my $user_inputs = analyse_user_inputs($Settings);
print Dumper($user_inputs);

##</code><code>##

$Settings =
{
batchplot_output_filename => "gps3", 
plot_all_variables => 'off', 
# DEFAULT PLOTS & VALUES
default_values =>
[
{
profiles => [qw(prof1 prof2)],
linewidth => ["2"],
single_dotnotes => 'On',
legend => ["On"],
},
],
#BEGIN CUSTOM PLOTS
custom_plots =>
[
  [ 
    {
        yvars => 'LATDIIP',
        xvars => 'ELONGI',
    },
  ],  
]
}

##</code><code>##

sub analyse_user_inputs {
    my $hashORarray_ref = shift @_;
    my @the_inputs;
        
if (ref $hashORarray_ref eq 'HASH') {
   foreach ( keys %{$hashORarray_ref} ){
#      print "$_ \n";
      push @the_inputs , $_ ;
      analyse_user_inputs($hashORarray_ref->{$_});
   }
}
if (ref $hashORarray_ref eq 'ARRAY') {
   for (my $i = 0; $i < scalar(@{$hashORarray_ref}); $i++) {
      analyse_user_inputs($hashORarray_ref->[$i]);
   }
}
   return(\@the_inputs);
}