Depending on the exact nature of the problem, even Digest::MD5 might be overkill.

If your probelm is just to compare an old file to a new file once to see if they differ, then MD5 is unnecessary. Simply compare their sizes. If they differ, you are done. If they are the same, open the two files and compare line by line, breaking out of the loop at the first difference. Easy and faster than hashing both files first.

If your problem is to compare a new file against many old files (to reject duplicates) or to compare many new files to an old file (sample and do something when a file is updated) then hashing to an MD5 signature is the fastest approach. Although it depends on differing files generating differing signatures, the chance of a collision is, welll, you should live so long :)

-Mark