User directory

Run this in irb:

puts Gem.user_dir

Or run this in the shell:

$ ruby -r rubygems -e 'puts Gem.user_dir'

On macOS and Linux this will be like:

~/.gem/ruby/2.7.0

The use of -r is to import the rubygems library before executing the script. I found that shell command and use it but I don’t know why -r is needed as I get the same result without it.