Unsolicited advice, but since you're "strictifying" the script, I'd recommend changing open IN, $filename to open my $in, '<', $filename (and if you don't use autodie, then also add or die("Couldn't open $filename: $!")). A global FILEHANDLE led to one of the nastiest bugs I've ever debugged. Also the code assumes $1, $2, and $3 were matched, so you might want to add a check on whether they're defined.