后视正则表达式问题 (Ruby) [英] Issue with a Look-behind Regular expression (Ruby)

问题描述

我编写了这个正则表达式来匹配 HTML 页面中的所有 href 和 src 链接；(我知道我应该使用解析器；这只是实验):

I wrote this regex to match all href and src links in an HTML page; (I know I should be using a parser; this just experimenting):

/((href|src)\=\").*?\"/ # 不看-后面

它工作正常，但是当我尝试将表达式的第一部分修改为后视模式时:

It works fine, but when I try to modify the first portion of the expression as a look-behind pattern:

/(?<=(href|src)\=\").*?\"/ # 带有后视

它抛出一个错误，指出无效的后视模式".任何想法，后视有什么问题?

It throws an error stating 'invalid look-behind pattern'. Any ideas, whats going wrong with the look-behind?

推荐答案

Lookbehind 有 限制:

Lookbehind has restrictions:

   (?<=subexp)        look-behind
   (?<!subexp)        negative look-behind

                      Subexp of look-behind must be fixed character length.
                      But different character length is allowed in top level
                      alternatives only.
                      ex. (?<=a|bc) is OK. (?<=aaa(?:b|cd)) is not allowed.

                      In negative-look-behind, captured group isn't allowed, 
                      but shy group(?:) is allowed.

您不能在(否定的)后视中将替代品放在非顶级中.

You cannot put alternatives in a non-top level within a (negative) lookbehind.

将它们放在顶层.您也不需要转义您所做的某些字符.

Put them at the top level. You also don't need to escape some characters that you did.

/(?<=href="|src=").*?"/

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