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.

See also: https://github.com/twaugh/patchutils