dyndns.sh

#!/usr/bin/env bash

SHA="Enter hash given by freedns.afraid.org"
BASE_URL="http://freedns.afraid.org/api/?action=getdyndns&v=2&sha=$SHA"

MY_DOMAIN="enter the domain this machine should have point to it"
MY_IP=`dig -4 @resolver1.opendns.com -t a myip.opendns.com +short`

RES=`curl -s $BASE_URL`
for LINE in $RES; do
   DOMAIN_INFO=(`echo $LINE | tr "|" "\n"`)

   DOMAIN=${DOMAIN_INFO[0]}
   IP_ADDRESS=${DOMAIN_INFO[1]}
   UPDATE_URL=${DOMAIN_INFO[2]}

   if [ "$DOMAIN" == "$MY_DOMAIN" ]; then
      if [ "$MY_IP" != "$IP_ADDRESS" ]; then
         curl -sk $UPDATE_URL
      fi
   fi
done