Updates a DtDNS Hostname with the current device public IP

dtdns-updater.sh

#!/bin/bash

# Updates a DtDNS Hostname with the current device public IP.
# You may run this script via an hourly CRON (DtDNS propagation is around 15min so a shorter rerun time is useless).
#
# Author: David Dérus
# Version: 1.1.3

# Config
HOSTNAME='MYHOSTNAME'
PASSWORD='MYPASSWORD'

# Gets the IP returned by an host request
# Usage: getIPByHost HOST RESOLVER
getIPByHost() {
  host -t A $1 $2 | tail -n 1 | cut -d ' ' -f4
}

# Validates an IP
# Usage: validateIP IP
validateIP() {
  if ! [[ $1 =~ ^[0-9]+\.[0-9]+\.[0-9]+\.[0-9]+$ ]] ; then
    echo "Invalid IP '$1'"
    exit 1
  fi
}

# Updates a DtDNS Hostname IP
# Usage: updateDnsEntry HOSTNAME PASSWORD NEW_IP
updateDnsEntry() {
  wget -qO- --user-agent="DtDNSUpdater/1.1.3" --header="Host:www.dtdns.com" "https://www.dtdns.com/api/autodns.cfm?id=$1&pw=$2&client=DtDNSUpdater_1.1.3&ip=$3" &> /dev/null
}

# Getting IPs
CURRENT_IP=$(getIPByHost myip.opendns.com resolver1.opendns.com)
LAST_KNOWN_IP=$(getIPByHost $HOSTNAME ns1.dtdns.com)

# Validating both IPs
validateIP $CURRENT_IP && validateIP $LAST_KNOWN_IP

# Updating if needed
if [ $CURRENT_IP != $LAST_KNOWN_IP ] ; then
  updateDnsEntry $HOSTNAME $PASSWORD $CURRENT_IP
  echo "IP changed from $LAST_KNOWN_IP to $CURRENT_IP"
fi

exit 0

Reminder: Even if OpenDNS resolver is safer than ifconfig.me and others, the best solution is to get your public IP from your router (if it's possible of course)