ufw-dynamic-dns.sh

#!/bin/bash
HOSTNAME=your.dns.here
UFW=/usr/sbin/ufw

if [[ $EUID -ne 0 ]]; then
   echo "This script must be run as root"
   exit 1
fi

new_ip=$(dig +short $HOSTNAME)
old_ip=$($UFW status | grep $HOSTNAME | head -n1 | tr -s ' ' | cut -f3 -d ' ')

if [ "$new_ip" = "$old_ip" ] ; then
    echo IP address has not changed
else
    if [ -n "$old_ip" ] ; then
        $UFW delete allow from $old_ip to any
    fi
    $UFW allow from $new_ip to any comment $HOSTNAME
    echo firewall has been updated
fi