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SCons / doc / user / help.in

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   <para>

   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:

   </para>

   <scons_example name="ex1">
      <file name="SConstruct" printme="1">
      Help("""
      Type: 'scons program' to build the production program,
            'scons debug' to build the debug version.
      """)
      </file>
   </scons_example>

   <para>

   (Note the above use of the Python triple-quote syntax,
   which comes in very handy for
   specifying multi-line strings like help text.)

   </para>

   <para>

   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; <literal>-h</literal> option:

   </para>

   <scons_output example="ex1">
      <scons_output_command>scons -h</scons_output_command>
   </scons_output>

   <para>

   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.

   </para>

   <para>

   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:

   </para>

   <scons_example name="ex2">
      <file name="SConstruct" printme="1">
      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")
      </file>
   </scons_example>

   <para>

   Will display the complete help text on Windows:

   </para>

   <scons_output example="ex2" os="win32">
      <scons_output_command>scons -h</scons_output_command>
   </scons_output>

   <para>

   But only show the relevant option on a Linux or UNIX system:

   </para>

   <scons_output example="ex2" os="posix">
      <scons_output_command>scons -h</scons_output_command>
   </scons_output>

   <para>

   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 <literal>-H</literal> option is used.

   </para>
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