WP Function to show current online users

functions.php

/** WP Function to show current online users
 *
 * https://www.nuno-sarmento.com
*/

function  ns_user_online_update(){

	if ( is_user_logged_in()) {

		// get the user activity the list
		$logged_in_users = get_transient('online_status');

		// get current user ID
		$user = wp_get_current_user();

		// check if the current user needs to update his online status;
		// he does if he doesn't exist in the list
		$no_need_to_update = isset($logged_in_users[$user->ID])

		    // and if his "last activity" was less than let's say ...1 minutes ago
		    && $logged_in_users[$user->ID] >  (time() - (1 * 60));

		// update the list if needed
		if(!$no_need_to_update){
		  $logged_in_users[$user->ID] = time();
		  set_transient('online_status', $logged_in_users, (2*60)); // 2 mins
		}
	}
}
add_action( 'wp', 'ns_user_online_update' );

function ns_display_logged_in_users(){
	// get the user activity the list
	$logged_in_users = get_transient('online_status');

	if ( !empty( $logged_in_users ) ) {
		echo "<br/><strong>Logged in users are as following :</strong>";
			foreach ( $logged_in_users as $key => $value) {
					$user = get_user_by( 'id', $key );
					echo '<br/> Looged in user name is ' . $user->display_name;
			}
	} else{
		echo "<br/><strong>No user is logged in.</strong>";
	}

}

template-file.php

// Add the below to where you want to display the users

<?php ns_display_logged_in_users();	?>