Re^3: sorting dates in YYYYMMDD format

..I solved the problem..
Good... but why not just use sort just as you have been told previously on this post.
Yes your regexes matched successfully, see

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";
[download]

...produces...

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: `"(..)(..)(....)"'
[download]

but even at that it a lot of work.
However, if you must use "Schwartzian transform", you can sort on the month, since the year is the same like this:

use warnings;
use strict;

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

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

But sincerely, for this use sort just like other monks told you.

If you tell me, I'll forget.
If you show me, I'll remember.
if you involve me, I'll understand.
--- Author unknown to me

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