#!/bin/sh
# bak -- move a file to file.bak (or back)
set -e
die() {
	echo "$*" 1>&2
	exit 1
}

[ -z "$1" ] && die "usage: bak FILE"

BAK="$1.bak"
if [ -e "$BAK" ] && [ -e "$1" ]; then
	die "$1 and $BAK exist, unable to bak or unbak"
elif [ -e "$BAK" ]; then
	mv "$BAK" "$1"
	echo "$BAK -> $1"
elif [ -e "$1" ]; then
	mv "$1" "$BAK"
	echo "$1 -> $BAK"
else
	die "Neither $1 nor $BAK exist, unable to bak or unbak"
fi