Title: Negating certain words from a custom rewrite expression?
Last modified: August 19, 2016

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# Negating certain words from a custom rewrite expression?

 *  [naifam](https://wordpress.org/support/users/naifam/)
 * (@naifam)
 * [15 years, 12 months ago](https://wordpress.org/support/topic/expression-for-a-custom-rewrite/)
 * Hi. I have a WP page named Book (/book/) which displays a book in various languages.
   The language and chapter variables
    are passed as query variables. So the URL
   structure looks like:
 * /book/english/ (This displays a list of chapters in English)
    /book/english/foreword/(
   This displays the Foreword of the book in English)
 * Here is what I have come up with:
 *     ```
       add_action('init', 'book_init');
       add_filter('rewrite_rules_array', 'book_rewrite_rules_array');
       add_filter('query_vars', 'book_query_vars');
   
       function book_init() {
       	global $wp_rewrite;
       	$wp_rewrite->flush_rules();
       }
       function book_rewrite_rules_array($rewrite_rules) {
       	global $wp_rewrite;
       	$custom['(book)/(.+)/(.+)$'] = 'index.php?pagename=$matches[1]&book_language=$matches[2]&book_chapter=$matches[3]';
       	$custom['(book)/(.+)$'] = 'index.php?pagename=$matches[1]&book_language=$matches[2]';
       	return $custom + $rewrite_rules;
       }
       function book_query_vars($query) {
       	array_push($query, 'book_language', 'book_chapter');
       	return $query;
       }
       ```
   
 * Everything is working but the problem is that, the rewrite rules I have added
   are also catching /book/feed/ which I don’t
    want. So I am looking for an expression
   which would negate feed from `'(book)/(.+)/(.+)$'` and `'(book)/(.+)$'`
 * Also I want to know, if assume the query variables supplied are invalid, which
   filter should I use to check this in and how
    can I stop WP from continuing and
   instead make it send a 404 error and have it show the 404 page?

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 * 0 replies
 * 1 participant
 * Last reply from: [naifam](https://wordpress.org/support/users/naifam/)
 * Last activity: [15 years, 12 months ago](https://wordpress.org/support/topic/expression-for-a-custom-rewrite/)
 * Status: not resolved

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