#!/usr/bin/perl
use strict;
use warnings;

my $string = '944|O|1234567890123|14NOV2010|15NOV2010|01JAN3000|C|45678|COMM||045 094|O|1099721190211|14NOV2010|15NOV2010|01JAN3000|C|35077|FREE||044 928|O|1234567890123|14NOV2010|15NOV2010|01JAN3000|C|45678|FREE||030 028|O|2009876543210|14NOV2010|15NOV2010|01JAN3000|C|99212|COMM||054';
my %months = (JAN => '01',
              FEB => '02',
              MAR => '03',
              APR => '04',
              MAY => '05',
              JUN => '06',
              JUL => '07',
              AUG => '08',
              SEP => '09',
              OCT => '10',
              NOV => '11',
              DEC => '12',
              );

$string =~ s/   (\d{2})     # Two digits
                ([A-Z]{3})  # Three capital letters
                (\d{4})     # Four digits
            
            /$months{$2}\\$1\\$3/xg;
print $string;