Since you didn't specify what your desired output should be, I can only guess. I suspect you want to push into your array. I also simplified the code using join.

change:

                @NAMESPACE = $APPCLASS . "~" . $INSTANCE . "~" . $PARA
+METER . "~" . $PARAM_TYPE;
[download]

to:

                push @NAMESPACE, join '~', $APPCLASS, $INSTANCE, $PARA
+METER, $PARAM_TYPE;
[download]

Output:

$VAR1 = 'ORACLE_AVAILABILITY~atecr~InstanceStatus~CONSUMER';
$VAR2 = 'ORACLE_AVAILABILITY~atecr~RSSpaceLeft~CONSUMER';
$VAR3 = 'ORACLE_AVAILABILITY~atecr~CannotExtend~CONSUMER';
$VAR4 = 'ORACLE_CAPACITY~atecq~FreeSpace~CONSUMER';
$VAR5 = 'ORACLE_CAPACITY~atecq~ExtentsLeft~CONSUMER';
$VAR6 = 'ORACLE_CAPACITY~atecq~CursorsLeft~CONSUMER';
[download]

Side note: Typically, you would pass a reference to Data::Dumper:

print Dumper(\@NAMESPACE);

__END__

$VAR1 = [
          'ORACLE_AVAILABILITY~atecr~InstanceStatus~CONSUMER',
          'ORACLE_AVAILABILITY~atecr~RSSpaceLeft~CONSUMER',
          'ORACLE_AVAILABILITY~atecr~CannotExtend~CONSUMER',
          'ORACLE_CAPACITY~atecq~FreeSpace~CONSUMER',
          'ORACLE_CAPACITY~atecq~ExtentsLeft~CONSUMER',
          'ORACLE_CAPACITY~atecq~CursorsLeft~CONSUMER'
        ];
[download]

Side note: use "readmore" tags for large code samples: Writeup Formatting Tips