SCons configuration file and default values

Question

Hi,

I have a project which I build using SCons (and MinGW/gcc depending on the platform). This project depends on several other libraries (lets call them libfoo and libbar) which can be installed on different places for different users.

Currently, my SConstruct file embeds hard-coded path to those libraries (say, something like: C:\libfoo).

Now, I'd like to add a configuration option to my SConstruct file so that a user who installed libfoo at another location (say C:\custom_path\libfoo) can do something like:

> scons --configure --libfoo-prefix=C:\custom_path\libfoo

Or:

> scons --configure
scons: Reading SConscript files ...
scons: done reading SConscript files.
### Environment configuration ###
Please enter location of 'libfoo' ("C:\libfoo"): C:\custom_path\libfoo
Please enter location of 'libbar' ("C:\libfoo"): C:\custom_path\libbar
### Configuration over ###

Once chosen, those configuration options should be written to some file and reread automatically every time scons runs.

Does scons provide such a mechanism ? How would I achieve this behavior ? I don't exactly master Python so even obvious (but complete) solutions are welcome.

Thanks.

Answer 1

SCons has a feature called "Variables". You can set it up so that it reads from command line argument variables pretty easily. So in your case you would do something like this from the command line:

scons LIBFOO=C:\custom_path\libfoo

... and the variable would be remembered between runs. So next time you just run scons and it uses the previous value of LIBFOO.

In code you use it like so:

# read variables from the cache, a user's custom.py file or command line
# arguments
var = Variables(['variables.cache', 'custom.py'], ARGUMENTS)
# add a path variable
var.AddVariables(PathVariable('LIBFOO',
        'where the foo library is installed',
        r'C:\default\libfoo', PathVariable.PathIsDir))

env = Environment(variables=var)
env.Program('test', 'main.c', LIBPATH='$LIBFOO')

# save variables to a file
var.Save('variables.cache', env)

If you really wanted to use "--" style options then you could combine the above with the AddOption function, but it is more complicated.

This SO question talks about the issues involved in getting values out of the Variables object without passing them through an Environment.