<!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
&consvars; in any argument strings,
including the
<parameter>action</parameter>
argument, at the time it is called
using the &consvars; in the
&consenv; 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>opt_str, ..., attr=value, ...</parameter>)</term>
    <listitem><para>
Adds a local (project-specific) command-line option.
One or more <parameter>opt_str</parameter> values are
the strings representing how the option can be called,
while the keyword arguments define attributes of the option.
For the most part these are the same as for the
<function>OptionParser.add_option</function>
method in the standard Python library module
<systemitem>optparse</systemitem>,
but with a few additional capabilities noted below.
See the
<ulink url="https://docs.python.org/3/library/optparse.html">
optparse documentation</ulink>
for a thorough discussion of its option-processing capabilities.
All options added through &f-AddOption; are placed
in a special "Local Options" option group.
</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 <literal>'?'</literal> (question mark)
to indicate that the option argument for
that option string may be omitted.
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;.
If the <parameter>settable=True</parameter> argument
was supplied in the &AddOption; call,
the value may also be set later using
&f-link-SetOption;
or
&f-link-env-SetOption;,
if conditions in an
&SConscript; file
require overriding any default value.
Note however that a
value specified on the command line will
<emphasis>always</emphasis>
override a value set in an SConscript file.
</para>

<para>
<emphasis>Changed in 4.8.0</emphasis>: added the
<parameter>settable</parameter> keyword argument
to enable an added option to be settable via &SetOption;.
</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>
Arrange for the specified
<parameter>action</parameter>
to be performed
after the specified
<parameter>target</parameter>
has been built.
<parameter>action</parameter> 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>

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

<para>
If a <parameter>target</parameter> is an &f-Alias;,
<parameter>action</parameter> is associated with the
action of the alias, if specified.
</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>
Arrange for the specified
<parameter>action</parameter>
to be performed
before the specified
<parameter>target</parameter>
is built.
<parameter>action</parameter> 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 action step that specifically
generates the specified target(s).
It may not always be obvious
if the process is multi-step - for example,
if you use the &Program; builder to
construct an executable program from a
<filename>.c</filename> source file,
&scons; builds an intermediate object file first;
the pre-action is invoked after this step
and just before the link command to
generate the executable program binary.
Example:
</para>

<example_commands>
foo = Program('foo.c')
AddPreAction(foo, 'echo "Running pre-action"')
</example_commands>

<screen>
$ scons -Q
gcc -o foo.o -c foo.c
echo "Running pre-action"
Running pre-action
gcc -o foo foo.o
</screen>

<para>
If a <parameter>target</parameter> is an &f-Alias;,
<parameter>action</parameter> is associated with the
action of the alias, if specified.
</para>

</listitem>
  </varlistentry>
  <varlistentry id="f-Alias">
    <term><function>Alias</function>(<parameter>alias, [source, [action]]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Alias</methodname>(<parameter>alias, [source, [action]]</parameter>)</term>
    <listitem><para>
Create an <firstterm>Alias</firstterm> node that
can be used as a reference to zero or more other targets,
specified by the optional <parameter>source</parameter> parameter.
Aliases provide a way to give a shorter or more descriptive
name to specific targets,
and to group multiple targets under a single name.
The alias name, or an Alias Node object,
may be used as a dependency of any other target,
including another alias.
</para>

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

<para>
&f-Alias; can be called for an existing alias,
which appends the <parameter>alias</parameter>
and/or <parameter>action</parameter> arguments
to the existing lists for that alias.
</para>

<para>
Returns a list of Alias Node objects representing the alias(es),
which exist outside of any physical file system.
The alias name space is separate from the name space for
tangible targets; to avoid confusion do not reuse
target names as alias names.
</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 ignored
when expanding &consvars;.
By default,
any &consvar; expansions that generate a
&NameError;
or
&IndexError;
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 ignored exceptions.
Calling it with no arguments means no exceptions will be ignored.
</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 evaluate 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>
Appends value(s) intelligently to &consvars; in
<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 having to think about the data type of an existing &consvar;.
Regular &Python; syntax can also be used to manipulate the &consvar;,
but for that you may need to know the types involved,
for example pure &Python; lets you directly "add" two lists of strings,
but adding a string to a list or a list to a string requires
different syntax - things &f-Append; takes care of.
Some pre-defined &consvars; do have type expectations
based on how &SCons; will use them:
for example &cv-link-CPPDEFINES; is often a string or a list of strings,
but can also be a list of tuples or a dictionary;
while &cv-link-LIBEMITTER;
is expected to be a callable or list of callables,
and &cv-link-BUILDERS; is expected to be a dictionary.
Consult the documentation for the various &consvars; for more details.
</para>

<para>
The following descriptions apply to both the &f-Append;
and &f-Prepend; methods, as well as their
<emphasis role="bold">Unique</emphasis> variants,
with the differences being the insertion point of the added values
and whether duplication is allowed.
</para>

