Bundle exec for isolated execution in Ruby - Practice Problems & Coding Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this Ruby code using bundle exec?

Consider you have a Gemfile specifying gem 'colorize', version '0.8.1'. You run the following Ruby script with bundle exec ruby script.rb:

Ruby

require 'colorize'
puts 'Hello'.colorize(:red)

A Raises LoadError because colorize gem is not found

B Prints 'Hello' without color

C Prints 'Hello' in red color in the terminal

D SyntaxError due to incorrect gem usage

💡 Hint

Using bundle exec ensures gems from Gemfile are loaded correctly.

Using bundle exec runs the script with the gems specified in the Gemfile, so 'colorize' gem version 0.8.1 is loaded and the string prints in red.

🧠 Conceptual

intermediate

Why use bundle exec when running Ruby scripts?

Choose the best reason why bundle exec is used before running Ruby commands.

A To run the command with gems specified in the Gemfile, avoiding conflicts with system gems

B To speed up Ruby script execution by caching gems

C To run the script without loading any gems

D To automatically update all gems before running the script

💡 Hint

Think about gem versions and conflicts.

bundle exec runs commands using the gems and versions locked in the Gemfile.lock, preventing conflicts with other installed gems.

🔧 Debug

advanced

What error occurs when running a Ruby script without bundle exec?

Given a project with a Gemfile specifying 'nokogiri' version 1.12.5, running ruby script.rb (without bundle exec) causes an error. What is the most likely error?

Ruby

require 'nokogiri'
puts Nokogiri::VERSION

A SyntaxError: unexpected end-of-input

B RuntimeError: gem version mismatch

C NoMethodError: undefined method 'VERSION' for Nokogiri:Module

D LoadError: cannot load such file -- nokogiri

💡 Hint

Without bundle exec, Ruby might not find the gem installed for this project.

Without bundle exec, Ruby uses system gems which may not include the required version or gem, causing LoadError.

📝 Syntax

advanced

Which command correctly runs a Rake task using bundle exec?

You want to run the Rake task named 'db:migrate' using bundle exec. Which command is correct?

A bundle exec rake db:migrate

B rake bundle exec db:migrate

C bundle rake exec db:migrate

D exec bundle rake db:migrate

💡 Hint

bundle exec should come before the command you want to run.

The correct syntax is 'bundle exec' followed by the command and its arguments.

🚀 Application

expert

How many gems are loaded when running bundle exec ruby script.rb with this Gemfile?

Given this Gemfile content:

source 'https://rubygems.org'
gem 'rails', '7.0.4'
gem 'puma', '~> 5.0'
gem 'nokogiri', '1.12.5'

And bundle install was run successfully. How many gems (including dependencies) are loaded when running bundle exec ruby script.rb?

A Exactly 3 gems only

B Only the gems explicitly required in script.rb

C At least 3 gems plus all their dependencies

D No gems are loaded automatically

💡 Hint

Bundler sets up the environment but does not automatically load (require) the gems; only those required in the script are loaded.

`bundle exec ruby script.rb` uses Bundler to set the correct LOAD_PATH for gems in Gemfile.lock. Gems are only loaded when explicitly required in script.rb, ensuring the correct versions and their dependencies are used.

Practice

1.

What is the main purpose of using bundle exec in a Ruby project?

easy

A. To create a new Ruby project with default settings

B. To update all gems to their latest versions globally

C. To uninstall unused gems from the system

D. To run commands using only the gems specified in the project's Gemfile

Solution

1. Step 1: Understand the role of bundle exec

   bundle exec runs commands using the gems listed in the project's Gemfile, isolating from other system gems.

2. Step 2: Compare options

   Options B, C, and D describe different gem or project management tasks unrelated to isolated execution.

3. Final Answer:

   To run commands using only the gems specified in the project's Gemfile -> Option D

4. Quick Check:

   bundle exec isolates gems = A [OK]

Hint: Remember: bundle exec uses project gems only, avoiding conflicts [OK]

Common Mistakes:

• Thinking bundle exec updates gems
• Confusing bundle exec with gem uninstall
• Assuming bundle exec creates projects

2.

