conditional include

[Urs Liska]

Hi list,

I don't know if I _could_ find this info myself, but I'm quite puzzled 
about it and so I'd rather ask:

I would like to \include files depending on the presence (or absence) of 
certain command-line options.
Basically it should do something like:
- if option A is present then \include A.ily
- if option B is present then \include B.ily
- if none of them is present then \include default.ily

Ideally this would be a function that I can define in a separate file 
and only include this file in my main .ly file.

Background is: A, B and default are style sheets that style the score 
according to their context (e.g. standalone score <--> part of a book or 
draft <--> final mode).
While I know how to deal with this decision by writing both includes in 
the file and comment out the one I don't need ATM, I would highly prefer 
to be able to do this with a command line option, so I can run a script 
on a potentially large number of files. (The only other workaround I can 
think of now is to let the script actually rewrite the .ly file before 
compiling it, but I think that's not really elegant).

I'd be grateful about any hints or solutions.
Best
Urs