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

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

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

<para>
Because &cv-link-CPPDEFINES; is intended for command-line
specification of C/C++ preprocessor macros,
additional syntax is accepted when adding to it.
The preprocessor accepts arguments to predefine a macro name by itself
(<computeroutput>-DFOO</computeroutput> for most compilers,
<computeroutput>/DFOO</computeroutput> for Microsoft C++),
which gives it an implicit value of <constant>1</constant>,
or can be given with a replacement value
(<computeroutput>-DBAR=TEXT</computeroutput>).
&SCons; follows these rules when adding to &cv-CPPDEFINES;:
</para>
<itemizedlist>
<listitem>
<para>A string is split on spaces,
giving an easy way to enter multiple macros in one addition.
Use an <literal>=</literal> to specify a valued macro.</para>
</listitem>
<listitem>
<para>A tuple is treated as a valued macro.
Use the value <constant>None</constant> if the macro should not have a value.
It is an error to supply more than two elements in such a tuple.</para>
</listitem>
<listitem>
<para>A list is processed in order,
adding each item without further interpretation.
In this case, space-separated strings are not split.</para>
</listitem>
<listitem>
<para>A dictionary is processed in order,
adding each key-value pair as a valued macro.
Use the value <constant>None</constant> if the macro should not have a value.
</para>
</listitem>
</itemizedlist>

<para>
Examples:
</para>

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

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

<para>
Examples of adding multiple macros:
</para>

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

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

<para>
<emphasis>Changed in version  4.5</emphasis>:
clarified the use of tuples vs. other types,
handling is now consistent across the four functions.
</para>

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

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

<para>
See &cv-link-CPPDEFINES; for more details.
</para>

<para>
Appending a string <parameter>val</parameter>
to a dictionary-typed &consvar; enters
<parameter>val</parameter> as the key in the dictionary,
and <literal>None</literal> as its value.
Using a tuple type to supply a key-value pair
only works for the special case of &cv-CPPDEFINES;
described above.
</para>

<para>
Although most combinations of types work without
needing to know the details, some combinations
do not make sense and &Python; raises an exception.
</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 you are only adding a single string.
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 directory paths from
<parameter>newpath</parameter> to
a search-path entry <parameter>name</parameter>
in &consvar; <parameter>envname</parameter>
in the current enviromment (<parameter>env</parameter>).
If <parameter>envname</parameter> is not given,
the default is <literal>"ENV"</literal>
(see &cv-link-ENV;).
<parameter>envname</parameter> is expected
to refer to a dictionary-like object;
if it does not exist in <parameter>env</parameter>
it will be created as an initially empty dict.
<parameter>newpath</parameter>
may be specified as a string,
a directory node, or a list of strings.
If a string, it may contain multiple paths separated
by the system path separator
(<systemitem>os.pathsep</systemitem>),
or, if specified, by the value of <parameter>sep</parameter>.
Top-relative path strings (starting with <literal>#</literal>) are recognized.
The type of the existing value
of <parameter>name</parameter> is preserved.
</para>

<para>
Paths will only appear once.
Duplicate paths in <parameter>newpath</parameter> are removed,
preserving the last occurrence to maintain path order.
If <parameter>delete_existing</parameter> is true (the default),
existing duplicates are removed before appending,
otherwise, new duplicates are skipped.
During comparisons, paths are normalized, to avoid
issues with case differences (on case-insensitive filesystems)
and with relative paths that may refer back to the same directory.
The stored values are not modified by this process.
</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;,
except that values that would become duplicates
are not added.
If <parameter>delete_existing</parameter>
is set to a true value, then for any duplicate,
the existing instance of <parameter>val</parameter> is first removed,
then <parameter>val</parameter> is appended,
having the effect of moving it 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
&consvars; in any arguments strings,
including the
<parameter>action</parameter>
argument,
at the time it is called
using the &consvars; in the
<varname>env</varname>
&consenv; 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>
Calling the environment method
&f-link-env-CacheDir;
limits the effect to targets built
through the specified &consenv;.
Calling the global function
&f-link-CacheDir;
sets a global default
that will be used by all targets built
through &consenvs;
that do not set up environment-specific
caching by calling &f-env-CacheDir;.
</para>

<para>
Caching behavior can be configured by passing a specialized cache
class as the optional <parameter>custom_class</parameter> parameter.
This class must be a subclass of
<classname>SCons.CacheDir.CacheDir</classname>.
&SCons; will internally invoke the custom class for performing
caching operations.
If the parameter is omitted or set to
<constant>None</constant>, &SCons; will use the default
<classname>SCons.CacheDir.CacheDir</classname> class.
</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 useful 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; changes printing
to always show the action that would
have been used to build the file without caching.
</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> option.
</para>

<para>
If the
<option>--cache-force</option>
option is used,
&scons;
will place a copy of
<emphasis>all</emphasis>
derived files into the cache,
even if they already existed
and were not built by this invocation.
This is useful to populate a cache
the first time a
<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, access control, etc. if needed.
</para>

</listitem>
  </varlistentry>
  <varlistentry id="f-Clean">
    <term><function>Clean</function>(<parameter>targets, files</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Clean</methodname>(<parameter>targets, files</parameter>)</term>
    <listitem><para>
Set additional <parameter>files</parameter>
for removal when any of
<parameter>targets</parameter> are selected
for cleaning
(<link linkend="opt-clean"><option>-c</option></link>
command line option).
<parameter>targets</parameter> and
<parameter>files</parameter>
can each be a single filename or node,
or a list of filenames or nodes.
These can refer to files or directories.
Calling this method repeatedly
has an additive effect.
</para>

<para>
The related
&f-link-NoClean;
method has higher priority:
any target specified to
&f-NoClean;
will not be cleaned even if also given as
a <parameter>files</parameter>
parameter to &f-Clean;.
</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>
&SCons; does not directly track directories as targets -
they are created if needed and not normally removed
in clean mode.
In this example,
installing the project creates a subdirectory for the documentation.
The &f-Clean; call ensures that the subdirectory is removed
if the project is uninstalled.
</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 an independent copy of a &consenv;.
If there are any unrecognized keyword arguments specified,
they are added as &consvars; in the copy,
overwriting any existing values
for those keywords.
See the manpage section "Construction Environments" for more details.
</para>

