/usr/lib/ruby/gems/2.1.0/gems/rake-10.1.0/bin/rake
/usr/lib/ruby/gems/2.1.0/gems/rdoc-4.1.0/bin/rdoc
/usr/lib/ruby/gems/2.1.0/gems/rdoc-4.1.0/bin/ri
/usr/lib/ruby/gems/2.1.0/gems/test-unit-2.1.5.0/bin/testrb
You may install this package on Debian with
apt-get
install libruby2.1