#!/usr/bin/perl
use strict;
use warnings;
use XML::LibXML;


 my $filename = "base.xml";
 
  my $parser = XML::LibXML->new();
  my $doc    = $parser->parse_file($filename);

  my $query  = "/base/text()";

  my ($node)  = $doc->findnodes($query); # man beachte die Klammern!
  $node->setData('bla');

  print $doc->toString;