[Webdev] Negative lookahead assertions in Perl regex

[Dave O Connor]

Someone called Dermot McGahon said on Wed, Aug 23, 2000 at 08:33:47PM +0100:
> Anyway, I now need to modify the commment stripping regex so that it
> only strips comments when they are not contained with <SCRIPT> and
> </SCRIPT>. I thought that negative lookahead assertion might be the
> way to go so I tried:
>  
>   $document =~ s{(<!--.*?-->)(?!\s*</script>)}{}gim;
>  
> and
>  
>   $document =~ s{<!--.*?-->\s*(?!</script>)}{}gim;
>  

Lookaheads, be they positive or negative, are immediate, so you need to allow
for any stuff between the opening <!-- and the <script> tags.


Just off the top of my head, the way I'd try and do this would be:

$document =~ s/<\!\-\-(?!.*?<\/script>).*?\-\->//isg;

If i didn't include the .*? inside the negative lookahead, it's try to match
the </SCRIPT> tag immedietely after the opening comment.

	- DoC