/usr/bin/ri2.3 is in ruby2.3 2.3.3-1+deb9u2.
This file is owned by root:root, with mode 0o755.
The actual contents of the file can be viewed below.
1 2 3 4 5 6 7 8 9 10 11 12 | #!/usr/bin/ruby2.3
begin
gem 'rdoc'
rescue NameError => e # --disable-gems
raise unless e.name == :gem
rescue Gem::LoadError
end
require 'rdoc/ri/driver'
RDoc::RI::Driver.run ARGV
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