Sounds like a diff script is what is wanted. I may have something lying around somewhere from a previous job, but no guarantees on that. In meantime, "diff" is also a shell command (on Un*x systems), and as noted there are certainly other apps written that do diffs as part of their operation (some of them, e.g., Wikipedia's Mediawiki, are even PHP-based - see its internal _DiffEngine class).
