grep returns the elements of a list for which expression is true. In this case, your list is the array ($line), and your expression is the /$pat/gi. Therefore, @apples will simply be set to ($line) if the pattern /$pat/gi matches, otherwise will be set to nothing.

Because each of your lines of data has at least one 'apple' in them, the grep count will simply equal the number of lines.

- Miller