Global variable in controller laravel 8

I don't know Laravel at all, but in other Controller-based frameworks, a controller will only exist for the current request and then it dies afterwards, taking any variables with it.

So, in your example, if a client calls uploaderFils, the controller instance will die after that call ends, taking the value of $X with it. The client call to AddProduct gets a new controller instance with nothing in it, and $X will be empty.

You seem to be thinking in terms of a normal desktop application, not a web application. A web application is stateless, and works in a request->response paradigm. Once the response is sent back to the client, the controller no longer exists, and a new controller is created upon a new request.

You're also thinking in terms of a single-user application. Web apps are multi-user, so setting a "global" variable can be overwritten by a new user request.

If you want to save state between requests for individual users, you have to save that state information somewhere else, like a database, or cookies if the state is small enough. Laravel should have some mechanism to save state somewhere.