Is there anyway to tell ruby to log the url it got as a request in the log?
I am seeing some crashing in my app and can't pin down what url that is doing it.
Yes, it's absolutely possible, but how you implement it will depend on your app. If you're using a framework like Rails or Rack use their built-in logging classes (Thin hooks into Rack's logging class automatically). If it's a vanilla Ruby script then you can include Thin::Logging in your class, which will give you log, trace, debug, and log_error methods.
As for logging the requested URL specifically, that depends entirely on your implementation.