Try this:

<?php

// configuration
$url = 'http://www.leonli.co.uk/path-to-editor.php'; //change this to your php file path
$file = '/path/to/file'; //change this to your target file path

// check if form has been submitted
if (isset($_POST['text']))
{
    // save the text contents
    file_put_contents($file, $_POST['text']);

    // redirect to form again
    header(sprintf('Location: %s', $url));
    printf('<a href="%s">Moved</a>.', htmlspecialchars($url));
    exit();
}

// read the textfile
$text = file_get_contents($file);

?>
<!-- HTML form -->
<form action="" method="post">
<textarea style="width:700;height:200;" name="text"><?php echo htmlspecialchars($text) ?></textarea>

<input type="submit" />
<input type="reset" />
</form>

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