sub test {
    my($pkg) = caller;
    print "I've been called from package $pkg\n";
}

package Foo;
main::test();

__END__
I've been called from package Foo

##</code><code>##

$Foo::x   # scalar
@Foo::y   # array
%Foo::z   # hash
$Foo:z{bar}  # hash item
# etc.

##</code><code>##

my $pkg = "Foo";
my $var = "x";
$Foo::x = 123;
{
    no strict 'refs';
    print ${$pkg . '::' . $var};
}

__END__
prints: "123";