Select in statement in Shell

select in usage

The select in loop is used to enhance the interactivity. It can display numbered menus. The user can select different menus and perform different functions by entering different numbers.
Select in is a unique loop of the shell, which is very suitable for interactive scenarios such as Terminal. This is not available in other languages.

usage:

select variable in value_list		#variable表示变量，value_list表示取值列表
do
	statements
done

1.#?用来提示用户输入菜单编号；^D表示按下Ctrl+D组合键，它的作用是结束select in循环
2.每次循环时，selevt都会要求用户输入菜单编号，并使用环境变量PS3的值作为提示符，PS3的默认值为#?，修改PS3的值就可以修改提示符
3.如果用户输入的菜单编号不在范围之内，那么就会给variable赋一个空值；如果用户输入一个空值，会重新显示一遍菜单

Example 1.

vim test.sh
#!/bin/bash
#test the usage of 'select in'.
echo "What is your favourite OS? "
select name in "Linux" "Windows" "Mac OS" "Unix" "Android"     '//“ ”可以省略'
do
        echo $name
done             ##此处不会自动跳出select in 循环，需要按ctrl+D跳出select in
echo "You have selected $name"

run:

[root@server1 ~]# chmod u+x test.sh 
[root@server1 ~]# ./test.sh
What is your favourite OS? 
1) Linux
2) Windows
3) Mac OS
4) Unix
5) Android
#? 1
Linux
#?          '//按ctrl+D'
You have selected Linux

=======================================================

[root@server1 ~]# ./test.sh
What is your favourite OS? 
1) Linux
2) Windows
3) Mac OS
4) Unix
5) Android
#? 5
Android
#? 3
Mac OS
#? 2
Windows
#?      '//按ctrl+D'
You have selected Windows

select in is usually used with case in

Example 2:

#!/bin/bash
#"select in" is usually used with "case in" 
echo "What is your favourite OS? "
select name in "Linux" "Windows" "Mac OS" "Unix" "Android"
do
    case $name in
        "Linux")
          echo "Linux是一个类Unix操作系统，它开源免费"
          break
          ;;
        "Windows")
          echo "Mac OS是微软开发的个人电脑操作系统，它是闭源收费的"
          break
          ;;
        "Mac OS")
          echo "Mac OS是苹果公司开发的一款图形界面操作系统"
          break
          ;;
        "Unix")
          echo "Unix是操作系统的开山鼻祖，现在只应用在一些特殊场合"
          break
          ;;
        "Android")
          echo "Android是由Google开发的手机操作系统"
          break
          ;;
        *)
          echo "没有这个选项！"
          break
    esac
done

run:

[root@server1 ~]# ./test2.sh
What is your favourite OS? 
1) Linux
2) Windows
3) Mac OS
4) Unix
5) Android
#? 1
Linux是一个类Unix操作系统，它开源免费

[root@server1 ~]# ./test2.sh
What is your favourite OS? 
1) Linux
2) Windows
3) Mac OS
4) Unix
5) Android
#? 2
Mac OS是微软开发的个人电脑操作系统，它是闭源收费的

[root@server1 ~]# ./test2.sh 
What is your favourite OS? 
1) Linux
2) Windows
3) Mac OS
4) Unix
5) Android
#? 5
Android是由Google开发的手机操作系统

Shell select in usage

Select in statement in Shell

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