input 之间如何传递数据是在同一页面

<input name="tfilename" type="hidden" id="tfilename" value="<?=$pripath?><?=$tfilename2?>">     
      <td height="25" bgcolor="#FFFFFF">根目录</td>
  <input name="pripath" type="text" id="pripath" value="<?=$pripath?>" size="30">
      <input name="tfilename2" type="text" id="tfilename2" value="<?=$tfilename2?>" size="16">

<script type="text/javascript">
function add(){
document.getElementById('tfilename').value = document.getElementById('pripath').value + '' + document.getElementById('tfilename2').value;
}
</script>
<input name="tfilename" type="hidden" id="tfilename" value="<?=$pripath?><?=$tfilename2?>">     
<td height="25" bgcolor="#FFFFFF">根目录</td>
<input name="pripath" type="text" id="pripath" value="<?=$pripath?>" size="30">
<input name="tfilename2" type="text" id="tfilename2" value="<?=$tfilename2?>" size="16">
<input type="button" name="b1" onclick="add()" value="传递" >

<?php
header("Content-type: text/html; charset=utf-8");
$pripath = "c:\windows\";
$tfilename2 = "test.txt";
?>
<form action="" method="post" name="file_form" id="file_form"/>
<table>
    <tr>
 <input name="tfilename" type="hidden" id="tfilename" value="<?php echo $pripath; ?><?php echo $tfilename2;  ?>" />     
      <td height="25" bgcolor="#FFFFFF">根目录</td>
      <input name="pripath" type="text" id="pripath" value="<?php echo $pripath; ?>" size="30">
      <input name="tfilename2" type="text" id="tfilename2" value="<?php echo $tfilename2; ?>" size="16">
      </tr>
      <tr>
          <td><input type="submit" name="submit"/></td>
      </tr>
</table>
</form>
<?php
if (isset($_POST['submit'])) {
    $pripath = $_POST['pripath'];
    $pripath = (!get_magic_quotes_gpc()) ? addslashes($pripath) : $pripath;
    $tfilename2 = $_POST['tfilename2'];
    $tfilename2 = (!get_magic_quotes_gpc()) ? addslashes($tfilename2) : $tfilename2;
    $str = "<script>
";
    $str .= "document.getElementById('tfilename').value = '{$pripath}{$tfilename2}';
";
    $str .= "document.getElementById('pripath').value = '{$pripath}';
";
    $str .= "document.getElementById('tfilename2').value = '{$tfilename2}';
";
    $str .=  "</script>
";    
    echo $str;
}
?>