<para>
Example:
</para>

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

<para>
A list of <parameter>tools</parameter>
and a <parameter>toolpath</parameter> 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 &consvars;
(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>

<para>
The <parameter>variables</parameter>
keyword argument is also recognized, to allow (re)initializing
&consvars; from a <literal>Variables</literal> object.
</para>

<para>
<emphasis>Changed in version 4.8.0:</emphasis>
the <parameter>variables</parameter> parameter was added.
</para>
</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>
Creates an anonymous builder and calls it,
thus recording <parameter>action</parameter>
to build <parameter>target</parameter>
from <parameter>source</parameter>
into the dependency tree.
This can be more convenient for a single special-case build
than having to define and add a new named Builder.
</para>

<para>
The
&Command; function accepts the
<parameter>source_scanner</parameter> and
<parameter>target_scanner</parameter>
keyword arguments which are used to specify
custom scanners for the specified sources or targets.
The value must be a Scanner object.
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 or function calls.
</para>

<para>
The
&Command; function also accepts the
<parameter>source_factory</parameter> and
<parameter>target_factory</parameter>
keyword arguments which are used to specify
factory functions to create &SCons; Nodes
from any sources or targets specified as strings.
If any sources or targets are already Node objects,
they are not further transformed even if
a factory is specified for them.
The default for each is the &Entry; factory.
</para>

<para>
These four arguments, if given, are used
in the creation of the Builder.
Other Builder-specific keyword arguments
are not recognized as such.
See the manpage section "Builder Objects"
for more information about how these
arguments work in a Builder.
</para>

<para>
Any remaining keyword arguments are passed on to the
generated builder when it is called,
and behave as described in the manpage section "Builder Methods",
in short:
recognized arguments have their specified meanings,
while the rest are used to override
any same-named existing &consvars;
from the &consenv;.
</para>

<para>
<parameter>action</parameter> 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', 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 <command>autoconf</command>.
See the manpage section "Configure Contexts"
for a complete explanation of the arguments and behavior.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-DebugOptions">
    <term><function>DebugOptions</function>(<parameter>[json]</parameter>)</term>
    <listitem><para>
Allows setting options for SCons debug options. Currently, the only supported value is
  <emphasis>json</emphasis> which sets the path to the JSON file created when
  <literal>--debug=json</literal> is set.
</para>
  <example_commands>
DebugOptions(json='#/build/output/scons_stats.json')
</example_commands>
<para><emphasis>New in version 4.6.0.</emphasis></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 &consenv;
will be handled by <parameter>function</parameter>.
<parameter>function</parameter> can be the name of
a function or one of the following strings
that specify a predefined decider function:
</para>

<para>
<variablelist>
<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 by performing a checksum
on the dependency's contents using the selected hash function,
and comparing it to the checksum recorded the
last time the target was built.
<literal>content</literal> is the default decider.
</para>
<para>
<emphasis>Changed in version 4.1:</emphasis>
The decider was renamed to <literal>content</literal>
since the hash function is now selectable.
The former name, <literal>MD5</literal>,
can still be used as a synonym, but 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.
</para>
<para>
<emphasis>Changed in version 4.1:</emphasis>
The decider was renamed to <literal>content-timestamp</literal>
since the hash function is now selectable.
The former name, <literal>MD5-timestamp</literal>,
can still be used as a synonym, but is deprecated.
</para>
</listitem>
</varlistentry>
<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>
</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 &consenv;.
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 time
<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 appropriate.
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>[key=value, ...]</parameter>)</term>
    <listitem><para>
Instantiates and returns the global &consenv; object.
The <firstterm>&DefEnv;</firstterm> is used internally by &SCons;
when executing a global function
or the global form of a Builder method
that requires access to a &consenv;.
</para>

<para>
On the first call,
arguments are interpreted as for the &f-link-Environment; function.
The &DefEnv; is a singleton;
subsequent calls to &f-DefaultEnvironment; return
the already-constructed object,
and any keyword arguments are silently ignored.
</para>

<para>
The &DefEnv; can be modified after instantiation,
similar to other &consenvs;,
although some &consenv; methods may be unavailable.
Modifying the &DefEnv; has no effect on any other &consenv;,
either existing or newly constructed.
</para>

<para>
It is not necessary to explicitly call &f-DefaultEnvironment;.
&SCons; instantiates the &defenv; automatically when the
build phase begins, if has not already been done.
However, calling it explicitly provides the opportunity to
affect and examine its contents.
Instantiation occurs even if nothing in the build system
appears to use it, due to internal uses.
</para>

<para>
If the project &SConscript; files do not use global functions or Builders,
a small performance gain may be achieved by calling
&f-DefaultEnvironment; with an empty tools list
(<userinput>DefaultEnvironment(tools=[])</userinput>).
This avoids the tool initialization cost for the &DefEnv;,
which is mainly of interest in the test suite
where &scons; is launched repeatedly in a short time period.
</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>[var, ...], [as_dict=]</parameter>)</term>
    <listitem><para>
Return an object containing &consvars; from
<parameter>env</parameter>.
If <parameter>var</parameter> is omitted,
all the &consvars; with their values
are returned in a <type>dict</type>.
If <parameter>var</parameter> is specified,
and <parameter>as_dict</parameter> is true,
the specified &consvars; are returned in a <type>dict</type>;
otherwise (the default, for backwards compatibility),
values only are returned,
as a scalar if one <parameter>var</parameter> is given,
or as a list if multiples.
</para>

