How to fix "Unknown ruby interpreter version (do not know how to handle): RUBY_VERSION."

So it looks like

bundle exec jekyll new

will create the a Gemfile with the line

ruby RUBY_VERSION

I believe you'll want to edit that file to be e.g.

ruby '2.1.1'

Coincidentally today I am also trying to setup Jekyll and am seeing the same problem. I am using RVM and it otherwise works fine (running multiple Rails dev sites locally). When I run env | grep 'RUBY' I get:

$ env | grep 'RUBY'
MY_RUBY_HOME=/Users/myusername/.rvm/rubies/ruby-2.0.0-p247
RUBY_VERSION=ruby-2.0.0-p247

However, I just continued and ran bundle install, then bundle exec jekyll serve and the site booted up without issue.

Seems like there is no variable RUBY_VERSION in your env.

Try in your shell: env | grep 'RUBY'

Output should be like this: RUBY_VERSION=ruby-2.3.0

If you don't see anything, you need to reinstall ruby.

Use RVM or other ruby version manager. Here is a good manual