Short-urls without index files?

I'm wondering how urls like these are generated: http://www.example.com/Xj7hF

This is a p开发者_开发问答ractice I have seen used by many url shorteners as well as other websites that supposedly don't want to display data in the url in a parameter format.

Surely they can't be placing index files in the folder destination /Xj7hF etc with a redirect to the actual url, so I'm wondering how this is done.

Any help would be very appreciated!

(I'm running on a Linux server with Apache).

Different web development frameworks and web servers do it in different ways, but, the most common is probably using mod_rewrite with apache. Basically, the web server sends the request to a dynamic scripting language (eg. PHP) rewritten in such a way that the script doesn't need to know what the original request URI looked like and the client browser doesn't need to know what script actually processed the request.

For example, You will often see:

http://something.com/123/

This is a request for /123 which Apache may rewrite as a request to /my_script.php?id=123 based on how the user configured mod_rewrite.

(.htaccess example)

# if the request is for a file or directory that
# does not actually exist, serve index.php
RewriteEngine on
RewriteCond %{REQUEST_FILENAME} !-f 
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule ^(.*)$ /index.php?url=$1

This is known as URL rewriting and is usually performed via proper configuration of the webserver. StackOverflow has several tags for this, so you should be able to find more information there.