open( FILE, "<filename") or die "Can't open file: $!\n";
my @lines = <FILE>;
close( FILE) or die "Can't close file: $!\n";

my $LastWasZero = 0;
foreach my $line (@lines) {
	chomp $line;
	my ($recType, $rest) = unpack "A2A*", $line;
	if ($recType = "00") {
		if ($lastWasZero) { # two consequative 00 recs
			my ($date,$headerNumber) = unpack "A10A20", $lastWasZero;
			#do delete processing on $headernumber $date...
		}
		my ($date,$headerNumber) = unpack "A10A20", $rest;
		$lastWasZero = $rest;
            next;
	}
	else $lastWasZero = "";
	if ($recType eq "01" ) {
		my ($field1,  $field2,....) = unpack "...", $rest;
		# process 01 records
            next;
	}
	if ($recType eq "02" ) {
		my ($field1,  $field2,....) = unpack "...", $rest;
		# process 02 records
            next;
	}
	....
}