The complex part would seem to be how to compute a meaningful "percentage".

For instance, I have 2 files of 39 lines each, that differ due to formatting. Just looking at line comparisons (using eq), 27 of the 39 lines match (69.23%). Using Algorithm::Diff, though, there are 4 "hunks" of changes reported by the diff() function, but those 4 "hunks" consisted of 17 changes (8 additions, 9 subtractions).

Thoughts?