use warnings;
use strict;

my @mon_yr = qw/ APR12 MAR13 APR11 MAR12 FEB13 APR13/;

my %mon_name = (
    'JAN' => 1,
    'FEB' => 2,
    'MAR' => 3,
    'APR' => 4,
    # add others if you want
);

print join $/ => map { $_->[0] }
  sort { 
        $a->[2] <=> $b->[2] 
        || 
        $a->[1] <=> $b->[1] }
  map {
    /(\w+?)(\d+?)$/;
    [ $_, $mon_name{$1}, $2 ]
  } @mon_yr;

print $/;