use of $route in routes.php

I used the "view source" in chrome to see what the hyperlink is. 

this is how it appears in the source:
Don't have an account? <a href="<?php echo base_url(); ?>users/registration">Register here</a></p>

This is how it appears in the browser: 
Don't have an account? <a href="/sub_crud/users/registration]http://[::1]/sub_crud/users/registration">Register here</a></p>

I don't understand why it appears twice and the link is malformed. Anyway when I click on that link I get 

http://[::1]/sub_crud/users/registration 404 (Not Found)

I do have a users.php controller and it contains a registration method.

proof that an old dog can learn new tricks