PHPPrintable

PHP Cheat Sheet

Output, strings, arrays, functions, forms, sessions, dates, regex, files, JSON, PDO, OOP, Composer, passwords, security and APIs on one printable page.

Back to the PHP tutorial

Tags, variables & strings

Syntax	What it does	Lesson
`<?php ... ?>` `<?= $x ?>`	Code block / print a value	Introduction
`php -S localhost:8000`	Start a local server	Introduction
`$name = "Ana";`	Create a variable	Variables
`"Hi $name"` `'Hi ' . $name`	Interpolate / join	Variables
`strlen()` `strtoupper()` `trim()` `str_replace()`	String helpers	Variables

Conditions, loops & arrays

Syntax	What it does	Lesson
`===` `!==` `??`	Strict compare / fallback	if/else
`match ($v) { 1 => "a", default => "b" }`	Pick a value	if/else
`foreach ($a as $k => $v) { }`	Loop keys and values	Loops
`$a[] = "x";` `count($a)`	Add, count	Arrays
`in_array()` `sort()` `asort()` `implode()` `explode()`	Array functions	Arrays

Functions & includes

Syntax	What it does	Lesson
`function f(int $x = 1): string { }`	Typed function with default	Functions
`f(name: "Ana")`	Named argument	Functions
`require __DIR__ . '/header.php';`	Include a required file	include
`require_once 'functions.php';`	Load only once	include

Forms & validation

Syntax	What it does	Lesson
`$_GET['q'] ?? ''` `$_POST['email'] ?? ''`	Read form values	Forms
`$_SERVER['REQUEST_METHOD'] === 'POST'`	Was the form submitted?	Forms
`htmlspecialchars($s)`	Escape output (prevent XSS)	Forms
`header('Location: thanks.php'); exit;`	Redirect after POST	Forms
`filter_var($e, FILTER_VALIDATE_EMAIL)`	Validate an email	Validation
`hash_equals($_SESSION['token'], $t)`	Check a CSRF token	Validation

Sessions, cookies & files

Syntax	What it does	Lesson
`session_start();` `$_SESSION['id'] = 5;`	Remember data on the server	Sessions
`session_destroy();`	Log out	Sessions
`setcookie('theme', 'dark', [...]);` `$_COOKIE['theme']`	Set / read a cookie	Sessions
`file_get_contents($p)` `file_put_contents($p, $s, FILE_APPEND)`	Read / write files	Files
`fgetcsv($handle)`	Read a CSV row	Files
`move_uploaded_file($tmp, $dest)`	Save an upload	Files

JSON & databases

Syntax	What it does	Lesson
`json_encode($data, JSON_PRETTY_PRINT)`	PHP to JSON	JSON
`json_decode($json, true)`	JSON to array	JSON
`header('Content-Type: application/json');`	Return JSON	JSON
`new PDO($dsn, $user, $pass, [...])`	Connect to a database	PDO
`$s = $pdo->prepare('... WHERE id = ?'); $s->execute([$id]);`	Prepared statement	PDO
`$s->fetchAll()` `$pdo->lastInsertId()`	Read rows / new id	PDO

Classes & exceptions

Syntax	What it does	Lesson
`class P { public function __construct(private string $n) {} }`	Class with promoted property	Classes
`$p = new P('x');` `$p->method();`	Create and use an object	Classes
`class B extends A` `parent::method()`	Inheritance	Classes
`interface I { }` `class C implements I`	Contracts	Classes
`try { } catch (Exception $e) { } finally { }`	Handle errors	Exceptions
`throw new InvalidArgumentException('msg');`	Report a problem	Exceptions

Strings & array functions

Syntax	What it does	Lesson
`trim($s)` `strtolower($s)` `ucwords($s)`	Tidy text	String Functions
`str_contains($s, "x")` `strpos($s, "x") === false`	Search text	String Functions
`substr($s, 0, 10)` `mb_strlen($s)`	Part of a string, real length	String Functions
`sprintf("%s: £%.2f", $n, $p)` `number_format($n, 2)`	Format values	String Functions
`array_map(fn($x) => $x * 2, $a)`	Transform every item	Array Functions
`array_filter($a, fn($x) => $x > 0)`	Keep matching items	Array Functions
`usort($a, fn($x, $y) => $x['p'] <=> $y['p'])`	Sort records	Array Functions
`array_column($rows, 'name', 'id')`	Pull out a field	Array Functions

