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<section id="sect-parseconfig"
         xmlns="http://www.scons.org/dbxsd/v1.0"
         xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
         xsi:schemaLocation="http://www.scons.org/dbxsd/v1.0 http://www.scons.org/dbxsd/v1.0/scons.xsd">
<title>Finding Installed Library Information: the &ParseConfig; Function</title>

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 <para>

 Configuring the right options to build programs to work with
 libraries--especially shared libraries--that are available
 on POSIX systems can be very complicated.
 To help this situation,
 various utilies with names that end in <filename>config</filename>
 return the command-line options for the GNU Compiler Collection (GCC)
 that are needed to use these libraries;
 for example, the command-line options
 to use a library named <filename>lib</filename>
 would be found by calling a utility named <filename>lib-config</filename>.

 </para>

 <para>

 A more recent convention is that these options
 are available from the generic <filename>pkg-config</filename> program,
 which has common framework, error handling, and the like,
 so that all the package creator has to do is provide the set of strings
 for his particular package.

 </para>

 <para>

 &SCons; construction environments have a &ParseConfig; method
 that executes a <filename>*config</filename> utility
 (either <filename>pkg-config</filename> or a
 more specific utility)
 and configures the appropriate construction variables
 in the environment
 based on the command-line options
 returned by the specified command.

 </para>

 <scons_example name="parseconfig_ex1">
   <file name="SConstruct" printme="1">
env = Environment()
env['CPPPATH'] = ['/lib/compat']
env.ParseConfig("pkg-config x11 --cflags --libs")
print env['CPPPATH']
   </file>
 </scons_example>

 <para>

 &SCons; will execute the specified command string,
 parse the resultant flags,
 and add the flags to the appropriate environment variables.

 </para>

 <!--
 This is how we used to generate the screen output below, but
 as of (at least) Ubuntu Karmic, the pkg-config output for x11
 no longer reports back an include directory.  Since this is just
 for example anyway, we're just hard-coding the output.

 <scons_output example="parseconfig_ex1" suffix="1">
    <scons_output_command>scons -Q</scons_output_command>
 </scons_output>
 -->

 <screen>
% <userinput>scons -Q</userinput>
['/lib/compat', '/usr/X11/include']
scons: `.' is up to date.
 </screen>

 <para>

 In the example above, &SCons; has added the include directory to
 <varname>CPPPATH</varname>.
 (Depending upon what other flags are emitted by the
 <filename>pkg-config</filename> command,
 other variables may have been extended as well.)

 </para>

 <para>

 Note that the options are merged with existing options using
 the &MergeFlags; method,
 so that each option only occurs once in the construction variable:

 </para>

 <scons_example name="parseconfig_ex2">
   <file name="SConstruct" printme="1">
env = Environment()
env.ParseConfig("pkg-config x11 --cflags --libs")
env.ParseConfig("pkg-config x11 --cflags --libs")
print env['CPPPATH']
   </file>
 </scons_example>

 <!--
 This is how we used to generate the screen output below, but
 as of (at least) Ubuntu Karmic, the pkg-config output for x11
 no longer reports back an include directory.  Since this is just
 for example anyway, we're just hard-coding the output.

 <scons_output example="parseconfig_ex2" suffix="1">
    <scons_output_command>scons -Q</scons_output_command>
 </scons_output>
 -->

 <screen>
% <userinput>scons -Q</userinput>
['/usr/X11/include']
scons: `.' is up to date.
 </screen>

</section>
