Completely Disable Search in WordPress

To completely disable WordPress search, add the following code to your theme’s functions.php file:

<?php function sv_filter_query($query, $error = true) {
    if (is_search()) {
        $query->is_search = false;
        $query->query_vars[s] = false;
        $query->query[s] = false;
        if ($error == true)
            $query->is_404 = true;
    }
}

add_action('parse_query', 'sv_filter_query');
add_filter('get_search_form', create_function('$a', "return null;"));
    
function remove_search_widget() {
    unregister_widget('WP_Widget_Search');
}

add_action('widgets_init', 'remove_search_widget');