GeKskill

add_filter( 'init', 'sku_from_title_and_variation', 10, 1);
function sku_from_title_and_variation(){
	set_time_limit(300);
$query = array(
    'numberposts' => -1,
    'post_status' => 'published',
    );
    $products = wc_get_products( $query );
	
    foreach ($products as $product) {
		
      if( $product->is_type('variable') ){
		  
		$product_id = $product->get_id();
		  
		$product_title = $product->get_title();
		  
		update_post_meta( $product_id, '_sku', $product_title );
		  
        wc_delete_product_transients( $product_id );
		  
        foreach( $product->get_available_variations() as $variation_values ){
			
          $variation_id = $variation_values['variation_id']; // variation id
		  $variation_attr = $variation_values['attributes'];
		  $variation_attr = $variation_attr['attribute_pa_variant'];
		  $variation_attr = get_term_by('slug', $variation_attr , 'pa_variant')->name;
			
          update_post_meta( $variation_id, '_sku', $product_title.$variation_attr );
			
          wc_delete_product_transients( $variation_id );
        }
        wc_delete_product_transients( $product->get_id() );
		  
      } else {
		  
		  update_post_meta( $product->get_id(), '_sku', $product->get_title());
		  
          wc_delete_product_transients( $product->get_id() );
      }
    }
  
}