i would recommend comparing $file().mtime to detect file edits rather than MD5 hashes (or mtime and then a hash to cover cases where the file was saved/modified at least once but there was no change in its contents, if applicable), even though as a user you're unlikely to notice a difference between the two unless the total filesize of your scripts is tremendous.
for small strings of text (such as the filenames up there), i'd suggest one of the 32-bit $hash( , 32) or $crc( , 0) or even a sensible character replacement if collisions would be disastrous for you.
even though MD5 hash generation is computationally expensive, it won't impact the performance of a script in most practical cases, but there's something about using it for these types of checks that seems a bit overkill :P
