code: func (c *runner) StartWithStdoutPipe(opts CommandOpts, name string, arg ...string) (io.ReadCloser, error) {
  	c.cmd = exec.Command(name, arg...)
  	if opts.Stderr != nil {
  		c.cmd.Stderr = opts.Stderr
  	}
  	if opts.Dir != "" {
  		c.cmd.Dir = opts.Dir
  	}
  	if len(opts.EnvAppend) > 0 {
  		c.cmd.Env = os.Environ()
  		c.cmd.Env = append(c.cmd.Env, opts.EnvAppend...)
  	}
  	r, err := c.cmd.StdoutPipe()
  	if err != nil {
  		return nil, err
  	}
  	return r, c.cmd.Start()
  }
docs: // StartWithStdoutPipe executes a command returning a ReadCloser connected to
  // the command's stdout.