#In this example, the 13 digit bill numbers are right after the date (20061212), eg. 123456789A101, C234567891011, A001122334455. The header line starts with 101010000 and bill details line starts with 301033000. The end of bill details line is identified by 999999.
101010000ABC	20060212123456789A1018880001000000001	123456789A10100216       4322489239649  342    10  00000    20060212                                   
105060000ABC	20060212123456789A1018880001000000002	ADDRESS		0
107660000ABC	20060212123456789A1018880001000000003	ADDRESS LINE 2		20
108250100ABC	20060212123456789A1018880001000000004	123456789A10100216                                                                                                  	
109300100ABC	20060212123456789A1018880001000000005	                                       	 303-0	0
101250100ABC	20060212123456789A1018880001000000006	IUSER@MAIL.DOMAIN.COM		
108430100ABC	20060212123456789A1018880001000000008	00000   123456789A10100216 0000000840M0000000000{0000000000{0000000000{0000000000{0000000000{0000000840M    0000000000{		
100550000ABC	20060212123456789A1018880001000000009	123456789A10100216 NC2005110920051208200512090000000000{0000000000{0000000000{0000000000{0000000000{0000000000{0000000000{000000000520
100610000ABC	20060212123456789A1018880001000000010	123456789A10100216 NC0000000000{0000000000{0000000000{0000000000{0000000000{0000000000{0000000000{0000000000{0000000000{0000000840M0000	520
102210000ABC	20060212123456789A1018880001000000011	* * * REVISED FINAL BILL MESSAGE * * *                     THIS REVISED FINAL BILL INCLUDES CHARGES OR CREDITS NOT PREVIOUSLY		
104500000ABC	20060212123456789A1018880001000000012	APPLIED TO YOUR ACCOUNT.  A SUMMARY IS PROVIDED ON ANOTHER PAGE OF         THIS BILL.  ANY CREDITS DUE YOU ARE REFLECTED ON THIS BILL.		
102250000ABC	20060212123456789A1018880001000000013	SHOULD YOU HAVE ANY QUESTIONS CONCERNING YOUR ACCOUNT, CONTACT		
101250100ABC	20060212123456789A1018880001000000014	YOUR CUSTOMER SERVICE CENTER		
105500000ABC	20060212123456789A1018880001000000015	THANK YOU FOR THE OPPORTUNITY TO SERVE YOU.		
108456100ABC	20060212123456789A1018880001000000016	123456789A10100216                                        0000000840M0000000000{0000000000{0000000840M		
107208000ABC	20060212123456789A1018880001000000017	0000000840M		
109080000ABC	20060212123456789A1018880001000000018	200602120000000000600000000005000000000000000000000000000000002000000000000000000000000000000000000000000000000000000000000000000  
102098100ABC	20060212123456789A1018880001000000019	200602124322489239649          1                                                         00000		
109990000ABC	20060212123456789A1018880001000000020		N10 NC0470	0
101010000ABC	20060212C2345678910118880003000000021	C23456789101100114      40002416789  3939    20U  00000    20060114                                              		
105060000ABC	20060212C2345678910118880003000000022	ADDRESS		
105060000ABC	20060212C2345678910118880003000000023	ADDRESS LINE 2		
107660000ABC	20060212C2345678910118880003000000024	C23456789101100114	                                                                                                                         	
109080000ABC	20060212C2345678910118880003000000025	IUSER@MAIL.DOMAIN.COM		
109990000ABC	20060212C2345678910118880003000000026	C23456789101100114		
301033000ABC	20060212123456789A1018880002000000001	200602124322489000000		
306020100ABC	20060212123456789A1018880002000000002	400		
306020100ABC	20060212123456789A1018880002000000003	1		
