package main
import (  "bytes"  "crypto/rand"  "flag"  "fmt"  "io/ioutil"  "log"  "math/big")
func main() {  var userfile string  var max int64  flag.StringVar(&userfile, "input", "", "set input user file")  flag.Int64Var(&max, "max", 1, "set max user")  flag.Parse()
  txt, err := ioutil.ReadFile(userfile)  if err != nil {    log.Println("read file", err)    return  }  lines := bytes.Split(txt, []byte("\n"))  if max >= int64(len(lines)) {    log.Println("max should little than users")    return  }  count := len(lines)  var flags = make([]bool, count)  var counter int64  for counter < max {    n, err := rand.Int(rand.Reader, big.NewInt(int64(count)-counter))    if err != nil {      log.Panic(err)    }    idx := n.Int64()    if flags[idx] {      continue    } else {      fmt.Printf("[%d] %v\n", counter+1, string(lines[idx]))      flags[idx] = true      counter++    }  }}