What are PHP $ and $$ Variables ?

 The $var (single dollar) is a normal variable with the name var that stores any value like string, integer, float, etc.

The $$var (double dollar) is a reference variable that stores the value of the $variable inside it.

To understand the difference better, let's see some examples.

Example 1

1. <?php  
2. $x = "abc";  
3. $$x = 200;  
4. echo $x."<br/>";  
5. echo $$x."<br/>";  
6. echo $abc;  
7. ?>  

Output:

In the above example, we have assigned a value to the variable x as abc. Value of reference variable $$x is assigned as 200.

Now we have printed the values $x, $$x and $abc.

Example2

1. <?php  
2.  $x="U.P";  
3. $$x="Lucknow";  
4. echo $x. "<br>";  
5. echo $$x. "<br>";  
6. echo "Capital of $x is " . $$x;  
7. ?>  

Output:

In the above example, we have assigned a value to the variable x as U.P. Value of reference variable $$x is assigned as Lucknow.

Now we have printed the values $x, $$x and a string.

Example3

1. <?php  
2. $name="Cat";  
3. ${$name}="Dog";  
4. ${${$name}}="Monkey";  
5. echo $name. "<br>";  
6. echo ${$name}. "<br>";  
7. echo $Cat. "<br>";  
8. echo ${${$name}}. "<br>";  
9. echo $Dog. "<br>";  
10. ?>  

Output:

In the above example, we have assigned a value to the variable name Cat. Value of reference variable ${$name} is assigned as Dog and ${${$name}} as Monkey.

Now we have printed the values as $name, ${$name}, $Cat, ${${$name}} and $Dog.

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