flipdiff

flipdiff [options] [file]

-p NUM
    Strip NUM leading components from filenames in paths.

-U NUM
    Set number of context lines to NUM (default from input).

-L LABEL
    Use LABEL instead of filename in output header.

-o FILE, --output=FILE
    Write output to FILE instead of stdout.

--help
    Display usage summary and exit.

--version
    Output version information and exit.

flipdiff is a command-line utility from the patchutils package designed to reverse the direction of differences in unified diff files. It transforms lines marked for deletion (-) into additions (+) and vice versa, while preserving unchanged context lines. This is particularly useful when a patch needs to be applied in reverse—for example, to undo changes or correct a patch generated from the wrong file order.

By flipping the hunk signs, flipdiff enables tools like patch to apply the inverted diff correctly. It handles standard unified diff format (diff -u) reliably and supports multiple files or stdin input. Common workflows include generating a reversed patch for distribution or testing revert scenarios.

Limitations apply to non-unified formats or complex diffs with binary files, where results may be unpredictable. Always verify the output with diff before applying.

Works only on unified diffs; context, normal, or ed formats are unsupported or produce errors. Complex diffs (e.g., with function headers or binaries) may flip incorrectly—validate output before use.

flipdiff input.patch > reversed.patch
Applies reversed patch: patch -p1 < reversed.patch

Developed by Tim Waugh as part of GNU patchutils (first released ~2002). Evolved to handle modern diff features; maintained in most Linux distros via patchutils package.

filterdiff(1), lsdiff(1), patch(1), diff(1)