rails generate model - ruby-on-rails

Question

I'm trying to follow instructions from the book "Head First Rails" and on page 50 it says to create a model but I am unable to create a model using the rails command.
When I type this at this prompt: localhost:~ home$
rails generate model ad name:string description:text price:decimal seller_id:integer email:string img_url:string
I get this:
Usage:
rails new APP_PATH [options]
Options:
-r, [--ruby=PATH] # Path to the Ruby binary of your choice
# Default: /Users/home/.rvm/rubies/ruby-1.9.3-p125/bin/ruby
-b, [--builder=BUILDER] # Path to a application builder (can be a filesystem path or URL)
-m, [--template=TEMPLATE] # Path to an application template (can be a filesystem path or URL)
[--skip-gemfile] # Don't create a Gemfile
[--skip-bundle] # Don't run bundle install
-G, [--skip-git] # Skip Git ignores and keeps
-O, [--skip-active-record] # Skip Active Record files
-S, [--skip-sprockets] # Skip Sprockets files
-d, [--database=DATABASE] # Preconfigure for selected database (options: mysql/oracle/postgresql/sqlite3/frontbase/ibm_db/sqlserver/jdbcmysql/jdbcsqlite3/jdbcpostgresql/jdbc)
# Default: sqlite3
-j, [--javascript=JAVASCRIPT] # Preconfigure for selected JavaScript library
# Default: jquery
-J, [--skip-javascript] # Skip JavaScript files
[--dev] # Setup the application with Gemfile pointing to your Rails checkout
[--edge] # Setup the application with Gemfile pointing to Rails repository
-T, [--skip-test-unit] # Skip Test::Unit files
[--old-style-hash] # Force using old style hash (:foo => 'bar') on Ruby >= 1.9
Runtime options:
-f, [--force] # Overwrite files that already exist
-p, [--pretend] # Run but do not make any changes
-q, [--quiet] # Suppress status output
-s, [--skip] # Skip files that already exist
Rails options:
-h, [--help] # Show this help message and quit
-v, [--version] # Show Rails version number and quit
Description:
The 'rails new' command creates a new Rails application with a default
directory structure and configuration at the path you specify.
You can specify extra command-line arguments to be used every time
'rails new' runs in the .railsrc configuration file in your home directory.
Note that the arguments specified in the .railsrc file don't affect the
defaults values shown above in this help message.
Example:
rails new ~/Code/Ruby/weblog
This generates a skeletal Rails installation in ~/Code/Ruby/weblog.
See the README in the newly created application to get going.
localhost:~ home$
I am using Rails -v 3.2.8
and Ruby 1.9.3p125

Answer 1

The code is okay but you are in the wrong directory. You must run these commands inside your rails project-directory.
The normal way to get there from scratch is:
$ rails new PROJECT_NAME
$ cd PROJECT_NAME
$ rails generate model ad \
name:string \
description:text \
price:decimal \
seller_id:integer \
email:string img_url:string

Answer 2

The error shows you either didn't create the rails project yet or you're not in the rails project directory.
Suppose if you're working on myapp project. You've to move to that project directory on your command line and then generate the model. Here are some steps you can refer.
Example: Assuming you didn't create the Rails app yet:
$> rails new myapp
$> cd myapp
Now generate the model from your commandline.
$> rails generate model your_model_name

Answer 3

For me what happened was that I generated the app with rails new rails new chapter_2
but the RVM --default had rails 4.0.2 gem, but my chapter_2 project use a new
gemset with rails 3.2.16.
So when I ran
rails generate scaffold User name:string email:string
the console showed
Usage:
rails new APP_PATH [options]
So I fixed the RVM and the gemset with the rails 3.2.16 gem , and then generated the app again
then I executed
rails generate scaffold User name:string email:string
and it worked

Answer 4

You need to create new rails application first. Run
rails new mebay
cd mebay
bundle install
rails generate model ...
And try to find Rails 3 tutorial, there are a lot of changes since 2.1 Guides (http://guides.rubyonrails.org/getting_started.html) are good start point.