--evaluate command line option

[Johan Vromans]

I often use my .ly files for different purposes, e.g., to print
self-contained sheet music and to print embedded sheet music. In the
latter case I do not want headings, and use different page settings.

I want to control this from the command line. For this purpose, I'd
like to set a variable that I can use in the .ly file to deal with the
different settings.

LulyPond's --define would be nice but it only understands a predefined
set of variables. 

--evaluate is more powerful and flexible, but it is not quite clear to
me how this must be done.

I could use a couple of hints or examples of things to do with
--evaluate.

Thanks for any help, pointers, ...

-- Johan
   Chord is alive! http://chordii.sourceforge.net