A command inside a command!

1

This script is giving me errors. How do you put a command inside a command?


PHP Code:
<? 
session_start(); 
header("Cache-control: private"); 

if((!$_SESSION['user_name'] === "") || (!$_SESSION['first_name'] === "") || (!$_SESSION['last_name'] === "")){ 
    echo "You must login to post! If you do not have an account you may register it for free!"; 
    include 'login.html'; 
    include 'signup.html'; 
    exit(); 
} 

else{ 
include 'db.php'; 

$title = $_POST['title']; 
$url = $_POST['url']; 
$message = $_POST['message']; 
$username = $_SESSION['user_name']; 
$firstname = $_SESSION['first_name']; 
$lastname = $_SESSION['last_name']; 

$title = stripslashes($title); 
$url = stripslashes($url); 
$message = stripslashes($message); 

if((!$title) || (!$url) || (!$message) || (!$username) || (!$firstname) || (!$lastname)){ 
    echo 'You did not submit the following required information! <br />'; 
    if(!$title){ 
        echo "Message Title is a required field. Please enter it below.<br />"; 
    } 
    if(!$url){ 
        echo "Url is a required field. Please enter it below.<br />"; 
    } 
    if(!$message){ 
        echo "Message is a required field. Please enter it below.<br />"; 
    } 
    if(!$username){ 
        echo "There was an error in recording your username. Please Login!<br />"; 
    } 
    if(!$firstname){ 
        echo "There was an error in recording your first name. Please Login!<br />"; 
    } 
    if(!$lastname){ 
        echo "There was an error in recording your last name. Please Login!<br />"; 
    } 
    include 'post.html'; 
    exit(); 
} 

$sql = mysql_query("INSERT INTO public (title, url, message, username, firstname, lastname, postdate) 
        VALUES('$title', '$url', '$message', '$username', '$firstname', '$lastname', 'now()')") 
} 
?>

thanks!