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.
""")
       

Optionally, you can specify the append flag:

Help("""
Type: 'scons program' to build the production program,
      'scons debug' to build the debug version.
""", append=True)
       

(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 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 SCons built-in 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 define fragments of help text together with the corresponding feature, even if spread 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.

Calling Help("text") overwrites the help text that otherwise would be collected from any command-line options defined in AddOption calls. To preserve the AddOption help text, add the append=True keyword argument when calling Help. This also preserves the option help for the scons command itself. To preserve only the AddOption help, also add the local_only=True keyword argument. (This only matters the first time you call Append, on any subsequent calls the text you passed is added to the existing help text).

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 SCons built-in 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 SCons built-in 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.