I assume that by "URL request" you actually mean a HTTP request. But they are never XML or HTML, they are just plain text.

So I suspect that you're actually talking about the content type of the HTTP response, rather than the request. In that case you can just look at the content type header. If it's "text/html" then the body is HTML, if it's "text/xml" then the body is XML.

You'd also have to account for other XML Content-types, such as application/xml, application/xhtml+xml, application/rdf+xml, and so on.

Something like this might work:

if ($content_type =~ m!(application|text)/(.*\+)?xml!) {
  # Treat as XML
}
[download]

The easiest way, is to do a HEAD on the URL in question and see what the returned headers tell you. So, something like:

use LWP::Simple qw/head/;

for('http://perlmonks.org/index.pl?displaytype=xml;node_id=484407',
    'http://perlmonks.org/index.pl?node_id=484407') 
{
   my ($type, $length, $modified_time, $expires, $server) = head($_);
   print "File is: $type\n";
}
[download]

The Content-Type will still be text/xml ?

Update: Or at least =~ /xml/ ;)

--
b10m

All code is usually tested, but rarely trusted.