in reply to
Going through a big file [solved]
I'd recommend following the advice pointed to by Anonymous Monk's question, and investigating a CPAN module to assist you with the XML processing. For example, I know XML::Twig can handle huge XML files, and I'm certain there are others available, too.
I love regular expressions, and they've helped me solve all sorts of nightmare formats, but XML is already a structured data source, using a tool that lets you take advantage of that structure will usually make things easier on you and more robust.