my $newline = "\n"; #or some other unique record separator

## if we're not at eof
if ($result > 0) {
	my $last_newline = rindex $buffer, $newline;
	my $remainderlen = length($buffer)-$last_newline-length($newline);
	if ($remainderlen <= 0) {
		$remainder = ''; 
	} else { 
		$remainder = substr($buffer, $last_newline+length($newline), 
			$remainderlen, ''); 
	}
}

## this is important: prefix the remainder before next chunk
$buffer = $remainder;