my $bufflen = 4 * 1024; #or w/e

do {
	$result = read ( IN, $buffer, 
			$bufflen-length($buffer), length($buffer) );
} while ( $result && ( length($buffer) < $bufflen ) );

##</code><code>##

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;

##</code><code>##

$buffer .= <IN>;

##</code><code>##

foreach my $regex (@conversions) {
	my @results = ( $buffer =~ s/$regex->{from}/$regex->{to}/g );
	my $reps_done = 0;
	grep { $reps_done += $_ } @results;
	$regex->{count} += $reps_done;	
}
## and do whatever with the result
print OUT $buffer;