Learning PHP 5

Appendix B. Regular Expression Basics

Behind the innocuous and generic phrase regular expression lives an intricate and powerful world of text pattern matching. With regular expressions, you can make sure that a user really entered a ZIP Code or an email address in a form field, or find all the HTML <a> tags in a page. If your web site relies on data feeds that come in text files, such as sports scores, news articles, or frequently updated headlines, regular expressions can help you make sense of these.

This appendix provides an overview of the most useful and commonly encountered parts of the regular expression menagerie. By learning the special meanings of 5 or 10 symbols and 2 or 3 PHP functions, you can use regular expressions to solve most of the text-processing problems you run into when building a web site with PHP. There are some dark corners and steep ravines of the regular expression landscape that are not covered here, however, such as locale support, lookahead and assertions, and conditional subpatterns. To learn more about regular expressions, see the PCRE section of the PHP Manual, at http://www.php.net/pcre, or read the comprehensive Mastering Regular Expressions by Jeffrey E.F. Friedl (O’Reilly).

To work with regular expressions in PHP, use the functions in the PCRE (Perl-compatible regular expressions) extension.^[1] These functions are included with PHP by default and are described in the online manual at http://www.php.net/pcre. Section B.6, later in this appendix, ...