Pipe child process stdout and stderr to main process in Ruby

main.rb

Open3.popen3("./tmp.sh") do |stdin, stdout, stderr, wait_thr|
  # Stream output
  # DEV: We'd like to stream both `stderr` and `stdout` but it was getting troublesome
  #   with `.alive?` and `gets()` blocking each other
  while line = stdout.gets()
    $stdout.puts(line)
  end

  # Finish any last stderr or stdout
  stdout_remainder = stdout.read()
  if stdout_remainder != ""
    $stdout.puts(stdout_remainder)
  end
  stderr_remainder = stderr.read()
  if stderr_remainder != ""
    $stderr.puts(stderr_remainder)
  end

  # If we had a non-zero exit status, exit similarly
  exitstatus = wait_thr.value.exitstatus
  if exitstatus != 0
    $stderr.puts("Exited with non-zero exit status: #{exitstatus}")
    exit(exitstatus)
  end
end