SCons - a Software Construction Tool
####################################

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What is SCons?
==============

SCons is an Open Source software construction tool which orchestrates the construction of software
(and other tangible products such as documentation files) by determining which
component pieces must be built or rebuilt and invoking the necessary
commands to build them.


Features:

  * Configuration files are Python scripts -
    use the power of a real programming language
    to solve build problems; no complex domain-specific language to learn.
  * Reliable, automatic dependency analysis built-in for C, C++ and FORTRAN.
    No more "make depend" or "make clean" to get all of the dependencies.
    Dependency analysis is easily extensible through user-defined
    dependency Scanners for other languages or file types.
  * Built-in support for C, C++, D, Java, FORTRAN, Yacc, Lex, Qt and SWIG,
    and building TeX and LaTeX documents.
    Easily extensible through user-defined Builders for other languages
    or file types.
  * Building from central repositories of source code and/or pre-built targets.
  * Built-in support for Microsoft Visual Studio, including generation of
    .dsp, .dsw, .sln and .vcproj files.
  * Reliable detection of build changes using cryptographic hashes;
    optionally can configure other algorithms including traditional timestamps.
  * Support for parallel builds - can keep multiple jobs running
    simultaneously regardless of directory hierarchy.
  * Integrated Autoconf-like support for finding #include files, libraries,
    functions and typedefs.
  * Global view of all dependencies - no more multiple build passes or
    reordering targets to build everything.
  * Ability to share built files in a cache to speed up multiple builds.
  * Designed from the ground up for cross-platform builds, and known to
    work on Linux, other POSIX systems (including AIX, BSD systems,
    HP/UX, IRIX and Solaris), Windows 7/8/10, MacOS, and OS/2.
  * Written in Python.


Documentation
=============

Documentation for SCons is available at
http://www.scons.org/documentation.html.


Latest Version
==============

If you already have SCons installed, you can check that the package you have
is the latest version at the
`SCons download page <https://www.scons.org/pages/download.html>`_.


Execution Requirements
======================

Running SCons requires Python 3.6 or higher. There should be no other
dependencies or requirements to run standard SCons.
The last release to support Python 3.5 was 4.2.0.

Some experimental features may require additional Python packages
to be installed - at the moment the Ninja feature requires the
supporting `ninja package <https://pypi.org/project/ninja/>`_.

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 ``gfortran`` (such as found
in the GNU Compiler Collection) on any other type of system.  You may
override these default values by appropriate configuration of variables
in a Construction Environment, or in the case of Cygwin on a Win32 system,
by selecting the 'cygwin' platform, which will set some of those Construction
Variables for you.

By default, SCons knows how to search for available programming tools on
various systems - see the
`SCons man page <https://scons.org/doc/production/HTML/scons-man.html>`_
for details.  You can override
the default SCons choices made by appropriate configuration of
construction variables.


Installation Requirements
=========================

SCons has no installation dependencies beyond a compatible version
of Python. The tools which will be used to actually construct the
project, such as compilers, documentation production tools, etc.
should of course be installed by the appropriate means.


Installation
============

The preferred way to install SCons is through the Python installer, ``pip``
(or equivalent alternatives, such as the Anaconda installer, ``conda``).
You can install either from a wheel package or from the source directory.
To work on a project that builds using SCons, installation lets you
just use ``scons`` as a command and not worry about things.  In this
case, we usually suggest using a virtualenv, to isolate the Python
environment to that project
(some notes on that:
`Python Packaging User Guide: Creating and using virtual environments
<https://packaging.python.org/guides/installing-using-pip-and-virtual-environments/#creating-a-virtual-environment>`_).

Some installation examples::

    # to do a system-level install:
    $ python -m pip install --user scons

    # Windows variant, assuming Python Launcher:
    C:\Users\me> py -m pip install --user scons

    # inside a virtualenv it's safe to use bare pip:
    (myvenv) $ pip install scons

    # install in a virtualenv from a wheel file:
    (myvenv) $ pip install SCons-4.3.0-py3-none-any.whl

    # install in a virtualenv from source directory:
    (myvenv) $ pip install --editable .

Note that on Windows, SCons installed via ``pip`` puts an executable
``scons.exe`` in the script directory of the Python installation,
or in a shadow script directory if you did a User Install.
To run ``scons`` as a command, you'll need this in your search path.

