use strict;

my @num = qw(1 2 3 4 5);

first();

sub first {
   print "\@num before: @num\n";
   # prints 1 2 3 4 5
   my $result = second(\@num);
   print "result: $result\n";
   print "\@num after: @num\n";
   # prints 1 2 3 4 5 6
   # But I would need it to still print
   # 1 2 3 4 5
}

sub second {
   my $num_ref = shift;

   push(@$num_ref, 6);

   my $sum = 0;

   foreach (@$num_ref) {
      $sum += $_;
   }

   return $sum;
}