Set repo sub dir as rails base dir to launch

[Basten Gao]

I have a git repo, dir structure like this. These is a config to set sub dir "a_rails_app" as rails base for running rails commands ? This config seems like capistrano repo_tree.

/a_rails_app/
    - app/
    - config/
    - Gemfile
    - Gemfile.lock
/another_dir