Let's say my site is example.com I want to create example.com/portfolio without creating a page.
I just want to execute some PHP code and display a bit of HTML.
Is there any way to create "sytem urls" (opposite to "content url") ?
Create a custom page template:
<?php
/**
* Template Name: Random PHP
*/
get_header();
//add random PHP
get_sidebar();
get_footer();
?>
Create a page in WordPress, give it the title portfolio. In the template select box choose Random PHP