my $filename = 'foo';
my $bufferSize = 1,000,000;
my $outFileSize = 512;

open (IN, $filename);
binmode IN;
seek (IN, 0, 0);

my $buffer;
my $i = 1;
my $j = 1;
open (OUT, "$filename$i");

while (read (IN, $buffer, $bufferSize)){

	if ($j > $outFileSize){

		$j = 1;
		$i++;
		close OUT;
		open (OUT, "$filename$i");

	}

	print OUT $buffer;
	$j++;

}

close OUT;