安装rubydns

sudo gem install rubydns

Password:

Fetching: console-1.4.0.gem (100%)

Successfully installed console-1.4.0

Fetching: nio4r-2.4.0.gem (100%)

ERROR:  Error installing rubydns:

nio4r requires Ruby version >= 2.3.

brew upgrade ruby

brew link --overwrite ruby

By default, binaries installed by gem will be placed into:

  /usr/local/lib/ruby/gems/2.6.0/bin

You may want to add this to your PATH.

ruby is keg-only, which means it was not symlinked into /usr/local,

because macOS already provides this software and installing another version in

parallel can cause all kinds of trouble.

If you need to have ruby first in your PATH run:

  echo 'export PATH="/usr/local/opt/ruby/bin:$PATH"' >> ~/.bash_profile

 . ~/.bash_profile

For compilers to find ruby you may need to set:

  export LDFLAGS="-L/usr/local/opt/ruby/lib"

  export CPPFLAGS="-I/usr/local/opt/ruby/include"

For pkg-config to find ruby you may need to set:

  export PKG_CONFIG_PATH="/usr/local/opt/ruby/lib/pkgconfig"

==> Summary

🍺  /usr/local/Cellar/ruby/2.6.3

然后，
sudo gem install rubydns