! /usr/bin/perl -w

use strict;

my %h = (
    a => 1,
    b => undef,
    c => 1,
    d => 1,
    e => undef,
);

my @def;

$def[ defined $_ ? 1 : 0]++ for values %h;

print "undefined=$def[0], defined=$def[1]\n";
__END__
produces:
undefined=2, defined=3