#! perl
use strict;
use warnings;

my @fields = (42, undef, 'abc', undef, 'foo', 'bar');
my $flags  = 0;
my $mask   = 0b1000_0000;

for my $field (@fields)
{
    $flags |= $mask if defined $field;
    $mask >>= 1;
}

printf "%08b\n", $flags;