linodedns.rb

#!/usr/bin/env ruby
# sudo gem install rick-linode

require 'rubygems'
require 'open-uri'
require 'linode'

LinodeAPIKey = '<LINODE_API_KEY_HERE>'
DomainID = '<DOMAIN_ID>'
ResourceID = '<RESOURCE_ID>'

myip_url = 'http://www.ocf.berkeley.edu/~abhi/myip/'
ip_address  = open(myip_url).read
puts ip_address
linode = Linode.new(:api_key => LinodeAPIKey)
puts linode.domain.resource.update(:DomainID => DomainID, :ResourceID => ResourceID, :Target => ip_address)

myip.php

<?php
 echo $_SERVER['REMOTE_ADDR'];
?>