No there is no copy. If you know about C you will know about *pointers*. Anyway even if you don't all that is passed is a pointer to the original array. @$list_ref just uses the array pointed to by $list_ref. No copy is made. This is why it is efficient to pass array refs to and from subs as you never copy an array you don't have to.

The is a way to implement things the way you wanted originally by passing $a and $b to the other package but this is far less efficient so don't do it! Here it is just to show you it can be done. We can even localise $a and $b :-)

package MyOrder;

use strict;
my %order = ();

sub SortMyWay { 
  my ($a,$b) = @_; 
  if ( exists $order{$a} and exists $order{$b} ) {
    return $order{$a} <=> $order{$b}
  } elsif ( exists $order{$a} ) {
    return 1
  } elsif ( exists $order{$b} ) { 
    return -1 
  } else { 
    return $a cmp $b 
  } 
} 

package main;

use strict;
my @foo = qw( j a p h , );
my @bar = sort { MyOrder::SortMyWay($a,$b) } @foo;
print "@bar";
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cheers

tachyon

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