code: func Env(env expand.Environ) func(*Runner) error {
  	return func(r *Runner) error {
  		if env == nil {
  			env = expand.ListEnviron(os.Environ()...)
  		}
  		r.Env = env
  		return nil
  	}
  }
docs: // Env sets the interpreter's environment. If nil, a copy of the current
  // process's environment is used.