SCons - a software construction tool

Welcome to the SCons development tree.  The real purpose of this tree
is to package SCons for production distribution in a variety of formats,
not just to hack SCons code.

If all you want to do is install and run SCons, it will be easier for you
to download and install the scons-{version}.tar.gz or scons-{version}.zip
package rather than to work with the packaging logic in this tree.

To the extent that this tree is about building SCons packages, the *full*
development cycle is not just to test the code directly, but to package
SCons, unpack the package, "install" SCons in a test subdirectory,
and then to run the tests against the unpacked and installed software.
This helps eliminate problems caused by, for example, failure to update
the list of files to be packaged.

For just working on making an individual change to the SCons source,
however, you don't actually need to build or install SCons; you
*can* actually edit and execute SCons in-place.  See the following
sections below for more information:

        How to edit and execute SCons in-place.

        Tips for debugging problems in SCons.

        How to use the automated regression tests.

        An example of how to put the edit/execute/test pieces
        together in a reasonable development workflow.


Before going further, you can check that this package you have is the
latest version at the SCons download page:



Running SCons requires Python version 2.4 or later.  There should be
no other dependencies or requirements to run SCons.

The default SCons configuration assumes use of the Microsoft Visual C++
compiler suite on WIN32 systems, and assumes a C compiler named 'cc',
a C++ compiler named 'c++', and a Fortran compiler named 'g77' (such
as found in the GNU C compiler suite) on any other type of system.
You may, of course, override these default values by appropriate
configuration of Environment construction variables.

By default, SCons knows how to search for available programming tools
on various systems--see the SCons man page for details.  You may,
of course, override the default SCons choices made by appropriate
configuration of Environment construction variables.


Nothing special.


You can execute the local SCons directly from the src/ subdirectory by
first setting the SCONS_LIB_DIR environment variable to the local
src/engine subdirectory, and then executing the local src/script/scons.py
script to populate the build/scons/ subdirectory.  You would do this as
follows on a Linux or UNIX system (using sh or a derivative like bash or

        $ setenv MYSCONS=`pwd`/src
        $ setenv SCONS_LIB_DIR=$MYSCONS/engine
        $ python $MYSCONS/script/scons.py [arguments]

Or on Windows:

        C:\scons>set MYSCONS=%cd%\src
        C:\scons>set SCONS_LIB_DIR=%MYSCONS%\engine
        C:\scons>python %MYSCONS%\script\scons.py [arguments]

An alternative approach is to skip the above and use:

        $ python bootstrap.py [arguments]

bootstrap.py keeps the src/ subdirectory free of compiled Python (*.pyc or
*.pyo) files by copying the necessary SCons files to a local bootstrap/
subdirectory and executing it from there.

You can use the -C option to have SCons change directory to another
location where you already have a build configuration set up.

    $ python bootstrap.py -C /some/other/location [arguments]

For simplicity in the following examples, we will only show the
bootstrap.py approach.


    NOTE: You don't need to build SCons packages or install SCons if
    you just want to work on developing a patch.  See the sections
    about MAKING CHANGES and TESTING below if you just want to submit
    a bug fix or some new functionality.  See the sections below about
    BUILDING PACKAGES and TESTING PACKAGES if your enhancement involves
    changing the way in which SCons is packaged and/or installed on an
    end-user system.

Assuming your system satisfies the installation requirements in the
previous section, install SCons from this package by first populating
the build/scons/ subdirectory.  (For an easier way to install SCons,
without having to populate this directory, use the scons-{version}.tar.gz
or scons-{version}.zip package.)

Populate build/scons/ using a pre-installed SCons

If you already have an appropriate version of SCons installed on your
system, populate the build/scons/ directory by running:

        $ scons build/scons

Populate build/scons/ using the SCons source

You can also use this version of SCons to populate its own build directory
by using a supplied bootstrap.py script (see the section above about

        $ python bootstrap.py build/scons

Install the built SCons files

Any of the above commands will populate the build/scons/ directory with
the necessary files and directory structure to use the Python-standard
setup script as follows on Linux or UNIX:

        # cd build/scons
        # python setup.py install

Or on Windows:

        C:\scons\>cd build\scons
        C:\scons\build\scons>python setup.py install

By default, the above commands will do the following:

    --  Install the version-numbered "scons-2.0.0" and "sconsign-2.0.0"
        scripts in the default system script directory (/usr/bin or
        C:\Python*\Scripts, for example).  This can be disabled by
        specifying the "--no-version-script" option on the command

    --  Install scripts named "scons" and "sconsign" scripts in the
        default system script directory (/usr/bin or C:\Python*\Scripts,
        for example).  This can be disabled by specifying the
        "--no-scons-script" option on the command line, which is useful
        if you want to install and experiment with a new version before
        making it the default on your system.

