use strict;
use File::Spec::Functions;
use File::Basename;

my $file = 'test.txt';

my ($base,$path,$type) = fileparse($file, qr/\.txt/);

print "base=$base path=$path type=$type\n";

print catfile($path, $base, '.xml');  #  test\.xml


##</code><code>##

print catfile($path, $base . '.xml');