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Plugin API/Filter Reference/the permalink

the_permalink is a filter applied to the permalink URL for a post prior to printing by the function the_permalink.

$url

(string) (required) The post URL

Default: None

Append the query string for the current page to permalink URLs (uses add_query_arg):

function append_query_string($url) {
    return add_query_arg($_GET, $url);
}
add_filter('the_permalink', 'append_query_string');

This filter is applied by: