Thanks for the input. The line:

$newPrices{ $key } = \@line_array;
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is what I had originally, but my understanding is that is a reference to the array, and since the array changes when the next line is read, it made all the values in my hash the same, the last line of the last file. I understand that using  $newPrices{ $key } = [@line_array] creates a copy of the array. It is quite possible that I am mistaken since this is the first time I have really sat down with Perl.