PHP: Variable variables - Manual

Tomos is right, the $$ represents a variable variable. Here's how they work

$foo = 'bar';
$name = 'foo';

echo $name; // foo
echo $$name; //bar
echo $foo; //bar

You first assign the value of a variable, $name, to the name of another variable. When you set $name to a value, it will replace that variablename with the value of the variable you provide it.

$test = 'asdf';
$$test = 'I am changing asdf\'s value!';
echo $$test; // I am changing asdf's value!
echo $test; // asdf
echo $asdf; // I am changing asdf's value!

I'd add the suggestion to not use this style if you can avoid it, it makes the code hard to read without a step through debugger.

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$name is variable where as $$name is reference variable

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$name is a variable while $$name is a reference variable.

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