sub list_files{
   my ($begin,$datei,$return) = @_;

   opendir(R_DIR,$begin) or die $begin,": ",$!," \n";
   my @content = readdir(R_DIR);
   closedir R_DIR;

   foreach my $con(@content){
      next if($con =~ /^\.\.?$/);
      my $path = $begin."/".$con;

      @files=split(/\//,$path);
      my $Anzahl = @files;

      if((-f $path) && (@files[($Anzahl-1)] eq $datei)){
         $return = $path;
      }
      elsif(-d $path){
         $return = list_files($path,$datei,$return); # hier ist die rekursion
      }
   }
   return $return;
}