Untitled

i want to ban certain prefix
<form name="frm" method="post" action="addlink.php">
url : <input type="text" name="url" id="url">
<button type="submit" class="options green">add</button>
</form>

$url = $_POST['url'];
$sql = "INSERT INTO $table_urls (url) VALUES ('$url')";
mysql_query($sql, $conn) or die(mysql_error());

<?PHP if(XXXXXXXX){
echo "somthing.com is not allowed";
}else{
$sql = "INSERT INTO $table_urls (url) VALUES ('$url')";
mysql_query($sql, $conn) or die(mysql_error());
}

if (preg_match('/something.com/i', $url) > 0) {
    // Your error message here
}

$parsed_url=parse_url($url);
if (strtolower($parsed_url['host']) == 'www.something.com' || strtolower($parsed_url['host']) == 'something.com')
  {
     $error=true;
  }