PHP regular expressions can be almost as indecipherable as the United States tax code. Rather than reaching for a manual every time you need to perform a particularly complex parsing task, just consult this handy Top 10 PHP Regex Cheat Sheet. It provides all the information you need to implement some basic regular expression functionality into your PHP pages, including regexes for validating usernames, credit card numbers, email addresses, phone numbers and more.

Download the PHP Regex Cheat Sheet from Developer.com:
Top 10 PHP Regex Cheat Sheet