sub get_xml_value{
        my ($document,$value) = @_;
        my $returnvalue = "";
        for($document->findnodes("//test/$value/text()")){$returnvalue = $_->toString();}
        return $returnvalue;
}
...
$xml = "<?xml version="1.0" encoding="utf-8"?>
<test>
   <val1>Zeile1\nZeile2\n</val1>
</test>
";
...
my $document = XML::LibXML->new->parse_string($xml);
my $output = get_xml_value($document,"val1");
print $output;