path: root/doc/man/scons.1

.\" __COPYRIGHT__
.\"
.\" Permission is hereby granted, free of charge, to any person obtaining
.\" a copy of this software and associated documentation files (the
.\" "Software"), to deal in the Software without restriction, including
.\" without limitation the rights to use, copy, modify, merge, publish,
.\" distribute, sublicense, and/or sell copies of the Software, and to
.\" permit persons to whom the Software is furnished to do so, subject to
.\" the following conditions:
.\"
.\" The above copyright notice and this permission notice shall be included
.\" in all copies or substantial portions of the Software.
.\"
.\" THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY
.\" KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE
.\" WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
.\" NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
.\" LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
.\" OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
.\" WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
.\"
.\" __FILE__ __REVISION__ __DATE__ __DEVELOPER__
.\"
.\" ES - Example Start - indents and turns off line fill
.de ES
.RS
.nf
..
.\" EE - Example End - ends indent and turns line fill back on
.de EE
.RE
.fi
..
.TH SCONS 1 "February 2003"
.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
.B 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.

.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 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
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
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
Clean() 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

.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 WIN32 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 systems,
.B scons
searches for the MIPSPro compiler tools
and the GCC tool chain.
And 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 Clean() function.

.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 "-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
.RI --debug=pdb
Re-run SCons under the control of the
.RI pdb
Python debugger.
The
.RI --debug=pdb
argument will be stripped from the command-line,
but all other arguments will be passed in-order
to the SCons invocation run by the debugger.

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

.TP
.RI --debug=dtree
Print the dependency tree
after each top-level target is built. This prints out only derived files.

.TP
.RI --debug=time
Prints various time profiling information: the time spent
executing each build command, the total build time, the total time spent
executing build commands, the total time spent executing SConstruct and
SConscript files, and the total time spent executing SCons itself.

.TP
.RI --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
-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.

.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 can cause 
.B scons
to miss changes in the implicit dependencies in cases where a new implicit
dependency is added earlier in the implicit dependency search path
(e.g. CPPPATH) than a current implicit dependency with the same name.

.TP
--implicit-deps-changed
Force 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
.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 old a file must be before its content signature
is cached. 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 content
signature cached. 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 cache the signature, no matter how old the file is.

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

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

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

.TP
.RI --warn=deprecated ", " --warn=no-deprecated
Enables or disables warnings about use of deprecated features.
These warnings are enabled by default.

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

.\" .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
Search the specified repository for any input and target
files not found in the local directory hierarchy.  Multiple
.B -Y
options may 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

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 SYSTEMROOT
variable 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 Win32 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 specified as an optional keyword argument:

.ES
env = Environment(tools = ['msvc', 'lex'])
.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 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 on all platforms:
.ES
386asm
ar
dvipdf
dvips
g++
g77
gs
icc
ifl
ilink
gas
gcc
gnulink
jar
javac
latex
lex
linkloc
masm
mingw
mslib
mslink
msvc
nasm
pdflatex
pdftex
sgiar
sgias
sgicc
sgif77
sgilink
tar
tex
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 win32 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 target files)
and
.B source
(a list of source files).

Because long lists of file names
can lead to a lot of quoting,
.B scons
supplies a
.B Split()
function that splits a single string
into a list, separated on
strings of white-space characters.
(This is similar to the
string.split() method
from the standard Python library.)

Like all Python arguments,
the target and source arguments to a builder
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:

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

When the target shares the same base name
as the source and only the suffix varies,
and if the builder 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

It is possible to override or add construction variables when calling a
builder 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 nonstandard suffix:

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

All Builders return a Node or a list of Nodes,
representing the target or targets that will be built.
A list of Nodes is returned if there is more than one target,
and a single Node is returned if there is only one target.
A
.I Node
is an internal SCons object
which represents
build targets or sources.

The returned Node(s)
can be passed to other builder methods as source(s)
or passed into 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 = env.StaticObject('bar.c', CCFLAGS='-DBAR')
env.Program(source = ['foo.c', bar_obj, '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.

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 = env.StaticObject('bar.c', CCFLAGS='-DBAR')
print "The path to bar_obj is:", str(bar_obj)
.EE

.B scons
provides the following builders:

.IP StaticObject
Builds a static object file
from one or more C, C++, or Fortran source files.
Source files must have one of the following extensions:
.ES
  .asm    assembly language file
  .ASM    assembly language file
  .c      C file
  .C      WIN32:  C file
          POSIX:  C++ file
  .cc     C++ file
  .cpp    C++ file
  .cxx    C++ file
  .cxx    C++ file
  .c++    C++ file
  .C++    C++ file
  .f      Fortran file
  .F      WIN32:  Fortran file
          POSIX:  Fortran file + C pre-processor
  .for    Fortran file
  .FOR    Fortran file
  .fpp    Fortran file + C pre-processor
  .FPP    Fortran file + C pre-processor
  .s      assembly language file
  .S      WIN32:  assembly language file
          POSIX:  assembly language file + C pre-processor
  .spp    assembly language file + C pre-processor
  .SPP    assembly language file + C pre-processor
.EE
.IP
The target object file prefix
(specified by the $OBJPREFIX construction variable; nothing by default)
and suffix
(specified by the $OBJSUFFIX construction variable;
\.obj on Windows systems, .o on POSIX systems)
are automatically added to the target if not already present.
Examples:

.ES
env.StaticObject(target = 'aaa', source = 'aaa.c')
env.StaticObject(target = 'bbb.o', source = 'bbb.c++')
env.StaticObject(target = 'ccc.obj', source = 'ccc.f')
.EE
.IP SharedObject
Builds an object file for
inclusion in a shared library.
Source files must have one of the same set of extensions
specified above for the
.B StaticObject
builder. On some platforms building a shared object requires additional
compiler options (e.g. -fPIC for gcc) in addition to those needed to build a
normal (static) object, but on some platforms there is no difference between a
shared object and a normal (static) one. When there is a difference, SCons
will only allow shared objects to be linked into a shared library, and will
use a different suffix for shared objects. On platforms where there is no
difference, SCons will allow both normal (static)
and shared objects to be linked into a
shared library, and will use the same suffix for shared and normal
(static) objects.
The target object file prefix
(specified by the $SHOBJPREFIX construction variable;
by default, the same as $OBJPREFIX)
and suffix
(specified by the $SHOBJSUFFIX construction variable)
are automatically added to the target if not already present. 
Examples:

.ES
env.SharedObject(target = 'ddd', source = 'ddd.c')
env.SharedObject(target = 'eee.o', source = 'eee.cpp')
env.SharedObject(target = 'fff.obj', source = 'fff.for')
.EE

.IP Object
A synonym for the
.B StaticObject
builder.

