skrypt uploadu

[logen1]

Kod: Zaznacz wszystko

<?php

$site_name = $_SERVER['HTTP_HOST'];
$url_dir = "http://".$_SERVER['HTTP_HOST'].dirname($_SERVER['PHP_SELF']);
$url_this =  "http://".$_SERVER['HTTP_HOST'].$_SERVER['PHP_SELF'];

$upload_dir = "";
$upload_url = $url_dir."";
$message ="";

//create upload_files directory if not exist
//If it does not work, create on your own and change permission.

if ($_FILES['userfile']) {
   $message = do_upload($upload_dir, $upload_url);
}
else {
   $message = "Invalid File Specified.";
}

print $message;

function do_upload($upload_dir, $upload_url) {

   $temp_name = $_FILES['userfile']['tmp_name'];
   $file_name = $_FILES['userfile']['name'];
   $file_type = $_FILES['userfile']['type'];
   $file_size = $_FILES['userfile']['size'];
   $result    = $_FILES['userfile']['error'];
   $file_url  = $upload_url.$file_name;
   $file_path = $upload_dir.$file_name;

   //File Name Check
    if ( $file_name =="") {
       $message = "Invalid File Name Specified";
       return $message;
    }
    //File Size Check
    else if ( $file_size > 500000) {
        $message = "The file size is over 500K.";
        return $message;
    }
    //File Type Check
    else if ( $file_type == "text/plain" ) {
        $message = "Sorry, You cannot upload any script file" ;
        return $message;
    }

    $result  =  move_uploaded_file($temp_name, $file_path);
    $message = ($result)?"Brawo! Zdjęcie zostalo dodane." :
             "Somthing is wrong with uploading a file.";

    return $message;
}
?>
<form name="upload" id="upload" ENCTYPE="multipart/form-data" method="post">
  Dodaj zdjęcie<input type="file" id="userfile" name="userfile">
  <input type="submit" name="upload" value="Dodaj">
</form>

Jak zrobić żeby skrypt nie nadpisywał plików na serwerze podczas wgrywania pliku o takiej samej nazwie która znajduje się już na serwerze?