title: Golang pipe output of subcommand real time
body: <p>I am trying to pipe the output of a command, but no data seems to be read from the pipe until the write end is closed. Eventually I want this to connect to a websocket that streams the status of a command while it is being executed. The problem is that while this code prints the messages line by line, it does not print anything until the program has finished executing.</p>
  
  <pre><code>cmd := exec.Command(MY_SCRIPT_LOCATION, args)
  
  // create a pipe for the output of the script
  // TODO pipe stderr too
  cmdReader, err := cmd.StdoutPipe()
  if err != nil {
      fmt.Fprintln(os.Stderr, "Error creating StdoutPipe for Cmd", err)
      return
  }
  
  scanner := bufio.NewScanner(cmdReader)
  go func() {
      for scanner.Scan() {
          fmt.Printf("\t &gt; %s\n", scanner.Text())
      }
  }()
  
  err = cmd.Start()
  if err != nil {
      fmt.Fprintln(os.Stderr, "Error starting Cmd", err)
      return
  }
  
  err = cmd.Wait()
  if err != nil {
      fmt.Fprintln(os.Stderr, "Error waiting for Cmd", err)
      return
  }
  </code></pre>
  
  <p>Is there any way I can do something similar and have a scanner actually read line by line as it is written to the pipe instead of after everything has been written? The program takes about 20 seconds to run, and there is a steady stream of updates, so it is annoying to have them all go through at once.</p>