.IP PCH
Builds a Microsoft Visual C++ precompiled header. Calling this builder
returns a list of two targets: the PCH as the first element, and the object
file as the second element. Normally the object file is ignored. This builder is only
provided when Microsoft Visual C++ is being used as the compiler. 
The PCH builder is generally used in
conjuction with the PCH construction variable to force object files to use
the precompiled header:

.ES
env['PCH'] = env.PCH('StdAfx.cpp')[0]
.EE

.IP Program
Builds an executable given one or more object files or C, C++
or Fortran source files.
If any C, C++ or Fortran source files are specified,
then they will be automatically
compiled to object files using the
.B Object
builder;
see that builder's description for
a list of legal source file suffixes
and how they are interpreted.
The target executable file prefix
(specified by the $PROGPREFIX construction variable; nothing by default)
and suffix
(specified by the $PROGSUFFIX construction variable;
by default, .exe on Windows systems, nothing on POSIX systems)
are automatically added to the target if not already present.
Example:

.ES
env.Program(target = 'foo', source = ['foo.o', 'bar.c', 'baz.f'])
.EE

.IP RES
Builds a Microsoft Visual C++ resource file.
This builder is only provided
when Microsoft Visual C++ or MinGW is being used as the compiler. The
.I .res
(or 
.I .o 
for MinGW) suffix is added to the target name if no other suffix is given. The source
file is scanned for implicit dependencies as though it were a C file. Example:

.ES
env.RES('resource.rc')
.EE

.IP StaticLibrary
Builds a static library given one or more object files
or C, C++ or Fortran source files.
If any source files are given,
then they will be automatically
compiled to object files.
The static library prefix and suffix (if any)
are automatically added to the target.
The target library file prefix
(specified by the $LIBPREFIX construction variable;
by default, lib on POSIX systems, nothing on Windows systems)
and suffix
(specified by the $LIBSUFFIX construction variable;
by default, .lib on Windows systems, .a on POSIX systems)
are automatically added to the target if not already present.
Example:

.ES
env.StaticLibrary(target = 'bar', source = ['bar.c', 'foo.o'])
.EE

.IP
Any object files listed in the
.B source
must have been built for a static library
(that is, using the
.B StaticObject
builder).
.B scons
will raise an error if there is any mismatch.

.IP SharedLibrary
Builds a shared library
(.so on a POSIX system, .dll on WIN32)
given one or more object files
or C, C++ or Fortran source files.
If any source files are given,
then they will be automatically
compiled to object files.
The static library prefix and suffix (if any)
are automatically added to the target.
The target library file prefix
(specified by the $SHLIBPREFIX construction variable;
by default, lib on POSIX systems, nothing on Windows systems)
and suffix
(specified by the $SHLIBSUFFIX construction variable;
by default, .dll on Windows systems, .so on POSIX systems)
are automatically added to the target if not already present.
Example:

.ES
env.SharedLibrary(target = 'bar', source = ['bar.c', 'foo.o'])
.EE
.IP
On WIN32 systems, the
.B SharedLibrary
builder will always build an import (.lib) library
in addition to the shared (.dll) library,
adding a .lib library with the same basename
if there is not already a .lib file explicitly
listed in the targets.

Any object files listed in the
.B source
must have been built for a shared library
(that is, using the
.B SharedObject
builder).
.B scons
will raise an error if there is any mismatch.

.IP Library
A synonym for the
.B StaticLibrary
builder.

.IP CFile
Builds a C source file given a lex (.l) or yacc (.y) input file.
The suffix specified by the $CFILESUFFIX construction variable
(.c by default)
is automatically added to the target
if it is not already present. Example:

.ES
# builds foo.c
env.CFile(target = 'foo.c', source = 'foo.l')
# builds bar.c
env.CFile(target = 'bar', source = 'bar.y')
.EE

.IP CXXFile
Builds a C++ source file given a lex (.ll) or yacc (.yy) input file.
The suffix specified by the $CXXFILESUFFIX construction variable
(.cc by default)
is automatically added to the target
if it is not already present. Example:

.ES
# builds foo.cc
env.CXXFile(target = 'foo.cc', source = 'foo.ll')
# builds bar.cc
env.CXXFile(target = 'bar', source = 'bar.yy')
.EE

.IP Jar
Builds a Java archive (.jar) file
from a source tree of .class files.
.ES
env.Jar(target = 'foo.jar', source = 'classes')
.EE

.IP Java
Builds one or more Java class files
from a source tree of .java files.
The class files will be placed underneath
the specified target directory.
SCons assumes that each .java file
contains a single public class
with the same name as the basename of the file;
that is, the file
.I Foo.java
contains a single public class named
.IR Foo .
SCons will search each Java file
for the Java package name,
which it assumes can be found on a line
beginning with the string
.B package
in the first column.
The resulting .class file
will be placed in a directory reflecting
the specified package name;
that is,
the file
.I Foo.java
with a package name of
.I sub.dir
will generate a corresponding
.IR sub/dir/Foo.class
class file.

Example:

.ES
env.Java(target = 'classes', source = 'src')
.EE

.IP DVI
Builds a .dvi file from a .tex, .ltx or .latex input file.
The suffix .dvi
(hard-coded within TeX itself)
is automatically added to the target
if it is not already present. Example:

.ES
# builds from aaa.tex
env.DVI(target = 'aaa.dvi', source = 'aaa.tex')
# builds bbb.dvi
env.DVI(target = 'bbb', source = 'bbb.ltx')
# builds from ccc.latex
env.DVI(target = 'ccc.dvi', source = 'ccc.latex')
.EE

.IP PDF
Builds a .pdf file from a .dvi input file
(or, by extension, a .tex, .ltx, or .latex input file).
The suffix specified by the $PDFSUFFIX construction variable
(.pdf by default)
is added automatically to the target
if it is not already present.  Example:

.ES
# builds from aaa.tex
env.PDF(target = 'aaa.pdf', source = 'aaa.tex')
# builds bbb.pdf from bbb.dvi
env.PDF(target = 'bbb', source = 'bbb.dvi')
.EE

.IP PostScript
Builds a .ps file from a .dvi input file
(or, by extension, a .tex, .ltx, or .latex input file).
The suffix specified by the $PSSUFFIX construction variable
(.ps by default)
is added automatically to the target
if it is not already present.  Example:

.ES
# builds from aaa.tex
env.PostScript(target = 'aaa.ps', source = 'aaa.tex')
# builds bbb.ps from bbb.dvi
env.PostScript(target = 'bbb', source = 'bbb.dvi')
.EE
.LP
.B scons
automatically scans
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,
so the dependencies do not need to be specified explicitly.
In addition, all builder
targets automatically depend on their sources.
An explicit dependency can
be specified using the 
.B Depends 
method of a construction environment (see below).

