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my %dupes = (); # name->count
my $dref = \%dupes;

  @file_info = qw(data1 data2 data3);
  %files = (
     X  => \@file_info
  )

  $file_info_ref = $files{X};
  push @$file_info_ref,'data5';
...
  or

  push @{$files{X}}, 'data5'

my %fileinfo;
my %dupes;
...
   # No need to re-store it in the hash, because $fileinfo{$_} 
   # and $saved_info both point to the same array
}