$RANDOM获得随机数

#!/bin/bash
n=$[$RANDOM%100]
while :
do
   read -p "Please input a number:" n1
   n2=`echo $n1 | sed 's/[0-9]//g'`
   if [ ! -z "$n2" ];then
      echo "You should input the number!"
      continue
   fi
   if [ $n1 -eq $n ];then
      echo "Bingo"
      break
   elif [ $n1 -gt $n ];then
      echo "Bigger"
      continue
   elif [ $n1 -lt $n ];then
      echo "Small"
      continue
   fi
done
解释：判断n2的值是否为空：
 n2=`echo $n1 | sed 's/[0-9]//g'`
   if [ ! -z "$n2" ];then
如果用-n判断时需要对"$n2"加上双引号，源码里对-n和-z判断解释是：
-z的判断是通过判断字符串首位是否为\0来完成，而-n则变成了0