# Regexp Question - Merb::Router **URL:** \ **Category:** Ruby\ **Created:** [July 13, 2007, 9:38am UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302 "2007-07-13T09:38:25Z")\ **Posts on this page:** 7\ **Page:** 1
**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [July 13, 2007, 9:38am UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302/1 "2007-07-13T09:38:25Z")
Hi, I’m looking through the Merb::Routing code and I’ve found a regexp that I can’t figure out how it works. Merb::Router::SECTION\_REGEXP #=\> /(?::([a-z\*\_]+))/ It takes a route definition string, like “/products/:model/:id” and extracts the “model” string on the first pass, and later the “id” string. Can anyone shed some light on what the ?:: part does? I haven’t found it in any of the documentation for Ruby Regexps that I’ve found. Cheers Daniel ---
**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [July 13, 2007, 9:51am UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302/2 "2007-07-13T09:51:27Z")
2007/7/13, Daniel N [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Can anyone shed some light on what the > ?:: > part does? I haven’t found it in any of the documentation for Ruby Regexps > that I’ve found. It’s actually _two_ parts: (?🙂 is a non capturing regexp group. The second “:” literally matches a single colon. Kind regards robert ---
**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [July 13, 2007, 10:13am UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302/3 "2007-07-13T10:13:29Z")
On 7/13/07, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > It takes a route definition string, like “/products/:model/:id” and > > second “:” literally matches a single colon. > > Kind regards > > robert > > Thanx Robert, I’ve not heard of that before. Makes searching on google much easier 🙂 /(?::([a-z\*\_]+))/ I guess this means that a nested group within this non capturing group (this case) is captured though since the $1 variable is refered to later. Cheers Daniel ---
**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [July 13, 2007, 10:23am UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302/4 "2007-07-13T10:23:31Z")
2007/7/13, Daniel N [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > > > > > > > It’s actually _two_ parts: (?🙂 is a non capturing regexp group. The > > /(?::([a-z\*\_]+))/ > > I guess this means that a nested group within this non capturing group (this > case) is captured though since the $1 variable is refered to later. Exactly. Btw, in your case I’d probably use another regexp. Some samples: irb(main):001:0\> “/products/:model/:id”.scan %r{/:([^/]+)} =\> [[“model”], [“id”]] irb(main):002:0\> “/products/:model/:id”.scan %r{:([^/]+)} =\> [[“model”], [“id”]] irb(main):004:0\> “/products/:model/:id”.scan %r{:[^/:]+} =\> [“:model”, “:id”] But of course I do not know the full spec of your input data. Kind regards robert ---
**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [July 13, 2007, 4:28pm UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302/5 "2007-07-13T16:28:45Z")
On Jul 13, 2007, at 3:12 AM, Daniel N wrote: > /(?::([a-z\*\_]+))/ > > I guess this means that a nested group within this non capturing > group (this > case) is captured though since the $1 variable is refered to later. Yes. The part without the colon is capture, because of the normal parenthesis. Unless this expression is later embedded in another expression, the non-capturing group does nothing here and could safely be removed. James Edward G. II ---
**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [July 13, 2007, 4:47pm UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302/6 "2007-07-13T16:47:48Z")
2007/7/13, James Edward G. II [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid): > Unless this expression is later embedded in another expression, the > non-capturing group does nothing here and could safely be removed. Even in that case the grouping can be removed: irb(main):002:0\> /foo/.to\_s =\> “(?-mix:foo)” irb(main):003:0\> /(?:foo)/.to\_s =\> “(?-mix:foo)” Kind regards robert ---
**Author:** ![liquid](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/l/47e85d/32.png) [@liquid](https://www.ruby-forum.com/u/liquid)\ **Post date:** [July 13, 2007, 10:34am UTC](https://www.ruby-forum.com/t/regexp-question-merb-router/109302/7 "2007-07-13T10:34:38Z")
On 7/13/07, Robert K. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > > can’t figure out how it works. > > > > Regexps > > irb(main):001:0\> “/products/:model/:id”.scan %r{/:([^/]+)} > robert I’m just trying to understand that regexp’s place in the Merb routing code at the moment. You’ve cleared it up nicely for me. Thankyou Daniel