If, as you say, this is for production code, then I really don't think you want the user to be able to change any arbitrary variable at any arbitrary time. There are (I must think) certain variables that it makes sense for them to alter, and certain specific times at which it makes sense for them to be able to do it.

Thus tye's suggestion is probably reasonable, given that your application is console-based. Then you don't have to (as he says) sprinkle the key checks throughout your program; just at the certain places where it makes sense. I wince at the idea of sprinkling things like that throughout a production system. And if the specific times at which it makes sense to alter the variables are known, and are rather infrequent, you could take the approach of always stopping to ask the user for values, and timing out the request with an alarm. I've done this in the past with some success.

jdporter
The 6th Rule of Perl Club is -- There is no Rule #6.