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Blog ยป Switching gem libraries using update-alternatives
Posted on 15 Dec 2010 13:13
Maintaining more than one rails and gems library at your development machine using update-alternatives is possible. But note that it's better done with RVM nowadays… You can still ready this article to learn more about update-alternatives. UPDATE: Using Hobo Edge On Rails 3 describes installing gems for both Rails 2 and Rails 3 in addition to installing Hobo on Rails3 using rvm. It also solves the problem here better. Go and do it: exit(0).
I wanted to switch the whole bunch of gems while I am developing in Rails 2 or Rails 3. I want to keep both sets intact and I want to be able to switch instantly. I prefer to use different sets for Rails 2 and 3 instead of trying to do everything with one installation. update-alternatives solves the problem easily.
Caution The code below assumes that your gems are in /usr/lib/ruby/gems … However on some systems, the gems are in /var/lib/gems … Please check it first and change the code accordingly.
Just do sth like this to create your alternatives:
cd /usr/lib/ruby/ sudo cp -a gems gems.rails2.x sudo cp -a gems gems.rails3.x sudo mv gems gems.bak sudo update-alternatives --install /usr/lib/ruby/gems gems /usr/lib/ruby/gems.rails2.x 50 sudo update-alternatives --install /usr/lib/ruby/gems gems /usr/lib/ruby/gems.rails3.x 50
You can check what gems alternatives you have anytime:
update-alternatives --display gems
You can switch the current alternative:
sudo update-alternatives --config gems
Then you'll see such an alternative:
Selection Path Priority Status
------------------------------------------------------------
* 0 /usr/lib/ruby/gems.rails2.x 50 auto mode
1 /usr/lib/ruby/gems.rails2.x 50 manual mode
2 /usr/lib/ruby/gems.rails3.x 50 manual mode
What you say? Both directories are the same? Now switch your alternative and install things accordingly…
You can continue to create alternatives as you like… I would do that before upgrading all gems for example. You can keep edge and stable collections…
I suggest to append "update-alternatives —query gems" to your ~/bashrc so that you know where you are when starting your day.
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