<para>
Example:
</para>

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

<note><para>
The object returned by &f-link-env-Dictionary; should be treated
as a read-only view into the &consvars;.
Some &consvars; require special internal handling,
and modifying them through the &f-env-Dictionary; object can bypass
that handling and cause data inconsistencies.
The primary use of &f-env-Dictionary; is for diagnostic purposes -
it is used widely by test cases specifically because
it bypasses the special handling so that behavior
can be verified.
</para></note>

<para>
<emphasis>Changed in 4.9.0</emphasis>:
<parameter>as_dict</parameter> added.
</para>

</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 "Filesystem Nodes"
for more information.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Dump">
    <term><replaceable>env</replaceable>.<methodname>Dump</methodname>(<parameter>[var, ...], [format=TYPE]</parameter>)</term>
    <listitem><para>
Serialize &consvars; from <parameter>env</parameter> to a string.
If <varname>var</varname> is omitted,
all the &consvars; are serialized.
If one or more <varname>var</varname> values are supplied,
only those variables and their values are serialized.
</para>

<para>
The optional <parameter>format</parameter> string
selects the serialization format:
</para>
<variablelist>
<varlistentry>
<term><literal>pretty</literal></term>
<listitem>
<para>
Returns a pretty-printed representation
of the &consvars; - the result will look like a
&Python; <type>dict</type>
(this is the default).
</para>
</listitem>
</varlistentry>
<varlistentry>
<term><literal>json</literal></term>
<listitem>
<para>
Returns a JSON-formatted representation of the variables.
The variables will be presented as a JSON object literal,
the JSON equivalent of a &Python; <type>dict</type>..
</para>
</listitem>
</varlistentry>
</variablelist>

<para>
<emphasis>Changed in 4.9.0</emphasis>:
More than one <parameter>key</parameter> can be specified.
The returned string always looks like a <type>dict</type>
(or equivalent in other formats);
previously a single key serialized only the value,
not the key with the value.
</para>

<para>
Examples: this &SConstruct;
</para>

<example_commands>
env = Environment()
print(env.Dump('CCCOM'))
print(env.Dump('CC', 'CCFLAGS', format='json'))
</example_commands>

<para>
will print something like:
</para>

<example_commands>
{'CCCOM': '$CC -o $TARGET -c $CFLAGS $CCFLAGS $_CCCOMCOM $SOURCES'}
{
    "CC": "gcc",
    "CCFLAGS": []
}
</example_commands>

<para>
While this &SConstruct;:
</para>

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

<para>
will print something like:
</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>
    <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>
    <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 &consenv;
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 specially recognized and do not lead to
&consvar; creation.
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>
    <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 for sharing with other SConscript files.
The variables are added to a global collection where
they can be imported by other SConscript files.
<parameter>vars</parameter> may be one or more
strings, or a list of strings. If any string
contains whitespace, it is split automatically
into individual strings. Each string must
match the name of a variable that is in scope
during evaluation of the current SConscript file,
or an exception is raised.
</para>

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

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

<para>
To use an exported variable, an SConscript must
call &f-link-Import; to bring it into its own scope.
Importing creates an additional reference to the object that
was originally exported, so if that object is mutable,
changes made will be visible to other users of that object.
</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 also supports an &exports;
argument that allows exporting one or more variables
to the SConscript files invoked by that call (only).
See the description of that function for details.
</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 "Filesystem 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>
    <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>
Query the value of settable option <parameter>name</parameter>,
which may have been set on the command line, via option defaults,
or using the &f-link-SetOption; function.
The value of the option is returned in a type matching how the
option was declared - see the documentation of the
corresponding command line option for information about each specific
option.
</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 that addition has been
processed 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 argument</entry>
  <entry align="left">Notes</entry>
</row>
</thead>

<tbody>
<row>
  <entry><varname>cache_debug</varname></entry>
  <entry>
    <link linkend="opt-cache-debug"><option>--cache-debug</option></link>
  </entry>

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

</tbody>
</tgroup>
</informaltable>
</listitem>
  </varlistentry>
  <varlistentry id="f-GetSConsVersion">
    <term><function>GetSConsVersion</function>()</term>
    <listitem><para>
Returns the current SCons version in the form of a Tuple[int, int, int],
representing the major, minor, and revision values respectively.
<emphasis>Added in 4.8.0</emphasis>.
</para>
</listitem>
  </varlistentry>
  <varlistentry id="f-Glob">
    <term><function>Glob</function>(<parameter>pattern, [ondisk=True, source=False, strings=False, exclude=None]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Glob</methodname>(<parameter>pattern, [ondisk=True, source=False, strings=False, exclude=None]</parameter>)</term>
    <listitem><para>
Returns a possibly empty list of Nodes (or strings) that match
pathname specification <parameter>pattern</parameter>.
<parameter>pattern</parameter> can be absolute,
top-relative,
or (most commonly) relative to the directory of the current
&SConscript; file.
&f-Glob; matches both files stored on disk and Nodes
which &SCons; already knows about, even if any corresponding
file is not currently stored on disk.
The environment method form (&f-env-Glob;)
performs string substitution on
<parameter>pattern</parameter>
and returns whatever matches the resulting expanded pattern.
The results are sorted, unlike for the similar &Python;
<systemitem>glob.glob</systemitem> function,
to ensure build order will be stable.
</para>