.IP Tar
Builds a tar archive of the specified files
and/or directories.
Unlike most builders,
the
.B Tar
builder may be called multiple times
for a given target;
each additional call
adds to the list of entries
that will be built into the archive.

.ES
env.Tar('src.tar', 'src')

# Create the stuff.tar file.
env.Tar('stuff', ['subdir1', 'subdir2'])
# Also add "another" to the stuff.tar file.
env.Tar('stuff', 'another')

# Set TARFLAGS to create a gzip-filtered archive.
env = Environment(TARFLAGS = '-c -z')
env.Tar('foo.tar.gz', 'foo')

# Also set the suffix to .tgz.
env = Environment(TARFLAGS = '-c -z',
                  TARSUFFIX = '.tgz')
env.Tar('foo')
.EE

.IP Zip
Builds a zip archive of the specified files
and/or directories.
Unlike most builders,
the
.B Zip
builder may be called multiple times
for a given target;
each additional call
adds to the list of entries
that will be built into the archive.

.ES
env.Zip('src.zip', 'src')

# Create the stuff.zip file.
env.Zip('stuff', ['subdir1', 'subdir2'])
# Also add "another" to the stuff.tar file.
env.Zip('stuff', 'another')
.EE

.SS Other Construction Environment Methods
Additional construction environment methods include:

.TP
.RI Alias( alias ", " targets )
Creates a phony target that
expands to one or more other targets.
Returns the Node object representing the alias,
which exists outside of any file system.
This Node object, or the alias name,
may be used as a dependency of any other target,
including another alias. Alias can be called multiple times for the same
alias to add additional targets to the alias.

.ES
env.Alias('install', ['/usr/local/bin', '/usr/local/lib'])
env.Alias('install', ['/usr/local/man'])
.EE

.TP
.RI 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.)

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

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

.TP
.RI Command( target ", " source ", " commands )
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.

Note that an action can be an external command,
specified as a string,
or a callable Python object;
see "Action Objects," below.
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"])

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

.TP
.RI Copy([ 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.

.ES
env2 = env.Copy()
env3 = env.Copy(CCFLAGS = '-g')
.EE

.TP
.RI 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:

.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 Depends( target ", " dependency )
Specifies an explicit dependency;
the target file(s) will be rebuilt
whenever the dependency file(s) has changed.
This should only be necessary
for cases where the dependency
is not caught by a Scanner
for the file.

.ES
env.Depends('foo', 'other-input-file-for-foo')
.EE

.TP
.RI 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.

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

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

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

.TP
.RI Install( dir ", " source )
Installs one or more files in a destination directory.
The file names remain the same.

.ES
env.Install(dir = '/usr/local/bin', source = ['foo', 'bar'])
.EE

.TP
.RI InstallAs( target ", " source )
Installs one or more files as specific file names,
allowing changing a file name as part of the
installation.
It is an error if the target and source
list different numbers of files.

.ES
env.InstallAs(target = '/usr/local/bin/foo',
              source = 'foo_debug')
env.InstallAs(target = ['../lib/libfoo.a', '../lib/libbar.a'],
              source = ['libFOO.a', 'libBAR.a'])
.EE

.TP
.RI 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:
.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 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 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.)

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

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

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

.TP
.RI 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:
.ES
env.SourceCode('.', env.SCCS())
.EE
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 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 that is created
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.
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.

.TP
.RI 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

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 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:
'\"
'\".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

.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 construction
variables that are used by built-in or user-supplied build rules. 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:

.IP AR
The static library archiver.

.IP ARCOM
The command line used to generate a static library from object files.

.IP ARFLAGS
General options passed to the static library archiver.

.IP AS
The assembler.

.IP ASCOM
The command line used to generate an object file
from an assembly-language source file.

.IP ASFLAGS
General options passed to the assembler.

.IP ASPPCOM
The command line used to assemble an assembly-language
source file into an object file
after first running the file through the C preprocessor.
Any options specified in the $ASFLAGS and $CPPFLAGS construction variables
are included on this command line.

.IP BITKEEPER
The BitKeeper executable.

.IP BITKEEPERCOM
The command line for
fetching source files using BitKEeper.

.IP BITKEEPERGET
The command ($BITKEEPER) and subcommand
for fetching source files using BitKeeper.

.IP BITKEEPERGETFLAGS
Options that are passed to the BitKeeper
.B get
subcommand.

.IP BUILDERS
A dictionary mapping the names of the builders
available through this environment
to underlying Builder objects.
Builders named
Alias, CFile, CXXFile, DVI, Library, Object, PDF, PostScript, and Program
are available by default.
If you initialize this variable when an
Environment is created:
.ES
env = Environment(BUILDERS = {'NewBuilder' : foo})
.EE
the default Builders will no longer be available.
To use a new Builder object in addition to the default Builders,
add your new Builder object like this:
.ES
env = Environment()
env.Append(BUILDERS = {'NewBuilder' : foo})
.EE
or this:
.ES
env = Environment()
env['BUILDERS]['NewBuilder'] = foo
.EE

.IP CC 
The C compiler.

.IP CCCOM 
The command line used to compile a C source file to a (static) object file.
Any options specified in the $CCFLAGS and $CPPFLAGS construction variables
are included on this command line.

.IP CCFLAGS 
General options that are passed to the C compiler.

.IP CFILESUFFIX
The suffix for C source files.
This is used by the internal CFile builder
when generating C files from Lex (.l) or YACC (.y) input files.
The default suffix, of course, is
.I .c
(lower case).
On case-insensitive systems (like Win32),
SCons also treats
.I .C
(upper case) files
as C files.

.IP _concat
A function used to produce variables like $_CPPINCFLAGS. It takes six
arguments: a prefix to concatenate onto each element, a list of elements, a
suffix to concatenate onto each element, a dictionary of global variables
for variable interpolation, a list of local variables for variable
interpolation, and an optional function that will be called to transform the list
before concatenation.

.ES
env['_CPPINCFLAGS'] = '$( ${_concat(INCPREFIX, CPPPATH, INCSUFFIX, locals(), globals(), RDirs)} $)',
.EE

.IP CPPFLAGS
C preprocessor options.
These will be included in any command that uses the C preprocessor,
including not just compilation of C and C++ source files
via the $CCCOM, $SHCCCOM, $CXXCOM and $SHCXXCOM command lines,
but also the $F77PPCOM command line
used to compile a Fortran source file,
and the $ASPPCOM command line
used to assemble an assembly language source file,
after first running each file through the C preprocessor.

