From: Phrogz <gavin@...>
Date: 2007-04-10T22:50:10+09:00
Subject: Re: regexp -how to match this?

On Apr 10, 7:00 am, Nanyang Zhan <s...@hotmail.com> wrote:
> so ?= makes pattern lookAHEAD. How to make pattern lookBEHIND?

http://phrogz.net/ProgrammingRuby/language.html#extensions

Zero-width positive and negative lookaheads are supported in Ruby's
regexp engine in 1.8. Zero-width lookbehind assertions are not
supported by the current regexp engine. (However, they are supported
by Oniguruma, the regexp engine used in 1.9 and future builds of
Ruby.)

> example sentence:
> This forum is connected to a mailing list that is read by <span
> class="wow">thousands</span> of people.
>
> question:
> how to make a Regexp to match the words followed by the </span> tag?

Just because you consume them doesn't mean you have to use them. Use
parentheses to saved parts of text extracted by your regular
expression.

irb(main):001:0> str = 'is read by <span class="wow">thousands</span>
of people.'
=> "is read by <span class=\"wow\">thousands</span> of people."

irb(main):002:0> str[ /<\/span>(.+)/, 1 ]
=> " of people."

irb(main):003:0> %r{</span>(.+)}.match( str ).to_a
=> ["</span> of people.", " of people."]