The Perl debugger interface, to me, is too cluttered for this purpose, especially considering the -- what are they, ANSI control codes? -- formatting. Python's interactive mode is somewhat better, but Python doesn't do math quite as well as Perl, I think. Interactive Ruby (irb), out of the three, is IMHO the best; as two examples, Ruby automatically switches to bignums when necessary, and is not as whitespace-dependent as Python (important in interactive mode)... the major disadvantage is that it is much less common than Perl and Python, or so I've seen.