#!/usr/bin/perl
use strict;
use warnings;
use CGI;

my $q = CGI->new();
our $cookie = '';

if ( defined $q->cookie('cookiename') ) {
    $cookie = $q->cookie('cookiename')
    # validate cookie here based on whatever
}
elsif ($q->param('some_field_name') {
    # form submitted

    $cookie = 'whatever';
}
else {
    # show the html form
}

##</code><code>##

# at beginning of script
use CGI;
our @cookie_jar = ();
our $q = CGI->new();

# when you want to set a cookie
push @cookies, $q->cookie(-name=>'sessionID',
			  -value=>'xyzzy',
			  -expires=>'+1h');

# when you print a page, instead of calling $q->header
# use this instead
print cookie_header;

# which sends all cookies
sub cookie_header {
    return $q->header(-cookie=>\@cookie_jar); 
}

# if you're on mod_perl, you also need to empty 
# the cookie jar here, so amend
sub cookie_header {
    my header = $q->header(-cookie=>\@cookie_jar); 
    @cookie_jar = ();
    return $header;
}