How to run a .rb file from IRB?

You can "run" a file in irb by just requiring or loading it.

$ irb
>> load './filename.rb'

To change your current working directory within irb, you can use FileUtils:

>> require 'fileutils'
>> FileUtils.pwd # prints working directory
>> FileUtils.cd '/path/to/somewhere' # changes the directory

In case you want to have your file loaded in the irb session and you are using Ruby 2+ you can load a file in irb like this:

irb -r ./the_name_of_your_file.rb

This opens an irb session with the given file loaded.

Imagine you have file with a class like this:

class Example
  def initialize(name)
    @name = name
  end

  def print__example
    p name
  end
end

You will be able to use the Example class in the irb session.

We can just create a .rb file in the directory which you are currently working in using any text editor and type all the code in that and then use the command ruby filename.rb in the terminal, not in the irb, then it shows the output in irb.