How to rewrite a URL and pass on the original URL as a parameter

mod_rewrite it what you need.

This is quite easy and its a powerfull tool.

I suggest to read this -> http://httpd.apache.org/docs/2.0/misc/rewriteguide.html

And example :

this estarts de rewriteengine, then applies some conditions and if they are true then applies the rewrite itself. its like a while/case codeblock.

The most helpful part is the log .;)

    RewriteEngine on
RewriteLogLevel 0
RewriteLog "/var/www/rewrite.log"

<Directory /var/www>

    Options -ExecCGI -Indexes
    AllowOverride none
    Order allow,deny
    allow from all
    #SetHandler none

    RewriteEngine On
    RewriteBase /
    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} -d
    RewriteCond %{REQUEST_URI} !=/favicon.ico
    RewriteRule ^(\w+.\w+)/(es|ca|en)/$ index.php?user=$1&lang=$2 [L]

    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} -d
    RewriteCond %{REQUEST_URI} !=/favicon.ico
    RewriteRule ^(\w+.\w+)/$ index.php?user=$1&lang= [L]

    RewriteCond %{REQUEST_FILENAME} !-f
    RewriteCond %{REQUEST_FILENAME} !-d
    RewriteCond %{REQUEST_URI} !=/favicon.ico
    RewriteRule ^(\w+.\w+)/(\w+)?(/(.*))?$ index.php?user=$1&lang=$2$4 [L,QSA]

also, you can look at mod_proxy, it will do the trick but it's not the 'good way' in my opinion.

hope it helps.

What Lairsdragon said is correct. However, if you have more than one rewrite rule in your config, you will want to add the [L] flag to the end in order to prevent other rules from being applied.