devel/unidiff - The NetBSD Packages Collection

Unify will accept either a regular context diff (old- or new-style) or
a unified context diff as input, and generate either a unified diff or
a new-style context diff as output.  The default is to output the
opposite style of whatever was input, but this can be overridden by
the -c or -u options.  If the source file is not mentioned, it will be
read from the standard input.

Various other options allow you to echo the non-diff (comment) lines
to stderr, modify the diff by removing the comment lines, and/or tweak
the diff into a format that is good for releasing patches.

Unipatch is a filter to turn a unified diff into a degenerate context
diff (no '!'s) for patch.