<para>
<parameter>pattern</parameter>
can contain POSIX-style shell metacharacters for matching:
</para>

<informaltable rowsep="1" colsep="1" frame="topbot">
<tgroup cols="2">
<thead>
  <row>
    <entry>Pattern</entry>
    <entry>Meaning</entry>
  </row>
</thead>
<tbody>
  <row>
    <entry><literal>*</literal></entry>
    <entry>matches everything</entry>
  </row>
  <row>
      <entry><literal>?</literal></entry>
      <entry>matches any single character</entry>
  </row>
  <row>
      <entry><literal>[seq]</literal></entry>
      <entry>matches any character in <emphasis>seq</emphasis>
      (can be a list or a range).</entry>
  </row>
  <row>
      <entry><literal>[!seq]</literal></entry>
      <entry>matches any character not in <emphasis>seq</emphasis></entry>
  </row>
</tbody>
</tgroup>
</informaltable>

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

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

<para>
&f-Glob;
understands 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) match
in the local (SConscript) directory
if a matching Node is found
anywhere in a corresponding
repository or source directory.
</para>

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

<para>
If the optional
<parameter>source</parameter>
argument evaluates true,
and the local directory is a variant directory,
then &f-Glob; returns Nodes from
the corresponding source directory,
rather than the local directory.
<!-- XXX what about generated files that don't exist in src but will be sources? -->
</para>

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

<para>
The optional
<parameter>exclude</parameter>
argument may be set to a pattern or a list of patterns
describing files or directories
to filter out of the match list.
Elements matching a least one specified pattern will be excluded.
These patterns use the same syntax as for
<parameter>pattern</parameter>.
</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, local_only=False</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Help</methodname>(<parameter>text, append=False, local_only=False</parameter>)</term>
    <listitem><para>
Adds <parameter>text</parameter> to the help message shown when
&scons; is called with the
<option>-h</option> or <option>--help</option>
argument.
</para>
<para>
On the first call to &f-Help;,
if <parameter>append</parameter> is <constant>False</constant>
(the default), any existing help text is discarded.
The default help text is the help for the &scons;
command itself plus help collected from any
project-local &f-link-AddOption; calls.
This is the help printed if &f-Help; has never been called.
If <parameter>append</parameter> is <constant>True</constant>,
<parameter>text</parameter> is appended to
the existing help text.
If <parameter>local_only</parameter> is also <constant>True</constant>
(the default is <constant>False</constant>),
the project-local help from &f-AddOption; calls is preserved
in the help message but the &scons; command help is not.
</para>
<para>
Subsequent calls to
&f-Help; ignore the keyword arguments
<parameter>append</parameter> and
<parameter>local_only</parameter>
and always append to the existing help text.
</para>
<para>
<emphasis>Changed in 4.6.0</emphasis>: added <parameter>local_only</parameter>.
</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>
Ignores <parameter>dependency</parameter>
when deciding if
<parameter>target</parameter> needs to be rebuilt.
<parameter>target</parameter> and
<parameter>dependency</parameter>
can each be a single filename or Node
or a list of filenames or Nodes.
</para>

<para>
&f-Ignore; can also be used to
remove a target from the default build
by specifying the directory the target will be built in as
<parameter>target</parameter>
and the file you want to skip selecting for building as
<parameter>dependency</parameter>.
Note that this only removes the target from
the default target selection algorithm:
if it is a dependency of another object being
built &SCons; still builds it normally.
See the third and forth examples below.
</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 scope of 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 the
&f-link-SConscript; function.
Variables exported by the
&f-SConscript; call
take precedence.
Multiple variable names can be passed to
&f-Import;
as separate arguments, as a list of strings,
or as words in a space-separated string.
The wildcard <literal>"*"</literal> can be used to import all
available variables.
</para>

<para>
If the imported variable is mutable,
changes made locally will be reflected in the object the
variable is bound to. This allows subsidiary SConscript files
to contribute to building up, for example, a &consenv;.
</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 &consvars; 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 <parameter>env</parameter>.
If <parameter>arg</parameter> is a dictionary,
each key-value pair represents a
&consvar; name and the corresponding flags to merge.
If <parameter>arg</parameter>
is not a dictionary,
&MergeFlags; attempts to convert it to one
before the values are merged.
&f-link-env-ParseFlags; is used for this,
so values to be converted are subject to the
same limitations:
&ParseFlags; has knowledge of which &consvars; certain
flags should go to, but not all;
and only for GCC and compatible compiler chains.
<parameter>arg</parameter>
must be a single object,
so to pass multiple strings,
enclose them in a list.
</para>

<para>
If <literal>unique</literal> is true (the default),
duplicate values are not retained.
In case of duplication,
any &consvar; names that end in
<literal>PATH</literal>
keep the left-most value so the
path search order is not altered.
All other &consvars; keep
the right-most value.
If <literal>unique</literal> is false,
values are appended even if they are duplicates.
</para>

<para>
Examples:
</para>

<example_commands>
# Add an optimization flag to $CCFLAGS.
env.MergeFlags({'CCFLAGS': '-O3'})

# Combine the flags returned from running pkg-config with an optimization
# flag and merge the result into the construction variables.
env.MergeFlags(['!pkg-config gtk+-2.0 --cflags', '-O3'])

