itunes_control.rb

require "rubygems"
require "sinatra"

get "/next" do
  tell_itunes "next track"
end

get "/previous" do
  tell_itunes "previous track"
end

get "/pause" do
  tell_itunes "pause"
end

get "/play" do
  tell_itunes "play"
end

def tell_itunes(something)
  %x{osascript -e 'tell application "itunes"' -e "#{something}" -e "end tell"}
end