Alberto Grespan

Installing platform specific gems with Bundler

— October 10, 2014

Sometimes we’ll need to install specific gems to make our project compatible in different platforms such as MRI, Rubinius, a particular Ruby version, JRuby, windows, etc…

As you may know, dependency management in Ruby is done through Bundler Gemfile. Bundler comes with a handy CLI command that can help us gather some information about our current platform and help us see a bigger picture of what’s going on with our project Gemfile e.g:

$ bundle platform
Your platform is: x86_64-darwin13.0

Your app has gems that work on these platforms:
* ruby

Your Gemfile does not specify a Ruby version requirement.

That’s cool, but how do we manage platform specific gems?

Managing platforms

Apart from the bundler’s platform command it also have a platforms option that can be used within the Gemfile and applied to a group of gems in a block form or to a single gem in the same way we do it with groups.

# Gemfile
platforms :ruby do
  gem "ruby-debug"
  gem "sqlite3"

gem 'jdbc-postgres', '~> 9.3.1102', :platforms => :jruby

The platforms block tells that these two gems are only going to be installed when using C Ruby (MRI) or Rubinius, but NOT Windows and the jdbc-postgres gem will only be installed when the platform is JRuby. You can check more here.

This can help us be more subtle with servers and probably with our application load times.

But wait, there’s another “solution” that can be used and it’s pure Ruby.

Let’s test it:

$ irb

=> "x86_64-darwin13.0"
> puts "YAY" if RUBY_PLATFORM=~ /x86_64-darwin13.0/
=> YAY

I’m currently running under OS X so my platform will be Darwin. The output above is telling me that. But what is RUBY_PLATFORM ?

RUBY_PLATFORM is a Ruby constant that will give us our current platform, it’s also the same constant that Bundler uses when we type bundle platform. You might be thinking how can we apply this to a Gemfile… Well, easy, in the same we just did.

# Gemfile
if RUBY_PLATFORM =~ /x86_64-linux/
  gem 'libv8', '~>'
  gem 'therubyracer', '~> 0.12.1'

As you see we are using it to install some dependencies only on Linux. One thing I’ve notice when using RUBY_PLATFORM is that it’s a bit “unreliable”. I haven’t test it in all possible platforms but when using this constant an JRuby the output will be “Java” and not the current OS, this may be the intended behaviour, but it wasn’t for me, so be careful with this if you are planing on using it for gem installation purposes, it may be better and safer to just stick with Bundler’s platforms.

Thanks for reading!