scaffold command does not work with Rails 4.2.2 -

i'm trying generate rails app scaffold command in every beginner's tutorial:

rails generate scaffold post name:string title:string content:text 

i'm getting junk:

>     usage: >       rails new app_path [options] >      >     options: >       -r, [--ruby=path]                                      # path ruby binary of choice >                                                              # default: /users/etayluz/.rvm/rubies/ruby-2.2.1/bin/ruby >       -m, [--template=template]                              # path application template (can filesystem path or url) 

what missing here?

you cannot create rails app scaffold command. first create new rails application using

rails new app_name 

then use scaffold command generate migration file, model, controller etc