Logging in Go: Overview of the Standard log Library and Alternatives

What is logging in Go?

Logging is the process of recording events that occur in a program during its execution. In Go, built-in logging support is implemented through the log package from the standard library. This package provides a simple and efficient way to output messages to stdout/stderr, write them to files, and manage the output format. Logs are necessary for debugging, monitoring application performance, security auditing, and analyzing errors in a production environment.

Why is logging needed?

• Debugging: quickly detect and fix errors during development.
• Monitoring: track the application's state in real time.
• Auditing: record user actions and system events.
• Performance analysis: identify bottlenecks and performance issues.

Installation

The log package is part of the Go standard library, so no additional installation is required. Simply import it into your project:

import "log"

For advanced logging, there are popular third-party libraries that can be installed via go get:

go get github.com/sirupsen/logrus# orgo get go.uber.org/zap

Main functions of the standard log library

• log.Print(), log.Printf(), log.Println() — output messages.
• log.Fatal(), log.Fatalf(), log.Fatalln() — output a message and terminate the program with exit code 1.
• log.Panic(), log.Panicf(), log.Panicln() — output a message and trigger a panic.

Go code example

package main

import (\t"log"\t"os")

func main() {\t// Configure output to a file\tfile, err := os.OpenFile("app.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)\tif err != nil {\t\tlog.Fatal(err)\t}\tdefer file.Close()

\t// Create a logger with a prefix and flags\tlogger := log.New(file, "INFO: ", log.Ldate|log.Ltime|log.Lshortfile)

\t// Logging examples\tlogger.Println("Application started")\tlogger.Printf("User %s logged in", "admin")

\t// Using the standard logger\tlog.Println("This is a message to stdout")}

When to use

• Standard log: for simple projects, scripts, command-line utilities.
• Logrus: for production applications that need logging levels (Info, Warn, Error, Debug) and structured logs in JSON format.
• Zap: for high-load systems where performance is critical (minimal memory allocation).
• Zerolog: another fast logger with zero allocation support.

The choice of library depends on performance requirements, project complexity, and the need for structured logs.