Much good info from cowboy, Roy J. et al.

And if the code you posted is merely an attempt to show us concisely your desire, please ignore this... but if it's reflective of your actual plan of attack, the reference to "dynamically" suggests (to me, anyway) that you need to think thru the meaning of "dynamically" or maybe provide a different term which reflects your actual intent.

The elements of the regex -- $wday, $mon, $mday and $year -- are hard coded here. Only if you actually intend to get their values from STDIN or somesuch, this would qualify (in my book, which may not be yours) as "dynamic."

and suggest perlretut and perlrequick for more on regexen.