#!/usr/local/bin/perl -w
use strict;

use Data::Dumper;

my %records;

{
    local $/ = 'calendar: '; # record separator.

    while ( <DATA> )
    {
        push( @{$records{$1}}, split(/\n+|calendar: /) )
            if ( s/Calendar_([0-9]+)_test\n+// );
    }
}

print Dumper( \%records );

__DATA__
calendar: Calendar_1_test
11/01/03
11/02/03
calendar: Calendar_2_test
01/02/03
01/04/03
calendar: Calendar_3_test
03/01/03
03/02/03

##</code><code>##

:!./test.pl
$VAR1 = {
          '1' => [
                   '11/01/03',
                   '11/02/03'
                 ],
          '2' => [
                   '01/02/03',
                   '01/04/03'
                 ],
          '3' => [
                   '03/01/03',
                   '03/02/03'
                 ]
        };