dns_record_change_alert.sh

#!/bin/bash
#
# Very simple Script that checks a configured DNS Record, 
# If it changed since the Last time this script was run, 
# it alerts a specified Mail Recipient
# http://tecadmin.net/ways-to-send-email-from-linux-command-line/
#

# Config Stuff
DOMAIN="example.com"
DNS_SERVER="8.8.8.8"
MAIL_RECIPIENT="alert@example.com"
MAIL_SUBJECT="Mail Alert DynDNS"

# Dont touch stuf after this comment, if you dont know what you are doing!
OLDIP_FILE="OLDIP.txt"
CURRENTIP=$(dig +noall +answer +nocomments ${DOMAIN} @${DNS_SERVER} | awk '{print $5}')
OLDIP=$(cat "${OLDIP_FILE}")
echo "${CURRENTIP}" > "${OLDIP_FILE}"

if [ "${OLDIP}" == "${CURRENTIP}" ]; then
  exit 0
else
  echo "ERROR=DNS RECORD CHANGED!"
  echo "DOMAIN=\"${DOMAIN}\""
  echo "DNS_SERVER=\"${DNS_SERVER}\""
  echo "OLD_IP=\"${OLDIP}\""
  echo "NEW_IP=\"${CURRENTIP}\""
  # Send Mail
  echo "DNS RECORD for \"${DOMAIN}\" changed from \"${OLDIP}\" to \"${CURRENTIP}\"" | mail -s ${MAIL_SUBJECT} ${MAIL_RECIPIENT} 
  exit 1
fi