generate random binary number in perl

I want to generate 64 iteration of non-repetitive 6 digits that only consist of 0 and 1 (eg. 111111, 101111, 000000) by using perl. I found code that can generate random hex and try to modify it but I think my code is all wrong. This is my code:

use strict;
use warnings;

my %a;

foreach (1 .. 64) {
    my $r;
    do {
        $r = int(rand(2));
    }
until (!exists($a{$r}));
printf "%06d\n", $r;
$a{$r}++;
}