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

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

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

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

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

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

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

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);

PHP QUICK REFERENCE