grack.com

I wanted to move all of my old articles into yearly subdirectories, but I didn’t want to break any of the incoming links to my site.  Thankfully, mod_rewrite allows me to redirect incoming requests as necessary!

RewriteEngine on

RewriteCond         %{REQUEST_FILENAME} ^(.*/news)/
RewriteCond         %1/2004/$1          -f
RewriteRule         ^news/([^/]+)$       /news/2004/$1 [R,L] 

RewriteCond         %{REQUEST_FILENAME} ^(.*/news)/
RewriteCond         %1/2003/$1          -f
RewriteRule         ^news/([^/]+)$       /news/2003/$1 [R,L]

RewriteRule   ^(.+)  -  [PT]

Basically, these rules check to see if the file exists in the /news/2004/ or /news/2003 subdirectories and, if so, redirects immediately to the yearly subdirectory.

It took me a while to figure out how to do this, but I think I’ve got a good idea of what’s going on.

The strange (but cool?) thing about mod_rewrite is that you can use the “back-references” captured in the RewriteRule in the RewriteCond lines! In the rules above, %1 represents the request filename captured in the first RewriteCond, while $1 represents the URI segment captured in the RewriteRule below. See figure 1 in the mod_rewrite manual page for more information on how this works.

If you want to figure this stuff out for your own nefarious purposes, here are some links to help:

• http://www.modrewrite.com/: A gateway to a number of different sites
• Apache mod_rewrite module manual page: The official reference, complete but lacks some detail and examples
• A Users Guide to URL Rewriting with the Apache Webserver: The best example reference there is