From: Florian Gilcher <flo@...>
Date: 2008-03-01T04:33:52+09:00
Subject: Re: Need a regex searching html code


On Feb 29, 2008, at 8:19 PM, Jari Williamsson wrote:

> Mark Thomas wrote:
>> All the regex solutions provided will break with the following
>> perfectly valid HTML:
>> <div class="info">
>> <h5 >Tagline:</h5>
>> Yippee Ki Yay Mo - John 6:27
>> </div>
>> This is one of many reasons it is a BAD idea to use regexes to parse
>> HTML. Regular expressions are simply not the right tool for the job.
>
> Sorry if I'm missing the point:
> ---
> the_text = %q{
> <div class="info">
> <h5 >Tagline:</h5>
> Yippee Ki Yay Mo - John 6:27
> </div>
> }
>
> the_text.each_line do |line|
>   puts "Within DIV tags: #{line}" if (line=~/<div/)..(line=~/<\/div/)
>   puts "Within H5 tags: #{line}" if (line=~/<h5/)..(line=~/<\/h5/)
> end
> ---
>
> Result:
> Within DIV tags: <div class="info">
> Within DIV tags: <h5 >Tagline:</h5>
> Within H5 tags: <h5 >Tagline:</h5>
> Within DIV tags: Yippee Ki Yay Mo - John 6:27
> Within DIV tags: </div>
>
>
>
> Best regards,
>
> Jari Williamsson
>

This may work on this short snippet. Consider this:

the_text = %q{
<div class="info">
   <div class="nextinfo">
   <h5 >Tagline:</h5>
   Yippee Ki Yay Mo - John 6:27
   </div>
</div>
}

the_text.each_line do |line|
   puts "Within DIV tags: #{line}" if (line=~/<div/)..(line=~/<\/div/)
   puts "Within H5 tags: #{line}" if (line=~/<h5/)..(line=~/<\/h5/)
end

It doesn't see the second </div> as it considers _both_ divs closed.  
(which isn't even possible to determine, as we did not save any  
state). Second question: which <div> am I in at a certain point? Or,  
in other words: whats the #innerText of .info, whats the #innerText  
of .nextinfo? You won't get far without a stack and that can be proven  
[1].
If this is of interest to you, consider reading a book about computer  
theory. It may be hard stuff, but it pays off :).[2]

Greetings
Florian Gilcher

[1] Up to the reader ;).
[2] Don't feel bad if you didn't and don't consider this as an  
offense. I know many good programmers that never read any theory. But  
it certainly isn't bad to know about it.