正则表达式基本上就是为进行文本处理而构建的一种小型的子语言，用来进行字符串的匹配和替换。

Regular expressions are basically a small sub-language built for text processing, used to match and replace strings of characters.

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即使在这样一小段脚本中，您也可以找到一些参数扩展，包括长度、子字符串、模式匹配和模式替换。

You'll recognize several parameter expansions, including length, substring, pattern matching, and pattern replacement in even this short piece of script.

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替换字符串可能包含对在之前的匹配中捕获的子序列的引用。

The replacement string may contain references to subsequences captured during the previous match.

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