#!/usr/bin/perl -w
use strict;

use constant REQUIRED_FIELDS => qw/zero one two three four five six seven/;

my $a_ref = [qw/three one two/];

my @missing_fields = verify($a_ref);
print "missing fields: @missing_fields\n";

sub verify
{
    my $a_ref = shift;
    
    my %seen = map{$_ => 1}@$a_ref;
    
    return (grep{!$seen{$_}}REQUIRED_FIELDS);
}

__END__ 
Prints:
missing fields: zero four five six seven