Honestly, I still write a lot of perl, and while interpolation is nice and good to have for simple things, I find myself using sprintf more and more in production code, especially in the cases the examples always show off, such as needing to alter the variable, add two together, etc. I assume those are just shown to illustrate you you can do that, and not imply you should, because commonly using arbitrary code execution within interpolation is something I'd feel compelled to beat out of my coworkers if I encountered it regularly.