Question

I’ve a ruby gem that has different dependencies for each OS. I have to explicitly write all of them down:

On Mac OS X:

gem install livereload

on Linux:

gem install rb-inotify livereload

on Windows:

gem install eventmachine-win32 win32-changenotify win32-event livereload

Can I tweak a gemspec a bit so installation instructions would look like plain gem install livereload for every OS?

Answer 1

The proper way to do this is outlined here. Since the gemspec is evaluated at package time, you need to do it in a native extension. Don’t worry, it’s not that scary since its still just Ruby code (not compiling C or anything).

We are currently using this approach for some client tools for OpenShift (source). Then in your gemspec/Rakefile, instead of adding dependencies, you would add an extension. Note that the file needs to be named ext/mkrf_conf.rb for this to work.