use re 'debug';

@dates = ('20130601', '20130401', '20130501');
my @sorted =
   map $_->[1],
   sort { $a->[1] <=> $b->[1] }
   map [ $_, join('', (/(..)(..)(....)/)[0,1,2]) ],
   @dates;  # DD-MM-YYYY
print "@sorted\n";

##</code><code>##

Compiling REx `(..)(..)(....)'
size 21 Got 172 bytes for offset annotations.
first at 3
   1: OPEN1(3)
   3:   REG_ANY(4)
   4:   REG_ANY(5)
   5: CLOSE1(7)
   7: OPEN2(9)
   9:   REG_ANY(10)
  10:   REG_ANY(11)
  11: CLOSE2(13)
  13: OPEN3(15)
  15:   REG_ANY(16)
  16:   REG_ANY(17)
  17:   REG_ANY(18)
  18:   REG_ANY(19)
  19: CLOSE3(21)
  21: END(0)
minlen 8 
Offsets: [21]
	1[1] 0[0] 2[1] 3[1] 4[1] 0[0] 5[1] 0[0] 6[1] 7[1] 8[1] 0[0] 9[1] 0[0] 10[1] 11[1] 12[1] 13[1] 14[1] 0[0] 15[0] 
Matching REx `(..)(..)(....)' against `20130601'
  Setting an EVAL scope, savestack=12
   0 <> <20130601>        |  1:  OPEN1
   0 <> <20130601>        |  3:  REG_ANY
   1 <2> <0130601>        |  4:  REG_ANY
   2 <20> <130601>        |  5:  CLOSE1
   2 <20> <130601>        |  7:  OPEN2
   2 <20> <130601>        |  9:  REG_ANY
   3 <201> <30601>        | 10:  REG_ANY
   4 <2013> <0601>        | 11:  CLOSE2
   4 <2013> <0601>        | 13:  OPEN3
   4 <2013> <0601>        | 15:  REG_ANY
   5 <20130> <601>        | 16:  REG_ANY
   6 <201306> <01>        | 17:  REG_ANY
   7 <2013060> <1>        | 18:  REG_ANY
   8 <20130601> <>        | 19:  CLOSE3
   8 <20130601> <>        | 21:  END
Match successful!
Matching REx `(..)(..)(....)' against `20130401'
  Setting an EVAL scope, savestack=12
   0 <> <20130401>        |  1:  OPEN1
   0 <> <20130401>        |  3:  REG_ANY
   1 <2> <0130401>        |  4:  REG_ANY
   2 <20> <130401>        |  5:  CLOSE1
   2 <20> <130401>        |  7:  OPEN2
   2 <20> <130401>        |  9:  REG_ANY
   3 <201> <30401>        | 10:  REG_ANY
   4 <2013> <0401>        | 11:  CLOSE2
   4 <2013> <0401>        | 13:  OPEN3
   4 <2013> <0401>        | 15:  REG_ANY
   5 <20130> <401>        | 16:  REG_ANY
   6 <201304> <01>        | 17:  REG_ANY
   7 <2013040> <1>        | 18:  REG_ANY
   8 <20130401> <>        | 19:  CLOSE3
   8 <20130401> <>        | 21:  END
Match successful!
Matching REx `(..)(..)(....)' against `20130501'
  Setting an EVAL scope, savestack=12
   0 <> <20130501>        |  1:  OPEN1
   0 <> <20130501>        |  3:  REG_ANY
   1 <2> <0130501>        |  4:  REG_ANY
   2 <20> <130501>        |  5:  CLOSE1
   2 <20> <130501>        |  7:  OPEN2
   2 <20> <130501>        |  9:  REG_ANY
   3 <201> <30501>        | 10:  REG_ANY
   4 <2013> <0501>        | 11:  CLOSE2
   4 <2013> <0501>        | 13:  OPEN3
   4 <2013> <0501>        | 15:  REG_ANY
   5 <20130> <501>        | 16:  REG_ANY
   6 <201305> <01>        | 17:  REG_ANY
   7 <2013050> <1>        | 18:  REG_ANY
   8 <20130501> <>        | 19:  CLOSE3
   8 <20130501> <>        | 21:  END
Match successful!
20130401 20130501 20130601
Freeing REx: `"(..)(..)(....)"'

##</code><code>##

use warnings;
use strict;

my @dates = ('20130601', '20130401', '20130501');

print join ' ' => map{$_->[0]}
              sort{$a->[1] <=> $b->[1]}
              map{/.{4}(.{2})/;[$_,$1]} @dates;