Something
public text v1 · immutable<td width="60%" class="tableb" valign="top">
<?php
preg_match( '#^\/([^\/]+)\/#', $_SERVER['REQUEST_URI'], $match );
$chemin = $match[1];
?>
<input type="text" class="textinput" name="table_prefix" value="<?php echo ($_POST['table_prefix'] ? $_POST['table_prefix'] : $chemin) ?>" />
</td>