use strict;
use CGI;

my $cgi=CGI->new;

print $cgi->header;

my @un_filled;
foreach ($cgi->param)
{
	unless($cgi->param($_))
	{
		push @un_filled, $_;
	}
}
if(@un_filled)
{
	print "You've forgotten to fill in the following
		fields: @un_filled";
	exit;
}
# do stuff...