实现一个让用户输入不超过3次的程序，直到输入正确的值

  
  
  
  

   
   
   
   #
   
   
   
   /
   
   
   
   bin
   
   
   
   /
   
   
   
   bash count
   
   
   
   =
   
   
   
   3
   
   
   
    
   
   
   
   while
   
   
   
    :;
   
   
   
   do
   
   
   
    read 
   
   
   
   -
   
   
   
   p 
   
   
   
   "
   
   
   
   username:
   
   
   
   "
   
   
   
    username echo 
   
   
   
   "
   
   
   
   input username is $username
   
   
   
   "
   
   
   
    
   
   
   
   if
   
   
   
    [[ $username 
   
   
   
   !=
   
   
   
    
   
   
   
   "
   
   
   
   haha
   
   
   
   "
   
   
   
    ]];then #如果输入的不是预定的值则 ((count
   
   
   
   --
   
   
   
   )) #计数器减一 echo 
   
   
   
   "
   
   
   
   Error! try $count
   
   
   
   "
   
   
   
    #显示提示信息 ((count
   
   
   
   ==
   
   
   
   0
   
   
   
   ))
   
   
   
   &&
   
   
   
   break
   
   
   
   ||
   
   
   
   continue
   
   
   
    #当次数用完的时候则循环结束否则循环继续 
   
   
   
   else
   
   
   
    
   
   
   
   break
   
   
   
    #当输入正确的时候，跳出循环 fi done