My regex expression is both lazy and greedy. Why?

Question

Suppose I'm searching for anchor links in a web page. A regex that works is:

 "\<a\s+.*?\>"

However, lets add a complication. Lets suppose that I only want links which surround specific text, for instance, the word 'next'. Normally, I would think all I had to do is:

 "\<a\s+.*?\>next"

But I find that now, if there are 3 anchor tags in a page, and the third one has 'next' after it, that the regex search finds a huge string extending from the first anchor tag, and extending to the third anchor tag. This makes sense if the period-asterisk-questionmark is finding all characters until it comes across ">next". But that is not what I want. I want to find all characters until it comes across ">", and then an additional constraint should be that right after the ">" there should be "next".

How do I get this to work?

Sergey Kalinichenko · Accepted Answer · 2016-04-03 11:20:32Z

6

You can fix your regex by prohibiting it from matching > inside the tag, i.e. by replacing . with [^>]:

"\<a\s+[^>]*?\>next"

.*? matches any number of characters. The fact that you made it reluctant does not make it stop at >: it continues matching past it, until it finds >next at the end. This is not greedy, because the expression matched as little as possible to obtain a match. It's just that no shorter matches were available.

Demo.

answered Apr 3, 2016 at 11:20

Sergey Kalinichenko

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