func (c *Cmd) StdoutPipe() (io.ReadCloser, error) {
	if c.Stdout != nil {
		return nil, errors.New("exec: Stdout already set")
	}
	if c.Process != nil {
		return nil, errors.New("exec: StdoutPipe after process started")
	}
	pr, pw, err := os.Pipe()
	if err != nil {
		return nil, err
	}
	c.Stdout = pw
	c.closeAfterStart = append(c.closeAfterStart, pw)
	c.closeAfterWait = append(c.closeAfterWait, pr)
	return pr, nil
}
func (c *Cmd) StdoutPipe() (io.ReadCloser, error) {
	if c.Stdout != nil {
		return nil, errors.New("exec: Stdout already set")
	}
	if c.Process != nil {
		return nil, errors.New("exec: StdoutPipe after process started")
	}
	pr, pw, err := os.Pipe()
	if err != nil {
		return nil, err
	}
	c.Stdout = pw
	c.closeAfterStart = append(c.closeAfterStart, pw)
	c.closeAfterWait = append(c.closeAfterWait, pr)
	return pr, nil
}
// StdoutPipe returns a pipe that will be connected to the command's
// standard output when the command starts.
//
// Wait will close the pipe after seeing the command exit, so most callers
// need not close the pipe themselves; however, an implication is that
// it is incorrect to call Wait before all reads from the pipe have completed.
// For the same reason, it is incorrect to call Run when using StdoutPipe.
// See the example for idiomatic usage.