Enhancement: command line option to transpose N halftones up or down

[Michael Schuerig]

I've only been using LilyPond for a rather short time, so far mostly for 
engraving short snippets transposed into several keys for practicing. Of 
course, the transpose command works nicely for this.

However, it made me think of how transposing could be even nicer and now I'm 
wishing for a command line option to the lilypond command to transpose the 
engraved document by N halftones up or down. The particular advantage would 
be that this way the original document doesn't need to be changed in any way 
in order to transpose it.

Does this sound reasonable?

Michael