shell使用for循环计算1到100的和

shell提供4中计算算术运算的方法，如下：

#!/bin/bash

unset sum
for i in {1..100}
do
    sum=$(($sum + $i))
done
echo $sum      //5050

unset sum
for i in {1..100}
do
    sum=$[ $sum + $i ]
done
echo $sum      //5050

unset sum
for i in {1..100}
do
    let sum=sum+i
done
echo $sum      //5050

unset sum
for i in {1..100}
do
    sum=`expr $sum + $i`
done
echo $sum      //5050