Agreed with BrowserUk. Tie::File is the most ideal in this case.

As Tie::File hides the physical layout at some level (the layout among lines, obviously you still need to worry the internal structure of each record, which is your pack), and now each line of the file is presented as an element of an array.

I had a post analyzing how Tie::File uses memory, and you would see that Tie::File's author used memory in a very smart way.