flipdiff

flipdiff [OPTIONS] [FILE...]

--help (-h)
    Displays a usage message and exits.

--version (-v)
    Shows version information and exits.

--silent (-s), --quiet (-q)
    Suppresses warning messages during processing.

--force (-f)
    Forces flipdiff to proceed even if warnings are encountered, attempting to generate output despite potential issues.

--check (-c)
    Checks if the reversed patch contains any reversed chunks, which can indicate issues if the intention was to truly reverse the patch's effect.

--no-check
    Disables the check for reversed chunks, even if default behavior would include it.

FILE...
    One or more patch files to process. If no files are specified, flipdiff reads the patch from standard input.

flipdiff is a utility from the patchutils suite designed to reverse the direction of a patch. When provided with a patch generated by diff -u old new, flipdiff produces a new patch that effectively swaps the 'old' and 'new' file contexts in the diff header, making it suitable for operations expecting diff -u new old. This operation is functionally similar to preparing a patch to be undone using patch -R, as it sets up the diff to indicate the original 'new' file as the 'old' and vice versa. It reads the patch from standard input or specified files and writes the reversed patch to standard output.

While flipdiff reverses the order of files in a diff header (e.g., from 'a/old' to 'b/new' to 'b/new' to 'a/old'), it does not inherently reverse the *effect* of the patch. For example, if a patch adds lines, flipdiff will produce a diff that still shows those lines, but from the perspective of the original 'new' file being the 'old' file. To truly *undo* a patch's changes, the patch -R command is typically used. flipdiff is primarily useful for manipulating the directionality of diffs for comparison or reapplication purposes.

flipdiff returns an exit status of 0 on successful execution. An exit status of 1 indicates minor problems, such as warnings that occurred during processing (unless suppressed by --silent or --force). A status of 2 signifies serious errors that prevented the command from processing the patch.

The command typically takes a patch as input via standard input (e.g., `cat patchfile | flipdiff`) or directly from one or more specified files (e.g., `flipdiff patchfile.diff`). The resulting reversed patch is then printed to standard output, which can be redirected to a new file or piped to another command.

flipdiff is part of the patchutils package, a suite of small, specialized utilities for manipulating and analyzing diff files. This collection was developed by Simon Michael to address common needs in patch management workflows that were not covered by standard tools like diff and patch alone. Its development, like the rest of patchutils, has been community-driven within the open-source ecosystem, aiming to provide robust and flexible tools for developers working with patches.

patch(1), diff(1), interdiff(1), lsdiff(1), combinediff(1), splitdiff(1), recountdiff(1)