path: root/doc/man/scons.1

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.\" doc/man/scons.1 4629 2010/01/17 22:23:21 scons
.\"
.TH SCONS 1 "January 2010"
.\" ES - Example Start - indents and turns off line fill
.rm ES
.de ES
.RS
.nf
..
.\" EE - Example End - ends indent and turns line fill back on
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.RE
..
.SH NAME
scons \- a software construction tool
.SH SYNOPSIS
.B scons
[
.IR options ...
]
[
.IR name = val ...
]
[
.IR targets ...
]
.SH DESCRIPTION

The
.B scons
utility builds software (or other files) by determining which
component pieces must be rebuilt and executing the necessary commands to
rebuild them.

By default,
.B scons
searches for a file named
.IR SConstruct ,
.IR Sconstruct ,
or
.I sconstruct
(in that order) in the current directory and reads its
configuration from the first file found.
An alternate file name may be
specified via the
.B -f
option.

The
.I SConstruct
file can specify subsidiary
configuration files using the
.BR SConscript ()
function.
By convention,
these subsidiary files are named
.IR SConscript ,
although any name may be used.
(Because of this naming convention,
the term "SConscript files"
is sometimes used to refer
generically to all
.B scons
configuration files,
regardless of actual file name.)

The configuration files
specify the target files to be built, and
(optionally) the rules to build those targets.  Reasonable default
rules exist for building common software components (executable
programs, object files, libraries), so that for most software
projects, only the target and input files need be specified.

Before reading the
.I SConstruct
file,
.B scons
looks for a directory named
.I site_scons
in the directory containing the
.I SConstruct
file; if it exists,
.I site_scons
is added to sys.path,
the file
.IR site_scons/site_init.py ,
is evaluated if it exists,
and the directory
.I site_scons/site_tools
is added to the default toolpath if it exist.
See the
.I --no-site-dir
and
.I --site-dir
options for more details.

.B scons
reads and executes the SConscript files as Python scripts,
so you may use normal Python scripting capabilities
(such as flow control, data manipulation, and imported Python libraries)
to handle complicated build situations.
.BR scons ,
however, reads and executes all of the SConscript files
.I before
it begins building any targets.
To make this obvious,
.B scons
prints the following messages about what it is doing:

.ES
$ scons foo.out
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons: Building targets  ...
cp foo.in foo.out
scons: done building targets.
$
.EE

The status messages
(everything except the line that reads "cp foo.in foo.out")
may be suppressed using the
.B -Q
option.

.B scons
does not automatically propagate
the external environment used to execute
.B scons
to the commands used to build target files.
This is so that builds will be guaranteed
repeatable regardless of the environment
variables set at the time
.B scons
is invoked.
This also means that if the compiler or other commands
that you want to use to build your target files
are not in standard system locations,
.B scons
will not find them unless
you explicitly set the PATH
to include those locations.
Whenever you create an
.B scons
construction environment,
you can propagate the value of PATH
from your external environment as follows:

.ES
import os
env = Environment(ENV = {'PATH' : os.environ['PATH']})
.EE

Similarly, if the commands use external environment variables
like $PATH, $HOME, $JAVA_HOME, $LANG, $SHELL, $TERM, etc.,
these variables can also be explicitly propagated:

.ES
import os
env = Environment(ENV = {'PATH' : os.environ['PATH'],
                         'HOME' : os.environ['HOME']})
.EE

Or you may explicitly propagate the invoking user's
complete external environment:

.ES
import os
env = Environment(ENV = os.environ)
.EE

This comes at the expense of making your build
dependent on the user's environment being set correctly,
but it may be more convenient for many configurations.

.B scons
can scan known input files automatically for dependency
information (for example, #include statements
in C or C++ files) and will rebuild dependent files appropriately
whenever any "included" input file changes.
.B scons
supports the
ability to define new scanners for unknown input file types.

.B scons
knows how to fetch files automatically from
SCCS or RCS subdirectories
using SCCS, RCS or BitKeeper.

.B scons
is normally executed in a top-level directory containing a
.I SConstruct
file, optionally specifying
as command-line arguments
the target file or files to be built.

By default, the command

.ES
scons
.EE

will build all target files in or below the current directory.
Explicit default targets
(to be built when no targets are specified on the command line)
may be defined the SConscript file(s)
using the
.B Default()
function, described below.

Even when
.B Default()
targets are specified in the SConscript file(s),
all target files in or below the current directory
may be built by explicitly specifying
the current directory (.)
as a command-line target:

.ES
scons .
.EE

Building all target files,
including any files outside of the current directory,
may be specified by supplying a command-line target
of the root directory (on POSIX systems):

.ES
scons /
.EE

or the path name(s) of the volume(s) in which all the targets
should be built (on Windows systems):

.ES
scons C:\\ D:\\
.EE

To build only specific targets,
supply them as command-line arguments:

.ES
scons foo bar
.EE

in which case only the specified targets will be built
(along with any derived files on which they depend).

Specifying "cleanup" targets in SConscript files is not usually necessary.
The
.B -c
flag removes all files
necessary to build the specified target:

.ES
scons -c .
.EE

to remove all target files, or:

.ES
scons -c build export
.EE

to remove target files under build and export.
Additional files or directories to remove can be specified using the
.BR Clean()
function.
Conversely, targets that would normally be removed by the
.B -c
invocation
can be prevented from being removed by using the
.BR NoClean ()
function.

A subset of a hierarchical tree may be built by
remaining at the top-level directory (where the
.I SConstruct
file lives) and specifying the subdirectory as the target to be
built:

.ES
scons src/subdir
.EE

or by changing directory and invoking scons with the
.B -u
option, which traverses up the directory
hierarchy until it finds the
.I SConstruct
file, and then builds
targets relatively to the current subdirectory:

.ES
cd src/subdir
scons -u .
.EE

.B scons
supports building multiple targets in parallel via a
.B -j
option that takes, as its argument, the number
of simultaneous tasks that may be spawned:

.ES
scons -j 4
.EE

builds four targets in parallel, for example.

.B scons
can maintain a cache of target (derived) files that can
be shared between multiple builds.  When caching is enabled in a
SConscript file, any target files built by
.B scons
will be copied
to the cache.  If an up-to-date target file is found in the cache, it
will be retrieved from the cache instead of being rebuilt locally.
Caching behavior may be disabled and controlled in other ways by the
.BR --cache-force ,
.BR --cache-disable ,
and
.B --cache-show
command-line options.  The
.B --random
option is useful to prevent multiple builds
from trying to update the cache simultaneously.

Values of variables to be passed to the SConscript file(s)
may be specified on the command line:

.ES
scons debug=1 .
.EE

These variables are available in SConscript files
through the ARGUMENTS dictionary,
and can be used in the SConscript file(s) to modify
the build in any way:

.ES
if ARGUMENTS.get('debug', 0):
    env = Environment(CCFLAGS = '-g')
else:
    env = Environment()
.EE

The command-line variable arguments are also available
in the ARGLIST list,
indexed by their order on the command line.
This allows you to process them in order rather than by name,
if necessary.
ARGLIST[0] returns a tuple
containing (argname, argvalue).
A Python exception is thrown if you
try to access a list member that
does not exist.

.B scons
requires Python version 1.5.2 or later.
There should be no other dependencies or requirements to run
.B scons.

.\" The following paragraph reflects the default tool search orders
.\" currently in SCons/Tool/__init__.py.  If any of those search orders
.\" change, this documentation should change, too.
By default,
.B scons
knows how to search for available programming tools
on various systems.
On Windows systems,
.B scons
searches in order for the
Microsoft Visual C++ tools,
the MinGW tool chain,
the Intel compiler tools,
and the PharLap ETS compiler.
On OS/2 systems,
.B scons
searches in order for the
OS/2 compiler,
the GCC tool chain,
and the Microsoft Visual C++ tools,
On SGI IRIX, IBM AIX, Hewlett Packard HP-UX, and Sun Solaris systems,
.B scons
searches for the native compiler tools
(MIPSpro, Visual Age, aCC, and Forte tools respectively)
and the GCC tool chain.
On all other platforms,
including POSIX (Linux and UNIX) platforms,
.B scons
searches in order
for the GCC tool chain,
the Microsoft Visual C++ tools,
and the Intel compiler tools.
You may, of course, override these default values
by appropriate configuration of
Environment construction variables.

.SH OPTIONS
In general,
.B scons
supports the same command-line options as GNU
.BR make ,
and many of those supported by
.BR cons .

.TP
-b
Ignored for compatibility with non-GNU versions of
.BR make.

.TP
-c, --clean, --remove
Clean up by removing all target files for which a construction
command is specified.
Also remove any files or directories associated to the construction command
using the
.BR Clean ()
function.
Will not remove any targets specified by the
.BR NoClean ()
function.

.TP
.RI --cache-debug= file
Print debug information about the
.BR CacheDir ()
derived-file caching
to the specified
.IR file .
If
.I file
is
.B \-
(a hyphen),
the debug information are printed to the standard output.
The printed messages describe what signature file names are
being looked for in, retrieved from, or written to the
.BR CacheDir ()
directory tree.

.TP
--cache-disable, --no-cache
Disable the derived-file caching specified by
.BR CacheDir ().
.B scons
will neither retrieve files from the cache
nor copy files to the cache.

.TP
--cache-force, --cache-populate
When using
.BR CacheDir (),
populate a cache by copying any already-existing, up-to-date
derived files to the cache,
in addition to files built by this invocation.
This is useful to populate a new cache with
all the current derived files,
or to add to the cache any derived files
recently built with caching disabled via the
.B --cache-disable
option.

.TP
--cache-show
When using
.BR CacheDir ()
and retrieving a derived file from the cache,
show the command
that would have been executed to build the file,
instead of the usual report,
"Retrieved `file' from cache."
This will produce consistent output for build logs,
regardless of whether a target
file was rebuilt or retrieved from the cache.

.TP
.RI --config= mode
This specifies how the
.B Configure
call should use or generate the
results of configuration tests.
The option should be specified from
among the following choices:

.TP
--config=auto
scons will use its normal dependency mechanisms
to decide if a test must be rebuilt or not.
This saves time by not running the same configuration tests
every time you invoke scons,
but will overlook changes in system header files
or external commands (such as compilers)
if you don't specify those dependecies explicitly.
This is the default behavior.

.TP
--config=force
If this option is specified,
all configuration tests will be re-run
regardless of whether the
cached results are out of date.
This can be used to explicitly
force the configuration tests to be updated
in response to an otherwise unconfigured change
in a system header file or compiler.

.TP
--config=cache
If this option is specified,
no configuration tests will be rerun
and all results will be taken from cache.
Note that scons will still consider it an error
if --config=cache is specified
and a necessary test does not
yet have any results in the cache.

.TP
.RI "-C" " directory" ",  --directory=" directory
Change to the specified
.I directory
before searching for the
.IR SConstruct ,
.IR Sconstruct ,
or
.I sconstruct
file, or doing anything
else.  Multiple
.B -C
options are interpreted
relative to the previous one, and the right-most
.B -C
option wins. (This option is nearly
equivalent to
.BR "-f directory/SConstruct" ,
except that it will search for
.IR SConstruct ,
.IR Sconstruct ,
or
.I sconstruct
in the specified directory.)

.\" .TP
.\" -d
.\" Display dependencies while building target files.  Useful for
.\" figuring out why a specific file is being rebuilt, as well as
.\" general debugging of the build process.

.TP
-D
Works exactly the same way as the
.B -u
option except for the way default targets are handled.
When this option is used and no targets are specified on the command line,
all default targets are built, whether or not they are below the current
directory.

.TP
.RI --debug= type
Debug the build process.
.I type
specifies what type of debugging:

.TP
--debug=count
Print how many objects are created
of the various classes used internally by SCons
before and after reading the SConscript files
and before and after building targets.
This is not supported when run under Python versions earlier than 2.1,
when SCons is executed with the Python
.B -O
(optimized) option,
or when the SCons modules
have been compiled with optimization
(that is, when executing from
.B *.pyo
files).

.TP
--debug=dtree
A synonym for the newer
.B --tree=derived
option.
This will be deprecated in some future release
and ultimately removed.

.TP
--debug=explain
Print an explanation of precisely why
.B scons
is deciding to (re-)build any targets.
(Note:  this does not print anything
for targets that are
.I not
rebuilt.)

.TP
--debug=findlibs
Instruct the scanner that searches for libraries
to print a message about each potential library
name it is searching for,
and about the actual libraries it finds.

.TP
--debug=includes
Print the include tree after each top-level target is built.
This is generally used to find out what files are included by the sources
of a given derived file:

.ES
$ scons --debug=includes foo.o
.EE

.TP
--debug=memoizer
Prints a summary of hits and misses using the Memoizer,
an internal subsystem that counts
how often SCons uses cached values in memory
instead of recomputing them each time they're needed.
Only available when using Python 2.2 or later.

.TP
--debug=memory
Prints how much memory SCons uses
before and after reading the SConscript files
and before and after building targets.

.TP
--debug=nomemoizer
A deprecated option preserved for backwards compatibility.

.TP
--debug=objects
Prints a list of the various objects
of the various classes used internally by SCons.
This only works when run under Python 2.1 or later.

.TP
--debug=pdb
Re-run SCons under the control of the
.RI pdb
Python debugger.

.TP
--debug=presub
Print the raw command line used to build each target
before the construction environment variables are substituted.
Also shows which targets are being built by this command.
Output looks something like this:
.ES
$ scons --debug=presub
Building myprog.o with action(s):
  $SHCC $SHCFLAGS $SHCCFLAGS $CPPFLAGS $_CPPINCFLAGS -c -o $TARGET $SOURCES
\&...
.EE

.TP
--debug=stacktrace
Prints an internal Python stack trace
when encountering an otherwise unexplained error.

.TP
--debug=stree
A synonym for the newer
.B --tree=all,status
option.
This will be deprecated in some future release
and ultimately removed.

.TP
--debug=time
Prints various time profiling information:
the time spent executing each individual build command;
the total build time (time SCons ran from beginning to end);
the total time spent reading and executing SConscript files;
the total time spent SCons itself spend running
(that is, not counting reading and executing SConscript files);
and both the total time spent executing all build commands
and the elapsed wall-clock time spent executing those build commands.
(When
.B scons
is executed without the
.B -j
option,
the elapsed wall-clock time will typically
be slightly longer than the total time spent
executing all the build commands,
due to the SCons processing that takes place
in between executing each command.
When
.B scons
is executed
.I with
the
.B -j
option,
and your build configuration allows good parallelization,
the elapsed wall-clock time should
be significantly smaller than the
total time spent executing all the build commands,
since multiple build commands and
intervening SCons processing
should take place in parallel.)

.TP
--debug=tree
A synonym for the newer
.B --tree=all
option.
This will be deprecated in some future release
and ultimately removed.

.TP
.RI --diskcheck= types
Enable specific checks for
whether or not there is a file on disk
where the SCons configuration expects a directory
(or vice versa),
and whether or not RCS or SCCS sources exist
when searching for source and include files.
The
.I types
argument can be set to:
.BR all ,
to enable all checks explicitly
(the default behavior);
.BR none ,
to disable all such checks;
.BR match ,
to check that files and directories on disk
match SCons' expected configuration;
.BR rcs ,
to check for the existence of an RCS source
for any missing source or include files;
.BR sccs ,
to check for the existence of an SCCS source
for any missing source or include files.
Multiple checks can be specified separated by commas;
for example,
.B --diskcheck=sccs,rcs
would still check for SCCS and RCS sources,
but disable the check for on-disk matches of files and directories.
Disabling some or all of these checks
can provide a performance boost for large configurations,
or when the configuration will check for files and/or directories
across networked or shared file systems,
at the slight increased risk of an incorrect build
or of not handling errors gracefully
(if include files really should be
found in SCCS or RCS, for example,
or if a file really does exist
where the SCons configuration expects a directory).

.TP
.RI --duplicate= ORDER
There are three ways to duplicate files in a build tree: hard links,
soft (symbolic) links and copies. The default behaviour of SCons is to
prefer hard links to soft links to copies. You can specify different
behaviours with this option.
.IR ORDER
must be one of
.IR hard-soft-copy
(the default),
.IR soft-hard-copy ,
.IR hard-copy ,
.IR soft-copy
or
.IR copy .
SCons will attempt to duplicate files using
the mechanisms in the specified order.

.\" .TP
.\" -e, --environment-overrides
.\" Variables from the execution environment override construction
.\" variables from the SConscript files.

.TP
.RI -f " file" ", --file=" file ", --makefile=" file ", --sconstruct=" file
Use
.I file
as the initial SConscript file.
Multiple
.B -f
options may be specified,
in which case
.B scons
will read all of the specified files.

.TP
-h, --help
Print a local help message for this build, if one is defined in
the SConscript file(s), plus a line that describes the
.B -H
option for command-line option help.  If no local help message
is defined, prints the standard help message about command-line
options.  Exits after displaying the appropriate message.

.TP
-H, --help-options
Print the standard help message about command-line options and
exit.

.TP
-i, --ignore-errors
Ignore all errors from commands executed to rebuild files.

.TP
.RI -I " directory" ", --include-dir=" directory
Specifies a
.I directory
to search for
imported Python modules.  If several
.B -I
options
are used, the directories are searched in the order specified.

.TP
--implicit-cache
Cache implicit dependencies.
This causes
.B scons
to use the implicit (scanned) dependencies
from the last time it was run
instead of scanning the files for implicit dependencies.
This can significantly speed up SCons,
but with the following limitations:
.IP
.B scons
will not detect changes to implicit dependency search paths
(e.g.
.BR CPPPATH ", " LIBPATH )
that would ordinarily
cause different versions of same-named files to be used.
.IP
.B scons
will miss changes in the implicit dependencies
in cases where a new implicit
dependency is added earlier in the implicit dependency search path
(e.g.
.BR CPPPATH ", " LIBPATH )
than a current implicit dependency with the same name.

.TP
--implicit-deps-changed
Forces SCons to ignore the cached implicit dependencies. This causes the
implicit dependencies to be rescanned and recached. This implies
.BR --implicit-cache .

.TP
--implicit-deps-unchanged
Force SCons to ignore changes in the implicit dependencies.
This causes cached implicit dependencies to always be used.
This implies
.BR --implicit-cache .

.TP
--interactive
Starts SCons in interactive mode.
The SConscript files are read once and a
.B "scons>>>"
prompt is printed.
Targets may now be rebuilt by typing commands at interactive prompt
without having to re-read the SConscript files
and re-initialize the dependency graph from scratch.

SCons interactive mode supports the following commands:

.RS 10
.TP 6
.BI build "[OPTIONS] [TARGETS] ..."
Builds the specified
.I TARGETS
(and their dependencies)
with the specified
SCons command-line
.IR OPTIONS .
.B b
and
.B scons
are synonyms.

The following SCons command-line options affect the
.B build
command:

.ES
--cache-debug=FILE
--cache-disable, --no-cache
--cache-force, --cache-populate
--cache-show
--debug=TYPE
-i, --ignore-errors
-j N, --jobs=N
-k, --keep-going
-n, --no-exec, --just-print, --dry-run, --recon
-Q
-s, --silent, --quiet
--taskmastertrace=FILE
--tree=OPTIONS
.EE

.IP "" 6
Any other SCons command-line options that are specified
do not cause errors
but have no effect on the
.B build
command
(mainly because they affect how the SConscript files are read,
which only happens once at the beginning of interactive mode).

.TP 6
.BI clean "[OPTIONS] [TARGETS] ..."
Cleans the specified
.I TARGETS
(and their dependencies)
with the specified options.
.B c
is a synonym.
This command is itself a synonym for
.B "build --clean"

.TP 6
.BI exit
Exits SCons interactive mode.
You can also exit by terminating input
(CTRL+D on UNIX or Linux systems,
CTRL+Z on Windows systems).

.TP 6
.BI help "[COMMAND]"
Provides a help message about
the commands available in SCons interactive mode.
If
.I COMMAND
is specified,
.B h
and
.B ?
are synonyms.

.TP 6
.BI shell "[COMMANDLINE]"
Executes the specified
.I COMMANDLINE
in a subshell.
If no
.I COMMANDLINE
is specified,
executes the interactive command interpreter
specified in the
.B SHELL
environment variable
(on UNIX and Linux systems)
or the
.B COMSPEC
environment variable
(on Windows systems).
.B sh
and
.B !
are synonyms.

.TP 6
.B version
Prints SCons version information.
.RE

.IP
An empty line repeats the last typed command.
Command-line editing can be used if the
.B readline
module is available.

.ES
$ scons --interactive
scons: Reading SConscript files ...
scons: done reading SConscript files.
scons>>> build -n prog
scons>>> exit
.EE

.TP
.RI -j " N" ", --jobs=" N
Specifies the number of jobs (commands) to run simultaneously.
If there is more than one
.B -j
option, the last one is effective.
.\" ??? If the
.\" .B -j
.\" option
.\" is specified without an argument,
.\" .B scons
.\" will not limit the number of
.\" simultaneous jobs.

.TP
-k, --keep-going
Continue as much as possible after an error.  The target that
failed and those that depend on it will not be remade, but other
targets specified on the command line will still be processed.

.\" .TP
.\" .RI  -l " N" ", --load-average=" N ", --max-load=" N
.\" No new jobs (commands) will be started if
.\" there are other jobs running and the system load
.\" average is at least
.\" .I N
.\" (a floating-point number).

.\"
.\" .TP
.\" --list-derived
.\" List derived files (targets, dependencies) that would be built,
.\" but do not build them.
.\" [XXX This can probably go away with the right
.\" combination of other options.  Revisit this issue.]
.\"
.\" .TP
.\" --list-actions
.\" List derived files that would be built, with the actions
.\" (commands) that build them.  Does not build the files.
.\" [XXX This can probably go away with the right
.\" combination of other options.  Revisit this issue.]
.\"
.\" .TP
.\" --list-where
.\" List derived files that would be built, plus where the file is
.\" defined (file name and line number).  Does not build the files.
.\" [XXX This can probably go away with the right
.\" combination of other options.  Revisit this issue.]

.TP
-m
Ignored for compatibility with non-GNU versions of
.BR make .

.TP
.RI --max-drift= SECONDS
Set the maximum expected drift in the modification time of files to
.IR SECONDS .
This value determines how long a file must be unmodified
before its cached content signature
will be used instead of
calculating a new content signature (MD5 checksum)
of the file's contents.
The default value is 2 days, which means a file must have a
modification time of at least two days ago in order to have its
cached content signature used.
A negative value means to never cache the content
signature and to ignore the cached value if there already is one. A value
of 0 means to always use the cached signature,
no matter how old the file is.

.TP
.RI --md5-chunksize= KILOBYTES
Set the block size used to compute MD5 signatures to
.IR KILOBYTES . 
This value determines the size of the chunks which are read in at once when
computing MD5 signatures.  Files below that size are fully stored in memory
before performing the signature computation while bigger files are read in
block-by-block. A huge block-size leads to high memory consumption while a very
small block-size slows down the build considerably.

The default value is to use a chunk size of 64 kilobytes, which should
be appropriate for most uses.

.TP
-n, --just-print, --dry-run, --recon
No execute.  Print the commands that would be executed to build
any out-of-date target files, but do not execute the commands.

.TP
.RI --no-site-dir
Prevents the automatic addition of the standard
.I site_scons
dir to
.IR sys.path .
Also prevents loading the
.I site_scons/site_init.py
module if it exists, and prevents adding
.I site_scons/site_tools
to the toolpath.

.\" .TP
.\" .RI -o " file" ", --old-file=" file ", --assume-old=" file
.\" Do not rebuild
.\" .IR file ,
.\" and do
.\" not rebuild anything due to changes in the contents of
.\" .IR file .
.\" .TP
.\" .RI --override " file"
.\" Read values to override specific build environment variables
.\" from the specified
.\" .IR file .
.\" .TP
.\" -p
.\" Print the data base (construction environments,
.\" Builder and Scanner objects) that are defined
.\" after reading the SConscript files.
.\" After printing, a normal build is performed
.\" as usual, as specified by other command-line options.
.\" This also prints version information
.\" printed by the
.\" .B -v
.\" option.
.\"
.\" To print the database without performing a build do:
.\"
.\" .ES
.\" scons -p -q
.\" .EE

.TP
.RI --profile= file
Run SCons under the Python profiler
and save the results in the specified
.IR file .
The results may be analyzed using the Python
pstats module.

.TP
-q, --question
Do not run any commands, or print anything.  Just return an exit
status that is zero if the specified targets are already up to
date, non-zero otherwise.
.TP
-Q
Quiets SCons status messages about
reading SConscript files,
building targets
and entering directories.
Commands that are executed
to rebuild target files are still printed.

