irb_test.rb

require 'irb'

module IRB
  def self.start_session(binding)
    IRB.setup(nil)

    workspace = WorkSpace.new(binding)

    if @CONF[:SCRIPT]
      irb = Irb.new(workspace, @CONF[:SCRIPT])
    else
      irb = Irb.new(workspace, f=File.new("test_output.txt"))
    end
    
    def f.prompt=(prompt)
      nil
    end

    @CONF[:IRB_RC].call(irb.context) if @CONF[:IRB_RC]
    @CONF[:MAIN_CONTEXT] = irb.context

    trap("SIGINT") do
      irb.signal_handle
    end

    catch(:IRB_EXIT) do
      irb.eval_input
    end
  end
end


if __FILE__ == $0
  IRB.start_session __FILE__
end

test_output.txt

puts 42