open(FILE,"textfile.txt");
while(1)
	{
	$line=<FILE>||last;
	@line=split("\t",$line);
	$last=0;
	if($line[0]ne$previous_value)
		{
		# do something
		$last=1
		}
	elsif($line[1]>=1)
		{
		# do something
		}
	$previous_value=$line[0];
	if($last==1)
		{
		seek(MAP,-length$line,1);
		last;
		}
	}
close FILE;
exit;