From: Tim Greer <tim@...>
Date: 2009-01-28T04:42:48+09:00
Subject: Re: A bug in Ruby regexp lib?

Artc5abras c5a0lajus wrote:

> ruby 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
> 
> x11@www:~$ irb
> irb(main):001:0> s = "www.myspace.com/djmamania
> www.myspace.com/djmantini"
> => "www.myspace.com/djmamania www.myspace.com/djmantini"
> irb(main):002:0> s1 = s.gsub(%r{(\s|^)(www\..*?)(\s|$)}m, '\1<a
> href="http://\2">\2</a>\3')
> => "<a
>
href=\"http://www.myspace.com/djmamania\">www.myspace.com/djmamania</a>
> www.myspace.com/djmantini"
> irb(main):003:0> s1.gsub(%r{(\s|^)(www\..*?)(\s|$)}m, '\1<a
> href="http://\2">\2</a>\3')
> => "<a
>
href=\"http://www.myspace.com/djmamania\">www.myspace.com/djmamania</a>
> <a
>
href=\"http://www.myspace.com/djmantini\">www.myspace.com/djmantini</a>"
> 
> Why I have to call gsub two times for this to work? Same regexp works
> fine in Firefox JS :)

Did you mean:

s1 = s.gsub(%r{(^|\s)?(www\..*?)(\s|$)}m, '\1<a
href="http://\2">\2</a>\3')

irb(main):035:0> s1 = s.gsub(%r{(^|\s)?(www\..*?)(\s|$)}m, '\1<a
href="http://\2">\2</a>\3')
=> "<a
href=\"http://www.myspace.com/djmamania\">www.myspace.com/djmamania</a>
<a
href=\"http://www.myspace.com/djmantini\">www.myspace.com/djmantini</a>"

Note the \1 is using (^|\s), as it's either the start of the string (^)
or a white space between the two URLs (\s), but you also have \3, which
is either the end of the string ($) or white space between the URLs (or
following) (\s), and since there's only one white space between the two
URLs, it throws is off.

To account for both \1 and \3, above I've set it to be optional (^|\s)?
because this will allow you to use \3 without is breaking it.  There
are other ways to do this, but just working with what you were using,
that's a change you could make to get the desired results on the first
one... unless I misunderstood what you were trying to do?
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