# Handling Common Tasks

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;.

## Wildcard globbing to create a list of filenames

    files = Glob(wildcard)

## Filename extension substitution

    import os.path
    filename = os.path.splitext(filename)[0]+extension

## Appending a path prefix to a list of filenames

    import os.path
    filenames = [os.path.join(prefix, x) for x in filenames]

## Substituting a path prefix with another one

    if filename.find(old_prefix) == 0:
        filename = filename.replace(old_prefix, new_prefix)

## Filtering a filename list to exclude/retain only a specific set of extensions

    import os.path
    filenames = [x for x in filenames if os.path.splitext(x)[1] in extensions]

## The "backtick function": run a shell command and capture the output

    import subprocess
    output = subprocess.check_output(command)

## Generating source code: how code can be generated and used by SCons

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;.

#### SConstruct env = Environment() env.Append(CPPPATH = "#")

## Header example env.Append(BUILDERS = {'Copy1' : Builder(action = 'cat < $SOURCE > $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 < $SOURCE > $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.
#include "test.h"
// nothing here
//// main2.cpp
// nothing here

Where main.cpp looks like this:

produces this:

scons -Q