gistfile1.rb

if Rails.env == 'production' && File.exists?(File.join(Rails.root, 'REVISION'))
  revision = File.read(File.join(Rails.root, 'REVISION')).strip
  ActionController::Base.asset_host = "yourcdn.s3.amazon.com/#{revision}"
end

module Sass::Script::Functions
  def url(string)
    if Rails.env == 'production' && File.exists?(File.join(Rails.root, 'REVISION'))
      revision = File.read(File.join(Rails.root, 'REVISION')).strip
      path = string.value

      pre = 'url('
      post = ''

      if (path[0..0] == "\"" || path[0..0] == "'")
        pre += path[0..0]
        path = path[1..-1]
      end

      if (path[-1..-1] == "\"" || path[-1..-1] == "'")
        post += path[-1..-1]
        path = path[0..-2]
      end
      pre += "http://yourcdn.s3.amazon.com"

      if path[0..0] == '/'
        pre += "/"
        path = path[1..-1] unless pre == ''
      end
      post += ")"

      Sass::Script::String.new(pre + (revision ? "#{revision}/" : "") + path + post)
    else
      Sass::Script::String.new("url(#{string.value})")
    end
  end
end