Instead of creating an anonymous sub which you call and then discard, you could use do with a block:

$header{"Number of Drills"} = do {  
                                      my $ret;
                                      foreach my $l ( @drill_arr ) {
                                          foreach ( values %{$l->tool}
+ ) {
                                              $ret += $_->count;
                                          }
                                      }
                                      $ret;
                                  };
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