Ruby: Erb tag and when to use @

Variables prefixed with an @ are instance variables. You can use them if have defined the previously. Let's say you have a simple model:

class User < ActiveRecord::Base
  attr_accessible :email, :user_name
end

…then your controller may look like this:

class UsersController < ApplicationController
  def index
  @users = User.all
end

now, in your view you can use this instance variable, e.g.:

  We have <%= pluralize (@users.count, "user") %><br>
  Here's a list of all our users:
  <% @users.each do |user| %>
    <%= user.user_name %>
  <% end %>

Where these instance variables come from was a huge mistery for me when first trying to understand Rails code. The key is that you define these variables in the controller. I could just as easily have used @all_of_the_users instead of @users.

BTW: The last line has userwithout the @, because it's a local variable within the block of the .each method.