To reverse a patch, use /dev/null for diff2.
To reduce the amount of context in a patch, use:
interdiff -U1 /dev/null patchfile
Since interdiff doesn't have the advantage of being able to look at the files that are to be modified, it has stricter requirements on the input format than patch(1) does. The output of GNU diff will be okay, even with extensions, but if you intend to use a hand-edited patch it might be wise to clean up the offsets and counts using recountdiff(1) first.
Note, however, that the two patches must both be relative to the versions of the same original set of files.
The diffs may be in context format. The output, however, will be in unified format.
-p n, --strip-match=n
-U n, --unified=n
-d PATTERN, --drop-context=PATTERN
Note that the interpretation of the shell wildcard pattern does not count slash characters or periods as special (in other words, no flags are given to fnmatch). This is so that "*/basename"-type patterns can be given without limiting the number of pathname components.
interdiff -z 3.2pre1.patch.gz 3.2pre2.patch.gz
Reversing a patch:
interdiff patch /dev/null
Reversing part of a patch (and ignoring the rest):
filterdiff -i file.c patchfile | \ interdiff /dev/stdin /dev/null
There are currently no known bugs in interdiff; but there are some caveats. If you find a bug, please report it (along with a minimal test case) to Tim Waugh <email@example.com>.
There are some sets of patches in which there is just not enough information to produce a proper interdiff. In this case, the strategy employed is to revert the original patch and apply the new patch. This, unfortunately, means that interdiffs are not guaranteed to be reversible.
Tim Waugh <firstname.lastname@example.org>
Michael K. Johnson <email@example.com>