Snobol4 语言 模式匹配否定字符集案例 只允许字母数字

阿木博主一句话概括：深入Snobol4语言：模式匹配否定字符集在字母数字主题中的应用

阿木博主为你简单介绍：
Snobol4是一种古老的编程语言，以其强大的字符串处理能力而闻名。在Snobol4中，模式匹配是一种核心特性，允许程序员定义复杂的字符串模式。本文将探讨如何在Snobol4中使用模式匹配的否定字符集功能，以实现只允许字母数字字符的主题。

关键词：Snobol4，模式匹配，否定字符集，字母数字，字符串处理

一、
Snobol4（String-oriented Programming and Symbolic Operations on Binary and List）是一种高级编程语言，最初于1962年由David J. Farber和Ralph E. Griswold设计。它以其强大的字符串处理能力而著称，特别是在模式匹配方面。在Snobol4中，否定字符集是一种强大的工具，可以用来排除特定的字符或字符集，从而实现复杂的字符串匹配。

二、Snobol4中的模式匹配
在Snobol4中，模式匹配是通过使用模式表达式来完成的。模式表达式可以包含多种元素，包括普通字符、特殊字符、字符集和否定字符集等。

三、否定字符集的概念
否定字符集是一种特殊的字符集，它包含所有不在其内部的字符。在Snobol4中，否定字符集通常由一个感叹号（!）后跟一个方括号开始，然后列出要排除的字符。

四、案例：只允许字母数字
以下是一个使用Snobol4模式匹配否定字符集的案例，该案例旨在确保字符串只包含字母数字字符。

```snobol
:input line
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