If you have package variables in either of the two packages, the other will be able to read or write on them. For exemple you could have in a.pl :
$SUBS::option = getOption(); and if you declare our $option in the package SUBS, it will be the same variable.
If neither files have a package statement, then all variables declared by our will be in package Main, a variable declared our $option in one file will be the same as our $option in the other.
If you feel that messing around with another package's variables isn't clean enough, you could write accessor subs to get and set them.