需求：

　　需要监听一个目录中所有文件，当文件大小增加到一定阀值，则将文件清空。

　　需要引入第三方包："github.com/howeyc/fsnotify"

　　代码如下：

package main

import (
"log"
"github.com/howeyc/fsnotify"
"os"
"fmt"
"strconv"
)

func usage() {
fmt.Println("")
fmt.Printf("Usage: %s Montior-directory file-max-bytes-limit\n",os.Args[0])
fmt.Println("For example:")
fmt.Printf("%s /opt/logs 1024\n",os.Args[0])
os.Exit(1)
}

func isDir(dirname string) bool {
fhandler, err := os.Stat(dirname);
if(! (err == nil || os.IsExist(err)) ) {
return false
}else {
return fhandler.IsDir()
}
}

func isFile(filename string) bool {
fhandler, err := os.Stat(filename);
if(! (err == nil || os.IsExist(err)) ) {
return false
}else if (fhandler.IsDir()){
return false
}
return true
}

func emptiedFile(filename string) bool {
FN,err := os.Create(filename)
defer FN.Close()
if err != nil {
return false
}
fmt.Fprint(FN,"")
return true
}

func getFileByteSize(filename string) (bool,int64) {
if (! isFile(filename)) {
return false,0
}
fhandler, _ := os.Stat(filename);
return true,fhandler.Size()
}

func main() {
var maxByte int64 = 1024*1024
if (len(os.Args) < 2) { usage() } if (len(os.Args) >= 3) {
maxByte_,err := strconv.Atoi(os.Args[2])
if err != nil {
log.SetPrefix("[ERROR] ")
log.Println(os.Args[2],"Is not a legitimate int number")
usage()
}
maxByte = int64(maxByte_)
}
dirpath := os.Args[1]
if (!isDir(dirpath)){
log.SetPrefix("[ERROR] ")
log.Println(dirpath,"Is not a legitimate directory")
usage()
}
watcher, err := fsnotify.NewWatcher()
if err != nil {
log.Fatal(err)
}
done := make(chan bool)

//Process event  
go func() {  
    for {  
        select {  
        case ev := <-watcher.Event:  
            if(ev.IsModify()){  
                \_,size := getFileByteSize(ev.Name)  
                log.Println("event:",ev,",byte:",size)  
                if (size >= maxByte){  
                    if ( ! emptiedFile(ev.Name) ) {  
                        log.SetPrefix("\[ERROR\] ")  
                        log.Printf("%s :Can not empty file\\n",ev.Name)  
                    }  
                }  
            }  
        case err := <-watcher.Error:  
            log.Println("error:",err)  
        }  
    }  
}()  
err = watcher.Watch(dirpath)  
if err != nil {  
    log.Fatal(err)  
}  
<-done

watcher.Close()  

}

运行实例：