Perl has a module for finding files, called File::Find, and there are also File::Find::Rule, which even has an XML-file-searcher I think, and merlyns File::Finder, which is similar yet different from File::Find.

Your code with File::Find::Rule would look like this:

use strict;
use File::Find::Rule;

sub loopDir {
  File::Find::Rule->file->name(/\.xml$/i)->in(@_);
};
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But maybe you want also to search within the XML files in one go, then File::Find::Rule::Wellformed and File::Find::Rule::XPath might become of interest.