use warnings FATAL => 'all';
use strict;


my %hash = (
    article => [
      { InternalSKU     => '179',
        Name            => 'wiggle',
        external_source => [
          { mfg => 'AMD',    SKU => 'CDS00013',  count => 100, },
          { mfg => 'Intel',  SKU => 'FOO00099',  count =>  42, },
          ],
        },
      { InternalSKU     => '180',
        Name            => 'woggle',
        external_source => [
          { mfg => 'AMD',    SKU => 'CDS00014',  count => 102, },
          { mfg => 'Intel',  SKU => 'BAR00042',  count =>  99, },
          ],
        },
      ],
      );

my $ref_to_article_anon_array = $hash{article};

for my $hashref (@$ref_to_article_anon_array) {

    my $i_sku = $hashref->{InternalSKU};
    my $name  = $hashref->{Name};
    print "Name $name;  Internal SKU: $i_sku;  Source(s): \n";

    my $grand_total = 0;
    for my $hr_external (@{ $hashref->{external_source} }) {
        # my $mfg   = $hr_external->{mfg};
        # my $sku   = $hr_external->{SKU};
        # my $count = $hr_external->{count};
        my ($mfg, $sku, $count) =  # either way works
            @$hr_external{ qw(mfg SKU count) };
        $grand_total += $count;
        print "    mfg $mfg;  mfg's SKU: $sku;  count: $count \n";
        }

    print "total ${name}'s on hand: $grand_total \n\n";

    }

##</code><code>##

Name wiggle;  Internal SKU: 179;  Source(s):
    mfg AMD;  mfg's SKU: CDS00013;  count: 100
    mfg Intel;  mfg's SKU: FOO00099;  count: 42
total wiggle's on hand: 142

Name woggle;  Internal SKU: 180;  Source(s):
    mfg AMD;  mfg's SKU: CDS00014;  count: 102
    mfg Intel;  mfg's SKU: BAR00042;  count: 99
total woggle's on hand: 201