code: def get_command(options, vexrc, environ):
      
      command = options.rest
      if not command:
          command = vexrc.get_shell(environ)
      if command and command[0].startswith('--'):
          raise exceptions.InvalidCommand(
              "don't put flags like '%s' after the virtualenv name."
              % command[0])
      if not command:
          raise exceptions.InvalidCommand("no command given")
      return command
docs: Get a command to run.
  
      :returns:
          a list of strings representing a command to be passed to Popen.