Suppressing warnings is usually a bad idea but if you understand the risk and want to carry on regardless. When ruby to call a script then the warning level can be set via:

$ ruby -W0 ./script.rb
$ ruby -W1 ./script.rb
$ ruby -W2 ./script.rb

Where 0=silence, 1=medium, 2=verbose

In an executable with a shebang line this is a little harder. This is the method I have found:

#!/usr/bin/env ruby
##                      $VERBOSE
## -W0  NO Warnings     nil
## -W1  Quiet           false
## -W2  Verbose         true
BEGIN { $VERBOSE = nil }

#Rest of ruby script

The script can then be called directly with the warning level set:

$ executable_ruby_script