How do I import ruby classes into the main file?

You need to instruct the Ruby runtime to load the file that contains your Book class. You can do this with require or require_relative.

The latter is better in this case, because it loads the file relative to the directory in which the file containing the require is specified. Since that's probably the same directory, you can just require_relative the file name, without the .rb extension by convention.

You can google 'require vs require_relative ruby' to find out more about the differences.

In order to include classes, modules, etc into other files you have to use require_relative or require (require_relative is more Rubyish.) For example this module:

module Format

  def green(input)
    puts"\e[32m#{input}[0m\e"
  end
end

Now I have this file:

require_relative "format" #<= require the file

include Format #<= include the module

def example
  green("this will be green") #<= call the formatting 
end

The same concept goes for classes:

class Example

  attr_accessor :input

  def initialize(input)
    @input = input
  end

  def prompt
    print "#{@input}: "
    gets.chomp
  end
end

example = Example.new(ARGV[0])

And now I have the main file:

require_relative "class_example"

example.prompt

In order to call any class, or module from another file, you have to require it.

I hope this helps, and answers your question.