for while until 循环

#!/bin/bash




# 遍历列表, 数组
#列表： {1..20} 、{a..z}、 {A..Z}
for item in {1..20}
do
    echo $item
done

echo ========================

#c语言格式
for ((i=0; i<=20; i++))
do
    echo $i
done

echo ========================

count=0
while [ $count -le 20 ]
do
    echo $count
    let count++
done

echo ========================


count=0

while :
do
    if [ $count -gt 20 ]
    then
        break
    fi
    echo $count
    count=$[ count + 1 ]
done

echo ========================

count=0



##当条件符合时，退出循环
until [ $count -gt 20 ]
do
    echo $count
    count=$(($count + 1))
done