#!/bin/bash
#无限循环，除非主机不通自动退出
for ((i=1;;i++)) 
  do

   read -p "输入一个IP地址：" ack
#-c 4 只发送四个包
ping -c 4 $ack &> /dev/null

   if [ $? -eq 0 ]

     then

       echo "Host is up "

     else

       echo "Host is down"

     break

 

  fi

  done