email-dyndns.sh

#!/bin/bash
# Send an e-mail with your IP address if it has changed

set +e
old_ipaddr=$(cat /tmp/ipv4.log)

set -e

get_ipv4()
{
    # Return string with current IPv4 address
    ipv4=$(dig TXT -4 +short o-o.myaddr.l.google.com @ns1.google.com |
            awk -F'"' '{ print $2}')
    echo "${ipv4}"
}

ipaddr=$(get_ipv4)

if [[ "$old_ipaddr" == "$ipaddr" ]]; then
        exit 0
fi

echo "To: john.doe@gmail.com
Subject: IPv4 Address
From: cron@myhost.com

Current IP address: ${ipaddr}" | sendmail -v john.doe@gmail.com

echo $ipaddr > /tmp/ipv4.log