Redirect stdout pipe of child process in Go

Question

I\'m writing a program in Go that executes a server like program (also Go). Now I want to have the stdout of the child program in my terminal window where I started the parent p

Answer 1

Now I want to have the stdout of the child program in my terminal window where I started the parent program.

No need to mess with pipes or goroutines, this one is easy.

func main() {
    // Replace `ls` (and its arguments) with something more interesting
    cmd := exec.Command("ls", "-l")
    cmd.Stdout = os.Stdout
    cmd.Stderr = os.Stderr
    cmd.Run()
}

Answer 2

I believe that if you import io and os and replace this:

//fmt.Println(out)

with this:

go io.Copy(os.Stdout, out)

(see documentation for io.Copy and for os.Stdout), it will do what you want. (Disclaimer: not tested.)

By the way, you'll probably want to capture standard-error as well, by using the same approach as for standard-output, but with cmd.StderrPipe and os.Stderr.

Answer 3

For those who don't need this in a loop, but would like the command output to echo into the terminal without having cmd.Wait() blocking other statements:

package main

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

func checkError(err error) {
    if err != nil {
        log.Fatalf("Error: %s", err)
    }
}

func main() {
    // Replace `ls` (and its arguments) with something more interesting
    cmd := exec.Command("ls", "-l")

    // Create stdout, stderr streams of type io.Reader
    stdout, err := cmd.StdoutPipe()
    checkError(err)
    stderr, err := cmd.StderrPipe()
    checkError(err)

    // Start command
    err = cmd.Start()
    checkError(err)

    // Don't let main() exit before our command has finished running
    defer cmd.Wait()  // Doesn't block

    // Non-blockingly echo command output to terminal
    go io.Copy(os.Stdout, stdout)
    go io.Copy(os.Stderr, stderr)

    // I love Go's trivial concurrency :-D
    fmt.Printf("Do other stuff here! No need to wait.\n\n")
}