gistfile1.rb

Open3.popen3 cmd do |sin, sout, serr, wait_thr|
  loop do
    rs, _, _ = IO.select([sout,serr]) # no multi-assign in conditions
    break if (sout.eof? and serr.eof?) or (sout.closed? and serr.closed?)
    next if rs.empty?
    rs.each do |readable_io|
      log readable_io.gets  # read a line from it
    end
  end
  exit_status = wait_thr.value
  raise "#{cmd} returned as failed" unless exit_status.success?
end