#!/bin/bash -e

# Use with crontab entry like:
#   */5 *   *   *   *     $HOME/bin/monitor-dir /path/to/something

if [ -z "$1" ]; then
	echo "Usage $0 dir [monitor_file] [ls]"
	exit 1
fi
mon="${2:-$1/.monitor_dir}"
mon_tmp="${mon}_tmp"

${3:-ls} "$1" > "$mon_tmp"
if [ -r "$mon" ] && ! cmp -s "$mon" "$mon_tmp" && [ -n "$(ls "$1")" ]; then
	comm -13 "$mon" "$mon_tmp"
fi
mv "$mon_tmp" "$mon"