$ operator
Operator is used to define variables in php. For example, message. Such variables can contain any type of value like int, string, etc.
$$ operator
$$ is a special operator that contains the name of another variable and can be used to access the value of that variable.
Example
Following the example, shows the usage of '′vs′$' operators.
<!DOCTYPE html>
<html>
<head>
<title>PHP Example</title>
</head>
<body>
<?php
$welcome = "message";
$message = "Welcome to Tutorialspoint";
echo $welcome;
print("<br/>");
echo $$welcome;
?>
</body>
</html>Output
message Welcome to Tutorialspoint