As the error message suggests, your BigFileFullOfSubs.pl won't compile because you have not declared $logLine in it.

One solution would be to share this variable among your scripts but that would get very messy very quickly. However, since you don't actually need $logLine anywhere else, just move the declaration of it out of index.mojo and into BigFileFullOfSubs.pl (outside the subroutine) and you may find this solves your problems.