San modified version

This modified version of logutils includes fatih/color libary. I used a simple math operation to determine the color we want to attach to each log line.

Assuming the highest severity log is always RED, we pre-determine the color for the last 4 highest severity from Blue, Green, Yellow and Red. Anything fall outside of this will have default terminal color.

Considering most of the time, my filter ares: []logutils.LogLevel{"DEBUG","INFO", "WARN", "ERROR"},, this will color all 4 log severity levels.

logutils

logutils is a Go package that augments the standard library "log" package to make logging a bit more modern, without fragmenting the Go ecosystem with new logging packages.

The simplest thing that could possibly work

Presumably your application already uses the default log package. To switch, you'll want your code to look like the following:

package main

import (
	"log"
	"os"

	"github.com/hashicorp/logutils"
)

func main() {
	filter := &logutils.LevelFilter{
		Levels: []logutils.LogLevel{"DEBUG", "WARN", "ERROR"},
		MinLevel: logutils.LogLevel("WARN"),
		Writer: os.Stderr,
	}
	log.SetOutput(filter)

	log.Print("[DEBUG] Debugging") // this will not print
	log.Print("[WARN] Warning") // this will
	log.Print("[ERROR] Erring") // and so will this
	log.Print("Message I haven't updated") // and so will this
}

This logs to standard error exactly like go's standard logger. Any log messages you haven't converted to have a level will continue to print as before.