How to get pretty URLs with add_query_arg in permalinks

With add_query_arg() it is nice to add additional parameters to an URL and it is also easy to create a rewrite rule. So far so good. But the problem is the URL replacement done by wordpress.

When I have an URL, like:

www.mysite.com/?page_id=1&myvar=test

and I type this URL into the address line of the browser with activated permalinks. This link will become to:

www.example.com/pagename/?myvar=test

BUT: what I would like to get is:

www.example.com/pagename/test

Finally, I would like to use code like:

<a href="https://wordpress.stackexchange.com/questions/127141/<?php add_query_arg("myvar', 'test', get_permalink() ) ?>"> .... </a>

which would result in:

www.example.com/pagename/test

How can this be achieved? I have spent hours in reading documents and I couldn’t found a solution.

Just faced the same situation and stumbled upon this question while googling.

It seems like this isn’t possible. Core itself just appends strings to the URL if pretty permalinks are enabled, see https://core.trac.wordpress.org/browser/tags/3.9.1/src/wp-includes/link-template.php#L571

For anyone interested in this: You can do something like this in your code:

if ( '' != get_option('permalink_structure') ) {
    // using pretty permalinks, append to url
    $read = user_trailingslashit( get_permalink() . 'test' ); // www.example.com/pagename/test
  } else {
    $read = add_query_arg( 'test', '', get_permalink() ); // www.example.com/pagename/?test
  }

This solution is also was also recommended by Jon Cave in a comment on the official make blog: https://make.wordpress.org/plugins/2012/06/07/rewrite-endpoints-api/#comment-686