        On UNIX or Linux systems, you can have the "scons" and "sconsign"
        scripts be hard links or symbolic links to the "scons-2.0.0" and
        "sconsign-2.0.0" scripts by specifying the "--hardlink-scons" or
        "--symlink-scons" options on the command line.

    --  Install "scons-2.0.0.bat" and "scons.bat" wrapper scripts in the
        Python prefix directory on Windows (C:\Python*, for example).
        This can be disabled by specifying the "--no-install-bat" option
        on the command line.

        On UNIX or Linux systems, the "--install-bat" option may be
        specified to have "scons-2.0.0.bat" and "scons.bat" files installed
        in the default system script directory, which is useful if you
        want to install SCons in a shared file system directory that can
        be used to execute SCons from both UNIX/Linux and Windows systems.

    --  Install the SCons build engine (a Python module) in an
        appropriate version-numbered SCons library directory
        (/usr/lib/scons-2.0.0 or C:\Python*\scons-2.0.0, for example).
        See below for more options related to installing the build
        engine library.

    --  Install the troff-format man pages in an appropriate directory
        on UNIX or Linux systems (/usr/share/man/man1 or /usr/man/man1,
        for example).  This can be disabled by specifying the
        "--no-install-man" option on the command line.  The man pages
        can be installed on Windows systems by specifying the
        "--install-man" option on the command line.

Note that, by default, SCons does not install its build engine library
in the standard Python library directories.  If you want to be able to
use the SCons library modules (the build engine) in other Python
scripts, specify the "--standard-lib" option on the command line, as

        # python setup.py install --standard-lib

This will install the build engine in the standard Python library
directory (/usr/lib/python*/site-packages or

Alternatively, you can have SCons install its build engine library in a
hard-coded standalone library directory, instead of the default
version-numbered directory, by specifying the "--standalone-lib" option
on the command line, as follows:

        # python setup.py install --standalone-lib

This is usually not recommended, however.

Note that, to install SCons in any of the above system directories,
you should have system installation privileges (that is, "root" or
"Administrator") when running the setup.py script.  If you don't have
system installation privileges, you can use the --prefix option to
specify an alternate installation location, such as your home directory:

        $ python setup.py install --prefix=$HOME

This will install SCons in the appropriate locations relative to
$HOME--that is, the scons script itself $HOME/bin and the associated
library in $HOME/lib/scons, for example.


Because SCons is implemented in a scripting language, you don't need to
build it in order to make changes and test them.

Virtually all of the SCons functionality exists in the "build engine,"
the src/engine/SCons subdirectory hierarchy that contains all of the
modules that make up SCons.  The src/script/scons.py wrapper script exists
mainly to find the appropriate build engine library and then execute it.

In order to make your own changes locally and test them by hand, simply
edit modules in the local src/engine/SCons subdirectory tree and use the
local bootstrap.py script (see the section above about EXECUTING SCONS

    $ python bootstrap.py [arguments]

If you want to be able to just execute your modified version of SCons from
the command line, you can make it executable and add its directory to your
$PATH like so:

    $ chmod 755 src/script/scons.py
    $ export PATH=$PATH:`pwd`/src/script

You should then be able to run this version of SCons by just typing
"scons.py" at your UNIX or Linux command line.

Note that the regular SCons development process makes heavy use of
automated testing.  See the TESTING and DEVELOPMENT WORKFLOW sections
below for more information about the automated regression tests and how
they can be used in a development cycle to validate that your changes
don't break existing functionality.


