A script to determine whether one git commit is the ancestor of another

git-is-related

#!/bin/sh

if [ $# -lt 1 ]; then
    echo "Expecting one or two arguments" >&2
    exit 2
fi
a=$1
b=$2
[ -z "$b" ] && b=HEAD

if git merge-base --is-ancestor "$a" "$b"; then
    echo "$a is an ancestor of $b"
elif git merge-base --is-ancestor "$b" "$a"; then
    echo "$b is an ancestor of $a"
else
    echo "$a and $b are not related"
    exit 1
fi