popen3_test.rb

require 'open3'

module Enumerable
  alias :all_are? :all?
end

Open3.popen3(%(ruby -e 'STDOUT.sync = true; STDERR.sync = true;3.times { |i| STDOUT.puts(i); STDERR.puts(i); sleep 1 }')) do |stdin, stdout, stderr, wait_thr|
  maxlen = 1024
  pipes = {
    stdout => :stdout,
    stderr => :stderr
  }
  until pipes.empty?
    IO.select(pipes.keys).first.each do |io|
      begin
        puts "#{pipes[io]}: #{io.read_nonblock(maxlen)}"
      rescue EOFError
        pipes.delete(io)
      end
    end
  end
end