From: Robert Klemme <shortcutter@...>
Date: 2009-03-10T18:25:02+09:00
Subject: Re: Regexp problem

2009/3/10 The Higgs bozo <higgs.bozo@gmail.com>:
> 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).

Lookbehind is not needed:

09:35:18 ~$ irb
Ruby version 1.8.7
irb(main):001:0> url = "http://example.com/id=12345"
=> "http://example.com/id=12345"
irb(main):002:0> id = url[/id=(\d+)/, 1]
=> "12345"

Depending on what else should be done with the url a more appropriate
tool might be class URI

irb(main):006:0> require 'uri'
=> true
irb(main):007:0> u2 = URI.parse url
=> #<URI::HTTP:0x7ff186bc URL:http://example.com/id=12345>
irb(main):008:0> u2.path
=> "/id=12345"
irb(main):009:0> u2.path[/id=(\d+)/, 1]
=> "12345"

Kind regards

robert

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