<form name= "form1"  action= "go.php"  method= "POST" >
 <font size= "-4 ">Выберите нужную категорию >></font>
 <select name= "doclist" >
 <option value= "none"  selected>Категория документа
   <option value= "www.ranbler.ru" >Rambler
   <option value= "www.scabler.h1.ru" >ScableR
 </select>
 <input name= "Submit"  type= "submit"  value= "Выполнить вход"  >
 </form>

<?PHP
   header( "Location: $doclist" );
   exit;
?>

$_POST

$HTTP_POST_VARS
$HTTP_GET_VARS

   REQUIRE( "config.php" );

 <?php
 php_track_vars;

       echo  "Список доступных документов" ;
           echo  "<br>" ;
           $dir= "d:/www/documents/instruct/" ;
             $docs_dir= "documents/instruct/" ;
   
           chdir($dir);
           $current_dir = opendir($dir);
           while ($current_file=readdir($current_dir))
           ....
           echo  "<a href='file2.php?dir=$dir&docs_dir=$docs_dir'>" ;
           ...
?>

<?PHP
...
php_track_vars;
$q=trim($q);
echo  "dir=" . "$dir" ;
...
chdir($dir);
   $current_dir=opendir($dir);
       while ($current_file=readdir($current_dir))
           {
           if ($current_file== "."  || $current_file== ".." ) continue;
...
?>

<?PHP
echo "<a href='file2.php?to=hi_man!!!'>LINK</a>" ;
?>

<?PHP
echo "$to" ;
?>