#!/bin/bash
set -euo pipefail
IFS=$'\n\t'

# Create symlink after backing up the target.

usage="Usage: ${0##*/} source_file target_file"
src=${1:?$usage}
tgt=${2:?$usage}
backup=~/.backup

[[ ! -d $backup ]] && mkdir $backup
[[ -e "$tgt" ]] && mv "$tgt" "$backup/${tgt##*/}-$(date '+%Y-%m-%d-%H%M%S')" || true
ln -sf "$src" "$tgt"