golang os / exec：分部分从stdout获取数据

Question

I want to run an external application from my go code using os/exec . The application my_external_script.sh outputs data to stdout in two parts: the first part is quite fast (it writes "A" to stdout after three seconds) and the second part ("B) is being written only after 10 seconds.

For example:

./my_external_script.sh
.....
.....
A (3 seconds elapsed)
.....
.....
.....
.....
.....
.....
B (10 seconds elapsed)
(program exits with 0 status code)

I'm currently executing this like so from my go code:

func execMyExternalCmd() (*string, error) {
    cmd := exec.Command("my_external_script.sh")
    var out bytes.Buffer
    cmd.Stdout = &out
    err := cmd.Run()
    if err != nil {
        return nil, err
    }
    var res = out.String()
    return &res, nil
}

The problem is, execMyExternalCmd will only return after 10 seconds, where both "A" and "B" have been written and the program exited. I would like to use "A" as soon as it's available on the stdout (but also use "B" later on when it's available). How can I achieve this?

Answer 1

package main

import (
    "bufio"
    "log"
    "os/exec"
)

func main() {
    cmd := exec.Command("sh", "-c", "echo 1;sleep 10;echo 2;")

    outPipe, _ := cmd.StdoutPipe()
    scanner := bufio.NewScanner(outPipe)

    go func() {
        for scanner.Scan() {
            log.Println(scanner.Text())
        }
    }()

    cmd.Start()
    cmd.Wait()

    log.Println("Done")
}

Output:

2016/12/04 17:11:09 1
2016/12/04 17:11:19 2
2016/12/04 17:11:19 Done

Use channels to send data from the function instead of return.