brew install [email protected]

==> [email protected]
By default, binaries installed by gem will be placed into:
/usr/local/lib/ruby/gems/2.7.0/bin

You may want to add this to your PATH.

[email protected] is keg-only, which means it was not symlinked into /usr/local,
because this is an alternate version of another formula.

If you need to have [email protected] first in your PATH, run:
  echo 'export PATH="/usr/local/opt/[email protected]/bin:$PATH"' >> ~/.zshrc 

For compilers to find [email protected] you may need to set:
  export LDFLAGS="-L/usr/local/opt/[email protected]/lib"
  export CPPFLAGS="-I/usr/local/opt/[email protected]/include"

See also

• Ruby, Sinatra, Ruby on rails, RubyGems, gem, bundle, Rack, Gemfile, Keg-only, brew install [email protected], bundle, JRuby, CocoaPods, apt install ruby, Fog, Puma