Multiple lines separated by "\n" would constitute a regular text file; hence, for that I'd do something like this:

#!/usr/bin/perl

use strict;
use warnings;

my $lines = 0;
my $filename = '/path/to/tar.gz';
die "Can't open '${filename}': $!" unless open FILE, $filename;
while (sysread FILE, my $buffer, 4096) {
               $lines += ($buffer =~ tr/\n//);
}
close FILE;
[download]