RubyGems adds the gem
method to allow activation of specific gem versions and overrides the require method on Kernel
to make gems appear as if they live on the $LOAD_PATH
. See the documentation of these methods for further detail.
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