git-undo-commit

#!/bin/sh
set -e

usage () {
    echo "usage: git undo-commit [-fh] <file> [<file> ...]" >&2
    echo >&2
    echo "Remove the last commit, but keep its changes staged (like right before the commit)." >&2
    echo "If you specify the -f flag, it removes the changes too." >&2
    echo >&2
    echo "Options:" >&2
    echo "-f    Don't keep the commit's changes (destructive)" >&2
    echo "-h    Show this help" >&2
}

force=0
while getopts fh flag; do
    case "$flag" in
        f) force=1;;
        h) usage; exit 2;;
    esac
done
shift $(($OPTIND - 1))

if [ $force -eq 1 ]; then
    opts="--hard"
else
    opts="--soft"
fi

git reset $opts HEAD~1