Download all Railscasts Episodes

railscasts.rb

require 'rubygems'
require 'hpricot'
require 'open-uri'

doc             = open('http://railscasts.com/') { |f| Hpricot(f) }
total_episodes  = (doc/'div.number').first.inner_html[1,3].to_i
total_pages     = (total_episodes / 10).ceil

(1..total_pages).each do |i| 
  puts "PAGE #{i} ================================"
  
  doc = open("http://railscasts.com/?page=#{i}") { |f| Hpricot(f) }
  
  (doc/'div.episode').each do |episode|
    puts "#{episode.at('div.number').inner_html} - #{episode.at('h2/a').inner_html}"
    media = episode.at('div.download/a')['href'].scan(/http:\/\/(.*)\/videos(\S*)/)[0]

    Net::HTTP.start(media[0]) { |http|
      resp = http.get("/videos/#{media[1]}")
      open("/Volumes/External\ HD/Tutorials/#{media[1]}", "wb") { |file|
        file.write(resp.body)
      }
    }

    puts "================================"
  end
end

can u plz tell me
how to execute this script & how to download all railscasts videos (free & pro)..?

railscasts.rb:6:in <main>': undefined methodinner_html' for nil:NilClass (NoMethodError)

this script is showing the above error