These files go into This/is/the/full/path/file.abc.MERGED.txt:
   part-1, part-2, part-3
These files go into This/is/the/full/path/file.def.MERGED.txt:
   part-1, part-2
$VAR1 = {
          'This/is/the/full/path/file.' => {
                                             'jkl' => [
                                                        'part-2'
                                                      ],
                                             'abc' => [
                                                        'part-1',
                                                        'part-2',
                                                        'part-3'
                                                      ],
                                             'mno' => [
                                                        'part-5'
                                                      ],
                                             'def' => [
                                                        'part-1',
                                                        'part-2'
                                                      ],
                                             'ghi' => [
                                                        'part-1'
                                                      ]
                                           }
        };