Golang : Capture stdout of a child process and act according to the result

Tags : golang stdout child-process shell exec

Let say you want to execute a shell command of a child process in your main program and want to capture the output of the child process via stdout pipe. This tutorial will show you how to execute a child process, capture the output, convert the output into a slice and then process according to the child process output.

Here it is :

 package main

 import (

 func handleError(err error) {
 if err != nil {

 func main() {
 // ls -la command might not be the best because it will always return something
 // and cause the lenght of allText(below) to be more than 1

 cmd := exec.Command("ls", "-la")

 // capture the output and error pipes
 stdout, err := cmd.StdoutPipe()
 stderr, err := cmd.StderrPipe()

 // Start digging !
 err = cmd.Start()

 // 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) //  <---- commented out because we will print out with buff.Scan()
 go io.Copy(os.Stderr, stderr)

 // here is where we want to know the child output
 // and depending on the output, display different result
 // in the main program

 buff := bufio.NewScanner(stdout)
 var allText []string

 for buff.Scan() {
 allText = append(allText, buff.Text()+"\n")

 if len(allText) > 1 {
 // if the allText has value, then do a count down
 ticker := time.Tick(time.Second)
 fmt.Println("Scanner detected something. Counting down to finding the biggest treasure...\n\n")

 for i := 9; i >= 0; i-- {
 //fmt.Printf("\x0cOn 10/%d", i) // use \x0c for play.golang.org
 fmt.Printf("\rstill counting the dig 10/%d", i) // use \r if you are running this in terminal

 fmt.Println("\nFinished digging.\n")

 } else {
 fmt.Println("Scanner returns zero. Nothing to do")


Tags : golang stdout child-process shell exec

By Adam Ng

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