use Data::Dumper;
local $Data::Dumper::Sortkeys = \&dumper_filter;
sub dumper_filter {
  my ($hash) = @_;
  return [(sort {lc $a cmp lc $b} keys %$hash)];
}
my $d = Data::Dumper -> new ([\%ENV]);
print '<pre>' . $d -> Dump . '</pre>';