?= 在正则表达式中是什么意思? [英] What does ?= mean in a regular expression?

问题描述

我可以知道 ?= 在正则表达式中的含义吗?例如，它在这个表达式中的意义是什么:

May I know what ?= means in a regular expression? For example, what is its significance in this expression:

(?=.*\d).

推荐答案

?= 是一个积极的前瞻，一种 零宽度断言.它的意思是捕获的匹配必须后跟括号内的任何内容，但该部分未被捕获.

?= is a positive lookahead, a type of zero-width assertion. What it's saying is that the captured match must be followed by whatever is within the parentheses but that part isn't captured.

您的示例意味着匹配需要后跟零个或多个字符，然后是一个数字(但同样不会捕获该部分).

Your example means the match needs to be followed by zero or more characters and then a digit (but again that part isn't captured).

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