SCons - Advanced

2018-02-23 · 434 words · 3 minute read

Tool

SCons · Advanced

Table of Contents

Controlling Output
- Help function
- Progress function
Running any command
Searching in PATH and directories
- Specify PATH Environment Variable
- Specify folders for #include files

Controlling Output

Extract from this section: http://scons.org/doc/HTML/scons-user.html#chap-output

Help function

You can specify some help message:

Help("""
Type: 'scons program' to build the production program,
      'scons debug' to build the debug version.
""")  # You can append to existing message with 'append=True'

The help message is display with

$ scons -h

Progress function

This function helps to show which files are evaluated to decide if they are up-to-date or not.

Progress('Evaluating $TARGET\n')
Program('f1.c')
Program('f2.c')

You can some options to write in a file for example

Progress('$TARGET\r',
         file=open('build.log', 'w'),
         overwrite=True)
Program('f1.c')
Program('f2.c')

Or even write your own function

def progress_function(node)
    print("Evaludating %s" % node)
    # Do something with the node

Progress(progress_function)

Running any command

The list of built-in builders can be found here.
The list of tools it uses can be found here.

Additionally, any command can easily be added via the Command Builder.

An example of Command Builder with sed:

SConstruct

env = Environment()
env.Command('foo.out', 'foo.in', "sed 's/x/y/' < $SOURCE > $TARGET")

Another example using a custom Python function:

SConstruct

def build(target, source, env):
    # Whatever it takes to build
    return None

env = Environment()
env.Command('foo.out', 'foo.in', build)

Tip	You can also use variable expansion `env.Command('${SOURCE.basename}.out', 'foo.in', build)`

Searching in PATH and directories

Refer to FAQ for more details.

Specify `PATH` Environment Variable

The environment variable PATH for SCons is limited to Python to be system independent.

If you need to have the same PATH as your system, you can do the following:

import os
env = Environment(ENV = {'PATH' : os.environ['PATH']})

If you need the whole same enviroment as in Windows, you can do

import os
env = Environment(ENV = os.environ)

It is actually better to have a selection of the environment variables in the path. You can

Set the paths you want to specify
Add a filtered selection of the paths from your system

Solution 1

path= ['/bin', '/usr/bin', '/path/to/other/compiler/bin']
env = Environment(ENV = {'PATH' : path})

Solution 2

paths = os.environ['PATH'].split(os.pathsep)
# Only adding Path related to Ruby
extra_paths = [p for p in paths if 'ruby' in p.lower()]
cust_path = sys.path + extra_paths

# ENVIRONMENT
env = Environment(ENV={'PATH':cust_path})

Specify folders for `#include` files

If your program has #include files in various directories, SCons must somehow be told in which directories it should look for the #include files. You do this by setting the CPPPATH variable to the list of directories that contain .h files that you want to search for:

env = Environment(CPPPATH='inc')
env.Program('foo', 'foo.c')