IRB customization in Ruby - Mini Project: Build & Apply

IRB Customization

📖 Scenario: You often use IRB (Interactive Ruby) to test small Ruby code snippets quickly. Customizing IRB can make your work easier and more fun by adding colors, changing prompts, or loading helpful methods automatically.

🎯 Goal: You will create a simple IRB configuration file that changes the prompt and adds a helper method to greet the user.

📋 What You'll Learn

Create a Ruby hash called IRB.conf with a nested hash for :PROMPT containing a custom prompt named :MY_PROMPT

Set the :MY_PROMPT prompt to show "MyIRB> " as the prompt string

Add a helper method called greet that takes a name parameter and returns "Hello, <name>!"

Print the result of calling greet("Friend") to show the greeting

💡 Why This Matters

🌍 Real World

Customizing IRB helps Ruby developers work faster and more comfortably by tailoring the interactive console to their preferences.

💼 Career

Many Ruby developers customize IRB or similar REPLs to improve productivity, making this skill useful for software development roles.

1

Create the IRB prompt configuration

Create a Ruby hash called IRB.conf with a nested hash for :PROMPT containing a custom prompt named :MY_PROMPT that has a key :PROMPT_I set to the string "MyIRB> ".

Ruby

# Your code here

Hint

Use a nested hash structure with keys :PROMPT and :MY_PROMPT. Set :PROMPT_I to "MyIRB> "

2

Add a helper method called greet

Define a method called greet that takes one parameter called name and returns the string "Hello, <name>!" where <name> is replaced by the parameter value.

Ruby

IRB = {} unless defined?(IRB)
IRB.conf = {
  PROMPT: {
    MY_PROMPT: {
      PROMPT_I: "MyIRB> "
    }
  }
}

# Your code here

Hint

Use string interpolation with #{name} inside double quotes to create the greeting.

3

Call the greet method with "Friend"

Call the method greet with the argument "Friend" and assign the result to a variable called message.

Ruby

IRB = {} unless defined?(IRB)
IRB.conf = {
  PROMPT: {
    MY_PROMPT: {
      PROMPT_I: "MyIRB> "
    }
  }
}

def greet(name)
  "Hello, #{name}!"
end

# Your code here

Hint

Assign the result of greet("Friend") to message.

4

Print the greeting message

Print the variable message to display the greeting.

Ruby

IRB = {} unless defined?(IRB)
IRB.conf = {
  PROMPT: {
    MY_PROMPT: {
      PROMPT_I: "MyIRB> "
    }
  }
}

def greet(name)
  "Hello, #{name}!"
end

message = greet("Friend")

# Your code here

Hint

Use puts message to print the greeting.

Practice

1. What is the main purpose of customizing the ~/.irbrc file in Ruby's IRB?

easy

A. To create new Ruby classes

B. To install new Ruby gems automatically

C. To change how the IRB shell looks and behaves

D. To compile Ruby code faster

Solution

1. Step 1: Understand the role of ~/.irbrc

   The ~/.irbrc file is used to customize the IRB shell environment.

2. Step 2: Identify customization effects

   Customizations include changing the prompt, loading libraries, and saving history, which affect how IRB looks and works.

3. Final Answer:

   To change how the IRB shell looks and behaves -> Option C

4. Quick Check:

   IRB customization = change shell behavior [OK]

Hint: Remember ~/.irbrc customizes IRB shell behavior [OK]

Common Mistakes:

• Thinking it installs gems automatically
• Confusing with Ruby code compilation
• Assuming it creates Ruby classes

2. Which of the following is the correct way to load the 'date' library automatically when IRB starts by editing ~/.irbrc?

easy

A. require 'date'

B. load 'date'

C. import 'date'

D. include 'date'

Solution

1. Step 1: Recall Ruby syntax for loading libraries

   Ruby uses require 'library_name' to load external libraries.

2. Step 2: Check each option

   require 'date' is correct; load expects a file path, import and include are incorrect here.

