Golang管道实时输出子命令

Question

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.

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 > %s
", 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
}

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.

Answer 1

Turns out that the issue was not in the code I posted above. That works as expected. The problem was that the C program that was being executed was not properly flushing stdout. When running it interactively, it worked as expected, but when stdout was piped, it would not actually get written until I called flush. After manually adding some flush statements to the c program, the go code worked as expected.