PHP Variables - GeeksforGeeks

PHP Variables

Last Updated : 30 Oct, 2026

A variable in PHP stores data such as strings, numbers, arrays, and objects. Variables can be updated during script execution, and PHP determines their data types automatically.

  • Declaration: Variable names begin with $, followed by a valid identifier.
  • Dynamic Typing: Variables do not require explicit type declarations.
  • Case Sensitivity: $name and $Name are different variables.
  • Value Assignment: Variables can store and update different values.

Declaring Variables in PHP

PHP variables are created by assigning a value using the = operator.

Syntax:

$variable_name = value;

Example:

PHP 
<?php
$name = "XYZ";
$age = 30;
$salary = 45000.50;
$isEmployed = true;
?>

Variable Naming Rules

  • Variable names must start with a letter or underscore (_), not a number.
  • Names can contain letters, numbers, and underscores.
  • Variable names are case-sensitive.
  • Use descriptive names such as $userName and $totalAmount.
  • Avoid reserved keywords and names that conflict with PHP syntax.

Valid and Invalid Variable Names

<?php
$firstName = "Alen";  // Valid
$_age = 25;            // Valid

// $2ndPlace = "Ben";  // Invalid: starts with a number
$class = "Physics";    // Valid
?>

PHP Variable Scope

Variable scope determines where a variable can be accessed. PHP supports local variables, global variables, static local variables, and superglobals.

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1. Local Variables

Variables declared inside a function are local to that function and cannot be accessed directly outside it.

PHP 
<?php
$num = 60;

function local_var() {
    $num = 50;
    echo "Inside function: $num\n";
}

local_var();
echo "Outside function: $num";
?>

2. Global Variables

Variables declared outside functions have global scope. Use the global keyword to access them inside a function.

PHP 
<?php
$num = 20;

function global_var() {
    global $num;
    echo "Inside function: $num\n";
}

global_var();
echo "Outside function: $num";
?>

3. Static Variables

A static local variable retains its value between function calls instead of being reinitialized each time.

PHP 
<?php
function static_var() {
    static $num = 5;
    $sum = 2;

    $sum++;
    $num++;

    echo $num . "\n";
    echo $sum . "\n";
}
static_var();
static_var();
?>

Here, $num retains its updated value between calls, while $sum is initialized again on each call.

4. Superglobals

Superglobals are built-in PHP variables accessible from any scope, including inside functions. Common examples include $_GET, $_POST, $_SESSION, $_COOKIE, $_SERVER, and $GLOBALS.

PHP 
<?php
echo $_SERVER['SERVER_NAME'];
?>

This example displays the server name provided by the server environment.

Variable Variables

Variable variables allow a variable's value to determine the name of another variable. PHP uses $$ syntax for this purpose.

PHP 
<?php
$a = 'hello';
$$a = 'World';

echo $hello;
?>

Here, $a contains hello, so $$a creates the variable $hello with the value World.

Best Practices for Using Variables

  • Use descriptive names such as $totalAmount instead of $x.
  • Follow a consistent naming convention, such as camelCase.
  • Initialize variables before using them.
  • Avoid reserved keywords and confusing variable names.
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