#!/usr/bin/perl 

#1 add use strict
use strict;
use warnings; 

#2 add ''
use File::Glob('bsd_glob');  
############################################
## Output to a TEXT File using file handle: 
############################################
 my $output="Joint.txt";
open (my $fh,">",$output) or die"Cannot open file
  '$output'.\n";     

#3 declare variables 
my (@array,@DNA,@list);
my ($filename,$combi,$entry,$number,$DNA);
do { 
  
  print"\n\n Press 1 to Enter New File or 2 to Combine:  ";
  $entry=<STDIN>; 
  chomp $entry;  

  if ($entry==1) { 
    print"\n\n    Enter New File Name (.txt):  "; 
    $filename = <STDIN>; 
    chomp $filename;
    unless ( open(FILE, $filename) ) {
      print "Cannot open file \"$filename\"\n\n";
      exit;
    } 
    @DNA= <FILE>;
    close FILE;
    #5 add chomp
    chomp(@DNA);
    #6 add join by comma
    $DNA = join(',',@DNA);    
    push @array, $DNA;
    #7 not needed array1=array;
  } elsif ($entry==2) { 
  
    # Curly brace for entry2 starts
    $number=@array; 
    print"\n\n No. of Elements in Joined Array: $number\n";
    print $fh "\n\n No. of Elements in Joined Array: $number\n";       
    # To produce all possible combinations of different elements: 
    #10 use simple $_ on @array
     
    $combi = join('',map {'{'.$_.'}'} @array);
    @list = bsd_glob($combi); 
  
    print"\n Results:\n"; 
    print $fh "\n Results:\n"; 
    #11 print each element on new line
    print join "\n",@list;
    print $fh join "\n",@list; 

  } # Curly brace for Entry 2 ends: 

} until ($entry==2); # Square bracket for do-until: 


close $output; 
exit;