Before checking the version, ensure RubyGems is installed by running:

which gem

This should return the path to your gem executable, typically something like /usr/bin/gem or /home/username/.rbenv/shims/gem.

The standard command to check your RubyGems version is:

gem --version

This will output the version number directly, for example:

3.2.3

For more comprehensive information including Ruby version and platform details:

gem env

This displays output similar to:

RubyGems Environment:
  - RUBYGEMS VERSION: 3.2.3
  - RUBY VERSION: 2.7.0 (2019-12-25 patchlevel 0) [x86_64-linux]
  - INSTALLATION DIRECTORY: /usr/local/lib/ruby/gems/2.7.0
  - USER INSTALLATION DIRECTORY: /home/user/.gem/ruby/2.7.0
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-linux
  - GEM PATHS:
     - /usr/local/lib/ruby/gems/2.7.0
     - /home/user/.gem/ruby/2.7.0
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - https://rubygems.org/
  - SHELL PATH:
     - /usr/local/sbin
     - /usr/local/bin
     - /usr/sbin
     - /usr/bin
     - /sbin
     - /bin

If you're using RVM or rbenv, you can check versions for different Ruby installations:

rvm list gemsets

Or for rbenv:

rbenv versions

Then check the version for each Ruby installation:

rbenv global 2.7.0
gem --version

If you need to update RubyGems:

gem update --system

You may need sudo privileges for system-wide installation:

sudo gem update --system

If you encounter the "command not found" error:

sudo apt install ruby-full

This installs Ruby along with RubyGems on Ubuntu.

When writing scripts that require specific RubyGems versions:

if Gem::Version.new(Gem::VERSION) < Gem::Version.new('3.0.0')
  abort "RubyGems 3.0.0 or later required"
end

---

The simplest way to check your RubyGems version is through the terminal. Open your Ubuntu terminal and run:

gem --version

This will output the currently installed version, for example:

3.1.6

For more detailed information about your RubyGems installation, use:

gem env

This command displays comprehensive environment information including:

• RubyGems version
• Installation directory
• Ruby version compatibility
• Configuration details

You can also verify the version through IRB (Interactive Ruby):

irb
require 'rubygems'
Gem::VERSION

This method is particularly useful when debugging Ruby scripts that depend on specific gem versions.

To see which version is available in Ubuntu's official repositories:

apt-cache policy rubygems

This helps determine if you're using the system-packaged version or a manually installed one.

When working with multiple Ruby projects, consider using a version manager:

rvm rubygems current
# or
rbenv gemset list

These tools help maintain different RubyGems versions for different projects.