Email when a DNS change has propagated to a certain nameserver.

notify-on-dns-propagated.sh

#!/usr/bin/env bash

# The IP to which you just updated your DNS
NEW_IP="127.0.0.1"

# The domain for which you're awaiting propagation
DOMAIN="EXAMPLE.COM"

# Polling interval in seconds
WAIT=30

until [ "$(host "${DOMAIN}" | awk 'NR==1{print $4}')" = "${NEW_IP}" ]; do
  echo "$(date) Still waiting..."
  sleep ${WAIT};
done

echo "The DNS migration for ${DOMAIN} has propagated and the server which can now see itself as ${NEW_IP}." | \
mail -s "DNS update for ${DOMAIN} to ${NEW_IP} propagated" you@example.com

# If you run this script but abort it before the condition is met, don't send any emails.
trap "exit" SIGHUP SIGINT SIGTERM