正则表达式字边界和特殊字符 [英] Regular Expression Word Boundary and Special Characters

问题描述

我有一个正则表达式来转义搜索字符串中的所有特殊字符.这很好用，但是我似乎无法让它与单词边界一起使用.例如，用干草堆

I have a regular expression to escape all special characters in a search string. This works great, however I can't seem to get it to work with word boundaries. For example, with the haystack

add +

或

add (+)

和针

+

正则表达式 /\+/gi 匹配+".但是正则表达式 /\b\+/gi 没有.关于如何完成这项工作的任何想法?

the regular expression /\+/gi matches the "+". However the regular expression /\b\+/gi doesn't. Any ideas on how to make this work?

使用

add (plus)

作为干草堆和 /\bplus/gi 作为正则表达式，它匹配得很好.我就是不明白为什么转义字符有问题.

as the haystack and /\bplus/gi as the regex, it matches fine. I just can't figure out why the escaped characters are having problems.

推荐答案

\b 是一个零宽度断言:它不消耗任何字符，它只是断言某个条件在给定位置成立.单词边界断言该位置要么在一个单词字符前面不跟一个，要么在一个单词字符后面不跟一个.(单词字符"是字母、数字或下划线.)在您的字符串中:

\b is a zero-width assertion: it doesn't consume any characters, it just asserts that a certain condition holds at a given position. A word boundary asserts that the position is either preceded by a word character and not followed by one, or followed by a word character and not preceded by one. (A "word character" is a letter, a digit, or an underscore.) In your string:

add +

...开头有一个单词边界，因为 a 前面没有单词字符，第二个 d 后面有一个，因为它后面没有一个单词字符.正则表达式 (/\b\+/) 中的 \b 试图在空格和 + 之间进行匹配，但不匹配工作，因为这两个都不是单词字符.

...there's a word boundary at the beginning because the a is not preceded by a word character, and there's one after the second d because it's not followed by a word character. The \b in your regex (/\b\+/) is trying to match between the space and the +, which doesn't work because neither of those is a word character.

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