I came upon the need to ensure that the keys for values slurped into a nested hash via XML::Simple reading an XML config file matched what I was referring to them as in my script. After playing around with various Tie::* modules I decided it was just easier for me to force the entire nested hash into one or the other case for my access. The following was the outcome of my trials: Note that duplicate name keys with differing case will be squashed. Now this hash:

$nestedhash = {
    'REJECTED'  => 'REJECTED',
    'FREQUENCY' => 'FREQUENCY',
    'INCOMING'  => {
                  'DIR' => 'DIR'
    },
    'CONNECTIONSTRING' => 'CONNECTIONSTRING',
    'REGEX' => 'REGEX',
    'EMAIL' => {
               'GENERAL'    => 'GENERAL',
               'CRITICAL'   => 'CRITICAL',
               'SMTPSERVER' => 'SMTPSERVER'
    },
    'DIR' => ['DIR1', 'DIR2']
};
[download]

becomes this:

$VAR1 = {
          'incoming' => {
                          'dir' => 'DIR'
                        },
          'frequency' => 'FREQUENCY',
          'regex' => 'REGEX',
          'rejected' => 'REJECTED',
          'dir' => [
                     'DIR1',
                     'DIR2'
                   ],
          'connectionstring' => 'CONNECTIONSTRING',
          'email' => {
                       'general' => 'GENERAL',
                       'critical' => 'CRITICAL',
                       'smtpserver' => 'SMTPSERVER'
                     }
        };
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Update: Good eye, blakem, I never had occasion to run my hash through twice, but the added check fixes that problem.

sub force_uc_hash {
    my $hashref = shift;
    foreach my $key (keys %{$hashref} ) {
        $hashref->{uc($key)} = $hashref->{$key};
        force_uc_hash($hashref->{uc($key)}) if ref $hashref->{$key} eq
+ 'HASH';
        delete($hashref->{$key}) unless $key eq uc($key);
    }
}

sub force_lc_hash {
    my $hashref = shift;
    foreach my $key (keys %{$hashref} ) {
        $hashref->{lc($key)} = $hashref->{$key};
        force_lc_hash($hashref->{lc($key)}) if ref $hashref->{$key} eq
+ 'HASH';
        delete($hashref->{$key}) unless $key eq lc($key);;
    }
}
[download]