generate a list of all current UTC offsets for a given country

current_utc_offsets.rb

#!/usr/bin/env duct # ruby
# Usage:
#   duct current_uts_offsets.rb <Country as its ISO 3166 code> <strftime-format>
# Example:
#   duct current_uts_offsets.rb US
#     #=> US: -0500 -0600 -0700 -0800 -0900 -1000
#   duct current_uts_offsets.rb RU '%:z'
#     #=> RU: +02:00 +03:00 +04:00 +05:00 +06:00 +07:00 +08:00 +09:00 +10:00 +11:00 +12:00

require 'time'
require 'tzinfo'
require 'active_support/time'

identifier = ARGV[0] || "US"
format = ARGV[1] || "%z"
now    = Time.now.utc
zones  = TZInfo::Country.get(identifier).zone_identifiers.map { |z|
  now.in_time_zone(z).strftime(format)
}.uniq

puts "#{identifier}: #{zones.join(" ")}"

__END__
@@ Gemfile
source 'https://rubygems.org'
gem 'activesupport', '~> 3.2.22'
gem 'tzinfo', '~> 1.2.2'
gem 'tzinfo-data'

@@ Gemfile.lock
GEM
  remote: https://rubygems.org/
  specs:
    activesupport (3.2.22)
      i18n (~> 0.6, >= 0.6.4)
      multi_json (~> 1.0)
    i18n (0.7.0)
    multi_json (1.11.2)
    thread_safe (0.3.5)
    tzinfo (1.2.2)
      thread_safe (~> 0.1)
    tzinfo-data (1.2015.7)
      tzinfo (>= 1.0.0)

PLATFORMS
  ruby

DEPENDENCIES
  activesupport (~> 3.2.22)
  tzinfo (~> 1.2.2)
  tzinfo-data

BUNDLED WITH
   1.10.6

Figured, that activesupport 3.2 can work with tzinfo 1.2 and also tzinfo-data can be added to make current IANA database available.
Bad news: activerecord 3.2 has a "tzinfo (~> 0.3.29)" pin