git-merged

#!/bin/sh
set -eu
    
usage () {
    echo "usage: git merged [-uh] [<branch>]" >&2
    echo >&2
    echo "Shows what local branches have been merged into branch (defaults to main branch)." >&2
    echo >&2
    echo "Options:" >&2
    echo "-u    Show unmerged branches instead of merged branches" >&2
    echo "-h    Show this help" >&2
}

unmerged=0
while getopts uh flag; do
    case "$flag" in
        u) unmerged=1;;
        h) usage; exit 2;;
    esac
done
shift $(($OPTIND - 1))

if [ $unmerged -eq 1 ]; then
    opts="--no-merged"
else
    opts="--merged"
fi

if [ $# -gt 0 ]; then
    base="$1"
    shift 1
else
    base="$(git main-branch)"
fi

git branch $opts "$base" | cut -c3- | grep -vxF "$base"