%version; %scons; %builders-mod; %functions-mod; %tools-mod; %variables-mod; ]> This chapter will take you through the basic steps of installing &SCons; on your system, and building &SCons; if you don't have a pre-built package available (or simply prefer the flexibility of building it yourself). Before that, however, this chapter will also describe the basic steps involved in installing Python on your system, in case that is necessary. Fortunately, both &SCons; and Python are very easy to install on almost any system, and Python already comes installed on many systems.

Because &SCons; is written in Python, you need to have Python installed on your system to use &SCons;. Before you try to install Python, you should check to see if Python is already available on your system by typing python -V (capital 'V') or python --version at your system's command-line prompt. For Linux/Unix/MacOS/BSD type systems this looks like: $ python -V Python 3.7.1 In a cmd shell or PowerShell on a Windows system (note PoweShell needs it spelled "python.exe" rather than "python"): C:\>python -V Python 3.7.1 If Python is not installed on your system, you will see an error message stating something like "command not found" (on UNIX or Linux) or "'python' is not recognized as an internal or external command, operable progam or batch file" (on Windows). In that case, you need to install Python before you can install &SCons;. The standard location for information about downloading and installing Python is http://www.python.org/download/. See that page and associated links to get started. For Linux systems, Python is almost certainly available as a supported package, possibly installed by default; this is often preferred to installing by other means, and is easier than installing from source code. Many such systems have separate packages for Python 2 and Python 3. Building from source may still be a useful option if you need a version that is not offered by the distribution you are using. &SCons; will work with Python 2.7.x or with Python 3.5 or later. If you need to install Python and have a choice, we recommend using the most recent Python version available. Newer Pythons have significant improvements that help speed up the performance of &SCons;.

The canonical way to install &SCons; is from the Python Package Index (PyPi): % python -m pip install scons If you prefer not to install to the Python system location, or do not have privileges to do so, you can add a flag to install to a location specific to your own account: % python -m pip install --user scons &SCons; comes pre-packaged for installation on many Linux systems Check your package installation system to see if there is an &SCons; package available. Many people prefer to install distribution-native packages if available, as they provide a central point for management and updating. Some distributions have two &SCons; packages available, one which uses Python 2 and one which uses Python 3. If you need a specific version of &SCons; that is different from the package available, pip has a version option or you can follow the instructions in the next section.

If a pre-built &SCons; package is not available for your system, and installing using pip is not suitable, then you can still easily build and install &SCons; using the native Python distutils package. The first step is to download either the scons-&buildversion;.tar.gz or scons-&buildversion;.zip, which are available from the SCons download page at http://www.scons.org/download.html. Unpack the archive you downloaded, using a utility like tar on Linux or UNIX, or WinZip on Windows. This will create a directory called scons-&buildversion;, usually in your local directory. Then change your working directory to that directory and install &SCons; by executing the following commands: # cd scons-&buildversion; # python setup.py install This will build &SCons;, install the &scons; script in the python which is used to run the setup.py's scripts directory (/usr/local/bin or C:\Python27\Scripts), and will install the &SCons; build engine in the corresponding library directory for the python used (/usr/local/lib/scons or C:\Python27\scons). Because these are system directories, you may need root (on Linux or UNIX) or Administrator (on Windows) privileges to install &SCons; like this.

The &SCons; setup.py script has some extensions that support easy installation of multiple versions of &SCons; in side-by-side locations. This makes it easier to download and experiment with different versions of &SCons; before moving your official build process to a new version, for example. To install &SCons; in a version-specific location, add the --version-lib option when you call setup.py: # python setup.py install --version-lib This will install the &SCons; build engine in the /usr/lib/scons-&buildversion; or C:\Python27\scons-&buildversion; directory, for example. If you use the --version-lib option the first time you install &SCons;, you do not need to specify it each time you install a new version. The &SCons; setup.py script will detect the version-specific directory name(s) and assume you want to install all versions in version-specific directories. You can override that assumption in the future by explicitly specifying the --standalone-lib option.

You can install &SCons; in locations other than the default by specifying the --prefix= option: # python setup.py install --prefix=/opt/scons This would install the scons script in /opt/scons/bin and the build engine in /opt/scons/lib/scons, Note that you can specify both the --prefix= and the --version-lib options at the same type, in which case setup.py will install the build engine in a version-specific directory relative to the specified prefix. Adding --version-lib to the above example would install the build engine in /opt/scons/lib/scons-&buildversion;.

If you don't have the right privileges to install &SCons; in a system location, simply use the --prefix= option to install it in a location of your choosing. For example, to install &SCons; in appropriate locations relative to the user's $HOME directory, the &scons; script in $HOME/bin and the build engine in $HOME/lib/scons, simply type: $ python setup.py install --prefix=$HOME You may, of course, specify any other location you prefer, and may use the --version-lib option if you would like to install version-specific directories relative to the specified prefix. This can also be used to experiment with a newer version of &SCons; than the one installed in your system locations. Of course, the location in which you install the newer version of the &scons; script ($HOME/bin in the above example) must be configured in your &PATH; variable before the directory containing the system-installed version of the &scons; script.