【shell】1～100を加算

cat sum1.sh 
#/bin/bash
sum=0
a=1
b=100
while [ $a -lt $b ]
do
	c=`expr $a + $b`
	sum=`expr $sum + $c`
	a=`expr $a + 1`
	b=`expr $b - 1`
done
echo $sum

cat sum2.sh
#/bin/bash
number=0
while [ $number -le 100 ]
do
	a=`expr $a + $number`
	number=`expr $number + 1`
done
echo $a

echo |awk '{for (i=1;i<=100;i=i+1) a=a+i} { print a}'
5050