open (IN, "<daten.xml");
@file_lines = <IN>;
close IN;


open (OUT, ">daten2.xml") || die "cannot open file";
while (@file_lines)
{
$file_line=~s/ü/&uuml\;/g;
$file_line=~s/ö/&ouml\;/g;
$file_line=~s/ä/&auml\;/g;
print OUT  "$file_line";
}
close (OUT);