Which of the following is the correct syntax to run a Ruby script app.rb using bundle exec?

easy

A. bundle exec ruby app.rb

B. ruby bundle exec app.rb

C. bundle ruby exec app.rb

D. exec bundle ruby app.rb

Solution

1. Step 1: Recall correct command order

   The correct syntax places bundle exec before the command to run, here ruby app.rb.

2. Step 2: Validate options

   Only bundle exec ruby app.rb correctly places bundle exec before ruby app.rb. Others mix order incorrectly.

3. Final Answer:

   bundle exec ruby app.rb -> Option A

4. Quick Check:

   bundle exec before command = C [OK]

Hint: Put 'bundle exec' right before the command you want to run [OK]

Common Mistakes:

• Swapping order of bundle exec and ruby
• Inserting exec or bundle in wrong places
• Omitting bundle exec entirely

3.

Given a Ruby project with a Gemfile specifying rspec version 3.10.0, what will be the output of running rspec --version vs bundle exec rspec --version if the system has rspec 4.0.0 installed globally?

medium

A. rspec --version shows 4.0.0, bundle exec rspec --version shows 3.10.0

B. rspec --version shows 3.10.0, bundle exec rspec --version shows 4.0.0

C. Both commands show 4.0.0

D. Both commands show 3.10.0

Solution

1. Step 1: Understand gem version usage

   Running rspec --version uses the system's global gem version, which is 4.0.0 here.

2. Step 2: Effect of bundle exec

   bundle exec rspec --version runs using the project's Gemfile version, 3.10.0, isolating from global gems.

3. Final Answer:

   rspec --version shows 4.0.0, bundle exec rspec --version shows 3.10.0 -> Option A

4. Quick Check:

   bundle exec uses Gemfile version = D [OK]

Hint: Without bundle exec uses global gems; with it uses project gems [OK]

Common Mistakes:

• Assuming both commands show same version
• Confusing global and project gem versions
• Ignoring Gemfile gem isolation

4.

Consider this command run inside a Ruby project folder:
rspec spec/test_spec.rb
The test fails due to a gem version conflict. How can you fix this using bundle exec?

medium

A. Run gem install rspec to update the gem globally

B. Run bundle exec rspec spec/test_spec.rb to use project gems

C. Run rspec --update to fix conflicts automatically

D. Delete the Gemfile and try again

Solution

1. Step 1: Identify cause of failure

   Failure is due to gem version conflict between global and project gems.

2. Step 2: Use bundle exec to isolate gems

   Running bundle exec rspec spec/test_spec.rb forces use of project Gemfile gems, resolving conflicts.

3. Final Answer:

   Run bundle exec rspec spec/test_spec.rb to use project gems -> Option B

4. Quick Check:

   bundle exec fixes gem conflicts = A [OK]

Hint: Use bundle exec before commands to fix gem conflicts [OK]

Common Mistakes:

• Trying to update gems globally instead of isolating
• Using invalid rspec options
• Deleting Gemfile which breaks project setup

5.

You have a Ruby project with multiple gems and versions specified in the Gemfile. You want to run a custom Ruby script script.rb that depends on these gems. Which command ensures your script uses the correct gem versions and avoids conflicts?

hard

A. ruby script.rb

B. gem install script.rb

C. bundle exec ruby script.rb

D. bundle install script.rb

Solution

1. Step 1: Understand gem version isolation need

   Running ruby script.rb alone may use system gems, causing version conflicts.

2. Step 2: Use bundle exec to run script with project gems

   bundle exec ruby script.rb runs the script using gems specified in the Gemfile, ensuring correct versions.

3. Step 3: Eliminate incorrect options

   gem install script.rb and bundle install script.rb are invalid commands for running scripts.

4. Final Answer:

   bundle exec ruby script.rb -> Option C

5. Quick Check:

   Use bundle exec to run scripts with project gems = B [OK]

Hint: Always prefix scripts with bundle exec to use project gems [OK]

Common Mistakes:

• Running scripts without bundle exec causing conflicts
• Confusing gem install with running scripts
• Trying to bundle install a script file