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...