module Kernel

Use Kernel#gem to activate a specific version of gem_name.

requirements is a list of version requirements that the specified gem must match, most commonly “= example.version.number”. See Gem::Requirement for how to specify a version requirement.

If you will be activating the latest version of a gem, there is no need to call Kernel#gem, Kernel#require will do the right thing for you.

Kernel#gem returns true if the gem was activated, otherwise false. If the gem could not be found, didn’t match the version requirements, or a different version was already activated, an exception will be raised.

Kernel#gem should be called before any require statements (otherwise RubyGems may load a conflicting library version).

Kernel#gem only loads prerelease versions when prerelease requirements are given:

gem 'rake', '>= 1.1.a', '< 2'

In older RubyGems versions, the environment variable GEM_SKIP could be used to skip activation of specified gems, for example to test out changes that haven’t been installed yet. Now RubyGems defers to -I and the RUBYLIB environment variable to skip activation of a gem.

Example:

GEM_SKIP=libA:libB ruby -I../libA -I../libB ./mycode.rb

# File rubygems/core_ext/kernel_gem.rb, line 41
def gem(gem_name, *requirements) # :doc:
  skip_list = (ENV['GEM_SKIP'] || "").split(/:/)
  raise Gem::LoadError, "skipping #{gem_name}" if skip_list.include? gem_name

  if gem_name.kind_of? Gem::Dependency
    unless Gem::Deprecate.skip
      warn "#{Gem.location_of_caller.join ':'}:Warning: Kernel.gem no longer "\
        "accepts a Gem::Dependency object, please pass the name "\
        "and requirements directly"
    end

    requirements = gem_name.requirement
    gem_name = gem_name.name
  end

  dep = Gem::Dependency.new(gem_name, *requirements)

  loaded = Gem.loaded_specs[gem_name]

  return false if loaded && dep.matches_spec?(loaded)

  spec = dep.to_spec

  if spec
    if Gem::LOADED_SPECS_MUTEX.owned?
      spec.activate
    else
      Gem::LOADED_SPECS_MUTEX.synchronize { spec.activate }
    end
  end
end