Dyndns2 Bash update script

dyndns2.sh

#!/bin/bash

if [ -r "${0%.sh}.conf" ]; then {
  . "${0%.sh}.conf"
} else {
  echo -e "\n\tAdd the variables HOSTNAME, USERNAME and PASSWORD to the file ${0%.sh}.conf, adjust the update URL and run this script once a minute!\n"
}; fi


DIG="`which dig` +short"
NS0_NAME=`${DIG} SOA  ${HOSTNAME}             | sed -e 's/\. .*//'`
DNS_IPv4=`${DIG} A    ${HOSTNAME}             @${NS0_NAME}`
DNS_IPv6=`${DIG} AAAA ${HOSTNAME}             @${NS0_NAME}`
NET_IPv4=`${DIG} TXT  o-o.myaddr.l.google.com @ns1.google.com -4`
NET_IPv6=`${DIG} TXT  o-o.myaddr.l.google.com @ns1.google.com -6`
NET_IPv4="${NET_IPv4//\"/}"
NET_IPv6="${NET_IPv6//\"/}"

echo -e "NS0 NAME: ${NS0_NAME}\nDNS IPv4: ${DNS_IPv4}\nNET IPv4: ${NET_IPv4}\nDNS IPv6: ${DNS_IPv6}\nNET IPv6: ${NET_IPv6}"

[ -z "${NET_IPv4}" ] && exit
[ -z "${NET_IPv6}" ] && exit
[ "${DNS_IPv4}" = "${NET_IPv4}" ] && [ "${DNS_IPv6}" = "${NET_IPv6}" ] && exit

/usr/bin/curl --silent --user "${USERNAME}:${PASSWORD}" "https://dyndns.inwx.com/nic/update?myip=${NET_IPv4}&myipv6=${NET_IPv6}"
echo