Fortunately, ``pip`` will warn you about this - pay attention to any
messages during installation like this::

  WARNING: The scripts scons-configure-cache.exe, scons.exe and sconsign.exe
  are installed in 'C:\Users\me\AppData\Roaming\Python\Python310\Scripts'
  which is not on PATH.
  Consider adding this directory to PATH or, if you prefer to suppress this warning,
  use --no-warn-script-location.

If you are running on a system which uses a package manager
(for example most Linux distributions), you may, at your option,
use the package manager (e.g. ``apt``, ``dnf``, ``yum``,
``zypper``, ``brew``, ``pacman`` etc.) to install a version
of SCons.  Some distributions keep up to date with SCons releases
very quickly, while others may delay, so the version of SCons
you want to run may factor into your choice.


Getting Started Using SCons
===========================

If you're new to SCons, the first couple of chapters of the
`SCons User Guide <https://scons.org/doc/production/HTML/scons-user.html>`_
provide an excellent starting spot.


Contributing to SCons
=====================

Please see `<CONTRIBUTING.rst>`_


License
=======

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


Reporting Bugs
==============

The SCons project welcomes bug reports and feature requests.

Please make sure you send email with the problem or feature request to
the SCons users mailing list, which you can join at
https://two.pairlist.net/mailman/listinfo/scons-users,
or on the SCons Discord server in
`#scons-help <https://discord.gg/bXVpWAy#scons-help>`_.

Once you have discussed your issue on the users mailing list and the
community has confirmed that it is either a new bug or a duplicate of an
existing bug, then please follow the instructions the community provides
(including the issue template presented by GitHub)
to file a new bug or to add yourself to the CC list for an existing bug.

You can explore the list of existing bugs, which may include workarounds
for the problem you've run into, on the
`GitHub issue tracker <https://github.com/SCons/scons/issues>`_.

Bug-fix Policy
--------------

At this time, the application of bug-fix pull requests *normally* happens
at the head of the main branch. In other words fixes are likely to appear
in the next regular release and there probably won't be a bugfix update
to a past release.  Consumers are of course free to internally maintain
releases on their own by taking submitted patches and applying them.


Mailing Lists and Other Contacts
================================

In addition to the scons-users list, an active mailing list for developers
of SCons is available.  You may send questions or comments to the list
at scons-dev@scons.org.

You may subscribe to the developer's mailing list using the form at
https://two.pairlist.net/mailman/listinfo/scons-dev.  The same page
contains archives of past postings.

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 are other ways to contact the SCons community.  An active Discord
server is the most direct.  The server includes a channel for code
notifications and other GitHub events (``#github-update``),
if those are of interest. See the website for more contact information:
https://scons.org/contact.html.

Reproducible Builds
===================
SCons itself is set up to do "reproducible builds"
(see (https://reproducible-builds.org/specs/source-date-epoch/)
if environment variables ``SOURCE_DATE_EPOCH`` is set - that is,
fields in the package which could change each time the package is
constructed are forced to constant values.

To support other projects which wish to do the same, a sample script
is provided which can be placed in a site directory, which imports
``SOURCE_DATE_EPOCH`` and sets it in the execution environment of
every created construction envirionment. There's also an installer
script (POSIX shell only). See packaging/etc/README.txt for more details.

Donations
=========

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 https://www.scons.org/donate.html
or the GitHub Sponsors button on https://github.com/scons/scons.

For More Information
====================

Check the SCons web site at https://www.scons.org/


Author Info
===========

SCons was originally written by Steven Knight, knight at baldmt dot com.
Since around 2010 it has been maintained by the SCons
development team, co-managed by Bill Deegan and Gary Oberbrunner, with
many contributors, including but not at all limited to:

- Chad Austin
- Dirk Baechle
- Charles Crain
- William Deegan
- Steve Leblanc
- Rob Managan
- Greg Noel
- Gary Oberbrunner
- Anthony Roach
- Greg Spencer
- Tom Tanner
- Anatoly Techtonik
- Christoph Wiedemann
- Russel Winder
- Mats Wichmann

\... and many others.

Copyright (c) 2001 - 2024 The SCons Foundation