#!/usr/bin/perl
use strict;
use warnings;

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

my %files_alt = read_dir_files($dir_alt);
my %files_neu = read_dir_files($dir_neu);
my %files_all=(%files_alt,%files_neu);

my @new;
for my $file (keys(%files_all))
{
  next if($files_alt{$file} && $files_neu{$file});
  push(@new,$file);
}

print join("\n",@new)."\n";
############################################################

sub read_dir_files
{
  my $dir=shift;
  opendir(my $dh, $dir) or die("Error opendir $dir ($!)\n");
  my @files=grep { -f "$dir/$_" } readdir($dh);
  closedir($dh);
  return map {$_ => 1} @files;  
}