3. Final Answer:

   require 'date' -> Option A

4. Quick Check:

   Load library = require 'library' [OK]

Hint: Use require to load libraries in ~/.irbrc [OK]

Common Mistakes:

• Using import which is not Ruby syntax
• Using include which mixes modules, not load libs
• Using load without full file path

3. Given this ~/.irbrc snippet:

IRB.conf[:PROMPT_MODE] = :SIMPLE
IRB.conf[:SAVE_HISTORY] = 1000

What effect does this have when you start IRB?

medium

A. Disables command history and uses default prompt

B. Changes prompt color but does not save history

C. Causes a syntax error and IRB won't start

D. Sets a simple prompt and saves last 1000 commands in history

Solution

1. Step 1: Understand IRB.conf[:PROMPT_MODE]

   Setting :PROMPT_MODE to :SIMPLE changes IRB prompt to a simple style.

2. Step 2: Understand IRB.conf[:SAVE_HISTORY]

   Setting :SAVE_HISTORY to 1000 means IRB saves the last 1000 commands in history.

3. Final Answer:

   Sets a simple prompt and saves last 1000 commands in history -> Option D

4. Quick Check:

   Prompt = simple, History saved = 1000 [OK]

Hint: Look for keys in IRB.conf to know prompt and history settings [OK]

Common Mistakes:

• Thinking it disables history
• Assuming syntax error from valid config
• Confusing prompt style with color only

4. You wrote this in your ~/.irbrc file:

IRB.conf[:SAVE_HISTORY] = '1000'

But IRB does not save history as expected. What is the problem?

medium

A. The key :SAVE_HISTORY is invalid

B. The value should be an integer, not a string

C. IRB does not support saving history

D. You must restart the computer for changes to apply

Solution

1. Step 1: Check the data type of the value

   :SAVE_HISTORY expects an integer number, not a string.

2. Step 2: Identify the error cause

   Using a string like '1000' causes IRB to ignore the setting, so history is not saved.

3. Final Answer:

   The value should be an integer, not a string -> Option B

4. Quick Check:

   Integer value needed for history count [OK]

Hint: Use numbers, not strings, for numeric IRB config values [OK]

Common Mistakes:

• Using quotes around numbers
• Thinking IRB can't save history
• Believing a full restart is needed

5. You want to customize IRB so that it automatically requires the 'json' library, sets a custom prompt showing the current time, and saves 500 commands in history. Which ~/.irbrc snippet correctly does this?

hard

A. require 'json'
IRB.conf[:PROMPT][:CUSTOM] = { PROMPT_I: "[#{Time.now.strftime('%H:%M:%S')}] > " }
IRB.conf[:PROMPT_MODE] = :CUSTOM
IRB.conf[:SAVE_HISTORY] = 500

B. require 'json'
IRB.conf[:PROMPT_MODE] = :SIMPLE
IRB.conf[:SAVE_HISTORY] = '500'

C. load 'json'
IRB.conf[:PROMPT_MODE] = :DEFAULT
IRB.conf[:SAVE_HISTORY] = 500

D. require 'json'
IRB.conf[:PROMPT_MODE] = :CUSTOM
IRB.conf[:SAVE_HISTORY] = 1000

Solution

1. Step 1: Load the 'json' library correctly

   Use require 'json' to load the library automatically.

2. Step 2: Define a custom prompt with current time

   Set IRB.conf[:PROMPT][:CUSTOM] with a prompt string showing current time using Ruby's Time.now.strftime.

3. Step 3: Set prompt mode and save history

   Assign IRB.conf[:PROMPT_MODE] = :CUSTOM to use the custom prompt and set IRB.conf[:SAVE_HISTORY] = 500 as an integer to save 500 commands.

4. Final Answer:

   require 'json', custom prompt with current time, :CUSTOM mode, SAVE_HISTORY = 500 -> Option A

5. Quick Check:

   Require json, custom prompt with time, save 500 history [OK]

Hint: Combine require, custom prompt hash, and integer history save [OK]

Common Mistakes:

• Using string instead of integer for history
• Not defining custom prompt hash properly
• Using load instead of require for libraries