.IP _CPPINCFLAGS
An automatically-generated construction variable
containing the C preprocessor command-line options
for specifying directories to be searched for include files.
The value of $_CPPINCFLAGS is created
by appending $INCPREFIX and $INCSUFFIX
to the beginning and end
of each directory in $CPPPATH.

.IP CPPPATH
The list of directories that the C preprocessor will search for include
directories. The C/C++ implicit dependency scanner will search these
directories for include files. Don't explicitly put include directory
arguments in CCFLAGS or CXXFLAGS because the result will be non-portable
and the directories will not be searched by the dependency scanner. Note:
directory names in CPPPATH will be looked-up relative to the SConscript
directory when they are used in a command. To force 
.B scons
to look-up a directory relative to the root of the source tree use #:

.ES
env = Environment(CPPPATH='#/include')
.EE

.IP
The directory look-up can also be forced using the 
.BR Dir ()
function:

.ES
include = Dir('include')
env = Environment(CPPPATH=include)
.EE

.IP
The directory list will be added to command lines
through the automatically-generated
$_CPPINCFLAGS
construction variable,
which is constructed by
appending the values of the
$INCPREFIX and $INCSUFFIX
construction variables
to the beginning and end
of each directory in $CPPPATH.
Any command lines you define that need
the CPPPATH directory list should
include $_CPPINCFLAGS:

.ES
env = Environment(CCCOM="my_compiler $_CPPINCFLAGS -c -o $TARGET $SOURCE")
.EE

.IP CVS
The CVS executable.

.IP CVSCOFLAGS
Options that are passed to the CVS checkout subcommand.

.IP CVSCOM
The command line used to
fetch source files from a CVS repository.

.IP CVSFLAGS
General options that are passed to CVS.
By default, this is set to
"-d $CVSREPOSITORY"
to specify from where the files must be fetched.

.IP CVSREPOSITORY
The path to the CVS repository.
This is referenced in the default
$CVSFLAGS value.

.IP CXX
The C++ compiler.

.IP CXXFILESUFFIX
The suffix for C++ source files.
This is used by the internal CXXFile builder
when generating C++ files from Lex (.ll) or YACC (.yy) input files.
The default suffix is
.IR .cc .
SCons also treats files with the suffixes
.IR .cpp ,
.IR .cxx ,
.IR .c++ ,
and
.I .C++
as C++ files.
On case-sensitive systems (Linux, UNIX, and other POSIX-alikes),
SCons also treats
.I .C
(upper case) files
as C++ files.

.IP CXXCOM
The command line used to compile a C++ source file to an object file.
Any options specified in the $CXXFLAGS and $CPPFLAGS construction variables
are included on this command line.

.IP CXXFLAGS 
General options that are passed to the C++ compiler.

.IP Dir
A function that converts a file name into a Dir instance relative to the
target being built. 

.IP DVIPDF
The TeX DVI file to PDF file converter.

.IP DVIPDFFLAGS
General options passed to the TeX DVI file to PDF file converter.

.IP DVIPDFCOM
The command line used to convert TeX DVI files into a PDF file.

.IP DVIPS
The TeX DVI file to PostScript converter.

.IP DVIPSFLAGS
General options passed to the TeX DVI file to PostScript converter.

.IP ENV
A dictionary of environment variables
to use when invoking commands.
Note that, by default,
.B scons
does
.I not
propagate the environment in force when you
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.

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

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

.RS
Note that you can choose only to propagate
certain environment variables.
A common example is
the system
.B PATH
environment variable,
so that
.B scons
uses the same utilities
as the invoking shell (or other process):
.RE

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

.IP ESCAPE
A function that will be called to escape shell special characters in
command lines. The function should take one argument: the command line
string to escape; and should return the escaped command line.

.IP F77
The Fortran compiler.

.IP F77COM 
The command line used to compile a Fortran source file to an object file.

.IP F77FLAGS
General options that are passed to the Fortran compiler.

.IP _F77INCFLAGS
An automatically-generated construction variable
containing the Fortran compiler command-line options
for specifying directories to be searched for include files.
The value of $_F77INCFLAGS is created
by appending $INCPREFIX and $INCSUFFIX
to the beginning and end
of each directory in $F77PATH.

.IP F77PATH
The list of directories that the Fortran compiler will search for include
directories. The Fortran implicit dependency scanner will search these
directories for include files. Don't explicitly put include directory
arguments in F77FLAGS because the result will be non-portable
and the directories will not be searched by the dependency scanner. Note:
directory names in F77PATH will be looked-up relative to the SConscript
directory when they are used in a command. To force 
.B scons
to look-up a directory relative to the root of the source tree use #:

.ES
env = Environment(F77PATH='#/include')
.EE

.IP
The directory look-up can also be forced using the 
.BR Dir ()
function:

.ES
include = Dir('include')
env = Environment(F77PATH=include)
.EE

.IP
The directory list will be added to command lines
through the automatically-generated
$_F77INCFLAGS
construction variable,
which is constructed by
appending the values of the
$INCPREFIX and $INCSUFFIX
construction variables
to the beginning and end
of each directory in $F77PATH.
Any command lines you define that need
the F77PATH directory list should
include $_F77INCFLAGS:

.ES
env = Environment(F77COM="my_compiler $_F77INCFLAGS -c -o $TARGET $SOURCE")
.EE

.IP F77PPCOM 
The command line used to compile a Fortran source file to an object file
after first running the file through the C preprocessor.
Any options specified in the $F77FLAGS and $CPPFLAGS construction variables
are included on this command line.

.IP File
A function that converts a file name into a File instance relative to the
target being built. 

.IP GS
The Ghostscript program used to convert PostScript to PDF files.

.IP GSFLAGS
General options passed to the Ghostscript program
when converting PostScript to PDF files.

.IP GSCOM
The Ghostscript command line used to convert PostScript to PDF files.

.IP INCPREFIX
The prefix used to specify an include directory on the C compiler command
line.
This will be appended to the beginning of each directory
in the $CPPPATH and $F77PATH construction variables
when the $_CPPINCFLAGS and $_F77INCFLAGS
variables are automatically generated.

.IP INCSUFFIX
The suffix used to specify an include directory on the C compiler command
line.
This will be appended to the end of each directory
in the $CPPPATH and $F77PATH construction variables
when the $_CPPINCFLAGS and $_F77INCFLAGS
variables are automatically generated.

