You say you have an array (@t_loop), but you dumped a hash ref. If you did print(Dumper(@t_loop)), you should have done print(Dumper(\@t_loop)) so we can see the entire structure. Dumper expects a list of *scalars*.

Your code is actually already correct for the second dump. The following will handle both data structures you presented:

foreach (@t_loop) {
   my $label = $_->{label};

   my $value;
   if (exists($_->{value_loop})) {
      $value = join(' ', map { $_->{value} } @{$_->{value_loop});
   } else {
      $value = $_->{value};
   }

   $final .= "$label=$value\n";
}
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It's complicated, but that's because your data structure is needlessly complex.

%t_loop = (
   Dow => [ 'Sun', 'Mon', 'Tue', 'Wed' ],
);
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%t_loop = (
   UK => 'Country',
);
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while (my ($key, $val) = each %t_loop) {
   $val = join(' ', @$val)
      if ref $val;

   $final .= "$key=$val\n";
}
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Update: oy! My initial code was very wrong.