Appendix E. 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.

Example E.1. Wildcard globbing to create a list of filenames

files = Glob(wildcard)

Example E.2. Filename extension substitution

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

Example E.3. Appending a path prefix to a list of filenames

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

Example E.4. Substituting a path prefix with another one

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

Example E.5. 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]

Example E.6. The "backtick function": run a shell command and capture the output

import subprocess
output = subprocess.check_output(command)

Example E.7. 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('') # produces test.h from
env.Program('app','main.cpp') # indirectly depends on

## 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.

Where main.cpp looks like this:

#include "test.h"

produces this:

% scons -Q
cat < > test.h
cc -o app main.cpp
cat < foo.bar2 > foo.cpp
cc -o app2 main2.cpp foo.cpp