bash while/until循环学习

while循环：条件满足，则循环；失败，则退出

如何退出？

必须有时刻，条件测试不成功

? :条件控制变量

while 条件测试：do

循环体

done

until循环；条件不满足，则循环；否则，退出

until 测试条件；do

循环体

done

bash编程之组合测试条件

逻辑与：多个条件同时满足

[ CONDITION1 ] && [ CONDITION2 ]

[ CONDITION1 -a CONDITION2 ]

[[ CONDITION1 && CONDITION2 ]]

注意：前两个使用单双中括号都可，但&&不允许用于单个中括号中，所有第三者只能用于双中括号中

逻辑或：多个条件满足一个

[ CONDITION1 ] || [ CONDITION2 ]

[ CONDITION1 -o CONDITION2 ]

[[ CONDITION1 || CONDITION2 ]]

注意 || 不允许出现在单中括号中

得摩根定律

!(条件1或者条件2) = !条件1 并且!条件2

!（条件1且条件2）=！条件1 或者 !条件2

练习:

1.：通过键盘提示用户输入字符，将用户输入的小写字母转换为大写，转换一次之后，在此提醒，再输入再转换，直到输入quit退出；

#！ /bin/bash

#

read -p -t 5 "Enter a Word: " word

while [[ "$word" != "quit" ]]; do

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

read -p -t 5 "Enter a Word again: " word

done

2.写一个脚本，实现如下功能；

1、显示如下菜单：

CPU) show cpu info;

men) show memory info;

disk) show disk info;

quit) quit

Enter your option:

2、根据用户的选择输出相应信息，每次执行后，不退出，而由用户咋此指定新的选项

#! /bin/bash

#

cat <<EOF

cpu) print cpu infomation

men) print memory infomation

disk) print disk infomation

quit) Quit

EOF

read -p "Enter your option: " option

option=`echo $option | tr 'a-z' 'A-Z'`

while [[ "$option" != "QUIT" ]]; do

if [[ "$option" == "CPU" ]]; then

cat /proc/cpuinfo

elif [[ "$option" == "MEM" ]]; then

free -m

elif [[ "$option" == "DISK" ]]; then

df -Th

else

echo "Wrong Option..."

fi

read -p "Enter your option: " option

option=`echo $option | tr 'a-z' 'A-Z'`

done

3.提示用户输入一个用户名，显示用户名UID和SHELl信息，否则，则显示无此用户，显示完成后，提示用户再次输入，如果quit则退出；

#! /bin/bash

#

cat <<EOF

Username)Enter your Username..

quit)quit..

EOF

read -p "Enter Your userName: " userName

userName=`echo $userName | tr 'A-Z' 'a-z'`

while [[ "$userName" != "QUIT" ]]; do

sysUser=`cat /etc/passwd | grep ^$userName | cut -d: -f1 | tr 'A-Z' 'a-z'`

if [[ "$userName" == "$sysUser" ]]; then

echo "This $userName `cat /etc/passwd | grep -i ^$userName | cut -d: -f3,7`"

else

echo "No Such $userName.."

fi

read -p "Enter Your userName: " userName

userName=`echo $userName | tr 'A-Z' 'a-z'`

done

#! /bin/bash

#

read -t 2 -p "Enter a user name: " userName

userName=`echo $userName | tr 'A-Z' 'a-z'`

UID=`grep "^$userName\>" /etc/passwd | cut -d: -f3`

SH=`grep "^$userName\>" /etc/passwd | cut -d: -f7`

while [[ "$userName" != "quit" ]]; do

if [ -z "$userName" ]; then

echo "Username null...."

elif id $userName &> /dev/null; then

echo "$userName uid: $UID"

echo "$userName Shell: $SH"

else

echo "No such user...."

