#! /usr/bin/perl

use strict;
use warnings;


my $dir_alt = 'C:\Users\alt';
my $dir_neu = 'C:\Users\neu';

opendir my $dh_alt, $dir_alt or die $!;
opendir my $dh_neu, $dir_neu or die $!;

my @files_alt = grep { -f "$dir_alt/$_" } readdir $dh_alt;  
closedir $dh_alt;
my @files_neu = grep { -f "$dir_neu/$_" } readdir $dh_neu;  
closedir $dh_neu;


my @alle=( @files_alt,@files_neu);
@alle = sort(@alle);
my $laenge = @alle;
my $n = 0;
my @new = ();

while($n <$laenge)
{
        print "bin bei ",$alle[$n]," ","\n";
        push @new,$alle[$n];
        if (not exists $alle[$n+1]){
            last;
        }
        if( $alle[$n] eq $alle[$n+1]){
            pop @new;
        }
        $n+=1;  
}