How to have a custom URI path for specific page template

Question

You need to add a rewrite rule to WordPress. There are several options to do it depending on your exact needs.

Maybe the most general is using add_rewrite_tag() and add_rewrite_rule():

add_action( 'init', 'cyb_rewrite_rules' );
function cyb_rewrite_rules() {
    add_rewrite_tag( '%variable1%', '([^&]+)' );
    add_rewrite_tag( '%variable2%', '([^&]+)' );
    add_rewrite_rule( ^system/([^/]*)/([^/]*)/?', 'index.php?pagename=$matches[1]&variable1=$matches[2]&variable2=$matches[3]', 'top' );
}

Now, if the URL match the regext “system/([^/])/([^/])/”, for example this one:

https://example.com/system/value1/value2

The page “system” will be queried by WordPress and you will be able to get the extra values using get_query_var():

$variable1 = get_query_var( 'variable1' );
$variable2 = get_query_var( 'variable2' );

Both functions, add_rewrite_tag() and add_rewrite_rule(), are wrappers of WP_Rewrite methods.

Note: after a new rewrite rule is added to WordPress, the set of rules need to be flushed and rebuild. This can be done with flush_rewrite_rules() function. This function makes a database operation that it’s needed only once, that is why it is commonly used in plugin activation/deactivation hooks:

register_deactivation_hook( __FILE__, 'flush_rewrite_rules' );
register_activation_hook( __FILE__, 'cyb_activation_hook' );
function cyb_activation_hook() {
    flush_rewrite_rules();
}

Rewrite rules can be flushed also in “Settings -> Permalinks”; just click “Save” button and rewrite are rebuilt.