Print / Printf / Println
log.Println("server started on :8080")
log.Printf("user %s logged in", name)log
Classic unstructured logger. Fine for small tools; prefer log/slog for structured logs in new code.
Default logger
Fatal exits with status 1
log.Fatal("cannot open db:", err) // log + os.Exit(1)
log.Fatalf("bad config: %v", err)Panic logs and panics
log.Panic("invariant violated")Custom logger
New
l := log.New(os.Stderr, "api: ", log.LstdFlags|log.Lshortfile)
l.Println("hello") // api: 2024/01/02 15:04:05 main.go:42: helloSetFlags / SetPrefix on default
log.SetFlags(log.LstdFlags | log.Lmicroseconds)
log.SetPrefix("worker: ")SetOutput
f, _ := os.Create("app.log")
log.SetOutput(f)