use XML::LibXML;
  # load
  open my $fh, '<', 'file.xml';
  binmode $fh; # drop all PerlIO layers possibly created by a use open pragma
  $doc = XML::LibXML->load_xml(IO => $fh);

  # save
  open my $out, '>', 'out.xml';
  binmode $out; # as above
  $doc->toFH($out);
  # or
  print {$out} $doc->toString();