unless ($title) {
$errorcount = 1;
$error_title = "<br><font color='red'>Please enter a title.</font>";
}
unless ($url) {
$errorcount = 1;
$error_url = "<br><font color='red'>Please enter a valid address.</font>";
}
unless ($description) {
$errorcount = 1;
$error_description = "<br><font color='red'>Please enter a description.</font>";
}
unless ($keywords) {
$errorcount = 1;
$error_keywords = "<br><font color='red'>Please enter some keywords.</font>";
}

if ($errorcount) {
print errors blah blah
}