Working with Logs in Go

Intro

Logs allow you to send info or errors during your program for debugging purposes. In practice, logging is often used in conjunction with something like Elastic Search to monitor and track down issues. In this article, we will learn how to use logs in Go.

The Log Packages

Go provides us with a log package. We can use this by importing the package.

import "log"

The basic usage is the Println method which is similar to that in the fmt package.

log.Println("info log")

The output

Service: 2021/11/29 08:18:42.304512 info log

We can also use the log.Fatalln which will print then call the os.Exist(1).

log.Fatalln("Fatal log")

The output

Service: 2021/11/29 08:18:42.305032 Fatal log
exit status 1

And on more example, we can use log.Panicln which will call panic after printing.

log.Panicln("Panic log")

The output

Service: 2021/11/29 08:19:25.671978 Panic log
panic: Panic log


goroutine 1 [running]:
log.Panicln({0xc000119f60, 0x49d1b4, 0x406e65})
        C:/Program Files/Go/src/log/log.go:368 +0x65
main.main()
        C:/Users/krh12/Documents/r-data-vis/GoLang/logs/main.go:11 +0xa5    
exit status 2

Configuring the Log

The log package also has some configuration. For example, you often want to prefix your logs, usually when working with multiple services or layers. We can do this with the following:

log.SetPrefix("Service: ")

This will add the prefix when printing each log.

We can also SetFlags to add other configuration. For example, we can modify the date display like so.

log.SetFlags(log.Ldate | log.Lmicroseconds)

You can find more flags here: https://pkg.go.dev/log#pkg-constants

Full Example

You can run the full example code by copying the code below to a file called main.go and run go run main.go

package main

import "log"

func main() {
	log.SetPrefix("Service: ")
	log.SetFlags(log.Ldate | log.Lmicroseconds)

	log.Println("info log")
	log.Fatalln("Fatal log")
	log.Panicln("Panic log")
}