Bash循环定义无限while循环

Bash循环定义无限while循环

 (2018-08-17 14:00:26)

转载▼http://blog.sina.com.cn/s/blog_6436b8ec0102xfyb.html

定义一个无限while循环可以使用如下3种命令：
true命令 ：不做任何事，表示成功，总是返回退出状态码0。
fail命令 ：不做任何事，表示成功，总是返回退出状态码1。
：           ：无作用，此命令也不做任何事，但是返回退出状态码0。

使用“:”命令定义一个无限循环实例
[root@aa ~]# cat infinitewhile_colon.sh
#!/bin/bash -

while :
do
    echo "Do something..."
    echo "Hit [ CTRL+C ] to stop!"
    sleep 3
done
[root@aa ~]# ./infinitewhile_colon.sh
Do something...
Hit [ CTRL+C ] to stop!
Do something...
Hit [ CTRL+C ] to stop!
Do something...
Hit [ CTRL+C ] to stop!
^C

使用true命令定义一个无限循环实例
[root@aa ~]# cat infinitewhile_true.sh
#!/bin/bash -

while true
do
    echo "Do something..."
    echo "Hit [ CTRL+C ] to stop!"
    sleep 3
done
[root@aa ~]# ./infinitewhile_true.sh
Do something...
Hit [ CTRL+C ] to stop!
^C

菜单驱动程序实例
[root@aa ~]# cat whilemenu.sh
#!/bin/bash -

while :
do
    clear                   #清理终端屏幕
    echo "================================"
    echo "         MAIN - MENU         "
    echo "================================"
    echo "1. Display date and time."
    echo "2. Display system information."
    echo "3. Display what users are doing."
    echo "4. Exit."

    read -p "Enter your choice [ 1-4 ]: " choice  #从标准输入中读取用户的输入，并赋值给变量choice

    case $choice in
    1)
        echo "Today is $(date +%Y-%m-%d)." #打印当前日期，格式为“YYYY-MM-DD”
        echo "Current time: $(date +%H:%M:%S)" #打印当前时间，格式为“hh:mm:ss”
        read -p "Press [Enter] key to continue..." readEnterKey
        #只读入回车换行符
        ;;
    2)
        uname -a #打印系统信息
        read -p "Press [Enter] key to continue..." readEnterKey
        ;;
    3)
        w
        read -p "Press [Enter] key to continue..." readEnterKey
        ;;
    4)
        echo "Bye!"
        exit 0
        ;;
    *)
        echo "Error: Invalid option!"
        read -p "Press [Enter] key to continue..." readEnterKey
        ;;
    esac
done

[root@aa ~]# ./whilemenu.sh

================================
         MAIN - MENU        
================================
1. Display date and time.
2. Display system information.
3. Display what users are doing.
4. Exit.
Enter your choice [ 1-4 ]: 1
Today is 2018-08-17.
Current time: 14:05:13
Press [Enter] key to continue...