git-diff-directory

#!/usr/bin/env bash

stat=true
if [[ "$1" == "-p" ]]; then
    stat=false
    shift 1
fi

HERE=$(pwd)

(cd "$1" && git --git-dir="$HERE/.git" diff "${2:-HEAD}") | \
    if [[ $stat == true ]]; then \
        diffstat | grep -v only$; \
    else \
        cat; \
    fi