/*
golang log example

*/
package main

import (
  "log"
  "os"
)

func main() {
  logFile,err := os.Create("test1.log")
  defer logFile.Close()
  if err != nil {
    log.Fatalln("open file error!")
  }
  logger := log.New(logFile,"[Debug]",log.Ldate | log.Ltime | log.Lshortfile)
  logger.Println("test debug message")
  logger.SetPrefix("[Info]")
  logger.Println("test info message")

}

[root@local t2]# go build logTest1.go
[root@local t2]# ./logTest1
[root@local t2]# cat test1.log
[Debug]2017/06/13 23:18:36 logTest1.go:19: test debug message
[Info]2017/06/13 23:18:36 logTest1.go:21: test info message
[root@local t2]#

/*
  golang log rotate example

*/

package main

import (
  "fmt"
  "log"
  "os"
  "time"
)

const (
  BACKUP_COUNT = 5
  MAX_FILE_BYTES = 2 * 1024
)

func doRotate(fPrefix string) {
  for j := BACKUP_COUNT; j >= 1; j-- {
    curFileName := fmt.Sprintf("%s_%d.log",fPrefix,j)
    k := j-1
    preFileName := fmt.Sprintf("%s_%d.log",fPrefix,k)

    if k == 0 {
      preFileName = fmt.Sprintf("%s.log", fPrefix)
    }
    _,err := os.Stat(curFileName)
    if err == nil {
      os.Remove(curFileName)
      fmt.Println("remove : ", curFileName)
    }
    _,err = os.Stat(preFileName)
    if err == nil {
      fmt.Println("rename : ", preFileName, " => ", curFileName)
      err = os.Rename(preFileName, curFileName)
      if err != nil {
        fmt.Println(err)
      }
    }
  }
}

func NewLogger(fPrefix string) (*log.Logger, *os.File) {
  var logger *log.Logger
  fileName := fmt.Sprintf("%s.log", fPrefix)
  fmt.Println("fileName :", fileName)
  logFile, err := os.OpenFile(fileName, os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)

  if err != nil {
    fmt.Println("open file error!")
  } else {
    logger = log.New(logFile, "[Debug]", log.Ldate|log.Ltime|log.Lshortfile)
  }
  return logger, logFile
}

func logWorker(msgQueue <-chan string) {
  fPrefix := "msg"
  logger, logFile := NewLogger(fPrefix)
  for msg := range msgQueue {
    logger.Println(msg)
    fi, err2 := logFile.Stat()
    if err2 == nil {
      if fi.Size() > MAX_FILE_BYTES {
        logFile.Close()
        doRotate(fPrefix)
        logger,logFile = NewLogger(fPrefix)
      }
    }
  }
  logFile.Close()
}

func main() {
  msgQueue := make(chan string, 1000)
  go logWorker(msgQueue)

  for j := 1; j <= 1000; j++ {
    msgQueue <- fmt.Sprintf("msg_%d", j)
    time.Sleep(1 * time.Second)
  }
  close(msgQueue)
  return
}

[root@local t2]# ./logRotateTest1
fileName : msg.log
rename : msg.log => msg_1.log
fileName : msg.log
rename : msg_1.log => msg_2.log
rename : msg.log => msg_1.log
fileName : msg.log
rename : msg_2.log => msg_3.log
rename : msg_1.log => msg_2.log
rename : msg.log => msg_1.log
fileName : msg.log
^C