code: def shell(
      state,
      fancy=False,
      shell_args=None,
      anyway=False,
  ):
      
      from ..core import load_dot_env, do_shell
  
      # Prevent user from activating nested environments.
      if "PIPENV_ACTIVE" in os.environ:
          # If PIPENV_ACTIVE is set, VIRTUAL_ENV should always be set too.
          venv_name = os.environ.get("VIRTUAL_ENV", "UNKNOWN_VIRTUAL_ENVIRONMENT")
          if not anyway:
              echo(
                  "{0} {1} {2}\nNo action taken to avoid nested environments.".format(
                      crayons.normal("Shell for"),
                      crayons.green(venv_name, bold=True),
                      crayons.normal("already activated.", bold=True),
                  ),
                  err=True,
              )
              sys.exit(1)
      # Load .env file.
      load_dot_env()
      # Use fancy mode for Windows.
      if os.name == "nt":
          fancy = True
      do_shell(
          three=state.three,
          python=state.python,
          fancy=fancy,
          shell_args=shell_args,
          pypi_mirror=state.pypi_mirror,
      )
docs: Spawns a shell within the virtualenv.