pdo

/* Function */
function connectDatabase($host, $db, $user, $pass, $charset) {

$dsn = 'mysql:host=$host;dbname=$db;charset=$charset';
$opt = [
    \PDO::ATTR_ERRMODE            => \PDO::ERRMODE_EXCEPTION,
    \PDO::ATTR_DEFAULT_FETCH_MODE => \PDO::FETCH_ASSOC,
    \PDO::ATTR_EMULATE_PREPARES   => false,
];

try
{
   $pdo = new \PDO($dsn, $user, $pass, $opt);
}
catch (PDOException $e)
{
   echo $e->getMessage();
}

}

/* Variables */
$_base['host'] = 'localhost';
$_base['db'] = 'dbname';
$_base['user'] = 'username';
$_base['pass'] = 'password';
$_base['charset'] = 'utf8';

/* Execute */
connectDatabase($_base['host'], $_base['db'], $_base['user'], $_base['pass'], $_base['charset']);

Error:
SQLSTATE[HY000] [2005] Unknown MySQL server host '$host' (2)
Fatal error: Uncaught Error: Call to a member function prepare() on null in /public_html/functions/file:11 Stack trace: #0 /public_html/settings.php(10): functionusingpdo('4') #1 {main} thrown in /public_html/functions/is_teacher.php on line 11