my $length = $#array;
my $fileNR = 1;

for (my $x = 0; $x < $length; $x++)
{
    open ($fileNR, ">$fileNR.txt") or die "can't open";
    print $fileNR "$array[$x]\n";
    
    if ($x % 1000 == 999)
    {
        close ($fileNR);
        $fileNR++;
    }
}