The following was successful on Mac OSX El Capitan (10.11.6)
$ brew install ruby
$ brew install rbenv
$ rbenv init
# Load rbenv automatically by appending
# the following to ~/.bash_profile:
eval "$(rbenv init -)"
echo 'eval "$(rbenv init -)"' >> ~/.bash_profile
Close and reopen your terminal session in order to invoke the previous change.
$ curl -fsSL https://github.com/rbenv/rbenv-installer/raw/master/bin/rbenv-doctor | bash
Checking for rbenv in PATH: /usr/local/bin/rbenv
Checking for rbenv shims in PATH: OK
Checking rbenv install support: /usr/local/bin/rbenv-install (ruby-build 20180224)
Counting installed Ruby versions: none
There aren't any Ruby versions installed under `/Users/rwhitear/.rbenv/versions'.
You can install Ruby versions like so: rbenv install 2.2.4
Checking RubyGems settings: OK
Auditing installed plugins: OK
$ brew upgrade rbenv ruby-build
Updating Homebrew...
$ rbenv install 2.5.0
ruby-build: use openssl from homebrew
...
Installed ruby-2.5.0 to /Users/rwhitear/.rbenv/versions/2.5.0
$ ruby --version
ruby 2.5.0p0 (2017-12-25 revision 61468) [x86_64-darwin15]
$ sudo gem install jekyll bundler
Fetching: public_suffix-3.0.2.gem (100%)
...
bundler's executable "bundle" conflicts with /usr/local/bin/bundle
Overwrite the executable? [yN] y
bundler's executable "bundler" conflicts with /usr/local/bin/bundler
Overwrite the executable? [yN] y
Successfully installed bundler-1.16.1
Parsing documentation for bundler-1.16.1
Installing ri documentation for bundler-1.16.1
Done installing documentation for bundler after 4 seconds
26 gems installed
$ jekyll new myblog
Running bundle install in /Users/.../myblog...
Enter sudo password when requested
New jekyll site installed in...
$ cd myblog/
$ bundle exec jekyll serve
Server address: http://127.0.0.1:4000/ Server running... press ctrl-c to stop.