golang package log

package main

import (
	"log"
	"os"
)

var logger *log.Logger

func main() {
	file, err := os.OpenFile("test.log", os.O_APPEND|os.O_CREATE, 666)
	if err != nil {
		log.Fatalln("fail to create test.log file!")
	}
	defer file.Close()
	logger = log.New(file, "", log.LstdFlags|log.Lshortfile) // 日志文件格式:log包含时间及文件行数
	log.Println("输出日志到命令行终端")
	logger.Println("将日志写入文件")

	logger.SetFlags(log.LstdFlags | log.Lshortfile) // 设置日志格式

	log.Panicln("在命令行终端输出panic，并中断程序执行")
	logger.Panicln("在日志文件中写入panic，并中断程序执行")

	log.Fatal("在命令行终端输出日志并执行os.exit(1)")
	logger.Fatal("在日志文件中写入日志并执行os.exit(1)")
}

Logger结构体所有字段都是私有的，提供了一个工厂函数获取结构体实例

// New creates a new Logger. The out variable sets the
// destination to which log data will be written.
// The prefix appears at the beginning of each generated log line.
// The flag argument defines the logging properties.
func New(out io.Writer, prefix string, flag int) *Logger {
   return &Logger{out: out, prefix: prefix, flag: flag}
}

flag参数的常量

const (
   Ldate         = 1 << iota     // the date in the local time zone: 2009/01/23
   Ltime                         // the time in the local time zone: 01:23:23
   Lmicroseconds                 // microsecond resolution: 01:23:23.123123.  assumes Ltime.
   Llongfile                     // full file name and line number: /a/b/c/d.go:23
   Lshortfile                    // final file name element and line number: d.go:23. overrides Llongfile
   LUTC                          // if Ldate or Ltime is set, use UTC rather than the local time zone
   LstdFlags     = Ldate | Ltime // initial values for the standard logger
)