Ruby-on-rails – How to use RVM and create globally available gems

Where are my Gems?

You can find where your gems are stored using the gem environment command. For example:

chris@chris-laptop:~$ gem environment
RubyGems Environment:
  - RUBYGEMS VERSION: 1.3.2

  - RUBY VERSION: 1.8.7 (2008-08-11 patchlevel 72) [i486-linux]
  - INSTALLATION DIRECTORY: /usr/lib/ruby/gems/1.8
  - RUBY EXECUTABLE: /usr/bin/ruby1.8
  - EXECUTABLE DIRECTORY: /usr/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86-linux
  - GEM PATHS:
     - /usr/lib/ruby/gems/1.8
     - /home/chris/.gem/ruby/1.8
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:

If you look at the "GEM PATHS:" section you can see that gems can be stored in two places on my laptop: /usr/lib/ruby/gems/1.8 or in the .gem directory in my home dir.

You can also see that executables are stored in EXECUTABLE DIRECTORY which in this case is /usr/bin.

Because /usr/bin is in my path this lets me run cap, merb, rails etc.

Updating your PATH

If for some reason your EXECUTABLE DIRECTORY isn't on your path (for example if it is /var/lib/gems/1.8/bin) then you need to update your PATH variable.

Assuming that you are using the bash shell. You can do this quickly for the current session by typing the following at the shell prompt; let's pretend that you want to add /var/lib/gems/1.8/bin to the path:

export PATH=$PATH:/var/lib/gems/1.8/bin

and press return. That appends the new directory to the end of the current path. Note the colon between $PATH and /var/lib/gems/1.8/bin

To set the value for all sessions you will need to edit either your .profile or .bashrc file and add the same line to the end of the file. I usually edit my .bashrc file for no reason other than that's what I've always done. When finished, save the file and then refresh your environment by typing:

bash

at the shell prompt. That will cause the .bashrc to get reread.

At any point you can check the current value of $PATH by typing

echo $PATH

at the shell prompt.

Here's a sample from one of my own servers, where my username is "chris" and the machine name is "chris-laptop":

chris@chris-laptop:~$ 
chris@chris-laptop:~$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games
chris@chris-laptop:~$ 
chris@chris-laptop:~$ export PATH=$PATH:/var/lib/gems/1.8/bin
chris@chris-laptop:~$ 
chris@chris-laptop:~$ echo $PATH
/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/var/lib/gems/1.8/bin
chris@chris-laptop:~$ 

My Gem won't load!

"Ruby gems won't load even though installed" highlights a common problem using multiple different versions of Ruby; Sometimes the Gem environment and Gem path get out of sync:

rb(main):003:0> Gem.path

=> ["/opt/ruby1.9/lib/ruby1.9/gems/1.9.1"]
irb(main):004:0> exit

Any Ruby process here is looking only in one place for its Gems.

:~/$ gem env
RubyGems Environment:
  - RUBYGEMS VERSION: 1.3.7
  - RUBY VERSION: 1.9.1 (2009-05-12 patchlevel 129) [x86_64-linux]
  - INSTALLATION DIRECTORY: /opt/ruby1.9/lib/ruby/gems/1.9.1
  - RUBY EXECUTABLE: /opt/ruby1.9/bin/ruby1.9
  - EXECUTABLE DIRECTORY: /opt/ruby1.9/bin
  - RUBYGEMS PLATFORMS:
    - ruby
    - x86_64-linux
  - GEM PATHS:
     - /opt/ruby1.9/lib/ruby/gems/1.9.1
     - /home/mark/.gem/ruby/1.9.1
  - GEM CONFIGURATION:
     - :update_sources => true
     - :verbose => true
     - :benchmark => false
     - :backtrace => false
     - :bulk_threshold => 1000
  - REMOTE SOURCES:
     - http://rubygems.org/

Look carefully at the output of gem environment:

  - GEM PATHS:
     - /opt/ruby1.9/lib/ruby/gems/1.9.1

This isn't the same path as returned by Gem.path:

["/opt/ruby1.9/lib/ruby1.9/gems/1.9.1"]

It's hard to say what exactly caused lib/ruby to change to lib/ruby1.9 but most likely the developer was working with multiple Ruby versions. A quick mv or ln will solve the problem.

If you do need to work with multiple Ruby versions then you really should be using rvm.

From the RVM support site:

RVM installs everything into ~/.rvm. To remove RVM from your system run 'rm -rf ~/.rvm'. You may have one additional config file in ~/.rvmrc and of course the RVM hook in your bash/zsh startup files.

So, just go to the command line and type rm -rf ~/.rvm

All the installed gems are in the ~/.rvm folders, so doing the above will remove the gems and installed rubies in one go.

Gems you added pre-RVM with the default ruby install can be removed by typing this at the command prompt:

for x in `gem list --no-versions`; do gem uninstall $x -a -x -I; done