/usr/bin/irb2.1 is in ruby2.1 2.1.5-2+deb8u3.
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 | #!/usr/bin/ruby2.1
#
# irb.rb - interactive ruby
# $Release Version: 0.9.6 $
# $Revision$
# by Keiju ISHITSUKA(keiju@ruby-lang.org)
#
require "irb"
IRB.start(__FILE__)
|