Specify output filename from within lilypond?

[Ian Hawthorn]

How do you specify the output file name from within
lilypond? Can you in fact do this at all? What I have in
mind is a template for producing part specific music
and learning midis for a quartet from a single lilypond file.
It would be simple enough to write multiple score blocks
in a template to build the desired types of output. However
how could you make each score block send its output to a
different place.

When arranging music I prefer to work with a full score. Once
the arrangement is complete however, building the part specific
learning  midis is a tedious process requiring me to rewrite the
file to separate out the music definitions from the score block
and then create a bunch of special files with appropriate names
which input the music definition file by name (so I can't just reuse them -
they have to be edited each time anew) and contain a score block
to construct the desired midi part files. Finally I have to run lilypond on
each of these separately ( a slow repetitive and boring process).

I can't help thinking that there has to be a better way. The only real
reason why all those separate files are needed at all is to set different
names for the MIDI and pdf output files produced by the score
blocks they contain. If this could be done directly from within lilypond,
I could set up a template to produce all the different types of output
I want from a single ly file on a single pass without all this hassle.