#!/bin/sh

if [ $# -ne 2 ]; then
    echo "error: revert-merge needs exactly two arguments, the <commit>-ish to revert and the <commit>-ish of the mainline parent" >&2
    exit 1
fi
git rev-parse "$2" >/dev/null || exit 1
set -- $(git rev-list --parents -n 1 "$1")
parent=$(( $# - 1 ))
git revert "$1" -m $parent