Assuming you mean between the first ENERGY and the last ENERGY,

while (<>) {
   if (/\bENERGY\b/) {
      ++$energy;
      if ($energy == 1) {
         $start = $.+1;
      } else {
         $end = $.;
      }
   }
}

say $energy;
say $energy >= 2 ? $end-$start : 0;
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