Check for Ruby Gem availability

user_31667 0
Viewed 24270

Is there a way to check if some gem is currently installed, via the Gem module? From ruby code, not by executing 'gem list'...

To clarify - I don't want to load the library. I just want to check if it's available, so all the rescue LoadError solutions don't help me. Also I don't care if the gem itself will work or not, only whether it's installed.

gem rubygems package ruby
7 Answers

IMHO the best way is to try to load/require the GEM and rescue the Exception, as Ray has already shown. It's safe to rescue the LoadError exception because it's not raised by the GEM itself but it's the standard behavior of the require command.

You can also use the gem command instead.

begin
  gem "somegem"
  # with requirements
  gem "somegem", ">=2.0"
rescue Gem::LoadError
  # not installed
end

The gem command has the same behavior of the require command, with some slight differences. AFAIK, it still tries to autoload the main GEM file.

Digging into the rubygems.rb file (line 310) I found the following execution

matches = Gem.source_index.find_name(gem.name, gem.version_requirements)
report_activate_error(gem) if matches.empty?

It can provide you some hints about how to make a dirty check without actually loading the library.

user_1235270

You could:

begin
  require "somegem"
rescue LoadError
  # not installed
end

This wouldn't, however, tell you if the module was installed through gem or some other means.

user_1077160

Didn't see this anywhere here, but you can also pass fuzzy version strings to find_by_name and find_all_by_name:

Gem::Specification.find_all_by_name('gemname', '>= 4.0').any?
user_3724790
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