-

$ sudo apt-get install ruby-switch

$ ruby -v
ruby 1.8.7 (2012-02-08 MBARI 8/0x8770 on patchlevel 358) [i486-linux], MBARI 0x8770, Ruby Enterprise Edition 2012.02

$ ruby-switch --list
ruby1.8
ruby1.9.1
ruby2.0
ruby2.1
ruby2.2

$ sudo ruby-switch --set ruby1.9.1
update-alternatives: using /usr/bin/ruby1.9.1 to provide /usr/bin/ruby (ruby) in manual mode.
update-alternatives: using /usr/bin/gem1.9.1 to provide /usr/bin/gem (gem) in manual mode.

$ ruby -v
ruby 1.9.3p545 (2014-02-24) [x86_64-linux] Brightbox