prefix executed commands output

main.go

package main

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

func prefix(s string) string {
	return "prefix: " + s
}

func main() {
	reader, writer := io.Pipe()
	ctx, cancel := context.WithCancel(context.Background())

	scannerStopped := make(chan struct{})
	go func() {
		defer close(scannerStopped)

		scanner := bufio.NewScanner(reader)
		for scanner.Scan() {
			fmt.Println(prefix(scanner.Text()))
		}
	}()

	cmd := exec.Command("cat", "main.go")
	cmd.Stdout = writer
	_ = cmd.Start()
	go func() {
		_ = cmd.Wait()
		cancel()
		writer.Close()
	}()
	<-ctx.Done()

	<-scannerStopped
}