check_dyndns.sh

#!/bin/sh

cip=`ifconfig eth0.1 | grep inet | cut -d ':' -f 2 | awk 'NR==1{print $1}'`
lip=`nslookup hostname.homeunix.net| grep Address | cut -d ' ' -f 2 | awk 'NR==2{print $1}' `

if [ x$cip != x$lip ]; then
  /bin/update_dyndns.sh
else
  echo "good"
fi
exit 0

update_dyndns.sh

#!/bin/sh
IP=`ifconfig eth0.1 | grep inet | cut -d ':' -f 2 | cut -d ' ' -f 1`
URL="http://username:password@members.dyndns.org/nic/update?hostname=hostname.homeunix.net&myip=$IP&wildcard=NOCHG&mx=NOCHG&backmx=NOCHG"

curl $URL > /dev/null
exit 0