I use ruby-debug quite a bit (too much? perhaps). And every time I start it, I find myself setting a few options (always the same ones), and it finally got to the point where I thought there had to be a better way. And there was! (Thank you, Kent)
The solution is even documented in some recent release notes:
Create a .rdebugrc in your home directory (it also looks for one in the current directory first):
set autolist set autoeval set autoreload set forcestep
And voila! Each time you start rdebug, it executes this script.
An other good tip: run with -n to avoid stopping on the first instruction, now that you don’t need to run all these commands.
Update: with version 0.10, -n does not seem to be recognized, but —no-stop still works.