#!/your/perl/here

use strict;
use warnings;

my $string = <<EOS;
one
two
three
four
five
six
EOS

my @strings = split "\n", $string;
my @lookup;
$lookup[0] = 0;
foreach my $i ( 1..$#strings )
{
	# byte offset of 1st char on this line
	$lookup[$i] = length($strings[$i-1]) + $lookup[$i-1];
}

my ($line, $offset) = find_line_offset( $ARGV[0] );
print "line: $line, offset: $offset\n";

exit;

sub find_line_offset
{
	my $offset = shift;
	
	my $lo = 0;
	my $hi = $#lookup;
	my $line;
	while ($lo+1 < $hi)
	{
		$line = int(($hi+$lo)/2);
		if ( $lookup[$line] > $offset )
		{
			$hi = $line;
		}
		elsif ( $lookup[$line] < $offset )
		{
			$lo = $line;
		}
		else
		{
			# small chance it's equal
			last;
		}
	}
	
	# could have overshot 1
	if ( $lookup[$line] > $offset )
	{
		$line--;
	}
	
	if ( $lookup[$line+1] > $offset )
	{
		# this is the one
		my $line_offset = ($offset - $lookup[$line]);
		return ($line, $line_offset);
	}
	else
	{
		return;
	}
}