But what's in that string? That still counts. What I should have done was put an additional restriction on what IO is available. Otherwise, something like "eval `cat f`" or something could be all powerful.

My first attempt shows Ruby simulating a cyclic tag system with only 15 unique characters including newlines and spaces: https://github.com/elitheeli/oddities/raw/master/only_a_few_...

EDIT: down to 14 characters.