Matching valid alternative in SKIP-FAIL regex

Question

I have a working regex:

~<([A-Za-z_\-]+)[^>]*>(*SKIP)(*F)|([A-Za-z0-9<>:\[\]\s]|^|\n)text([A-Za-z0-9<>:\[\]\s]|$|\n)~sig

Now, I want to match wanna_match_this in <blockquote>wanna_match_this</blockquote> and I am trying to fix this:

<([A-Za-z_\-]+)[^>]*>(*SKIP)(*F)|([A-Za-z0-9<>:\[\]\s]|^|\n)wanna_match_this([A-Za-z0-9<>:\[\]\s]|$|\n)

It should match wanna_match_this in <blockquote>wanna_match_this</blockquote>, but it does not.

This one matches but I need the other one that is more precise.

I have a problem, not a question. The only question is if anyone can help me fixing it? — Wellenbrecher, Aug 02 '15 at 16:30
What is the problem? Describe the problem rather that providing regex101 links — anubhava, Aug 02 '15 at 16:33
I've written "wanna_match_this" in regex101 links. Isn't the problem clear enough? — Wellenbrecher, Aug 02 '15 at 16:37
No it's not. Please include all the relevant information in your question on this site, not in external links. — yole, Aug 02 '15 at 16:42

Wiktor Stribiżew · Answer 1 · 2019-07-30T09:11:15.893

The problem is due to the fact the first alternative (with SKIP-FAIL) consumes any <TAG> and proceeds searching for a match right after the end of the unsuccessfully matched text. The wanna_match_this text starts right after that text and [A-Za-z0-9<>:\[\]\s] consumes the w char preventing this match from occurring.

So, you need a zero-width asertion, a positive lookbehind here, best coupled with a positive lookahead:

<([A-Za-z_-]+)[^>]*>(*SKIP)(*F)|(?<=[A-Za-z0-9<>:\[\]\s]|^)wanna_match_this(?=[A-Za-z0-9<>:\[\]\s]|$)

See demo

Notice I removed \n as it is already covered with \s.

Matching valid alternative in SKIP-FAIL regex

1 Answers1