WP_Importer::set_blog() WordPress Method

	public function set_blog( $blog_id ) {
		if ( is_numeric( $blog_id ) ) {
			$blog_id = (int) $blog_id;
		} else {
			$blog   = 'http://' . preg_replace( '#^https?://#', '', $blog_id );
			$parsed = parse_url( $blog );
			if ( ! $parsed || empty( $parsed['host'] ) ) {
				fwrite( STDERR, "Error: can not determine blog_id from $blog_id\n" );
				exit;
			}
			if ( empty( $parsed['path'] ) ) {
				$parsed['path'] = '/';
			}
			$blogs = get_sites(
				array(
					'domain' => $parsed['host'],
					'number' => 1,
					'path'   => $parsed['path'],
				)
			);
			if ( ! $blogs ) {
				fwrite( STDERR, "Error: Could not find blog\n" );
				exit;
			}
			$blog    = array_shift( $blogs );
			$blog_id = (int) $blog->blog_id;
		}

		if ( function_exists( 'is_multisite' ) ) {
			if ( is_multisite() ) {
				switch_to_blog( $blog_id );
			}
		}

		return $blog_id;
	}