#!/usr/bin/perl

use strict;
use warnings;
use Data::Dumper;

my %hash;
my $file = '/path/to/file';

{
    local $/ = "\n\n---"; # mehr zu $/ siehe perldoc perlvar
    open my $fh, '<',$file or die $!;
    while(my $entry = <$fh>){
        chomp $entry;
        my ($kd,@daten) = split /\n/,$entry;
        $kd =~ s/^\s*Kundennummer:\s*//;
        $hash{$kd} = \@daten;
    }
    close $fh;
}

print Dumper(\%hash);