Linux shell编程学习笔记20：case ... esac、continue 和break语句

男娘i 2024-02-20 12:20 21阅读 0赞

## 一、case ... esac语句说明 ##

在实际编程中，我们有时会请到多条件多分支选择的情况，用if…else语句来嵌套处理不烦琐，于是JavaScript等语言提供了多选择语句switch ... case。与此类似，Linux Shell脚本编程中提供了case...in...esac 语句，来实现多条件多分支选择结构：其语法结构为：

> case 变量名 in
> 
> 值1\[|值2……\])  
> 命令1  
> \[...\]  
> \[命令N\]  
> ;;
> 
> \[...\]  
> 值a\[|值b……\])  
> 命令a  
> \[...\]  
> \[命令b\]  
> \[break\]  
> ;;
> 
> \[\*)\]
> 
> \[命令x\]
> 
> \[...\]  
> \[命令y\]  
> esac

在每个 case 分支语句中，首先列出该分支对应的值（多个值之间用|分隔）并以半角右圆括号开始，然后列出要执行的语句或命令序列，最后用两个分号 ;; 表示该分支结束。

在把我们想处理的值列出来后，对于其它情况，在C和JavaScript等语言的switch语句中是用default:来表示的，在Matlab等语言的switch语句中是用otherwise来表示，在Linux shell编程中，是用下面的格式来表示的：

> \*)

case语句以 esac 结束，esac就是case的反序，这与if语句以fi结束相类。

其中的\[\]的内容是可选的。

## 二、break语句说明 ##

在很多编程语言中，为了实现在循环过程中，有时候需要在未达到循环结束条件时强制跳出循环而提供了break语句，Linux Shell脚本编程同样提供了break语句。

## 三、实例1（在一重无限循环中） ##

为了演示case ... esac、和break语句的功能和用法，我们将创建一个演示脚本文件：

while : 
     do
     echo -n "Please enter a nummber or letter: "
     read c
     case $c in 
       0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"
       ;;
       a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Contine."
       ;;
      A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Contine." 
       ;;
       *)  echo "You entered another character:$c \nGame over!"
         break;
       ;;
     esac
    done

脚本文件的功能是：

通过while : 语句执行一个无限循环

在循环体中：

首先 用echo -n 命令显示提示信息："Please enter a nummber or letter: "，其中 -n选项的作用是显示信息后不自动换行。

接着用read命令读取一个字符保存到变量c中

然后用case 语句对变量c保存的用户输入字符进行判断：

1.  如果是0-9，就输出：You entered a nammber:，以及具体的字符，然后跳到循环体首部继续执行
2.  如果是a-z，就输出：You entered a lowercase letter: ，具体的字符，及 Continue.，然后跳到循环体首部继续执行
3.  如果是A-Z，就输出：You entered a capital letter: ，具体的字符，及 Continue.然后跳到循环体首部继续执行
4.  如果输入的是不属于以上字符范围的其它字符，就输出：You entered another character:$c "，具体的字符，换行输出 Game over!，然后使用break语句跳出循环

下面我们分别在zsh和bash中测试

### （一）在zsh中 ###

#### 1.创建测试脚本a.sh ####

我们用 echo 和 输出重定向来创建。

> \# csdn @ edu in ~ \[20:01:21\]  
> $ echo 'while : ' > a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' do' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' echo -n "Please enter a nummber or letter: "' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' read c' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' case $c in ' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue." ' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' \*) echo "You entered another character:$c \\\\nGame over!"' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' break;' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo ' esac' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $ echo 'done' >> a.sh
> 
> \# csdn @ edu in ~ \[20:01:52\]  
> $

![aafec9fe3e804803bc70876a21505e58.png][]

#### 2. 用cat命令查看创建的测试脚本a.sh内容 ####

> \# csdn @ edu in ~ \[20:05:43\]  
> $ cat a.sh  
> while :  
> do  
> echo -n "Please enter a nummber or letter: "  
> read c  
> case $c in  
> 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"  
> ;;  
> a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."  
> ;;  
> A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue."  
> ;;  
> \*) echo "You entered another character:$c \\nGame over!"  
> break;  
> ;;  
> esac  
> done
> 
> \# csdn @ edu in ~ \[20:05:47\]  
> $