.\" .TP
.\" -r, -R, --no-builtin-rules, --no-builtin-variables
.\" Clear the default construction variables.  Construction
.\" environments that are created will be completely empty.

.TP
--random
Build dependencies in a random order.  This is useful when
building multiple trees simultaneously with caching enabled,
to prevent multiple builds from simultaneously trying to build
or retrieve the same target files.

.TP
-s, --silent, --quiet
Silent.  Do not print commands that are executed to rebuild
target files.
Also suppresses SCons status messages.

.TP
-S, --no-keep-going, --stop
Ignored for compatibility with GNU
.BR make .

.TP
.RI --site-dir= dir
Uses the named dir as the site dir rather than the default
.I site_scons
dir.  This dir will get prepended to
.IR sys.path ,
the module
.IR dir /site_init.py
will get loaded if it exists, and
.IR dir /site_tools
will get added to the default toolpath.

.TP
.RI --stack-size= KILOBYTES
Set the size stack used to run threads to
.IR KILOBYTES .
This value determines the stack size of the threads used to run jobs.
These are the threads that execute the actions of the builders for the
nodes that are out-of-date.
Note that this option has no effect unless the
.B num_jobs
option, which corresponds to -j and --jobs, is larger than one.  Using
a stack size that is too small may cause stack overflow errors.  This
usually shows up as segmentation faults that cause scons to abort
before building anything.  Using a stack size that is too large will
cause scons to use more memory than required and may slow down the entire
build process.

The default value is to use a stack size of 256 kilobytes, which should
be appropriate for most uses.  You should not need to increase this value
unless you encounter stack overflow errors.

.TP
-t, --touch
Ignored for compatibility with GNU
.BR make .
(Touching a file to make it
appear up-to-date is unnecessary when using
.BR scons .)

.TP
.RI --taskmastertrace= file
Prints trace information to the specified
.I file
about how the internal Taskmaster object
evaluates and controls the order in which Nodes are built.
A file name of
.B -
may be used to specify the standard output.

.TP
.RI -tree= options
Prints a tree of the dependencies
after each top-level target is built.
This prints out some or all of the tree,
in various formats,
depending on the
.I options
specified:

.TP
--tree=all
Print the entire dependency tree
after each top-level target is built.
This prints out the complete dependency tree,
including implicit dependencies and ignored dependencies.

.TP
--tree=derived
Restricts the tree output to only derived (target) files,
not source files.

.TP
--tree=status
Prints status information for each displayed node.

.TP
--tree=prune
Prunes the tree to avoid repeating dependency information
for nodes that have already been displayed.
Any node that has already been displayed
will have its name printed in
.BR "[square brackets]" ,
as an indication that the dependencies
for that node can be found by searching
for the relevant output higher up in the tree.

.IP
Multiple options may be specified,
separated by commas:

.ES
# Prints only derived files, with status information:
scons --tree=derived,status

# Prints all dependencies of target, with status information
# and pruning dependencies of already-visited Nodes:
scons --tree=all,prune,status target
.EE

.TP
-u, --up, --search-up
Walks up the directory structure until an
.I SConstruct ,
.I Sconstruct
or
.I sconstruct
file is found, and uses that
as the top of the directory tree.
If no targets are specified on the command line,
only targets at or below the
current directory will be built.

.TP
-U
Works exactly the same way as the
.B -u
option except for the way default targets are handled.
When this option is used and no targets are specified on the command line,
all default targets that are defined in the SConscript(s) in the current
directory are built, regardless of what directory the resultant targets end
up in.

.TP
-v, --version
Print the
.B scons
version, copyright information,
list of authors, and any other relevant information.
Then exit.

.TP
-w, --print-directory
Print a message containing the working directory before and
after other processing.

.TP
--no-print-directory
Turn off -w, even if it was turned on implicitly.

.TP
.RI --warn= type ", --warn=no-" type
Enable or disable warnings.
.I type
specifies the type of warnings to be enabled or disabled:

.TP
--warn=all, --warn=no-all
Enables or disables all warnings.

.TP
--warn=cache-write-error, --warn=no-cache-write-error
Enables or disables warnings about errors trying to
write a copy of a built file to a specified
.BR CacheDir ().
These warnings are disabled by default.

.TP
--warn=corrupt-sconsign, --warn=no-corrupt-sconsign
Enables or disables warnings about unfamiliar signature data in
.B .sconsign
files.
These warnings are enabled by default.

.TP
--warn=dependency, --warn=no-dependency
Enables or disables warnings about dependencies.
These warnings are disabled by default.

.TP
--warn=deprecated, --warn=no-deprecated
Enables or disables all warnings about use of
currently deprecated features.
These warnings are enabled by default.
Note that the
.B --warn=no-deprecated
option does not disable warnings about absolutely all deprecated features.
Warnings for some deprecated features that have already been through
several releases with deprecation warnings
may be mandatory for a release or two
before they are officially no longer supported by SCons.
Warnings for some specific deprecated features
may be enabled or disabled individually;
see below.

.RS
.TP
--warn=deprecated-copy, --warn=no-deprecated-copy
Enables or disables warnings about use of the deprecated
.B env.Copy()
method.

.TP
--warn=deprecated-source-signatures, --warn=no-deprecated-source-signatures
Enables or disables warnings about use of the deprecated
.B SourceSignatures()
function or
.B env.SourceSignatures()
method.

.TP
--warn=deprecated-target-signatures, --warn=no-deprecated-target-signatures
Enables or disables warnings about use of the deprecated
.B TargetSignatures()
function or
.B env.TargetSignatures()
method.
.RE

.TP
--warn=duplicate-environment, --warn=no-duplicate-environment
Enables or disables warnings about attempts to specify a build
of a target with two different construction environments
that use the same action.
These warnings are enabled by default.

.TP
--warn=fortran-cxx-mix, --warn=no-fortran-cxx-mix
Enables or disables the specific warning about linking
Fortran and C++ object files in a single executable,
which can yield unpredictable behavior with some compilers.

.TP
--warn=future-deprecated, --warn=no-future-deprecated
Enables or disables warnings about features
that will be deprecated in the future.
These warnings are disabled by default.
Enabling this warning is especially
recommended for projects that redistribute
SCons configurations for other users to build,
so that the project can be warned as soon as possible
about to-be-deprecated features
that may require changes to the configuration.

.TP
--warn=link, --warn=no-link
Enables or disables warnings about link steps.

.TP
--warn=misleading-keywords, --warn=no-misleading-keywords
Enables or disables warnings about use of the misspelled keywords
.B targets
and
.B sources
when calling Builders.
(Note the last
.B s
characters, the correct spellings are
.B target
and
.B source.)
These warnings are enabled by default.

.TP
--warn=missing-sconscript, --warn=no-missing-sconscript
Enables or disables warnings about missing SConscript files.
These warnings are enabled by default.

.TP
--warn=no-md5-module, --warn=no-no-md5-module
Enables or disables warnings about the version of Python
not having an MD5 checksum module available.
These warnings are enabled by default.

.TP
--warn=no-metaclass-support, --warn=no-no-metaclass-support
Enables or disables warnings about the version of Python
not supporting metaclasses when the
.B --debug=memoizer
option is used.
These warnings are enabled by default.

.TP
--warn=no-object-count, --warn=no-no-object-count
Enables or disables warnings about the
.B --debug=object
feature not working when
.B scons
is run with the python
.B \-O
option or from optimized Python (.pyo) modules.

.TP
--warn=no-parallel-support, --warn=no-no-parallel-support
Enables or disables warnings about the version of Python
not being able to support parallel builds when the
.B -j
option is used.
These warnings are enabled by default.

.TP
--warn=python-version, --warn=no-python-version
Enables or disables the warning about running
SCons with a deprecated version of Python.
These warnings are enabled by default.

.TP
--warn=reserved-variable, --warn=no-reserved-variable
Enables or disables warnings about attempts to set the
reserved construction variable names
.BR CHANGED_SOURCES ,
.BR CHANGED_TARGETS ,
.BR TARGET ,
.BR TARGETS ,
.BR SOURCE ,
.BR SOURCES ,
.BR UNCHANGED_SOURCES
or
.BR UNCHANGED_TARGETS .
These warnings are disabled by default.

.TP
--warn=stack-size, --warn=no-stack-size
Enables or disables warnings about requests to set the stack size
that could not be honored.
These warnings are enabled by default.

.\" .TP
.\" .RI --write-filenames= file
.\" Write all filenames considered into
.\" .IR file .
.\"
.\" .TP
.\" .RI -W " file" ", --what-if=" file ", --new-file=" file ", --assume-new=" file
.\" Pretend that the target
.\" .I file
.\" has been
.\" modified.  When used with the
.\" .B -n
.\" option, this
.\" show you what would be rebuilt if you were to modify that file.
.\" Without
.\" .B -n
.\" ... what? XXX
.\"
.\" .TP
.\" --warn-undefined-variables
.\" Warn when an undefined variable is referenced.

.TP
.RI -Y " repository" ", --repository=" repository ", --srcdir=" repository
Search the specified repository for any input and target
files not found in the local directory hierarchy.  Multiple
.B -Y
options may be specified, in which case the
repositories are searched in the order specified.

.SH CONFIGURATION FILE REFERENCE
.\" .SS Python Basics
.\" XXX Adding this in the future would be a help.
.SS Construction Environments
A construction environment is the basic means by which the SConscript
files communicate build information to
.BR scons .
A new construction environment is created using the
.B Environment
function:

.ES
env = Environment()
.EE

Variables, called
.I construction
.IR variables ,
may be set in a construction environment
either by specifying them as keywords when the object is created
or by assigning them a value after the object is created:

.ES
env = Environment(FOO = 'foo')
env['BAR'] = 'bar'
.EE

As a convenience,
construction variables may also be set or modified by the
.I parse_flags
keyword argument, which applies the
.B ParseFlags
method (described below) to the argument value
after all other processing is completed.
This is useful either if the exact content of the flags is unknown
(for example, read from a control file)
or if the flags are distributed to a number of construction variables.

.ES
env = Environment(parse_flags = '-Iinclude -DEBUG -lm')
.EE

This example adds 'include' to
.BR CPPPATH ,
\&'EBUG' to
.BR CPPDEFINES ,
and 'm' to
.BR LIBS .

By default, a new construction environment is
initialized with a set of builder methods
and construction variables that are appropriate
for the current platform.
An optional platform keyword argument may be
used to specify that an environment should
be initialized for a different platform:

.ES
env = Environment(platform = 'cygwin')
env = Environment(platform = 'os2')
env = Environment(platform = 'posix')
env = Environment(platform = 'win32')
.EE

Specifying a platform initializes the appropriate
construction variables in the environment
to use and generate file names with prefixes
and suffixes appropriate for the platform.

Note that the
.B win32
platform adds the
.B SystemDrive
and
.B SystemRoot
variables from the user's external environment
to the construction environment's
.B ENV
dictionary.
This is so that any executed commands
that use sockets to connect with other systems
(such as fetching source files from
external CVS repository specifications like
.BR :pserver:anonymous@cvs.sourceforge.net:/cvsroot/scons )
will work on Windows systems.

The platform argument may be function or callable object,
in which case the Environment() method
will call the specified argument to update
the new construction environment:

.ES
def my_platform(env):
    env['VAR'] = 'xyzzy'

env = Environment(platform = my_platform)
.EE

Additionally, a specific set of tools
with which to initialize the environment
may be specified as an optional keyword argument:

.ES
env = Environment(tools = ['msvc', 'lex'])
.EE

Non-built-in tools may be specified using the toolpath argument:

.ES
env = Environment(tools = ['default', 'foo'], toolpath = ['tools'])
.EE

This looks for a tool specification in tools/foo.py (as well as
using the ordinary default tools for the platform).  foo.py should
have two functions: generate(env, **kw) and exists(env).
The
.B generate()
function
modifies the passed-in environment
to set up variables so that the tool
can be executed;
it may use any keyword arguments
that the user supplies (see below)
to vary its initialization.
The
.B exists()
function should return a true
value if the tool is available.
Tools in the toolpath are used before
any of the built-in ones.  For example, adding gcc.py to the toolpath
would override the built-in gcc tool.
Also note that the toolpath is
stored in the environment for use
by later calls to
.BR Clone ()
and
.BR Tool ()
methods:

.ES
base = Environment(toolpath=['custom_path'])
derived = base.Clone(tools=['custom_tool'])
derived.CustomBuilder()
.EE

The elements of the tools list may also
be functions or callable objects,
in which case the Environment() method
will call the specified elements
to update the new construction environment:

.ES
def my_tool(env):
    env['XYZZY'] = 'xyzzy'

env = Environment(tools = [my_tool])
.EE

The individual elements of the tools list
may also themselves be two-element lists of the form
.RI ( toolname ", " kw_dict ).
SCons searches for the
.I toolname
specification file as described above, and
passes
.IR kw_dict ,
which must be a dictionary, as keyword arguments to the tool's
.B generate
function.
The
.B generate
function can use the arguments to modify the tool's behavior
by setting up the environment in different ways
or otherwise changing its initialization.

.ES
# in tools/my_tool.py:
def generate(env, **kw):
  # Sets MY_TOOL to the value of keyword argument 'arg1' or 1.
  env['MY_TOOL'] = kw.get('arg1', '1')
def exists(env):
  return 1

# in SConstruct:
env = Environment(tools = ['default', ('my_tool', {'arg1': 'abc'})],
                  toolpath=['tools'])
.EE

The tool definition (i.e. my_tool()) can use the PLATFORM variable from
the environment it receives to customize the tool for different platforms.

If no tool list is specified, then SCons will auto-detect the installed
tools using the PATH variable in the ENV construction variable and the
platform name when the Environment is constructed. Changing the PATH
variable after the Environment is constructed will not cause the tools to
be redetected.

SCons supports the following tool specifications out of the box:

.ES
386asm
aixc++
aixcc
aixf77
aixlink
ar
as
bcc32
c++
cc
cvf
dmd
dvipdf
dvips
f77
f90
f95
fortran
g++
g77
gas
gcc
gfortran
gnulink
gs
hpc++
hpcc
hplink
icc
icl
ifl
ifort
ilink
ilink32
intelc
jar
javac
javah
latex
lex
link
linkloc
m4
masm
midl
mingw
mslib
mslink
mssdk
msvc
msvs
mwcc
mwld
nasm
pdflatex
pdftex
qt
rmic
rpcgen
sgiar
sgic++
sgicc
sgilink
sunar
sunc++
suncc
sunf77
sunf90
sunf95
sunlink
swig
tar
tex
textfile
tlib
yacc
zip
.EE

Additionally, there is a "tool" named
.B default
which configures the
environment with a default set of tools for the current platform.

On posix and cygwin platforms
the GNU tools (e.g. gcc) are preferred by SCons,
on Windows the Microsoft tools (e.g. msvc)
followed by MinGW are preferred by SCons,
and in OS/2 the IBM tools (e.g. icc) are preferred by SCons.

.SS Builder Methods

Build rules are specified by calling a construction
environment's builder methods.
The arguments to the builder methods are
.B target
(a list of targets to be built,
usually file names)
and
.B source
(a list of sources to be built,
usually file names).

Because long lists of file names
can lead to a lot of quoting,
.B scons
supplies a
.B Split()
global function
and a same-named environment method
that split a single string
into a list, separated on
strings of white-space characters.
(These are similar to the
string.split() method
from the standard Python library,
but work even if the input isn't a string.)

Like all Python arguments,
the target and source arguments to a builder method
can be specified either with or without
the "target" and "source" keywords.
When the keywords are omitted,
the target is first,
followed by the source.
The following are equivalent examples of calling the Program builder method:

.ES
env.Program('bar', ['bar.c', 'foo.c'])
env.Program('bar', Split('bar.c foo.c'))
env.Program('bar', env.Split('bar.c foo.c'))
env.Program(source =  ['bar.c', 'foo.c'], target = 'bar')
env.Program(target = 'bar', Split('bar.c foo.c'))
env.Program(target = 'bar', env.Split('bar.c foo.c'))
env.Program('bar', source = string.split('bar.c foo.c'))
.EE

Target and source file names
that are not absolute path names
(that is, do not begin with
.B /
on POSIX systems
or
.B \\
on Windows systems,
with or without
an optional drive letter)
are interpreted relative to the directory containing the
.B SConscript
file being read.
An initial
.B #
(hash mark)
on a path name means that the rest of the file name
is interpreted relative to
the directory containing
the top-level
.B SConstruct
file,
even if the
.B #
is followed by a directory separator character
(slash or backslash).

Examples:

.ES
# The comments describing the targets that will be built
# assume these calls are in a SConscript file in the
# a subdirectory named "subdir".

# Builds the program "subdir/foo" from "subdir/foo.c":
env.Program('foo', 'foo.c')

# Builds the program "/tmp/bar" from "subdir/bar.c":
env.Program('/tmp/bar', 'bar.c')

# An initial '#' or '#/' are equivalent; the following
# calls build the programs "foo" and "bar" (in the
# top-level SConstruct directory) from "subdir/foo.c" and
# "subdir/bar.c", respectively:
env.Program('#foo', 'foo.c')
env.Program('#/bar', 'bar.c')

# Builds the program "other/foo" (relative to the top-level
# SConstruct directory) from "subdir/foo.c":
env.Program('#other/foo', 'foo.c')
.EE

When the target shares the same base name
as the source and only the suffix varies,
and if the builder method has a suffix defined for the target file type,
then the target argument may be omitted completely,
and
.B scons
will deduce the target file name from
the source file name.
The following examples all build the
executable program
.B bar
(on POSIX systems)
or
.B bar.exe
(on Windows systems)
from the bar.c source file:

.ES
env.Program(target = 'bar', source = 'bar.c')
env.Program('bar', source = 'bar.c')
env.Program(source = 'bar.c')
env.Program('bar.c')
.EE

As a convenience, a
.B srcdir
keyword argument may be specified
when calling a Builder.
When specified,
all source file strings that are not absolute paths
will be interpreted relative to the specified
.BR srcdir .
The following example will build the
.B build/prog
(or
.B build/prog.exe
on Windows)
program from the files
.B src/f1.c
and
.BR src/f2.c :

.ES
env.Program('build/prog', ['f1.c', 'f2.c'], srcdir='src')
.EE

It is possible to override or add construction variables when calling a
builder method by passing additional keyword arguments.
These overridden or added
variables will only be in effect when building the target, so they will not
affect other parts of the build. For example, if you want to add additional
libraries for just one program:

.ES
env.Program('hello', 'hello.c', LIBS=['gl', 'glut'])
.EE

or generate a shared library with a non-standard suffix:

.ES
env.SharedLibrary('word', 'word.cpp',
                  SHLIBSUFFIX='.ocx',
                  LIBSUFFIXES=['.ocx'])
.EE

(Note that both the $SHLIBSUFFIX and $LIBSUFFIXES variables must be set
if you want SCons to search automatically
for dependencies on the non-standard library names;
see the descriptions of these variables, below, for more information.)

It is also possible to use the
.I parse_flags
keyword argument in an override:

.ES
env = Program('hello', 'hello.c', parse_flags = '-Iinclude -DEBUG -lm')
.EE

This example adds 'include' to
.BR CPPPATH ,
\&'EBUG' to
.BR CPPDEFINES ,
and 'm' to
.BR LIBS .

Although the builder methods defined by
.B scons
are, in fact,
methods of a construction environment object,
they may also be called without an explicit environment:

.ES
Program('hello', 'hello.c')
SharedLibrary('word', 'word.cpp')
.EE

In this case,
the methods are called internally using a default construction
environment that consists of the tools and values that
.B scons
has determined are appropriate for the local system.

Builder methods that can be called without an explicit
environment may be called from custom Python modules that you
import into an SConscript file by adding the following
to the Python module:

.ES
from SCons.Script import *
.EE

All builder methods return a list-like object
containing Nodes that
represent the target or targets that will be built.
A
.I Node
is an internal SCons object
which represents
build targets or sources.

The returned Node-list object
can be passed to other builder methods as source(s)
or passed to any SCons function or method
where a filename would normally be accepted.
For example, if it were necessary
to add a specific
.B -D
flag when compiling one specific object file:

.ES
bar_obj_list = env.StaticObject('bar.c', CPPDEFINES='-DBAR')
env.Program(source = ['foo.c', bar_obj_list, 'main.c'])
.EE

Using a Node in this way
makes for a more portable build
by avoiding having to specify
a platform-specific object suffix
when calling the Program() builder method.

Note that Builder calls will automatically "flatten"
the source and target file lists,
so it's all right to have the bar_obj list
return by the StaticObject() call
in the middle of the source file list.
If you need to manipulate a list of lists returned by Builders
directly using Python,
you can either build the list by hand:

.ES
foo = Object('foo.c')
bar = Object('bar.c')
objects = ['begin.o'] + foo + ['middle.o'] + bar + ['end.o']
for object in objects:
    print str(object)
.EE

Or you can use the
.BR Flatten ()
function supplied by scons
to create a list containing just the Nodes,
which may be more convenient:

.ES
foo = Object('foo.c')
bar = Object('bar.c')
objects = Flatten(['begin.o', foo, 'middle.o', bar, 'end.o'])
for object in objects:
    print str(object)
.EE

Note also that because Builder calls return
a list-like object, not an actual Python list,
you should
.I not
use the Python
.B +=
operator to append Builder results to a Python list.
Because the list and the object are different types,
Python will not update the original list in place,
but will instead create a new Node-list object
containing the concatenation of the list
elements and the Builder results.
This will cause problems for any other Python variables
in your SCons configuration
that still hold on to a reference to the original list.
Instead, use the Python
.B .extend()
method to make sure the list is updated in-place.
Example:

.ES
object_files = []

# Do NOT use += as follows:
#
#    object_files += Object('bar.c')
#
# It will not update the object_files list in place.
#
# Instead, use the .extend() method:
object_files.extend(Object('bar.c'))

.EE

The path name for a Node's file may be used
by passing the Node to the Python-builtin
.B str()
function:

.ES
bar_obj_list = env.StaticObject('bar.c', CPPDEFINES='-DBAR')
print "The path to bar_obj is:", str(bar_obj_list[0])
.EE

Note again that because the Builder call returns a list,
we have to access the first element in the list
.B (bar_obj_list[0])
to get at the Node that actually represents
the object file.

Builder calls support a
.B chdir
keyword argument that
specifies that the Builder's action(s)
should be executed
after changing directory.
If the
.B chdir
argument is
a string or a directory Node,
scons will change to the specified directory.
If the
.B chdir
is not a string or Node
and is non-zero,
then scons will change to the
target file's directory.

.ES
# scons will change to the "sub" subdirectory
# before executing the "cp" command.
env.Command('sub/dir/foo.out', 'sub/dir/foo.in',
            "cp dir/foo.in dir/foo.out",
            chdir='sub')

# Because chdir is not a string, scons will change to the
# target's directory ("sub/dir") before executing the
# "cp" command.
env.Command('sub/dir/foo.out', 'sub/dir/foo.in',
            "cp foo.in foo.out",
            chdir=1)
.EE

Note that scons will
.I not
automatically modify
its expansion of
construction variables like
.B $TARGET
and
.B $SOURCE
when using the chdir
keyword argument--that is,
the expanded file names
will still be relative to
the top-level SConstruct directory,
and consequently incorrect
relative to the chdir directory.
If you use the chdir keyword argument,
you will typically need to supply a different
command line using
expansions like
.B ${TARGET.file}
and
.B ${SOURCE.file}
to use just the filename portion of the
targets and source.

.B scons
provides the following builder methods:

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
'\" BEGIN GENERATED BUILDER DESCRIPTIONS
'\"
'\" The descriptions below of the various SCons Builders are generated
'\" from the .xml files that live next to the various Python modules in
'\" the build enginer library.  If you're reading this [gnt]roff file
'\" with an eye towards patching this man page, you can still submit
'\" a diff against this text, but it will have to be translated to a
'\" diff against the underlying .xml file before the patch is actually
'\" accepted.  If you do that yourself, it will make it easier to
'\" integrate the patch.
'\"
'\" BEGIN GENERATED BUILDER DESCRIPTIONS
'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.so builders.man
'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
'\" END GENERATED BUILDER DESCRIPTIONS
'\"
'\" The descriptions above of the various SCons Builders are generated
'\" from the .xml files that live next to the various Python modules in
'\" the build enginer library.  If you're reading this [gnt]roff file
'\" with an eye towards patching this man page, you can still submit
'\" a diff against this text, but it will have to be translated to a
'\" diff against the underlying .xml file before the patch is actually
'\" accepted.  If you do that yourself, it will make it easier to
'\" integrate the patch.
'\"
'\" END GENERATED BUILDER DESCRIPTIONS
'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

.P
All
targets of builder methods automatically depend on their sources.
An explicit dependency can
be specified using the
.B Depends
method of a construction environment (see below).

