How do you create a php file editor in php - php

Question

I am trying to create a php file that can edit other php files on my website. I am able to do this except for when there is html in the php file that I want to edit. Since I am using a textarea to display/edit the php file contents, what I have built does not work when there is a textarea tag in the php file that I want to edit. What I have so far is below. The solution does not need to resemble this.
<?php
if ($_POST['file_text']){
file_put_contents($_POST['filename'], $_POST['file_text']);
$filename = $_POST['filename'];
echo "<script>
window.location = '_editor.php?filenm=$filename'
</script>";
}
else {
$myfilename = $_GET['filenm'];
if(file_exists($myfilename)){
$file_text= file_get_contents($myfilename);
}
echo "
<h3>$myfilename</h3>
<form name='input' action='_editor.php?filenm=$myfilename' method='post'>
<textarea name='contrib_entrybox' id='contrib_entrybox' rows='50' cols='180'>
$file_text
</textarea>";
?>

Answer 1

<?php
// configuration
$url = 'http://domain.com/backend/editor.php';
$yourfilePath = '/path/to/txt/file';
// check if form has been submitted
if (isset($_POST['text'])){
// save the text contents
file_put_contents($yourfilePath, $_POST['text']);
// redirect to form again
header(sprintf('Location: %s', $url));
printf('Moved.', htmlspecialchars($url));
exit();
}
// read the textfile
$text = file_get_contents($yourfilePath);
?>
<!-- HTML form -->
<form action="" method="post">
<textarea name="text"><?php echo htmlspecialchars($text) ?></textarea>
<input type="submit" />
<input type="reset" />
</form>

Answer 2

<div id="sample">
<script type="text/javascript" src="http://js.nicedit.com/nicEdit-latest.js"></script> <script type="text/javascript">
bkLib.onDomLoaded(function() { nicEditors.allTextAreas() });
</script>
<h4>
Second Textarea
</h4>
<textarea name="area2" style="width: 100%;">
Some Initial Content was in this textarea
</textarea><br />
</div>