Being of the ornery sort, this (to me) begs the following question:
Efficiency aside, is there a *safe* way to utilise eval as a solution to this problem? Not a "good" way, or even a "mediocre" way, just safe?

The intrinsic problem with eval is the possibility of hostile data being introduced into to evaluated string. So, is there a way of rendering the data safe?
The obvious way is via taint checking, and string sanitising with tr or s, but is there a better way?

Not that this should be construed as approval of the idea - the process startup overheads alone should be reason enough to do it any other way!
-R