code: func getPrivKey(ctx *cli.Context) *ecdsa.PrivateKey {
  	// booting up the swarm node just as we do in bzzd action
  	bzzconfig, err := buildConfig(ctx)
  	if err != nil {
  		utils.Fatalf("unable to configure swarm: %v", err)
  	}
  	cfg := defaultNodeConfig
  	if _, err := os.Stat(bzzconfig.Path); err == nil {
  		cfg.DataDir = bzzconfig.Path
  	}
  	utils.SetNodeConfig(ctx, &cfg)
  	stack, err := node.New(&cfg)
  	if err != nil {
  		utils.Fatalf("can't create node: %v", err)
  	}
  	defer stack.Close()
  
  	return getAccount(bzzconfig.BzzAccount, ctx, stack)
  }
docs: // getPrivKey returns the private key of the specified bzzaccount
  // Used only by client commands, such as `feed`