![708837b0164e4ddb817b7a233bbd0a4f.png][]

#### 3.执行测试脚本a.sh ####

> \# csdn @ edu in ~ \[20:05:47\]  
> $ . ./a.sh  
> Please enter a nummber or letter: 3  
> You entered a nammber:3  
> Please enter a nummber or letter: 9  
> You entered a nammber:9  
> Please enter a nummber or letter: A  
> You entered a capital letter：A. Continue.  
> Please enter a nummber or letter: x  
> You entered a lowercase letter: x. Continue.  
> Please enter a nummber or letter: b  
> You entered a lowercase letter: b. Continue.  
> Please enter a nummber or letter: Z  
> You entered a capital letter：Z. Continue.  
> Please enter a nummber or letter: D  
> You entered a capital letter：D. Continue.  
> Please enter a nummber or letter: \*  
> You entered another character:\*  
> Game over!
> 
> \# csdn @ edu in ~ \[20:07:07\]  
> $

![f3770c0b26bd4b758f44f269f4f14c19.png][]

我们依次输入字符3、9、A、x、b、z、D和\*，当输入的字符是数字或字母时，循环继续，直到我们输入\*，才跳出循环。

### （二）在bash中 ###

#### 1.创建测试脚本a.sh ####

> \# csdn @ edu in ~ \[20:07:07\]  
> $ exec bash  
> \[csdn ~\]$ echo 'while : ' > a.sh  
> \[csdn ~\]$ echo ' do' >> a.sh  
> \[csdn ~\]$ echo ' echo -n "Please enter a nummber or letter: "' >> a.sh  
> \[csdn ~\]$ echo ' read c' >> a.sh  
> \[csdn ~\]$ echo ' case $c in ' >> a.sh  
> \[csdn ~\]$ echo ' 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue." ' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' \*) echo "You entered another character:$c \\\\nGame over!"' >> a.sh  
> \[csdn ~\]$ echo ' break;' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' esac' >> a.sh  
> \[csdn ~\]$ echo 'done' >> a.sh

![b54a763189f94dd5a955cd7c6ed8a12a.png][]

#### 2. 用cat命令查看创建的测试脚本a.sh内容 ####

> \[csdn ~\]$ cat a.sh  
> while :  
> do  
> echo -n "Please enter a nummber or letter: "  
> read c  
> case $c in  
> 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"  
> ;;  
> a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."  
> ;;  
> A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue."  
> ;;  
> \*) echo "You entered another character:$c \\\\nGame over!"  
> break;  
> ;;  
> esac  
> done  
> \[csdn ~\]$

![903ec7b846054657a58354a6cf9fd9d2.png][]

#### 3.执行测试脚本a.sh ####

> \[csdn ~\]$ . a.sh  
> Please enter a nummber or letter: 4  
> You entered a nammber:4  
> Please enter a nummber or letter: A  
> You entered a capital letter：A. Continue.  
> Please enter a nummber or letter: d  
> You entered a lowercase letter: d. Continue.  
> Please enter a nummber or letter: D  
> You entered a capital letter：D. Continue.  
> Please enter a nummber or letter: /  
> You entered another character:/ \\nGame over!  
> \[csdn ~\]$

![88a3e6181a664c6bbc902b0c3e5f0b78.png][]

我们依次输入字符4、A、d、D和/，当输入的字符是数字或字母时，循环继续，直到我们输入/，才跳出循环。

### （三）小结 ###

通过上面的实例，可以看到：

1.zsh和bash对case ... esac和break语句都提供了支持。

2.;zsh和bash对字符串"\\\\n"的处理是不同的。如：

> echo ' \*) echo "You entered another character:$c \\\\nGame over!"' >> a.sh

在zsh中生成的语句是：

> \*) echo "You entered another character:$c \\nGame over!"

在bash中生成的语句是：

> \*) echo "You entered another character:$c \\\\nGame over!"

