How to set correct Ruby version in gem environment - ruby

Question

Note: This question relates to How can I get bundler to use the Ruby version set by chruby and .ruby-version?.
Using chruby I have Ruby 1.8.7 installed on macOS:
$ ruby -v
ruby 1.8.7 (2013-06-27 patchlevel 374) [i686-darwin17.4.0]
Also, I have used gem update --system 1.8.30 to install a specific version of RubyGems which I am hoping is compatible. This would appear to be installed properly:
$ gem --version
1.8.30
However, my RubyGems environment shows the incorrect version of Ruby (2.5.0):
$ gem env
RubyGems Environment:
- RUBYGEMS VERSION: 1.8.30
- RUBY VERSION: 2.5.0 (2017-12-25 patchlevel 0) [x86_64-darwin17]
- INSTALLATION DIRECTORY: /Users/keithpitty/.gem/ruby/1.8.7
- RUBY EXECUTABLE: /usr/local/opt/ruby/bin/ruby
- EXECUTABLE DIRECTORY: /Users/keithpitty/.gem/ruby/1.8.7/bin
- RUBYGEMS PLATFORMS:
- ruby
- x86_64-darwin-17
- GEM PATHS:
- /Users/keithpitty/.gem/ruby/1.8.7
- GEM CONFIGURATION:
- :update_sources => true
- :verbose => true
- :benchmark => false
- :backtrace => false
- :bulk_threshold => 1000
- REMOTE SOURCES:
- http://rubygems.org/
How can I fix the RubyGems environment to use the version of Ruby that chruby has set?

Answer 1

My missing step was installing RubyGems 1.6.2 from source. Following advice elsewhere from Dan Cheail, I did the following:
curl -O https://rubygems.org/rubygems/rubygems-1.6.2.tgz
(and then unzipped it)
cd rubygems-1.6.2
chruby ruby-1.8.7-p374
ruby setup.rb
gem update --system 1.8.25
And then my RubyGems environment was fixed:
$ gem env
RubyGems Environment:
- RUBYGEMS VERSION: 1.8.25
- RUBY VERSION: 1.8.7 (2013-06-27 patchlevel 374) [i686-darwin17.4.0]
- INSTALLATION DIRECTORY: /Users/keithpitty/.gem/ruby/1.8.7
- RUBY EXECUTABLE: /Users/keithpitty/.rubies/ruby-1.8.7-p374/bin/ruby
- EXECUTABLE DIRECTORY: /Users/keithpitty/.gem/ruby/1.8.7/bin
- RUBYGEMS PLATFORMS:
- ruby
- x86-darwin-17
- GEM PATHS:
- /Users/keithpitty/.gem/ruby/1.8.7
- /Users/keithpitty/.rubies/ruby-1.8.7-p374/lib/ruby/gems/1.8
- GEM CONFIGURATION:
- :update_sources => true
- :verbose => true
- :benchmark => false
- :backtrace => false
- :bulk_threshold => 1000
- REMOTE SOURCES:
- http://rubygems.org/