This is a fastlane plugin which will provide an action to retrieve a list of names and UDIDs of each device registered with your Apple Certificate. This list is exactly the same as the list used to compare against what is/isn't registered in the register_device/s action.
Check out the example Fastfile to see how to use this plugin. Try it by cloning the repo, running fastlane install_plugins and bundle exec fastlane test.
Note to author: Please set up a sample project to make it easy for users to explore what your plugin does. Provide everything that is necessary to try out the plugin in this project (including a sample Xcode/Android project if necessary)
fastlane is the easiest way to automate beta deployments and releases for your iOS and Android apps. To learn more, check out fastlane.tools.