Question about output of swagger-codegen

Description

I am trying to run

swagger-codegen generate -i http://petstore.swagger.io/v2/swagger.json -l php -o ./petstore

My understanding is that it should build an ApliClient.php file, but I'm not seeing it after running the command. This appears to be the class that is used by the individual API files passed as an optional argument as seen here:

public function __construct(
        ClientInterface $client = null,
        Configuration $config = null,
        HeaderSelector $selector = null
    ) {
        $this->client = $client ?: new Client();
        $this->config = $config ?: new Configuration();
        $this->headerSelector = $selector ?: new HeaderSelector();
    }

Am I just misunderstanding something here or what is the trick to get the ApiClient.php file to be generated?

Swagger-codegen version

3.0.14 (installed via Homebrew)