if (length($html[$i]) > 1000000) {
    my $z=0;
    while ($html[$i] ne '') {
        open (my $file, '>', "giant_${i}_$z.htm") or die $!;
        print $file substr($html[$i],0,500000,'');
        close $file;
        push(@lists, "giant_${i}_$z.htm");
        $z++;
    }
} else {
    # ...