code: func ShowCommandHelp(ctx *Context, command string) error {
  	// show the subcommand help for a command with subcommands
  	if command == "" {
  		HelpPrinter(ctx.App.Writer, SubcommandHelpTemplate, ctx.App)
  		return nil
  	}
  
  	for _, c := range ctx.App.Commands {
  		if c.HasName(command) {
  			if c.CustomHelpTemplate != "" {
  				HelpPrinterCustom(ctx.App.Writer, c.CustomHelpTemplate, c, nil)
  			} else {
  				HelpPrinter(ctx.App.Writer, CommandHelpTemplate, c)
  			}
  			return nil
  		}
  	}
  
  	if ctx.App.CommandNotFound == nil {
  		return NewExitError(fmt.Sprintf("No help topic for '%v'", command), 3)
  	}
  
  	ctx.App.CommandNotFound(ctx, command)
  	return nil
  }
docs: // ShowCommandHelp prints help for the given command