code: func (p *Process) watchOutput(w io.Writer, r io.Reader) {
  	go func() {
  		if _, err := io.Copy(w, r); err != nil {
  			p.log.Errorf("Output watcher error: %v", err)
  		}
  	}()
  }
docs: // Watch output (either standard or custom). Terminates with process, since io.Copy reaches EOF.