get the realtime output for a shell command in golang|-|{"files":{"shell_output.go":{"env":"plain"}},"tag":"bigdata"}

shell_output.go

package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"os/exec"
	"strings"
)

func main() {
	cmdName := "ping 127.0.0.1"
	cmdArgs := strings.Fields(cmdName)

	cmd := exec.Command(cmdArgs[0], cmdArgs[1:len(cmdArgs)]...)
	stdout, _ := cmd.StdoutPipe()
	cmd.Start()
	oneByte := make([]byte, 100)
	num := 1
	for {
		_, err := stdout.Read(oneByte)
		if err != nil {
			fmt.Printf(err.Error())
			break
		}
		r := bufio.NewReader(stdout)
		line, _, _ := r.ReadLine()
		fmt.Println(string(line))
		num = num + 1
		if num > 3 {
			os.Exit(0)
		}
	}

	cmd.Wait()
}

For people coming from google - I revised a bit.

package main

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

func main() {
  cmd := exec.Command("ping", "127.0.0.1")
  stdout, err := cmd.StdoutPipe()
  if err != nil {
    log.Fatal(err)
  }
  cmd.Start()

  buf := bufio.NewReader(stdout) // Notice that this is not in a loop
  num := 1
  for {
    line, _, _ := buf.ReadLine()
    if num > 3 {
      os.Exit(0)
    }
    num += 1
    fmt.Println(string(line))
  }
}

when I ran this, the ping command is stopping after an interval of time.
I use windows and ping in windows pings 4 times as default similar to ping -c4 127.0.0.1
but is there a way where we can get the return value of the command and stop the for loop?

Still up to date, March 21 2022

Nice !

Here is another example that I made based on the code posted above:

func RunCmd(ctx context.Context, cmdstr string) error {
	args := strings.Fields(cmdstr)
	cmd := exec.CommandContext(ctx, args[0], args[1:]...)

	stdout, err := cmd.StdoutPipe()
	if err != nil {
		return err
	}

	var wg sync.WaitGroup
	wg.Add(1)

	scanner := bufio.NewScanner(stdout)
	go func() {
		for scanner.Scan() {
			log.Printf("out: %s", scanner.Text())
		}
		wg.Done()
	}()

	if err = cmd.Start(); err != nil {
		return err
	}

	wg.Wait()

	return cmd.Wait()
}

Maybe you should use multiwritter:

cmd.Stdout = io.MultiWriter(os.Stdout, &stdout) cmd.Stderr = io.MultiWriter(os.Stderr, &stderr)