linux_while及until循环

脚本编程：

顺序结构

选择结构

if

case

循环结构

for

while

until

while循环：适合循环次数未知的场景，一定要有退出条件

while

进入循环：条件满足

退出循环：条件不满足

语法：

while CONDITON;do

statement

…

done

-+

计算100以内所有整数的合

#!/bin/bash

#

declare -i I=1

declare -i SUM=0

while [ $I -le 100];do

let SUM+=$I

let I+=1

done

echo"$SUM"

练习2：写一个脚本，用户输入任何字母都变成大写，输入quit退出

#!/bin/bash

#

read -p "Inputsometing:" STRING

while [ $STRING !=‘quit‘ ];do

echo $STRING |tr‘a-z‘ ‘A-Z‘

read -p "Inputsometing:" STRING

done

练习3.写一个脚本每隔5秒钟检测一下admin用户是否登录。

#!/bin/bash

#

who |grep admin&>/dev/null

RETVAL=$?

while [ $RETVAL -ne0 ];do

echo "`date`,admin is not log."

sleep 5

who |grep admin&>/dev/null

RETVAL=$?

done

echo "admin islogged in."

until

进入循环：条件不满足

退出循环：条件满足

until CONDITION;do

statement

…

done

练习，写一个脚本，当用户输入quit时退出，输入小写字母时自动变成大写字母

#!/bin/bash

#

read -p"shuru": R

until [ $R = ‘quit‘];do

echo $R |tr ‘a-z‘‘A-Z‘

read -p"shuru": R

done

练习，写一个脚本，每隔五秒钟判断admin是否登录

#!/bin/bash

#

who|grep admin&>/dev/null

R=$?

until [ $R -eq 0];do

echo"`date`,admin not come"

sleep 5

who|grep admin&>/dev/null

R=$?

done

echo “admin loggedin.”