Update DynV6.net DynDNS via Bash Script

update-ipv6.sh

#!/bin/bash

set -euo pipefail

IP4=$(curl -sS -f https://api.ipify.org)
IP4_DNS=$(dig +short myhostname.dynv6.net A @dynv6.com)

IP6=$(curl -sS -f https://api64.ipify.org)
IP6_DNS=$(dig +short myhostname.dynv6.net AAAA @dynv6.com)

if [[ "${IP6}" == "${IP6_DNS}"  ]] && [[ "${IP4}" == "${IP4_DNS}" ]]; then
 echo "No update necessary." 1>&2
 exit 0;
fi

echo "Updating DynV6.net" 1>&2
curl -sS -f "http://dynv6.com/api/update?hostname=myhostname.dynv6.net&ipv4=${IP4}&ipv6=${IP6}&token=mysecrettoken" > /dev/null