my @required = qw(name site siteid email email2 pass repass);

my $req_err;
for (@required) {
  next if $q->param($_);
  $req_err++; last;
}
if ($req_err) {
  &error("You forgot some required fields"); 
}
elsif ($q->param('email') ne $q->param('email2')) {
  &error("The two e-mail addresses you entered don't match"); 
}
elsif($q->param('pass') ne $q->param('repass')) {
  &error("Your passwords don't match");
 }
else {
  # do whatever...
}