In addition,
.B scons
automatically scans
source files for various programming languages,
so the dependencies do not need to be specified explicitly.
By default, SCons can
C source files,
C++ source files,
Fortran source files with
.B .F
(POSIX systems only),
.B .fpp,
or
.B .FPP
file extensions,
and assembly language files with
.B .S
(POSIX systems only),
.B .spp,
or
.B .SPP
files extensions
for C preprocessor dependencies.
SCons also has default support
for scanning D source files,
You can also write your own Scanners
to add support for additional source file types.
These can be added to the default
Scanner object used by the
.BR Object (),
.BR StaticObject (),
and
.BR SharedObject ()
Builders by adding them
to the
.B SourceFileScanner
object as follows:

See the section "Scanner Objects,"
below, for a more information about
defining your own Scanner objects.

.SS Methods and Functions to Do Things
In addition to Builder methods,
.B scons
provides a number of other construction environment methods
and global functions to
manipulate the build configuration.

Usually, a construction environment method
and global function with the same name both exist
so that you don't have to remember whether
to a specific bit of functionality
must be called with or without a construction environment.
In the following list,
if you call something as a global function
it looks like:
.ES
.RI Function( arguments )
.EE
and if you call something through a construction
environment it looks like:
.ES
.RI env.Function( arguments )
.EE
If you can call the functionality in both ways,
then both forms are listed.

Global functions may be called from custom Python modules that you
import into an SConscript file by adding the following
to the Python module:

.ES
from SCons.Script import *
.EE

Except where otherwise noted,
the same-named
construction environment method
and global function
provide the exact same functionality.
The only difference is that,
where appropriate,
calling the functionality through a construction environment will
substitute construction variables into
any supplied strings.
For example:

.ES
env = Environment(FOO = 'foo')
Default('$FOO')
env.Default('$FOO')
.EE

In the above example,
the first call to the global
.B Default()
function will actually add a target named
.B $FOO
to the list of default targets,
while the second call to the
.B env.Default()
construction environment method
will expand the value
and add a target named
.B foo
to the list of default targets.
For more on construction variable expansion,
see the next section on
construction variables.

Construction environment methods
and global functions supported by
.B scons
include:

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Action( action ", [" cmd/str/fun ", [" var ", ...]] [" option = value ", ...])"
.TP
.IR env .Action( action ", [" cmd/str/fun ", [" var ", ...]] [" option = value ", ...])"
Creates an Action object for
the specified
.IR action .
See the section "Action Objects,"
below, for a complete explanation of the arguments and behavior.

Note that the
.BR env.Action ()
form of the invocation will expand
construction variables in any argument strings,
including the
.I action
argument, at the time it is called
using the construction variables in the
.I env
construction environment through which
.BR env.Action ()
was called.
The
.BR Action ()
form delays all variable expansion
until the Action object is actually used.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI AddMethod( object, function ", [" name ])
.TP
.RI env.AddMethod( function ", [" name ])
When called with the
.BR AddMethod ()
form,
adds the specified
.I function
to the specified
.I object
as the specified method
.IR name .
When called with the
.BR env.AddMethod ()
form,
adds the specified
.I function
to the construction environment
.I env
as the specified method
.IR name .
In both cases, if
.I name
is omitted or
.BR None ,
the name of the
specified
.I function
itself is used for the method name.

Examples:

.ES
# Note that the first argument to the function to
# be attached as a method must be the object through
# which the method will be called; the Python
# convention is to call it 'self'.
def my_method(self, arg):
    print "my_method() got", arg

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

# Add the function as a method, using the function
# name for the method call.
env = Environment()
env.AddMethod(my_method, 'other_method_name')
env.other_method_name('another arg')
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI AddOption( arguments )
This function adds a new command-line option to be recognized.
The specified
.I arguments
are the same as supported by the standard Python
.BR optparse.add_option ()
method (with a few additional capabilities noted below);
see the documentation for
.B optparse
for a thorough discussion of its option-processing capabities.
(Note that although the
.B optparse
module was not a standard module until Python 2.3,
.B scons
contains a compatible version of the module
that is used to provide identical functionality
when run by earlier Python versions.)

In addition to the arguments and values supported by the
.B optparse.add_option ()
method,
the SCons
.BR AddOption ()
function allows you to set the
.B nargs
keyword value to
.B '?'
(a string with just the question mark)
to indicate that the specified long option(s) take(s) an
.I optional
argument.
When
.B "nargs = '?'"
is passed to the
.BR AddOption ()
function, the
.B const
keyword argument
may be used to supply the "default"
value that should be used when the
option is specified on the command line
without an explicit argument.

If no
.B default=
keyword argument is supplied when calling
.BR AddOption (),
the option will have a default value of
.BR None .

Once a new command-line option has been added with
.BR AddOption (),
the option value may be accessed using
.BR GetOption ()
or
.BR env.GetOption ().
\" NOTE: in SCons 1.x or 2.0, user options will be settable, but not yet.
\" Uncomment this when that works.  See tigris issue 2105.
\" The value may also be set, using
\" .BR SetOption ()
\" or
\" .BR env.SetOption (),
\" if conditions in a
\" .B SConscript
\" require overriding any default value.
\" Note, however, that a
\" value specified on the command line will
\" .I always
\" override a value set by any SConscript file.

Any specified
.B help=
strings for the new option(s)
will be displayed by the
.B -H
or
.B -h
options
(the latter only if no other help text is
specified in the SConscript files).
The help text for the local options specified by
.BR AddOption ()
will appear below the SCons options themselves,
under a separate
.B "Local Options"
heading.
The options will appear in the help text
in the order in which the
.BR AddOption ()
calls occur.

Example:

.ES
AddOption('--prefix',
          dest='prefix',
          nargs=1, type='string',
          action='store',
          metavar='DIR',
          help='installation prefix')
env = Environment(PREFIX = GetOption('prefix'))
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI AddPostAction( target ", " action )
.TP
.RI env.AddPostAction( target ", " action )
Arranges for the specified
.I action
to be performed
after the specified
.I target
has been built.
The specified action(s) may be
an Action object, or anything that
can be converted into an Action object
(see below).

When multiple targets are supplied,
the action may be called multiple times,
once after each action that generates
one or more targets in the list.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI AddPreAction( target ", " action )
.TP
.RI env.AddPreAction( target ", " action )
Arranges for the specified
.I action
to be performed
before the specified
.I target
is built.
The specified action(s) may be
an Action object, or anything that
can be converted into an Action object
(see below).

When multiple targets are specified,
the action(s) may be called multiple times,
once before each action that generates
one or more targets in the list.

Note that if any of the targets are built in multiple steps,
the action will be invoked just
before the "final" action that specifically
generates the specified target(s).
For example, when building an executable program
from a specified source
.B .c
file via an intermediate object file:

.ES
foo = Program('foo.c')
AddPreAction(foo, 'pre_action')
.EE

The specified
.B pre_action
would be executed before
.B scons
calls the link command that actually
generates the executable program binary
.BR foo ,
not before compiling the
.B foo.c
file into an object file.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Alias( alias ", [" targets ", [" action ]])
.TP
.RI env.Alias( alias ", [" targets ", [" action ]])
Creates one or more phony targets that
expand to one or more other targets.
An optional
.I action
(command)
or list of actions
can be specified that will be executed
whenever the any of the alias targets are out-of-date.
Returns the Node object representing the alias,
which exists outside of any file system.
This Node object, or the alias name,
may be used as a dependency of any other target,
including another alias.
.B Alias
can be called multiple times for the same
alias to add additional targets to the alias,
or additional actions to the list for this alias.

Examples:

.ES
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")
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI AllowSubstExceptions([ exception ", ...])"
Specifies the exceptions that will be allowed
when expanding construction variables.
By default,
any construction variable expansions that generate a
.B NameError
or
.BR IndexError
exception will expand to a
.B ''
(a null string) and not cause scons to fail.
All exceptions not in the specified list
will generate an error message
and terminate processing.

If
.B AllowSubstExceptions
is called multiple times,
each call completely overwrites the previous list
of allowed exceptions.

Example:

.ES
# Requires that all construction variable names exist.
# (You may wish to do this if you want to enforce strictly
# that all construction variables must be defined before use.)
AllowSubstExceptions()

# Also allow a string containing a zero-division expansion
# like '${1 / 0}' to evalute to ''.
AllowSubstExceptions(IndexError, NameError, ZeroDivisionError)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI AlwaysBuild( target ", ...)"
.TP
.RI env.AlwaysBuild( target ", ...)"
Marks each given
.I target
so that it is always assumed to be out of date,
and will always be rebuilt if needed.
Note, however, that
.BR 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
.I always
be built if so specified.
Multiple targets can be passed in to a single call to
.BR AlwaysBuild ().

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.Append( key = val ", [...])"
Appends the specified keyword arguments
to the end of construction variables in the environment.
If the Environment does not have
the specified construction variable,
it is simply added to the environment.
If the values of the construction variable
and the keyword argument are the same type,
then the two values will be simply added together.
Otherwise, the construction variable
and the value of the keyword argument
are both coerced to lists,
and the lists are added together.
(See also the Prepend method, below.)

Example:

.ES
env.Append(CCFLAGS = ' -g', FOO = ['foo.yyy'])
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.AppendENVPath( name ", " newpath ", [" envname ", " sep ", " delete_existing ])
This appends new path elements to the given path in the
specified external environment
.RB ( ENV
by default).
This will only add
any particular path once (leaving the last one it encounters and
ignoring the rest, to preserve path order),
and to help assure this,
will normalize all paths (using
.B os.path.normpath
and
.BR os.path.normcase ).
This can also handle the
case where the given old path variable is a list instead of a
string, in which case a list will be returned instead of a string.

If 
.I delete_existing
is 0, then adding a path that already exists
will not move it to the end; it will stay where it is in the list.

Example:

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

yields:
before: /foo:/biz
after: /biz:/foo/bar:/foo
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.AppendUnique( key = val ", [...], delete_existing=0)"
Appends the specified keyword arguments
to the end of construction variables in the environment.
If the Environment does not have
the specified construction variable,
it is simply added to the environment.
If the construction variable being appended to is a list,
then any value(s) that already exist in the
construction variable will
.I not
be added again to the list.
However, if delete_existing is 1, 
existing matching values are removed first, so
existing values in the arg list move to the end of the list.

Example:

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
env.BitKeeper()
A factory function that
returns a Builder object
to be used to fetch source files
using BitKeeper.
The returned Builder
is intended to be passed to the
.B SourceCode
function.

Example:

.ES
env.SourceCode('.', env.BitKeeper())
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI BuildDir( build_dir ", " src_dir ", [" duplicate ])
.TP
.RI env.BuildDir( build_dir ", " src_dir ", [" duplicate ])
Deprecated synonyms for
.BR VariantDir ()
and
.BR env.VariantDir ().
The
.I build_dir
argument becomes the
.I variant_dir
argument of
.BR VariantDir ()
or
.BR env.VariantDir ().

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Builder( action ", [" arguments ])
.TP
.RI env.Builder( action ", [" arguments ])
Creates a Builder object for
the specified
.IR action .
See the section "Builder Objects,"
below, for a complete explanation of the arguments and behavior.

Note that the
.BR env.Builder ()
form of the invocation will expand
construction variables in any arguments strings,
including the
.I action
argument,
at the time it is called
using the construction variables in the
.B env
construction environment through which
.BR env.Builder ()
was called.
The
.BR Builder ()
form delays all variable expansion
until after the Builder object is actually called.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI CacheDir( cache_dir )
.TP
.RI env.CacheDir( cache_dir )
Specifies that
.B scons
will maintain a cache of derived files in
.I cache_dir .
The derived files in the cache will be shared
among all the builds using the same
.BR CacheDir ()
call.
Specifying a
.I cache_dir
of
.B None
disables derived file caching.

Calling
.BR env.CacheDir ()
will only affect targets built
through the specified construction environment.
Calling
.BR CacheDir ()
sets a global default
that will be used by all targets built
through construction environments
that do
.I not
have an
.BR env.CacheDir ()
specified.

When a
.BR CacheDir ()
is being used and
.B scons
finds a derived file that needs to be rebuilt,
it will first look in the cache to see if a
derived file has already been built
from identical input files and an identical build action
(as incorporated into the MD5 build signature).
If so,
.B scons
will retrieve the file from the cache.
If the derived file is not present in the cache,
.B scons
will rebuild it and
then place a copy of the built file in the cache
(identified by its MD5 build signature),
so that it may be retrieved by other
builds that need to build the same derived file
from identical inputs.

Use of a specified
.BR CacheDir()
may be disabled for any invocation
by using the
.B --cache-disable
option.

If the
.B --cache-force
option is used,
.B scons
will place a copy of
.I all
derived files in the cache,
even if they already existed
and were not built by this invocation.
This is useful to populate a cache
the first time
.BR CacheDir ()
is added to a build,
or after using the
.B --cache-disable
option.

When using
.BR CacheDir (),
.B scons
will report,
"Retrieved `file' from cache,"
unless the
.B --cache-show
option is being used.
When the
.B --cache-show
option is used,
.B scons
will print the action that
.I would
have been used to build the file,
without any indication that
the file was actually retrieved from the cache.
This is useful to generate build logs
that are equivalent regardless of whether
a given derived file has been built in-place
or retrieved from the cache.

The
.BR 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.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Clean( targets ", " files_or_dirs )
.TP
.RI env.Clean( targets ", " files_or_dirs )
This specifies a list of files or directories which should be removed
whenever the targets are specified with the
.B -c
command line option.
The specified targets may be a list
or an individual target.
Multiple calls to
.BR Clean ()
are legal,
and create new targets or add files and directories to the
clean list for the specified targets.

Multiple files or directories should be specified
either as separate arguments to the
.BR Clean ()
method, or as a list.
.BR Clean ()
will also accept the return value of any of the construction environment
Builder methods.
Examples:

The related
.BR NoClean ()
function overrides calling
.BR Clean ()
for the same target,
and any targets passed to both functions will
.I not
be removed by the
.B -c
option.

Examples:

.ES
Clean('foo', ['bar', 'baz'])
Clean('dist', env.Program('hello', 'hello.c'))
Clean(['foo', 'bar'], 'something_else_to_clean')
.EE

In this example,
installing the project creates a subdirectory for the documentation.
This statement causes the subdirectory to be removed
if the project is deinstalled.
.ES
Clean(docdir, os.path.join(docdir, projectname))
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Command( target ", " source ", " action ", [" key = val ", ...])"
.TP
.RI env.Command( target ", " source ", " action ", [" key = val ", ...])"
Executes a specific action
(or list of actions)
to build a target file or files.
This is more convenient
than defining a separate Builder object
for a single special-case build.

As a special case, the
.B source_scanner
keyword argument can
be used to specify
a Scanner object
that will be used to scan the sources.
(The global
.B DirScanner
object can be used
if any of the sources will be directories
that must be scanned on-disk for
changes to files that aren't
already specified in other Builder of function calls.)

Any other keyword arguments specified override any
same-named existing construction variables.

An action can be an external command,
specified as a string,
or a callable Python object;
see "Action Objects," below,
for more complete information.
Also note that a string specifying an external command
may be preceded by an
.B @
(at-sign)
to suppress printing the command in question,
or by a
.B \-
(hyphen)
to ignore the exit status of the external command.

Examples:

.ES
env.Command('foo.out', 'foo.in',
            "$FOO_BUILD < $SOURCES > $TARGET")

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

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

env.Command('baz.out', 'baz.in',
            ["$BAZ_BUILD < $SOURCES > .tmp",
	     rename ])
.EE

.IP
Note that the
.BR Command ()
function will usually assume, by default,
that the specified targets and/or sources are Files,
if no other part of the configuration
identifies what type of entry it is.
If necessary, you can explicitly specify
that targets or source nodes should
be treated as directoriese
by using the
.BR Dir ()
or
.BR env.Dir ()
functions.

Examples:

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

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

.IP
(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.)

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Configure( env ", [" custom_tests ", " conf_dir ", " log_file ", " config_h ])
.TP
.RI env.Configure([ custom_tests ", " conf_dir ", " log_file ", " config_h ])
Creates a Configure object for integrated
functionality similar to GNU autoconf.
See the section "Configure Contexts,"
below, for a complete explanation of the arguments and behavior.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.Clone([ key = val ", ...])"
Return a separate copy of a construction environment.
If there are any keyword arguments specified,
they are added to the returned copy,
overwriting any existing values
for the keywords.

Example:

.ES
env2 = env.Clone()
env3 = env.Clone(CCFLAGS = '-g')
.EE
.IP
Additionally, a list of tools and a toolpath may be specified, as in
the Environment constructor:

.ES
def MyTool(env): env['FOO'] = 'bar'
env4 = env.Clone(tools = ['msvc', MyTool])
.EE

The
.I parse_flags
keyword argument is also recognized:

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.Copy([ key = val ", ...])"
A now-deprecated synonym for
.BR env.Clone() .

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.CVS( repository ", " module )
A factory function that
returns a Builder object
to be used to fetch source files
from the specified
CVS
.IR repository .
The returned Builder
is intended to be passed to the
.B SourceCode
function.

The optional specified
.I module
will be added to the beginning
of all repository path names;
this can be used, in essence,
to strip initial directory names
from the repository path names,
so that you only have to
replicate part of the repository
directory hierarchy in your
local build directory.

Examples:

.ES
# Will fetch foo/bar/src.c
# from /usr/local/CVSROOT/foo/bar/src.c.
env.SourceCode('.', env.CVS('/usr/local/CVSROOT'))

# Will fetch bar/src.c
# from /usr/local/CVSROOT/foo/bar/src.c.
env.SourceCode('.', env.CVS('/usr/local/CVSROOT', 'foo'))

# Will fetch src.c
# from /usr/local/CVSROOT/foo/bar/src.c.
env.SourceCode('.', env.CVS('/usr/local/CVSROOT', 'foo/bar'))
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Decider( function )
.TP
.RI env.Decider( function )
Specifies that all up-to-date decisions for
targets built through this construction environment
will be handled by the specified
.IR function .
The
.I function
can be one of the following strings
that specify the type of decision function
to be performed:

.RS 10
.HP 6
.B timestamp-newer
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
.B make
can be used a synonym for
.BR timestamp-newer .

.HP 6
.B timestamp-match
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
.I earlier
timestamp, such as can happen when restoring files from backup archives.

.HP 6
.B MD5
Specifies that a target shall be considered out of date and rebuilt
if the dependency's content has changed sine the last time
the target was built,
as determined be performing an MD5 checksum
on the dependency's contents
and comparing it to the checksum recorded the
last time the target was built.
.B content
can be used as a synonym for
.BR MD5 .

.HP 6
.B MD5-timestamp
Specifies that a target shall be considered out of date and rebuilt
if the dependency's content has changed sine 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
.I not
rebuilt.
This provides behavior very similar
to the
.B MD5
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
.I not
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.
.RE

.IP
Examples:

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

# Use MD5 content signatures for any targets built
# with the attached construction environment.
env.Decider('content')
.EE

.IP
In addition to the above already-available functions,
the
.I function
argument may be an actual Python function
that takes the following three arguments:

.RS 10
.IP dependency
The Node (file) which
should cause the
.I target
to be rebuilt
if it has "changed" since the last tme
.I target was built.

.IP target
The Node (file) being built.
In the normal case,
this is what should get rebuilt
if the
.I dependency
has "changed."

.IP prev_ni
Stored information about the state of the
.I dependency
the last time the
.I target
was built.
This can be consulted to match various
file characteristics
such as the timestamp,
size, or content signature.
.RE

.IP
The
.I function
should return a
.B True
(non-zero)
value if the
.I dependency
has "changed" since the last time
the
.I target
was built
(indicating that the target
.I should
be rebuilt),
and
.B False
(zero)
otherwise
(indicating that the target should
.I not
be rebuilt).
Note that the decision can be made
using whatever criteria are appopriate.
Ignoring some or all of the function arguments
is perfectly normal.

Example:

.ES
def my_decider(dependency, target, prev_ni):
    return not os.path.exists(str(target))

env.Decider(my_decider)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Default( targets )
.TP
.RI env.Default( targets )
This specifies a list of default targets,
which will be built by
.B scons
if no explicit targets are given on the command line.
Multiple calls to
.BR Default ()
are legal,
and add to the list of default targets.

Multiple targets should be specified as
separate arguments to the
.BR Default ()
method, or as a list.
.BR Default ()
will also accept the Node returned by any
of a construction environment's
builder methods.

Examples:

.ES
Default('foo', 'bar', 'baz')
env.Default(['a', 'b', 'c'])
hello = env.Program('hello', 'hello.c')
env.Default(hello)
.EE
.IP
An argument to
.BR Default ()
of
.B None
will clear all default targets.
Later calls to
.BR Default ()
will add to the (now empty) default-target list
like normal.

The current list of targets added using the
.BR Default ()
function or method is available in the
.B DEFAULT_TARGETS
list;
see below.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI DefaultEnvironment([ args ])
Creates and returns a default construction environment object.
This construction environment is used internally by SCons
in order to execute many of the global functions in this list,
and to fetch source files transparently
from source code management systems.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Depends( target ", " dependency )
.TP
.RI env.Depends( target ", " dependency )
Specifies an explicit dependency;
the
.I target
will be rebuilt
whenever the
.I dependency
has changed.
Both the specified
.I target
and
.I dependency
can be a string
(usually the path name of a file or directory)
or Node objects,
or a list of strings or Node objects
(such as returned by a Builder call).
This should only be necessary
for cases where the dependency
is not caught by a Scanner
for the file.

Example:

.ES
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)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.Dictionary([ vars ])
Returns a dictionary object
containing copies of all of the
construction variables in the environment.
If there are any variable names specified,
only the specified construction
variables are returned in the dictionary.

Example:

.ES
dict = env.Dictionary()
cc_dict = env.Dictionary('CC', 'CCFLAGS', 'CCCOM')
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Dir( name ", [" directory ])
.TP
.RI env.Dir( name ", [" directory ])
This returns a Directory Node,
an object that represents the specified directory
.IR name .
.I name
can be a relative or absolute path.
.I directory
is an optional directory that will be used as the parent directory.
If no
.I directory
is specified, the current script's directory is used as the parent.

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

Directory Nodes can be used anywhere you
would supply a string as a directory name
to a Builder method or function.
Directory Nodes have attributes and methods
that are useful in many situations;
see "File and Directory Nodes," below.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.Dump([ key ])
Returns a pretty printable representation of the environment.
.IR key ,
if not
.IR None ,
should be a string containing the name of the variable of interest.

This SConstruct:
.ES
env=Environment()
print env.Dump('CCCOM')
.EE
.IP
will print:
.ES
\&'$CC -c -o $TARGET $CCFLAGS $CPPFLAGS $_CPPDEFFLAGS $_CPPINCFLAGS $SOURCES'
.EE

.ES
env=Environment()
print env.Dump()
.EE
.IP
will print:
.ES
{ 'AR': 'ar',
  'ARCOM': '$AR $ARFLAGS $TARGET $SOURCES\n$RANLIB $RANLIBFLAGS $TARGET',
  'ARFLAGS': ['r'],
  'AS': 'as',
  'ASCOM': '$AS $ASFLAGS -o $TARGET $SOURCES',
  'ASFLAGS': [],
  ...
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI EnsurePythonVersion( major ", " minor )
.TP
.RI env.EnsurePythonVersion( major ", " minor )
Ensure that the Python version is at least
.IR major . minor .
This function will
print out an error message and exit SCons with a non-zero exit code if the
actual Python version is not late enough.

Example:

.ES
EnsurePythonVersion(2,2)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI EnsureSConsVersion( major ", " minor ", [" revision ])
.TP
.RI env.EnsureSConsVersion( major ", " minor ", [" revision ])
Ensure that the SCons version is at least
.IR major.minor ,
or
.IR major.minor.revision .
if
.I revision
is specified.
This function will
print out an error message and exit SCons with a non-zero exit code if the
actual SCons version is not late enough.