.IP INSTALL
A function to be called to install a file into a
destination file name.
The default function copies the file into the destination
(and sets the destination file's mode and permission bits
to match the source file's).
The function takes the following arguments:

.ES
def install(dest, source, env):
.EE
.IP
.I dest
is the path name of the destination file.
.I source
is the path name of the source file.
.I env
is the construction environment
(a dictionary of construction values)
in force for this file installation.

.IP JAR
The Java archive tool.

.IP JARCOM
The command line used to call the Java archive tool.

.IP JARFLAGS
General options passed to the Java archive tool.
By default this is set to
.B cf
to create the necessary
.I jar
file.

.IP JARSUFFIX
The suffix for Java archives:
.B .jar
by default.

.IP JAVAC
The Java compiler.

.IP JAVACCOM
The command line used to compile a directory tree containing
Java source files to
corresponding Java class files.
Any options specified in the $JAVACFLAGS construction variable
are included on this command line.

.IP JAVACFLAGS
General options that are passed to the Java compiler.

.IP JAVACLASSSUFFIX
The suffix for Java class files;
.B .class
by default.

.IP JAVASUFFIX
The suffix for Java files;
.B .java
by default.

.IP LATEX
The LaTeX structured formatter and typesetter.

.IP LATEXCOM
The command line used to call the LaTeX structured formatter and typesetter.

.IP LATEXFLAGS
General options passed to the LaTeX structured formatter and typesetter.

.IP LEX
The lexical analyzer generator.

.IP LEXFLAGS
General options passed to the lexical analyzer generator.

.IP LEXCOM
The command line used to call the lexical analyzer generator
to generate a source file.

.IP _LIBDIRFLAGS
An automatically-generated construction variable
containing the linker command-line options
for specifying directories to be searched for library.
The value of $_LIBDIRFLAGS is created
by appending $LIBDIRPREFIX and $LIBDIRSUFFIX
to the beginning and end
of each directory in $LIBPATH.

.IP LIBDIRPREFIX
The prefix used to specify a library directory on the linker command line.
This will be appended to the beginning of each directory
in the $LIBPATH construction variable
when the $_LIBDIRFLAGS variable is automatically generated.

.IP LIBDIRSUFFIX
The suffix used to specify a library directory on the linker command line.
This will be appended to the end of each directory
in the $LIBPATH construction variable
when the $_LIBDIRFLAGS variable is automatically generated.

.IP _LIBFLAGS
An automatically-generated construction variable
containing the linker command-line options
for specifying libraries to be linked with the resulting target.
The value of $_LIBFLAGS is created
by appending $LIBLINKPREFIX and $LIBLINKSUFFIX
to the beginning and end
of each directory in $LIBS.

.IP LIBLINKPREFIX
The prefix used to specify a library to link on the linker command line.
This will be appended to the beginning of each library
in the $LIBS construction variable
when the $_LIBFLAGS variable is automatically generated.

.IP LIBLINKSUFFIX
The suffix used to specify a library to link on the linker command line.
This will be appended to the end of each library
in the $LIBS construction variable
when the $_LIBFLAGS variable is automatically generated.

.IP LIBPATH
The list of directories that will be searched for libraries.
The implicit dependency scanner will search these
directories for include files. Don't explicitly put include directory
arguments in LINKFLAGS because the result will be non-portable
and the directories will not be searched by the dependency scanner. Note:
directory names in LIBPATH will be looked-up relative to the SConscript
directory when they are used in a command. To force 
.B scons
to look-up a directory relative to the root of the source tree use #:

.ES
env = Environment(LIBPATH='#/libs')
.EE

.IP
The directory look-up can also be forced using the 
.BR Dir ()
function:

.ES
libs = Dir('libs')
env = Environment(LIBPATH=libs)
.EE

.IP
The directory list will be added to command lines
through the automatically-generated
$_LIBDIRFLAGS
construction variable,
which is constructed by
appending the values of the
$LIBDIRPREFIX and $LIBDIRSUFFIX
construction variables
to the beginning and end
of each directory in $LIBPATH.
Any command lines you define that need
the LIBPATH directory list should
include $_LIBDIRFLAGS:

.ES
env = Environment(LINKCOM="my_linker $_LIBDIRFLAGS $_LIBFLAGS -o $TARGET $SOURCE")
.EE

.IP LIBPREFIX
The prefix used for (static) library file names.

.IP LIBPREFIXES
An array of legal prefixes for library file names.

.IP LIBS
A list of one or more libraries
that will be linked with
any executable programs
created by this environment.

.IP
The library list will be added to command lines
through the automatically-generated
$_LIBFLAGS
construction variable,
which is constructed by
appending the values of the
$LIBLINKPREFIX and $LIBLINKSUFFIX
construction variables
to the beginning and end
of each directory in $LIBS.
Any command lines you define that need
the LIBS library list should
include $_LIBFLAGS:

.ES
env = Environment(LINKCOM="my_linker $_LIBDIRFLAGS $_LIBFLAGS -o $TARGET $SOURCE")
.EE

.IP LIBSUFFIX 
The suffix used for (static) library file names.

.IP LIBSUFFIXES
An array of legal suffixes for library file names.

.IP LINK
The linker.

.IP LINKFLAGS
General options passed to the linker.

.IP LINKCOM
The command line used to link object files into an executable.

.IP OBJPREFIX 
The prefix used for (static) object file names.

.IP OBJSUFFIX 
The suffix used for (static) object file names.

.IP P4
The Perforce executable.

.IP P4COM
The command line used to
fetch source files from Perforce.

.IP P4FLAGS
General options that are passed to Perforce.

.IP PCH
The Microsoft Visual C++ precompiled header that will be used when compiling
object files. This variable is ignored by tools other than Microsoft Visual C++.
When this variable is
defined SCons will add options to the compiler command line to
cause it to use the precompiled header, and will also set up the
dependencies for the PCH file. Example: 

.ES
env['PCH'] = 'StdAfx.pch'
.EE

.IP PCHSTOP
This variable specifies how much of a source file is precompiled. This
variable is ignored by tools other than Microsoft Visual C++, or when
the PCH variable is not being used. When this variable is define it
must be a string that is the name of the header that
is included at the end of the precompiled portion of the source files, or
the empty string if the "#pragma hrdstop" construct is being used:

.ES
env['PCHSTOP'] = 'StdAfx.h'
.EE

.IP PDB
The Microsoft Visual C++ PDB file that will store debugging information for
object files, shared libraries, and programs. This variable is ignored by
tools other than Microsoft Visual C++.
When this variable is
defined SCons will add options to the compiler and linker command line to
cause them to generate external debugging information, and will also set up the
dependencies for the PDB file. Example:

.ES
env['PDB'] = 'hello.pdb'
.EE

.IP PDFCOM
A deprecated synonym for $DVIPDFCOM.

