How do you know? Snippets were shown, not necessarily running code. Maybe @data is scoped higher than the while-loop for other reasons. Maybe strict isn't being used in this code for various reasons. (Did you know that CGI doesn't use strict?) There are a ton of completely legitimate reasons why a my may have been left out. Commenting upon it without actually helping out the OP is a complete waste of my time, for having to read your reply.
Being right, does not endow the right to be rude; politeness costs nothing. Being unknowing, is not the same as being stupid. Expressing a contrary opinion, whether to the individual or the group, is more often a sign of deeper thought than of cantankerous belligerence. Do not mistake your goals as the only goals; your opinion as the only opinion; your confidence as correctness. Saying you know better is not the same as explaining you know better.