Commands to backup and unbackup files rotating its names

bak.sh

#!/usr/bin/bash

function bak() {
    name=${1%/}
    prefix=${name%.bak}
    if [[ $prefix == $name ]]; then
        backup $name
    else
        unbackup $name
    fi
}

function backup() {
    local name=${1%/} n=${2:--1} cur_name next_name
    if (( $n == -1 )); then
        if [[ ! (-f $name || -d $name) ]]; then
            echo $name is invalid or does not exist
            return 1
        fi
        cur_name=$name
        next_name=$name.bak
    elif (( $n == 0 )); then
        cur_name=$name.bak
        next_name=$name.bak.1
    else
        cur_name=$name.bak.$n
        next_name=$name.bak.$((n+1))
    fi

    if [[ -f $next_name || -d $next_name ]]; then
        backup $name $((n+1))
        if (( $? )); then
            return $?
        fi
    fi

    mv $cur_name $next_name
}

function unbackup() {
    local name=${1%.bak?(/)}
    local cur_name=$name next_name=$name.bak n=0

    if [[ ! (-f $next_name || -d $next_name) ]]; then
        echo $next_name is invalid or does not exist
        return 1
    fi

    while [[ -f $next_name || -d $next_name ]]; do
        (( n++ ))
        mv $next_name $cur_name
        cur_name=$next_name
        next_name=$name.bak.$n
    done
}