.IP PDFPREFIX
The prefix used for PDF file names.

.IP PDFSUFFIX
The suffix used for PDF file names.

.IP PLATFORM
The name of the platform used to create the Environment.  If no platform is
specified when the Environment is created,
.B SCons
autodetects the platform.

.ES
env = Environment(tools = [])
if env['PLATFORM'] == 'cygwin':
    Tool('mingw')(env)
else:
    Tool('msvc')(env)
.EE

.IP PROGPREFIX
The prefix used for executable file names.

.IP PROGSUFFIX
The suffix used for executable file names.

.IP PSCOM
The command line used to convert TeX DVI files into a PostScript file.

.IP PSPREFIX
The prefix used for PostScript file names.

.IP PSSUFFIX
The prefix used for PostScript file names.

.IP RANLIB
The archive indexer.

.IP RANLIBFLAGS
General options passed to the archive indexer.

.IP RC
The resource compiler used by the RES builder.

.IP RCCOM
The command line used by the RES builder.

.IP RCFLAGS
The flags passed to the resource compiler by the RES builder.

.IP RCS
The RCS executable.
Note that this variable is not actually used
for the command to fetch source files from RCS;
see the
.B RCS_CO
construction variable, below.

.IP RCS_CO 
The RCS "checkout" executable,
used to fetch source files from RCS.

.IP RCS_COCOM
The command line used to
fetch (checkout) source files from RCS.

.IP RCS_COFLAGS
Options that are passed to the $RCS_CO command.

.IP RDirs
A function that converts a file name into a list of Dir instances by
searching the repositories. 

.IP SCANNERS
A list of the available implicit dependency scanners. [CScan] by default.

.IP SCCS
The SCCS executable.

.IP SCCSCOM
The command line used to
fetch source files from SCCS.

.IP SCCSFLAGS
General options that are passed to SCCS.

.IP SCCSGETFLAGS
Options that are passed specifically to the SCCS "get" subcommand.
This can be set, for example, to
.I -e
to check out editable files from SCCS.

.IP SHCC
The C compiler used for generating shared-library objects.

.IP SHCCCOM
The command line used to compile a C source file
to a shared-library object file.
Any options specified in the $SHCCFLAGS and $CPPFLAGS construction variables
are included on this command line.

.IP SHCCFLAGS
Options that are passed to the C compiler
to generate shared-library objects.

.IP SHCXX
The C++ compiler used for generating shared-library objects.

.IP SHCXXCOM
The command line used to compile a C++ source file
to a shared-library object file.
Any options specified in the $SHCXXFLAGS and $CPPFLAGS construction variables
are included on this command line.

.IP SHCXXFLAGS
Options that are passed to the C++ compiler
to generate shared-library objects.

.IP SHELL
A string naming the shell program that will be passed to the 
.I SPAWN 
function. 
See the 
.I SPAWN 
construction variable for more information.

.IP SHF77
The Fortran compiler used for generating shared-library objects.

.IP SHF77COM
The command line used to compile a Fortran source file
to a shared-library object file.

.IP SHF77FLAGS
Options that are passed to the Fortran compiler
to generated shared-library objects.

.IP SHF77PPCOM
The command line used to compile a Fortran source file to a
shared-library object file
after first running the file through the C preprocessor.
Any options specified in the $SHF77FLAGS and $CPPFLAGS construction variables
are included on this command line.

.IP SHLIBPREFIX
The prefix used for shared library file names.

.IP SHLIBSUFFIX
The suffix used for shared library file names.

.IP SHLINK
The linker for programs that use shared libraries.

.IP SHLINKFLAGS
General options passed to the linker for programs using shared libraries.

.IP SHOBJPREFIX 
The prefix used for shared object file names.

.IP SHOBJSUFFIX 
The suffix used for shared object file names.

.IP SOURCE
A reserved variable name
that may not be set or used in a construction environment.
(See "Variable Substitution," below.)

.IP SOURCES
A reserved variable name
that may not be set or used in a construction environment.
(See "Variable Substitution," below.)

.IP SPAWN
A command interpreter function that will be called to execute command line
strings. The function must expect 4 arguments:

.ES
def spawn(shell, escape, cmd, args, env):
.EE
.IP
.I sh
is a string naming the shell program to use.
.I escape
is a function that can be called to escape shell special characters in
the command line. 
.I cmd
is the path to the command to be executed.
.I args
is that arguments to the command.
.I env
is a dictionary of the environment variables
in which the command should be executed.
'\"
'\".IP SVN
'\"The Subversion executable (usually named
'\".BR svn ).
'\"
'\".IP SVNCOM
'\"The command line used to
'\"fetch source files from a Subversion repository.
'\"
'\".IP SVNFLAGS
'\"General options that are passed to Subversion.

.IP TAR
The tar archiver.

.IP TARCOM
The command line used to call the tar archiver.

.IP TARFLAGS
General options passed to the tar archiver.

.IP TARGET
A reserved variable name
that may not be set or used in a construction environment.
(See "Variable Substitution," below.)

.IP TARGETS
A reserved variable name
that may not be set or used in a construction environment.
(See "Variable Substitution," below.)

.IP TARSUFFIX 
The suffix used for tar file names.

.IP TEX
The TeX formatter and typesetter.

.IP TEXCOM
The command line used to call the TeX formatter and typesetter.

.IP TEXFLAGS
General options passed to the TeX formatter and typesetter.

.IP WIN32_INSERT_DEF
When this is set to true,
a library build of a WIN32 shared library (.dll file)
will also build a corresponding .def file at the same time,
if a .def file is not already listed as a build target.
The default is 0 (do not build a .def file).

.IP WIN32DEFPREFIX
The prefix used for WIN32 .def file names.

.IP WIN32DEFSUFFIX
The suffix used for WIN32 .def file names.

.IP YACC
The parser generator.

.IP YACCCOM
The command line used to call the parser generator
to generate a source file.

.IP YACCFLAGS
General options passed to the parser generator.

.IP ZIP
The zip compression and file packaging utility.

.IP ZIPCOM
The command line used to call the zip utility.

.IP ZIPFLAGS
General options passed to the zip utility.

