go logrotate + verbose stdout example

example.go

package main

import (
	"flag"
	"fmt"
	"io"
	"log"
	"os"
	"strconv"

	"github.com/natefinch/lumberjack/v3"
)

// flags
var (
	logFilePtr    = flag.String("log_file", "/tmp/mylog.log", "Path to the log file")
	logSizePtr    = flag.Int64("log_size", 500, "Max size of the log (in MiB)")
	logBackupsPtr = flag.Int("log_backups", 5, "Max number of old log files to retain)")
	verbosePtr    = flag.Bool("verbose", false, "Should print to both the log file AND stdout?")
)

func init() {
	flag.Parse()
}

func main() {
	l, _ := lumberjack.NewRoller(
		*logFilePtr,
		(*logSizePtr)*1024*1024, // 500 megabytes
		&lumberjack.Options{
			MaxBackups: *logBackupsPtr,
			LocalTime:  true,
			Compress:   true,
		})

	ws := []io.Writer{l}
	if *verbosePtr {
		ws = append(ws, os.Stdout)
	}

	mw := io.MultiWriter(ws...)
	log.SetOutput(l)
	log.SetOutput(mw)
	for i := 0; i < 100_000_000; i++ {
		log.Println("hello world! #" + strconv.Itoa(i))
	}

	fmt.Println("done")
}