Overview

Reading the code of irb.

Preparation

1. Clone the irb source code

• git clone git@github.com:ruby/irb.git

2. Modify the entry point Since the original state runs the irb located in the Ruby installation directory, we will run the local irb instead.

#!/usr/bin/env ruby
#
#   irb.rb - interactive ruby
#    by Keiju ISHITSUKA(keiju@ruby-lang.org)
#

$LOAD_PATH.unshift(File.expand_path("../lib", __dir__)) # Add this line
require "irb"

IRB.start(__FILE__)

3. Debug at any point

Code Reading

1. Executing the irb command

• ruby/irb/blob/master/exe/irb#L9
  • Executes IRB.start(__FILE__) with the filename of the executing file as an argument.

2. Setup process at startup

• ruby/irb/blob/master/lib/irb.rb#L895

3. Starting irb

• ruby/irb/blob/master/lib/irb.rb#L1001
  • Loads the history
    • History is the execution history of commands. It is written to a file (~/.irb_history).

4. Executing input values

• ruby/irb/blob/master/lib/irb.rb#L1041
• ruby/irb/blob/master/lib/irb/context.rb#L589
  • Processes are branched and executed based on the input values.
  • For expressions:
    • ruby/irb/blob/master/lib/irb/context.rb#L589
    • ruby/irb/blob/master/lib/irb/context.rb#L609
    • ruby/irb/blob/master/lib/irb/workspace.rb#L120
      • Evaluates the expression with eval.
  • For commands:
    • ruby/irb/blob/master/lib/irb/command/base.rb#L55
      • It was unclear what the command was, but it does not seem to be a feature for users.