What is the difference between $message and $$message?

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$message stores variable data while $$message is used to store variable of variables.

$message stores fixed data whereas the data stored in $$message may be changed dynamically.

In PHP, the difference between $message and $$message lies in the way variables are referenced.

  1. $message: This is a regular variable. It holds the value assigned to it directly. For example:
    php
    $message = "Hello, world!";
    echo $message; // Outputs: Hello, world!
  2. $$message: This involves variable variable usage in PHP. It allows you to create variables dynamically based on the value of another variable. Essentially, it takes the value of the variable on the right side of $$ and treats it as the name of a variable. For example:
    php
    $message = "variable_name";
    $$message = "Hello, world!";
    echo $variable_name; // Outputs: Hello, world!

So, the key difference is that $message is a regular variable, while $$message is a variable variable, meaning it creates a variable based on the value of another variable.