# open my $pipe, '|-', 'pv -perlt | external-command' or die $!;
my $pipe = *STDOUT{IO};

# https://stackoverflow.com/questions/63172427/why-does-perl-qx-hang-in-mojoliciouslite-but-not-in-an-ordinary-program/63178400#63178400
my $qfn = '/dev/urandom';
open my $fh, '<:raw', $qfn or die "$qfn: $!";

while (1) {
    my ($num, $buf) = (32, '');
    while ($num) {
        my $rv = sysread($fh, $buf, $num, length $buf) // die "$qfn: $!";
        die "$qfn: Premature EOF\n" unless $rv;
        $num -= $rv;
    }

    # For each chunk of random data, derive 1023 extra chunks. This reduces
    # entropy consumption and increases throughput.
    #
    # Negate bits
    for my $bytes ($buf, ~$buf) {
        # Reverse bits
        for my $bits ($bytes, pack('b*', unpack 'B*', $bytes)) {
            # Reverse nibbles
            for my $hex (unpack("H*", $bits), unpack("h*", $bits)) {
                # Reverse hex string
                for my $str ($hex, scalar reverse $hex) {
                    say {$pipe} $str;
                    # Rotate hex string
                    say {$pipe} substr($str, $_), substr($str, 0, $_)
                        for 1 .. 63;
                }
            }
        }
    }
}

close $pipe;