Dates & regex

Syntax	What it does	Lesson
`date('Y-m-d H:i:s')`	Current date and time	Dates & Times
`new DateTimeImmutable('2024-07-05')`	Create a date	Dates & Times
`$d->modify('+3 days')` `$a->diff($b)->days`	Move a date, days between	Dates & Times
`preg_match('/^[a-z]{3,15}$/i', $s)`	Validate by pattern	Regular Expressions
`preg_match_all('/#(\w+)/', $s, $m)`	Find every match	Regular Expressions
`preg_replace('/\s+/', ' ', $s)`	Replace by pattern	Regular Expressions

OOP & Composer

Syntax	What it does	Lesson
`abstract class Shape { abstract public function area(): float; }`	Abstract class	Interfaces, Traits & Enums
`class Card implements PaymentMethod`	Implement an interface	Interfaces, Traits & Enums
`trait Loggable { }` and `use Loggable;`	Share methods	Interfaces, Traits & Enums
`enum Status: string { case Paid = 'paid'; }`	Fixed set of values	Interfaces, Traits & Enums
`namespace App\Models;` `use App\Models\User;`	Namespaces	Namespaces & Composer
`composer require vendor/package`	Install a package	Namespaces & Composer
`require __DIR__ . '/vendor/autoload.php';`	Autoload classes	Namespaces & Composer

Apps, security & APIs

Syntax	What it does	Lesson
`header('Location: index.php'); exit;`	Redirect after POST	CRUD App
`password_hash($p, PASSWORD_DEFAULT)`	Hash a password	Login & Passwords
`password_verify($typed, $hash)`	Check a password	Login & Passwords
`session_regenerate_id(true)`	New session id at login	Login & Passwords
`htmlspecialchars($s, ENT_QUOTES, 'UTF-8')`	Escape output (XSS)	Web Security
`hash_equals($_SESSION['csrf'], $_POST['csrf'])`	Check a CSRF token	Web Security
`json_decode(file_get_contents('php://input'), true)`	Read a JSON request	REST API
`http_response_code(201)`	Set the status code	REST API

How to use this PHP cheat sheet

This PHP cheat sheet collects the syntax you'll reach for most often, in the same order as the course: tags and output, variables and strings, conditions, loops, arrays and array functions, functions, includes, forms and validation, sessions and cookies, dates, regular expressions, files, JSON, PDO, classes, interfaces and enums, exceptions, Composer, security and APIs. Each row links to the lesson that explains it with examples and common mistakes.

Keep it open while you build pages with PHP's built-in server or a package like XAMPP. When you can't remember which array function keeps keys while sorting, how to append to a file, or the shape of a prepared statement, a quick look answers it. Type a function name into the filter box to jump straight to it, or print the page as a one-sheet reference.

PHP gotchas worth remembering

Use === rather than ==. Loose comparison converts types, so "abc" == 0 was true before PHP 8 and still trips people up with other values. Strict comparison checks the type too.
strpos can return 0. A match at the start of the string returns 0, which is falsy. Test with !== false, or use str_contains in PHP 8.
Single quotes don't interpolate. 'Hi $name' prints the dollar sign literally. Use double quotes or concatenation.
Escape on output. Wrap anything from users in htmlspecialchars() before printing it, and use prepared statements with PDO for every query.
Sessions start before output. session_start() and header() must run before any HTML, even a blank line, is sent.

Revisit the linked lessons for anything that surprises you, then check yourself with the PHP quiz.

PHP Cheat Sheet

Tags, variables & strings

Conditions, loops & arrays

Functions & includes

Forms & validation

Sessions, cookies & files

JSON & databases

Classes & exceptions

Strings & array functions

Dates & regex

OOP & Composer

Apps, security & APIs

How to use this PHP cheat sheet

PHP gotchas worth remembering

The PHP lessons behind this cheat sheet

Beginner

Intermediate

Advanced

Fundamentals reference

Arrays and functions reference

OOP reference

Web requests and data reference

Database reference

Professional PHP