$mydata=<INPUT>;
while(<INPUT>){
#Handle data file line by line splitting it at every new line \n
    my(@data)=split/\n/,$_;
#Now lets go through the whole input data file line by line
    for($i=0;$i<@data;$i++){
	$mydata=$data[$i];
        if($mydata=~/^Blah$some_regex(\d+)$some_more_regex_perhaps/){
#Get the sector value which is listed in each matching line of data
           $DataSector=$1;
#Output line of matching data to output file for the relevant sector
           print $fh[$dataSector] "$mydata\n";
    }
}