Check whether the current branch has <git hash> as an ancestor

is-ancestor-hash.sh

#!/bin/bash

export hash=$1

if [[ "$hash" == '' ]]; then
    echo usage: $0 '<git hash>'
    exit -1
fi

if git merge-base --is-ancestor $hash HEAD 2> /dev/null; then
    echo $hash is an ancestor of the current branch
else
    echo $hash is not an ancestor of the current branch
fi