Including input files via command line

[Benjamin Bruce]

Is there a way to compile multiple input files into one output file via the 
command line? Currently I am using \include, but I would like to be able to 
choose the included file on the fly without editing the main file.

Another thought I had was maybe there is a way to pass a value to the .ly file 
via the command line and use Scheme to choose the appropriate file to import 
based on that value. But that may be even more far-fetched.

Thanks for your help!