方式一：计数器控制while的循环

#!/bin/bash

sum=0
i=0
while (( i <= 100 ))
do
        let "sum=sum+$i"
        let "i=i+2"
done
echo $sum

方式二：结束标记控制循环

read -p "please input a num[1-10] " num2

while [[ "$num" != 5 ]]
do
        if [ "$num" -lt 5 ];then
                echo "too small,try again"
                read num
        elif [ "$num" -gt 5 ];then
                echo "too big ,try again"
                read num
        else
                exit 0
        fi
done
echo "you are right"

方式三：标志控制的while循环

#!/bin/bash

read -p "please input a num [1-10]" num
signal=0
while [[ "$signal" != 1 ]]
do
        if [ "$num" -lt 4 ];then
                echo "too small ,try again"
                read num
        elif [ "$num" -gt 4 ];then
                echo "too big,try again"
                read num
        else
                signal=1
        fi
done
echo "you are right"

方式四：命令行控制的while循环

#!/bin/bash

##第四种while使用方式
echo "number of arguement: $#"
echo "what you input is:"
while [[ "$*" != "" ]]
do
        echo "$1"
        shift
done