twitter-intersect.rb

#!/usr/bin/env ruby
gem "twitter", "~> 5.3.0"
require "twitter"

def usage
  abort "Usage: twitter-intersect (<username>.following|<username>.followers)..."
end

usage if ARGV.empty?

$client = Twitter::REST::Client.new do |config|
  config.consumer_key        = "nope"
  config.consumer_secret     = "nope"

  config.access_token        = "nope"
  config.access_token_secret = "nope"
end

ids = []

ARGV.map { |arg| arg.split(".") }.each do |handle, command|
  case command
  when "following"
    ids << $client.friend_ids(handle, count: 5000).attrs[:ids]
  when "followers"
    ids << $client.follower_ids(handle, count: 5000).attrs[:ids]
  else
    puts "Unknown command: #{command}"
    puts
    usage
  end
end

puts $client.users(ids.reduce(:&)).map(&:screen_name)