Examples:

.ES
EnsureSConsVersion(0,14)

EnsureSConsVersion(0,96,90)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Environment([ key = value ", ...])"
.TP
.RI env.Environment([ key = value ", ...])"
Return a new construction environment
initialized with the specified
.IR key = value
pairs.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Execute( action ", [" strfunction ", " varlist ])
.TP
.RI env.Execute( action ", [" strfunction ", " varlist ])
Executes an Action object.
The specified
.IR action
may be an Action object
(see the section "Action Objects,"
below, for a complete explanation of the arguments and behavior),
or it may be a command-line string,
list of commands,
or executable Python function,
each of which will be converted
into an Action object
and then executed.
The exit value of the command
or return value of the Python function
will be returned.

Note that
.B scons
will print an error message if the executed
.I action
fails--that is,
exits with or returns a non-zero value.
.B scons
will
.I not ,
however,
automatically terminate the build
if the specified
.I action
fails.
If you want the build to stop in response to a failed
.BR Execute ()
call,
you must explicitly check for a non-zero return value:

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

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Exit([ value ])
.TP
.RI env.Exit([ value ])
This tells
.B scons
to exit immediately
with the specified
.IR value .
A default exit value of
.B 0
(zero)
is used if no value is specified.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Export( vars )
.TP
.RI env.Export( vars )
This tells
.B scons
to export a list of variables from the current
SConscript file to all other SConscript files.
The exported variables are kept in a global collection,
so subsequent calls to
.BR Export ()
will over-write previous exports that have the same name.
Multiple variable names can be passed to
.BR Export ()
as separate arguments or as a list.
Keyword arguments can be used to provide names and their values.
A dictionary can be used to map variables to a different name when exported.
Both local variables and global variables can be exported.

Examples:

.ES
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})
.EE

.IP
Note that the
.BR SConscript ()
function supports an
.I exports
argument that makes it easier to to export a variable or
set of variables to a single SConscript file.
See the description of the
.BR SConscript ()
function, below.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI File( name ", [" directory ])
.TP
.RI env.File( name ", [" directory ])
This returns a
File Node,
an object that represents the specified file
.IR name .
.I name
can be a relative or absolute path.
.I directory
is an optional directory that will be used as the parent directory.

If
.I name
is a list, SCons returns a list of File nodes.
Construction variables are expanded in
.IR name .

File Nodes can be used anywhere you
would supply a string as a file name
to a Builder method or function.
File Nodes have attributes and methods
that are useful in many situations;
see "File and Directory Nodes," below.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI FindFile( file ", " dirs )
.TP
.RI env.FindFile( file ", " dirs )
Search for
.I file
in the path specified by
.IR dirs .
.I dirs
may be a list of directory names or a single directory name.
In addition to searching for files that exist in the filesytem,
this function also searches for derived files
that have not yet been built.

Example:

.ES
foo = env.FindFile('foo', ['dir1', 'dir2'])
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI FindInstalledFiles( )
.TP
.RI env.FindInstalledFiles( )
Returns the list of targets set up by the
.B Install()
or
.B InstallAs()
builders.

This function serves as a convenient method to select the contents of
a binary package.

Example:

.ES
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()
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI FindSourceFiles( node = '"."' )
.TP
.RI env.FindSourceFiles( node = '"."' )

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
.B node
which defaults to the '"."'-node. It will then return all leaves of
.B node.
These are all children which have no further children.

This function is a convenient method to select the contents of a Source
Package.

Example:

.ES
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' )
.EE

.IP
As you can see build support files (SConstruct in the above example)
will also be returned by this function.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI FindPathDirs( variable )
Returns a function
(actually a callable Python object)
intended to be used as the
.B path_function
of a Scanner object.
The returned object will look up the specified
.I variable
in a construction environment
and treat the construction variable's value as a list of
directory paths that should be searched
(like
.BR CPPPATH ,
.BR LIBPATH ,
etc.).

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

Example:

.ES
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'))
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Flatten( sequence )
.TP
.RI env.Flatten( sequence )
Takes a sequence (that is, a Python list or tuple)
that may contain nested sequences
and returns a flattened list containing
all of the individual elements in any sequence.
This can be helpful for collecting
the lists returned by calls to Builders;
other Builders will automatically
flatten lists specified as input,
but direct Python manipulation of
these lists does not.

Examples:

.ES
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)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI GetBuildFailures()
Returns a list of exceptions for the
actions that failed while
attempting to build targets.
Each element in the returned list is a
.B BuildError
object
with the following attributes
that record various aspects
of the build failure:

.B .node
The node that was being built
when the build failure occurred.

.B .status
The numeric exit status
returned by the command or Python function
that failed when trying to build the
specified Node.

.B .errstr
The SCons error string
describing the build failure.
(This is often a generic
message like "Error 2"
to indicate that an executed
command exited with a status of 2.)

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

.B .executor
The SCons Executor object
for the target Node
being built.
This can be used to retrieve
the construction environment used
for the failed action.

.B .action
The actual SCons Action object that failed.
This will be one specific action
out of the possible list of
actions that would have been
executed to build the target.

.B .command
The actual expanded command that was executed and failed,
after expansion of
.BR $TARGET ,
.BR $SOURCE ,
and other construction variables.

Note that the
.BR GetBuildFailures ()
function
will always return an empty list
until any build failure has occurred,
which means that
.BR GetBuildFailures ()
will always return an empty list
while the
.B 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
.BR atexit.register ()
function.
Example:

.ES
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)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI GetBuildPath( file ", [" ... ])
.TP
.RI env.GetBuildPath( file ", [" ... ])
Returns the
.B scons
path name (or names) for the specified
.I file
(or files).
The specified
.I file
or files
may be
.B scons
Nodes or strings representing path names.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI GetLaunchDir()
.TP
.RI env.GetLaunchDir()
Returns the absolute path name of the directory from which
.B scons
was initially invoked.
This can be useful when using the
.BR \-u ,
.BR \-U
or
.BR \-D
options, which internally
change to the directory in which the
.B SConstruct
file is found.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI GetOption( name )
.TP
.RI env.GetOption( name )
This function provides a way to query the value of
SCons options set on scons command line
(or set using the
.IR SetOption ()
function).
The options supported are:

.RS 10
.TP 6
.B cache_debug
which corresponds to --cache-debug;
.TP 6
.B cache_disable
which corresponds to --cache-disable;
.TP 6
.B cache_force
which corresponds to --cache-force;
.TP 6
.B cache_show
which corresponds to --cache-show;
.TP 6
.B clean
which corresponds to -c, --clean and --remove;
.TP 6
.B config
which corresponds to --config;
.TP 6
.B directory
which corresponds to -C and --directory;
.TP 6
.B diskcheck
which corresponds to --diskcheck
.TP 6
.B duplicate
which corresponds to --duplicate;
.TP 6
.B file
which corresponds to -f, --file, --makefile and --sconstruct;
.TP 6
.B help
which corresponds to -h and --help;
.TP 6
.B ignore_errors
which corresponds to --ignore-errors;
.TP 6
.B implicit_cache
which corresponds to --implicit-cache;
.TP 6
.B implicit_deps_changed
which corresponds to --implicit-deps-changed;
.TP 6
.B implicit_deps_unchanged
which corresponds to --implicit-deps-unchanged;
.TP 6
.B interactive
which corresponds to --interact and --interactive;
.TP 6
.B keep_going
which corresponds to -k and --keep-going;
.TP 6
.B max_drift
which corresponds to --max-drift;
.TP 6
.B no_exec
which corresponds to -n, --no-exec, --just-print, --dry-run and --recon;
.TP 6
.B no_site_dir
which corresponds to --no-site-dir;
.TP 6
.B num_jobs
which corresponds to -j and --jobs;
.TP 6
.B profile_file
which corresponds to --profile;
.TP 6
.B question
which corresponds to -q and --question;
.TP 6
.B random
which corresponds to --random;
.TP 6
.B repository
which corresponds to -Y, --repository and --srcdir;
.TP 6
.B silent
which corresponds to -s, --silent and --quiet;
.TP 6
.B site_dir
which corresponds to --site-dir;
.TP 6
.B stack_size
which corresponds to --stack-size;
.TP 6
.B taskmastertrace_file
which corresponds to --taskmastertrace; and
.TP 6
.B warn
which corresponds to --warn and --warning.
.RE

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Glob( pattern ", [" ondisk ", " source ", " strings ])
.TP
.RI env.Glob( pattern ", [" ondisk ", " source ", " strings ])
Returns Nodes (or strings) that match the specified
.IR pattern ,
relative to the directory of the current
.B SConscript
file.
The
.BR env.Glob ()
form performs string substition on
.I pattern
and returns whatever matches
the resulting expanded pattern.

The specified
.I pattern
uses Unix shell style metacharacters for matching:

.ES
  *       matches everything
  ?       matches any single character
  [seq]   matches any character in seq
  [!seq]  matches any char not in seq
.EE

.IP
If the first character of a filename is a dot,
it must be matched explicitly.
Character matches do
.I not
span directory separators.

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

The
.B ondisk
argument may be set to
.B False
(or any other non-true value)
to disable the search for matches on disk,
thereby only returning matches among
already-configured File or Dir Nodes.
The default behavior is to
return corresponding Nodes
for any on-disk matches found.

The
.B source
argument may be set to
.B True
(or any equivalent value)
to specify that,
when the local directory is a
.BR VariantDir (),
the returned Nodes should be from the
corresponding source directory,
not the local directory.

The
.B strings
argument may be set to
.B True
(or any equivalent value)
to have the
.BR Glob ()
function return strings, not Nodes,
that represent the matched files or directories.
The returned strings will be relative to
the local (SConscript) directory.
(Note that This may make it easier to perform
arbitrary manipulation of file names,
but if the returned strings are
passed to a different
.B SConscript
file,
any Node translation will be relative
to the other
.B SConscript
directory,
not the original
.B SConscript
directory.)

Examples:

.ES
Program('foo', Glob('*.c'))
Zip('/tmp/everything', Glob('.??*') + Glob('*'))
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
'\".TP
'\".RI GlobalBuilders( flag )
'\"When
'\".B flag
'\"is non-zero,
'\"adds the names of the default builders
'\"(Program, Library, etc.)
'\"to the global name space
'\"so they can be called without an explicit construction environment.
'\"(This is the default.)
'\"When
'\".B
'\"flag is zero,
'\"the names of the default builders are removed
'\"from the global name space
'\"so that an explicit construction environment is required
'\"to call all builders.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Help( text )
.TP
.RI env.Help( text )
This specifies help text to be printed if the
.B -h
argument is given to
.BR scons .
If
.BR Help
is called multiple times, the text is appended together in the order
that
.BR Help
is called.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Ignore( target ", " dependency )
.TP
.RI env.Ignore( target ", " dependency )
The specified dependency file(s)
will be ignored when deciding if
the target file(s) need to be rebuilt.

You can also use
.BR Ignore()
to remove a target from the default build.
In order to do this you must specify the directory the target will
be built in as the target, and the file you want to skip building
as the dependency.

Note that this will only remove the dependencies listed from 
the files built by default.  It will still be built if that 
dependency is needed by another object being built. 
See the third and forth examples below.

Examples:

.ES
env.Ignore('foo', 'foo.c')
env.Ignore('bar', ['bar1.h', 'bar2.h'])
env.Ignore('.','foobar.obj')
env.Ignore('bar','bar/foobar.obj')
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Import( vars )
.TP
.RI env.Import( vars )
This tells
.B scons
to import a list of variables into the current SConscript file. This
will import variables that were exported with
.BR Export ()
or in the
.I exports
argument to
.BR SConscript ().
Variables exported by
.BR SConscript ()
have precedence.
Multiple variable names can be passed to
.BR Import ()
as separate arguments or as a list. The variable "*" can be used
to import all variables.

Examples:

.ES
Import("env")
Import("env", "variable")
Import(["env", "variable"])
Import("*")
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Literal( string )
.TP
.RI env.Literal( string )
The specified
.I string
will be preserved as-is
and not have construction variables expanded.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Local( targets )
.TP
.RI env.Local( targets )
The specified
.I targets
will have copies made in the local tree,
even if an already up-to-date copy
exists in a repository.
Returns a list of the target Node or Nodes.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
\" .TP
\" .RI env.MergeShellPaths( arg ", [" prepend ])
\" Merges the elements of the specified
\" .IR arg ,
\" which must be a dictionary, to the construction
\" environment's copy of the shell environment
\" in env['ENV'].
\" (This is the environment which is passed
\" to subshells spawned by SCons.)
\" Note that
\" .I arg
\" must be a single value,
\" so multiple strings must
\" be passed in as a list,
\" not as separate arguments to
\" .BR env.MergeShellPaths ().

\" New values are prepended to the environment variable by default,
\" unless prepend=0 is specified.  
\" Duplicate values are always eliminated, 
\" since this function calls
\" .B AppendENVPath
\" or
\" .B PrependENVPath
\" depending on the
\" .I prepend
\" argument.  See those functions for more details.

\" Examples:

\" .ES
\" # Prepend a path to the shell PATH.
\" env.MergeShellPaths({'PATH':'/usr/local/bin'} )
\" # Append two dirs to the shell INCLUDE.
\" env.MergeShellPaths({'INCLUDE':['c:/inc1', 'c:/inc2']}, prepend=0 )

.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.MergeFlags( arg ", [" unique ])
Merges the specified
.I arg
values to the construction environment's construction variables.
If the
.I arg
argument is not a dictionary,
it is converted to one by calling
.B env.ParseFlags()
on the argument
before the values are merged.
Note that
.I arg
must be a single value,
so multiple strings must
be passed in as a list,
not as separate arguments to
.BR env.MergeFlags ().

By default,
duplicate values are eliminated;
you can, however, specify
.B unique=0
to allow duplicate
values to be added.
When eliminating duplicate values,
any construction variables that end with
the string
.B PATH
keep the left-most unique value.
All other construction variables keep
the right-most unique value.

Examples:

.ES
# Add an optimization flag to $CCFLAGS.
env.MergeFlags('-O3')

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

# Combine an optimization flag with the flags returned from running pkg-config
# twice and merge the result into the construction variables.
env.MergeFlags(['-O3',
               '!pkg-config gtk+-2.0 --cflags --libs',
               '!pkg-config libpng12 --cflags --libs'])
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI NoCache( target ", ...)"
.TP
.RI env.NoCache( target ", ...)"
Specifies a list of files which should
.I not
be cached whenever the
.BR CacheDir ()
method has been activated.
The specified targets may be a list
or an individual target.

Multiple files should be specified
either as separate arguments to the
.BR NoCache ()
method, or as a list.
.BR NoCache ()
will also accept the return value of any of the construction environment
Builder methods.

Calling
.BR NoCache ()
on directories and other non-File Node types has no effect because
only File Nodes are cached.

Examples:

.ES
NoCache('foo.elf')
NoCache(env.Program('hello', 'hello.c'))
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI NoClean( target ", ...)"
.TP
.RI env.NoClean( target ", ...)"
Specifies a list of files or directories which should
.I not
be removed whenever the targets (or their dependencies)
are specified with the
.B -c
command line option.
The specified targets may be a list
or an individual target.
Multiple calls to
.BR NoClean ()
are legal,
and prevent each specified target
from being removed by calls to the
.B -c
option.

Multiple files or directories should be specified
either as separate arguments to the
.BR NoClean ()
method, or as a list.
.BR NoClean ()
will also accept the return value of any of the construction environment
Builder methods.

Calling
.BR NoClean ()
for a target overrides calling
.BR Clean ()
for the same target,
and any targets passed to both functions will
.I not
be removed by the
.B -c
option.

Examples:

.ES
NoClean('foo.elf')
NoClean(env.Program('hello', 'hello.c'))
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.ParseConfig( command ", [" function ", " unique ])
Calls the specified
.I function
to modify the environment as specified by the output of
.I command .
The default
.I function
is
.BR env.MergeFlags (),
which expects the output of a typical
.I *-config command
(for example,
.BR gtk-config )
and adds the options
to the appropriate construction variables.
By default,
duplicate values are not
added to any construction variables;
you can specify
.B unique=0
to allow duplicate
values to be added.

Interpreted options
and the construction variables they affect
are as specified for the
.BR env.ParseFlags ()
method (which this method calls).
See that method's description, below,
for a table of options and construction variables.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI ParseDepends( filename ", [" must_exist ", " only_one ])
.TP
.RI env.ParseDepends( filename ", [" must_exist ", " only_one ])
Parses the contents of the specified
.I filename
as a list of dependencies in the style of
.BR Make
or
.BR mkdep ,
and explicitly establishes all of the listed dependencies.

By default,
it is not an error
if the specified
.I filename
does not exist.
The optional
.I must_exist
argument may be set to a non-zero
value to have
scons
throw an exception and
generate an error if the file does not exist,
or is otherwise inaccessible.

The optional
.I only_one
argument may be set to a non-zero
value to have
scons
thrown an exception and
generate an error
if the file contains dependency
information for more than one target.
This can provide a small sanity check
for files intended to be generated
by, for example, the
.B gcc -M
flag,
which should typically only
write dependency information for
one output file into a corresponding
.B .d
file.

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.ParseFlags( flags ", ...)"
Parses one or more strings containing
typical command-line flags for GCC tool chains
and returns a dictionary with the flag values
separated into the appropriate SCons construction variables.
This is intended as a companion to the
.BR env.MergeFlags ()
method, but allows for the values in the returned dictionary
to be modified, if necessary,
before merging them into the construction environment.
(Note that
.BR env.MergeFlags ()
will call this method if its argument is not a dictionary,
so it is usually not necessary to call
.BR env.ParseFlags ()
directly unless you want to manipulate the values.)

If the first character in any string is
an exclamation mark (!),
the rest of the string is executed as a command,
and the output from the command is
parsed as GCC tool chain command-line flags
and added to the resulting dictionary.

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

.ES
-arch               CCFLAGS, LINKFLAGS
-D                  CPPDEFINES
-framework          FRAMEWORKS
-frameworkdir=      FRAMEWORKPATH
-include            CCFLAGS
-isysroot           CCFLAGS, LINKFLAGS
-I                  CPPPATH
-l                  LIBS
-L                  LIBPATH
-mno-cygwin         CCFLAGS, LINKFLAGS
-mwindows           LINKFLAGS
-pthread            CCFLAGS, LINKFLAGS
-std=               CFLAGS
-Wa,                ASFLAGS, CCFLAGS
-Wl,-rpath=         RPATH
-Wl,-R,             RPATH
-Wl,-R              RPATH
-Wl,                LINKFLAGS
-Wp,                CPPFLAGS
-                   CCFLAGS
+                   CCFLAGS, LINKFLAGS
.EE

.IP
Any other strings not associated with options
are assumed to be the names of libraries
and added to the
.B LIBS
construction variable.

Examples (all of which produce the same result):

.ES
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')
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
env.Perforce()
A factory function that
returns a Builder object
to be used to fetch source files
from the Perforce source code management system.
The returned Builder
is intended to be passed to the
.B SourceCode
function.

Example:

.ES
env.SourceCode('.', env.Perforce())
.EE
.IP
Perforce uses a number of external
environment variables for its operation.
Consequently, this function adds the
following variables from the user's external environment
to the construction environment's
ENV dictionary:
P4CHARSET,
P4CLIENT,
P4LANGUAGE,
P4PASSWD,
P4PORT,
P4USER,
SystemRoot,
USER,
and
USERNAME.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Platform( string )
Returns a callable object
that can be used to initialize
a construction environment using the
platform keyword of the Environment() method.

Example:

.ES
env = Environment(platform = Platform('win32'))
.EE
.TP
.RI env.Platform( string )
Applies the callable object for the specified platform
.I string
to the environment through which the method was called.

.ES
env.Platform('posix')
.EE
.IP
Note that the
.B win32
platform adds the
.B SystemDrive
and
.B SystemRoot
variables from the user's external environment
to the construction environment's
.B ENV
dictionary.
This is so that any executed commands
that use sockets to connect with other systems
(such as fetching source files from
external CVS repository specifications like
.BR :pserver:anonymous@cvs.sourceforge.net:/cvsroot/scons )
will work on Windows systems.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Progress( callable ", [" interval ])
.TP
.RI Progress( string ", [" interval ", " file ", " overwrite ])
.TP
.RI Progress( list_of_strings ", [" interval ", " file ", " overwrite ])
Allows SCons to show progress made during the build
by displaying a string or calling a function while
evaluating Nodes (e.g. files).

If the first specified argument is a Python callable
(a function or an object that has a
.BR __call__ ()
method),
the function will be called
once every
.I interval
times a Node is evaluated.
The callable will be passed the evaluated Node
as its only argument.
(For future compatibility,
it's a good idea to also add
.B *args
and
.B **kw
as arguments to your function or method.
This will prevent the code from breaking
if SCons ever changes the interface
to call the function with additional arguments in the future.)

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

.ES
def my_progress_function(node, *args, **kw):
    print 'Evaluating node %s!' % node
Progress(my_progress_function, interval=10)
.EE
.IP
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
.B \\\\r
(a carriage return)
at the end so that the string
will overwrite itself on a display:

.ES
import sys
class ProgressCounter:
    count = 0
    def __call__(self, node, *args, **kw):
        self.count += 100
        sys.stderr.write('Evaluated %s nodes\\r' % self.count)
Progress(ProgressCounter(), interval=100)
.EE
.IP
If the first argument
.BR Progress ()
is a string,
the string will be displayed
every
.I interval
evaluated Nodes.
The default is to print the string on standard output;
an alternate output stream
may be specified with the
.B file=
argument.
The following will print a series of dots
on the error output,
one dot for every 100 evaluated Nodes:

.ES
import sys
Progress('.', interval=100, file=sys.stderr)
.EE
.IP
If the string contains the verbatim substring
.B $TARGET,
it will be replaced with the Node.
Note that, for performance reasons, this is
.I not
a regular SCons variable substition,
so you can not use other variables
or use curly braces.
The following example will print the name of
every evaluated Node,
using a
.B \\\\r
(carriage return) to cause each line to overwritten by the next line,
and the
.B overwrite=
keyword argument to make sure the previously-printed
file name is overwritten with blank spaces:

.ES
import sys
Progress('$TARGET\\r', overwrite=True)
.EE
.IP
If the first argument to
.BR Progress ()
is a list of strings,
then each string in the list will be displayed
in rotating fashion every
.I interval
evaluated Nodes.
This can be used to implement a "spinner"
on the user's screen as follows:

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Precious( target ", ...)"
.TP
.RI env.Precious( target ", ...)"
Marks each given
.I target
as precious so it is not deleted before it is rebuilt. Normally
.B scons
deletes a target before building it.
Multiple targets can be passed in to a single call to
.BR Precious ().

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.Prepend( key = val ", [...])"
Appends the specified keyword arguments
to the beginning of construction variables in the environment.
If the Environment does not have
the specified construction variable,
it is simply added to the environment.
If the values of the construction variable
and the keyword argument are the same type,
then the two values will be simply added together.
Otherwise, the construction variable
and the value of the keyword argument
are both coerced to lists,
and the lists are added together.
(See also the Append method, above.)

Example:

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.PrependENVPath( name ", " newpath ", [" envname ", " sep ", " delete_existing ])
This appends new path elements to the given path in the
specified external environment
.RB ( ENV
by default).
This will only add
any particular path once (leaving the first one it encounters and
ignoring the rest, to preserve path order),
and to help assure this,
will normalize all paths (using
.B os.path.normpath
and
.BR os.path.normcase ).
This can also handle the
case where the given old path variable is a list instead of a
string, in which case a list will be returned instead of a string.

If
.I delete_existing
is 0, then adding a path that already exists
will not move it to the beginning;
it will stay where it is in the list.

Example:

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

The above exmaple will print:

.ES
before: /biz:/foo
after: /foo/bar:/foo:/biz
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.PrependUnique( key = val ", delete_existing=0, [...])"
Appends the specified keyword arguments
to the beginning of construction variables in the environment.
If the Environment does not have
the specified construction variable,
it is simply added to the environment.
If the construction variable being appended to is a list,
then any value(s) that already exist in the
construction variable will
.I not
be added again to the list.
However, if delete_existing is 1, 
existing matching values are removed first, so
existing values in the arg list move to the front of the list.

Example:

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
env.RCS()
A factory function that
returns a Builder object
to be used to fetch source files
from RCS.
The returned Builder
is intended to be passed to the
.B SourceCode
function:

Examples:

.ES
env.SourceCode('.', env.RCS())
.EE
.IP
Note that
.B scons
will fetch source files
from RCS subdirectories automatically,
so configuring RCS
as demonstrated in the above example
should only be necessary if
you are fetching from
RCS,v
files in the same
directory as the source files,
or if you need to explicitly specify RCS
for a specific subdirectory.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.Replace( key = val ", [...])"
Replaces construction variables in the Environment
with the specified keyword arguments.

