How to undo after patch is applied? .rej/.orig files

If you're not giving any option to patch other than -pN, it only creates those files when a patch fails to apply cleanly.

So, one option is to stop creating (or accepting) bad patches. :)

Back in the real world, this is a feature. When patch(1) fails to apply a patch segment to the original file, it saves the temporary original file copy out durably as *.orig, dumps the rejected segment to *.rej, and continues trying to apply patch segments. The idea is that you can open the *.rej file and complete the patch process manually by copying bits and pieces over to the patched file. The *.orig file can also be useful when the patch process accidentally wrecks something, and you need to refer to the original version to fix it.

I don't always fix a bad patch with text from the *.rej and *.orig files, but it's nice to have them in case I need them.

Once I've fixed up a bad patch, I run the following script at the project root to quickly clean things up:

#!/bin/bash
find . '(' \
    -name \*-baseline -o \
    -name \*-merge -o \
    -name \*-original -o \
    -name \*.orig -o \
    -name \*.rej \
')' -delete

I call it cleanup-after-bad-patch because the long name partially insures against running this accidentally, since it could remove files you still need. To be honest, though, I normally run it by typing cleanTabEnter, that being sufficient to find this script in the PATH on my development machines.

The additional patterns it checks for are for the files output by my version control system of choice when it encounters the same problem during a merge operation. You may wish to adjust it for your VCS/SCM tools.

You'll need patchutils installed for this.

This script will split one large patch into smaller separate paches, each of them containing only one hunk for one file. You can then apply these patches with patch --forward.

#!/bin/sh -eu

PATCH=$1
OUTDIR=$2

test -f "$PATCH" && test -d "$OUTDIR"

TDIR=$(mktemp -d)
trap 'rm -rf $TDIR' 0

INDEX=0
TEMPHUNK=$TDIR/current_hunk

lsdiff $1 | while read FNAME
do
    HUNK=1
    while :
    do
        filterdiff --annotate --hunks=$HUNK -i "$FNAME" "$PATCH" > "$TEMPHUNK"
        HUNK=$((HUNK+1))
        test -s "$TEMPHUNK" && \
            {
                mv "$TEMPHUNK" "$OUTDIR/$INDEX.diff"
                INDEX=$((INDEX+1))
            } || break
    done
done

Edit: save script to hunks.sh, and call it:

./hunks.sh path/to/big.diff path/to/output/directory