Free

/**
 * Search by product SKU
 */
function wpninja_product_search_sku( $join, $query ) {
	if ( ! $query->is_main_query() || is_admin() || ! is_search() || ! is_woocommerce() ) {
		return $join;
	}

	global $wpdb;

	$join .= " LEFT JOIN {$wpdb->postmeta} wpninja_post_meta ON {$wpdb->posts}.ID = wpninja_post_meta.post_id ";

	return $join;
}

add_filter( 'posts_join', 'wpninja_product_search_sku', 10, 2 );

/**
 * Modify the search query with posts_where.
 */
function wpninja_product_search_where( $where, $query ) {
	if ( ! $query->is_main_query() || is_admin() || ! is_search() || ! is_woocommerce() ) {
		return $where;
	}

	global $wpdb;

	$where = preg_replace(
		"/\(\s*{$wpdb->posts}.post_title\s+LIKE\s*(\'[^\']+\')\s*\)/",
		"({$wpdb->posts}.post_title LIKE $1) OR (wpninja_post_meta.meta_key = '_sku' AND wpninja_post_meta.meta_value LIKE $1)", $where );

	return $where;
}

add_filter( 'posts_where', 'wpninja_product_search_where', 10, 2 );

//Show SKU above the product title
function fdesign_show_sku(){
    global $product;
    echo '<small>Cikkszám:</small> <small>' . $product->get_sku() .'</small>';
}
add_action( 'woocommerce_before_single_product_summary', 'fdesign_show_sku', 5 );

//Show Product Search in Header
function new_nav_menu_items($items, $args) {
    
    $my_product_search = get_product_search_form( $echo );
    
    if($args->theme_location == 'main_navigation'){
       $items = $items . $my_product_search;
    }

    return $items;
}
add_filter('wp_nav_menu_items', 'new_nav_menu_items', 10, 2);

jQuery(function($){
    $( "a.woocommerce-terms-and-conditions-link" ).unbind( "click" );
    $( "body" ).on('click', 'a.woocommerce-terms-and-conditions-link', function( event ) {

         $(this).attr("target", "_blank");
        window.open( $(this).attr("href"));

        return false;
    });

});