By default Perl uses an I/O translation layer to convert between whatever character it uses internally for \n and the native line ending sequence on the host OS so that generally Perl just does the right thing for native text files.

Not directly related to your immediate question: using regexen for hand parsing XML is thought a bad thing because it is really hard to get right in in the general case. You may do much better to investigate modules like XML::Twig to do the heavy lifting of parsing the XML.