Another method, one liner using two splits:

use strict;
use Data::Dumper;

my $list = "1-5,6a-e,7,9-12,89xDC-G";

my @s = map { my @t = split /-/;
              my $l = length($t[0]) - 1;    # length less 1
              $#t == 0 ? $_ :
                $t[0] + 0 eq $t[0] ?        # pure number?
                  $t[0] .. $t[1] :
                  map { substr($t[0],0,$l) . $_ }
                    substr($t[0],$l,1) .. $t[1]
            } split /,/, $list;

print Dumper(\@s);
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And the output is:

$VAR1 = [
          1,
          2,
          3,
          4,
          5,
          '6a',
          '6b',
          '6c',
          '6d',
          '6e',
          '7',
          9,
          10,
          11,
          12,
          '89xDC',
          '89xDD',
          '89xDE',
          '89xDF',
          '89xDG'
        ];
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Update: Typo fixed - 89xDC-G (was 89xFC-G). Thanks OverlordQ!