in reply to
question for perl book & magazine authors
As to the question of grep and map being used as much as they could, I couldn't agree more. At work, I've had to train a few people to use them instead of foreach when they made sense ... and then untrain them a bit when they started using them where they didn't make sense. The point isn't to religiously worship them, but to make your code do what it says: if you're converting one list into another, you're mapping from one to the other. If you're finding elements in a list, you're grepping for them.
By speaking idiomatically perl, you may get a speed benefit (as you did in your benchmark), but, more importantly, you get a maintenance benefit: your code looks like a design document!
That is actually part of the reason why I don't like map's and grep's used in void context - they are no longer reading like plain English. "Map from @common to ... nothing?" Instead, just use for/foreach: "For each element in @common, do..." That reads like exactly the solution you're attempting to do. Which is probably how you're thinking of the problem - and, any time your can code your solution in the domain of the problem instead of the domain of the solution, you're going to end up with clearer and more flexible code.