# line processing program
my ($file,$start,$stop) = @ARGV;
$start ||= 0;
$stop ||= -s $file;

open my $fh, '<', $file;
seek $fh, $start, 0;

# now position at the first line <i>after</i> $start
# if we're not starting at the beginning of a file
if ($start) {
    <$fh>;
};

my $position = tell $fh;
while (<$fh> and $position <= $end) {
    $position += length $_;
    ...
};