Hardly worth a whole blog post but it may help somebody… is_numeric() is the function to use for validating numeric-only user input with PHP but unfortunately there is no is_alphanumeric(). Or so I thought. Meet ctype_alnum() Here’s an example of its usage: if (ctype_alnum($_POST['username'])) { echo "Thanks - that's a good username."; } else { … Continue reading How to do alphanumeric validation with PHP →