Mine

<td width="60%" class="tableb" valign="top">
 <?php
    preg_match( '#^\/([^\/]+)\/#', $_SERVER['REQUEST_URI'], $match ); 
    $chemin = $match[1]; 
    if ( isset($_POST['table_prefix']) && $_POST['table_prefix'] != '' ) { $chemin = $_POST['table_prefix']; } 
// echo $chemin;
?>
    <input type="text" class="textinput" name="table_prefix" value="<?php echo $chemin; ?>" />
</td>