use strict;
use warnings;
use Data::Dumper;
{
    my @arra = (10,20);

    #no need for & and you can just pass a reference
    #&doublevalue(*arra);
    doublevalue(\@arra); 
}

sub doublevalue {
  #my is preferred to local
  #local *a = shift ;
  my $a = shift;
  print Dumper @$a;
}