target_file = $target_dir . time()."_abc.jpg";

basename($_FILES["files"]["name"]="abc.jpg";

$target_file = $target_dir . time()."_abc.jpg";
if (file_exists($target_file)) {
   if (move_uploaded_file($_FILES['files']['tmp_name'], $target_file)) {
       echo "File Uploaded";
   } else {
       echo "File Not Uploaded";
   }
}