print common follower screen names of specified twitter accounts

common_followers.rb

require "net/https"
require "uri"

def get(url)
  parsed = URI.parse(url)
  https = Net::HTTP.new(parsed.host, parsed.port)
  https.use_ssl = parsed.scheme == "https"
  https.start { |w| w.get(url).body }
end

def get_ids(screen_name)
  # fetches up to 5000 followers' ids
  ids_response = get("https://api.twitter.com/1/followers/ids.json?screen_name=" + screen_name)
  /\[(.*)\]/.match(ids_response)[1].split(",")
end

common_followers = get_ids(ARGV.shift)
while (screen_name = ARGV.shift)
  common_followers = common_followers & get_ids(screen_name)
end
# assuming the specified two have only up to 100 common followers
users = get("https://api.twitter.com/1/users/lookup.json?user_id=" + common_followers.join(","))

users.scan(/(?:"screen_name":")([a-zA-Z0-9_]*)(?:")/).each do |screen_name|
  puts "@" + screen_name[0]
end