# Combine an optimization flag with the flags returned from running pkg-config
# for two distinct packages and merge into the construction variables.
env.MergeFlags(
    [
        '-O3',
        '!pkg-config gtk+-2.0 --cflags --libs',
        '!pkg-config libpng12 --cflags --libs',
    ]
)
</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 &consenv;
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>targets, ...</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>NoClean</methodname>(<parameter>targets, ...</parameter>)</term>
    <listitem><para>
Specifies files or directories which should not
be removed whenever a specified
<parameter>target</parameter> (or its dependencies)
is selected and clean mode is active
(<link linkend="opt-clean"><option>-c</option></link>
command line option).
<parameter>targets</parameter>
may be one or more file or directory names
or nodes,
and/or lists of names or nodes.
&f-NoClean; can be called multiple times.
</para>

<para>
Calling
&f-NoClean;
for a target overrides calling
&f-link-Clean;
for the same target,
so any targets passed to both functions will
<emphasis>not</emphasis>
be removed in clean mode.
</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 &consvars;;
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 table of options and corresponding &consvars;.
To provide alternative processing of the output of
<parameter>command</parameter>,
you can supply 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 &consvars;.
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 &consenv;.
(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 &consvars;:
</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
-stdlib=                CXXFLAGS
-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; &consvar;.
</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 &consenv; 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 <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 a single call,
and may be strings and/or nodes.
Returns a list of the affected target nodes.
</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 directory paths from
<parameter>newpath</parameter> to
a search-path entry <parameter>name</parameter>
in &consvar; <parameter>envname</parameter>
in the current enviromment (<parameter>env</parameter>).
If <parameter>envname</parameter> is not given,
the default is <literal>"ENV"</literal>
(see &cv-link-ENV;).
<parameter>envname</parameter> is expected
to refer to a dictionary-like object;
if it does not exist in <parameter>env</parameter>
it will be created as an initially empty dict.
<parameter>newpath</parameter>
may be specified as a string,
a directory node, or a list of strings.
If a string, it may contain multiple paths separated
by the system path separator
(<systemitem>os.pathsep</systemitem>),
or, if specified, by the value of <parameter>sep</parameter>.
Top-relative path strings (starting with <literal>#</literal>) are recognized.
The type of the existing value
of <parameter>name</parameter> is preserved.
</para>

<para>
Paths will only appear once.
Duplicate paths in <parameter>newpath</parameter> are removed,
preserving the first occurrence to maintain path order.
If <parameter>delete_existing</parameter> is true (the default),
existing duplicates are removed before prepending,
otherwise, new duplicates are skipped.
During comparisons, paths are normalized, to avoid
issues with case differences (on case-insensitive filesystems)
and with relative paths that may refer back to the same directory.
The stored values are not modified by this process.
</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;,
except that values are added to the front,
rather than the end, of the &consvar;,
and values that would become duplicates
are not added.
If <parameter>delete_existing</parameter>
is set to a true value, then for any duplicate,
the existing instance of <parameter>val</parameter> is first removed,
then <parameter>val</parameter> is inserted,
having the effect of moving it 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 substitution,
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>
Marks <parameter>target</parameter> as a pseudo target,
not representing the production of any physical target file.
If any pseudo <parameter>target</parameter> does exist,
&SCons; will abort the build with an error.
Multiple targets can be passed in a single call,
and may be strings and/or Nodes.
Returns a list of the affected target nodes.
</para>

<para>
&f-Pseudo; may be useful in conjuction with a builder
call (such as &f-link-Command;) which does not create a physical target,
and the behavior if the target accidentally existed would be incorrect.
This is similar in concept to the GNU <application>make</application>
<literal>.PHONY</literal> target.
&SCons; also provides a powerful target alias capability
(see &f-link-Alias;) which may provide more flexibility
in many situations when defining target names that are not directly built.
</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>
Finds the location of <parameter>modulename</parameter>,
which can be a string or a sequence of strings,
each representing the name of a &Python; module.
Construction variables are expanded in
<parameter>modulename</parameter>.
Returns a Directory Node (see &f-link-Dir;),
or a list of Directory Nodes if
<parameter>modulename</parameter> is a sequence.
<literal>None</literal> is returned for any module not found.
</para>

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

<para>
Example:
</para>

<example_commands>
env = Environment(
    tools=["default", "ExampleTool"],
    toolpath=[PyPackageDir("example_tool")]
)
</example_commands>
</listitem>
  </varlistentry>
  <varlistentry id="f-Replace">
    <term><replaceable>env</replaceable>.<methodname>Replace</methodname>(<parameter>key=val, [...]</parameter>)</term>
    <listitem><para>
Replaces &consvars; 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>
Sets
<parameter>directory</parameter>
as a repository to be searched for files contributing to the build.
Multiple calls to
&f-Repository;
are allowed,
with repositories searched in the given order.
Repositories specified via command-line option
have higher priority.
</para>

<para>
In
&scons;,
a repository is partial or complete copy of the source tree,
from the top-level directory down,
containing source files
that can be used to build targets in
the current worktree.
Repositories can also contain derived files.
An example might be an official source tree maintained by an integrator.
If a repository contains derived files,
they should be the result of building with &SCons;,
so a signature database (sconsign) is present
in the repository,
allowing better decisions on whether they are
up-to-date or not.
</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.
If you need a local copy to 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 <parameter>target</parameter>
and <parameter>prerequisite</parameter>.
The prerequisites
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.
<parameter>target</parameter> and
<parameter>prerequisite</parameter> may each
be a string or Node, or a list of strings or Nodes.
If there are multiple
<parameter>target</parameter> values,
the prerequisite(s) are added to each one.
Returns a list of the affected target nodes.
</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 containing 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>scriptnames, [exports, variant_dir, duplicate, must_exist]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>SConscript</methodname>(<parameter>scriptnames, [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 subsidiary SConscript (build configuration) file(s).
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,
which can be a string or a list of strings.
If there is a second positional argument,
it is treated as if the
<varname>exports</varname>
keyword argument had been given (see below).
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'])
SConscript(Split('src/SConscript doc/SConscript'))
config = SConscript('MyConfig.py')
</example_commands>

