RegEx: My Expression doesn't match nested group

Question

The following Regular Expression (url) pattern doesn't match the named group :

^/(.+?)/(.+)?(_p(?<Page>\d+))?

I don't know why this doesn't work in optional block:

?()?

What's the problem with this pattern and how can i get the correct result?

Answer 1

The 2nd group (.+)? is greedy. Therefore it will match the whole File_p2. Since the 3rd group is optional, it will just be skipped.

You could change the regex to

^/([^/]+)/(.+?)(?:_p(?<Page>\d+))?$

or, slightly more efficiently,

^/([^/]+)/([^_]+(?:_[^_]+)*?)(?:_p(?<Page>\d+))?$