xdatacar to input for fittin program

#!/usr/bin/perl
use strict;
use warnings;

my $i ; my $j ; my $buf ; my $line ; my $aa=8.4216417639317700 ;
my @empline ; my @ener; my @xdatcar ; my $xdhead=7 ;

open (XDAT, '<', 'XDATCAR') or die "'XDATCAR' $!";
open (ENER, '<', 'energy.dat') or die "'energy.dat' $!";

@ener=<ENER> ; chomp for @ener ;            ## reading energy.dat
my $Ndata = scalar @ener ;                 ## getting total lines number in energy.dat
foreach $buf (@ener) { $buf=sprintf("%.10f",$buf); }   ##convert string to float
close (ENER) ;

@xdatcar=<XDAT>; chomp for @xdatcar;    ## reading XDATCAR
close (XDAT) ;

my @nspe = split(' ',$xdatcar[$xdhead-1]) ;         ##getting number of species array from XDATCAR
my $Nat=0 ; foreach $buf (@nspe) { $Nat+=$buf }    ## sumup nspe array

$i = 0 ;
$j = 0 ;
foreach $line (@xdatcar) {          ## searching for empty line or Direct line, to be replaced with energy values
  $i++ ;
  if ( $line ~~ /^\s*$/ or $line ~~ /Direct/i ) {   ##matching empty lines with any kind of whitespaces, or lines containing 'Direct' word
      $empline[$j]= $i ;                    ## saving pointer to those lines, empline
      $line = "    $aa    $ener[$j]   $Nat   1" ;                  ## replacing those empty lines with energies and data
      $j++ ;
  }
}

my $off=$xdhead+1 ;

for($i = 0; $i < $Ndata-1; $i++) {
  my @block = @xdatcar[$empline[$i]..$empline[$i]+$Nat-1] ;   ## extracting blocks between empty lines
  my @revblock = reverse(@block) ;                            ## inverting block

  my @sub_block = @revblock[$Nat-5..$Nat-1] ;                            ## inverting molecule sub_block
  my @revsub_block = reverse(@sub_block) ;
  splice(@revblock,$Nat-5,5,@revsub_block) ;

  splice(@xdatcar, $off+$i*($Nat+1), $Nat, @revblock) ;       ## replacing with correct block
}

splice(@xdatcar, 0, $xdhead) ;       ## removing header

open(OUT,'>','tofit.in');
foreach $line (@xdatcar) { print OUT "$line \n" ; }