<para>
The second calling style is to omit the positional argument naming
the script and instead specify directory names using the
<varname>dirs</varname> keyword argument.
The value can be a string or list of strings.
In this case,
&scons;
will execute a subsidiary configuration file named
&SConscript; (by default)
in each of the specified directories.
You may specify a name other than
&SConscript;
by supplying an optional
<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 specifies variables to make available
for use by the called SConscripts,
which are evaluated in an isolated context
and otherwise do not have access to local variables
from the calling SConscript.
The value may be a string or list of strings representing
variable names, or a dictionary mapping local names to
the names they can be imported by.
For the first (scriptnames) calling style,
a second positional argument will also be interpreted as
<varname>exports</varname>;
the second (directory) calling style accepts no
positional arguments and must use the keyword form.
These variables are locally exported only to the called
SConscript file(s), and take precedence over any same-named
variables in the global pool managed by the
&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 into their local scope.
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> (the default),
an exception is raised if a requested
SConscript file is not found.
To allow missing scripts to be silently ignored
(the default behavior prior to &SCons; version 3.1),
pass
<literal>must_exist=False</literal> in the &f-SConscript; call.
</para>

<para>
<emphasis>Changed in 4.6.0</emphasis>: <parameter>must_exist</parameter>
now defaults to <constant>True</constant>.
</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>
    <listitem><para>
By default,
&scons;
changes its working directory
to the directory in which each
subsidiary SConscript file lives
while reading and processing that script.
This behavior may be disabled
by specifying an argument which
evaluates false, in which case
&scons;
will stay in the top-level directory
while reading all SConscript files.
(This may be necessary when building from repositories,
when all the directories in which SConscript files may be found
don't necessarily exist locally.)
You may enable and disable
this ability by calling
&f-SConscriptChdir;
multiple times.
</para>

<para>
Example:
</para>

<example_commands>
SConscriptChdir(False)
SConscript('foo/SConscript')	# will not chdir to foo
SConscriptChdir(True)
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 measure 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 &consvars; 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>
Set option variable <parameter>name</parameter>
to <parameter>value</parameter>.
Settable  options have corresponding command-line
arguments, which can be used for one-time overrides,
as a value set via command-line option will take
precedence over one set with &f-SetOption;.
The table shows the correspondence between the
option name and the command-line argument(s).
&f-SetOption; calls can also be placed in a
<filename>site_init.py</filename> file.
</para>

<para>
The behavior of the options is described in the
manpage entry for the command-line version.
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>
For project-specific options (sometimes called
<firstterm>local options</firstterm>)
added via an &f-link-AddOption; call,
&f-SetOption; is available only after the
&f-AddOption; call has completed successfully,
and only if that call included the
<parameter>settable=True</parameter> keyword argument.
</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 argument</entry>
  <entry align="left">Notes</entry>
</row>
</thead>

<tbody>
<row>
  <entry><varname>clean</varname></entry>
  <entry>
    <link linkend="opt-clean">
      <option>-c</option>,
      <option>--clean</option>,
      <option>--remove</option>
    </link>
  </entry>
</row>

<row>
  <entry><varname>diskcheck</varname></entry>
  <entry>
    <link linkend="opt-diskcheck"><option>--diskcheck</option></link>
  </entry>
</row>

<row>
  <entry><varname>duplicate</varname></entry>
  <entry>
    <link linkend="opt-duplicate"><option>--duplicate</option></link>
  </entry>
</row>

<row>
  <entry><varname>experimental</varname></entry>
  <entry>
    <link linkend="opt-experimental"><option>--experimental</option></link>
  </entry>
  <entry><emphasis>Since 4.2</emphasis>.</entry>
</row>

<row>
  <entry><varname>hash_chunksize</varname></entry>
  <entry>
    <link linkend="opt-hash-chunksize"><option>--hash-chunksize</option></link>
  </entry>
  <entry>
    Replaces <option>md5_chunksize</option>. <emphasis>Since 4.2</emphasis>
  </entry>
</row>

<row>
  <entry><varname>hash_format</varname></entry>
  <entry>
    <link linkend="opt-hash-format"><option>--hash-format</option></link>
  </entry>
  <entry><emphasis>Since 4.2</emphasis></entry>
</row>

<row>
  <entry><varname>help</varname></entry>
  <entry>
    <link linkend="opt-H"><option>-h</option>, <option>--help</option></link>
  </entry>
</row>

<!-- XXX   <varlistentry id="opt-ignore-errors"> ?? -->

<row>
  <entry><varname>implicit_cache</varname></entry>
  <entry>
    <link linkend="opt-implicit-cache"><option>--implicit-cache</option></link>
  </entry>
</row>

<row>
  <entry><varname>implicit_deps_changed</varname></entry>
  <entry>
    <link linkend="opt-implicit-deps-changed">
      <option>--implicit-deps-changed</option>
    </link>
  </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>
    <link linkend="opt-implicit-deps-unchanged">
      <option>--implicit-deps-unchanged</option>
    </link>
  </entry>
  <entry>
    Also sets <varname>implicit_cache</varname>.
    <emphasis>Settable since 4.2</emphasis>
  </entry>
</row>

