PHP Cheatsheet

Updated September 2026 · Quick reference

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PHP powers many websites and APIs. Modern PHP has types, Composer packages, and cleaner object-oriented tools.

Prefer current PHP versions, escape output for HTML, and keep secrets out of the document root.

Full lessons: PHP Tutorials

Basics

Tags and echo

PHP code lives inside <?php ... ?>. Output with echo.

Variables

Names start with $. Loose typing exists; add types where you can.

$name = "Ada";
$count = 3;

Strings

Double quotes interpolate variables; single quotes are literal.

$hi = "Hello, $name";
$raw = 'Hello, $name';

Null coalescing

Provide defaults for missing values.

$user = $_GET["user"] ?? "guest";

php -S

Built-in server for local learning (not production).

php -S localhost:8000

Arrays & control

Arrays

Lists and maps use the same array type.

$nums = [1, 2, 3];
$user = ["name" => "Ada", "id" => 1];

foreach

Iterate values or key/value pairs.

foreach ($user as $key => $value) {
  echo "$key=$value\n";
}

if / switch

Branching works like other C-family languages.

if ($count > 0) {
  echo "yes";
}

array functions

Helpers like count, in_array, array_map.

count($nums);
in_array(2, $nums, true);

Functions & types

Function

Declare parameters and return types in modern PHP.

function add(int $a, int $b): int {
  return $a + $b;
}

Nullable types

Allow null with a leading question mark.

function find(string $id): ?User {
  // ...
}

Classes

Properties and methods with visibility keywords.

class User {
  public function __construct(public string $name) {}
}

Namespaces

Avoid name clashes; autoload with Composer PSR-4.

namespace App\Models;

class User {}

Web & Composer

Superglobals

$_GET, $_POST, $_SERVER hold request data—validate before use.

$id = (int) ($_GET["id"] ?? 0);

Escape HTML

Prevent XSS when printing user data.

echo htmlspecialchars($name, ENT_QUOTES, "UTF-8");

Composer require

Install libraries and generate the autoloader.

composer require monolog/monolog
require 'vendor/autoload.php';

JSON API peek

Set headers and encode arrays/objects.

header("Content-Type: application/json");
echo json_encode(["ok" => true]);

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