PHP Cheat Sheet
PHP syntax, associative arrays, superglobals, and object-oriented features for server-side web development and dynamic scripting.
2 PagesBeginnerMar 22, 2026
Basic Syntax
Variables, control flow, and output.
php
<?php$age = 30;$name = "Ada";$pi = 3.14159;if ($age >= 18) { echo "$name is an adult\n";}for ($i = 0; $i < 5; $i++) { echo "Count: $i\n";}?>
Arrays
Indexed and associative arrays.
php
<?php$nums = [5, 3, 1, 4, 2];sort($nums); // [1, 2, 3, 4, 5]$ages = ["Alice" => 30, "Bob" => 25]; // associative array$ages["Carol"] = 28;echo $ages["Alice"]; // 30$doubled = array_map(fn($n) => $n * 2, $nums);$evens = array_filter($nums, fn($n) => $n % 2 === 0);?>
Object-Oriented PHP
Classes, constructors, and visibility.
php
<?phpclass Person { public string $name; private int $age; public function __construct(string $name, int $age) { $this->name = $name; $this->age = $age; } public function greet(): string { return "Hello, {$this->name}"; }}$p = new Person("Ada", 30);echo $p->greet();?>
Superglobals
Built-in arrays always available in scope.
- $_GET- associative array of URL query string parameters
- $_POST- associative array of form data sent via POST
- $_SESSION- persists data across requests for a logged-in user
- $_SERVER- server and execution environment information (e.g. REQUEST_METHOD)
- $_ENV- environment variables available to the script
- $_FILES- info about files uploaded via HTTP POST
String Functions
Commonly used string helpers.
php
$s = "Hello World";strlen($s); // 11strtoupper($s); // "HELLO WORLD"str_replace("World", "PHP", $s); // "Hello PHP"substr($s, 0, 5); // "Hello"explode(" ", $s); // ["Hello", "World"]implode("-", ["a", "b"]); // "a-b"trim(" x "); // "x"str_contains($s, "World"); // true (PHP 8+)sprintf("%05.2f", 3.1); // "03.10"
PDO Database Access
Prepared statements to prevent SQL injection.
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$pdo = new PDO("mysql:host=localhost;dbname=app", $user, $pass, [ PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION, PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,]);$stmt = $pdo->prepare("SELECT * FROM users WHERE age > :age");$stmt->execute(["age" => 18]);$rows = $stmt->fetchAll();$insert = $pdo->prepare("INSERT INTO users (name) VALUES (?)");$insert->execute(["Ada"]);echo $pdo->lastInsertId();
Modern PHP Features
Syntax from PHP 7.4 through 8.x.
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// Arrow functions (7.4)$doubled = array_map(fn($x) => $x * 2, [1, 2, 3]);// Named arguments + nullsafe (8.0)$name = $user?->getProfile()?->name;// Match expression (8.0)$label = match($code) { 200, 201 => "OK", 404 => "Not Found", default => "Unknown",};// Constructor promotion (8.0)class Point { public function __construct( public float $x = 0, public float $y = 0, ) {}}
Array Functions
Frequently used array utilities.
- array_map- apply a callback to every element
- array_filter- keep elements passing a callback test
- array_reduce- fold an array into a single value
- array_merge- combine arrays, re-indexing numeric keys
- in_array- check whether a value exists (use strict flag)
- array_keys / array_values- extract keys or values
- array_column- pluck one column from an array of rows
- usort- sort in place with a comparison callback
Pro Tip
Always use prepared statements (PDO with bound parameters) instead of concatenating user input into SQL strings, to prevent SQL injection.
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