PHP edit file on server?

[Inventor]

Hello,

I am getting a error when I use a post variable to edit a file on the server.
What I want is to enter the name of the file and then edit it.
Here is my code:

First file "editor.php"

PHP Code:

<form action="editpage-2.php" method="post" />
      <input type="text" name="page" />  
    <input type="submit" value="Submit" />  
</form> 


Second file "editpage-2.php"

PHP Code:

<?php
$firstfile =  $_POST['page'];
echo $firstfile;   // the file is shown, and is there
$fn = $firstfile;

 
if (isset($_POST['content']))
{     
    $content = stripslashes($_POST['content']);
    $fp = fopen($fn,"w") or die ("Error opening file in write mode!");
    fputs($fp,$content);
     
    fclose($fp) or die ("Error closing file!");
}
?>
<form action="<?php echo $_SERVER["PHP_SELF"] ?>" method="post">
    <textarea rows="10" cols="100" name="content"><?php readfile($fn); ?></textarea><br />
    <input type="submit" value="Save" VALUE="Refresh">  
</form> 


The problem is when I hit the save button, it shows this error:


Notice: Undefined index: page in C:\xampp\..\editpage-2.php on line 3

Warning: fopen() [function.fopen]: Filename cannot be empty in C:\xampp...\editpage-2.php on line 11
Error opening file in write mode!

Is there any thing that I missed?

Thank you all,

Inventor