If you're on Linux and need a block of randomness of decent quality, you may defer to system's random generator. Tools like shuf use the same under the hood.

#! /usr/bin/perl

use strict;
use warnings;

sub rnd_bytes {
    local $/ = \( shift || 8 );
    open my $fh, '<', '/dev/urandom';
    scalar <$fh>
}

for my $n (unpack "Q*", rnd_bytes(20 * 8)) {
        printf "\r%064b %016X\n",$n,$n;
}
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