这也导致zsh和bas在显示该行信息时存在一点差异。

## 四、实例2（在双重无限循环中） ##

为了测试不同的shell中对break语句功能的支持程度是否存在不同。

我们在实例1的外面再加上一个while : 无限循环，看看用break语句能跳出几重循环。

### （一）在zsh中 ###

#### 1.创建测试脚本a.sh ####

> \# csdn @ edu in ~ \[19:00:42\]  
> $ echo 'while : ' > a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo 'do' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo 'while : ' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' do' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' echo -n "Please enter a nummber or letter: "' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' read c' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' case $c in ' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue." ' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' \*) echo "You entered another character:$c \\\\nGame over!"' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' break;' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' ;;' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo ' esac' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]  
> $ echo 'done' >> a.sh
> 
> \# csdn @ edu in ~ \[19:01:08\]

![69cb1b6b81524c7794ed7711b27d98b3.png][]

#### 2. 用cat命令查看创建的测试脚本a.sh内容 ####

> \# csdn @ edu in ~ \[19:02:56\]  
> $ cat a.sh  
> while :  
> do  
> while :  
> do  
> echo -n "Please enter a nummber or letter: "  
> read c  
> case $c in  
> 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"  
> ;;  
> a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."  
> ;;  
> A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue."  
> ;;  
> \*) echo "You entered another character:$c \\nGame over!"  
> break;  
> ;;  
> esac  
> done  
> done
> 
> \# csdn @ edu in ~ \[19:03:56\]  
> $

![53a7cc6994484a5ca4483d59d16b1409.png][]

#### 3.执行测试脚本a.sh ####

> \# csdn @ edu in ~ \[19:04:41\] C:127  
> $ . ./a.sh  
> Please enter a nummber or letter: 3  
> You entered a nammber:3  
> Please enter a nummber or letter: 9  
> You entered a nammber:9  
> Please enter a nummber or letter: d  
> You entered a lowercase letter: d. Continue.  
> Please enter a nummber or letter: X  
> You entered a capital letter：X. Continue.  
> Please enter a nummber or letter: Y  
> You entered a capital letter：Y. Continue.  
> Please enter a nummber or letter: \*  
> You entered another character:\*  
> Game over!  
> Please enter a nummber or letter: ^C%
> 
> \# csdn @ edu in ~ \[19:06:06\] C:126  
> $

![4237ea08b41e4d30a55be745ad2f077e.png][]

### （二）在bash中 ###

#### 1.创建脚本文件a.sh ####

> \[csdn ~\]$ echo 'while : ' > a.sh  
> \[csdn ~\]$ echo 'do' >> a.sh  
> \[csdn ~\]$ echo 'while : ' >> a.sh  
> \[csdn ~\]$ echo ' do' >> a.sh  
> \[csdn ~\]$ echo ' echo -n "Please enter a nummber or letter: "' >> a.sh  
> \[csdn ~\]$ echo ' read c' >> a.sh  
> \[csdn ~\]$ echo ' case $c in ' >> a.sh  
> \[csdn ~\]$ echo ' 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue." ' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' \*) echo "You entered another character:$c \\\\nGame over!"' >> a.sh  
> \[csdn ~\]$ echo ' break;' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' esac' >> a.sh  
> \[csdn ~\]$ echo 'done' >> a.sh  
> \[csdn ~\]$ echo 'done' >> a.sh

![76545c429441479d8cd2d04ef7a5e667.png][]

#### 2.用cat命令查看创建的测试脚本文件a.sh的内容 ####

> \[csdn ~\]$ cat a.sh  
> while :  
> do  
> while :  
> do  
> echo -n "Please enter a nummber or letter: "  
> read c  
> case $c in  
> 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"  
> ;;  
> a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."  
> ;;  
> A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue."  
> ;;  
> \*) echo "You entered another character:$c \\\\nGame over!"  
> break;  
> ;;  
> esac  
> done  
> done  
>   
> \[csdn ~\]$

![5cc95c3df01548c4af8129889c00fc18.png][]

#### 3.执行测试脚本a.sh ####

> \[csdn ~\]$ . a.sh  
> Please enter a nummber or letter: 6  
> You entered a nammber:6  
> Please enter a nummber or letter: a  
> You entered a lowercase letter: a. Continue.  
> Please enter a nummber or letter: B  
> You entered a capital letter：B. Continue.  
> Please enter a nummber or letter: \*  
> You entered another character:\* \\nGame over!  
> Please enter a nummber or letter: -  
> You entered another character:- \\nGame over!  
> Please enter a nummber or letter: ^C  
> \[csdn ~\]$

