这段代码运行良好的上传和扩展检查，但不是当文件已经存在

页面从索引开始，但其他东西运行良好，所以页面从上传开始。代码只在文件已经存在的情况下删除文件。我是php的新手。代码有问题吗?

upload.php

<?php
        if($action=="upload"){
        echo '<script language="javascript">';
        echo 'alert("File Uploaded")';
        echo '</script>';
        }
        ?>
        <?php
        if($action=="error"){
        echo '<script language="javascript">';
        echo 'alert("Please Upload only (xls,pdf,doc)files.")';
        echo '</script>';
        }
        ?>
        <?php
        if($action=="error_dct"){
        //var_dump($name);
        echo '<script language="javascript">';
        echo 'var x=confirm("Selected file already exists.");';
        echo 'if(x==true)';
        echo '{';
        $path="uploads_masterdata/".$name;
        unlink($path);
        //var_dump($tmp);
        move_uploaded_file($tmp, $path);
        echo '}';
        echo '</script>';
        } 
        ?>

    <?php
            define('ROOT_DIR', dirname(__FILE__));
            define('ROOT_URL', substr($_SERVER['PHP_SELF'], 0, - (strlen($_SERVER['SCRIPT_FILENAME']) - strlen(ROOT_DIR))));
            session_start();
            //$errors= array();
            $expensions= array(".xls",".xlsx",".doc",".docx",".pdf"); 
             //$file_ext=strtolower(end(explode('.',$_FILES['userFile']['name'])));
             $file_name = $_FILES['userFile']['name'];
              $file_ext=substr($file_name, strrpos($file_name, '.'));
              var_dump($file_ext);
            $info = pathinfo($_FILES['userFile']['name']);
            $tmp=$_FILES['userFile']['tmp_name'];
            $ext = $info['extension']; // get the extension of the file
            $newname = $file_name; 
            if(in_array($file_ext,$expensions)=== false){
                     $errors[]="extension not allowed, please choose a .xls file.";
                     header("location: masterdata.php?action=error&name=$newname&fe=$file_ext");
                  }
             if(file_exists(ROOT_DIR."/uploads/uploads_masterdata/".$_FILES['userFile']['name']))
            {
            $errors[]="file already exists";
            header("location: masterdata.php?action=error_dct&tmp=$tmp&name=$newname");
            }    
                  if(empty($errors)==true){
             $target = ROOT_DIR.'/uploads/uploads_masterdata/'.$newname;
             //$target = 'uploads_masterdata/'.$newname;
             //move_uploaded_file( $_FILES['userFile']['tmp_name'], $target);
             move_uploaded_file( $_FILES['userFile']['tmp_name'], $target);
            header("location: masterdata.php?action=upload");
                  }
                  else{
                     //print_r($errors);
                     //header("location: masterdata.php");
                  }
            ?>

index . php

<?php
if($action=="upload"){
echo '<script language="javascript">';
echo 'alert("File Uploaded")';
echo '</script>';
}
?>
<?php
if($action=="error"){
echo '<script language="javascript">';
echo 'alert("Please Upload only (xls,pdf,doc)files.")';
echo '</script>';
}
?>
<?php
if($action=="error_dct"){
//var_dump($name);
echo '<script language="javascript">';
echo 'var x=confirm("Selected file already exists.");';
echo 'if(x==true)';
echo '{';
$path="uploads_masterdata/".$name;
unlink($path);
//var_dump($tmp);
move_uploaded_file($tmp, $path);
echo '}';
echo '</script>';
} 
?>