show progress and capture example for https://blog.kowalczyk.info/article/wOYk/advanced-command-execution-in-go-with-osexec.html (made with https://codeeval.dev)

main.go

package main

// https://blog.kowalczyk.info/article/wOYk/advanced-command-execution-in-go-with-osexec.html

import (
	"bytes"
	"fmt"
	"io"
	"log"
	"os"
	"os/exec"
	"runtime"
	"sync"
)

// CapturingPassThroughWriter is a writer that remembers
// data written to it and passes it to w
type CapturingPassThroughWriter struct {
	buf bytes.Buffer
	w   io.Writer
}

// NewCapturingPassThroughWriter creates new CapturingPassThroughWriter
func NewCapturingPassThroughWriter(w io.Writer) *CapturingPassThroughWriter {
	return &CapturingPassThroughWriter{
		w: w,
	}
}

// Write writes data to the writer, returns number of bytes written and an error
func (w *CapturingPassThroughWriter) Write(d []byte) (int, error) {
	w.buf.Write(d)
	return w.w.Write(d)
}

// Bytes returns bytes written to the writer
func (w *CapturingPassThroughWriter) Bytes() []byte {
	return w.buf.Bytes()
}

func main() {
	cmd := exec.Command("ls", "-lah")
	if runtime.GOOS == "windows" {
		cmd = exec.Command("tasklist")
	}

	var errStdout, errStderr error
	stdoutIn, _ := cmd.StdoutPipe()
	stderrIn, _ := cmd.StderrPipe()
	stdout := NewCapturingPassThroughWriter(os.Stdout)
	stderr := NewCapturingPassThroughWriter(os.Stderr)
	err := cmd.Start()
	if err != nil {
		log.Fatalf("cmd.Start() failed with '%s'\n", err)
	}

	var wg sync.WaitGroup
	wg.Add(1)

	go func() {
		_, errStdout = io.Copy(stdout, stdoutIn)
		wg.Done()
	}()

	_, errStderr = io.Copy(stderr, stderrIn)
	wg.Wait()

	err = cmd.Wait()
	if err != nil {
		log.Fatalf("cmd.Run() failed with %s\n", err)
	}
	if errStdout != nil || errStderr != nil {
		log.Fatal("failed to capture stdout or stderr\n")
	}
	outStr, errStr := string(stdout.Bytes()), string(stderr.Bytes())
	fmt.Printf("\nout:\n%s\nerr:\n%s\n", outStr, errStr)
}