### （三）小结 ###

从上面的测试结果来看，无论是在zsh中，还是在bash中，break都只能跳出一层循环。

所以在上面的例子中，我们使用^C来终止脚本执行。

## 五、continue语句 ##

linux shell 脚本 编程中的continue语句的作用，跟C、JavaScript等其它编程语言一样，就是跳转，重新开始循环。

## 六、实例三 ##

为了验证continue语句的作用，我对实例1中最后一个case分支的代码：

*)  echo "You entered another character:$c \nGame over!"
         break;
       ;;

改为：

*)  echo "You entered another character:$c"
       continue
       echo "Game over!"
       break;
       ;;

即：

while : 
     do
     echo -n "Please enter a nummber or letter: "
     read c
     case $c in 
       0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"
       ;;
       a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Contine."
       ;;
      A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Contine." 
       ;;
       *)  echo "You entered another character:$c"
       continue
       echo "Game over!"
       break;
       ;;
     esac
    done

这样，当我们输入一个非数字或字母字符时，看看会代码执行结果发生什么样的变化？

### （一）在zsh中 ###

#### 1.创建测试脚本文件a.sh ####

> echo 'while : ' > a.sh  
> echo ' do' >> a.sh  
> echo ' echo -n "Please enter a nummber or letter: "' >> a.sh  
> echo ' read c' >> a.sh  
> echo ' case $c in ' >> a.sh  
> echo ' 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"' >> a.sh  
> echo ' ;;' >> a.sh  
> echo ' a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."' >> a.sh  
> echo ' ;;' >> a.sh  
> echo ' A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue." ' >> a.sh  
> echo ' ;;' >> a.sh  
> echo ' \*) echo "You entered another character:$c"' >> a.sh  
> echo ' continue' >> a.sh  
> echo ' echo "Game over!"' >> a.sh  
> echo ' break;' >> a.sh  
> echo ' ;;' >> a.sh  
> echo ' esac' >> a.sh  
> echo 'done' >> a.sh

![3c5b7e734c4e48f1baa0bb93ec6c28db.png][]

#### 2.查看生成的脚本文件a.sh ####

> \# csdn @ edu in ~ \[21:18:17\] C:126  
> $ cat a.sh  
> while :  
> do  
> echo -n "Please enter a nummber or letter: "  
> read c  
> case $c in  
> 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"  
> ;;  
> a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."  
> ;;  
> A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue."  
> ;;  
> \*) echo "You entered another character:$c"  
> continue  
> echo "Game over!"  
> break;  
> ;;  
> esac  
> done
> 
> \# csdn @ edu in ~ \[21:19:29\]  
> $

![377d0dccffff42d6bc9d4d077b55304e.png][]

#### 3.运行脚本文件a.sh ####

> \# csdn @ edu in ~ \[21:16:42\]  
> $ . ./a.sh  
> Please enter a nummber or letter: b  
> You entered a lowercase letter: b. Continue.  
> Please enter a nummber or letter: 1  
> You entered a nammber:1  
> Please enter a nummber or letter: c  
> You entered a lowercase letter: c. Continue.  
> Please enter a nummber or letter: \*  
> You entered another character:\*  
> Please enter a nummber or letter: ^C%
> 
> \# csdn @ edu in ~ \[21:18:17\] C:126  
> $

![e64491cc3c23428c9bfc191295ff4a4a.png][]

### （二）在bash中 ###

#### 1.创建测试脚本文件a.sh ####

> \# csdn @ edu in ~ \[23:25:46\]  
> $ exec bash\[csdn ~\]$ echo 'while : ' > a.sh  
> \[csdn ~\]$ echo ' do' >> a.sh  
> \[csdn ~\]$ echo ' echo -n "Please enter a nummber or letter: "' >> a.sh  
> \[csdn ~\]$ echo ' read c' >> a.sh  
> \[csdn ~\]$ echo ' case $c in ' >> a.sh  
> \[csdn ~\]$ echo ' 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue." ' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' \*) echo "You entered another character:$c"' >> a.sh  
> \[csdn ~\]$ echo ' continue' >> a.sh  
> \[csdn ~\]$ echo ' echo "Game over!"' >> a.sh  
> \[csdn ~\]$ echo ' break;' >> a.sh  
> \[csdn ~\]$ echo ' ;;' >> a.sh  
> \[csdn ~\]$ echo ' esac' >> a.sh  
> \[csdn ~\]$ echo 'done' >> a.sh