Example:

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Repository( directory )
.TP
.RI env.Repository( directory )
Specifies that
.I directory
is a repository to be searched for files.
Multiple calls to
.BR Repository ()
are legal,
and each one adds to the list of
repositories that will be searched.

To
.BR scons ,
a repository is a copy of the source tree,
from the top-level directory on down,
which may contain
both source files and derived files
that can be used to build targets in
the local source tree.
The canonical example would be an
official source tree maintained by an integrator.
If the repository contains derived files,
then the derived files should have been built using
.BR scons ,
so that the repository contains the necessary
signature information to allow
.B scons
to figure out when it is appropriate to
use the repository copy of a derived file,
instead of building one locally.

Note that if an up-to-date derived file
already exists in a repository,
.B scons
will
.I not
make a copy in the local directory tree.
In order to guarantee that a local copy
will be made,
use the
.B Local()
method.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Requires( target ", " prerequisite )
.TP
.RI env.Requires( target ", " prerequisite )
Specifies an order-only relationship
between the specified target file(s)
and the specified prerequisite file(s).
The prerequisite file(s)
will be (re)built, if necessary,
.I before
the target file(s),
but the target file(s) do not actually
depend on the prerequisites
and will not be rebuilt simply because
the prerequisite file(s) change.

Example:

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Return([ vars "... , " stop= ])
By default,
this stops processing the current SConscript
file and returns to the calling SConscript file
the values of the variables named in the
.I vars
string arguments.
Multiple strings contaning variable names may be passed to
.BR Return ().
Any strings that contain white space

The optional
.B stop=
keyword argument may be set to a false value
to continue processing the rest of the SConscript
file after the
.BR 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
.I vars
at the point
.BR Return ()
is called.

Examples:

.ES
# Returns without returning a value.
Return()

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

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

# Returns the values of Python variables 'val1' and 'val2'.
Return('val1 val2')
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Scanner( function ", [" argument ", " keys ", " path_function ", " node_class ", " node_factory ", " scan_check ", " recursive ])
.TP
.RI env.Scanner( function ", [" argument ", " keys ", " path_function ", " node_class ", " node_factory ", " scan_check ", " recursive ])
Creates a Scanner object for
the specified
.IR function .
See the section "Scanner Objects,"
below, for a complete explanation of the arguments and behavior.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
env.SCCS()
A factory function that
returns a Builder object
to be used to fetch source files
from SCCS.
The returned Builder
is intended to be passed to the
.B SourceCode
function.

Example:

.ES
env.SourceCode('.', env.SCCS())
.EE
.IP
Note that
.B scons
will fetch source files
from SCCS subdirectories automatically,
so configuring SCCS
as demonstrated in the above example
should only be necessary if
you are fetching from
.I s.SCCS
files in the same
directory as the source files,
or if you need to explicitly specify SCCS
for a specific subdirectory.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI SConscript( scripts ", [" exports ", " variant_dir ", " duplicate ])
'\" .RI SConscript( scripts ", [" exports ", " variant_dir ", " src_dir ", " duplicate ])
.TP
.RI env.SConscript( scripts ", [" exports ", " variant_dir ", " duplicate ])
'\" .RI env.SConscript( scripts ", [" exports ", " variant_dir ", " src_dir ", " duplicate ])
.TP
.RI SConscript(dirs= subdirs ", [name=" script ", " exports ", " variant_dir ", " duplicate ])
'\" .RI SConscript(dirs= subdirs ", [name=" script ", " exports ", " variant_dir ", " src_dir ", " duplicate ])
.TP
.RI env.SConscript(dirs= subdirs ", [name=" script ", " exports ", " variant_dir ", " duplicate ])
'\" .RI env.SConscript(dirs= subdirs ", [name=" script ", " exports ", " variant_dir ", " src_dir ", " duplicate ])
This tells
.B scons
to execute
one or more subsidiary SConscript (configuration) files.
Any variables returned by a called script using
.BR Return ()
will be returned by the call to
.BR SConscript ().
There are two ways to call the
.BR SConscript ()
function.

The first way you can call
.BR SConscript ()
is to explicitly specify one or more
.I scripts
as the first argument.
A single script may be specified as a string;
multiple scripts must be specified as a list
(either explicitly or as created by
a function like
.BR Split ()).
Examples:
.ES
SConscript('SConscript')      # run SConscript in the current directory
SConscript('src/SConscript')  # run SConscript in the src directory
SConscript(['src/SConscript', 'doc/SConscript'])
config = SConscript('MyConfig.py')
.EE

The second way you can call
.BR SConscript ()
is to specify a list of (sub)directory names
as a
.RI dirs= subdirs
keyword argument.
In this case,
.B scons
will, by default,
execute a subsidiary configuration file named
.B SConscript
in each of the specified directories.
You may specify a name other than
.B SConscript
by supplying an optional
.RI name= script
keyword argument.
The first three examples below have the same effect
as the first three examples above:
.ES
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')
.EE

The optional
.I exports
argument provides a list of variable names or a dictionary of
named values to export to the
.IR script(s) .
These variables are locally exported only to the specified
.IR script(s) ,
and do not affect the global pool of variables used by the
.BR Export ()
function.
'\"If multiple dirs are provided, each script gets a fresh export.
The subsidiary
.I script(s)
must use the
.BR Import ()
function to import the variables.
Examples:
.ES
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')
.EE

If the optional
.I variant_dir
argument is present, it causes an effect equivalent to the
.BR VariantDir ()
method described below.
(If
.I variant_dir
is not present, the
'\" .IR src_dir and
.I duplicate
'\" arguments are ignored.)
argument is ignored.)
The
.I variant_dir
'\" and
'\" .I src_dir
'\" arguments are interpreted relative to the directory of the calling
argument is interpreted relative to the directory of the calling
.B SConscript
file.
See the description of the
.BR VariantDir ()
function below for additional details and restrictions.

If
.I variant_dir
is present,
'\" but
'\" .IR src_dir " is not,"
the source directory is the directory in which the
.B SConscript
file resides and the
.B SConscript
file is evaluated as if it were in the
.I variant_dir
directory:
.ES
SConscript('src/SConscript', variant_dir = 'build')
.EE
is equivalent to
.ES
VariantDir('build', 'src')
SConscript('build/SConscript')
.EE
This later paradigm is often used when the sources are
in the same directory as the
.BR SConstruct:
.ES
SConscript('SConscript', variant_dir = 'build')
.EE
is equivalent to
.ES
VariantDir('build', '.')
SConscript('build/SConscript')
.EE

'\" If
'\" .IR variant_dir " and"
'\" .IR src_dir " are both present,"
'\" xxxxx everything is in a state of confusion.
'\" .ES
'\" 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.
'\" .EE
'\" is equivalent to
'\" .ES
'\" ????????????????
'\" .EE
'\" and what about this alternative?
'\"TODO??? SConscript('build/SConscript', src_dir='src')

Here are some composite examples:

.ES
# 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')
.EE

.ES
# 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)
.EE

.ES
# 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)
.EE

.ES
# 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)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI SConscriptChdir( value )
.TP
.RI env.SConscriptChdir( value )
By default,
.B scons
changes its working directory
to the directory in which each
subsidiary SConscript file lives.
This behavior may be disabled
by specifying either:

.ES
SConscriptChdir(0)
env.SConscriptChdir(0)
.EE
.IP
in which case
.B scons
will stay in the top-level directory
while reading all SConscript files.
(This may be necessary when building from repositories,
when all the directories in which SConscript files may be found
don't necessarily exist locally.)
You may enable and disable
this ability by calling
SConscriptChdir()
multiple times.

Example:

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

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

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

The optional
.I dbm_module
argument can be used to specify
which Python database module
The default is to use a custom
.B SCons.dblite
module that uses pickled
Python data structures,
and which works on all Python versions from 1.5.2 on.

Examples:

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

# Stores signatures in the file "etc/scons-signatures"
# relative to the top-level SConstruct directory.
SConsignFile("etc/scons-signatures")

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

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.SetDefault(key = val ", [...])"
Sets construction variables to default values specified with the keyword
arguments if (and only if) the variables are not already set.
The following statements are equivalent:

.ES
env.SetDefault(FOO = 'foo')

if not env.has_key('FOO'): env['FOO'] = 'foo'
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI SetOption( name ", " value )
.TP
.RI env.SetOption( name ", " value )
This function provides a way to set a select subset of the scons command
line options from a SConscript file. The options supported are:

.RS 10
.TP 6
.B clean
which corresponds to -c, --clean and --remove;
.TP 6
.B duplicate
which corresponds to --duplicate;
.TP 6
.B help
which corresponds to -h and --help;
.TP 6
.B implicit_cache
which corresponds to --implicit-cache;
.TP 6
.B max_drift
which corresponds to --max-drift;
.TP 6
.B no_exec
which corresponds to -n, --no-exec, --just-print, --dry-run and --recon;
.TP 6
.B num_jobs
which corresponds to -j and --jobs;
.TP 6
.B random
which corresponds to --random; and
.TP 6
.B stack_size
which corresponds to --stack-size.
.RE

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

Example:

.ES
SetOption('max_drift', 1)
.EE

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

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI SourceCode( entries ", " builder )
.TP
.RI env.SourceCode( entries ", " builder )
Arrange for non-existent source files to
be fetched from a source code management system
using the specified
.IR builder .
The specified
.I entries
may be a Node, string or list of both,
and may represent either individual
source files or directories in which
source files can be found.

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

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

.ES
env.SourceCode('.', None)
.EE

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

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

.ES
env.SourceCode('.', env.BitKeeper('/usr/local/BKsources'))
env.SourceCode('src', env.CVS('/usr/local/CVSROOT'))
env.SourceCode('/', env.RCS())
env.SourceCode(['f1.c', 'f2.c'], env.SCCS())
env.SourceCode('no_source.c', None)
.EE
'\"env.SourceCode('.', env.Subversion('file:///usr/local/Subversion'))

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI env.subst( input ", [" raw ", " target ", " source ", " conv ])
Performs construction variable interpolation
on the specified string or sequence argument
.IR input .

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

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

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

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

Example:

.ES
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)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
'\".TP
'\".RI Subversion( repository ", " module )
'\"A factory function that
'\"returns a Builder object
'\"to be used to fetch source files
'\"from the specified Subversion
'\".IR repository .
'\"The returned Builder
'\"is intended to be passed to the
'\".B SourceCode
'\"function.
'\"
'\"The optional specified
'\".I module
'\"will be added to the beginning
'\"of all repository path names;
'\"this can be used, in essence,
'\"to strip initial directory names
'\"from the repository path names,
'\"so that you only have to
'\"replicate part of the repository
'\"directory hierarchy in your
'\"local build directory.
'\"
'\"Example:
'\"
'\".ES
'\"# Will fetch foo/bar/src.c
'\"# from /usr/local/Subversion/foo/bar/src.c.
'\"env.SourceCode('.', env.Subversion('file:///usr/local/Subversion'))
'\"
'\"# Will fetch bar/src.c
'\"# from /usr/local/Subversion/foo/bar/src.c.
'\"env.SourceCode('.', env.Subversion('file:///usr/local/Subversion', 'foo'))
'\"
'\"# Will fetch src.c
'\"# from /usr/local/Subversion/foo/bar/src.c.
'\"env.SourceCode('.', env.Subversion('file:///usr/local/Subversion', 'foo/bar'))
'\".EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI SourceSignatures( type )
.TP
.RI env.SourceSignatures( type )
Note:  Although it is not yet officially deprecated,
use of this function is discouraged.
See the
.BR Decider ()
function for a more flexible and straightforward way
to configure SCons' decision-making.

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

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

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

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

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

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

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

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

Example:

.ES
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
""")
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Tag( node ", " tags )
Annotates file or directory Nodes with
information about how the
.BR Package ()
Builder should package those files or directories.
All tags are optional.

Examples:

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

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI TargetSignatures( type )
.TP
.RI env.TargetSignatures( type )
Note:  Although it is not yet officially deprecated,
use of this function is discouraged.
See the
.BR Decider ()
function for a more flexible and straightforward way
to configure SCons' decision-making.

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

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

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

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

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

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

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

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

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI Tool( string [, toolpath ", " **kw ])
Returns a callable object
that can be used to initialize
a construction environment using the
tools keyword of the Environment() method.
The object may be called with a construction
environment as an argument,
in which case the object will
add the necessary variables
to the construction environment
and the name of the tool will be added to the
.B $TOOLS
construction variable.

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

Examples:

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

env = Environment()
t = Tool('msvc')
t(env)  # adds 'msvc' to the TOOLS variable
u = Tool('opengl', toolpath = ['tools'])
u(env)  # adds 'opengl' to the TOOLS variable
.EE
.TP
.RI env.Tool( string [, toolpath ", " **kw ])
Applies the callable object for the specified tool
.I string
to the environment through which the method was called.

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

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

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

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

Examples:

.ES
env = Environment()

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

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

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

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

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

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

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

.BR VariantDir ()
can be called multiple times with the same
.I  src_dir
to set up multiple builds with different options
.RI ( variants ).
The
.I src_dir
location must be in or underneath the SConstruct file's directory, and
.I variant_dir
may not be underneath
.IR src_dir .
'\"TODO: Can the above restrictions be clarified or relaxed?
'\"TODO: The latter restriction is clearly not completely right;
'\"TODO: src_dir = '.' works fine with a build dir under it.

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

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

Duplicating the source tree may be disabled by setting the
.I duplicate
argument to 0 (zero).
This will cause
.B scons
to invoke Builders using the path names of source files in
.I src_dir
and the path names of derived files within
.IR variant_dir .
This is always more efficient than
.IR duplicate =1,
and is usually safe for most builds
(but see above for cases that may cause problems).

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

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

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

Examples:

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

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

.ES
# 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)
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
.RI WhereIs( program ", [" path  ", " pathext ", " reject ])
.TP
.RI env.WhereIs( program ", [" path  ", " pathext ", " reject ])

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

.SS SConscript Variables
In addition to the global functions and methods,
.B scons
supports a number of Python variables
that can be used in SConscript files
to affect how you want the build to be performed.
These variables may be accessed from custom Python modules that you
import into an SConscript file by adding the following
to the Python module:

.ES
from SCons.Script import *
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
ARGLIST
A list
.IR keyword = value
arguments specified on the command line.
Each element in the list is a tuple
containing the
.RI ( keyword , value )
of the argument.
The separate
.I keyword
and
.I value
elements of the tuple
can be accessed by
subscripting for element
.B [0]
and
.B [1]
of the tuple, respectively.

Example:

.ES
print "first keyword, value =", ARGLIST[0][0], ARGLIST[0][1]
print "second keyword, value =", ARGLIST[1][0], ARGLIST[1][1]
third_tuple = ARGLIST[2]
print "third keyword, value =", third_tuple[0], third_tuple[1]
for key, value in ARGLIST:
    # process key and value
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
ARGUMENTS
A dictionary of all the
.IR keyword = value
arguments specified on the command line.
The dictionary is not in order,
and if a given keyword has
more than one value assigned to it
on the command line,
the last (right-most) value is
the one in the
.B ARGUMENTS
dictionary.

Example:

.ES
if ARGUMENTS.get('debug', 0):
    env = Environment(CCFLAGS = '-g')
else:
    env = Environment()
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
BUILD_TARGETS
A list of the targets which
.B scons
will actually try to build,
regardless of whether they were specified on
the command line or via the
.BR Default ()
function or method.
The elements of this list may be strings
.I or
nodes, so you should run the list through the Python
.B str
function to make sure any Node path names
are converted to strings.

Because this list may be taken from the
list of targets specified using the
.BR Default ()
function or method,
the contents of the list may change
on each successive call to
.BR Default ().
See the
.B DEFAULT_TARGETS
list, below,
for additional information.

Example:

.ES
if 'foo' in BUILD_TARGETS:
    print "Don't forget to test the `foo' program!"
if 'special/program' in BUILD_TARGETS:
    SConscript('special')
.EE
.IP
Note that the
.B BUILD_TARGETS
list only contains targets expected listed
on the command line or via calls to the
.BR Default ()
function or method.
It does
.I not
contain all dependent targets that will be built as
a result of making the sure the explicitly-specified
targets are up to date.

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
COMMAND_LINE_TARGETS
A list of the targets explicitly specified on
the command line.
If there are no targets specified on the command line,
the list is empty.
This can be used, for example,
to take specific actions only
when a certain target or targets
is explicitly being built.

Example:

.ES
if 'foo' in COMMAND_LINE_TARGETS:
    print "Don't forget to test the `foo' program!"
if 'special/program' in COMMAND_LINE_TARGETS:
    SConscript('special')
.EE

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.TP
DEFAULT_TARGETS
A list of the target
.I nodes
that have been specified using the
.BR Default ()
function or method.
The elements of the list are nodes,
so you need to run them through the Python
.B str
function to get at the path name for each Node.

Example:

.ES
print str(DEFAULT_TARGETS[0])
if 'foo' in map(str, DEFAULT_TARGETS):
    print "Don't forget to test the `foo' program!"
.EE
.IP
The contents of the
.B DEFAULT_TARGETS
list change on on each successive call to the
.BR Default ()
function:

.ES
print map(str, DEFAULT_TARGETS)   # originally []
Default('foo')
print map(str, DEFAULT_TARGETS)   # now a node ['foo']
Default('bar')
print map(str, DEFAULT_TARGETS)   # now a node ['foo', 'bar']
Default(None)
print map(str, DEFAULT_TARGETS)   # back to []
.EE
.IP
Consequently, be sure to use
.B DEFAULT_TARGETS
only after you've made all of your
.BR Default ()
calls,
or else simply be careful of the order
of these statements in your SConscript files
so that you don't look for a specific
default target before it's actually been added to the list.

.SS Construction Variables
.\" XXX From Gary Ruben, 23 April 2002:
.\" I think it would be good to have an example with each construction
.\" variable description in the documentation.
.\" eg.
.\" CC     The C compiler
.\"    Example: env["CC"] = "c68x"
.\"    Default: env["CC"] = "cc"
.\"
.\" CCCOM  The command line ...
.\"    Example:
.\"        To generate the compiler line c68x -ps -qq -mr -o $TARGET $SOURCES
.\"        env["CC"] = "c68x"
.\"        env["CFLAGS"] = "-ps -qq -mr"
.\"        env["CCCOM"] = "$CC $CFLAGS -o $TARGET $SOURCES
.\"    Default:
.\"        (I dunno what this is ;-)
A construction environment has an associated dictionary of
.I construction variables
that are used by built-in or user-supplied build rules.
Construction variables must follow the same rules for
Python identifiers:
the initial character must be an underscore or letter,
followed by any number of underscores, letters, or digits.

A number of useful construction variables are automatically defined by
scons for each supported platform, and additional construction variables
can be defined by the user. The following is a list of the automatically
defined construction variables:

'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
'\" BEGIN GENERATED CONSTRUCTION VARIABLE DESCRIPTIONS
'\"
'\" The descriptions below of the various SCons construction variables
'\" are generated from the .xml files that live next to the various
'\" Python modules in the build enginer library.  If you're reading
'\" this [gnt]roff file with an eye towards patching this man page,
'\" you can still submit a diff against this text, but it will have to
'\" be translated to a diff against the underlying .xml file before the
'\" patch is actually accepted.  If you do that yourself, it will make
'\" it easier to integrate the patch.
'\"
'\" BEGIN GENERATED CONSTRUCTION VARIABLE DESCRIPTIONS
'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
.so variables.man
'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""
'\" END GENERATED CONSTRUCTION VARIABLE DESCRIPTIONS
'\"
'\" The descriptions above of the various SCons construction variables
'\" are generated from the .xml files that live next to the various
'\" Python modules in the build enginer library.  If you're reading
'\" this [gnt]roff file with an eye towards patching this man page,
'\" you can still submit a diff against this text, but it will have to
'\" be translated to a diff against the underlying .xml file before the
'\" patch is actually accepted.  If you do that yourself, it will make
'\" it easier to integrate the patch.
'\"
'\" END GENERATED CONSTRUCTION VARIABLE DESCRIPTIONS
'\"""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""""

.LP
Construction variables can be retrieved and set using the
.B Dictionary
method of the construction environment:

.ES
dict = env.Dictionary()
dict["CC"] = "cc"
.EE

or using the [] operator:

.ES
env["CC"] = "cc"
.EE

Construction variables can also be passed to the construction environment
constructor:

.ES
env = Environment(CC="cc")
.EE

or when copying a construction environment using the
.B Clone
method:

.ES
env2 = env.Clone(CC="cl.exe")
.EE

.SS Configure Contexts

.B scons
supports
.I configure contexts,
an integrated mechanism similar to the
various AC_CHECK macros in GNU autoconf
for testing for the existence of C header
files, libraries, etc.
In contrast to autoconf,
.B scons
does not maintain an explicit cache of the tested values,
but uses its normal dependency tracking to keep the checked values
up to date. However, users may override this behaviour with the
.B --config
command line option.

The following methods can be used to perform checks:

.TP
.RI Configure( env ", [" custom_tests ", " conf_dir ", " log_file ", " config_h ", " clean ", " help])
.TP
.RI env.Configure([ custom_tests ", " conf_dir ", " log_file ", " config_h ", " clean ", " help])
This creates a configure context, which can be used to perform checks.
.I env
specifies the environment for building the tests.
This environment may be modified when performing checks.
.I custom_tests
is a dictionary containing custom tests.
See also the section about custom tests below.
By default, no custom tests are added to the configure context.
.I conf_dir
specifies a directory where the test cases are built.
Note that this directory is not used for building
normal targets.
The default value is the directory
#/.sconf_temp.
.I log_file
specifies a file which collects the output from commands
that are executed to check for the existence of header files, libraries, etc.
The default is the file #/config.log.
If you are using the
.BR VariantDir ()
method,
you may want to specify a subdirectory under your variant directory.
.I config_h
specifies a C header file where the results of tests
will be written, e.g. #define HAVE_STDIO_H, #define HAVE_LIBM, etc.
The default is to not write a
.B config.h
file.
You can specify the same
.B config.h
file in multiple calls to Configure,
in which case
.B scons
will concatenate all results in the specified file.
Note that SCons
uses its normal dependency checking
to decide if it's necessary to rebuild
the specified
.I config_h
file.
This means that the file is not necessarily re-built each
time scons is run,
but is only rebuilt if its contents will have changed
and some target that depends on the
.I config_h
file is being built.

The optional
.B clean
and
.B help
arguments can be used to suppress execution of the configuration
tests when the
.B -c/--clean
or
.B -H/-h/--help
options are used, respectively.
The default behavior is always to execute
configure context tests,
since the results of the tests may
affect the list of targets to be cleaned
or the help text.
If the configure tests do not affect these,
then you may add the
.B clean=False
or
.B help=False
arguments
(or both)
to avoid unnecessary test execution.

.EE
A created
.B Configure
instance has the following associated methods:

.TP
.RI SConf.Finish( context )
.TP
.IR sconf .Finish()
This method should be called after configuration is done.
It returns the environment as modified
by the configuration checks performed.
After this method is called, no further checks can be performed
with this configuration context.
However, you can create a new
.RI Configure
context to perform additional checks.
Only one context should be active at a time.

The following Checks are predefined.
(This list will likely grow larger as time
goes by and developers contribute new useful tests.)

.TP
.RI SConf.CheckHeader( context ", " header ", [" include_quotes ", " language ])
.TP
.IR sconf .CheckHeader( header ", [" include_quotes ", " language ])
Checks if
.I header
is usable in the specified language.
.I header
may be a list,
in which case the last item in the list
is the header file to be checked,
and the previous list items are
header files whose
.B #include
lines should precede the
header line being checked for.
The optional argument
.I include_quotes
must be
a two character string, where the first character denotes the opening
quote and the second character denotes the closing quote.
By default, both characters  are " (double quote).
The optional argument
.I language
should be either
.B C
or
.B C++
and selects the compiler to be used for the check.
Returns 1 on success and 0 on failure.

.TP
.RI SConf.CheckCHeader( context ", " header ", [" include_quotes ])
.TP
.IR sconf .CheckCHeader( header ", [" include_quotes ])
This is a wrapper around
.B SConf.CheckHeader
which checks if
.I header
is usable in the C language.
.I header
may be a list,
in which case the last item in the list
is the header file to be checked,
and the previous list items are
header files whose
.B #include
lines should precede the
header line being checked for.
The optional argument
.I include_quotes
must be
a two character string, where the first character denotes the opening
quote and the second character denotes the closing quote (both default
to \N'34').
Returns 1 on success and 0 on failure.

