Leveled logs with Cobra and Logrus

I recently wrote a CLI using Cobra, a widely adopted CLI framework for Golang that’s used in Kubectl, Docker, Terraform, Hugo, and other industry-standard CLIs.

I wanted to use Logrus, a highly regarded structured logging framework for Go. I wanted informative, colorized, leveled logs, but I also wanted to be able to log simple, user-facing output without all of the bells and whistles. I was surprised at the lack of documentation around this simple goal.

Here’s one way to solve this problem.

Create a file called logging.go in your cmd package:

package cmd

import (
	"fmt"
	log "github.com/sirupsen/logrus"
	"github.com/spf13/cobra"
)

var debug bool

type PlainFormatter struct {
}

func (f *PlainFormatter) Format(entry *log.Entry) ([]byte, error) {
	return []byte(fmt.Sprintf("%s\n", entry.Message)), nil
}
func toggleDebug(cmd *cobra.Command, args []string) {
	if debug {
		log.Info("Debug logs enabled")
		log.SetLevel(log.DebugLevel)
		log.SetFormatter(&log.TextFormatter{})
	} else {
		plainFormatter := new(PlainFormatter)
		log.SetFormatter(plainFormatter)
	}
}

Add a PreRun to each of your Cobra commands:

var addCmd = &cobra.Command{
    ...
	PreRun: toggleDebug, // This. 
	Run: func(cmd *cobra.Command, args []string) {
    // Subcommand logic goes here.
    }
}

Add a global persistent flag to root.go:

func init() {
    ...
	rootCmd.PersistentFlags().BoolVarP(&debug, "debug", "d", false, "verbose logging")
}

It’s as simple as that. Now you can reap the benefits of flag-toggled leveled logs. Use the following invocations anywhere in your code:

log.Info()
log.Debug()
log.Warning()
log.Error()
log.Fatal()

Debug logs are suppressed by default. You can pass the --debug or -d flag to any command to print more verbose, colorized debug logs, which are super helpful when troubleshooting.

I hope you found this helpful.