A little challenge...

challenge.rb

#!/usr/bin/env ruby
require 'net/http'
require 'json'

def http_get_request(url)
  puts "http_get: #{url}"
  response = Net::HTTP.get(URI(url))

  if response['You should try JSON']
    http_get_request(url.sub 'challenge?id', 'challenge.json?id')
  elsif response =~ /id=\d+/
    http_get_request(JSON.parse(response).fetch('follow').sub 'challenge?id', 'challenge.json?id')
  else
    puts response
  end
  return nil
end

http_get_request(ARGV.shift)