Guide to Using Mod_Rewrite for Search Engine Friendly URL's

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Search Engine Friendly URL's are an advanced part of SEO. By using Apache mod_rewrite we can use this to change numbered URL's to simple keyword URL's that are better for SERP's.

1. Background of Mod Rewrite

In the starting days of the Web, each site was made up of one file made out of HTML which would consist of one page. It was very easy to move around sites and links as each page was a self contained file.

The following developments were CGI scripts to server dynamic content. This changed to URLs such as:

http://www.sample.net/cgi-bin/page.cgi
http://www.sample.net/cgi-bin/script...l1&param2=val2

The GET parameters could be incorporated into the URI and cleaned up a little:

http://www.sample.net/cgi-bin/script/param1/param2

Then scripting languages came trotting along that allowed pages to be dynamic without the necessity of the pages to sit in one directory:

http://www.sample.net/script.php?par...l1&param2=val2
http://www.sample.net/script/param1/param2

The second example in this scenario would use in most cases Content Negotiation to recognize the address in the example as a call to the script, with the what was left of the address (/param1/param2) obtainable as an environment variable.

Search engines started to emerge like Google, Yahoo, and MSN that required everything to be "indexable" by the search engine spiders such as Googlebot and other programs like Slurp. The ultimate ideal was to make all the sites look like they were composed of individual pages in order to bump up the hits that were made with the bot.

The following samples will show how to do this process using URLs for complex dynamic content.

2. Search Friendly URL's

The most popular part of a site is usually the News section database. These would usually be brought up as:

http://www.sample.net/news.php?id=20050901

(a request to the news.php script passing one GET parameter which shows which item to display)

Now the RewriteRule shows up for the first time:
RewriteRule ^news/([0-9]+) /news.php?id=$1
Code (markup):
Meaning:

IF the request starts with news/ followed by some digits or only one.

THEN call the news.php script with the exact id set up to those digits.

The URI then becomes:

http://www.sample.net/news/20050701

Or, since we left the RHS of the normal expression open, we may also use:

http://www.sample.net/news/20050701.html

We have a problem though, if Content Negotiation is shown to be enabled, that URI could be interpreted as a call to the news.php script with the other parts of the URL (/20050701.html) being not used. This is because there are no files called /news/20050701.html, and no files called /news, but /news.php do not exist and Content Negotiation is pretty much all that is. If this were to happen, the correct news item would not show up.

What is the answer? If we wanted to, we could re-name the script, Change the URI's format, or simply switch off Content Negotiation (which is probably a good idea anyway), but there's an easier choice:
RewriteRule ^news/([0-9]+) /scripts/news.php?id=$1
Code (markup):
If you move the script into a sub-directory, which we can do since it is no longer named 'in place', a conflict will not arise. The /scripts/ directory may, and really should, be secured to avoid direct access.

One of the many huge benefits of using these rewriting rules and 'hiding' that script is Only those requests matching the regular expression can obtain it. There's no way someone could use a non-numeric number, and if they tried, they would end up (surely) with a 404 error.

Yet there is even a better rule than that:
RewriteRule ^news/([0-9]{8}) /scripts/news.php?id=$1
Code (markup):
or, if you really want to follow the book and reinforce the .html extension:
RewriteRule ^news/([0-9]{8})\.html$ /scripts/news.php?id=$1
Code (markup):
We're now going to see what happens if other sites are already linking to your Dynamic Pages.

3. Converting Dynamic Pages to URL's that are Search Engine Friendly

If you see a lot of 404's popping up, that's probably normal since a lot of your stuff has been deprecated.

That's when the PURL comes in to save the day.

There's nothing to it actually:
RewriteCond %{QUERY_STRING} ^id=([0-9]+) RewriteRule ^news\.php /news/%1.html? [R=301,L]
Code (markup):
Meaning:

IF the sring starts with id=(1 to infinity digits)

AND a request is put out for /news.php

THEN redirect (301) to a search-engine-friendly URL sans query string

There is a reason for having a 301 Permanent redirect, and that is that search engines such as Yahoo or Google will understand that the the previously indexed page is now at that new location, and then transfer any http://www.google.com/search?q=defineageRankPageRank that was at that previous location.

Make sure you don't have more than one way to access content or pages otherwise you might receive a search engine penalty.

If you ever feel the need to change your URL structure more than one time ever, there's a good chance that you're going to end up with a chain of 301 redirects from your oldest to newest, so before you do anything, map out the details on a piece of paper before continuing.

4. Common Mistakes Everyone Makes

Trying to match query strings using the RewriteRule:

The Rewrite Rule can never see the Query String - The RewriteRule only sees the particular address portion of said request. As you remember from above, RewriteCond on %{QUERY_STRING} only before your RewriteRule.
Appending QUERY_STRING to the rewrite able target

That sounds like it would have been a great answer before:
RewriteRule ^book/([0-9]+)\.html /scripts/book.html?id=$1&%{QUERY_STRING}
Code (markup):
It's best just to use the built in QSA flag:
RewriteRule ^book/([0-9]+)\.html /scripts/book.html?id=$1 [QSA]
Code (markup):
Sidenote: QSA means Query String Append.
Trying to connect page anchors

Page anchors are - addresses finishing with #anchor - used entirely on the client-side are never exchanged with the server. It should make sense as you can, without reloading, jump from anchor to the next.

Missing images and style-sheets

After using a redirect like:
RewriteRule ^book/([0-9]+)\.html /showbook.php?id=$1
Code (markup):
Relative paths to your images will cease to function. This is because, as far as the browser is aware of, you're still in the folder of books.

Links:

Apache module mod_rewrite
Apache Content Negotiation
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Guide to Using Mod_Rewrite for Search Engine Friendly URL's

Ratman2050 Well-Known Member

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Guide to Using Mod_Rewrite for Search Engine Friendly URL's

Ratman2050 Well-Known Member

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