If we're going as far as having access to "cat" and "shell", then it might be fun to tinker with "dd" as well. Then the OP can get to just the part of the file he wants to:

open(THIRDMB, "dd if=$filename bs=1024 skip=2048 count=1024|") or die;
while(<>) { ... } # Reads third MB of file only.
close(THIRDMB);
[download]

dd's useful in Unix for skipping around in large files at the shell level where seek(2) might be a bit more complicated.