In PHP language,  $(dollar sign) is used to store variable data. $$ can be used to store a variable of a variable. Data stored in $ is fixed while data stored in $$(double dollar sign) can be changed dynamically.

such as:

• $x represents a variable
• $$x represents a variable with the content of $x

Example 1

<?php  
$x = "php";  
$$x = 500;  
echo $x."<br/>";  
echo $$x."<br/>";  
echo $php;  
?>  

Output :  php ,500, 500

In the above example, we have assigned a value to the variable x as PHP. The value of the reference variable $$x is assigned as 500.

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

Example 2

<?php  
 $var="Hello";  
 $$var="World";  
 echo $var. "<br>";  
 echo $$var. "<br>";  
 echo "Welcome to $var " . $$var;  
?>  

Output: Hello, World, Welcome to Hello World

In the above example, we have assigned a value to the variable var as Hello Value of reference variable $$var is assigned as World.

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