306020100ABC	20060212123456789A1018880002000000005	1 CUSTOMER NAME ABBREVIATION		
306020100ABC	20060212123456789A1018880002000000006	1 CUSTOMER TERMINAL LOCATION		
306020100ABC	20060212123456789A1018880002000000007	1 CUSTOMER'S CARRIER NAME ABBREVIATION		
306020100ABC	20060212123456789A1018880002000000008	1 AREA IDENTIFICATION		
306020100ABC	20060212123456789A1018880002000000009	1TAR  TAX AREA
309990000ABC	20060212123456789A1018880002000000010	1TAX  TAX APPLICATION
999999		200602121635         30
301033000ABC	20060212C2345678910118880001000000001	200601164322489000000
306020100ABC	20060212C2345678910118880001000000002	
306020100ABC	20060212C2345678910118880001000000003	1
306020100ABC	20060212C2345678910118880001000000004	1 CUSTOMER NAME ABBREVIATION
306020100ABC	20060212C2345678910118880001000000005	1 CUSTOMER TERMINAL LOCATION
306020100ABC	20060212C2345678910118880001000000006	1 CUSTOMER'S CARRIER NAME ABBREVIATION
306020100ABC	20060212C2345678910118880001000000007	1 AREA IDENTIFICATION
306020100ABC	20060212C2345678910118880001000000008	1TAR  TAX AREA
309990000ABC	20060212C2345678910118880001000000009	1TAX  TAX APPLICATION
999999		200601161635         30
#Sometimes, the data can also look like this or any other variation
101010000Z98765420060212A0011223344558880001000000001	123456789A10100216       4322489239649  3424    10N  00000    20060212                                        
105060000Z98765420060212A0011223344558880001000000002	ADDRESS		0
107660000Z98765420060212A0011223344558880001000000003	ADDRESS LINE 2		20
108250100Z98765420060212A0011223344558880001000000004	123456789A10100216                                                                                                            	
109300100Z98765420060212A0011223344558880001000000005	                                       	 343-0	0
101250100Z98765420060212A0011223344558880001000000006	IUSER@MAIL.DOMAIN.COM		
108430100Z98765420060212A0011223344558880001000000008	00000 R49431957005313   0000000840M0000000000
301033000Z98765420060212A0011223344558880001000000001	200601164322489000000
306020100Z98765420060212A0011223344558880001000000002	
306020100Z98765420060212A0011223344558880001000000003	1
306020100Z98765420060212A0011223344558880001000000004	1 CUST NAME
306020100Z98765420060212A0011223344558880001000000005	1 CUSTOMER LOC
306020100Z98765420060212A0011223344558880001000000006	1 CUSTOMER'S ABBREVIATION
306020100Z98765420060212A0011223344558880001000000007	1 AREA IDENTIFICATION
306020100Z98765420060212A0011223344558880001000000008	1TAR  TAX AREA
309990000Z98765420060212A0011223344558880001000000009	1TAX  TAX APPLICATION
999999		200601161635         30


##</code><code>##

use warnings;
use strict;
use diagnostics;

my %bills;
my $currBill = 'void';
my $type = 'header';

$datafile = "datafile.txt";
open(DATA, $datafile) || die ("Cannot open $datafile: $!");

while (<DATA>) {
  chomp;
  if ($_ =~ /^101010000/) {
    $currBill = $1;
    $type = 'header';
  } elsif ($_ =~ /^301033000/) {
    $currBill = $1;
    $type = 'data';
  } else {
    push @{$bills{$currBill}{$type}}, $_;
  }
}
close(DATA);

open($outputdata, '>', 'outputfile.txt' || die "Cannot open output file 

output.txt: $!");

for my $bill (sort keys %bills) {
    print $outputdata ">>>> $bill\n";
    print $outputdata "Header\n" . (join "\n", @{$bills{$bill}{'header'}}) 

. "\n"
        if exists $bills{$bill}{'header'};
    print $outputdata "Data\n" . (join "\n", @{$bills{$bill}{'data'}}) . 

"\n"
        if exists $bills{$bill}{'data'};
}