.TP
.RI SConf.CheckCXXHeader( context ", " header ", [" include_quotes ])
.TP
.IR sconf .CheckCXXHeader( header ", [" include_quotes ])
This is a wrapper around
.B SConf.CheckHeader
which checks if
.I header
is usable in the C++ language.
.I header
may be a list,
in which case the last item in the list
is the header file to be checked,
and the previous list items are
header files whose
.B #include
lines should precede the
header line being checked for.
The optional argument
.I include_quotes
must be
a two character string, where the first character denotes the opening
quote and the second character denotes the closing quote (both default
to \N'34').
Returns 1 on success and 0 on failure.

.TP
.RI SConf.CheckFunc( context, ", " function_name ", [" header ", " language ])
.TP
.IR sconf .CheckFunc( function_name ", [" header ", " language ])
Checks if the specified
C or C++ function is available.
.I function_name
is the name of the function to check for.
The optional
.I header
argument is a string
that will be
placed at the top
of the test file
that will be compiled
to check if the function exists;
the default is:
.ES
#ifdef __cplusplus
extern "C"
#endif
char function_name();
.EE
The optional
.I language
argument should be
.B C
or
.B C++
and selects the compiler to be used for the check;
the default is "C".

.TP
.RI SConf.CheckLib( context ", [" library ", " symbol ", " header ", " language ", " autoadd=1 ])
.TP
.IR sconf .CheckLib([ library ", " symbol ", " header ", " language ", " autoadd=1 ])
Checks if
.I library
provides
.IR symbol .
If the value of
.I autoadd
is 1 and the library provides the specified
.IR symbol ,
appends the library to the LIBS construction environment variable.
.I library
may also be None (the default),
in which case
.I symbol
is checked with the current LIBS variable,
or a list of library names,
in which case each library in the list
will be checked for
.IR symbol .
If
.I symbol
is not set or is
.BR None ,
then
.BR SConf.CheckLib ()
just checks if
you can link against the specified
.IR library .
The optional
.I language
argument should be
.B C
or
.B C++
and selects the compiler to be used for the check;
the default is "C".
The default value for
.I autoadd
is 1.
This method returns 1 on success and 0 on error.

.TP
.RI SConf.CheckLibWithHeader( context ", " library ", " header ", " language ", [" call ", " autoadd ])
.TP
.IR sconf .CheckLibWithHeader( library ", " header ", " language ", [" call ", " autoadd ])

In contrast to the
.RI SConf.CheckLib
call, this call provides a more sophisticated way to check against libraries.
Again,
.I library
specifies the library or a list of libraries to check.
.I header
specifies a header to check for.
.I header
may be a list,
in which case the last item in the list
is the header file to be checked,
and the previous list items are
header files whose
.B #include
lines should precede the
header line being checked for.
.I language
may be one of 'C','c','CXX','cxx','C++' and 'c++'.
.I call
can be any valid expression (with a trailing ';').
If
.I call
is not set,
the default simply checks that you
can link against the specified
.IR library .
.I autoadd
specifies whether to add the library to the environment (only if the check
succeeds). This method returns 1 on success and 0 on error.

.TP
.RI SConf.CheckType( context ", " type_name ", [" includes ", " language ])
.TP
.IR sconf .CheckType( type_name ", [" includes ", " language ])
Checks for the existence of a type defined by
.BR typedef .
.I type_name
specifies the typedef name to check for.
.I includes
is a string containing one or more
.B #include
lines that will be inserted into the program
that will be run to test for the existence of the type.
The optional
.I language
argument should be
.B C
or
.B C++
and selects the compiler to be used for the check;
the default is "C".
Example:
.ES
sconf.CheckType('foo_type', '#include "my_types.h"', 'C++')
.EE

.TP
.RI Configure.CheckCC( self )
Checks whether the C compiler (as defined by the CC construction variable) works
by trying to compile a small source file.

By default, SCons only detects if there is a program with the correct name, not
if it is a functioning compiler.

This uses the exact same command than the one used by the object builder for C
source file, so it can be used to detect if a particular compiler flag works or
not.

.TP
.RI Configure.CheckCXX( self )
Checks whether the C++ compiler (as defined by the CXX construction variable)
works by trying to compile a small source file. By default, SCons only detects
if there is a program with the correct name, not if it is a functioning compiler.

This uses the exact same command than the one used by the object builder for
CXX source files, so it can be used to detect if a particular compiler flag
works or not.

.TP
.RI Configure.CheckSHCC( self )
Checks whether the C compiler (as defined by the SHCC construction variable) works
by trying to compile a small source file. By default, SCons only detects if
there is a program with the correct name, not if it is a functioning compiler.

This uses the exact same command than the one used by the object builder for C
source file, so it can be used to detect if a particular compiler flag works or
not. This does not check whether the object code can be used to build a shared
library, only that the compilation (not link) succeeds.

.TP
.RI Configure.CheckSHCXX( self )
Checks whether the C++ compiler (as defined by the SHCXX construction variable)
works by trying to compile a small source file. By default, SCons only detects
if there is a program with the correct name, not if it is a functioning compiler.

This uses the exact same command than the one used by the object builder for
CXX source files, so it can be used to detect if a particular compiler flag
works or not. This does not check whether the object code can be used to build
a shared library, only that the compilation (not link) succeeds.

.EE
Example of a typical Configure usage:

.ES
env = Environment()
conf = Configure( env )
if not conf.CheckCHeader( 'math.h' ):
    print 'We really need math.h!'
    Exit(1)
if conf.CheckLibWithHeader( 'qt', 'qapp.h', 'c++',
        'QApplication qapp(0,0);' ):
    # do stuff for qt - usage, e.g.
    conf.env.Append( CPPFLAGS = '-DWITH_QT' )
env = conf.Finish()
.EE

.TP
.RI SConf.CheckTypeSize( context ", " type_name ", [" header ", " language ", " expect ])
.TP
.IR sconf .CheckTypeSize( type_name ", [" header ", " language ", " expect ])
Checks for the size of a type defined by
.BR typedef .
.I type_name
specifies the typedef name to check for.
The optional
.I header
argument is a string
that will be
placed at the top
of the test file
that will be compiled
to check if the function exists;
the default is empty.
The optional
.I language
argument should be
.B C
or
.B C++
and selects the compiler to be used for the check;
the default is "C".
The optional
.I expect
argument should be an integer.
If this argument is used,
the function will only check whether the type
given in type_name has the expected size (in bytes).
For example,
.B "CheckTypeSize('short', expect = 2)"
will return success only if short is two bytes.

.ES
.EE

.TP
.RI SConf.CheckDeclaration( context ", " symbol ", [" includes ", " language ])
.TP
.IR sconf .CheckDeclaration( symbol ", [" includes ", " language ])
Checks if the specified
.I symbol
is declared.
.I includes
is a string containing one or more
.B #include
lines that will be inserted into the program
that will be run to test for the existence of the type.
The optional
.I language
argument should be
.B C
or
.B C++
and selects the compiler to be used for the check;
the default is "C".

.TP
.RI SConf.Define( context ", " symbol ", [" value ", " comment ])
.TP
.IR sconf .Define( symbol ", [" value ", " comment ])
This function does not check for anything, but defines a
preprocessor symbol that will be added to the configuration header file.
It is the equivalent of AC_DEFINE,
and defines the symbol
.I name
with the optional
.B value
and the optional comment
.BR comment .

.IP
Examples:

.ES
env = Environment()
conf = Configure( env )

# Puts the following line in the config header file:
#    #define A_SYMBOL
conf.Define('A_SYMBOL')

# Puts the following line in the config header file:
#    #define A_SYMBOL 1
conf.Define('A_SYMBOL', 1)
.EE

.IP
Be careful about quoting string values, though:

.ES
env = Environment()
conf = Configure( env )

# Puts the following line in the config header file:
#    #define A_SYMBOL YA
conf.Define('A_SYMBOL', "YA")

# Puts the following line in the config header file:
#    #define A_SYMBOL "YA"
conf.Define('A_SYMBOL', '"YA"')
.EE

.IP
For comment:

.ES
env = Environment()
conf = Configure( env )

# Puts the following lines in the config header file:
#    /* Set to 1 if you have a symbol */
#    #define A_SYMBOL 1
conf.Define('A_SYMBOL', 1, 'Set to 1 if you have a symbol')
.EE

.EE
You can define your own custom checks.
in addition to the predefined checks.
These are passed in a dictionary to the Configure function.
This dictionary maps the names of the checks
to user defined Python callables
(either Python functions or class instances implementing the
.I __call__
method).
The first argument of the call is always a
.I CheckContext
instance followed by the arguments,
which must be supplied by the user of the check.
These CheckContext instances define the following methods:

.TP
.RI CheckContext.Message( self ", " text )

Usually called before the check is started.
.I text
will be displayed to the user, e.g. 'Checking for library X...'

.TP
.RI CheckContext.Result( self, ", " res )

Usually called after the check is done.
.I res
can be either an integer or a string. In the former case, 'yes' (res != 0)
or 'no' (res == 0) is displayed to the user, in the latter case the
given string is displayed.

.TP
.RI CheckContext.TryCompile( self ", " text ", " extension )
Checks if a file with the specified
.I extension
(e.g. '.c') containing
.I text
can be compiled using the environment's
.B Object
builder. Returns 1 on success and 0 on failure.

.TP
.RI CheckContext.TryLink( self ", " text ", " extension )
Checks, if a file with the specified
.I extension
(e.g. '.c') containing
.I text
can be compiled using the environment's
.B Program
builder. Returns 1 on success and 0 on failure.

.TP
.RI CheckContext.TryRun( self ", " text ", " extension )
Checks, if a file with the specified
.I extension
(e.g. '.c') containing
.I text
can be compiled using the environment's
.B Program
builder. On success, the program is run. If the program
executes successfully
(that is, its return status is 0),
a tuple
.I (1, outputStr)
is returned, where
.I outputStr
is the standard output of the
program.
If the program fails execution
(its return status is non-zero),
then (0, '') is returned.

.TP
.RI CheckContext.TryAction( self ", " action ", [" text ", " extension ])
Checks if the specified
.I action
with an optional source file (contents
.I text
, extension
.I extension
= ''
) can be executed.
.I action
may be anything which can be converted to a
.B scons
.RI Action.
On success,
.I (1, outputStr)
is returned, where
.I outputStr
is the content of the target file.
On failure
.I (0, '')
is returned.

.TP
.RI CheckContext.TryBuild( self ", " builder ", [" text ", " extension ])
Low level implementation for testing specific builds;
the methods above are based on this method.
Given the Builder instance
.I builder
and the optional
.I text
of a source file with optional
.IR extension ,
this method returns 1 on success and 0 on failure. In addition,
.I self.lastTarget
is set to the build target node, if the build was successful.

.EE
Example for implementing and using custom tests:

.ES
def CheckQt(context, qtdir):
    context.Message( 'Checking for qt ...' )
    lastLIBS = context.env['LIBS']
    lastLIBPATH = context.env['LIBPATH']
    lastCPPPATH= context.env['CPPPATH']
    context.env.Append(LIBS = 'qt', LIBPATH = qtdir + '/lib', CPPPATH = qtdir + '/include' )
    ret = context.TryLink("""
#include <qapp.h>
int main(int argc, char **argv) {
  QApplication qapp(argc, argv);
  return 0;
}
""")
    if not ret:
        context.env.Replace(LIBS = lastLIBS, LIBPATH=lastLIBPATH, CPPPATH=lastCPPPATH)
    context.Result( ret )
    return ret

env = Environment()
conf = Configure( env, custom_tests = { 'CheckQt' : CheckQt } )
if not conf.CheckQt('/usr/lib/qt'):
    print 'We really need qt!'
    Exit(1)
env = conf.Finish()
.EE

.SS Command-Line Construction Variables

Often when building software,
some variables must be specified at build time.
For example, libraries needed for the build may be in non-standard
locations, or site-specific compiler options may need to be passed to the
compiler.
.B scons
provides a
.B Variables
object to support overriding construction variables
on the command line:
.ES
$ scons VARIABLE=foo
.EE
The variable values can also be specified in a text-based SConscript file.
To create a Variables object, call the Variables() function:

.TP
.RI Variables([ files "], [" args ])
This creates a Variables object that will read construction variables from
the file or list of filenames specified in
.IR files .
If no files are specified,
or the
.I files
argument is
.BR None ,
then no files will be read.
The optional argument
.I args
is a dictionary of
values that will override anything read from the specified files;
it is primarily intended to be passed the
.B ARGUMENTS
dictionary that holds variables
specified on the command line.
Example:

.ES
vars = Variables('custom.py')
vars = Variables('overrides.py', ARGUMENTS)
vars = Variables(None, {FOO:'expansion', BAR:7})
.EE

Variables objects have the following methods:

.TP
.RI Add( key ", [" help ", " default ", " validator ", " converter ])
This adds a customizable construction variable to the Variables object.
.I key
is the name of the variable.
.I help
is the help text for the variable.
.I default
is the default value of the variable;
if the default value is
.B None
and there is no explicit value specified,
the construction variable will
.I not
be added to the construction environment.
.I validator
is called to validate the value of the variable, and should take three
arguments: key, value, and environment.
The recommended way to handle an invalid value is
to raise an exception (see example below).
.I converter
is called to convert the value before putting it in the environment, and
should take either a value, or the value and environment, as parameters.
The
.I converter
must return a value,
which will be converted into a string
before being validated by the
.I validator
(if any)
and then added to the environment.

Examples:

.ES
vars.Add('CC', 'The C compiler')

def validate_color(key, val, env):
    if not val in ['red', 'blue', 'yellow']:
        raise "Invalid color value '%s'" % val
vars.Add('COLOR', validator=valid_color)
.EE

.TP
.RI AddVariables( list )
A wrapper script that adds
multiple customizable construction variables
to a Variables object.
.I list
is a list of tuple or list objects
that contain the arguments
for an individual call to the
.B Add
method.

.ES
opt.AddVariables(
       ('debug', '', 0),
       ('CC', 'The C compiler'),
       ('VALIDATE', 'An option for testing validation',
        'notset', validator, None),
    )
.EE

.TP
.RI Update( env ", [" args ])
This updates a construction environment
.I env
with the customized construction variables.
Any specified variables that are
.I not
configured for the Variables object
will be saved and may be
retrieved with the
.BR UnknownVariables ()
method, below.

Normally this method is not called directly,
but is called indirectly by passing the Variables object to
the Environment() function:

.ES
env = Environment(variables=vars)
.EE

.IP
The text file(s) that were specified
when the Variables object was created
are executed as Python scripts,
and the values of (global) Python variables set in the file
are added to the construction environment.

Example:

.ES
CC = 'my_cc'
.EE

.TP
.RI UnknownVariables( )
Returns a dictionary containing any
variables that were specified
either in the files or the dictionary
with which the Variables object was initialized,
but for which the Variables object was
not configured.

.ES
env = Environment(variables=vars)
for key, value in vars.UnknownVariables():
    print "unknown variable:  %s=%s" % (key, value)
.EE

.TP
.RI Save( filename ", " env )
This saves the currently set variables into a script file named
.I filename
that can be used on the next invocation to automatically load the current
settings.  This method combined with the Variables method can be used to
support caching of variables between runs.

.ES
env = Environment()
vars = Variables(['variables.cache', 'custom.py'])
vars.Add(...)
vars.Update(env)
vars.Save('variables.cache', env)
.EE

.TP
.RI GenerateHelpText( env ", [" sort ])
This generates help text documenting the customizable construction
variables suitable to passing in to the Help() function.
.I env
is the construction environment that will be used to get the actual values
of customizable variables. Calling with
an optional
.I sort
function
will cause the output to be sorted
by the specified argument.
The specific
.I sort
function
should take two arguments
and return
-1, 0 or 1
(like the standard Python
.I cmp
function).

.ES
Help(vars.GenerateHelpText(env))
Help(vars.GenerateHelpText(env, sort=cmp))
.EE

.TP
.RI FormatVariableHelpText( env ", " opt ", " help ", " default ", " actual )
This method returns a formatted string
containing the printable help text
for one option.
It is normally not called directly,
but is called by the
.IR GenerateHelpText ()
method to create the returned help text.
It may be overridden with your own
function that takes the arguments specified above
and returns a string of help text formatted to your liking.
Note that the
.IR GenerateHelpText ()
will not put any blank lines or extra
characters in between the entries,
so you must add those characters to the returned
string if you want the entries separated.

.ES
def my_format(env, opt, help, default, actual):
    fmt = "\n%s: default=%s actual=%s (%s)\n"
    return fmt % (opt, default. actual, help)
vars.FormatVariableHelpText = my_format
.EE

To make it more convenient to work with customizable Variables,
.B scons
provides a number of functions
that make it easy to set up
various types of Variables:

.TP
.RI BoolVariable( key ", " help ", " default )
Return a tuple of arguments
to set up a Boolean option.
The option will use
the specified name
.IR key ,
have a default value of
.IR default ,
and display the specified
.I help
text.
The option will interpret the values
.BR y ,
.BR yes ,
.BR t ,
.BR true ,
.BR 1 ,
.B on
and
.B all
as true,
and the values
.BR n ,
.BR no ,
.BR f ,
.BR false ,
.BR 0 ,
.B off
and
.B none
as false.

.TP
.RI EnumVariable( key ", " help ", " default ", " allowed_values ", [" map ", " ignorecase ])
Return a tuple of arguments
to set up an option
whose value may be one
of a specified list of legal enumerated values.
The option will use
the specified name
.IR key ,
have a default value of
.IR default ,
and display the specified
.I help
text.
The option will only support those
values in the
.I allowed_values
list.
The optional
.I map
argument is a dictionary
that can be used to convert
input values into specific legal values
in the
.I allowed_values
list.
If the value of
.I ignore_case
is
.B 0
(the default),
then the values are case-sensitive.
If the value of
.I ignore_case
is
.BR 1 ,
then values will be matched
case-insensitive.
If the value of
.I ignore_case
is
.BR 1 ,
then values will be matched
case-insensitive,
and all input values will be
converted to lower case.

.TP
.RI ListVariable( key ", " help ", " default ", " names ", [", map ])
Return a tuple of arguments
to set up an option
whose value may be one or more
of a specified list of legal enumerated values.
The option will use
the specified name
.IR key ,
have a default value of
.IR default ,
and display the specified
.I help
text.
The option will only support the values
.BR all ,
.BR none ,
or the values in the
.I names
list.
More than one value may be specified,
with all values separated by commas.
The default may be a string of
comma-separated default values,
or a list of the default values.
The optional
.I map
argument is a dictionary
that can be used to convert
input values into specific legal values
in the
.I names
list.

.TP
.RI PackageVariable( key ", " help ", " default )
Return a tuple of arguments
to set up an option
whose value is a path name
of a package that may be
enabled, disabled or
given an explicit path name.
The option will use
the specified name
.IR key ,
have a default value of
.IR default ,
and display the specified
.I help
text.
The option will support the values
.BR yes ,
.BR true ,
.BR on ,
.BR enable
or
.BR search ,
in which case the specified
.I default
will be used,
or the option may be set to an
arbitrary string
(typically the path name to a package
that is being enabled).
The option will also support the values
.BR no ,
.BR false ,
.BR off
or
.BR disable
to disable use of the specified option.

.TP
.RI PathVariable( key ", " help ", " default ", [" validator ])
Return a tuple of arguments
to set up an option
whose value is expected to be a path name.
The option will use
the specified name
.IR key ,
have a default value of
.IR default ,
and display the specified
.I help
text.
An additional
.I validator
may be specified
that will be called to
verify that the specified path
is acceptable.
SCons supplies the
following ready-made validators:
.BR PathVariable.PathExists
(the default),
which verifies that the specified path exists;
.BR PathVariable.PathIsFile ,
which verifies that the specified path is an existing file;
.BR PathVariable.PathIsDir ,
which verifies that the specified path is an existing directory;
.BR PathVariable.PathIsDirCreate ,
which verifies that the specified path is a directory
and will create the specified directory if the path does not exist;
and
.BR PathVariable.PathAccept ,
which simply accepts the specific path name argument without validation,
and which is suitable if you want your users
to be able to specify a directory path that will be
created as part of the build process, for example.
You may supply your own
.I validator
function,
which must take three arguments
.RI ( key ,
the name of the variable to be set;
.IR val ,
the specified value being checked;
and
.IR env ,
the construction environment)
and should raise an exception
if the specified value is not acceptable.

.RE
These functions make it
convenient to create a number
of variables with consistent behavior
in a single call to the
.B AddVariables
method:

.ES
vars.AddVariables(
    BoolVariable('warnings', 'compilation with -Wall and similiar', 1),
    EnumVariable('debug', 'debug output and symbols', 'no'
               allowed_values=('yes', 'no', 'full'),
               map={}, ignorecase=0),  # case sensitive
    ListVariable('shared',
               'libraries to build as shared libraries',
               'all',
               names = list_of_libs),
    PackageVariable('x11',
                  'use X11 installed here (yes = search some places)',
                  'yes'),
    PathVariable('qtdir', 'where the root of Qt is installed', qtdir),
    PathVariable('foopath', 'where the foo library is installed', foopath,
               PathVariable.PathIsDir),

)
.EE

.SS File and Directory Nodes

The
.IR File ()
and
.IR Dir ()
functions return
.I File
and
.I Dir
Nodes, respectively.
python objects, respectively.
Those objects have several user-visible attributes
and methods that are often useful:

.IP path
The build path
of the given
file or directory.
This path is relative to the top-level directory
(where the
.B SConstruct
file is found).
The build path is the same as the source path if
.I variant_dir
is not being used.

.IP abspath
The absolute build path of the given file or directory.

.IP srcnode()
The
.IR srcnode ()
method
returns another
.I File
or
.I Dir
object representing the
.I source
path of the given
.I File
or
.IR Dir .
The

.ES
# Get the current build dir's path, relative to top.
Dir('.').path
# Current dir's absolute path
Dir('.').abspath
# Next line is always '.', because it is the top dir's path relative to itself.
Dir('#.').path
File('foo.c').srcnode().path   # source path of the given source file.

# Builders also return File objects:
foo = env.Program('foo.c')
print "foo will be built in %s"%foo.path
.EE

A
.I Dir
Node or
.I File
Node can also be used to create
file and subdirectory Nodes relative to the generating Node.
A
.I Dir
Node will place the new Nodes within the directory it represents.
A
.I File
node will place the new Nodes within its parent directory
(that is, "beside" the file in question).
If
.I d
is a
.I Dir
(directory) Node and
.I f
is a
.I File
(file) Node,
then these methods are available:

.TP
.IR d .Dir( name )
Returns a directory Node for a subdirectory of
.I d
named
.IR name .

.TP
.IR d .File( name )
Returns a file Node for a file within
.I d
named
.IR name .

.TP
.IR d .Entry( name )
Returns an unresolved Node within
.I d
named
.IR name .

.TP
.IR f .Dir( name )
Returns a directory named
.I name
within the parent directory of
.IR f .

.TP
.IR f .File( name )
Returns a file named
.I name
within the parent directory of
.IR f .

.TP
.IR f .Entry( name )
Returns an unresolved Node named
.I name
within the parent directory of
.IR f .

.RE
For example:

.ES
# Get a Node for a file within a directory
incl = Dir('include')
f = incl.File('header.h')

# Get a Node for a subdirectory within a directory
dist = Dir('project-3.2.1)
src = dist.Dir('src')

# Get a Node for a file in the same directory
cfile = File('sample.c')
hfile = cfile.File('sample.h')

# Combined example
docs = Dir('docs')
html = docs.Dir('html')
index = html.File('index.html')
css = index.File('app.css')
.EE

.SH EXTENDING SCONS
.SS Builder Objects
.B scons
can be extended to build different types of targets
by adding new Builder objects
to a construction environment.
.IR "In general" ,
you should only need to add a new Builder object
when you want to build a new type of file or other external target.
If you just want to invoke a different compiler or other tool
to build a Program, Object, Library, or any other
type of output file for which
.B scons
already has an existing Builder,
it is generally much easier to
use those existing Builders
in a construction environment
that sets the appropriate construction variables
(CC, LINK, etc.).

Builder objects are created
using the
.B Builder
function.
The
.B Builder
function accepts the following arguments:

.IP action
The command line string used to build the target from the source.
.B action
can also be:
a list of strings representing the command
to be executed and its arguments
(suitable for enclosing white space in an argument),
a dictionary
mapping source file name suffixes to
any combination of command line strings
(if the builder should accept multiple source file extensions),
a Python function;
an Action object
(see the next section);
or a list of any of the above.

An action function
takes three arguments:
.I source
- a list of source nodes,
.I target
- a list of target nodes,
.I env
- the construction environment.

