Script to update DNS on AWS ELB

#!/bin/bash

public_hostname="pushmeto-123456789.us-east-1.elb.amazonaws.com"
lastip_filename=/var/lib/bind/last-ip.txt
log_filename=/var/log/update-ip.log
update_key=/etc/bind/Kpushme.to.+157+12345.private


while (:)
do
        ip=`host -t a $public_hostname | cut -f 4 -d ' '`
        old_ip=`cat $lastip_filename`
        d=`date`

        if [ "$old_ip" = "$ip" ]
        then
                echo "$d ip is the same, $ip" >> $log_filename
        else
                echo "$d CHANGED. Was $old_ip, became $ip" >> $log_filename
        nsupdate_filename=/tmp/nsupdate.txt
                rm -f $nsupdate_filename
                echo "server 127.0.0.1" >> $nsupdate_filename
                echo "update delete pushme.to." >> $nsupdate_filename
                echo "update delete www.pushme.to." >> $nsupdate_filename

                echo "update add pushme.to. 300 IN A $ip" >> $nsupdate_filename
                echo "update add pushme.to. 300 MX 10 aspmx2.googlemail.COM." >> $nsupdate_filename
        # add more MX here and other @ records!

                echo "update add www.pushme.to. 300 IN A $ip" >> $nsupdate_filename
                echo "" >> $nsupdate_filename

                /usr/bin/nsupdate -k $update_key  -d $nsupdate_filename >> $log_filename 2>&1
                /usr/sbin/rndc freeze; /usr/sbin/rndc thaw
                echo $ip > $lastip_filename
        fi

        sleep 300
done