How to Capture stdout and stderr from External Commands in Go

Use exec.Command to run the external command, then assign cmd.Stdout and cmd.Stderr to &bytes.Buffer instances before calling cmd.Run() to capture the output.

package main

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

func main() {
	cmd := exec.Command("ls", "-l")
	var outBuf, errBuf bytes.Buffer
	cmd.Stdout = &outBuf
	cmd.Stderr = &errBuf

	if err := cmd.Run(); err != nil {
		fmt.Println("Error:", err)
	}

	fmt.Println("Output:", outBuf.String())
	fmt.Println("Errors:", errBuf.String())
}

Capturing stdout and stderr from external commands in Go lets your program run a system command and save its text output directly into memory instead of printing it to the screen. Think of it like holding a notepad under a printer to catch the paper as it comes out, so you can read or process the results later. You use it whenever you need to analyze what a command printed or log its errors without cluttering the console.