If your log file is large, considering using a binary search technique to locate the desired line. I'm sure there's a CPAN module to do this, but I can't seem to find it at the moment. I did find this perlmonks writeup which basically describes what to do: http://www.perlmonks.org/?node_id=260659

Another heuristic to use would be to begin the search near the end of the file (since it is a log file and today's entries will occupy the tail end of it -- unless, of course, your applications are running in the future.)