Choose which database connection to run

so i'm having my database connection in my project. The file has a local and an online request, one is commented out when i work on localhost.

is there a way in php for it to look up which one it has to use?

like if url = localhost/blabla use local else use online?

Here is the connection.

try{
    //local connection
    $db = new PDO('mysql:host = 127.0.0.1; dbname=XXXX', 'root','');

    //local online
    //$db = new PDO('mysql:host = XXXXX; dbname=XXXXX', 'xxxxx','*****');

    $db->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
}catch(PDOException $e){
    echo $e->getMessage();
    die();
}
$db->exec("set names utf8");

if (session_status() == PHP_SESSION_NONE) {
    session_start();
}

Hope somone can help if it's possible, thanks