Switching ruby version to run a command on server

Question

I have a Ruby application (non-Rails) which I deploy with capistrano. I can ssh into my server, cd into the /current directory and start it with the command

ruby tweet_tracker.rb start

However, if I cd up a level and run

ruby current/tweet_tracker.rb start

I get the error:

/home/deploy/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require': cannot load such file -- tweetstream (LoadError)
    from /home/deploy/.rvm/rubies/ruby-1.9.3-p194/lib/ruby/site_ruby/1.9.1/rubygems/custom_require.rb:36:in `require'
    from /home/deploy/dev/tweet_tracker/current/tweet_tracker.rb:4:in `<main>'

Now this is obviously because I'm running the command using different ruby versions in each directory.

I have a .ruby-version file in the application which specifies ruby-1.9.3-p392. My capistrano deploy script specifies set :rvm_ruby_string, '1.9.3-p392' and when it runs bundle install as part of the deploy process, it installs the gems for 193-p392.

Problem is, when I try to start the application from outside the application directory, it uses the default Ruby (set by RVM to be a lesser version of 193).

How do I ensure that the application uses the Ruby version specified by it's .ruby-version when run?

I'd rather not change RVM's default Ruby version since there are other applications running on the system.

You could create a script to cd into the correct folder and start the app? — Ian Kenney, Apr 24 '13 at 19:13

score 0 · Answer 1 · answered Apr 24 '13 at 19:48

Here's an example project:

myproject/
├── .ruby-version
└── subproject/
    ├── .ruby-version
    └── script.rb

myproject/.ruby_version:

system

myproject/subproject/.ruby_version:

ruby-1.9.3-p392

myproject/subproject/script.rb:

puts RUBY_VERSION

Now i suppose your problem can be mimicked like this:

$ cd myproject
$ ruby subproject/script.rb
1.8.7
$ cd subproject
$ ruby script.rb
1.9.3

One way around this is to use the poorly documented command rvm exec:

$ cd myproject
$ rvm 1.9.3-p392 exec ruby subproject/script.rb
1.9.3

Which you could extend to automatically read the .ruby-version file:

$ rvm `cat subproject/.ruby-version` exec ruby subproject/script.rb
1.9.3

score 0 · Answer 2 · answered Apr 24 '13 at 19:54

RVM is often quite painful when it comes to writing scripts that call Ruby applications. There exists a better Ruby version wrapper that many user have migrated to. One of the main problems with RVM that it is well suited for interactive shells, but not so much for scripts.

The main problem is that RVM sets-up an after_cd hook, and that's something you will only get in the interactive shell; as a result, the users are required to run a sequence of commands similar to this:

cd $APPDIR
source /home/$APPUSER/.rvm/scripts/rvm
rvm rvmrc trust && rvm rvmrc load
bundle exec ./bin/server start

You can use rvm wrapper to generate an init script. Though, for example, it is somewhat more tricky to integrate with Upstart configuration.

Switching ruby version to run a command on server

2 Answers2