in reply to changing the hash key as upper case.

Update: I just went back and checked the OP again and finally noticed that, because the OP code assigns to the hash from the output of a  map statement, the code is unquestionably changing all the keys! Consequently, this entire comment is misconceived and should be ignored. Rats. Nevermind...

Nodereaper, please bury my shame.

... requirement ... to change the hash key [to] upper case...
It is not clear to me if this means add an all-upper-case copy of any key that contains any lower case character or if it means add an all-upper-case copy of any key that contains any lower case character and delete the original key. The code of the OP certainly does the former, but, for reasons not clearly stated, that code is unacceptable.

If the latter of the two alternatives given above is needed, the following variation will do the trick. (The first hash operation is shown for demonstration purposes; only the second operation is needed for add-and-delete, i.e., change.) 

>perl -wMstrict -MData::Dumper -le
"my $hr = { qw(a 1  b 2  c 3  d 4) };
 print Dumper $hr;
 $hr->{ uc() } = $hr->{$_} for keys %$hr;
 print Dumper $hr;
 $hr->{ uc() } = delete $hr->{$_} for keys %$hr;
 print Dumper $hr;
"
$VAR1 = {
          'c' => '3',
          'a' => '1',
          'b' => '2',
          'd' => '4'
        };

$VAR1 = {
          'A' => '1',
          'a' => '1',
          'd' => '4',
          'B' => '2',
          'c' => '3',
          'b' => '2',
          'C' => '3',
          'D' => '4'
        };

$VAR1 = {
          'A' => '1',
          'B' => '2',
          'D' => '4',
          'C' => '3'
        };

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