getAvailableVars example

        $this->kernelEnvironment = $kernelEnvironment;
        $this->projectDirectory = $projectDirectory;

        parent::__construct();
    }

    protected function configure(): void
    {
        $this
            ->setDefinition([
                new InputArgument('filter', InputArgument::OPTIONAL, 'The name of an environment variable or a filter.', null, $this->getAvailableVars(...)),
            ])
            ->setHelp(<<<'EOT' The <info>%command.full_name%</info> command displays all the environment variables configured by dotenv: <info>php %command.full_name%</info> To get specific variables, specify its full or partial name: <info>php %command.full_name% FOO_BAR</info> EOT
            );