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foreach my $k1 (keys %$h1) {
    my @fields = split /,/, $h1->{$k1};
    ...
}

while (my ($k1, $v1) = each %$h1) {
    my @fields = split /,/, $v1;
    ...
}

use 5.010;
use strict;
...
    { push @{ $tmp{$_} }, $k for split /,/, $v }
for (values %tmp)
    { next if @$_ < 2; say join ',', @$_ }

say $_ for sort map { join ',', @$_ } grep { @$_ > 1 } values %tmp;