What does $$ (dollar dollar or double dollar) mean in PHP?

Example is a variable declaration within a function:

global $$link;

What does $$ mean?

A syntax such as $$variable is called Variable Variable.

For example, if you consider this portion of code :

$real_variable = 'test';
$name = 'real_variable';
echo $$name;

You will get the following output :

test

Here :

• $real_variable contains test
• $name contains the name of your variable : 'real_variable'
• $$name mean "the variable thas has its name contained in $name"
  • Which is $real_variable
  • And has the value 'test'

EDIT after @Jhonny's comment :

Doing a $$$ ?
Well, the best way to know is to try ;-)

So, let's try this portion of code :

$real_variable = 'test';
$name = 'real_variable';
$name_of_name = 'name';

echo $name_of_name . '<br />';
echo $$name_of_name . '<br />';
echo $$$name_of_name . '<br />';

And here's the output I get :

name
real_variable
test

So, I would say that, yes, you can do $$$ ;-)

The inner $ resolves the a variable to a string, and the outer one resolves a variable by that string.

So, consider this example

$inner = "foo";
$outer = "inner";

The variable:

$$outer

would equal the string "foo"