$host="aaaaa";
$dbname="aaaaa";
$user="aaaaa";
$pass="aaaaa";
try {
    # MS SQL Server and Sybase with PDO_DBLIB
    $dbh = new PDO("sqlsrv:Server=$host;Database=$dbname", $user, $pass);
} catch(PDOException $e) {
    echo $e->getMessage();
}