golang log标准库实现了简单日志服务。但不支持log分类、分级、过滤等复杂功能。由第三方库如glog(Github)、seelog(Github)
简单demo如下：

package main

import (
	"log"
	"os"
)
func main()  {

	file,err := os.Create("test.log")
	if err != nil {
		log.Fatalln("fail to create test.log file!")
	}
	defer file.Close()

	logger := log.New(file, "info:", log.LstdFlags|log.Lshortfile)

	logger.Println("this is phpddt.com testing")//info:2015/11/15 01:11:48 test.go:17: this is phpddt.com testing
}

可见，指定prefix可实现简单的分级。
通过查看源码可见logger结构：

type Logger struct {
	mu     sync.Mutex // ensures atomic writes; protects the following fields
	prefix string     // prefix to write at beginning of each line
	flag   int        // properties
	out    io.Writer  // destination for output
	buf    []byte     // for accumulating text to write
}

日志格式flag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
)

golang log实现了三类接口：

• print 一般消息输出
• fatal强行退出
• panic 输出log后进行panic