|laziness, impatience, and hubris|
I've found that keeping your code as simple and easy to read as possible is generally the best policy. It makes maintenance and debugging easier, and is kinder to people who inherit your project.
Additionally, the simplistic code generally runs faster than the "clever" methods.
That said, have fun with abusing the language to satisfy curiosity :)
I recently wrote this as an experiment in getting localtime in yyyy-mm-dd format without declaring any local variables, and satifying strict.
This is what I came up with:
I'll break it into components to make it easier to digest.
Create a list that contains the date tokens provided by localtime, and also contains the newly initialized $a. $a does not need to be declared, as $a and $b are exempted from strict due to their use in sort.
Take the above generated list, and extract indexes 5,4,3 (year,month,mday).
Iterate over the list that was generated in the previous step. For each entry check if there are any values left in @$a. If yes, add the current value to the next value in @$a, and shift that item from the list.
In effect $a is a list of modifiers.