From: "Ara.T.Howard" <Ara.T.Howard@...>
Date: 2005-09-14T03:47:23+09:00
Subject: Re: Surprising Regexp Behavior

On Wed, 14 Sep 2005, James Edward Gray II wrote:

> I keep running into some surprising points with Ruby's Regexp engine today 
> and this first one just looks plain wrong to me:
>
> irb(main):001:0> html = "<p>one</p>\n\n<p>two</p>"
> => "<p>one</p>\n\n<p>two</p>"
> irb(main):002:0> html.sub!(/<p>(.*?)<\/p>(.*)/) { $1.strip }
> => "one\n\n<p>two</p>"
> irb(main):003:0> $2
> => ""
>
> Can anyone explain to me how that isn't a bug?

   irb(main):001:0> html = "<p>one</p>\n\n<p>two</p>"
   => "<p>one</p>\n\n<p>two</p>"

   irb(main):002:0> html[ %r| <p> .*? |x ]
   => "<p>"

   irb(main):003:0> html[ %r| <p> .*? </p> |x ]
   => "<p>one</p>"

   irb(main):004:0> html[ %r| <p> .*? </p> .* |x ]
   => "<p>one</p>"

hmm?

but if we use 'm' to make '.' match newline:

   irb(main):005:0> html[ %r| <p> .*? </p> .* |xm ]
   => "<p>one</p>\n\n<p>two</p>"

alternatively we can name newline explicitly:

   irb(main):006:0> html[ %r| <p> .*? </p> [.\n]* |x ]
   => "<p>one</p>\n\n"

probably 'm' is better for html though.

   irb(main):007:0> html =~ %r| <p> (.*?) </p> (.*) |xm and p [$1, $2]
   ["one", "\n\n<p>two</p>"]

cheers.

-a
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