#!/usr/bin/perl
use v5.12; 
use warnings;

my $string = "Hello World";
my (%buchstaben, %paare);
 
for my $word (split( / /, uc $string)){
    my @paare = $word  =~ /(..)/g;
    push @paare, substr($word,1)  =~ /(..)/g;
    $buchstaben{$_}++ for split '', $word;
    $paare{$_}++ for @paare;
}
# Ausgabe