There are many cases we need to change ruby code besides implementing features, e.g. we will change old hash / lambda to new syntax when upgrading ruby to 1.9 or newer, every time when we upgrade rails, we have to replace old deprecated syntax or configs with new ones. Most of changes are repetitive, boring and time-consuming, I will introduce you how to write some simple ruby code to do these changes automatically, it saves your time and you don't need to repeat yourself again.