sub print_error {
    my $message = shift;
    print "<br><font color='red'>$message</font>";
    # etc..
}

unless($title and $url and $description and $keywords) {
    $title
        or print_error "Please enter a title.";

    $url
        or print_error "Please enter a valid address.";

    $description
        or print_error "Please enter a description.";

    $keywords
        or print_error "Please enter some keywords.";

    # ...
}