在 PCRE 中，是否存在“否定交替"或“否定字符串类"，即“否定字符类"之类的东西? [英] Is there a such thing as "negated alternation", or "negated string classes", a la "negated character classes", in PCRE?

问题描述

好的，所以当模式 [abc] 匹配单个字符 a、b 或 c，模式 [^abc] 匹配任何给定的字符，不是 a、b，或者c.

Alright, so while the pattern [abc] matches a single character that is a, b, or c, the pattern [^abc] matches any given character that isn't a, b, or c.

现在，如果我在上面的语句中用 string 替换 character，如果我还将第一个模式更改为替代结构，如 (abc|def|ghi).-- 它将匹配三个字符的连续字符串，等于 abc、def 或 ghi.我该怎么做才能匹配不等于abc、def或ghi的任何三个字符的字符串>?

Now if I substitue string for character in the above statement, it would still apply if I also changed the first pattern to an alternation construct like (abc|def|ghi). -- it would match a consecutive string of three characters equal to abc, def, or ghi. What can I do to match any string of three characters that isn't equal to abc, def, or ghi?

推荐答案

这是正则表达式的常见问题，简短的回答是否"，正则表达式的运行方式并没有提供任何 3- 除...之外的字母字符串.

This is a common question with regexes, and the short answer is "no", the way regular expressions operate doesn't provide a way of saying "any 3-letter string except ...".

然而，一些正则表达式引擎允许所谓的否定前瞻断言".这些有点难以理解 - 这种环视解释似乎涵盖了它很好，如果从技术上讲一点.

However, some regular expression engines allow for what are called "negative look-ahead assertions". These are a little tricky to get your head around - this explanation of lookaround seems to cover it quite well, if a little technically.

前瞻的重要之处在于它是零宽度"——它不会用完"任何字符串.所以在 Javascript 中你可以匹配这样的字符串: 'abc123ghi'.match(/abc(?!def)...ghi/) - (?!def) 表示在 'abc' 之后不能有字母 'def'，但是 ... 需要在那里说那里应该有其他 3 个字符.

The important thing about lookahead is that it is "zero-width" - it doesn't "use up" any of the string. So in Javascript you can match a string like this: 'abc123ghi'.match(/abc(?!def)...ghi/) - the (?!def) says that there mustn't be the letters 'def' after the 'abc', but the ... needs to be there to say that there should be some other 3 characters there instead.

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