JeffDeCola/my-go-examples

// my-go-examples logrus.go

package main

import (
    "errors"
    "flag"
    "fmt"
    "os"

    log "github.com/sirupsen/logrus"
)

var errLogLevel = errors.New("please use trace, info or error")

func setLogLevel(logLevel string) error {

    // SET LOG LEVEL (trace, info or error) None of which exit
    log.Trace("Set Log Level")

    switch logLevel {
    case "trace":
        log.SetLevel(log.TraceLevel)
    case "info":
        log.SetLevel(log.InfoLevel)
    case "error":
        log.SetLevel(log.ErrorLevel)
    default:
        log.SetLevel(log.ErrorLevel)
        return fmt.Errorf("%s", errLogLevel)
    }

    // SET FORMAT
    log.SetFormatter(&log.TextFormatter{
        DisableColors: false,
        FullTimestamp: false,
    })
    // log.SetFormatter(&log.JSONFormatter{})

    // SET OUTPUT (DEFAULT os.Stderr)
    log.SetOutput(os.Stdout)

    return nil

}

func createLogFile(filename string) (*os.File, error) {

    var myfile *os.File

    log.Info("Writing to log file")

    // LOGGING TO FILE (APPEND) (io.Writer)
    myfile, err := os.OpenFile(filename, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
    if err == nil {
        log.SetOutput(myfile)
    } else {
        return nil, fmt.Errorf("failed to log to file, using default stderr: %w", err)
    }

    return myfile, nil

}

func main() {

    // FLAGS
    logLevel := flag.String("loglevel", "error", "log level (trace, info or error)")
    logFile := flag.String("logfile", "", "log output to a file")
    flag.Parse()

    // SET LOG LEVEL (trace, info or error) None of which exit
    err := setLogLevel(*logLevel)
    if err != nil {
        log.Errorf("Error getting logLevel: %s", err)
    }

    // CREATE AND SENT TO LOG FILE IF FLAG IS SET
    if *logFile != "" {
        myfile, err := createLogFile(*logFile)
        if err != nil {
            log.Errorf("Error creating logfile: %s", err)
        }
        defer myfile.Close()
    }

    // LOGGING
    log.Error("Something failed but I'm not quitting.")
    log.Info("Something noteworthy happened!")
    log.Trace("Something very low level.")

    // WITH FORMATTING
    name := "jeff"
    log.Infof("This is from %s", name)

    // USING FIELDS
    log.WithFields(log.Fields{
        "animal": "cat",
    }).Trace("What animal is it?")

    // REUSING FIELDS
    jeffLogger := log.WithFields(log.Fields{
        "animal": "cat",
        "color":  "grey",
    })

    jeffLogger.Trace("Using the animal and color field")
    jeffLogger.Trace("Me too")

}