PHP Cheat Sheet
Last updated
Hello World & tags
PHP code lives inside <?php ... ?> tags; everything outside is sent as plain output.
| Operation | Syntax |
|---|---|
| Open / close PHP | <?php ... ?> |
| Print text | echo "Hello, World!"; |
| Print formatted | printf("%d items", $n); |
| Short echo (in HTML) | <?= $name ?> |
| Single-line comment | // comment or # comment |
| Block comment | /* comment */ |
| Statement terminator | ; |
| Run a file (CLI) | php index.php |
Variables & types
Variables start with $ and are dynamically typed.
| Operation | Syntax |
|---|---|
| Declare a variable | $name = "Ada"; |
| Constant | const PI = 3.14; or define("PI", 3.14); |
| Scalar types | int, float, string, bool |
| Null | $x = null; |
| Check the type | gettype($x), is_int($x), is_array($x) |
| Cast a type | (int) $str, (string) $num |
| Variable exists / set | isset($x), empty($x) |
| String interpolation | echo "Hi $name"; |
Strings
Double quotes interpolate variables; single quotes are literal.
| Operation | Syntax |
|---|---|
| Concatenate | $a . $b |
| Length | strlen($s) |
| Upper / lower case | strtoupper($s), strtolower($s) |
| Substring | substr($s, 0, 5) |
| Find position | strpos($s, "x") |
| Replace | str_replace("a", "b", $s) |
| Split into array | explode(",", $csv) |
| Join an array | implode(",", $arr) |
| Trim whitespace | trim($s) |
| Format a string | sprintf("%05.2f", $n) |
Arrays (incl. associative)
One array type covers both indexed lists and key-value maps.
| Operation | Syntax |
|---|---|
| Indexed array | $nums = [1, 2, 3]; |
| Associative array | $user = ["name" => "Ada", "age" => 30]; |
| Access an element | $nums[0], $user["name"] |
| Append | $nums[] = 4; |
| Set a key | $user["role"] = "admin"; |
| Length | count($nums) |
| Check a key | isset($user["name"]), array_key_exists("name", $user) |
| Remove an element | unset($nums[1]); |
| Merge arrays | array_merge($a, $b) |
| Iterate key => value | foreach ($user as $k => $v) { ... } |
Control flow
Conditionals and loops follow C-style syntax.
| Operation | Syntax |
|---|---|
| If / elseif / else | if ($x > 0) { ... } elseif (...) { ... } else { ... } |
| Ternary | $y = $x > 0 ? "pos" : "neg"; |
| Null coalescing | $name = $_GET["name"] ?? "guest"; |
| Switch | switch ($day) { case 1: ...; break; default: ... } |
| For loop | for ($i = 0; $i < 10; $i++) { ... } |
| While loop | while ($x < 100) { ... } |
| Foreach | foreach ($items as $item) { ... } |
| Match expression | $r = match($x) { 1 => "one", default => "?" }; |
| Break / continue | break;, continue; |
Functions
Functions can declare types, default values, and variadic parameters.
| Operation | Syntax |
|---|---|
| Basic function | function add($a, $b) { return $a + $b; } |
| Typed parameters & return | function add(int $a, int $b): int { ... } |
| Default value | function greet($name = "guest") { ... } |
| Variadic parameters | function sum(...$nums) { ... } |
| Pass by reference | function inc(&$x) { $x++; } |
| Anonymous function | $f = function($x) { return $x * 2; }; |
| Arrow function | $f = fn($x) => $x * 2; |
| Use outer variable | function() use ($n) { ... } |
Superglobals
Built-in arrays available in every scope, mostly for request data.
| Superglobal | What it holds |
|---|---|
$_GET | Query-string parameters from the URL |
$_POST | Form data sent via POST |
$_REQUEST | Combined $_GET, $_POST, and $_COOKIE |
$_SESSION | Per-user session data (after session_start()) |
$_COOKIE | Cookies sent by the browser |
$_SERVER | Server and request info (REQUEST_METHOD, etc.) |
$_FILES | Uploaded file metadata |
$_ENV | Environment variables |
Common array functions
PHP ships hundreds of array helpers; these are the workhorses.
| Function | What it does |
|---|---|
array_map($fn, $arr) | Transform every element |
array_filter($arr, $fn) | Keep elements where the callback is true |
array_reduce($arr, $fn, $init) | Fold to a single value |
in_array($v, $arr) | Check if a value is present |
array_keys($arr) / array_values($arr) | Get keys or values |
sort($arr) / rsort($arr) | Sort in place (asc / desc) |
usort($arr, $cmp) | Sort with a custom comparator |
array_slice($arr, 1, 3) | Extract a portion |
array_push($arr, $v) / array_pop($arr) | Add / remove from the end |
Classes & OOP
PHP supports classes, inheritance, interfaces, and visibility modifiers.
| Operation | Syntax |
|---|---|
| Define a class | class User { ... } |
| Property with visibility | public string $name; |
| Constructor | function __construct($name) { $this->name = $name; } |
| Constructor promotion | function __construct(public string $name) {} |
| Create an instance | $u = new User("Ada"); |
| Access a member | $u->name, $u->save() |
| Static member | User::$count, User::create() |
| Inheritance | class Admin extends User { ... } |
| Interface | interface Saveable { public function save(); } |
| Implement an interface | class User implements Saveable { ... } |
The PHP syntax you reach for most, on one page. This PHP cheat sheet is a quick reference for the core language - variables and types, strings, arrays (including associative arrays), control flow, functions, the superglobals like $_GET and $_POST, and classes.
Everything here is standard PHP that runs on modern versions. Copy what you need, or try every snippet live in the PHP playground - no server to set up.
PHP cheat sheet FAQ
Is this PHP cheat sheet free?
Yes. This PHP cheat sheet is completely free, with no sign-up required. Bookmark it and come back whenever you need to look up a string function, array helper, or superglobal.
What is the difference between == and === in PHP?
== is loose comparison: it converts the operands to a common type before comparing, so 0 == "0" and even 0 == "" can behave surprisingly across versions. === is strict comparison: it returns true only when the values are equal and of the same type, so 0 === "0" is false. Prefer === to avoid type-juggling bugs.What are associative arrays in PHP?
An associative array is a PHP array that uses named string keys instead of (or alongside) numeric indexes, like
["name" => "Ada", "age" => 30]. PHP has a single array type that doubles as both an ordered list and a key-value map, so you access values by key with $user["name"] and iterate with foreach ($user as $key => $value).Can I practice PHP online?
Yes. Open the PHP playground to run any snippet from this cheat sheet in your browser - no server or local PHP install needed. When you want structure, Coddy's free interactive PHP course takes you from variables and arrays to functions and OOP step by step.
Is this cheat sheet good for beginners?
Yes. It is organized from the most common topics (variables, strings, arrays, control flow) down to advanced ones (superglobals and OOP), so you can use the top sections on day one and grow into the rest.
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