See Tutorials: References

#!/usr/bin/perl --
use strict; use warnings;

my @foo = 0..3;
my @bar = 3..6;
my %blah = ( foo => \@foo, stillfoo => \@foo, bar => \@bar );
$blah{"why YES, this too is foo"} = \@foo;
$blah{"and this too is bar"} = \@bar;
my $THIS_IS_FOO_TOO = \@foo;
my $THIS_IS_BAR_TOO = \@bar;

## and now, lets modify $foo[1] five different ways
$foo[1] .= ' you ';
$blah{foo}[1] .= ' are ';
$blah{stillfoo}[1] .= ' still ';
$blah{"why YES, this too is foo"}[1] .= ' the '; 
$THIS_IS_FOO_TOO->[1] .= ' @foo ';

print "$foo[1]\n";
__END__
[download]

The output is 1 you are still the @foo

See also http://learn.perl.org/books/beginning-perl/ and the Modern Perl Book