allora il valore della var $id viene passato col metodo get dalla seguente pagina:

<html>
<head>
<title>Modifica php</title>
</head>
<body bgcolor="#99CCCC">
<table width="750" bgcolor="#666666" align="center" cellpadding="0" cellspacing="5" border="0">
<tr>
<td>
<div align="center"><h1><font color="#FFFFFF">MODIFICA I RECORD</font></h1></div>


</td>
</tr>
</table>


<table width="750" bgcolor="#FFFFCC" align="center" cellpadding="0" cellspacing="5" border="0">
<tr>
<td>
<form name="info" action="08_mod.php" method="post">
<?php
$id = $_GET["id"];
include("mysql.php");
$dati = mysql_query("select * from libri where lib_id = $id ");
$array = mysql_fetch_array($dati);
echo "<input type=\"hidden\" name=\"id\" value=\"$id\">";
echo "<input type=\"text\" name=\"titolo\" value=\"$array[lib_tit]\">Titolo
";
echo "<input type=\"text\" name=\"autore\" value=\"$array[lib_aut]\">Autore
";
echo "<input type=\"text\" name=\"prezzo\" value=\"$array[lib_prezzo]\">Prezzo
";
echo "<input type=\"textarea\" name=\"descrizione\" value=\"$array[lib_desc]\">Descrizione
";
mysql_close();
?>
<input type="submit" value="invia">
</form>
</td>
</tr>
</table>
</body>
</html>