Return the SHA of a parent commit that is equivalent to the current git commit. Useful for CI and DevOps purposes.

get_equal_parent.sh

TARGET_COMMIT=${1:-HEAD}

if [ $TARGET_COMMIT == "-h" ]; then
    echo "
Usage: ./get_equal_parent.sh <commit-hexsha>

Return the SHA of a parent commit that is equivalent (no diff) to the current
commit. If no equivalent parent commit exists, then return \"\".
"
    exit
fi

PARENTS=$(git rev-list --parents -n 1 $TARGET_COMMIT | cut -d' ' -f2-)
EQUAL_COMMIT=""

for PARENT in $PARENTS
do
    DIFF=$(git diff $TARGET_COMMIT..$PARENT)
    if [ -z "${DIFF}" ]; then
        EQUAL_COMMIT=$PARENT
    fi
done

echo $EQUAL_COMMIT