IRB customization in Ruby - Step-by-Step Execution

Concept Flow - IRB customization

Start IRB session

↓

Load .irbrc file if exists

↓

Apply custom settings

↓

User enters commands

↓

Commands run with customizations

↓

Repeat until exit

When IRB starts, it looks for a .irbrc file to load custom settings before running user commands.

Execution Sample

Ruby

require 'irb'
IRB.conf[:PROMPT_MODE] = :SIMPLE
puts "Custom prompt set"
# Start IRB session
IRB.start

This code sets a simple prompt style in IRB and prints confirmation before starting IRB.

Execution Table

Step	Action	Evaluation	Result
1	IRB starts	Check for .irbrc file	Found .irbrc, load it
2	Load .irbrc	Execute custom code	Custom prompt set
3	Set IRB.conf[:PROMPT_MODE]	Assign :SIMPLE	Prompt style changed
4	User enters command	"puts 'Hello'"	Prints Hello
5	User enters command	"1 + 2"	Returns 3
6	User exits IRB	Exit command	IRB session ends

💡 User types exit or Ctrl+D to end IRB session

Variable Tracker

Variable	Start	After Step 2	After Step 3	Final
IRB.conf[:PROMPT_MODE]	default	default	:SIMPLE	:SIMPLE

Key Moments - 2 Insights

Why doesn't my IRB customization work when I start IRB?

Make sure your .irbrc file is in your home directory and has correct Ruby syntax. See step 1 and 2 in the execution_table where IRB loads .irbrc.

How do I change the IRB prompt style?

Set IRB.conf[:PROMPT_MODE] to a symbol like :SIMPLE or :DEFAULT in your .irbrc file as shown in step 3.

Visual Quiz - 3 Questions

Look at the execution_table, what is the value of IRB.conf[:PROMPT_MODE] after step 3?

A nil

B :DEFAULT

C :SIMPLE

D false

💡 Hint

Check variable_tracker row for IRB.conf[:PROMPT_MODE] after step 3

At which step does IRB load the .irbrc file?

A Step 2

B Step 1

C Step 3

D Step 4

💡 Hint

Look at the action column in execution_table for loading .irbrc

If you remove the .irbrc file, what happens at step 2?

A IRB loads default settings

B IRB skips customization

C IRB crashes

D IRB prompts for file location

💡 Hint

Step 2 shows loading .irbrc; no file means skipping customization

Concept Snapshot

IRB customization uses a .irbrc file in your home directory.
Put Ruby code there to change IRB behavior.
Common changes: prompt style, history saving.
IRB loads .irbrc automatically on start.
If no .irbrc, IRB uses defaults.
Use IRB.conf hash to set options.

Full Transcript

When you start IRB, it looks for a file named .irbrc in your home folder. If it finds this file, it runs the Ruby code inside it. This lets you change how IRB works, like changing the prompt style or saving command history. For example, setting IRB.conf[:PROMPT_MODE] to :SIMPLE changes the prompt to a simpler style. If IRB does not find .irbrc, it just uses the default settings. You can type commands as usual, and IRB will run them with your custom settings. To stop IRB, type exit or press Ctrl+D.