- call by value
- call by reference

References are always a good idea - especially if you have large or complex datastructures, but using values is much easier in the beginning. Here's an example that I've posted earlier this day on a german perl-community site. Two array-references gets passed to a function in an anonymous hash:

#!/usr/bin/perl

use strict;
use warnings;

use Data::Dumper;

my @numbers = (1..10);
my @words = qw(hello world outside);

function( {NUMBERS=>\@numbers , WORDS=>\@words} );
exit;

sub function {
  die "no parameter!\n" unless @_;
  my %opt = %{ shift @_ };
  print Dumper \%opt;

  my @i_words = $opt{WORDS};
  print Dumper \@i_words;

  my @i_numbers = $opt{NUMBERS};
  print Dumper \@i_numbers;
}
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