Appendix A. Using Regular Expressions in Apache

A number of the Apache Web server’s configuration directives permit (or require!) the use of what are called regular expressions. Regular expressions are used to determine if a string, such as a URL or a user’s name, matches a pattern.

There are numerous resources that cover regular expressions in excruciating detail, so this Appendix is not designed to be a tutorial for their use. Instead, it documents the specific features of regular expressions used by Apache—what’s available and what isn’t. Even though there are quite a number of regular expression packages, with differing feature sets, there are some commonalities among them. The Perl language, for instance, has a particularly rich set of regular expressions, which have been mostly available in the Apache regex library since version 2.0 of the server.