IRB customization in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

IRB Prompt Customization Output

What will be the output of the following IRB prompt customization code snippet when you start IRB?

Ruby

IRB.conf[:PROMPT][:MY_PROMPT] = {
  PROMPT_I: "myirb> ",
  PROMPT_S: "myirb%l> ",
  PROMPT_C: "myirb* ",
  PROMPT_N: "myirb? ",
  RETURN: "=> %s\n"
}
IRB.conf[:PROMPT_MODE] = :MY_PROMPT

# Then start IRB

A The IRB prompt will show as 'myirb> ' for input lines.

B The IRB prompt will show as the default 'irb(main):001:0> '.

C The IRB prompt will show as '>> ' for input lines.

D The IRB prompt will be empty with no visible prompt.

💡 Hint

Look at the PROMPT_I key in the custom prompt hash and the PROMPT_MODE setting.

Setting IRB.conf[:PROMPT][:MY_PROMPT] defines a new prompt style named MY_PROMPT. Assigning IRB.conf[:PROMPT_MODE] = :MY_PROMPT activates it. PROMPT_I defines the main input prompt string, so the prompt will show as 'myirb> '.

🧠 Conceptual

intermediate

Purpose of IRB.conf[:SAVE_HISTORY]

What is the purpose of setting IRB.conf[:SAVE_HISTORY] = 1000 in IRB customization?

A It changes the prompt to show the last 1000 commands.

B It disables saving any command history in IRB.

C It sets the maximum number of concurrent IRB sessions to 1000.

D It limits the number of lines saved in the IRB command history to 1000.

💡 Hint

Think about what 'SAVE_HISTORY' might control in a command line tool.

IRB.conf[:SAVE_HISTORY] controls how many commands IRB remembers in its history file. Setting it to 1000 means IRB will save the last 1000 commands entered.

🔧 Debug

advanced

Fixing IRB Custom Prompt Syntax Error

This IRB customization code causes a syntax error. Which option fixes it correctly?

Ruby

IRB.conf[:PROMPT][:CUSTOM] = {
  PROMPT_I: '>> ',
  PROMPT_S: '>> ',
  PROMPT_C: '>> ',
  PROMPT_N: '>> ',
  RETURN: '=> %s\n'
}
IRB.conf[:PROMPT_MODE] = :CUSTOM

A Add a comma after the PROMPT_N line to separate the hash entries.

B Replace all single quotes with double quotes.

C Remove the RETURN key from the hash.

D Change the hash braces {} to square brackets [].

💡 Hint

Look carefully at the commas between hash entries in Ruby syntax.

In Ruby hashes, each key-value pair must be separated by a comma. The missing comma after PROMPT_N causes a syntax error. Adding it fixes the problem.

❓ Predict Output

advanced

IRB History File Location

Given this IRB configuration snippet, what will be the path of the history file used by IRB?

Ruby

IRB.conf[:HISTORY_FILE] = File.expand_path('~/.my_irb_history')

A The history file will be saved as 'history.txt' in the home directory.

B The history file will be saved in the current working directory as '.my_irb_history'.

C The history file will be saved as '.my_irb_history' in the user's home directory.

D IRB will not save any history file with this setting.

💡 Hint

File.expand_path with '~' expands to the user's home directory.

File.expand_path('~/.my_irb_history') resolves to the full path of the file named '.my_irb_history' inside the user's home directory. IRB will use this file to save command history.

🚀 Application

expert

Custom IRB Prompt with Dynamic Time

Which option correctly defines a custom IRB prompt that shows the current time before the prompt symbol?

A

IRB.conf[:PROMPT][:TIME_PROMPT] = {
  PROMPT_I: proc { "[Time.now] irb> " },
  PROMPT_S: 'irb%l> ',
  PROMPT_C: 'irb* ',
  PROMPT_N: 'irb? ',
  RETURN: '=> %s\n'
}
IRB.conf[:PROMPT_MODE] = :TIME_PROMPT

B

IRB.conf[:PROMPT][:TIME_PROMPT] = {
  PROMPT_I: -> { "[#{Time.now.strftime('%H:%M:%S')}] irb> " },
  PROMPT_S: 'irb%l> ',
  PROMPT_C: 'irb* ',
  PROMPT_N: 'irb? ',
  RETURN: '=> %s\n'
}
IRB.conf[:PROMPT_MODE] = :TIME_PROMPT

C

IRB.conf[:PROMPT][:TIME_PROMPT] = {
  PROMPT_I: "[#{Time.now.strftime('%H:%M:%S')}] irb> ",
  PROMPT_S: 'irb%l> ',
  PROMPT_C: 'irb* ',
  PROMPT_N: 'irb? ',
  RETURN: '=> %s\n'
}
IRB.conf[:PROMPT_MODE] = :TIME_PROMPT

D

IRB.conf[:PROMPT][:TIME_PROMPT] = {
  PROMPT_I: '[Time.now] irb> ',
  PROMPT_S: 'irb%l> ',
  PROMPT_C: 'irb* ',
  PROMPT_N: 'irb? ',
  RETURN: '=> %s\n'
}
IRB.conf[:PROMPT_MODE] = :TIME_PROMPT

💡 Hint

The prompt string must be a callable (like a lambda) to update dynamically each time.

To have a dynamic prompt showing current time, PROMPT_I must be a lambda or proc that returns the string with the current time. Option B uses a lambda with Time.now.strftime to format time dynamically. Other options use static strings or incorrect syntax.