imarith *.fits - dark.fits ds_//*.fits...though I can't remember right now how to do replacement etc.
imarith *.fits - dark.fits ds_//*.fits
mscred
setinstrument kpno CCDMosaThin1
msccmatch obj09*.fits coords="!mscgetcat $I $C" search=60 rsearch=1 nfit=30 accept=yes interactive=no fit=no