code: func (c *command) run() []byte {
  	cmd := exec.Command(c.program, c.args...)
  	var stdout, stderr bytes.Buffer
  	cmd.Stdout = &stdout
  	cmd.Stderr = &stderr
  	err := cmd.Run()
  	out := stdout.Bytes()
  	if err != nil {
  		log.Fatalf("Could not run %v: %v: %v: %v", c, err, string(out), stderr.String())
  	}
  	return out
  }
docs: // run runs the command and returns the output if it succeeds.
  // On error, the process dies.