FAQ: mod_rewrite, 301 redirects, and optimizing Apache.

mod_rewrite

Introduction.



Welcome to mod_rewrite, the Swiss Army Knife of URL manipulation! Despite the tons of examples and docs, mod_rewrite is voodoo!



This module uses a rule-based rewriting engine (based on a regular-expression parser) to rewrite requested URLs on the fly. It supports an unlimited number of rules and an unlimited number of attached rule conditions for each rule to provide a really flexible and powerful URL manipulation mechanism. The URL manipulations can depend on various tests, for instance server variables, environment variables, HTTP headers, time stamps and even external database lookups in various formats can be used to achieve a really granular URL matching.



This module operates on the full URLs (including the path-info part) both in per-server context (httpd.conf) and per-directory context (.htaccess) and can even generate query-string parts on result. The rewritten result can lead to internal sub-processing, external request redirection or even to an internal proxy throughput.



This module was invented and originally written in April 1996. [1]





How to change your URLs from dynamic to search engine friendly static URLs using mod_rewrite.





Get an example of the dynamic URL and the way you want it. For example



http://www.domain.com/cgi-bin/store.cgi?section=Nintendo&id=4867635&item=Pokemon

and

http://www.domain.com/store/Nintendo/4867635/Pokemon.html



Now that you got both URLs, make a domain.com/.htaccess file starting with...



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /

RewriteRule ^



Depending on the server, you might not need the first two lines.



Right after RewriteRule ^ enter the static URL, then a $, a space, and then original URL (with out the domain part for both URLs).



You now got...



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /

RewriteRule ^store/Nintendo/4867635/Pokemon.html$ cgi-bin/store.cgi?section=Nintendo&id=4867635&item=Pokemon



In the first URL, the static URL code, where ever the URL will change, replace it with a (.*) (Nintendo, 4867635

and Pokemon in the example above).



Then after .html add a $ and add a \ before the .html

If you have a hyphen (-) in the new static URL, add a \ before the hyphen, for example...



RewriteRule ^store\-(.*)\-(.*)\.html$ cgi-bin/store.cgi?section=Nintendo&id=4867635&item=Pokemon



If you don't add the \, you might get an Internal Server Error message, depending on the servers Apache version.



Now in the static part of the URL where the URL changes, in the first change, change it to $1, then $2 and so on. Then add an [L] at the very end, with a space before the [L].



You now got...



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /

RewriteRule ^store/(.*)/(.*)/(.*)\.html$ cgi-bin/store.cgi?section=$1&id=$2&item=3 [L]



Save the .htaccess file and upload it at domain.com/.htaccess and your static URLs will now work.

http://www.domain.com/store/Nintendo/4867635/Pokemon.html



Here's some other examples...



http://www.domain.com/cgi-bin/store.cgi?section=Nintendo&id=4867635

RewriteRule ^store/(.*)/(.*)\.html$ cgi-bin/store.cgi?section=$1&id=$2 [L]



http://www.domain.com/cgi-bin/store.cgi?section=Nintendo

RewriteRule ^store/(.*)\.html$ cgi-bin/store.cgi?section=$1 [L]



http://www.domain.com/cgi-bin/store.cgi

RewriteRule ^index\.html$ cgi-bin/store.cgi [L]



In this last example domain.com will show the index of the script. If the page shows nothing, try



RewriteRule ^$ cgi-bin/store.cgi [L]





With all the examples combined, you got...



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /

RewriteRule ^store/(.*)/(.*)/(.*)\.html$ cgi-bin/store.cgi?section=$1&id=$2&item=3 [L]

RewriteRule ^store/(.*)/(.*)\.html$ cgi-bin/store.cgi?section=$1&id=$2 [L]

RewriteRule ^store/(.*)\.html$ cgi-bin/store.cgi?section=$1 [L]

RewriteRule ^index\.html$ cgi-bin/store.cgi [L]



Notice the order. if you list it as...



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /

RewriteRule ^index\.html$ cgi-bin/store.cgi [L]

RewriteRule ^store/(.*)\.html$ cgi-bin/store.cgi?section=$1 [L]

RewriteRule ^store/(.*)/(.*)\.html$ cgi-bin/store.cgi?section=$1&id=$2 [L]

RewriteRule ^store/(.*)/(.*)/(.*)\.html$ cgi-bin/store.cgi?section=$1&id=$2&item=3 [L]



then mod_rewrite will freak out and it won't work! List the line with the most variables first, then the second most and so on.



