1 package main
 2
 3 import (
 4     "io"
 5     "io/ioutil"
 6     "log"
 7     "os"
 8 )
 9
10 var (
11     Trace   *log.Logger
12     Info    *log.Logger
13     Warning *log.Logger
14     Error   *log.Logger
15 )
16
17 func Init(
18     traceHandle io.Writer,
19     infoHandle io.Writer,
20     warningHandle io.Writer,
21     errorHandle io.Writer) {
22
23     Trace = log.New(traceHandle,
24         "TRACE: ",
25         log.Ldate|log.Ltime|log.Lshortfile)
26
27     Info = log.New(infoHandle,
28         "INFO: ",
29         log.Ldate|log.Ltime|log.Lshortfile)
30
31     Warning = log.New(warningHandle,
32         "WARNING: ",
33         log.Ldate|log.Ltime|log.Lshortfile)
34
35     Error = log.New(errorHandle,
36         "ERROR: ",
37         log.Ldate|log.Ltime|log.Lshortfile)
38 }
39
40 func main() {
41     Init(ioutil.Discard, os.Stdout, os.Stdout, os.Stderr)
42
43     Trace.Println("I have something standard to say")
44     Info.Println("Special Information")
45     Warning.Println("There is something you need to know about")
46     Error.Println("Something has failed")
47 }

1 INFO: 2013/11/05 18:11:01 main.go:44: Special Information
2 WARNING: 2013/11/05 18:11:01 main.go:45: There is something you need to know about
3 ERROR: 2013/11/05 18:11:01 main.go:46: Something has failed

var Trace *log.LoggerTrace = log.New(traceHandle,"TRACE: ",log.Ldate|log.Ltime|log.Lshortfile)Init(ioutil.Discard, os.Stdout, os.Stdout, os.Stderr)Trace.Println("I have something standard to say")

func New(out io.Writer, prefix string, flag int) *Logger
out:    The out variable sets the destination to which log data will be written. // 译注 out 变量设置将写入日志数据的目标
prefix: The prefix appears at the beginning of each generated log line. // 译注 前缀出现在每个生成的日志行的开头。
flags:  The flag argument defines the logging properties. // 译注 flag 参数定义日志记录属性
Flags:const (// Bits or’ed together to control what’s printed. There is no control over the// order they appear (the order listed here) or the format they present (as// described in the comments). A colon appears after these items:// 2009/01/23 01:23:23.123123 /a/b/c/d.go:23: messageLdate = 1 << iota // the date: 2009/01/23Ltime             // the time: 01:23:23Lmicroseconds     // microsecond resolution: 01:23:23.123123. assumes Ltime.Llongfile         // full file name and line number: /a/b/c/d.go:23Lshortfile        // final file name element and line number: d.go:23. overrides LlongfileLstdFlags = Ldate | Ltime // initial values for the standard logger
)

var Info *log.LoggerInfo = log.New(infoHandle,"INFO: ",log.Ldate|log.Ltime|log.Lshortfile)Init(ioutil.Discard, os.Stdout, os.Stdout, os.Stderr)Info.Println("Special Information")

var Error *log.LoggerError = log.New(errorHandle,"ERROR: ",  // 译注： 原文是 INFO 与原始定义不同，应该是笔误，故直接修改log.Ldate|log.Ltime|log.Lshortfile)Init(ioutil.Discard, os.Stdout, os.Stdout, os.Stderr)Error.Println("Something has failed") // 译注： 原文是 Special Information 与原始定义不同，应该是笔误，故直接修改

1 file, err := os.OpenFile("file.txt", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
2 if err != nil {
3     log.Fatalln("Failed to open log file", output, ":", err)
4 }
5
6 MyFile = log.New(file,
7     "PREFIX: ",
8     log.Ldate|log.Ltime|log.Lshortfile)

 1 file, err := os.OpenFile("file.txt", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
 2 if err != nil {
 3     log.Fatalln("Failed to open log file", output, ":", err)
 4 }
 5
 6 multi := io.MultiWriter(file, os.Stdout)
 7
 8 MyFile := log.New(multi,
 9     "PREFIX: ",
10     log.Ldate|log.Ltime|log.Lshortfile)

package mainimport ("log"
)func main() {log.Println("Hello World")
}

package mainimport ("log"
)func main() {log.SetFlags(0)log.Println("Hello World")
}

package mainimport ("io/ioutil""log"
)func main() {log.SetOutput(ioutil.Discard)log.Println("Hello World")
}