循环测试用户名与密码是否正确

#!/bin/bash
#循环测试用户的账户名和密码，最大测试 3 次，输入正确提示登录成功，否则提示登录失败
#用户名为 tom 并且密码为 123456  
for  i  in  {1..3}
do
read -p "请输入用户名:"    user 
read -p "请输入密码:"        pass 
if [ "$user" == 'tom' -a "$pass" == '123456' ];then 
      echo "Login successful"
         exit
fi 
done
echo "Login Failed"