my $done= 0;
  # ...
      my( @data, $row, $key );
      return   if   $done  ||  ! defined( $row= <$fh> );
      do {
          chomp( $row );
          # [SNIPPED] munge $row, set $key and @data
      } while(  $key < $min  &&  defined( $row= <$fh> )  );
      if(  $max < $key  ) {
          $done = 1;
          return;
      }
      return( $key, \@data );
  }