How to write logs to multiple log files in golang? - go

Question

I am writing an application in which i need to record logs in two different files. For Example weblogs.go and debuglogs.go. I tried using the log4go but my requirement is i need the logger to be created in main file and be accessible in sub directory as major of decoding and logging is done in sub file. Can anybody please help with that?

Answer 1

Here's one way to do it, using the standard log package:
package main
import (
"io"
"log"
"os"
)
func main() {
f1, err := os.Create("/tmp/file1")
if err != nil {
panic(err)
}
defer f1.Close()
f2, err := os.Create("/tmp/file2")
if err != nil {
panic(err)
}
defer f2.Close()
w := io.MultiWriter(os.Stdout, f1, f2)
logger := log.New(w, "logger", log.LstdFlags)
myfunc(logger)
}
func myfunc(logger *log.Logger) {
logger.Print("Hello, log file!!")
}
Notes:
io.MultiWriter is used to combine several writers together. Here, it creates a writer w - a write to w will go to os.Stdout as well as two files
log.New lets us create a new log.Logger object with a custom writer
The log.Logger object can be passed around to functions and used by them to log things

Answer 2

This is how you can manage logs for debugging and prod envoirments with multi log files:
First, make a type for managing multiple loggers you can make a separate file for this like logging.go
type LOGGER struct {
debug *log.Logger
prod *log.Logger
.
.
.
}
For getting the LOGGER pointer anywhere in your project the best approach will be to get it through the singleton pattern like
var lock = &sync.Mutex{}
var loggers *LOGGER
func GetLoggerInstance() *LOGGER {
if singleInstance == nil {
lock.Lock()
defer lock.Unlock()
if loggers == nil {
fmt.Println("Creating LOGGER instance now.")
loggers = &LOGGER{}
} else {
fmt.Println("LOGGER instance already created.")
}
} else {
fmt.Println("LOGGER instance already created.")
}
return loggers
}
Now setup logger for debug env in any pkg or directory level better is to setup it at the root level
logger := GetLoggerInstance()
f, err := os.OpenFile("path/to/debug/log/file", os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
if err != nil {
fmt.Println("debug log file not created", err.Error())
}
loggers.debug = log.New(f, "[DEBUG]", log.Ldate|log.Ltime|log.Lmicroseconds|log.LUTC)
loggers.debug.Println("This is debug log message")
With the same approach, you can also create prod or as many as you want.
logger := GetLoggerInstance()
f, err = os.OpenFile("path/to/prod/log/file", os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
if err != nil {
fmt.Println("prod log file not created", err.Error())
}
loggers.prod = log.New(f, "[PROD]", log.Ldate|log.Ltime|log.Lmicroseconds|log.LUTC)
loggers.prod.Println("This is prod log message")