namecheap_ddns.rb

#!/usr/bin/env ruby
# Simple script that update namecheap ddns.

require 'open-uri'
require 'nokogiri'
require 'json'

HOST=''
DOMAIN=''
PASSWORD=''
IP_TMP='/tmp/.namecheap_ddns_ip'

class NamecheapDDNSUpdater
  def initialize
    json = open('http://myip.ipip.net/json').read
    data = JSON.parse(json)
    @ip = data['data']['ip']
  end
  
  def run
    if File.exists?(IP_TMP)
      old_ip = open(IP_TMP).read
      if old_ip == @ip
        puts 'IP not changed, skip.'
        return
      end
    end
    save_ip
  end

  private
  def update
    url = "https://dynamicdns.park-your-domain.com/update?host=#{HOST}&domain=#{DOMAIN}&password=#{PASSWORD}&ip=#{@ip}"
    doc = Nokogiri::XML(open(url))
    if doc.xpath('//ErrCount').text.to_i == 0
      puts 'DDNS updated.'
    else
      reason = doc.xpath('//errors/Err1').text
      puts "DDNS update failed, reason: #{reason}."
    end
  end

  def save_ip
    update
    open(IP_TMP, 'w') do |f|
      f.write(@ip)
    end
  end
end

if __FILE__ == $0
    NamecheapDDNSUpdater.new.run
end