A key aspect of creating a usable build configuration is providing good output from the build so its users can readily understand what the build is doing and get information about how to control the build. SCons provides several ways of controlling output from the build configuration to help make the build more useful and understandable.
Help Function
It's often very useful to be able to give
users some help that describes the
specific targets, build options, etc.,
that can be used for your build.
SCons provides the Help function
to allow you to specify this help text:
Help("""
Type: 'scons program' to build the production program,
'scons debug' to build the debug version.
""")
(Note the above use of the Python triple-quote syntax, which comes in very handy for specifying multi-line strings like help text.)
When the SConstruct or SConscript files
contain such a call to the Help function,
the specified help text will be displayed in response to
the SCons -h option:
% scons -h
scons: Reading SConscript files ...
scons: done reading SConscript files.
Type: 'scons program' to build the production program,
'scons debug' to build the debug version.
Use scons -H for help about command-line options.
The SConscript files may contain
multiple calls to the Help function,
in which case the specified text(s)
will be concatenated when displayed.
This allows you to split up the
help text across multiple SConscript files.
In this situation, the order in
which the SConscript files are called
will determine the order in which the Help functions are called,
which will determine the order in which
the various bits of text will get concatenated.
Another use would be to make the help text conditional on some variable. For example, suppose you only want to display a line about building a Windows-only version of a program when actually run on Windows. The following SConstruct file:
env = Environment()
Help("\nType: 'scons program' to build the production program.\n")
if env['PLATFORM'] == 'win32':
Help("\nType: 'scons windebug' to build the Windows debug version.\n")
Will display the complete help text on Windows:
C:\>scons -h
scons: Reading SConscript files ...
scons: done reading SConscript files.
Type: 'scons program' to build the production program.
Type: 'scons windebug' to build the Windows debug version.
Use scons -H for help about command-line options.
But only show the relevant option on a Linux or UNIX system:
% scons -h
scons: Reading SConscript files ...
scons: done reading SConscript files.
Type: 'scons program' to build the production program.
Use scons -H for help about command-line options.
If there is no Help text in the SConstruct or
SConscript files,
SCons will revert to displaying its
standard list that describes the SCons command-line
options.
This list is also always displayed whenever
the -H option is used.