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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>
<programlisting>
Help("""
Type: 'scons program' to build the production program,
'scons debug' to build the debug version.
""")
</programlisting>
<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>
<screen>
% <userinput>scons -h</userinput>
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.
</screen>
<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>
<programlisting>
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")
</programlisting>
<para>
Will display the completely help text on Windows:
</para>
<screen>
C:\><userinput>scons -h</userinput>
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.
</screen>
<para>
But only show the relevant option on a Linux or UNIX system:
</para>
<screen>
% <userinput>scons -h</userinput>
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.
</screen>
<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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