Try using seek() on your file handler to read certain amount of data from the spot where you last stopped parsing this file. My understanding is that this should eliminate your "Out of Memory" problem and allow for greater control.

# $fh is your file handler
seek($fh, $old_position, 0);
my $buffer = read($fh, 200000); # read ~200KB from the file
# save current position
$old_position = tell($fh);

# do whatever you want with the buffer
# here..
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cheers

"There is no system but GNU, and Linux is one of its kernels." -- Confession of Faith