iban-tools is a Ruby library for manipulating and validating IBAN account numbers. You can read more about IBAN on Wikipedia
Iulianu wrote iban-tools. We just removed use of String#ord for compatibility with Ruby 1.8 and 1.9 and of course pushed the built gem to gemcutter.
You'll find the source code on Github. Our fork is also available on GitHub
The gem should be compatible with Ruby 1.8.6, 1.8.7 and 1.9.1.
You'll need to add http://gems.rubyforge.com as a gem source if you don't already have it.
You can accomplish this with the gemcutter gem.
gem install gemcutter
gem tumble
Once you have the gemcutter source added you can install iban-tools with a simple gem install.
gem install iban-tools
require 'rubygems'
require 'iban-tools'
IBANTools::IBAN.valid?("GB82 WEST 1234 5698 7654 32")
=> true
Advanced usage, gives more detailed error messages
IBANTools::IBAN.new("XQ75 BADCODE 666").validation_errors
=> [:unknown_country_code, :bad_check_digits]
Pretty print, canonicalize, and extract fields from an IBAN code
iban = IBANTools::IBAN.new(" ro49 aaaa 1B31007593840000")
iban.code
=> "RO49AAAA1B31007593840000"
iban.country_code
=> "RO"
iban.prettify
=> "RO49 AAAA 1B31 0075 9384 0000"
Very basic BIC validation
IBANTools::BIC.valid?("UNCRIT2B912")
=> true