fi

read -t 2 -p "Enter a user name again(quit to exit) " userName

done

4.求100以内所有正整数的和；

#! /bin/bash

#

declare -i sum=0

declare -i i=1

while [ $i -le 100 ];do

let sum+=$i

let i++

done

echo $sum

#! /bin/bash

#

declare -i sum=0

declare -i i=1

until [ $i -gt 100 ]; do

let sum+=$i

let i++

done

echo $sum

5.求100以内所有偶数之和；

#! /bin/bash

#

declare -i evensum=0

declare -i i=1

while [ $i -le 100 ]; do

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

let evensum+=$i

fi

let i++

done

echo $evensum

#! /bin/bash

#

declare -i sum=0

declare -i i=0

while [[ $i -le 100 ]]; do

let sum+=$i

let i+=2

done

echo $sum

6.用until求100以内整数之和；

#! /bin/bash

#

declare -i sum=0

declare -i i=1

until [ $i -gt 100 ]; do

let sum+=$i

let i++

done

echo $sum

7.提供一个用户名，判断用户是否登陆当前系统；

1.如果没有登陆，则停止5秒之后再次判断，直到用户登录系统，显示用户登录，而后退出

#! /bin/bash

#

read -t 5 -p "Enter Your userName: " userName

userName=`echo $userName | tr 'A-Z' 'a-z'`

who | grep "$userName" &> /dev/null

retVal=$?

while [ $retVal -ne 0 ]; do

sleep 5

read -t 5 -p "Enter Your userName: " userName

userName=`echo $userName | tr 'A-Z' 'a-z'`

done

echo "Welcome $userName login System..."

#! /bin/bash

#

read -t 5 -p "Enter Your userName: " userName

while ! id $userName &> /dev/null; do

read -t 5 -p "Enter Your userName: " userName

done

who | grep "^$userName" &> /dev/null

retVal=$?

while [ $retVal -ne 0 ]; do

sleep 5

who | grep "$userName" &> /dev/null

retVal=$?

done

echo "Welcome $userName login System..."

#! /bin/bash

#

read -t 5 -p "Enter Your userName: " userName

while ! id $userName &> /dev/null; do

read -t 5 -p "Enter Your userName again: " userName

done

while ! who | grep "^$userName" &> /dev/null; do

sleep 5

done

echo "Welcome $userName login System..."

#! /bin/bash

#

read -t 5 -p "Enter Your userName: " userName

until [ -n "$userName" ] && id $userName &> /dev/null ; do

read -t 5 -p "Enter Your userName again: " userName

done

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

sleep 5

done

echo "Welcome $userName login System..."

8.取出当前系统上，默认shell为bash的用户；

#! /bin/bash

#

while read line; do

[[ `echo $line | cut -d: -f7` == "/bin/bash" ]] && echo $line | cut -d: -f1

done < /etc/passwd

9.显示其ID号为偶数的用户；

#! /bin/bash

#

while read line; do

userID=`echo $line | cut -d: -f3`

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

echo -n "$userID: "

echo $line | cut -d: -f1

fi

done < /etc/passwd

10.显示/etc/rc.d/rc.sysinit文件中，其总字符个数大于30的行；

#! /bin/bash

#

while read line; do

charCounts=`echo $line | wc -c`

if [ $charCounts -gt 30 ]; then

echo -n "$charCounts: "

echo $line

fi

done < /etc/rc.d/rc.sysinit

11.显示用户其UID和GID均为偶数的用户；

#! /bin/bash

#

while read line; do

userID=`echo $line | cut -d: -f3`

groupID`echo $line | cut -d: -f4`

if [ $[$userID%2] -eq 0 -a $[$groupID%2] -eq 0 ]; then

echo -n "$userID,$groupID: "

echo $line | cut -d: -f1

fi

done < /etc/passwd

12.显示/etc/rc.d/rc.sysinit文件中，其总字符个数大于30且以非#开头的行；

#! /bin/bash

#

while read line; do

charCounts=`echo $line | wc -c`

if [ $charCounts -gt 30 ] && [["$line" =~ ^[^#] ]]; then

echo -n "$charCounts: "

echo $line

fi

done < /etc/rc.d/rc.sysinit

13.写一个脚本，完成如下任务；

1.提示用户输入一个磁盘设备文件路径不存在或不是一个块设备，则提示用户重新输入，知道输入正确为止，或者输入quit以9为退出码结束脚本

2.提示用户"下面的操作会清空磁盘的数据，并提问是否继续"

如果用户给出字符y或yes，则继续，否则，则提供以8为退出码结束脚本

3.将用户指定的磁盘上的分区清空，而后创建两个分区，大小分别为100M和512M

4.格式化这两个分区

5.将第一个分区挂载至/mnt/boot目录，第二个分区挂载至/mnt/sysroot目录

来自为知笔记(Wiz)

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bash while/until循环学习

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