Python comes with a good interactive debugger.  When debugging changes
by hand (i.e., when not using the automated tests), you can invoke SCons
under control of the Python debugger by specifying the --debug=pdb option:

    $ scons --debug=pdb [arguments]
    > /home/knight/SCons/src/engine/SCons/Script/Main.py(927)_main()
    -> default_warnings = [ SCons.Warnings.CorruptSConsignWarning,

Once in the debugger, you can set breakpoints at lines in files in the
build engine modules by providing the path name of the file relative to
the src/engine subdirectory (that is, including the SCons/ as the first
directory component):

    (Pdb) b SCons/Tool/msvc.py:158

The debugger also supports single stepping, stepping into functions,
printing variables, etc.

Trying to debug problems found by running the automated tests (see the
TESTING section, below) is more difficult, because the test automation
harness re-invokes SCons and captures output. Consequently, there isn't an
easy way to invoke the Python debugger in a useful way on any particular
SCons call within a test script.

The most effective technique for debugging problems that occur during an
automated test is to use the good old tried-and-true technique of adding
statements to print tracing information.  But note that you can't just use
"print" statement, or even "sys.stdout.write()," because those change the
SCons output, and the automated tests usually look for matches of specific
output strings to decide if a given SCons invocations passes the test.

To deal with this, SCons supports a Trace() function that (by default)
will print messages to your console screen ("/dev/tty" on UNIX or Linux,
"con" on Windows).  By adding Trace() calls to the SCons source code:

    def sample_method(self, value):
        from SCons.Debug import Trace
        Trace('called sample_method(%s, %s)\n' % (self, value))

You can then run automated tests that print any arbitrary information
you wish about what's going on inside SCons, without interfering with
the test automation.

The Trace() function can also redirect its output to a file, rather than
the screen:

    def sample_method(self, value):
        from SCons.Debug import Trace
        Trace('called sample_method(%s, %s)\n' % (self, value),

Where the Trace() function sends its output is stateful: once you use the
"file=" argument, all subsequent calls to Trace() send their output to
the same file, until another call with a "file=" argument is reached.


Tests are run by the runtest.py script in this directory.

There are two types of tests in this package:

    Unit tests for individual SCons modules live underneath the
    src/engine/ subdirectory and are the same base name as the module
    with "Tests.py" appended--for example, the unit test for the
    Builder.py module is the BuilderTests.py script.

    End-to-end tests of SCons live in the test/ subdirectory.

You may specifically list one or more tests to be run:

        $ python runtest.py src/engine/SCons/BuilderTests.py

        $ python runtest.py test/option-j.py test/Program.py

You also use the -f option to execute just the tests listed in a specified
text file:

        $ cat testlist.txt
        $ python runtest.py -f testlist.txt

One test must be listed per line, and any lines that begin with '#'
will be ignored (allowing you, for example, to comment out tests that
are currently passing and then uncomment all of the tests in the file
for a final validation run).

The runtest.py script also takes a -a option that searches the tree for
all of the tests and runs them:

        $ python runtest.py -a

If more than one test is run, the runtest.py script prints a summary
of how many tests passed, failed, or yielded no result, and lists any
unsuccessful tests.

The above invocations all test directly the files underneath the src/
subdirectory, and do not require that a build be performed first.  The
runtest.py script supports additional options to run tests against
unpacked packages in the build/test-*/ subdirectories.  See the "TESTING
PACKAGES" section below.


    CAVEAT:  The point of this section isn't to describe one dogmatic
    workflow.  Just running the test suite can be time-consuming, and
    getting a patch to pass all of the tests can be more so.  If you're
    genuinely blocked, it may make more sense to submit a patch with
    a note about which tests still fail, and how.  Someone else may be
    able to take your "initial draft" and figure out how to improve it
    to fix the rest of the tests.  So there's plenty of room for use of
    good judgement.

The various techniques described in the above sections can be combined
to create simple and effective workflows that allow you to validate
that patches you submit to SCons don't break existing functionality and
have adequate testing, thereby increasing the speed with which they can
be integrated.

For example, suppose your project's SCons configuration is blocked by
an SCons bug, and you decide you want to fix it and submit the patch.
Here's one possible way to go about doing that (using UNIX/Linux as the
development platform, Windows users can translate as appropriate)):

    --  Change to the top of your checked-out SCons tree.

    --  Confirm that the bug still exists in this version of SCons
        by using the -C option to run the broken build:

            $ python bootstrap.py -C /home/me/broken_project .

    --  Fix the bug in SCons by editing appropriate module files
        underneath src/engine/SCons.