.IP prefix
The prefix that will be prepended to the target file name.
This may be specified as a:

.RS 10
.HP 6
*
.IR string ,

.HP 6
*
.I callable object
- a function or other callable that takes
two arguments (a construction environment and a list of sources)
and returns a prefix,

.HP 6
*
.I dictionary
- specifies a mapping from a specific source suffix (of the first
source specified) to a corresponding target prefix.  Both the source
suffix and target prefix specifications may use environment variable
substitution, and the target prefix (the 'value' entries in the
dictionary) may also be a callable object.  The default target prefix
may be indicated by a dictionary entry with a key value of None.
.RE
.P

.ES
b = Builder("build_it < $SOURCE > $TARGET"
            prefix = "file-")

def gen_prefix(env, sources):
    return "file-" + env['PLATFORM'] + '-'
b = Builder("build_it < $SOURCE > $TARGET",
            prefix = gen_prefix)

b = Builder("build_it < $SOURCE > $TARGET",
            suffix = { None: "file-",
                       "$SRC_SFX_A": gen_prefix })
.EE

.IP suffix
The suffix that will be appended to the target file name.
This may be specified in the same manner as the prefix above.
If the suffix is a string, then
.B scons
will append a '.' to the beginning of the suffix if it's not already
there.  The string returned by callable object (or obtained from the
dictionary) is untouched and must append its own '.'  to the beginning
if one is desired.

.ES
b = Builder("build_it < $SOURCE > $TARGET"
            suffix = "-file")

def gen_suffix(env, sources):
    return "." + env['PLATFORM'] + "-file"
b = Builder("build_it < $SOURCE > $TARGET",
            suffix = gen_suffix)

b = Builder("build_it < $SOURCE > $TARGET",
            suffix = { None: ".sfx1",
                       "$SRC_SFX_A": gen_suffix })
.EE

.IP ensure_suffix
When set to any true value, causes
.B scons
to add the target suffix specified by the
.I suffix
keyword to any target strings
that have a different suffix.
(The default behavior is to leave untouched
any target file name that looks like it already has any suffix.)

.ES
b1 = Builder("build_it < $SOURCE > $TARGET"
             suffix = ".out")
b2 = Builder("build_it < $SOURCE > $TARGET"
             suffix = ".out",
             ensure_suffix)
env = Environment()
env['BUILDERS']['B1'] = b1
env['BUILDERS']['B2'] = b2

# Builds "foo.txt" because ensure_suffix is not set.
env.B1('foo.txt', 'foo.in')

# Builds "bar.txt.out" because ensure_suffix is set.
env.B2('bar.txt', 'bar.in')
.EE

.IP src_suffix
The expected source file name suffix.  This may be a string or a list
of strings.

.IP target_scanner
A Scanner object that
will be invoked to find
implicit dependencies for this target file.
This keyword argument should be used
for Scanner objects that find
implicit dependencies
based only on the target file
and the construction environment,
.I not
for implicit
(See the section "Scanner Objects," below,
for information about creating Scanner objects.)

.IP source_scanner
A Scanner object that
will be invoked to
find implicit dependences in
any source files
used to build this target file.
This is where you would
specify a scanner to
find things like
.B #include
lines in source files.
The pre-built
.B DirScanner
Scanner object may be used to
indicate that this Builder
should scan directory trees
for on-disk changes to files
that
.B scons
does not know about from other Builder or function calls.
(See the section "Scanner Objects," below,
for information about creating your own Scanner objects.)

.IP target_factory
A factory function that the Builder will use
to turn any targets specified as strings into SCons Nodes.
By default,
SCons assumes that all targets are files.
Other useful target_factory
values include
.BR Dir ,
for when a Builder creates a directory target,
and
.BR Entry ,
for when a Builder can create either a file
or directory target.

Example:

.ES
MakeDirectoryBuilder = Builder(action=my_mkdir, target_factory=Dir)
env = Environment()
env.Append(BUILDERS = {'MakeDirectory':MakeDirectoryBuilder})
env.MakeDirectory('new_directory', [])
.EE

.IP
Note that the call to the MakeDirectory Builder
needs to specify an empty source list
to make the string represent the builder's target;
without that, it would assume the argument is the source,
and would try to deduce the target name from it,
which in the absence of an automatically-added prefix or suffix
would lead to a matching target and source name
and a circular dependency.

.IP source_factory
A factory function that the Builder will use
to turn any sources specified as strings into SCons Nodes.
By default,
SCons assumes that all source are files.
Other useful source_factory
values include
.BR Dir ,
for when a Builder uses a directory as a source,
and
.BR Entry ,
for when a Builder can use files
or directories (or both) as sources.

Example:

.ES
CollectBuilder = Builder(action=my_mkdir, source_factory=Entry)
env = Environment()
env.Append(BUILDERS = {'Collect':CollectBuilder})
env.Collect('archive', ['directory_name', 'file_name'])
.EE

.IP emitter
A function or list of functions to manipulate the target and source
lists before dependencies are established
and the target(s) are actually built.
.B emitter
can also be a string containing a construction variable to expand
to an emitter function or list of functions,
or a dictionary mapping source file suffixes
to emitter functions.
(Only the suffix of the first source file
is used to select the actual emitter function
from an emitter dictionary.)

An emitter function
takes three arguments:
.I source
- a list of source nodes,
.I target
- a list of target nodes,
.I env
- the construction environment.
An emitter must return a tuple containing two lists,
the list of targets to be built by this builder,
and the list of sources for this builder.

Example:

.ES
def e(target, source, env):
    return (target + ['foo.foo'], source + ['foo.src'])

# Simple association of an emitter function with a Builder.
b = Builder("my_build < $TARGET > $SOURCE",
            emitter = e)

def e2(target, source, env):
    return (target + ['bar.foo'], source + ['bar.src'])

# Simple association of a list of emitter functions with a Builder.
b = Builder("my_build < $TARGET > $SOURCE",
            emitter = [e, e2])

# Calling an emitter function through a construction variable.
env = Environment(MY_EMITTER = e)
b = Builder("my_build < $TARGET > $SOURCE",
            emitter = '$MY_EMITTER')

# Calling a list of emitter functions through a construction variable.
env = Environment(EMITTER_LIST = [e, e2])
b = Builder("my_build < $TARGET > $SOURCE",
            emitter = '$EMITTER_LIST')

# Associating multiple emitters with different file
# suffixes using a dictionary.
def e_suf1(target, source, env):
    return (target + ['another_target_file'], source)
def e_suf2(target, source, env):
    return (target, source + ['another_source_file'])
b = Builder("my_build < $TARGET > $SOURCE",
            emitter = {'.suf1' : e_suf1,
                       '.suf2' : e_suf2})
.EE

.IP multi
Specifies whether this builder is allowed to be called multiple times for
the same target file(s). The default is 0, which means the builder
can not be called multiple times for the same target file(s). Calling a
builder multiple times for the same target simply adds additional source
files to the target; it is not allowed to change the environment associated
with the target, specify addition environment overrides, or associate a different
builder with the target.

.IP env
A construction environment that can be used
to fetch source code using this Builder.
(Note that this environment is
.I not
used for normal builds of normal target files,
which use the environment that was
used to call the Builder for the target file.)

.IP generator
A function that returns a list of actions that will be executed to build
the target(s) from the source(s).
The returned action(s) may be
an Action object, or anything that
can be converted into an Action object
(see the next section).

The generator function
takes four arguments:
.I source
- a list of source nodes,
.I target
- a list of target nodes,
.I env
- the construction environment,
.I for_signature
- a Boolean value that specifies
whether the generator is being called
for generating a build signature
(as opposed to actually executing the command).
Example:

.ES
def g(source, target, env, for_signature):
    return [["gcc", "-c", "-o"] + target + source]

b = Builder(generator=g)
.EE

.IP
The
.I generator
and
.I action
arguments must not both be used for the same Builder.

.IP src_builder
Specifies a builder to use when a source file name suffix does not match
any of the suffixes of the builder. Using this argument produces a
multi-stage builder.

.IP single_source
Specifies that this builder expects exactly one source file per call. Giving
more than one source files without target files results in implicitely calling
the builder multiple times (once for each source given). Giving multiple
source files together with target files results in a UserError exception.

.RE
.IP
The
.I generator
and
.I action
arguments must not both be used for the same Builder.

.IP source_ext_match
When the specified
.I action
argument is a dictionary,
the default behavior when a builder is passed
multiple source files is to make sure that the
extensions of all the source files match.
If it is legal for this builder to be
called with a list of source files with different extensions,
this check can be suppressed by setting
.B source_ext_match
to
.B None
or some other non-true value.
When
.B source_ext_match
is disable,
.B scons
will use the suffix of the first specified
source file to select the appropriate action from the
.I action
dictionary.

In the following example,
the setting of
.B source_ext_match
prevents
.B scons
from exiting with an error
due to the mismatched suffixes of
.B foo.in
and
.BR foo.extra .

.ES
b = Builder(action={'.in' : 'build $SOURCES > $TARGET'},
            source_ext_match = None)

env = Environment(BUILDERS = {'MyBuild':b})
env.MyBuild('foo.out', ['foo.in', 'foo.extra'])
.EE

.IP env
A construction environment that can be used
to fetch source code using this Builder.
(Note that this environment is
.I not
used for normal builds of normal target files,
which use the environment that was
used to call the Builder for the target file.)

.ES
b = Builder(action="build < $SOURCE > $TARGET")
env = Environment(BUILDERS = {'MyBuild' : b})
env.MyBuild('foo.out', 'foo.in', my_arg = 'xyzzy')
.EE

.IP chdir
A directory from which scons
will execute the
action(s) specified
for this Builder.
If the
.B chdir
argument is
a string or a directory Node,
scons will change to the specified directory.
If the
.B chdir
is not a string or Node
and is non-zero,
then scons will change to the
target file's directory.

Note that scons will
.I not
automatically modify
its expansion of
construction variables like
.B $TARGET
and
.B $SOURCE
when using the chdir
keyword argument--that is,
the expanded file names
will still be relative to
the top-level SConstruct directory,
and consequently incorrect
relative to the chdir directory.
Builders created using chdir keyword argument,
will need to use construction variable
expansions like
.B ${TARGET.file}
and
.B ${SOURCE.file}
to use just the filename portion of the
targets and source.

.ES
b = Builder(action="build < ${SOURCE.file} > ${TARGET.file}",
            chdir=1)
env = Environment(BUILDERS = {'MyBuild' : b})
env.MyBuild('sub/dir/foo.out', 'sub/dir/foo.in')
.EE

.B WARNING:
Python only keeps one current directory
location for all of the threads.
This means that use of the
.B chdir
argument
will
.I not
work with the SCons
.B -j
option,
because individual worker threads spawned
by SCons interfere with each other
when they start changing directory.

.RE
Any additional keyword arguments supplied
when a Builder object is created
(that is, when the Builder() function is called)
will be set in the executing construction
environment when the Builder object is called.
The canonical example here would be
to set a construction variable to
the repository of a source code system.

Any additional keyword arguments supplied
when a Builder
.I object
is called
will only be associated with the target
created by that particular Builder call
(and any other files built as a
result of the call).

These extra keyword arguments are passed to the
following functions:
command generator functions,
function Actions,
and emitter functions.

.SS Action Objects

The
.BR Builder ()
function will turn its
.B action
keyword argument into an appropriate
internal Action object.
You can also explicity create Action objects
using the
.BR Action ()
global function,
which can then be passed to the
.BR Builder ()
function.
This can be used to configure
an Action object more flexibly,
or it may simply be more efficient
than letting each separate Builder object
create a separate Action
when multiple
Builder objects need to do the same thing.

The
.BR Action ()
global function
returns an appropriate object for the action
represented by the type of the first argument:

.IP Action
If the first argument is already an Action object,
the object is simply returned.

.IP String
If the first argument is a string,
a command-line Action is returned.
Note that the command-line string
may be preceded by an
.B @
(at-sign)
to suppress printing of the specified command line,
or by a
.B \-
(hyphen)
to ignore the exit status from the specified command:

.ES
Action('$CC -c -o $TARGET $SOURCES')

# Doesn't print the line being executed.
Action('@build $TARGET $SOURCES')

# Ignores return value
Action('-build $TARGET $SOURCES')
.EE
.\" XXX From Gary Ruben, 23 April 2002:
.\" What would be useful is a discussion of how you execute command
.\" shell commands ie. what is the process used to spawn the shell, pass
.\" environment variables to it etc., whether there is one shell per
.\" environment or one per command etc.  It might help to look at the Gnu
.\" make documentation to see what they think is important to discuss about
.\" a build system. I'm sure you can do a better job of organising the
.\" documentation than they have :-)

.IP List
If the first argument is a list,
then a list of Action objects is returned.
An Action object is created as necessary
for each element in the list.
If an element
.I within
the list is itself a list,
the internal list is the
command and arguments to be executed via
the command line.
This allows white space to be enclosed
in an argument by defining
a command in a list within a list:

.ES
Action([['cc', '-c', '-DWHITE SPACE', '-o', '$TARGET', '$SOURCES']])
.EE

.IP Function
If the first argument is a Python function,
a function Action is returned.
The Python function must take three keyword arguments,
.B target
(a Node object representing the target file),
.B source
(a Node object representing the source file)
and
.B env
(the construction environment
used for building the target file).
The
.B target
and
.B source
arguments may be lists of Node objects if there is
more than one target file or source file.
The actual target and source file name(s) may
be retrieved from their Node objects
via the built-in Python str() function:

.ES
target_file_name = str(target)
source_file_names = map(lambda x: str(x), source)
.EE
.IP
The function should return
.B 0
or
.B None
to indicate a successful build of the target file(s).
The function may raise an exception
or return a non-zero exit status
to indicate an unsuccessful build.

.ES
def build_it(target = None, source = None, env = None):
    # build the target from the source
    return 0

a = Action(build_it)
.EE

If the action argument is not one of the above,
None is returned.
.PP

The second argument is optional and is used to define the output
which is printed when the Action is actually performed.
In the absence of this parameter,
or if it's an empty string,
a default output depending on the type of the action is used.
For example, a command-line action will print the executed command.
The argument must be either a Python function or a string.

In the first case,
it's a function that returns a string to be printed
to describe the action being executed.
The function may also be specified by the
.IR strfunction =
keyword argument.
Like a function to build a file,
this function must take three keyword arguments:
.B target
(a Node object representing the target file),
.B source
(a Node object representing the source file)
and
.BR env
(a construction environment).
The
.B target
and
.B source
arguments may be lists of Node objects if there is
more than one target file or source file.

In the second case, you provide the string itself.
The string may also be specified by the
.IR cmdstr =
keyword argument.
The string typically contains variables, notably
$TARGET(S) and $SOURCE(S), or consists of just a single
variable, which is optionally defined somewhere else.
SCons itself heavily uses the latter variant.

Examples:

.ES
def build_it(target, source, env):
    # build the target from the source
    return 0

def string_it(target, source, env):
    return "building '%s' from '%s'" % (target[0], source[0])

# Use a positional argument.
f = Action(build_it, string_it)
s = Action(build_it, "building '$TARGET' from '$SOURCE'")

# Alternatively, use a keyword argument.
f = Action(build_it, strfunction=string_it)
s = Action(build_it, cmdstr="building '$TARGET' from '$SOURCE'")

# You can provide a configurable variable.
l = Action(build_it, '$STRINGIT')
.EE

The third and succeeding arguments, if present,
may either be a construction variable or a list of construction variables
whose values will be included in the signature of the Action
when deciding whether a target should be rebuilt because the action changed.
The variables may also be specified by a
.IR varlist =
keyword parameter;
if both are present, they are combined.
This is necessary whenever you want a target to be rebuilt
when a specific construction variable changes.
This is not often needed for a string action,
as the expanded variables will normally be part of the command line,
but may be needed if a Python function action uses
the value of a construction variable when generating the command line.

.ES
def build_it(target, source, env):
    # build the target from the 'XXX' construction variable
    open(target[0], 'w').write(env['XXX'])
    return 0

# Use positional arguments.
a = Action(build_it, '$STRINGIT', ['XXX'])

# Alternatively, use a keyword argument.
a = Action(build_it, varlist=['XXX'])
.EE

The
.BR Action ()
global function
can be passed the following
optional keyword arguments
to modify the Action object's behavior:

.IP
.B chdir
The
.B chdir
keyword argument specifies that
scons will execute the action
after changing to the specified directory.
If the
.B chdir
argument is
a string or a directory Node,
scons will change to the specified directory.
If the
.B chdir
argument
is not a string or Node
and is non-zero,
then scons will change to the
target file's directory.

Note that scons will
.I not
automatically modify
its expansion of
construction variables like
.B $TARGET
and
.B $SOURCE
when using the chdir
keyword argument--that is,
the expanded file names
will still be relative to
the top-level SConstruct directory,
and consequently incorrect
relative to the chdir directory.
Builders created using chdir keyword argument,
will need to use construction variable
expansions like
.B ${TARGET.file}
and
.B ${SOURCE.file}
to use just the filename portion of the
targets and source.

.ES
a = Action("build < ${SOURCE.file} > ${TARGET.file}",
           chdir=1)
.EE

.IP
.B exitstatfunc
The
.BR Action ()
global function
also takes an
.B exitstatfunc
keyword argument
which specifies a function
that is passed the exit status
(or return value)
from the specified action
and can return an arbitrary
or modified value.
This can be used, for example,
to specify that an Action object's
return value should be ignored
under special conditions
and SCons should, therefore,
consider that the action always suceeds:

.ES
def always_succeed(s):
    # Always return 0, which indicates success.
    return 0
a = Action("build < ${SOURCE.file} > ${TARGET.file}",
           exitstatfunc=always_succeed)
.EE

.IP
.B batch_key
The
.B batch_key
keyword argument can be used
to specify that the Action can create multiple target files
by processing multiple independent source files simultaneously.
(The canonical example is "batch compilation"
of multiple object files
by passing multiple source files
to a single invocation of a compiler
such as Microsoft's Visual C / C++ compiler.)
If the
.B batch_key
argument is any non-False, non-callable Python value,
the configured Action object will cause
.B scons
to collect all targets built with the Action object
and configured with the same construction environment
into single invocations of the Action object's
command line or function.
Command lines will typically want to use the
.BR CHANGED_SOURCES
construction variable
(and possibly
.BR CHANGED_TARGETS
as well)
to only pass to the command line those sources that
have actually changed since their targets were built.

Example:

.ES
a = Action('build $CHANGED_SOURCES', batch_key=True)
.EE

The
.B batch_key
argument may also be
a callable function
that returns a key that
will be used to identify different
"batches" of target files to be collected
for batch building.
A
.B batch_key
function must take the following arguments:

.IP action
The action object.

.IP env
The construction environment
configured for the target.

.IP target
The list of targets for a particular configured action.

.IP source
The list of source for a particular configured action.

The returned key should typically
be a tuple of values derived from the arguments,
using any appropriate logic to decide
how multiple invocations should be batched.
For example, a
.B batch_key
function may decide to return
the value of a specific construction
variable from the
.B env
argument
which will cause
.B scons
to batch-build targets
with matching values of that variable,
or perhaps return the
.BR id ()
of the entire construction environment,
in which case
.B scons
will batch-build
all targets configured with the same construction environment.
Returning
.B None
indicates that
the particular target should
.I not
be part of any batched build,
but instead will be built
by a separate invocation of action's
command or function.
Example:

.ES
def batch_key(action, env, target, source):
    tdir = target[0].dir
    if tdir.name == 'special':
        # Don't batch-build any target
        # in the special/ subdirectory.
        return None
    return (id(action), id(env), tdir)
a = Action('build $CHANGED_SOURCES', batch_key=batch_key)
.EE

.SS Miscellaneous Action Functions

.B scons
supplies a number of functions
that arrange for various common
file and directory manipulations
to be performed.
These are similar in concept to "tasks" in the
Ant build tool,
although the implementation is slightly different.
These functions do not actually
perform the specified action
at the time the function is called,
but instead return an Action object
that can be executed at the
appropriate time.
(In Object-Oriented terminology,
these are actually
Action
.I Factory
functions
that return Action objects.)

In practice,
there are two natural ways
that these
Action Functions
are intended to be used.

First,
if you need
to perform the action
at the time the SConscript
file is being read,
you can use the
.B Execute
global function to do so:
.ES
Execute(Touch('file'))
.EE

Second,
you can use these functions
to supply Actions in a list
for use by the
.B Command
method.
This can allow you to
perform more complicated
sequences of file manipulation
without relying
on platform-specific
external commands:
that
.ES
env = Environment(TMPBUILD = '/tmp/builddir')
env.Command('foo.out', 'foo.in',
            [Mkdir('$TMPBUILD'),
             Copy('$TMPBUILD', '${SOURCE.dir}'),
             "cd $TMPBUILD && make",
             Delete('$TMPBUILD')])
.EE

.TP
.RI Chmod( dest ", " mode )
Returns an Action object that
changes the permissions on the specified
.I dest
file or directory to the specified
.IR mode .
Examples:

.ES
Execute(Chmod('file', 0755))

env.Command('foo.out', 'foo.in',
            [Copy('$TARGET', '$SOURCE'),
             Chmod('$TARGET', 0755)])
.EE

.TP
.RI Copy( dest ", " src )
Returns an Action object
that will copy the
.I src
source file or directory to the
.I dest
destination file or directory.
Examples:

.ES
Execute(Copy('foo.output', 'foo.input'))

env.Command('bar.out', 'bar.in',
            Copy('$TARGET', '$SOURCE'))
.EE

.TP
.RI Delete( entry ", [" must_exist ])
Returns an Action that
deletes the specified
.IR entry ,
which may be a file or a directory tree.
If a directory is specified,
the entire directory tree
will be removed.
If the
.I must_exist
flag is set,
then a Python error will be thrown
if the specified entry does not exist;
the default is
.BR must_exist=0 ,
that is, the Action will silently do nothing
if the entry does not exist.
Examples:

.ES
Execute(Delete('/tmp/buildroot'))

env.Command('foo.out', 'foo.in',
            [Delete('${TARGET.dir}'),
             MyBuildAction])

Execute(Delete('file_that_must_exist', must_exist=1))
.EE

.TP
.RI Mkdir( dir )
Returns an Action
that creates the specified
directory
.I dir .
Examples:

.ES
Execute(Mkdir('/tmp/outputdir'))

env.Command('foo.out', 'foo.in',
            [Mkdir('/tmp/builddir'),
             Copy('/tmp/builddir/foo.in', '$SOURCE'),
             "cd /tmp/builddir && make",
             Copy('$TARGET', '/tmp/builddir/foo.out')])
.EE

.TP
.RI Move( dest ", " src )
Returns an Action
that moves the specified
.I src
file or directory to
the specified
.I dest
file or directory.
Examples:

.ES
Execute(Move('file.destination', 'file.source'))

env.Command('output_file', 'input_file',
            [MyBuildAction,
             Move('$TARGET', 'file_created_by_MyBuildAction')])
.EE

.TP
.RI Touch( file )
Returns an Action
that updates the modification time
on the specified
.IR file .
Examples:

.ES
Execute(Touch('file_to_be_touched'))

env.Command('marker', 'input_file',
            [MyBuildAction,
             Touch('$TARGET')])
.EE

.SS Variable Substitution

Before executing a command,
.B scons
performs construction variable interpolation on the strings that make up
the command line of builders.
Variables are introduced by a
.B $
prefix.
Besides construction variables, scons provides the following
variables for each command execution:

.IP CHANGED_SOURCES
The file names of all sources of the build command
that have changed since the target was last built.

.IP CHANGED_TARGETS
The file names of all targets that would be built
from sources that have changed since the target was last built.

.IP SOURCE
The file name of the source of the build command,
or the file name of the first source
if multiple sources are being built.

.IP SOURCES
The file names of the sources of the build command.

.IP TARGET
The file name of the target being built,
or the file name of the first target
if multiple targets are being built.

.IP TARGETS
The file names of all targets being built.

.IP UNCHANGED_SOURCES
The file names of all sources of the build command
that have
.I not
changed since the target was last built.

.IP UNCHANGED_TARGETS
The file names of all targets that would be built
from sources that have
.I not
changed since the target was last built.

(Note that the above variables are reserved
and may not be set in a construction environment.)

