You need to tell the browser what sort of content it should be displaying.

To display as plaintext:

print header('text/plain');
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To use whatever method the browser defaults to for xml:

print header('text/xml');
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Personally I find the CGI header options limiting and tend to print them manually, e.g.:

print "Content-type: text/xml\n";
print "Content-Disposition: inline; filename=directory.xml\n\n";
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Note that the initial output is treated as headers that define what is to come, which is terminated by two '\n'.

The reason for including the Content-Disposition header in this case is to provide an extra hint to browsers that care about file extensions, like IE.