转至：从顶部将内容添加到输出

Question

In my go program, I need to run top to continuously monitoring a specific process. But top does not give me the timestamp when each line is recorded. I'm thinking about prepending it to the outputs my self:

top := exec.Command("top", "-p", pid)
r, w := os.Pipe()
top.Stdout = w
top.Start()

This way I can read the outputs from r at one end of the pipe. I wonder how can I fire an action to get the current timestamp and prepend it to the output whenever there's a new line from top.Stdout? I think it should be like a callback or Python's generator, but I'm not sure how to do it in Go.

Answer 1

Something along the lines of:

func main() {
    for ln := range topMon(2543) {
        fmt.Println(time.Now().UTC().Format(time.RFC3339), ln)
    }
}

func topMon(pids ...int) <-chan string {
    ch := make(chan string, 1)
    top := exec.Command("top", "-b")
    for _, pid := range pids {
        top.Args = append(top.Args, "-p", strconv.Itoa(pid))
    }
    r, w, _ := os.Pipe()
    go func() {
        sc := bufio.NewScanner(r)
        for sc.Scan() {
            ch <- sc.Text()
        }
        close(ch)
    }()
    top.Stdout = w
    top.Stderr = os.Stderr
    if err := top.Start(); err != nil {
        panic(err)
    }
    return ch
}

The channel usage is just an example, you can just return the rwader from the pipe directly.