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<para>
There is a common set of simple tasks that many build configurations rely
on as they become more complex. Most build tools have special
purpose constructs for performing these tasks, but since &SConscript;
files are &Python; scripts, you can use more flexible built-in &Python;
services to perform these tasks. This appendix lists a number of these
tasks and how to implement them in &Python; and &SCons;.
</para>

<example>
<title>Wildcard globbing to create a list of filenames</title>
<programlisting>
files = Glob(wildcard)
</programlisting>
</example>

<example>
<title>Filename extension substitution</title>
<programlisting>
import os.path
filename = os.path.splitext(filename)[0]+extension
</programlisting>
</example>

<example>
<title>Appending a path prefix to a list of filenames</title>
<programlisting>
import os.path
filenames = [os.path.join(prefix, x) for x in filenames]
</programlisting>
</example>

<example>
<title>Substituting a path prefix with another one</title>
<programlisting>
if filename.find(old_prefix) == 0:
    filename = filename.replace(old_prefix, new_prefix)
</programlisting>
</example>

<example>
<title>Filtering a filename list to exclude/retain only a specific set
of extensions</title>
<programlisting>
import os.path
filenames = [x for x in filenames if os.path.splitext(x)[1] in extensions]
</programlisting>
</example>

<example>
<title>The "backtick function": run a shell command and capture the
output</title>
<programlisting>import os
output = os.popen(command).read()
</programlisting>
</example>

<example>
<title>Generating source code: how code can be generated and used by SCons</title>

<para>

The Copy builders here could be any arbitrary shell or python function
that produces one or more files.  This example shows how to create
those files and use them in &SCons;.

</para>

<programlisting>
#### SConstruct
env = Environment()
env.Append(CPPPATH = "#")

## Header example
env.Append(BUILDERS =
   {'Copy1' : Builder(action = 'cat &lt; $SOURCE &gt; $TARGET',
                      suffix='.h', src_suffix='.bar')})
env.Copy1('test.bar') # produces test.h from test.bar. 
env.Program('app','main.cpp') # indirectly depends on test.bar

## Source file example
env.Append(BUILDERS =
  {'Copy2' : Builder(action = 'cat &lt; $SOURCE &gt; $TARGET',
                     suffix='.cpp', src_suffix='.bar2')})
foo = env.Copy2('foo.bar2') # produces foo.cpp from foo.bar2. 
env.Program('app2',['main2.cpp'] + foo) # compiles main2.cpp and foo.cpp into app2.
</programlisting>

<para>

Where main.cpp looks like this:

</para>

 
 <programlisting>
#include "test.h"
</programlisting>

<para>
produces this:
</para>

 <screen>
    % <userinput>scons -Q</userinput>
    cc -o app main.cpp
    cat &lt; foo.bar2 &gt; foo.cpp
    cc -o app2 main2.cpp foo.cpp
    cat &lt; test.bar &gt; test.h
 </screen>
    
</example>