# PHP Quick Reference *Syntax, arrays, OOP, database, file I/O essentials* > Source: PHP Manual (php.net) ยท MIT ## Basics ### Hello World ``` tags ``` ### Run PHP ``` php script.php # run a file php -r 'echo "hi\n";' # run inline code php -S localhost:8000 # built-in dev server ``` ### Comments ``` // single-line comment # also single-line /* multi-line comment */ ``` ## Variables & Types ### Variables ``` $name = "PHP"; // string $version = 8.3; // float $count = 42; // int $active = true; // bool $items = null; // null ``` ### Type Checking | Command | Description | |---------|-------------| | `gettype($x)` | Returns type as string | | `is_string($x)` | Check if string | | `is_int($x)` | Check if integer | | `is_array($x)` | Check if array | | `is_null($x)` | Check if null | | `isset($x)` | Check if set and not null | | `empty($x)` | Check if empty (falsy) | ### Type Casting ``` $n = (int) "42"; // 42 $s = (string) 3.14; // "3.14" $b = (bool) ""; // false $a = (array) $obj; // object to array ``` ### Constants ``` define("MAX_SIZE", 100); const API_VERSION = "v2"; echo MAX_SIZE; // 100 ``` ## Strings ### String Basics ``` $name = "World"; echo "Hello, $name!"; // variable interpolation echo 'Hello, $name!'; // literal (no interpolation) echo "Value: {$arr['key']}"; // complex expression ``` ### String Functions | Command | Description | |---------|-------------| | `strlen($s)` | String length in bytes | | `mb_strlen($s)` | String length in characters (multibyte-safe) | | `strtolower($s)` | Convert to lowercase | | `strtoupper($s)` | Convert to uppercase | | `trim($s)` | Strip whitespace from both ends | | `str_replace(a, b, $s)` | Replace `a` with `b` in `$s` | | `substr($s, 0, 5)` | Substring from position 0, length 5 | | `strpos($s, 'find')` | Find position of substring (false if not found) | | `explode(',', $s)` | Split string into array | | `implode(',', $a)` | Join array into string | ### Heredoc & Nowdoc ``` $html = <<Hello, $name

HTML; $raw = <<<'TEXT' No $interpolation here TEXT; ``` ## Arrays ### Indexed & Associative ``` $nums = [1, 2, 3]; // indexed $user = ["name" => "Alice", "age" => 30]; // associative $nums[] = 4; // append echo $user["name"]; // access ``` ### Array Functions | Command | Description | |---------|-------------| | `count($a)` | Number of elements | | `array_push($a, $v)` | Append to end | | `array_pop($a)` | Remove and return last element | | `array_merge($a, $b)` | Merge two arrays | | `in_array($v, $a)` | Check if value exists | | `array_key_exists($k, $a)` | Check if key exists | | `array_map($fn, $a)` | Apply function to each element | | `array_filter($a, $fn)` | Filter elements by callback | | `sort($a)` | Sort in place (reindexes) | | `array_keys($a)` | Return all keys | ### Iteration ``` foreach ($users as $user) { echo $user; } foreach ($map as $key => $value) { echo "$key: $value\n"; } ``` ## Functions ### Basic Function ``` function add(int $a, int $b): int { return $a + $b; } echo add(3, 5); ``` ### Default & Named Arguments ``` function greet(string $name, string $greeting = "Hello"): string { return "$greeting, $name!"; } greet("Alice"); greet(greeting: "Hi", name: "Bob"); // named args (PHP 8+) ``` ### Arrow Functions ``` $double = fn(int $x): int => $x * 2; $nums = array_map(fn($n) => $n * 10, [1, 2, 3]); ``` ### Closures ``` $factor = 3; $multiply = function(int $x) use ($factor): int { return $x * $factor; }; echo $multiply(5); // 15 ``` ## Classes & Objects ### Class Definition ``` class User { public function __construct( private string $name, private int $age = 0, ) {} public function greet(): string { return "Hi, {$this->name}"; } } ``` ### Inheritance & Interfaces ``` interface Printable { public function toString(): string; } class Admin extends User implements Printable { public function toString(): string { return "Admin"; } } ``` ### Visibility | Command | Description | |---------|-------------| | `public` | Accessible from anywhere | | `protected` | Accessible from class and subclasses | | `private` | Accessible only within the class | | `readonly` | Can only be assigned once (PHP 8.1+) | | `static` | Belongs to the class, not instances | | `abstract` | Must be implemented by subclass | ### Traits ``` trait Timestamped { public function createdAt(): string { return date('Y-m-d H:i:s'); } } class Post { use Timestamped; } ``` ## Error Handling ### Try / Catch / Finally ``` try { $result = riskyOperation(); } catch (InvalidArgumentException $e) { echo "Bad input: " . $e->getMessage(); } catch (Exception $e) { echo "Error: " . $e->getMessage(); } finally { cleanup(); } ``` ### Custom Exceptions ``` class ApiException extends RuntimeException { public function __construct(string $message, private int $statusCode = 500) { parent::__construct($message, $statusCode); } } ``` ### Null Safety (PHP 8+) ``` $len = $user?->address?->zip; // nullsafe operator $name = $input ?? "default"; // null coalescing $data ??= []; // null coalescing assignment ``` ## File I/O ### Read & Write Files ``` $content = file_get_contents("data.txt"); file_put_contents("out.txt", $content); $lines = file("data.txt", FILE_IGNORE_NEW_LINES); ``` ### File Handle ``` $f = fopen("log.txt", "a"); fwrite($f, "entry\n"); fclose($f); ``` ### File Functions | Command | Description | |---------|-------------| | `file_exists($path)` | Check if file exists | | `is_dir($path)` | Check if path is a directory | | `mkdir($path, 0755, true)` | Create directory recursively | | `unlink($path)` | Delete a file | | `glob('*.txt')` | Find files matching pattern | | `realpath($path)` | Resolve full absolute path | ## Database ### PDO Connection ``` $pdo = new PDO( "mysql:host=localhost;dbname=app", "user", "password", [PDO::ATTR_ERRMODE => PDO::ERRMODE_EXCEPTION] ); ``` ### Prepared Statements ``` $stmt = $pdo->prepare("SELECT * FROM users WHERE id = :id"); $stmt->execute([":id" => 42]); $user = $stmt->fetch(PDO::FETCH_ASSOC); ``` ### Insert & Update ``` $stmt = $pdo->prepare("INSERT INTO users (name, email) VALUES (?, ?)"); $stmt->execute(["Alice", "alice@example.com"]); $id = $pdo->lastInsertId(); ``` ### PDO Fetch Modes | Command | Description | |---------|-------------| | `fetch()` | Fetch single row | | `fetchAll()` | Fetch all rows | | `FETCH_ASSOC` | Return as associative array | | `FETCH_OBJ` | Return as anonymous object | | `FETCH_CLASS` | Return as instance of specified class | ## Common Functions ### JSON ``` $json = json_encode(["name" => "Alice", "age" => 30]); $data = json_decode($json, true); // true = assoc array $data = json_decode($json); // object ``` ### Date & Time ``` echo date("Y-m-d H:i:s"); // 2026-03-26 12:00:00 $ts = strtotime("+1 week"); $dt = new DateTime("2026-01-01"); echo $dt->format("D, M j"); // Thu, Jan 1 ``` ### Math & Random | Command | Description | |---------|-------------| | `abs($n)` | Absolute value | | `round($n, 2)` | Round to 2 decimal places | | `ceil($n) / floor($n)` | Round up / down | | `min($a, $b) / max($a, $b)` | Minimum / maximum | | `random_int(1, 100)` | Cryptographically secure random int | | `number_format($n, 2)` | Format with thousands separator | ### Regular Expressions ``` preg_match('/^[a-z]+$/i', $str, $matches); preg_match_all('/\d+/', $str, $all); $result = preg_replace('/\s+/', ' ', $str); ```