Clean form input to lowercase alphabetical using php

Question

I have a simple php file with a GET from a form to throw up some files from a directory. Quite simple code but I just need to strip from the string ANY characters that are NOT lowercase alpha. How would I go about doing that? (I'm a novice).

Here 'tis:

<?php $text = $_GET['text_string']; ?>

<form method="GET" action="index.php">Please enter some letters: <input type="text" name="text_string" value=""/> and hit <input type="submit" value="enter" />
</form>

<?php /* Split characters into an array */ $array = str_split($text); ?>

<?php foreach($array as $char) : ?>
   <img src="glyphs/<?php print ($char); ?>.jpg"/>
<?php endforeach ; ?>

Thanks!

Answer 1

To lowercase (note that you also can use mb_strtolower for better charset handling, but in this case you're only going to keep ASCII chars anyway so strtolower is enough):

$text = strtolower($text);

To remove all non-alpha chars using preg_replace:

$text = preg_replace('/[^a-z]/', '', $text);