relpath.zsh

relpath() {
    local -a components cur_components rel_path
    local i

    components=( ${(s:/:)1:a} )
    cur_components=( ${(s:/:)PWD:a} )

    while [[ $components[1] = $cur_components[1] ]]; do
        shift components cur_components
    done

    for (( i = 0; i <= $#cur_components; i++ )); do
        rel_path+=( .. )
    done
    shift rel_path

    rel_path+=( $components )

    REPLY=${(j:/:)rel_path}
}