#!/usr/bin/perl

use strict;
use warnings;

my $file = 'logdatei.txt';
my %hash;

{
    # wenn die Datensaetze durch leerzeile getrennt sind
    local $/ = "\n\n";
    open my $fh, '<', $file or die $!;
    while( my $entry = <$fh> ){
        my ($date) = $entry =~ /(\d{4}-\d\d-\d\d)/;
        next unless $date;
        $hash{$date}++;
    }
    close $fh;
}

for my $key ( keys %hash ){
    print "$key: ",$hash{$key},"\n";
}