#!/usr/bin/perl

use strict;
use warnings;

my $file1 = '/pfad/datei1.txt';
my $file2 = '/pfad/dat2.txt';
my $file3 = '/pfad/dat3.txt';

my %hash;

for my $file( $file1, $file2 ){
    open my $in, '<', $file or die $!;
    while( my $line = <$in> ){
        chomp $line;
        my ($count,$url) = split /\s*:\s*/, $line;
        $hash{$url} += $count;
    }
    close $in;
}

open my $out, '>', $file3 or die $!;
for my $key ( keys %hash ){
    print $out $hash{$key},": ", $key, "\n" or die $!;
}
close $out or die $!;