current user wordpress

function show_loggedin_function( $atts ) {

	global $current_user, $user_login;
	get_currentuserinfo();
	
	add_filter('widget_text', 'do_shortcode');
	if ($user_login) 
		return '<h4 class="logged-in-user">Hi ' . $current_user -> display_name . ' !</h4>';
	else
		return '<a href="' . wp_login_url() . ' ">Login</a>';
	
}
add_shortcode( 'show_loggedin_as', 'show_loggedin_function' );

//Shortcode
[show_loggedin_as]

$current_user_id = get_current_user_id();
$current_user = wp_get_current_user();