Gem installation with gem install in Ruby - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is a Ruby gem?

A Ruby gem is a packaged library or tool that you can add to your Ruby programs to use extra features without writing them yourself.

beginner

What command do you use to install a gem?

You use gem install gem_name to download and install a gem on your system.

intermediate

How do you install a specific version of a gem?

Use gem install gem_name -v 'version_number' to install that exact version.

beginner

What does the gem list command do?

It shows all the gems currently installed on your system.

intermediate

Why might you need to use sudo with gem install?

Because installing gems system-wide may require administrator rights, so sudo gives permission to install.

Which command installs the 'rails' gem?

A gem install rails

B install gem rails

C rails gem install

D gem rails install

The correct syntax is gem install rails to install the 'rails' gem.

How do you check which gems are installed on your system?

A gem show

B gem check

C gem list

D gem status

gem list shows all installed gems.

What option installs version 2.1.0 of a gem named 'nokogiri'?

A gem install nokogiri --version 2.1.0

B gem install nokogiri -v '2.1.0'

C gem install nokogiri version 2.1.0

D gem install nokogiri v2.1.0

Use -v 'version_number' to specify the version.

Why might you need to run sudo gem install?

A To get administrator permission for system-wide gem installation

B To speed up the installation

C To uninstall gems

D To update Ruby itself

sudo gives permission to install gems system-wide.

What happens if you run gem install without a gem name?

A It updates Ruby

B It installs all available gems

C It lists installed gems

D It shows an error asking for a gem name

You must specify a gem name to install; otherwise, it shows an error.

Explain how to install a Ruby gem and check if it is installed.

Think about the commands you type in the terminal to add and see gems.

Describe why you might need to use sudo when installing gems and how to install a specific version.

Consider system permissions and gem version control.

Practice

1. What does the command gem install do in Ruby?

easy

A. It installs a Ruby gem (library) on your system.

B. It runs Ruby code inside the gem file.

C. It updates Ruby to the latest version.

D. It removes a gem from your system.

Solution

1. Step 1: Understand the purpose of gem install

   This command is used to add new Ruby libraries (called gems) to your system so you can use them in your programs.

2. Step 2: Differentiate from other gem commands

   Running code, updating Ruby, or removing gems are done by other commands, not gem install.

3. Final Answer:

   It installs a Ruby gem (library) on your system. -> Option A

4. Quick Check:

   gem install = installs gem [OK]

Hint: Remember: install adds gems, require uses them [OK]

Common Mistakes:

• Confusing gem install with running Ruby code
• Thinking gem install updates Ruby itself
• Mixing up install with gem uninstall

2. Which of the following is the correct syntax to install the gem named nokogiri?

easy

A. ruby gem install nokogiri

B. install gem nokogiri

C. gem install nokogiri

D. gem add nokogiri

Solution

1. Step 1: Recall the standard gem installation syntax

   The correct command to install a gem is gem install gem_name, so for nokogiri it is gem install nokogiri.

2. Step 2: Identify incorrect syntax options

   Options like install gem, gem add, or prefixing with ruby are not valid commands.

3. Final Answer:

   gem install nokogiri -> Option C

4. Quick Check:

   Correct syntax = gem install [OK]

Hint: Use 'gem install' followed by gem name [OK]

Common Mistakes:

• Swapping order of 'gem' and 'install'
• Using 'gem add' instead of 'gem install'
• Adding 'ruby' before the command

3. What will happen if you run this command in the terminal?

gem install rails

medium

A. It will install the Rails gem and its dependencies on your system.

B. It will start a new Rails project in the current folder.

C. It will update the Rails gem to the latest version.

D. It will uninstall the Rails gem from your system.

Solution

1. Step 1: Understand the command purpose

   gem install rails installs the Rails gem and any required supporting gems on your computer.

2. Step 2: Differentiate from other Rails commands

   Starting a project uses rails new, updating uses gem update, and uninstalling uses gem uninstall.

3. Final Answer:

   It will install the Rails gem and its dependencies on your system. -> Option A

4. Quick Check:

   gem install rails = install gem [OK]

Hint: Install adds gems; creating projects uses 'rails new' [OK]

Common Mistakes:

• Confusing gem install with project creation
• Thinking gem install updates gems
• Assuming gem install removes gems

4. You tried to install a gem using gem install sinatra but got an error saying command not found: gem. What is the most likely cause?

medium

A. The gem name 'sinatra' is misspelled.

B. The gem is already installed, so it cannot be installed again.

C. You need to use ruby gem install sinatra instead.

D. You ran the command inside Ruby code instead of the terminal.

Solution

1. Step 1: Understand the error message

   The error command not found: gem means the system does not recognize the gem command where it was run.

2. Step 2: Identify correct usage context

   gem install must be run in the terminal (command line), not inside Ruby code or IRB.

3. Final Answer:

   You ran the command inside Ruby code instead of the terminal. -> Option D

4. Quick Check:

   Run gem commands in terminal, not Ruby code [OK]

Hint: Run gem commands in terminal, not inside Ruby scripts [OK]

Common Mistakes:

• Trying to run gem install inside Ruby code
• Adding 'ruby' before gem install command
• Assuming gem install fails if gem exists

5. You want to install the gem httparty but only for your current project, not system-wide. Which command should you use?

hard

A. gem install httparty --global

B. gem install httparty --user-install

C. gem install httparty --system

D. gem install httparty --local

Solution

1. Step 1: Understand gem installation scopes

   By default, gem install installs gems system-wide. To install only for the current user (project scope), use --user-install.

2. Step 2: Eliminate incorrect options

   --system installs system-wide, --global is not a valid gem option, and --local installs from local files, not scope.

3. Final Answer:

   gem install httparty --user-install -> Option B

4. Quick Check:

   Use --user-install for user-only gem install [OK]

Hint: Add --user-install to install gem only for current user [OK]

Common Mistakes:

• Using --system to limit install scope
• Confusing --local with user install
• Assuming --global is a valid option