Rails g migration doesn't work - ruby-on-rails

Question

When I run the command
rails g migration migration_name
I will get the "error" message:
Usage:
rails new APP_PATH [options]
Options:
-r, [--ruby=PATH] # Path to the Ruby binary of your choice
# Default: /Users/radek/.rvm/rubies/ruby-1.9.2-p290/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.
It's first time when I got this message. In other projects this command works well, but here I am still getting this message...
What caused that? Am I missing something?
(yes, I am in the root of the respective project)

Answer 1

You are not running it inside a rails generated project directory. You are running it outside it.
EDIT: It could also be if the script folder is missing. Or the rails script is missing inside the script folder if you are executing it inside the project folder.

Answer 2

I've got the same, and i fixed by doing :
cd /root/path/to/your/project
bundle install
bundle update
Voilà :)

Answer 3

Try adding a folder called script to your rails root.
in this folder add a file called rails and add to it
APP_PATH = File.expand_path('../../config/application', FILE)
require File.expand_path('../../config/boot', FILE)
require 'rails/commands'
and execute again
rails g migration migration_name