From: Edwin Fine <efine145-nospam01@...>
Date: 2006-12-08T14:17:37+09:00
Subject: Re: Need help with a regexp

rpheath wrote:
> Thanks for the reply.  I'm relatively new to regular expressions, and
> misinterpretted the ^s and $s.  I was thinking they were for that
> specific check, so it was either the first string "|" (or) the second
> string.
> 
> Here's sample text that would be passed into it.
> -----------------------
> <p>This is the first sentence.  Now I'll post a code snippet:</p>
> 
> <pre>
> def strip_blocks(text)
>   text.gsub([regex],'')
> end
> </pre>
> 
> <p>This is another sentence before the block quote.</p>
> 
> <blockquote>
>   <p>This is a quote</p>
> </blockquote>
> 
> <p>This is one more sentence</p>
> ----------------------
> 
> What I would like to have left is this:
> 
> ----------------------
> <p>This is the first sentence.  Now I'll post a code snippet:</p>
> 
> <p>This is another sentence before the block quote.</p>
> 
> <p>This is one more sentence</p>
> ----------------------
> 
> Hopefully that helps.  Sorry the question is not organized and kind of
> basic, but I'm new to this.  Thanks again for any help.

Try this. It uses the "non-greedy" operator '?' and multiline 
case-insensitive matching. Not using the 'non-greedy' operator would 
gobble up everything between  two tags, including nested tags of the 
same name. This is probably not what you would want.


def remove_tag_block(tag, text)
  text.gsub(/<#{tag}>.*?<\/#{tag}>/im, '')
end

irb(main):054:0> text
=> "<p>This is the first sentence.  Now I'll post a code 
snippet:</p>\n\n<pre>\ndef strip_blocks(text)\n 
text.gsub([regex],'')\nend\n</pre>\n\n<p>This is another sentence before 
the block quote.</p>\n\n<blockquote>\n  <p>This is a 
quote</p>\n</blockquote>\n\n<p>This is one more sentence</p>"

irb(main):055:0> t=remove_tag_block("pre", text)

=> "<p>This is the first sentence.  Now I'll post a code 
snippet:</p>\n\n\n\n<p>This is another sentence before the block 
quote.</p>\n\n<blockquote>\n  <p>This is a 
quote</p>\n</blockquote>\n\n<p>This is one more sentence</p>"

irb(main):056:0> remove_tag_block("blockquote", t)

=> "<p>This is the first sentence.  Now I'll post a code 
snippet:</p>\n\n\n\n<p>This is another sentence before the block 
quote.</p>\n\n\n\n<p>This is one more sentence</p>"

The problem is that this won't work with nested tags, e.g.

<table><tr><td><table>stuff</table></td></tr></table>

irb(main):065:0> 
x="<table><tr><td><table>stuff</table></td></tr></table>"
=> "<table><tr><td><table>stuff</table></td></tr></table>"
irb(main):066:0> remove_tag_block("table", x)
=> "</td></tr></table>"

This is because *regular* regular expressions :) can't match nested 
pairs, such as "((()(())()))". I think I read somewhere a phrase that 
regexp's can't count. You have to use *recursive* regular expressions, 
which are found in PCRE (Perl RE), but AFAIK not in the current Ruby 
regexp engine. Maybe Oniguruma has it - I dunno. I saw a PCRE extension 
for Ruby somewhere, but I don't know anything about it.

The Perl RE for matching nested parentheses is apparently as follows 
(from 
http://www.sitepoint.com/blogs/2006/09/26/the-joy-of-regular-expressions-1/)

\(((?>[^()]+)|(?R))*\)

I believe that to do this correctly without PCRE, you have to resort to 
some text parsing or use a SAX parser or similar. Maybe some Ruby guru 
(i.e. not me) will be able to pull out an RE or some easy way to do 
this.

-- 
Posted via http://www.ruby-forum.com/.