Can I have the .htaccess in a directory?



Yes.



In the above example, for having it at domain.com/store/.htaccess, change the code to...



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /store/

RewriteRule ^index\.html$ /cgi-bin/store.cgi [L]

RewriteRule ^(.*)\.html$ /cgi-bin/store.cgi?section=$1 [L]

RewriteRule ^(.*)/(.*)\.html$ /cgi-bin/store.cgi?section=$1&id=$2 [L]

RewriteRule ^(.*)/(.*)/(.*)\.html$ /cgi-bin/store.cgi?section=$1&id=$2&item=3 [L]



You moved store/ up to the RewriteBase line and added / before cgi-bin. If the script was in /store/store.cgi

you would of had store/ instead of cgi-bin/ and then just got rid of it, to look like...



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /store/

RewriteRule ^index\.html$ store.cgi [L]

RewriteRule ^(.*)\.html$ store.cgi?section=$1 [L]

RewriteRule ^(.*)/(.*)\.html$ store.cgi?section=$1&id=$2 [L]

RewriteRule ^(.*)/(.*)/(.*)\.html$ store.cgi?section=$1&id=$2&item=3 [L]



The URL to the index of the store will be domain.com/store/



Ack!!! Now it's messing up the rest of my site.



If you have domain.com/index.html for example, make sure your mod_rewrited URLs use another extension, like .htm or .shtml.



The original script URLs don't have the product name in the URL. Can I add the product name to the URL?



Yes! If you can change the script to put the product names in the URL, or edit the links to link to them, yes you can. Here's an example. Notice there are two (.*)'s and no $2.



RewriteRule ^(.*)/(.*)\.html$ cgi-bin/file.cgi?Item=$1 [L]



Just edit the script links, or links in the static page to link to domain.com/whatever/PRODUCT_NAME.html have the product name show up where the last (.*) is in the .htaccess code.



But how can I get rid of special characters or spaces?



For perl, you can do search and replaces, for example...



$value =~ s/ /_/g;

$value =~ s/?//g;

or

$value =~ s/[^\w\d\-_. ]//g;



which gets rid of almost everything but letters and numbers. Just make sure it only changes the URL and not the content. As for php or asp, I don't know how to do it there.



Can I rewrite a sub-domain to a directory?



Yes. Here's the code [url=http://forums.digitalpoint.com/member.php?find=lastposter&t=20416]mnemtsas came up with...



xxxxx.domain.com



to



www.domain.com/XXXXXX/



RewriteCond %{HTTP_HOST} ^[www\.]*xxxxx.domain-name.com [NC]

RewriteCond %{REQUEST_URL} !^/XXXXX/.*

RewriteRule ^(.*) /XXXXX/$1 [L]



Does .htaccess increase server load?



I have yet to ever see it increase server load on my dedicated server. IMO, that's just a rumor. I got about 30 domains with about 54 lines in the domain.com/.htaccess file and have yet to ever see it effect the server. The only effect I've ever got is getting GoogleBombed (Google chomping away at the static URLs so much that the server almost crashes or does crash!!!). Don't panic. This is why you have static URLs, to help search engines crawl your site.



If you ever see high server loads or a slow server, try optimizing Apache.



How do I optimize Apache?



You have to have access to the actual server through telnet as root.



Edit your httpd.conf file.



Here's the best settings I've found.



Timeout 50

KeepAlive On

MaxKeepAliveRequests 120

KeepAliveTimeout 10

MinSpareServers 10

MaxSpareServers 20

StartServers 16

MaxClients 125

MaxRequestsPerChild 5000



and then restart apache. Even when I have massively HIGH server loads, the sites are fast. Once I had the server load above 100, which is EXTREMELY high, and the static pages loaded as if nothing was high!!



Don't ask me how to do it. If you don't know what you're doing, don't mess with it. Ask your web host. Mess up and your sites can 'die' until it get's fixed! For example, simply pressing return can crash your sites until you go back and undo the return, geting it back to how it was before.



How can I do a 301 redirect?



at domain.com/.htaccess



Options +Indexes

Options +FollowSymlinks

RewriteEngine on

RewriteBase /

RewriteRule ^whatever/(.*)$ http://www.domain.com/$1/ [R=301,L]

or

RewriteRule ^index.htm$ http://www.domain.com/ [R=301,L]



The second example only changes one URL.



(.*) and $1 work the same way here as in mod_rewrite, so you can easily change a lot of URLs with one line. The only change with redirects and mod_rewrite is the R=301 (Redirect 301).