re Treewind's comments, I've just had a look (I tend not to remember these things) at the command line we use. It comes down to.

abc2abc inputfile -e -t semitones >outputfile;

-e turns off error reporting. (We do make other, ie. abcmps and amc2mid output messages available from the converter but not this progs output...)
-t transposes up t semitones if positive, down if negative.

There are other switches but I don't think I've used them.