Nice. But I would just use /\D/ to detect a non-numeric array element. No need to mess with automatically-generated classes:

# no "use autobox::universal"
# ...
for (@array) {
    if (/\D/) {
        $key=$_;
    } else {
        push @{$hash{$key}},$_;
    }
}
# ...
[download]

Alternatively, use looks_like_number() from Scalar::Util that wraps the Perl API function of the same name:

# ...
use Scalar::Util qw( looks_like_number );
# ...
for (@array) {
    if (looks_like_number($_)) {
        $key=$_;
    } else {
        push @{$hash{$key}},$_;
    }
}
# ...
[download]

Alexander

Autobox and \D play differently:

use autobox::universal qw(type);
use Data::Dumper;
use strict;
use warnings;

my @array = ('a', 1, 2, 3, 4, 'b', 6, 7, 8, '1', 2, 3, 4, 5); # note t
+he '1' which autobox will call a string.
my %hash = ();
my $key;
for (@array) {
    if (type($_) eq 'STRING') {
        $key=$_;
    }
    else {
         push @{$hash{$key}},$_;
    }
}
warn Data::Dumper->Dump([\%hash],[qw(*hash)]),' ';
[download]

The output from Data::Dumper:

%hash = (
          '1' => [
                   2,
                   3,
                   4,
                   5
                 ],
          'b' => [
                   6,
                   7,
                   8
                 ],
          'a' => [
                   1,
                   2,
                   3,
                   4
                 ]
        );
[download]