.LP
For example, given the construction variable CC='cc', targets=['foo'], and
sources=['foo.c', 'bar.c']:

.ES
action='$CC -c -o $TARGET $SOURCES'
.EE

would produce the command line:

.ES
cc -c -o foo foo.c bar.c
.EE

Variable names may be surrounded by curly braces ({})
to separate the name from the trailing characters.
Within the curly braces, a variable name may have
a Python slice subscript appended to select one
or more items from a list.
In the previous example, the string:

.ES
${SOURCES[1]}
.EE

would produce:

.ES
bar.c
.EE

Additionally, a variable name may
have the following special
modifiers appended within the enclosing curly braces
to modify the interpolated string:

.IP base
The base path of the file name,
including the directory path
but excluding any suffix.

.IP dir
The name of the directory in which the file exists.

.IP file
The file name,
minus any directory portion.

.IP filebase
Just the basename of the file,
minus any suffix
and minus the directory.

.IP suffix
Just the file suffix.

.IP abspath
The absolute path name of the file.

.IP posix
The POSIX form of the path,
with directories separated by
.B /
(forward slashes)
not backslashes.
This is sometimes necessary on Windows systems
when a path references a file on other (POSIX) systems.

.IP srcpath
The directory and file name to the source file linked to this file through
.BR VariantDir ().
If this file isn't linked,
it just returns the directory and filename unchanged.

.IP srcdir
The directory containing the source file linked to this file through
.BR VariantDir ().
If this file isn't linked,
it just returns the directory part of the filename.

.IP rsrcpath
The directory and file name to the source file linked to this file through
.BR VariantDir ().
If the file does not exist locally but exists in a Repository,
the path in the Repository is returned.
If this file isn't linked, it just returns the
directory and filename unchanged.

.IP rsrcdir
The Repository directory containing the source file linked to this file through
.BR VariantDir ().
If this file isn't linked,
it just returns the directory part of the filename.

.LP
For example, the specified target will
expand as follows for the corresponding modifiers:

.ES
$TARGET              => sub/dir/file.x
${TARGET.base}       => sub/dir/file
${TARGET.dir}        => sub/dir
${TARGET.file}       => file.x
${TARGET.filebase}   => file
${TARGET.suffix}     => .x
${TARGET.abspath}    => /top/dir/sub/dir/file.x

SConscript('src/SConscript', variant_dir='sub/dir')
$SOURCE              => sub/dir/file.x
${SOURCE.srcpath}    => src/file.x
${SOURCE.srcdir}     => src

Repository('/usr/repository')
$SOURCE              => sub/dir/file.x
${SOURCE.rsrcpath}   => /usr/repository/src/file.x
${SOURCE.rsrcdir}    => /usr/repository/src
.EE

Note that curly braces braces may also be used
to enclose arbitrary Python code to be evaluated.
(In fact, this is how the above modifiers are substituted,
they are simply attributes of the Python objects
that represent TARGET, SOURCES, etc.)
See the section "Python Code Substitution," below,
for more thorough examples of
how this can be used.

Lastly, a variable name
may be a callable Python function
associated with a
construction variable in the environment.
The function should
take four arguments:
.I target
- a list of target nodes,
.I source
- a list of source nodes,
.I env
- the construction environment,
.I for_signature
- a Boolean value that specifies
whether the function is being called
for generating a build signature.
SCons will insert whatever
the called function returns
into the expanded string:

.ES
def foo(target, source, env, for_signature):
    return "bar"

# Will expand $BAR to "bar baz"
env=Environment(FOO=foo, BAR="$FOO baz")
.EE

You can use this feature to pass arguments to a
Python function by creating a callable class
that stores one or more arguments in an object,
and then uses them when the
.B __call__()
method is called.
Note that in this case,
the entire variable expansion must
be enclosed by curly braces
so that the arguments will
be associated with the
instantiation of the class:

.ES
class foo:
    def __init__(self, arg):
        self.arg = arg

    def __call__(self, target, source, env, for_signature):
        return self.arg + " bar"

# Will expand $BAR to "my argument bar baz"
env=Environment(FOO=foo, BAR="${FOO('my argument')} baz")
.EE

.LP
The special pseudo-variables
.B "$("
and
.B "$)"
may be used to surround parts of a command line
that may change
.I without
causing a rebuild--that is,
which are not included in the signature
of target files built with this command.
All text between
.B "$("
and
.B "$)"
will be removed from the command line
before it is added to file signatures,
and the
.B "$("
and
.B "$)"
will be removed before the command is executed.
For example, the command line:

.ES
echo Last build occurred $( $TODAY $). > $TARGET
.EE

.LP
would execute the command:

.ES
echo Last build occurred $TODAY. > $TARGET
.EE

.LP
but the command signature added to any target files would be:

.ES
echo Last build occurred  . > $TARGET
.EE

.SS Python Code Substitution

Any python code within
.BR "${" - "}"
pairs gets evaluated by python 'eval', with the python globals set to
the current environment's set of construction variables.
So in the following case:
.ES
env['COND'] = 0
env.Command('foo.out', 'foo.in',
   '''echo ${COND==1 and 'FOO' or 'BAR'} > $TARGET''')
.EE
the command executed will be either
.ES
echo FOO > foo.out
.EE
or
.ES
echo BAR > foo.out
.EE
according to the current value of env['COND'] when the command is
executed.  The evaluation occurs when the target is being
built, not when the SConscript is being read.  So if env['COND'] is changed
later in the SConscript, the final value will be used.

Here's a more interesting example.  Note that all of COND, FOO, and
BAR are environment variables, and their values are substituted into
the final command.  FOO is a list, so its elements are interpolated
separated by spaces.

.ES
env=Environment()
env['COND'] = 0
env['FOO'] = ['foo1', 'foo2']
env['BAR'] = 'barbar'
env.Command('foo.out', 'foo.in',
    'echo ${COND==1 and FOO or BAR} > $TARGET')

# Will execute this:
#  echo foo1 foo2 > foo.out
.EE

SCons uses the following rules when converting construction variables into
command lines:

.IP String
When the value is a string it is interpreted as a space delimited list of
command line arguments.

.IP List
When the value is a list it is interpreted as a list of command line
arguments. Each element of the list is converted to a string.

.IP Other
Anything that is not a list or string is converted to a string and
interpreted as a single command line argument.

.IP Newline
Newline characters (\\n) delimit lines. The newline parsing is done after
all other parsing, so it is not possible for arguments (e.g. file names) to
contain embedded newline characters. This limitation will likely go away in
a future version of SCons.

.SS Scanner Objects

You can use the
.B Scanner
function to define
objects to scan
new file types for implicit dependencies.
Scanner accepts the following arguments:

.IP function
This can be either:
1) a Python function that will process
the Node (file)
and return a list of strings (file names)
representing the implicit
dependencies found in the contents;
or:
2) a dictionary that maps keys
(typically the file suffix, but see below for more discussion)
to other Scanners that should be called.

If the argument is actually a Python function,
the function must take three or four arguments:

    def scanner_function(node, env, path):

    def scanner_function(node, env, path, arg=None):

The
.B node
argument is the internal
SCons node representing the file.
Use
.B str(node)
to fetch the name of the file, and
.B node.get_contents()
to fetch contents of the file.
Note that the file is
.I not
guaranteed to exist before the scanner is called,
so the scanner function should check that
if there's any chance that the scanned file
might not exist
(for example, if it's built from other files).

The
.B env
argument is the construction environment for the scan.
Fetch values from it using the
.B env.Dictionary()
method.

The
.B path
argument is a tuple (or list)
of directories that can be searched
for files.
This will usually be the tuple returned by the
.B path_function
argument (see below).

The
.B arg
argument is the argument supplied
when the scanner was created, if any.

.IP name
The name of the Scanner.
This is mainly used
to identify the Scanner internally.

.IP argument
An optional argument that, if specified,
will be passed to the scanner function
(described above)
and the path function
(specified below).

.IP skeys
An optional list that can be used to
determine which scanner should be used for
a given Node.
In the usual case of scanning for file names,
this argument will be a list of suffixes
for the different file types that this
Scanner knows how to scan.
If the argument is a string,
then it will be expanded
into a list by the current environment.

.IP path_function
A Python function that takes four or five arguments:
a construction environment,
a Node for the directory containing
the SConscript file in which
the first target was defined,
a list of target nodes,
a list of source nodes,
and an optional argument supplied
when the scanner was created.
The
.B path_function
returns a tuple of directories
that can be searched for files to be returned
by this Scanner object.
(Note that the
.BR FindPathDirs ()
function can be used to return a ready-made
.B path_function
for a given construction variable name,
instead of having to write your own function from scratch.)

.IP node_class
The class of Node that should be returned
by this Scanner object.
Any strings or other objects returned
by the scanner function
that are not of this class
will be run through the
.B node_factory
function.

.IP node_factory
A Python function that will take a string
or other object
and turn it into the appropriate class of Node
to be returned by this Scanner object.

.IP scan_check
An optional Python function that takes two arguments,
a Node (file) and a construction environment,
and returns whether the
Node should, in fact,
be scanned for dependencies.
This check can be used to eliminate unnecessary
calls to the scanner function when,
for example, the underlying file
represented by a Node does not yet exist.

.IP recursive
An optional flag that
specifies whether this scanner should be re-invoked
on the dependency files returned by the scanner.
When this flag is not set,
the Node subsystem will
only invoke the scanner on the file being scanned,
and not (for example) also on the files
specified by the #include lines
in the file being scanned.
.I recursive
may be a callable function,
in which case it will be called with a list of
Nodes found and
should return a list of Nodes
that should be scanned recursively;
this can be used to select a specific subset of
Nodes for additional scanning.

Note that
.B scons
has a global
.B SourceFileScanner
object that is used by
the
.BR Object (),
.BR SharedObject (),
and
.BR StaticObject ()
builders to decide
which scanner should be used
for different file extensions.
You can using the
.BR SourceFileScanner.add_scanner ()
method to add your own Scanner object
to the
.B scons
infrastructure
that builds target programs or
libraries from a list of
source files of different types:

.ES
def xyz_scan(node, env, path):
    contents = node.get_text_contents()
    # Scan the contents and return the included files.

XYZScanner = Scanner(xyz_scan)

SourceFileScanner.add_scanner('.xyx', XYZScanner)

env.Program('my_prog', ['file1.c', 'file2.f', 'file3.xyz'])
.EE

.SH SYSTEM-SPECIFIC BEHAVIOR
SCons and its configuration files are very portable,
due largely to its implementation in Python.
There are, however, a few portability
issues waiting to trap the unwary.
.SS .C file suffix
SCons handles the upper-case
.B .C
file suffix differently,
depending on the capabilities of
the underlying system.
On a case-sensitive system
such as Linux or UNIX,
SCons treats a file with a
.B .C
suffix as a C++ source file.
On a case-insensitive system
such as Windows,
SCons treats a file with a
.B .C
suffix as a C source file.
.SS .F file suffix
SCons handles the upper-case
.B .F
file suffix differently,
depending on the capabilities of
the underlying system.
On a case-sensitive system
such as Linux or UNIX,
SCons treats a file with a
.B .F
suffix as a Fortran source file
that is to be first run through
the standard C preprocessor.
On a case-insensitive system
such as Windows,
SCons treats a file with a
.B .F
suffix as a Fortran source file that should
.I not
be run through the C preprocessor.
.SS Windows:  Cygwin Tools and Cygwin Python vs. Windows Pythons
Cygwin supplies a set of tools and utilities
that let users work on a
Windows system using a more POSIX-like environment.
The Cygwin tools, including Cygwin Python,
do this, in part,
by sharing an ability to interpret UNIX-like path names.
For example, the Cygwin tools
will internally translate a Cygwin path name
like /cygdrive/c/mydir
to an equivalent Windows pathname
of C:/mydir (equivalent to C:\\mydir).

Versions of Python
that are built for native Windows execution,
such as the python.org and ActiveState versions,
do not have the Cygwin path name semantics.
This means that using a native Windows version of Python
to build compiled programs using Cygwin tools
(such as gcc, bison, and flex)
may yield unpredictable results.
"Mixing and matching" in this way
can be made to work,
but it requires careful attention to the use of path names
in your SConscript files.

In practice, users can sidestep
the issue by adopting the following rules:
When using gcc,
use the Cygwin-supplied Python interpreter
to run SCons;
when using Microsoft Visual C/C++
(or some other Windows compiler)
use the python.org or ActiveState version of Python
to run SCons.
.SS Windows:  scons.bat file
On Windows systems,
SCons is executed via a wrapper
.B scons.bat
file.
This has (at least) two ramifications:

First, Windows command-line users
that want to use variable assignment
on the command line
may have to put double quotes
around the assignments:

.ES
scons "FOO=BAR" "BAZ=BLEH"
.EE

Second, the Cygwin shell does not
recognize this file as being the same
as an
.B scons
command issued at the command-line prompt.
You can work around this either by
executing
.B scons.bat
from the Cygwin command line,
or by creating a wrapper shell
script named
.B scons .

.SS MinGW

The MinGW bin directory must be in your PATH environment variable or the
PATH variable under the ENV construction variable for SCons
to detect and use the MinGW tools. When running under the native Windows
Python interpreter, SCons will prefer the MinGW tools over the Cygwin
tools, if they are both installed, regardless of the order of the bin
directories in the PATH variable. If you have both MSVC and MinGW
installed and you want to use MinGW instead of MSVC,
then you must explictly tell SCons to use MinGW by passing

.ES
tools=['mingw']
.EE

to the Environment() function, because SCons will prefer the MSVC tools
over the MinGW tools.

.SH EXAMPLES

To help you get started using SCons,
this section contains a brief overview of some common tasks.

.SS Basic Compilation From a Single Source File

.ES
env = Environment()
env.Program(target = 'foo', source = 'foo.c')
.EE

Note:  Build the file by specifying
the target as an argument
("scons foo" or "scons foo.exe").
or by specifying a dot ("scons .").

.SS Basic Compilation From Multiple Source Files

.ES
env = Environment()
env.Program(target = 'foo', source = Split('f1.c f2.c f3.c'))
.EE

.SS Setting a Compilation Flag

.ES
env = Environment(CCFLAGS = '-g')
env.Program(target = 'foo', source = 'foo.c')
.EE

.SS Search The Local Directory For .h Files

Note:  You do
.I not
need to set CCFLAGS to specify -I options by hand.
SCons will construct the right -I options from CPPPATH.

.ES
env = Environment(CPPPATH = ['.'])
env.Program(target = 'foo', source = 'foo.c')
.EE

.SS Search Multiple Directories For .h Files

.ES
env = Environment(CPPPATH = ['include1', 'include2'])
env.Program(target = 'foo', source = 'foo.c')
.EE

.SS Building a Static Library

.ES
env = Environment()
env.StaticLibrary(target = 'foo', source = Split('l1.c l2.c'))
env.StaticLibrary(target = 'bar', source = ['l3.c', 'l4.c'])
.EE

.SS Building a Shared Library

.ES
env = Environment()
env.SharedLibrary(target = 'foo', source = ['l5.c', 'l6.c'])
env.SharedLibrary(target = 'bar', source = Split('l7.c l8.c'))
.EE

.SS Linking a Local Library Into a Program

.ES
env = Environment(LIBS = 'mylib', LIBPATH = ['.'])
env.Library(target = 'mylib', source = Split('l1.c l2.c'))
env.Program(target = 'prog', source = ['p1.c', 'p2.c'])
.EE

.SS Defining Your Own Builder Object

Notice that when you invoke the Builder,
you can leave off the target file suffix,
and SCons will add it automatically.

.ES
bld = Builder(action = 'pdftex < $SOURCES > $TARGET'
              suffix = '.pdf',
              src_suffix = '.tex')
env = Environment(BUILDERS = {'PDFBuilder' : bld})
env.PDFBuilder(target = 'foo.pdf', source = 'foo.tex')

# The following creates "bar.pdf" from "bar.tex"
env.PDFBuilder(target = 'bar', source = 'bar')
.EE

Note also that the above initialization
overwrites the default Builder objects,
so the Environment created above
can not be used call Builders like env.Program(),
env.Object(), env.StaticLibrary(), etc.

.SS Adding Your Own Builder Object to an Environment

.ES
bld = Builder(action = 'pdftex < $SOURCES > $TARGET'
              suffix = '.pdf',
              src_suffix = '.tex')
env = Environment()
env.Append(BUILDERS = {'PDFBuilder' : bld})
env.PDFBuilder(target = 'foo.pdf', source = 'foo.tex')
env.Program(target = 'bar', source = 'bar.c')
.EE

You also can use other Pythonic techniques to add
to the BUILDERS construction variable, such as:

.ES
env = Environment()
env['BUILDERS]['PDFBuilder'] = bld
.EE

.SS Defining Your Own Scanner Object

The following example shows an extremely simple scanner (the
.BR kfile_scan ()
function)
that doesn't use a search path at all
and simply returns the
file names present on any
.B include
lines in the scanned file.
This would implicitly assume that all included
files live in the top-level directory:

.ES
import re

'\" Note:  the \\ in the following are for the benefit of nroff/troff,
'\" not inappropriate doubled escape characters within the r'' raw string.
include_re = re.compile(r'^include\\s+(\\S+)$', re.M)

def kfile_scan(node, env, path, arg):
    contents = node.get_text_contents()
    includes = include_re.findall(contents)
    return includes

kscan = Scanner(name = 'kfile',
                function = kfile_scan,
                argument = None,
                skeys = ['.k'])
scanners = Environment().Dictionary('SCANNERS')
env = Environment(SCANNERS = scanners + [kscan])

env.Command('foo', 'foo.k', 'kprocess < $SOURCES > $TARGET')

bar_in = File('bar.in')
env.Command('bar', bar_in, 'kprocess $SOURCES > $TARGET')
bar_in.target_scanner = kscan
.EE

Here is a similar but more complete example that searches
a path of directories
(specified as the
.B MYPATH
construction variable)
for files that actually exist:

.ES
include_re = re.compile(r'^include\\s+(\\S+)$', re.M)

def my_scan(node, env, path, arg):
   contents = node.get_text_contents()
   includes = include_re.findall(contents)
   if includes == []:
        return []
    results = []
    for inc in includes:
        for dir in path:
            file = dir + os.sep + inc
            if os.path.exists(file):
                results.append(file)
                break
    return results

scanner = Scanner(name = 'myscanner',
                 function = my_scan,
                 argument = None,
                 skeys = ['.x'],
                 path_function = FindPathDirs('MYPATH'),
                 )
scanners = Environment().Dictionary('SCANNERS')
env = Environment(SCANNERS = scanners + [scanner])
.EE

The
.BR FindPathDirs ()
function used in the previous example returns a function
(actually a callable Python object)
that will return a list of directories
specified in the
.B $MYPATH
construction variable.
If you need to customize how the search path is derived,
you would provide your own
.B path_function
argument when creating the Scanner object,
as follows:

.ES
# MYPATH is a list of directories to search for files in
def pf(env, dir, target, source, arg):
    top_dir = Dir('#').abspath
    results = []
    if env.has_key('MYPATH'):
        for p in env['MYPATH']:
            results.append(top_dir + os.sep + p)
    return results

scanner = Scanner(name = 'myscanner',
                 function = my_scan,
                 argument = None,
                 skeys = ['.x'],
                 path_function = pf,
                 )
.EE

.SS Creating a Hierarchical Build

Notice that the file names specified in a subdirectory's
SConscript
file are relative to that subdirectory.

.ES
SConstruct:

    env = Environment()
    env.Program(target = 'foo', source = 'foo.c')

    SConscript('sub/SConscript')

sub/SConscript:

    env = Environment()
    # Builds sub/foo from sub/foo.c
    env.Program(target = 'foo', source = 'foo.c')

    SConscript('dir/SConscript')

sub/dir/SConscript:

    env = Environment()
    # Builds sub/dir/foo from sub/dir/foo.c
    env.Program(target = 'foo', source = 'foo.c')
.EE

.SS Sharing Variables Between SConscript Files

You must explicitly Export() and Import() variables that
you want to share between SConscript files.

.ES
SConstruct:

    env = Environment()
    env.Program(target = 'foo', source = 'foo.c')

    Export("env")
    SConscript('subdirectory/SConscript')

subdirectory/SConscript:

    Import("env")
    env.Program(target = 'foo', source = 'foo.c')
.EE

.SS Building Multiple Variants From the Same Source

Use the variant_dir keyword argument to
the SConscript function to establish
one or more separate variant build directory trees
for a given source directory:

.ES
SConstruct:

    cppdefines = ['FOO']
    Export("cppdefines")
    SConscript('src/SConscript', variant_dir='foo')

    cppdefines = ['BAR']
    Export("cppdefines")
    SConscript('src/SConscript', variant_dir='bar')

src/SConscript:

    Import("cppdefines")
    env = Environment(CPPDEFINES = cppdefines)
    env.Program(target = 'src', source = 'src.c')
.EE

Note the use of the Export() method
to set the "cppdefines" variable to a different
value each time we call the SConscript function.

.SS Hierarchical Build of Two Libraries Linked With a Program

.ES
SConstruct:

    env = Environment(LIBPATH = ['#libA', '#libB'])
    Export('env')
    SConscript('libA/SConscript')
    SConscript('libB/SConscript')
    SConscript('Main/SConscript')

libA/SConscript:

    Import('env')
    env.Library('a', Split('a1.c a2.c a3.c'))

libB/SConscript:

    Import('env')
    env.Library('b', Split('b1.c b2.c b3.c'))

Main/SConscript:

    Import('env')
    e = env.Copy(LIBS = ['a', 'b'])
    e.Program('foo', Split('m1.c m2.c m3.c'))
.EE

The '#' in the LIBPATH directories specify that they're relative to the
top-level directory, so they don't turn into "Main/libA" when they're
used in Main/SConscript.

Specifying only 'a' and 'b' for the library names
allows SCons to append the appropriate library
prefix and suffix for the current platform
(for example, 'liba.a' on POSIX systems,
\&'a.lib' on Windows).

.SS Customizing construction variables from the command line.

The following would allow the C compiler to be specified on the command
line or in the file custom.py.

.ES
vars = Variables('custom.py')
vars.Add('CC', 'The C compiler.')
env = Environment(variables=vars)
Help(vars.GenerateHelpText(env))
.EE

The user could specify the C compiler on the command line:

.ES
scons "CC=my_cc"
.EE

or in the custom.py file:

.ES
CC = 'my_cc'
.EE

or get documentation on the options:

.ES
$ scons -h

CC: The C compiler.
    default: None
    actual: cc

.EE

.SS Using Microsoft Visual C++ precompiled headers

Since windows.h includes everything and the kitchen sink, it can take quite
some time to compile it over and over again for a bunch of object files, so
Microsoft provides a mechanism to compile a set of headers once and then
include the previously compiled headers in any object file. This
technology is called precompiled headers. The general recipe is to create a
file named "StdAfx.cpp" that includes a single header named "StdAfx.h", and
then include every header you want to precompile in "StdAfx.h", and finally
include "StdAfx.h" as the first header in all the source files you are
compiling to object files. For example:

StdAfx.h:
.ES
#include <windows.h>
#include <my_big_header.h>
.EE

StdAfx.cpp:
.ES
#include <StdAfx.h>
.EE

Foo.cpp:
.ES
#include <StdAfx.h>

/* do some stuff */
.EE

Bar.cpp:
.ES
#include <StdAfx.h>

/* do some other stuff */
.EE

SConstruct:
.ES
env=Environment()
env['PCHSTOP'] = 'StdAfx.h'
env['PCH'] = env.PCH('StdAfx.cpp')[0]
env.Program('MyApp', ['Foo.cpp', 'Bar.cpp'])
.EE

For more information see the document for the PCH builder, and the PCH and
PCHSTOP construction variables. To learn about the details of precompiled
headers consult the MSDN documention for /Yc, /Yu, and /Yp.

.SS Using Microsoft Visual C++ external debugging information

Since including debugging information in programs and shared libraries can
cause their size to increase significantly, Microsoft provides a mechanism
for including the debugging information in an external file called a PDB
file. SCons supports PDB files through the PDB construction
variable.

SConstruct:
.ES
env=Environment()
env['PDB'] = 'MyApp.pdb'
env.Program('MyApp', ['Foo.cpp', 'Bar.cpp'])
.EE

For more information see the document for the PDB construction variable.

.SH ENVIRONMENT

.IP SCONS_LIB_DIR
Specifies the directory that contains the SCons Python module directory
(e.g. /home/aroach/scons-src-0.01/src/engine).

.IP SCONSFLAGS
A string of options that will be used by scons in addition to those passed
on the command line.

.SH "SEE ALSO"
.B scons
User Manual,
.B scons
Design Document,
.B scons
source code.

.SH AUTHORS
Steven Knight <knight@baldmt.com>
.br
Anthony Roach <aroach@electriceyeball.com>