.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 Copy 
method:

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

.SS Construction Variable Options

Often when building software, various options need to be specified at build
time that are not known when the SConstruct/SConscript files are
written. 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 mechanism for overridding construction variables from the
command line or a text-based SConscript file through an Options
object. To create an Options object, call the Options() function:

.TP
.RI Options([ files ])
This creates an Options object that will read construction variables from
the file or list of filenames given in the  
.I files
argument. If no files are given, then no files will be read. Example:

.ES
opts = Options('custom.py')
.EE

Options objects have the following methods:

.TP
.RI Add( key ", [" help ", " default ", " validater ", " converter ])
This adds a customizable construction variable to the Options 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.
.I validater
is called to validate the value of the variable, and should take three
arguments: key, value, and environment
.I converter
is called to convert the value before putting it in the environment, and
should take a single argument: value. Example:

.ES
opts.Add('CC', 'The C compiler')
.EE

.TP
.RI Update( env )
This updates a construction environment
.I env
with the customized construction variables. Normally this method is not
called directly, but is called indirectly by passing the Options object to
the Environment() function:

.ES
env = Environment(options=opts)
.EE

.TP
.RI Save( filename ", " env )
This saves the currently set options 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 Options method can be used to
support caching of options between runs.

.ES
env = Environment()
opts = Options(['options.cache', 'custom.py'])
opts.Add(...)
opts.Update(env)
opts.Save('options.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(opts.GenerateHelpText(env))
Help(opts.GenerateHelpText(env, sort=cmp))
.EE

The text based SConscript file is executed as a Python script, and the
global variables are queried for customizable construction
variables. Example:

.ES
CC = 'my_cc'
.EE

.SS Other Functions

.B scons
also provides various additional functions,
not associated with a construction environment,
that SConscript files can use:

.TP 
.RI 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).

.TP 
.RI 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).

.TP
.RI BuildDir( build_dir ", " src_dir ", [" duplicate ])
This specifies a build directory
.I build_dir
in which to build all derived files
that would normally be built under
.IR src_dir .
Multiple build directories can be set up for multiple build variants, for
example. 
.I src_dir
must be underneath the SConstruct file's directory,
and
.I build_dir
may not be underneath the
.I src_dir .

The default behavior is for
.B scons
to duplicate all of the files in the tree underneath
.I src_dir
into
.IR build_dir ,
and then build the derived files within the copied tree.
(The duplication is performed by
linking or copying,
depending on the platform.)
This guarantees correct builds
regardless of whether intermediate source files
are generated during the build,
where preprocessors or other scanners search
for included files,
or whether individual compilers or other invoked tools
are hard-coded to put derived files in the same directory as source files.

This behavior of making a complete copy of the source tree
may be disabled by setting
.I duplicate
to 0.
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 build_dir .
This is always more efficient than
.IR duplicate =1,
and is usually safe for most builds.
Specifying
.IR duplicate =0,
however,
may cause build problems
if source files are generated during the build,
if any invoked tools are hard-coded to
put derived files in the same directory as the source files.

Note that specifying a
.B BuildDir
works most naturally
with a subsidiary SConscript file
in the source directory.
However,
you would then call the subsidiary SConscript file
not in the source directory,
but in the
.I build_dir ,
as if
.B scons
had made a virtual copy of the source tree
regardless of the value of 
.IR duplicate .
This is how you tell
.B scons
which variant of a source tree to build.
For example:

.ES
BuildDir('build-variant1', 'src')
SConscript('build-variant1/SConscript')
BuildDir('build-variant2', 'src')
SConscript('build-variant2/SConscript')
.EE

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

.TP 
.RI 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).

.TP 
.RI 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.

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.

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

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:

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

.TP 
.RI 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')
Default(['a', 'b', 'c'])
hello = env.Program('hello', 'hello.c')
Default(hello)
.EE

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.

.TP
.RI Dir( name ", [" directory ])
This returns an object that represents a given 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. 

.TP
.RI 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.

.ES
EnsurePythonVersion(2,2)
.EE

.TP
.RI EnsureSConsVersion( major ", " minor )
Ensure that the SCons 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 SCons version is not late enough.

.ES
EnsureSConsVersion(0,9)
.EE

.TP
.RI 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 )
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 should be passed to
.BR Export ()
as separate arguments. 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 to Import().
Export("env", "package")
.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 ])
This returns an object that represents a given 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. 

.TP
.RI FindFile( file ", " dirs )
Search for 
.I file 
in the path specified by 
.IR dirs .
.I file
may be a list of file names or a single file 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.

.ES
foo = FindFile('foo', ['dir1', 'dir2'])
.EE
.\"
.\".TP
.\".RI GetBuildPath( XXX )
.\"XXX
.\"
.\".TP
.\".RI GetLaunchDir( XXX )
.\"XXX

.TP
.RI GetJobs()
Get the number of jobs (commands) that will be run simultaneously. See also 
.I -j
and
.IR SetJobs() .

.TP
.RI Help( text )
This specifies help text to be printed if the 
.B -h 
argument is given to
.BR scons .
.B scons
will exit after printing out the help text.

.TP 
.RI 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 should be passed to 
.BR Import ()
as separate arguments.
Examples:

.ES
Import("env")
Import("env", "variable")
.EE

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

.TP
.RI 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.

.TP
.RI ParseConfig( env , command ", [" function ])
Calls the specified
.I function
to modify the specified environment
.I env
as specified by the output of
.I command .
The default
.I function
expects the output of a typical
.I *-config command
(for example,
.BR gtk-config )
and parses the returned
.BR -L ,
.BR -l ,
.B -I
and other options
into the
.BR LIBPATH ,
.BR LIBS ,
.B CPPPATH
and
.B CCFLAGS
variables,
respectively.

.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.

.ES
env = Environment(platform = Platform('win32'))
.EE
.IP
Note that the
.B win32
platform adds the
.B SYSTEMROOT
variable 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 Win32 systems.

.TP
.RI 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 Return( vars )
This tells
.B scons
what variable(s) to use as the return value(s) of the current SConscript
file. These variables will be returned to the "calling" SConscript file
as the return value(s) of 
.BR SConscript ().
Multiple variable names should be passed to 
.BR Return ()
as a list. Example:

.ES
Return("foo")
Return(["foo", "bar"])
.EE

.TP
.RI SConscript( script ", [" exports ", " build_dir ", " src_dir ", " duplicate ])
This tells
.B scons
to execute
.I script
as a SConscript (configuration) file.

The optional 
.I exports
argument provides a list of variable names to export to
.IR script ". "
These variables are locally exported only to the specified
.IR script ,
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
file must use the
.BR Import ()
function to import the variables.

