URL Rewriting based on form input - .htaccess

Question

I'm creating a frontpage for my website with a single form and input text, Google-style. It's working fine, however, I want to generate a pretty URL based on the input. Let's say, my input is called "id", and using the GET method of form, and the action defined to "/go/", on submission, the URL will be:
site.com/go/?id=whateverIType
and I want to change it to
site.com/go/whateverIType
I was thinking on Mod Rewrite, but if the user put something in the URL, like:
site.com/go/?dontwant=this&id=whateverIType&somemore=trash
I want to ignore the other variables but "id", and rewrite the rule.
What's the better way of get this done? Thanks in advance!
PS: I'm using CodeIgniter, maybe there's something I can use for it as well. I already have a controller for "go".

Answer 1

I'm not familiar with CodeIgniter, but you can try the following RewriteRule
RewriteEngine on
RewriteCond %{REQUEST_URI} ^\/go\/
RewriteCond %{QUERY_STRING} id=([^&]*)
RewriteRule (.*) /go/%1? [L,R]
The %1 references the regex group from the previous RewriteCond, and the trailing ? will strip the querystring from the redirected URL.
Hope this helps.

Answer 2

Mod_rewrite supports conditions and rules with RegEx, so you could have a rule that matched the ?id=XXXX, that would extract it from the URL (keeping the other parameters), and rewrote the URL accordingly.
However... I don't think you want to do this, because if you rewrite the URL to be /go/Some+Search+Query, you won't be able to pick it up with say, PHP, without parsing the URL out manually.
It's really tough to have custom, SEO-friendly URLs with user input, but it is technically possible. You're better off leaving in the ?id=XXX part, and instead, using mod_rewrite in the opposite approach... take all URLs that match the pattern /go/My+Search+Terms and translate that back into something like ?id=My+Search+Terms, that way you'll be able to easily parse out the value using the URL's GET parameters. This isn't an uncommon practice - Google actually still uses URL parameters for user input (example URL: http://www.google.com/search?q=test).
Just keep in mind that mod_rewrite rewrites the URL before anything else (even PHP), so anything you do to the URL you need to handle. Think of mod_rewrite as a regular expression-based, global "Find and Replace" for URLs, every time a page is called on the server. For example, if you remove the query string, you need to make sure your website/application/whatever accounts for that.

Answer 3

In application/config/routes.php
$route['go/(:any)'] = "go/index/$1";
Where go is your controller and index is the index action.
http://codeigniter.com/user_guide/general/routing.html
You can use something like this in your .htaccess if you aren't already:
RewriteEngine on
RewriteCond $1 !^(index\.php|images|css|js|robots\.txt)
RewriteRule ^(.*)$ /index.php/$1 [L]