From: The Higgs bozo <higgs.bozo@...>
Date: 2009-03-10T16:41:41+09:00
Subject: Re: Regexp problem

Albert Schlef wrote:
> I want to extract an "id" parameter from the URL. I use the following
> code:
> 
>   url = "http://example.com/id=12345"
>   id = url[ /(?<=id=)(\d+)/ ]
>   puts id
> 
> But I get a SyntaxError telling me "undefined (?...) sequence".
> 
> Why?

Because ruby 1.8 does not have look-behind.  1.9 has it, and your code 
runs on 1.9.

If you need 1.8 with look-behind, I guess you can compile 1.8 with the 
Oniguruma regexp engine (which is used in 1.9).
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