Why? #

Whenever you debug a program that produces a large amount of logs, sifting through them when a bug arises is only a matter of time. This tasks becomes more annoying when there is no consistent pattern you focus on with grep, especially when you want to find a pattern between related log lines that aren’t immediately next to each other in the log file. When I resort to manually looking through logs of programs I’m debugging, having colour-coded logs tends to make the experience more fun.

How? #

I recently found a logging library by Charm, a start-up dedicated to making pleasing-to-use libraries, utilities and application that are centered around the command-line experience. Since I never really thought of making my programs’ command-line output easy to read, I thought of giving it a try.

Custom Logger #

For my personal project, I override the default package settings with the following:

• Each log line reports what source code line printed it.
• RFC 3339 timestamp format
• In order to show debugging logs by default, the default logging level is be set to log.DebugLevel.

import (
	"time"

	"github.com/charmbracelet/log"
)

func init() {
	log.SetReportCaller(true)
	log.SetTimeFormat(time.RFC3339)
	log.SetLevel(log.DebugLevel)
}

Result #

In the following section, I’ll show some code snippets and the output they produce (captured with vhs).

Information/Success #

Regular logs are shown with a green-coloured INFO prefix.

log.Info("Hi there!", "version", runtime.Version())
log.Infof("%d + 0x%x = 0b%b", 22, 0x56, 22+0x56)

Debugging #

Debug logs are shown with a blue-coloured DEBU prefix.

log.Debug("Hi there!", "version", runtime.Version())
log.Debugf("%d + 0x%x = 0b%b", 22, 0x56, 22+0x56)

Warning #

Warning logs are shown with a yellow-coloured WARN prefix.

log.Warn("Hi there!", "version", runtime.Version())
log.Warnf("%d + 0x%x = 0b%b", 22, 0x56, 22+0x56)

Error & Fatal #

• Error logs are shown with a red-coloured ERRO prefix.
• Fatal logs are shown with a purple-coloured FATA prefix.
  • Any call to log.Fatal or to log.Fatalf will result in the program exiting immediately with code 1.

log.Error("Hi there!", "version", runtime.Version())
log.Errorf("%d + 0x%x = 0b%b", 22, 0x56, 22+0x56)
log.Fatal("goodbye")