main.go

package main

import (
	"fmt"
	"log/slog"
	"os"
)

func log(logger *slog.Logger) {
	logger.Debug("debug message")
	logger.Info("info message")
	logger.Warn("warn message")
	logger.Error("error message")
}

func main() {
	lv := &slog.LevelVar{}
	lv.Set(slog.LevelDebug)

	logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{Level: lv}))
	slog.SetDefault(logger)

	{
		fmt.Fprintln(os.Stderr, "debug level")
		lv.Set(slog.LevelDebug)
		log(logger)
	}

	{
		fmt.Fprintln(os.Stderr, "warn level")
		lv.Set(slog.LevelWarn)
		log(logger)
	}
}