    --  Confirm that you've fixed the bug affecting your project:

            $ python bootstrap.py -C /home/me/broken_project .

    --  Test to see if your fix had any unintended side effects
        that break existing functionality:

            $ python runtest.py -a -o test.log

        Be patient, there are more than 700 test scripts in the
        whole suite.  If you are on UNIX/Linux, you can use:

            $ python runtest.py -a | tee test.log

        instead so you can monitor progress from your terminal.

        If any test scripts fail, they will be listed in a summary at
        the end of the log file.  Some test scripts may also report
        NO RESULT because (for example) your local system is the wrong
        type or doesn't have some installed utilities necessary to run
        the script.  In general, you can ignore the NO RESULT list.

    --  Cut-and-paste the list of failed tests into a file:

            $ cat > failed.txt

    --  Now debug the test failures and fix them, either by changing
        SCons, or by making necessary changes to the tests (if, for
        example, you have a strong reason to change functionality, or
        if you find that the bug really is in the test script itself).
        After each change, use the runtest.py -f option to examine the
        effects of the change on the subset of tests that originally

            $ [edit]
            $ python runtest.py -f failed.txt

        Repeat this until all of the tests that originally failed
        now pass.

    --  Now you need to go back and validate that any changes you
        made while getting the tests to pass didn't break the fix
        you originally put in, and didn't introduce any *additional*
        unintended side effects that broke other tests:

            $ python bootstrap.py -C /home/me/broken_project .
            $ python runtest.py -a -o test.log

        If you find any newly-broken tests, add them to your "failed.txt"
        file and go back to the previous step.

Of course, the above is only one suggested workflow.  In practice, there
is a lot of room for judgment and experience to make things go quicker.
For example, if you're making a change to just the Java support, you
might start looking for regressions by just running the test/Java/*.py
tests instead of running all of "runtest.py -a".


We use SCons (version 0.96.93 later) to build its own packages.  If you
already have an appropriate version of SCons installed on your system,
you can build everything by simply running it:

        $ scons

If you don't have SCons version 0.96.93 later already installed on your
system, you can use the supplied bootstrap.py script (see the section

        $ python bootstrap.py build/scons

Depending on the utilities installed on your system, any or all of the
following packages will be built:


The SConstruct file is supposed to be smart enough to avoid trying to
build packages for which you don't have the proper utilities installed.
For example, if you don't have Debian packaging tools installed, it
should just not build the .deb package, not fail the build.

If you receive a build error, please report it to the scons-devel
mailing list and open a bug report on the SCons bug tracker.

Note that in addition to creating the above packages, the default build
will also unpack one or more of the packages for testing.


A full build will unpack and/or install any .deb, .rpm., .local.tar.gz,
.local.zip, .src.tar.gz, .src.zip, .tar.gz, and .zip packages into
separate build/test-*/ subdirectories.  (Of course, if a package was
not built on your system, it should not try to install it.)  The
runtest.py script supports a -p option that will run the specified tests
(individually or collectively via the -a option) against the unpacked
build/test-/* subdirectory:

        $ python runtest.py -p deb

        $ python runtest.py -p rpm

        $ python runtest.py -p local-tar-gz

        $ python runtest.py -p local-zip

        $ python runtest.py -p src-tar-gz

        $ python runtest.py -p src-zip

        $ python runtest.py -p tar-gz

        $ python runtest.py -p zip

(The canonical invocation is to also use the runtest.py -a option so
that all tests are run against the specified package.)


Not guaranteed to be up-to-date (but better than nothing):

        A subdirectory for benchmarking scripts, used to perform timing
        tests to decide what specific idioms are most efficient for
        various parts of the code base.  We check these in so they're
        available in case we have to revisit any of these decisions in
        the future.

        Miscellaneous utilities used in SCons development.  Right now,
        some of the stuff here includes:

            --  a copy of the script we use to translate an Aegis change
                into a CVS checkin
            --  a script that runs pychecker on our source tree
            --  a script that counts source and test files and numbers
                of lines in each
            --  a script for synchronizing the Aegis tree to SourceForge
            --  a prototype script for capturing sample SCons output
                in xml files
            --  a script that can profile and time a packaging build of
                SCons itself
            --  a copy of xml_export, which can retrieve project data
                from SourceForge
            --  scripts and a Python module for translating the SCons
                home-brew XML documentation tags into DocBook and
                man page format

        Build script for running SCons from the current source code
        checkout. This copies SCons files to bootstrap/ subdirectory,
        and then executes SCons with the supplied command-line arguments.

