Apache mod_rewrite Introduction

Introduction

The Apache module mod_rewrite is a very powerful and sophisticated module which provides a way to do URL manipulations. With it, you can do nearly all types of URL rewriting that you may need. It is, however, somewhat complex, and may be intimidating to the beginner. There is also a tendency to treat rewrite rules as magic incantation, using them without actually understanding what they do.

This document attempts to give sufficient background so that what follows is understood, rather than just copied blindly.

Regular Expressions

Basic regex building blocks

RewriteRule basics

Basic anatomy of a RewriteRule, with exhaustively annotated simple examples.

Rewrite Flags

Discussion of the flags to RewriteRule, and when and why one might use them.

Rewrite conditions

Discussion of RewriteCond, looping, and other related concepts.

Rewrite maps

Discussion of RewriteMap, including simple, but heavily annotated, examples.

.htaccess files

Discussion of the differences between rewrite rules in httpd.conf and in .htaccess files.

Environment Variables

This module keeps track of two additional (non-standard) CGI/SSI environment variables named SCRIPT_URL and SCRIPT_URI. These contain the logical Web-view to the current resource, while the standard CGI/SSI variables SCRIPT_NAME and SCRIPT_FILENAME contain the physical System-view.

Notice: These variables hold the URI/URL as they were initially requested, i.e., before any rewriting. This is important because the rewriting process is primarily used to rewrite logical URLs to physical pathnames.

SCRIPT_NAME=/sw/lib/w3s/tree/global/u/rse/.www/index.html
SCRIPT_FILENAME=/u/rse/.www/index.html
SCRIPT_URL=/u/rse/
SCRIPT_URI=http://en1.engelschall.com/u/rse/