There are several tools that can make your life enourmously easier when building and patching Perl. A context diff provides pretty much the same information as VMS diff does, however it has several features that VMS diff lacks. It's the accepted method of providing changes to Perl source on the Perl5-Porters mailing list Patch Patch is the opposite of diff.
Patch is fairly clever.
Patch is also clever enough to unapply patches if you need to back them out for some reason.