[root@localhost ~]# cat jiechen.sh #!/bin/bash#设计一个shell程序计算n的阶乘，要求：#1.从命令行接收参数n;#2.在程序开始后立即判断n的合法性，即是否有参数，若有是否为正整数，若非法请给错误提示。#3.最后出计算的结果
num=$1expr $num + 1 &>/dev/null[ $? -ne 0 ] && echo "please input a number." && exit 2[ $# -ne 1 ] && echo ‘Usage:$0 number‘ && exit 1[ $num -le 0 ] && echo "please input a number bigger than 0" && exit 3s=1for i in `seq 1 $num`do      s=$(($s*$i))doneecho $s[root@localhost ~]# bash jiechen.sh 5120[root@localhost ~]# bash jiechen.sh 36[root@localhost ~]# bash jiechen.sh 22[root@localhost ~]# bash jiechen.sh 11[root@localhost ~]#