logger

Logger is a simple cross platform Go logging library for Windows, Linux, FreeBSD, and macOS, it can log to the Windows event log, Linux/macOS syslog, and an io.Writer.

This is not an official Google product.

Usage

Set up the default logger to log the system log (event log or syslog) and a file, include a flag to turn up verbosity:

import (
  "flag"
  "os"

  "github.com/google/logger"
)

const logPath = "/some/location/example.log"

var verbose = flag.Bool("verbose", false, "print info level logs to stdout")

func main() {
  flag.Parse()

  lf, err := os.OpenFile(logPath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0660)
  if err != nil {
    logger.Fatalf("Failed to open log file: %v", err)
  }
  defer lf.Close()

  defer logger.Init("LoggerExample", *verbose, true, lf).Close()

  logger.Info("I'm about to do something!")
  if err := doSomething(); err != nil {
    logger.Errorf("Error running doSomething: %v", err)
  }
}

The Init function returns a logger so you can setup multiple instances if you wish, only the first call to Init will set the default logger:

lf, err := os.OpenFile(logPath, os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0660)
if err != nil {
  logger.Fatalf("Failed to open log file: %v", err)
}
defer lf.Close()

// Log to system log and a log file, Info logs don't write to stdout.
loggerOne := logger.Init("LoggerExample", false, true, lf)
defer loggerOne.Close()
// Don't to system log or a log file, Info logs write to stdout..
loggerTwo := logger.Init("LoggerExample", true, false, ioutil.Discard)
defer loggerTwo.Close()

loggerOne.Info("This will log to the log file and the system log")
loggerTwo.Info("This will only log to stdout")
logger.Info("This is the same as using loggerOne")

Custom Format

Code	Example
logger.SetFlags(log.Ldate)	ERROR: 2018/11/11 Error running Foobar: message
logger.SetFlags(log.Ltime)	ERROR: 09:42:45 Error running Foobar: message
logger.SetFlags(log.Lmicroseconds)	ERROR: 09:42:50.776015 Error running Foobar: message
logger.SetFlags(log.Llongfile)	ERROR: /src/main.go:31: Error running Foobar: message
logger.SetFlags(log.Lshortfile)	ERROR: main.go:31: Error running Foobar: message
logger.SetFlags(log.LUTC)	ERROR: Error running Foobar: message
logger.SetFlags(log.LstdFlags)	ERROR: 2018/11/11 09:43:12 Error running Foobar: message

func main() {
    lf, err := os.OpenFile(logPath, …, 0660)
    defer logger.Init("foo", *verbose, true, lf).Close()
    logger.SetFlags(log.LstdFlags)
}

More info: https://golang.org/pkg/log/#pkg-constants