code: public static void main(String[] argv) throws IOException {
      int ret;
      InstancedConfiguration conf = new InstancedConfiguration(ConfigurationUtils.defaults());
      if (!ConfigurationUtils.masterHostConfigured(conf)
          && argv.length > 0 && !argv[0].equals("help")) {
        System.out.println(ConfigurationUtils.getMasterHostNotConfiguredMessage("Alluxio fs shell"));
        System.exit(1);
      }
  
      // Reduce the RPC retry max duration to fall earlier for CLIs
      conf.set(PropertyKey.USER_RPC_RETRY_MAX_DURATION, "5s", Source.DEFAULT);
      try (FileSystemShell shell = new FileSystemShell(conf)) {
        ret = shell.run(argv);
      }
      System.exit(ret);
    }
docs: Main method, starts a new FileSystemShell.
  
  @param argv array of arguments given by the user's input from the terminal