gem install keepassx

or if you use bundler

gem 'keepassx'

require 'keepassx'

database = Keepassx::Database.open("/path/to/database.kdb")
database.unlock("the master password")
puts database.entry("entry's title").password

No attempt is made to protect the memory used by this library; there may be something we can do with libgcrypt's secure-malloc functions, but right now your master password is unencrypted in ram that could possibly be paged to disk.