Improving IRB experience with a custom .irbrc

Ruby’s IRB is a lovely interactive console. By leveraging a custom .irbrc configuration file, we can make the experience even better.The .irbrc file is nothing else than a Ruby file that gets evaluated whenever we start the console with irb or rails c. We can place it in a home directory (~/.irbrc) or in the project directory (to scope it per project). But only one of these files will take effect, and the global one has precedence.So what kind of things can we put there?.