Install from source:

git clone https://github.com/semaperepelitsa/chruby-fish.git
cd chruby-fish
set -U fish_function_path $fish_function_path $PWD/share/chruby/functions

Usage:

> ruby-install ruby 2.6.5
installing into ~/.rubies/ruby-2.6.5
> chruby 2.6.5
> which ruby
/Users/sema/.rubies/ruby-2.6.5/bin/ruby
> ruby -v
ruby 2.6.5p114 (2019-10-01 revision 67812) [x86_64-darwin18]
> gem env
- INSTALLATION DIRECTORY: /Users/sema/.gem/ruby/2.6.0
- USER INSTALLATION DIRECTORY: /Users/sema/.gem/ruby/2.6.0

See also:

• ruby-install
• chruby - original implementation for bash/zsh