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Simple logger for Go programs. Allows custom formats for messages.
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parkervcp and apsdehal Time format fix (#16)
This fixes the time format when it's not specified in SetFormat
Closes #13
Latest commit e1d9ff3 Sep 29, 2018
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examples Update README Feb 21, 2018
.travis.yml Travis dependencies Sep 28, 2014
LICENSE Adds BSD License Sep 28, 2014 Update bench command Feb 21, 2018
logger.go Time format fix (#16) Sep 29, 2018
logger_test.go Add log level filter (#14) Aug 6, 2018


Build Status GoDoc

A simple go logger for easy logging in your programs. Allows setting custom format for messages.


Example Output


go get

Use go get -u to update the package.


Example program demonstrates how to use the logger. See below for formatting instructions.

package main

import (

func main () {
	// Get the instance for logger class, "test" is the module name, 1 is used to
	// state if we want coloring
	// Third option is optional and is instance of type io.Writer, defaults to os.Stderr
	log, err := logger.New("test", 1, os.Stdout)
	if err != nil {
		panic(err) // Check for error

	// Critically log critical
	log.Critical("This is Critical!")
	log.CriticalF("%+v", err)
	// Debug
	log.Debug("This is Debug!")
	log.DebugF("Here are some numbers: %d %d %f", 10, -3, 3.14)
	// Give the Warning
	log.Warning("This is Warning!")
	log.WarningF("This is Warning!")
	// Show the error
	log.Error("This is Error!")
	log.ErrorF("This is Error!")
	// Notice
	log.Notice("This is Notice!")
	log.NoticeF("%s %s", "This", "is Notice!")
	// Show the info
	log.Info("This is Info!")
	log.InfoF("This is %s!", "Info")

	log.StackAsError("Message before printing stack");

	// Show warning with format
	log.SetFormat("[%{module}] [%{level}] %{message}")
	log.Warning("This is Warning!") // output: "[test] [WARNING] This is Warning!"
	// Also you can set your format as default format for all new loggers
	log2, _ := logger.New("pkg", 1, os.Stdout)
	log2.Error("This is Error!") // output: "This is Error!"


By default all log messages have format that you can see above (on pic). But you can override the default format and set format that you want.

You can do it for Logger instance (after creating logger) ...

log, _ := logger.New("pkgname", 1)

... or for package


If you do it for package, all existing loggers will print log messages with format that these used already. But all newest loggers (which will be created after changing format for package) will use your specified format.

But anyway after this, you can still set format of message for specific Logger instance.

Format of log message must contains verbs that represent some info about current log entry. Ofc, format can contain not only verbs but also something else (for example text, digits, symbols, etc)

Format verbs:

You can use the following verbs:

%{id}           - means number of current log message
%{module}       - means module name (that you passed to func New())
%{time}			- means current time in format "2006-01-02 15:04:05"
%{time:format}	- means current time in format that you want
					(supports all formats supported by go package "time")
%{level}		- means level name (upper case) of log message ("ERROR", "DEBUG", etc)
%{lvl}			- means first 3 letters of level name (upper case) of log message ("ERR", "DEB", etc)
%{file} 		- means name of file in what you wanna write log
%{filename}		- means the same as %{file}
%{line}			- means line number of file in what you wanna write log
%{message}		- means your log message

Non-existent verbs (like %{nonex-verb} or %{}) will be replaced by an empty string. Invalid verbs (like %{inv-verb) will be treated as plain text.



  • go test logger to run test on logger.
  • go test -bench=. for benchmarks.


Thanks goes to all go-loggers out there which I used as reference.


Following contributors have made major contributions to go-logger:


The BSD 3-Clause license, the same as the Go language.

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