Packages with Ruby scripts must depend on a valid Ruby interpreter. Those that have Ruby scripts that run under a specific version of Ruby need a dependency on the equivalent version of Ruby.
If a script in the package uses #!/usr/bin/ruby, the package needs a dependency on "ruby | ruby-interpreter". This allows users to choose which interpreter to use by default. If the package is intended to be used with a specific Ruby version, its scripts should use that version directly, such as #!/usr/bin/ruby1.8
If a script uses #!/usr/bin/ruby1.9, then the package needs a dependency on "ruby1.9".
In some cases a weaker relationship, such as Suggests or Recommends, will be more appropriate.