The diff algorithm computes the differences between two arrays of elements,
like the unix program "diff". diff.rb is a Ruby conversion of the Perl's
Algorithm::Diff. It can diff Arrays by each element or Strings by each
character, or your own class if you implement the interface. The algorithm
is complete, stable (TestUnit test available), but the interface may change
before a 1.0 release.

				-- excerpt from RAA (Ruby Application Archive)

WWW: http://www.rubynet.org/mirrors/diff/