WP_CLI::log PHP Method

    public static function log($message)
    {
        self::$logger->info($message);
    }

 /**
  * Migrate meta values to taxonomy terms. Delete meta after import
  *
  * ## OPTIONS
  *
  * <meta-key>
  * : Meta key to convert
  *
  * <taxonomy-slug>
  * : Taxonomy to move values into
  *
  * [--<field>=<value>]
  * : One or more args to pass to WP_Query.
  *
  * ## EXAMPLES
  *
  *     wp mtt migrate meta_key taxonomy_slug
  *     wp mtt migrate meta_key taxonomy_slug --posts_per_page=200 --paged=2
  *
  */
 function migrate($args, $assoc_args)
 {
     list($meta_key, $taxonomy) = $args;
     if (!($taxonomy_object = get_taxonomy($taxonomy))) {
         WP_CLI::error(sprintf("The taxonomy '%s' doesn't exist", $taxonomy));
     }
     $defaults = array('post_type' => $taxonomy_object->object_type, 'posts_per_page' => -1, 'post_status' => 'any');
     $query_args = array_merge($defaults, $assoc_args);
     $query = new WP_Query($query_args);
     // summary
     WP_CLI::log(sprintf("---\nPer page: %d \nPage: %d \nTotal pages: %d\n---", $query_args['posts_per_page'], isset($query_args['paged']) ? $query_args['paged'] : 1, $query->max_num_pages));
     while ($query->have_posts()) {
         $query->the_post();
         $id = get_the_id();
         // get meta
         $metas = get_post_meta($id, $meta_key);
         // create term
         if (!$metas) {
             WP_CLI::log(WP_CLI::colorize("%c[{$id}]%n No meta, skipped"));
         } else {
             if (!is_wp_error(wp_set_object_terms($id, $metas, $taxonomy, true))) {
                 WP_CLI::log(WP_CLI::colorize("%g[{$id}]%n Migrated: " . implode(', ', $metas)));
                 // clean meta
                 delete_post_meta($id, $meta_key);
             } else {
                 WP_CLI::log(WP_CLI::colorize("%r[{$id}]%n Error: Could not set terms for post"));
             }
         }
     }
 }