So as I understand it, you want to dump the current results and start a new %HOH when the $key changes.

When setting something like this up there are 3 things to consider:
1. What is the steady state, normal thing causes the desired action?
2. How do we get it started? (what is special about it?)
3. How do we get it stopped? (what is special about it?)

One approach for is to dump the results and reset %HOH when the $key changes. To do that perhaps:

my $prev_key = "";
my %HOH;
while ( a line read from file )
{
   ...get the current key .. code that you have already
   if (  $current_key ne $prev_key)
   {
      if ($prev_key ne "" ) #don't dump first time through!
      {
         ...dump the %HOH  #this is the previous result
      }
      $prev_key = $current_key;
      ...%HOH=();  #reset!
   }
   
   ...processing of the current_key
}
...dump the %HOH ... #the last record...
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To solve question (2), the first time through the loop, I don't dump the %HoH unless there is data there - there is more than one possible way to test for this (keys %HOH) or ($prev_key ne "" ). If the thing that does the dump/final processing of this time slice has some code to not do anything if there is no data, there is no nested "if".

To solve question (3), after the loop ends due to lack of data, dump the final incarnation of the hash.

There is of course more than one way to accomplish what you need, but the 3 questions are always the same : (1)steady-state operation, (2)getting started, (3)getting finished.

I recommend writing the "steady-state", question (1) code first and then "fiddle with it" until questions (2) and (3) work out ok.