#!/bin/bash
# Sends an email when a webpage has been changed. 
# Meant to be run with cron. Body of email is url.

ADDRESS="your@address.com"
TMPFILE=~/bin/.urlalert

[ "$1" ] || {
 echo " use: $(basename $0) url [subject of email]"
 exit
}

PAGE=$1
shift
SUBJECT="${*:-urlalert: page has changes}"

GET=$(curl -s -I "$PAGE" | awk -v p="$PAGE" '
 /Last-Modified/{sub(/^[^:]*: /,"",$0);x=$0}
 /Content-Length/{y=$2}
 END{ if( x ){ print p " " x }else print p " " y } 
')
OLD=$(awk -v a="$PAGE" '$1 == a {print $0}' $TMPFILE 2>/dev/null)

[ "$OLD" == "$GET" ] && exit 
echo "$PAGE" | mail -s "$SUBJECT" $ADDRESS

awk -v a="$PAGE" -v g="$GET" '
 $1 != a {print $0}
 END { print g }
' $TMPFILE 2>/dev/null > $TMPFILE.swp
mv $TMPFILE.swp $TMPFILE