open INFILE, "flatFile.csv" || die("Can't read flatFile.csv");
open OUTFILE, ">flatFile.out" || die("Can't open flatFile.out");

$MAX_PARAMS = 11;
$THIS_PAGE = "http://mypage.com/new/test.pl?opt_1=FIELD1&opt_2=FIELD2&opt_3=FIELD3&opt_4=FIELD4&opt_5=FIELD5&opt_6=FIELD6&opt_7=FIELD7&opt_8=FIELD8&opt_9=FIELD9&opt_10=FIELD10&ins_company=FIELD0&t=s";
$THIS_DELIMTER = ",";

while (<INFILE>) {
	@theseFields = split/$THIS_DELIMTER/;
	$paramLength = @theseFields;
	$paramLength == $MAX_PARAMS 
		|| warn("expected $MAX_PARAMS parameters, $paramLength parameters found:");
	$finalPage = $THIS_PAGE;
	for ($i = 0; $i < $MAX_PARAMS; $i++)  {
		$finalPage =~ s/FIELD$i/$theseFields[$i]/gi;
	}
	print OUTFILE "$finalPage\n";	
}

close OUTFILE;
close INFILE;