In Files

  • rubygems/core_ext/kernel_gem.rb
  • rubygems/core_ext/kernel_require.rb

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When RubyGems is required, Kernel#require is replaced with our own which is capable of loading gems on demand.

When you call require 'x', this is what happens:

  • If the file can be loaded from the existing Ruby loadpath, it is.

  • Otherwise, installed gems are searched for a file that matches. If it’s found in gem ‘y’, that gem is activated (added to the loadpath).

The normal require functionality of returning false if that file has already been loaded is preserved.

Public Instance Methods

gem_original_require(path) click to toggle source

The Kernel#require from before RubyGems was loaded.

Alias for: require

Private Instance Methods

gem(gem_name, *requirements) click to toggle source

Use #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 #gem, Kernel#require will do the right thing for you.

#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.

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

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.


GEM_SKIP=libA:libB ruby -I../libA -I../libB ./mycode.rb
               # File rubygems/core_ext/kernel_gem.rb, line 32
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"

    requirements = gem_name.requirement
    gem_name =

  spec =, *requirements).to_spec
  spec.activate if spec

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