Patchutils is a small collection of programs that operate on patch files.

 - Interdiff generates an incremental patch from two patches against a common
   source.
 - Combinediff generates a single patch from two incremental patches, allowing
   you to merge patches together.
 - Filterdiff will select the portions of a patch file that apply to files
   matching (or, alternatively, not matching) a shell wildcard.
 - Fixcvsdiff is for correcting the output of 'cvs diff'.
 - Rediff corrects hand-edited patches, by comparing the original patch with
   the modified one and adjusting the offsets and counts.
 - Lsdiff displays a short listing of affected files in a patch file, along
   with (optionally) the line numbers of the start of each patch.
 - Splitdiff separates out patches from a patch file so that each new patch
   file only alters any given file once.
 - Grepdiff displays a list of the files modified by a patch where the patch
   contains a given regular expression.
 - Recountdiff fixes up counts and offsets in a unified diff.
 - Unwrapdiff fixes word-wrapped unified diffs.

WWW: http://cyberelk.net/tim/software/patchutils/