Update a DNS record automatically after getting an IP address from DHCP

nsupdate.sh

#!/bin/sh
# /etc/dhcp/dhclient-exit-hooks.d/nsupdate

[ "$interface" != "eth0" ] && return
[ "$new_domain_name" != "example.org" ] && return

if [ "$reason" = BOUND ]  || [ "$reason" = RENEW ] ||
   [ "$reason" = REBIND ] || [ "$reason" = REBOOT ]
then
    host="$(hostname)"
    nsupdatecmds=/var/tmp/nsupdatecmds
    echo "update delete $host.$new_domain_name a" > $nsupdatecmds
    echo "update add $host.$new_domain_name 3600 a $new_ip_address" >> $nsupdatecmds
    echo "send" >> $nsupdatecmds

    nsupdate $nsupdatecmds
fi