适用于循环次数未知的情况，要有退出条件。

while CONDITION; do

statement

...

done

例如：

1.写一个脚本，输入任何字符，小写转换为大写。输入quit退出。

#!/bin/bash

read -p "Input Something" STRING

while [ $STRING != ‘quit‘ ]; do

echo $STRING|tr ‘a-z‘ ‘A-Z ‘

read -p "Input Something" STRING

done

2.写一个脚本，每个5秒检测用户是否登陆，如果登陆则显示已经登陆。

#!/bin/bash

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

LOG=$?

while [ $LOG -ne 0 ];do

echo `date ,hadoop is not log`

sleep 5

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

LOG=$?

done

echo "hadoop is logged in"

3.写一个脚本：

显示一个菜单给用户，当用户给定相应选项后显示形影的内容。

#!/bin/bash

cat << EOF

d|D) show disk usages.

m|M) show memory usages.

s|S) show swap usages.

*) quit.

EOF

read -p "your choice:" CHO

while [ $CHO ！= ‘quit‘ ];do

case  $CHO in

d|D) show disk usages.

echo "disk usages:"

df -h

;;

m|M) show memory usages.

echo "memory usage:"

free- m|grep "Mem"

;;

s|S) show swap usages.

echo "swap usagee:"

free -m| grep "swap"

;;

*) quit.

echo "Unkown"

;;

esac

read -p "your choice again:" CHO

done

本文出自 “小私的blog” 博客，请务必保留此出处http://ggvylf.blog.51cto.com/784661/1606398

while循环