        This doesn't exist yet if you're looking at a vanilla source
        tree.  This is generated as part of our build process, and it's
        where, believe it or not, we *build* everything.

        The Aegis configuration, governing much of how we use Aegis to
        build, test, control source, etc.

        Files needed to construct a Debian package. The contents of this
        directory are dictated by the Debian Policy Manual
        (http://www.debian.org/doc/debian-policy). The package will not be
        accepted into the Debian distribution unless the contents of this
        directory satisfy the relevant Debian policies.

        SCons documentation.  A variety of things here, in various
        stages of (in)completeness.

        Stuff to generate files for Gentoo Linux.

        Documentation of SCons administrative procedures (making a
        change, releasing a new version).  Maybe other administrative
        stuff in the future.

        A copy of the copyright and terms under which SCons is
        distributed (the Open Source Initiative-approved MIT license).

        A copy of the copyright and terms under which SCons is
        distributed for inclusion in the scons-local-{version} packages.
        This is the same as LICENSE with a preamble that specifies
        the licensing terms are for SCons itself, not any other
        package that includes SCons.

        The Python modules we use for testing, some generic modules
        originating elsewhere and some specific to SCons.

        What you're looking at right now.

        A README file for inclusion in the scons-local-{version}
        packages.  Similar to this file, but stripped down and modified
        for people looking at including SCons in their shipped software.

        Script for uploading changes for review to Rietveld installation
        at http://codereview.appspot.com

        The .spec file for building our RPM packages.

        Script for running SCons tests.  By default, this will run a
        test against the code in the local src/ tree, so you don't
        have to do a build before testing your changes.  Aegis uses
        it with an option that requires that you've done a build
        (aeb) before running tests.

        The "Makefile" for the SCons distribution.

        (It has been pointed out that it's hard to find the SCons API
        in this SConstruct file, and that it looks a lot more like a
        pure Python script than a build configuration file.  That's
        mainly because all of the magick we have to perform to deal with
        all of the different packaging formats requires a lot of pure
        Python manipulation.  In other words, don't look at this file
        for an example of how easy it is to use SCons to build "normal"

        Where the actual source code is kept, of course.

        Template files, used by Aegis to give you a head start when you
        aenf or aent a new file.

        End-to-end tests of the SCons utility itself.  These are
        separate from the individual module unit tests, which live
        side-by-side with the modules under src/.


See the src/RELEASE.txt file for notes about this specific release,
including known problems.  See the src/CHANGES.txt file for a list of
changes since the previous release.

The doc/man/scons.1 man page is included in this package, and contains a
section of small examples for getting started using SCons.

Additional documentation for SCons is available at:



SCons is distributed under the MIT license, a full copy of which is
available in the LICENSE file.


Please report bugs by following the detailed instructions on our Bug
Submission page:


You can also send mail to the SCons developers' mailing list:


But even if you send email to the mailing list please make sure that you
ALSO submit a bug report to the project page bug tracker, because bug
reports in email often get overlooked in the general flood of messages.


An active mailing list for developers of SCons is available.  You may
send questions or comments to the list at:


You may request a subscription to the developer's mailing list by sending
email to:


Subscription to the developer's mailing list is by approval.  In practice,
no one is refused list membership, but we reserve the right to limit
membership in the future and/or weed out lurkers.

There is also a low-volume mailing list available for announcements
about SCons.  Subscribe by sending email to:


There are other mailing lists available for SCons users, for notification
of SCons code changes, and for notification of updated bug reports and
project documents.  Please see our mailing lists page for details.


If you find SCons helpful, please consider making a donation (of cash,
software, or hardware) to support continued work on the project.
Information is available at:



Check the SCons web site at:



Steven Knight
knight at baldmt dot com

With plenty of help from the SCons Development team:
        Chad Austin
        Charles Crain
        William Deegan
        Steve Leblanc
        Greg Noel
        Gary Oberbrunner
        Anthony Roach
        Greg Spencer
        Christoph Wiedemann