在Linux中shell编程求M-N的阶乘，M、N用户输入

在Linux中shell编程求M-N的阶乘，M、N用户输入

#!/bin/bash

echo "请输入整数M、N(M>N)"
echo "M："
read M

#判断M是否非空且为整数
if [ -z $M ]
then
echo "M 必须非空"
exit 1
elif ! [[ $M =~ ^-?[0-9]*$ ]]
then
echo "M 必须为整数"
exit 1
fi

echo "N："
read N

#判断N是否非空且小于N的整数
if [ -z $N ]
then
echo "N 必须非空"
exit 1
elif ! [[ $N =~ ^-?[0-9]*$ ]]
then
echo "N 必须为整数"
exit 1
elif [ $M -le $N ]
then
echo "N必须小于M"
exit 1
fi

let "base = M-N"
result=1

#阶乘函数，引入result实现运算的线性增长
fac (){
base=$1
result=$2

if [ $base -gt 0 ]
then
let "result *= base"
let "base -= 1"
fac $base $result
fi
}

#计算阶乘
fac $base $result

echo "M-N的阶乘为$result"
exit 0

上次看错题目了2011-01-08