my $buffer;
foosub( \$bufffer );
print $buffer, "\n";

sub foosub
{
    my $rs_buffer = shift;
    $$rs_buffer = "Hello, world";
}

##</code><code>##

my $buffer;
foosub( $buffer);
print $buffer, "\n";

sub foosub
{
    my $buffer = shift;
    $buffer = "Hello, world";
}