git-what-the-hell-just-happened

#!/usr/bin/env bash

set -e

ref=${1:-"HEAD"}

old="${ref}@{1}"
new=$ref

log() {
    git log --graph --pretty=short -1 "$1"
}

echo "Old revision:"
log "$old"
echo
echo "New revision:"
log "$new"
echo
echo "Changes:"
git diff --stat --summary "$new" "$old"