The optional
.I build_dir
argument specifies that all of the target files
(for example, object files and executables)
that would normally be built in the subdirectory in which
.I script
resides should actually
be built in
.IR build_dir .
The optional
.I src_dir
argument specifies that the
source files from which
the target files should be built
can be found in
.IR src_dir .
By default,
.B scons
will link or copy (depending on the platform)
all the source files into the build directory.
This behavior may be disabled by
setting the optional
.I duplicate
argument to 0
(it is set to 1 by default),
in which case
.B scons
will refer directly to
the source files in their source directory
when building target files.
(Setting
.IR duplicate =0
is usually safe, and always more efficient
than the default of
.IR duplicate =1,
but it may cause build problems in certain end-cases,
such as compiling from source files that
are generated by the build.)

Any variables returned by 
.I script 
using 
.BR Return ()
will be returned by the call to
.BR SConscript (). 

Examples:

.ES
SConscript('subdir/SConscript')
foo = SConscript('sub/SConscript', exports='env')
SConscript('dir/SConscript', exports=['env', 'variable'])
SConscript('src/SConscript', build_dir='build', duplicate=0)
SConscript('bld/SConscript', src_dir='src', exports='env')
.EE

.TP
.RI 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:
.ES
SConscriptChdir(0)
.EE
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:

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

.TP 
.RI SetBuildSignatureType( type )

This function tells SCons what type of build signature to use: "build" or
"content". "build" means to concatenate the signatures of all source files
of a derived file to make its signature, and "content" means to use
the derived files content signature as its signature. "build" signatures
are usually faster to compute, but "content" signatures can prevent
redundant rebuilds. The default is "build".

.TP
.RI SetContentSignatureType( type )

This function tells SCons what type of content signature to use: "MD5" or
"timestamp". "MD5" means to use the MD5 checksum of a files contents as
its signature, and "timestamp" means to use a files timestamp as its
signature. When using "timestamp" signatures, changes in the
command line will not cause files to be rebuilt. "MD5" signatures take
longer to compute, but "timestamp" signatures are less accurate. The
default is "MD5".

.TP
.RI SetJobs( num )
Specifies the number of jobs (commands) to run simultaneously. 
.I -j
overrides this function. See also 
.I -j
and 
.IR GetJobs() .

.TP
.RI 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.

.ES
files = Split("f1.c f2.c f3.c")
files = Split("""
	f4.c
	f5.c
	f6.c
""")
.EE

.TP
.RI Tool( string )
Returns a callable object
that can be used to initialize
a construction environment using the
tools keyword of the Environment() method.

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

.TP
.RI WhereIs( program ", [" path  ", [" pathext ]])

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,
or the user's current PATH
(os.environ['PATH'])
by default.
On Win32 systems, searches for executable
programs with any of the file extensions
listed in the specified
.I pathext,
or the user's current PATHEXT
(os.environ['PATHEXT'])
by default.

.SH EXTENDING SCONS
.SS Builder Objects
.B scons
can be extended by adding new builders to a construction
environment 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 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 prefix 
The prefix that will be prepended to the target file name.

.IP suffix
The suffix that will be appended to the target file name.

.IP src_suffix
The expected source file name suffix.

.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 emitter
A function that is passed the target, source, and environment,
and which returns a tuple containing two lists,
the list of targets to be built by this builder,
and the list of sources for this builder.
This allows the target and source lists to
be manipulated before the target(s) are actually built.

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

Example:

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

b = Builder(emitter=e)
.EE

.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

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

.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 overrides
A dictionary of construction variables
that will be set in the executing
construction environment when this
Builder is invoked.
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 object is called
will be associated with the target
(and any other files built as a
result of the call).

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

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

.SS Action Objects

The Builder function will turn its
.B action
keyword argument into an appropriate
internal Action object.
Occasionally, it may be more efficient
to create an explicit Action object
and use it to initialize multiple
Builder objects,
rather than let each separate Builder object
create a separate Action.

The Action method takes one or two arguments
and 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.

.ES
Action('$CC -c -o $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 takes 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

The second, optional argument
is a Python function that returns
a string to be printed to describe the action being executed.
Like the function to build a file,
this function takes three 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.
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.
a = Action(build_it, string_it)

# Alternatively, use a keyword argument.
a = Action(build_it, strfunction=string_it)
.EE

The third, also optional argument
is 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.
This is necessary whenever you want a target to
be rebuilt when a specific
construction variable changes,
because the underlying Python code for a function
will not change when the value of the construction variable does.

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

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

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

# Alternatively, use a keyword argument.
a = Action(build_it, varlist=['XXX'])
.EE
.PP
If the action argument is not one of the above,
None is returned.

.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 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 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.

(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 Win32 systems
when a path references a file on other (POSIX) systems.

.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
.EE

Lastly, a variable name
may be a callable Python function
associated with a
construction variable in the environment.
The function should
take three arguments:
.I target
- a list of target nodes,
.I source 
- a list of source nodes, 
.I env
- the construction environment.
SCons will insert whatever
the called function returns
into the expanded string:

.ES
def foo(target, source, env):
    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):
        return 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
.R $(
and
.R $)
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
.R $(
and
.R $)
will be removed from the command line
before it is added to file signatures,
and the
.R $(
and
.R $)
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

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
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.
The function takes three or four arguments:

    def scanner_function(node, env, path):

    def scanner_function(node, env, path, arg):

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.

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 array will be a list of suffixes
for the different file types that this
Scanner knows how to scan.

.IP path_function
A Python function that takes
two or three arguments:
a construction environment, directory Node,
and 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.

.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 a Node (file)
as an argument 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.

.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 WIN32:  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 WIN32:  scons.bat file
On WIN32 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.

NOTE:  SCons does
.I not
build all of its targets by default,
like other build tools do.
The canonical way to invoke SCons
is with a target of '.' (dot)
to represent all targets in and below the current directory:

.ES
scons .
.EE

One or more default targets may be specified
via the Default() method
in the SConstruct file.

.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

.ES
import re

include_re = re.compile(r'^include\\s+(\\S+)$', re.M)

def kfile_scan(node, env, path, arg):
    contents = node.get_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

.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 BuildDir() method to establish
one or more separate build directories for
a given source directory,
then use the SConscript() method
to specify the SConscript files
in the build directories:

.ES
SConstruct:

    ccflags = '-DFOO'
    Export("ccflags")
    BuildDir('foo', 'src')
    SConscript('foo/SConscript')

    ccflags = '-DBAR'
    Export("ccflags")
    BuildDir('bar', 'src')
    SConscript('bar/SConscript')

src/SConscript:

    Import("ccflags")
    env = Environment(CCFLAGS = ccflags)
    env.Program(target = 'src', source = 'src.c')
.EE

Note the use of the Export() method
to set the "ccflags" variable to a different
value for each variant build.

.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 contruction 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
opts = Options('custom.py')
opts.Add('CC', 'The C compiler.')
env = Environment(options=opts)
Help(opts.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>