Determine ruby version from within Rails

Is there a way to determine what version of Ruby is running from within Rails (either on the web or through script/console)? I have Ruby 1.8.6 installed but I've also installed Ruby Enterprise Edition 1.8.7-20090928 and want to ensure that it's using the right installation.

Use this global constant:

RUBY_VERSION

Other relevant global constants include:

RUBY_PATCHLEVEL
RUBY_PLATFORM
RUBY_RELEASE_DATE

Usage example via irb session:

irb(main):001:0> RUBY_VERSION
=> "1.8.7"

Try the constant RUBY_VERSION. I use this extensively to determine whether I'm running under 1.8 or JRuby.

Also, if you're not in production mode, you can do a quick check by hitting the URL "/rails/info/properties"

Use RUBY_VERSION as mentioned by others.

You can then use Gem::Version to do version string comparison:

require 'rubygems' # Only needed for ruby pre-1.9.0 but it's safe for later versions (evaluates to false).
if Gem::Version.new(RUBY_VERSION) < Gem::Version.new('1.9.0')
    extend DL::Importable                                    
else                                                         
    extend DL::Importer                                      
end                                                          

In addition to the RUBY_VERSION constant and friends you may also want to check out Config::CONFIG. This hash contains not only the version numbers but also a ton of other useful runtime information, like the path to the binary, the hostname, ...