-s is the right switch: you'll note that there are references (but no assignments to) $d,$g, $p and $matchstr? These are supposed to be set via the command line, and the -s switch. As in: objdump -matchstr=freddy li < input That's just an example, btw. I haven't figured out what the blasted thing does (except machstr is not optional, and should be a regexp capturing three components).