#!/bin/bash
HOSTNAME="all.dnsomatic.com"
USER="YourUserName"
PASS="YourPassword"
TMPFILE="/home/yourname/oldip.DNS-O-Matic.tmp"
LOGFILE="/var/log/DNS-O-Matic.log"
DATENOW=$(date)
HOUR=$((`date +"%k"`))

IP=$(curl -s http://whatismyip.akamai.com/)

if [[ "$HOUR" -ge 21 && "$HOUR" -le 23 ]]; then
  echo "" > $TMPFILE
fi

if [ -e "$TMPFILE" ]; then
  OLDIP=`cat $TMPFILE`
  echo $DATENOW ": found:" $IP " cached IP:" $OLDIP >> $LOGFILE
  if [ "$OLDIP" = "$IP" ]; then
    exit 0
  else
    RETURN=$(curl -s https://${USER}:${PASS}@updates.dnsomatic.com/nic/update?hostname=${HOSTNAME}&myip=$IP&wildcard=NOCHG&mx=NOCHG&backmx=NOCHG)
    echo "Return message of DNS-O-Matic : " $RETURN
    echo $RETURN | grep "good" > /dev/null 2>&1
    if [ "$?" -eq "0" ]; then
      echo $IP > $TMPFILE
    else
      echo "" > $TMPFILE
    fi
  fi
else
  touch $TMPFILE
fi