How to "unlink" a Perl array reference from the referenced variable?
In Perl 5.10.1:

	#!/usr/bin/perl

	my @a = (1, 2, 3);
	my $b = \@a;
	print join('', @{$b}) . "\n";
	@a = (6, 7, 8);
	print join('', @{$b}) . "\n";

This prints 123 then 678.  However, I'd like to get 123 both times (i.e. reassigning the value of `@a` will not change the array that `$b` references).  How can I do this?
How to "unlink" a Perl array reference from the referenced variable?
===

In Perl 5.10.1:

	#!/usr/bin/perl

	my @a = (1, 2, 3);
	my $b = \@a;
	print join('', @{$b}) . "\n";
	@a = (6, 7, 8);
	print join('', @{$b}) . "\n";

This prints 123 then 678.  However, I'd like to get 123 both times (i.e. reassigning the value of `@a` will not change the array that `$b` references).  How can I do this?