Get a 0KB file after using PHP unlink() method

Question

I'm trying to delete a file on the server. Below is the code I use.

function ServerDel($file){
        $file = realpath($file);
        echo ($file);
        $fh = fopen($file, 'w') or die("can't open file");
        fclose($fh);
        if(unlink($file))
            echo"Delete the file successfully.";
        else
            echo "Failed to delete.";
}

But after I run the code, the file still exists and becomes 0KB. Anyone knows how to get around this?

Thanks in advance.