Exec a shell command in Go

go shellexecute

I'm looking to execute a shell command in Go and get the resulting output as a string in my program. I saw the Rosetta Code version:

package main
import "fmt"
import "exec"

func main() {
  cmd, err := exec.Run("/bin/ls", []string{"/bin/ls"}, []string{}, "", exec.DevNull, exec.PassThrough, exec.PassThrough)
  if (err != nil) {
    fmt.Println(err)
    return
  }
  cmd.Close()

But this doesn't capture the actual standard out or err in a way that I can programatically access - those still print out to the regular stdout / stderr. I saw that using Pipe as the out or err could help elsewhere, but no example of how to do so. Any ideas?

The package "exec" was changed a little bit. The following code worked for me.

package main

import (
    "fmt"
    "os/exec"
)

func main() {
    app := "echo"

    arg0 := "-e"
    arg1 := "Hello world"
    arg2 := "\n\tfrom"
    arg3 := "golang"

    cmd := exec.Command(app, arg0, arg1, arg2, arg3)
    stdout, err := cmd.Output()

    if err != nil {
        fmt.Println(err.Error())
        return
    }

    // Print the output
    fmt.Println(string(stdout))
}

I hope this helps!

None of the provided answers allow to separate stdout and stderr so I try another answer.

First you get all the info you need, if you look at the documentation of the exec.Cmd type in the os/exec package. Look here: https://golang.org/pkg/os/exec/#Cmd

Especially the members Stdin and Stdout,Stderr where any io.Reader can be used to feed stdin of your newly created process and any io.Writer can be used to consume stdout and stderr of your command.

The function Shellout in the following programm will run your command and hand you its output and error output separatly as strings:

package main

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

const ShellToUse = "bash"

func Shellout(command string) (error, string, string) {
    var stdout bytes.Buffer
    var stderr bytes.Buffer
    cmd := exec.Command(ShellToUse, "-c", command)
    cmd.Stdout = &stdout
    cmd.Stderr = &stderr
    err := cmd.Run()
    return err, stdout.String(), stderr.String()
}

func main() {
    err, out, errout := Shellout("ls -ltr")
    if err != nil {
        log.Printf("error: %v\n", err)
    }
    fmt.Println("--- stdout ---")
    fmt.Println(out)
    fmt.Println("--- stderr ---")
    fmt.Println(errout)
}

This answer does not represent the current state of the Go standard library. Please take a look at @Lourenco's answer for an up-to-date method!

Your example does not actually read the data from stdout. This works for me.

package main

import (
   "fmt"
   "exec"
   "os"
   "bytes"
   "io"
)

func main() {
    app := "/bin/ls"
    cmd, err := exec.Run(app, []string{app, "-l"}, nil, "", exec.DevNull, exec.Pipe, exec.Pipe)

    if (err != nil) {
       fmt.Fprintln(os.Stderr, err.String())
       return
    }

    var b bytes.Buffer
    io.Copy(&b, cmd.Stdout)
    fmt.Println(b.String())

    cmd.Close()
}

// 封装exec ，有shell= true 这样的选项

func Cmd(cmd string, shell bool) []byte {

if shell {
    out, err := exec.Command("bash", "-c", cmd).Output()
    if err != nil {
        panic("some error found")
    }
    return out
} else {
    out, err := exec.Command(cmd).Output()
    if err != nil {
        panic("some error found")
    }
    return out

}
}

you may try this .

Here is a simple function that will run your command and capture the error, stdout, and stderr for you to inspect. You can easily see anything that might go wrong or be reported back to you.

// RunCMD is a simple wrapper around terminal commands
func RunCMD(path string, args []string, debug bool) (out string, err error) {

    cmd := exec.Command(path, args...)

    var b []byte
    b, err = cmd.CombinedOutput()
    out = string(b)

    if debug {
        fmt.Println(strings.Join(cmd.Args[:], " "))

        if err != nil {
            fmt.Println("RunCMD ERROR")
            fmt.Println(out)
        }
    }

    return
}

You can use it like this (Converting a media file):

args := []string{"-y", "-i", "movie.mp4", "movie_audio.mp3", "INVALID-ARG!"}
output, err := RunCMD("ffmpeg", args, true)

if err != nil {
    fmt.Println("Error:", output)
} else {
    fmt.Println("Result:", output)
}

I've used this with Go 1.2-1.7

Exec a shell command in Go

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