![309ea6dff573491eb8094e1e46fe26bc.png][]

2.用cat命令查看脚本文件的内容

> \[csdn ~\]$ cat a.sh  
> while :  
> do  
> echo -n "Please enter a nummber or letter: "  
> read c  
> case $c in  
> 0|1|2|3|4|5|6|7|8|9) echo "You entered a nammber:$c"  
> ;;  
> a|b|c|d|e|f|g|h|i|j|k|l|m|n|o|p|q|r|s|t|u|v|w|x|y|z) echo "You entered a lowercase letter: $c. Continue."  
> ;;  
> A|B|C|D|E|F|G|H|I|J|K|L|M|N|O|P|Q|R|S|T|U|V|W|X|Y|Z) echo "You entered a capital letter：$c. Continue."  
> ;;  
> \*) echo "You entered another character:$c"  
> continue  
> echo "Game over!"  
> break;  
> ;;  
> esac  
> done  
> \[csdn ~\]$

![1e65b35dda954ae68ddc25101490c05f.png][]

#### 3.执行脚本文件 ####

> \[csdn ~\]$ . a.sh  
> Please enter a nummber or letter: 3  
> You entered a nammber:3  
> Please enter a nummber or letter: a  
> You entered a lowercase letter: a. Continue.  
> Please enter a nummber or letter: C  
> You entered a capital letter：C. Continue.  
> Please enter a nummber or letter: \*  
> bash: echo: command not found  
> Please enter a nummber or letter: ^C  
> \[csdn ~\]$

![01453c4a21f245d8a34d57fa8b2cf314.png][]

#### 3.小结 ####

在上面的实例中，当我们输入字符\*时，程序执行代码：

> \*) echo "You entered another character:$c"

输出信息：

> You entered another character:\*

后，就遇到 了continue语句，重新开始循环。

continue语句后面的代码：

> echo "Game over!"  
> break;

没有执行。

所以我们还是要用Ctrl+C来终止脚本的运行。

[aafec9fe3e804803bc70876a21505e58.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/9a3f9ad8b45e43e4a26b7f4a5facc87e.png
[708837b0164e4ddb817b7a233bbd0a4f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/8ea354e363d54d64a55b0e1ab3b3f8d8.png
[f3770c0b26bd4b758f44f269f4f14c19.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/67b5aa44751d41e1b6d9b15a663be4da.png
[b54a763189f94dd5a955cd7c6ed8a12a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/a6b9db78106b4d70a4643c70e845ec9e.png
[903ec7b846054657a58354a6cf9fd9d2.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/e10d36a804664759a98ed8d94c4fde4f.png
[88a3e6181a664c6bbc902b0c3e5f0b78.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/3879487a54624b0c80b67a5b794ede51.png
[69cb1b6b81524c7794ed7711b27d98b3.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/d368cc21b8074d62b850d878e7e0da5d.png
[53a7cc6994484a5ca4483d59d16b1409.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/aaa1735e5db44010bca452a7243744ba.png
[4237ea08b41e4d30a55be745ad2f077e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/f96a58d86da545e2bc668292a016c4e2.png
[76545c429441479d8cd2d04ef7a5e667.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/942231799d1e432cafbec4b23c453930.png
[5cc95c3df01548c4af8129889c00fc18.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/5ef7a5802d4243c9b1aa426d1175c885.png
[3c5b7e734c4e48f1baa0bb93ec6c28db.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/0cb69216f8a24869a654fb587b5b68c7.png
[377d0dccffff42d6bc9d4d077b55304e.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/d0c98689a58b42e192ee9fc08a2e88c2.png
[e64491cc3c23428c9bfc191295ff4a4a.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/a6d5ccf65b0b4f19967bd2d0cd8ea28b.png
[309ea6dff573491eb8094e1e46fe26bc.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/15b19512bf374873998d58a92a189af1.png
[1e65b35dda954ae68ddc25101490c05f.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/a615bf20f60b4df9baffda7df7bf6f95.png
[01453c4a21f245d8a34d57fa8b2cf314.png]: https://image.dandelioncloud.cn/pgy_files/images/2024/02/20/3b8d48038a8f401b9d0840b457e4179e.png