gistfile1.rb

#!/usr/bin/env ruby

require 'open-uri'
require 'nokogiri'
require 'growl'

doc = Nokogiri::HTML(open("http://shop.github.com/products/octodex-sticker-pack"))
if doc.css('#puchase-form .sold-out').empty?
  Growl.notify do |n|
    n.message = 'Octodex Sticker Packs are back!'
    n.sticky!
  end
end