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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.
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The Gem command is included with Ruby 1.9+ now, and is a standard addition to Ruby pre-1.9. Because local_gems relies on group_by , it returns a hash of the gems, where the key is the gem's name, and the value is an array of the gem specifications.
Since your goal is to verify a gem is installed with the correct version, use gem list . You can limit to the specific gem by using gem list data_mapper . To verify that it's installed and working, you'll have to try to require the gem and then use it in your code.
Using gem, the closest I can get is gem list -d [gemname] , which appears to list only the latest version installed.
When you use the --user-install option, RubyGems will install the gems to a directory inside your home directory, something like ~/. gem/ruby/1.9. 1 . The commands provided by the gems you installed will end up in ~/.
In Ruby 1.9.3 only there is also:
Gem.available?('somegem') You can use regex expressions too. Handy if I want to allow 'rcov' and GitHub variants like 'relevance-rcov':
Gem.available?(/-?rcov$/) Looking at the Gem API documentation, using Gem::Specification::find_all_by_name to test for gem availability seems reasonable.
if Gem::Specification::find_all_by_name('gemname').any? do stuff end find_all_by_name always returns an array (of Specification objects), as opposed to find_by_name which raises an exception if no match is found.
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