shell脚本之while和until

leng

bash编程的循环：while和until

while 测试条件; do

语句1

语句2

...

done

Count=2

if [ $Count -le 5 ]; then

fi

while [ $Count -le 5 ]; do

let Count++

done

条件满足时就循环，直到条件不再满足，则退出循环；

for如何退出循环？遍历列表中的元素完成；

while循环呢？在循环体改变测试条件相应变量等的值。

补充：算术运算符

Sum=$[$Sum+$I]

Sum+=$I

+=

-=

*=

/=

%=

Sum=$[$Sum+1]

Sum+=1

let Sum++

let Count--

and --> AND

exit --> EXIT

quit

计算100以内所有正整数的和；

Sum=0

for I in {1..100}; do

Sum+=$I

done

echo $Sum

#!/bin/bash

Sum=0

Count=1

while [ $Count -le 100 ]; do

let Sum+=$Count

let Count++

done

echo $Sum

计算100以内所有偶数的和；

#!/bin/bash

#

EvenSum=0

Count=0

while [ $Count -le 100 ]; do

let Sum+=$Count

let Count+=2

done

while [ $Count -le 100 ]; do

if [ $[$Count%2] -eq 0 ]; then

Sum+=$Count

fi

let Count++

done

while循环遍历文件的每一行：

while read LINE; do

statement1

statement2

...

done < /path/to/somefile

练习：如果用户的ID号为偶数，则显示其名称和shell；对所有用户执行此操作；

while read LINE; do

Uid=`echo $LINE | cut -d: -f3`

if [ $[$Uid%2] -eq 0 ]; then

echo $LINE | cut -d: -f1,7

fi

done < /etc/passwd

练习：转换用户输入的字符为大写，除了quit（遇见quit退出）；

read -p "A string: " String

while [ "$String" != 'quit' ]; do

echo $String | tr 'a-z' 'A-Z'

read -p "Next [quit for quiting]: " String

done

until 测试条件; do

语句1

语句2

...

done

条件不满足就循环，直到满足时，退出循环；

例子：计算100以内所有正整数的和；

Sum=0

Count=1

until [ $Count -gt 100 ]; do

let Sum+=$Count

let Count++

done

echo $Sum

练习：转换用户输入的字符为大写，除了quit（遇见quit退出）；

read -p "A string: " String

until [ "$String" == 'quit' ]; do

echo $String | tr 'a-z' 'A-Z'

read -p "Next [quit for quiting]: " String

done

练习：每隔5秒查看hadoop用户是否登录，如果登录，显示其登录并退出；否则，显示当前时间，并说明hadoop尚未登录：

who | grep "^hadoop" &> /dev/null

RetVal=$?

until [ $RetVal -eq 0 ]; do

date

sleep 5

who | grep "^hadoop" &> /dev/null

RetVal=$?

done

echo "hadoop is here."

until who | grep "^hadoop" &> /dev/null; do

date

sleep 5

done

echo "hadoop is here."

who | grep "^hadoop" &> /dev/null

RetVal=$?

while [ $RetVal -ne 0 ]; do

date

sleep 5

who | grep "^hadoop" &> /dev/null

RetVal=$?

done

echo "hadoop is here."

练习：使用while循环统计/etc/rc.d/init.d/functions中#开头的行数；

let Count=0

declare -i Count=0

#!/bin/bash

Count=0

while read LINE ; do

if echo $LINE | grep "^[[:space:]]*#" &> /dev/null ; then

let Count++

fi

done < /etc/rc.d/init.d/functions

echo -e "\n\ttotal $Count lines start with #.\n"

#!/bin/bash

#

Num=0

while read LINE; do

echo $LINE |grep "^#.*" &> /dev/null && let Num++

done < /etc/rc.d/init.d/functions

echo "#Number: $Num"

计算100以内所有偶数的和以及奇数的和；在一个循环中实现；

要求：分别使用while和until各自独立实现。

#!/bin/bash

Evensum=0

Oddsum=0

Count=0

while [ $Count -le 100 ];do

if [ $[$Count%2] -eq 0 ];then

let Evensum+=$Count

else

let Oddsum+=$Count

fi

let Count++

done

echo "The Evensum is : $Evensum"

echo "The Oddsum is : $Oddsum"

#!/bin/bash

Evensum=0

Oddsum=0

Count=0

until [ $Count -gt 100 ]; do

if [ $[$Count%2] -eq 0 ];then

let Evensum+=$Count

else

let Oddsum+=$Count

fi

let Count++

done

echo "The Evensum is : $Evensum"

echo "The Oddsum is : $Oddsum"

搜鞥都哦

自从我变成了狗屎,就再也没有人踩在我头上了。

2653885

你不能把我的心当泡踩、

shaoqin

我头也不回的走，背影或许很是狼狈吧

绝对绿茶

爱你不用合情理但愿用直觉本能去抓住你

yanghongjun

过去的一页，能不要翻就不要翻，翻落了的灰尘会迷了双眼

9AMC

恐慌会让人变得坚强再坚强,所以不要害怕