What Version of Ruby Am I Using?
So you go to a different machine, and you spot Ruby on it (hallelujah), and you really have nothing to so, so out of curiosity you are wondering: What version of Ruby is it?
Go ahead and execute:
ruby -v
And you should get:
ruby 1.8.5 (2006-08-25) [i486-linux]
Within an Application
But what if you want access to that information inside a Ruby application?
Ruby comes with a set of constants which you can exploit to find out which version you have installed.
Testing for Version Compatibility
But what if the software only runs on certain versions of of Ruby, how do I throw an error if that criteria isn’t met?
For example Rails v1.2.3 only runs on Ruby v1.8.2 and above, except v1.8.3. In fact in v1.8.5 breakpoints are broken! (This is due to how breakpoints were initially implemented by exploiting a bug in Ruby, which got fixed in v1.8.5. Don’t worry though, in Rails 2.0 breakpoints are functional once again, without utilizing the Ruby bug.)
Well that makes for a (somewhat) complicated setup don’t you think?
The simple way is to split the RUBY_VERSION.
Giving you the major, minor, and tiny release numbers. Allowing you to do some version checking through conditions.
The Rails Way
Located at rails/lib/ruby_version_check.rb 
- Line 3 does a simple regular expression check to ensure that its not running v1.8.3.
- Line 10 just does a basic string comparison to ensure that the current version, is not less than the require minimum version.
Conclusion
Well thats enough to get you started, so get hacking!
Updated to reflect hindsight on my part
mypapit said,
May 30, 2007 @ 12:28 pm
awww… hopefully rails team can overcome ruby compatibility problems, makes my head spins already
inactiva » Blog Archive » What Version of Ruby Am I Using? said,
May 30, 2007 @ 9:53 pm
[…] want to find out what version of Ruby you’re using? I’d like to present my rather simpler […]
ken said,
January 23, 2008 @ 7:48 am
Assuming Ruby uses the “rational versioning” system that all the gems use, string comparison will fail if they ever make it to an x.y.10.