<!-- XXX id="opt-keep-going" ?? -->

<row>
  <entry><varname>max_drift</varname></entry>
  <entry>
    <link linkend="opt-max-drift"><option>--max-drift</option></link>
  </entry>
</row>

<row>
  <entry><varname>md5_chunksize</varname></entry>
  <entry>
    <link linkend="opt-hash-chunksize"><option>--hash-chunksize</option></link>
  </entry>
  <entry>
    Synonym for <option>hash_chunksize</option>.
    <emphasis>Deprecated since 4.2</emphasis>
  </entry>
</row>

<row>
  <entry><varname>no_exec</varname></entry>
  <entry>
    <link linkend="opt-no-exec">
      <option>-n</option>,
      <option>--no-exec</option>,
      <option>--just-print</option>,
      <option>--dry-run</option>,
      <option>--recon</option>
    </link>
  </entry>
</row>

<row>
  <entry><varname>no_progress</varname></entry>
  <entry>
    <link linkend="opt-Q"><option>-Q</option></link>
  </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>
    <link linkend="opt-jobs"><option>-j</option>, <option>--jobs</option></link>
  </entry>
</row>

<row>
  <entry><varname>random</varname></entry>
  <entry><link linkend="opt-random"><option>--random</option></link></entry>
</row>

<row>
  <entry><varname>silent</varname></entry>
  <entry>
    <link linkend="opt-silent">
      <option>-s</option>,
      <option>--silent</option>,
      <option>--quiet</option>
    </link>
  </entry>
</row>

<row>
  <entry><varname>stack_size</varname></entry>
  <entry>
    <link linkend="opt-stack-size"><option>--stack-size</option></link>
  </entry>
</row>

<row>
  <entry><varname>warn</varname></entry>
  <entry><link linkend="opt-warn"><option>--warn</option></link></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, key=value, ...]</parameter>)</term>
    <term><replaceable>env</replaceable>.<methodname>Tool</methodname>(<parameter>name, [toolpath, key=value, ...]</parameter>)</term>
    <listitem><para>
Locates the tool specification module <parameter>name</parameter>
and returns a callable tool object for that tool.
When the environment method (&f-env-Tool;) form is used,
the tool object is automatically called before the method returns
to update <varname>env</varname>,
and <parameter>name</parameter> is
appended to the &cv-link-TOOLS;
&consvar; in that environment.
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,
and the returned object needs to be used to arrange for the call.
</para>

<para>
The tool module is searched for in the tool search paths (see the
<emphasis role="bold">Tools</emphasis> section in the manual page
for details)
and in any paths specified by the optional
<parameter>toolpath</parameter> parameter,
which must be a list of strings.
If <parameter>toolpath</parameter> is omitted,
the <parameter>toolpath</parameter>
supplied when the environment was created,
if any, is used.
</para>

<para>
Any remaining keyword arguments are saved in
the tool object,
and will be passed to the tool module's
<function>generate</function> function
when the tool object is actually called.
The <function>generate</function> function
can update the &consenv; with &consvars; and arrange
any other initialization
needed to use the mechanisms that tool describes,
and can use these extra arguments to help
guide its actions.
</para>

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

<para>
Examples:
</para>

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

<para>
The returned 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>
</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
        &SCons; built-in options or defined via calls to &f-link-AddOption;.
        &SCons; will eventually fail on unknown options anyway, but calling
        this function allows the build to "fail fast" before executing
        expensive logic later in the build.
      </para>

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

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

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

      <screen>
$ <userinput>scons --compilers=mingw</userinput>  # the correct flag is --compiler
      </screen>

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

      <programlisting language="python">
from SCons.Script.SConsOptions import SConsBadOptionError

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

# ... other SConscript logic ...

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

      <para><emphasis>New in version 4.5.0</emphasis></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;
<parameter>value</parameter>.
Value Nodes can be used as dependencies of targets.
If the string representation of the Value Node
changes between &SCons; runs, it is considered
out-of-date and any targets depending on it will be rebuilt.
Since Value Nodes have no filesystem representation,
timestamps are not used; the timestamp deciders
perform the same content-based up to date check.
</para>
<para>
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."
</para>

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

<para>
Value Nodes have a
<methodname>write</methodname>
method that can be used to "build" a Value Node
by setting a new value.
The corresponding
<methodname>read</methodname>
method returns the built value of the Node.
</para>

<para>
<emphasis>Changed in version 4.0:</emphasis>
the <parameter>name</parameter> parameter was added.
</para>

<para>
Examples:
</para>

<example_commands>
env = Environment()

def create(target, source, env):
    """Action function to create a file from a Value.

    Writes 'prefix=$SOURCE' into the file name given as $TARGET.
    """
    with open(target[0], 'wb') as f:
        f.write(b'prefix=' + source[0].get_contents() + b'\n')

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

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

def build_value(target, source, env):
    """Action function to "build" a Value.

    Writes contents of $SOURCE into $TARGET, thus updating if it existed.
    """
    target[0].write(source[0].get_contents())

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

# Attach a builder named UpdateValue to the construction environment
# using the 'build_value' action function above.
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> must 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-Virtualenv">
    <term><function>Virtualenv</function>()</term>
    <listitem><para>
If the &SCons; process is running inside a &Python;
virtual environment,
return the path to the directory where that environment is stored,
else an empty string.
The result can be treated as a boolean value if the path is unneeded.
</para>
</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>
