PHP Variables

In programming, variables act like physical storage containers holding critical chunks of data. You label the container with an identifiable name, place a value deep inside, and whenever you reference that label again, the PHP engine retrieves whatever value it holds.

Declaring a Variable

Unlike Java or C++, PHP is incredibly straightforward. A variable strictly begins with the $ sign, followed perfectly by the name of the variable.

<?php
  $userName = "John Doe"; // Stores a string of text
  $age = 35;              // Stores an integer
  $price = 10.50;         // Stores a floating decimal number
  
  echo $userName;
?>

[!NOTE] Have you noticed? In PHP, you do not declare the type of the variable (like String x or int y). Because PHP is a loosely typed language, it intelligently determines the correct data type on the fly depending entirely on the value loaded into it!

Strict PHP Naming Conventions

The PHP engine is incredibly unforgiving if you violate its naming conventions. For a variable name to be considered valid, it must abide by these absolute rules:

1. A variable starts strictly with the $ sign.
2. A variable name must start with a letter or the underscore character _.
3. A variable name cannot start with a number! $1name is completely invalid.
4. A variable name can only contain highly standardized alpha-numeric characters and underscores (A-z, 0-9, and _).
5. Variables are fiercely case-sensitive ($price and $PRICE are two completely different containers).

<?php
  // Valid Variables
  $car = "Volvo";
  $_location = "New York";
  $user99 = "Admin";
  $first_name = "Sarah";

  // INVALID Variables (These crash the system!)
  // $99user = "Admin"; (Starts with a number)
  // $my-car = "Audi";  (Contains a hyphen)
  // $user name = "Jim";(Contains a space)
?>

Outputting Variables inside Strings

One of PHP’s most famous and wildly praised features is how wonderfully simple it is to interject variables directly inside text strings using double quotes (").

<?php
  $favoriteColor = "Blue";
  
  // Method 1: The Magic Method (Interpolation)
  echo "My beautiful car is $favoriteColor!";
  
  // Method 2: The Concatenation Method (Using periods)
  echo "My beautiful car is " . $favoriteColor . "!"; 
?>

(Both techniques generate the exact same HTML output!)

Interactive Sandbox

Try utilizing different variables in the live environment below. See what happens if you inadvertently create an illegal variable name!