n</option>,
    <option>--no-exec</option>,
    <option>--just-print</option>,
    <option>--dry-run</option>,
    <option>--recon</option>
  </entry>
</row>

<row>
  <entry><varname>no_progress</varname></entry>
  <entry><option>-Q</option></entry>
  <entry>See
    <footnote>
      <para>If <varname>no_progress</varname> is set via &f-SetOption;
      in an SConscript file
      (but not if set in a <filename>site_init.py</filename> file)
      there will still be an initial status message about
      reading SConscript files since &SCons; has
      to start reading them before it can see the
      &f-SetOption;.
      </para>
    </footnote>
  </entry>
</row>

<row>
  <entry><varname>num_jobs</varname></entry>
  <entry><option>-j</option>, <option>--jobs</option></entry>
</row>

<row>
  <entry><varname>random</varname></entry>
  <entry><option>--random</option></entry>
</row>

<row>
  <entry><varname>silent</varname></entry>
  <entry>
    <option>-s</option>,
    <option>--silent</option>,
    <option>--quiet</option>
  </entry>
</row>

<row>
  <entry><varname>stack_size</varname></entry>
  <entry><option>--stack-size</option></entry>
</row>

<row>
  <entry><varname>warn</varname></entry>
  <entry><option>--warn</option></entry>
</row>

</tbody>
</tgroup>
</informaltable>

<para>
Example:
</para>

<example_commands>
SetOption('max_drift', 0)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-SideEffect">
    <term><function>SideEffect</function>(<parameter>side_effect, target</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>SideEffect</methodname>(<parameter>side_effect, target</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Split">
    <term><function>Split</function>(<parameter>arg</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Split</methodname>(<parameter>arg</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-subst">
    <term><replaceable>env</replaceable>.<methodname>subst</methodname>(<parameter>input, [raw, target, source, conv]</parameter>)</term>
    <listitem><para>
Performs &consvar; interpolation
(<firstterm>substitution</firstterm>)
on <parameter>input</parameter>,
which can be a string or a sequence.
Substitutable elements take the form
<literal>${<replaceable>expression</replaceable>}</literal>,
although if there is no ambiguity in recognizing the element,
the braces can be omitted.
A literal <emphasis role="bold">$</emphasis> can be entered by
using <emphasis role="bold">$$</emphasis>.
</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 <parameter>input</parameter> 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>
</listitem>
  </varlistentry>
  <varlistentry id="f-Tag">
    <term><function>Tag</function>(<parameter>node, tags</parameter>)</term>
    <listitem><para>
Annotates file or directory Nodes with
information about how the
&b-link-Package;
Builder should package those files or directories.
All Node-level tags are optional.
</para>

<para>
Examples:
</para>

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

# marks file2.txt to be a documentation file
Tag('file2.txt', DOC)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-Tool">
    <term><function>Tool</function>(<parameter>name, [toolpath, **kwargs]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Tool</methodname>(<parameter>name, [toolpath, **kwargs]</parameter>)</term>
    <listitem><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>
</listitem>
  </varlistentry>
  <varlistentry id="f-ValidateOptions">
    <term><function>ValidateOptions</function>(<parameter>[throw_exception=False]</parameter>)</term>
    <listitem><para>
                Check that all the options specified on the command line are either defined by SCons itself
                or defined by calls to &f-link-AddOption;.
            </para>
            <para>
                This function should only be called after the last &f-link-AddOption; call in your &SConscript;
                logic.
            </para>
            <para>
                Be aware that some tools call &f-link-AddOption;, if you are getting error messages for arguments
                that they add, you will need to ensure that you load those tools before you call &f-ValidateOptions;.
            </para>
            <para>
                If there are any command line options not defined, calling this function will cause SCons to issue an
                error message and then exit with an error exit
                status.</para>
            <para>If the optional <parameter>throw_exception</parameter> is <literal>True</literal>, &f-ValidateOptions; will raise a
                <exceptionname>SConsBadOptionError</exceptionname>
                exception. This would allow the calling
                &SConscript; logic can catch that exception and handle invalid options itself.
            </para>

            <para>
                Example:
            </para>

            <example_commands>
try:
    ValidateOptions(throw_exception=True)
except SConsBadOptionError as e:
    print("Parser is SConsOptionParser:%s" % (isinstance(e.parser, SConsOptionParser)))
    print("Message is :%s" % e.opt_str)
    Exit(3)
            </example_commands>
            
            <para>
                This function is useful to force SCons to fail fast before you execute any expensive logic later in your
                build logic.
                For example if you specify build options via any flags, a simple typo could yield the incorrect build
                option throughout your entire build.
            </para>
            <example_commands>
scons --compilers=mingw (the correct flag is --compiler)
            </example_commands>
            <para>
                Could cause SCons to run configure steps with the incorrect compiler. Costing developer time trying to
                track down why the configure logic failed with a compiler which should work.
            </para>



        </listitem>
  </varlistentry>
  <varlistentry id="f-Value">
    <term><function>Value</function>(<parameter>value, [built_value], [name]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Value</methodname>(<parameter>value, [built_value], [name]</parameter>)</term>
    <listitem><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 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>
</listitem>
  </varlistentry>
  <varlistentry id="f-VariantDir">
    <term><function>VariantDir</function>(<parameter>variant_dir, src_dir, [duplicate]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>VariantDir</methodname>(<parameter>variant_dir, src_dir, [duplicate]</parameter>)</term>
    <listitem><para>
Sets up a mapping to define a variant build directory in
<parameter>variant_dir</parameter>.
<parameter>src_dir</parameter> may not be underneath
<parameter>variant_dir</parameter>.
A &f-VariantDir; mapping is global, even if called using the
&f-env-VariantDir; form.
&f-VariantDir;
can be called multiple times with the same
<parameter>src_dir</parameter>
to set up multiple variant builds with different options.
</para>

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

<para>
When files in <parameter>variant_dir</parameter> are referenced,
&SCons; backfills as needed with files from <parameter>src_dir</parameter>
to create a complete build directory.
By default, &SCons;
physically duplicates the source files, SConscript files,
and directory structure as needed into the variant directory.
Thus, a build performed in the variant directory is guaranteed to be identical
to a build performed in the source directory even if
intermediate source files are generated during the build,
or if preprocessors or other scanners search for included files
using paths relative to the source file,
or if individual compilers or other invoked tools are hard-coded
to put derived files in the same directory as source files.
Only the files &SCons; calculates are needed for the build are
duplicated into <parameter>variant_dir</parameter>.
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 duplicating,
and is safe for most builds;
revert to <literal>duplicate=True</literal>
if it causes problems.
</para>

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

<example_commands>
env1 = Environment(...settings for variant1...)
env2 = Environment(...settings for variant2...)

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

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

<para>
More 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>
</listitem>
  </varlistentry>
  <varlistentry id="f-WhereIs">
    <term><function>WhereIs</function>(<parameter>program, [path, pathext, reject]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>WhereIs</methodname>(<parameter>program, [path, pathext, reject]</parameter>)</term>
    <listitem><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>

</listitem>
  </varlistentry>
</variablelist>
