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PHP cheatsheet

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A cheatsheet for modern PHP (8.0+).

Variables

Variable variables

You can refer to a dynamic variable with $$. Probably avoid this feature.

$color = 'red';
$prop = 'color';

echo $$prop; // => red
echo ${$prop}; // => red

Variable scope

Variables in PHP have global and function scope. To refer to global variables in function scope, use the global keyword. A set of superglobal variables can be accessed in all scopes without using the global keyword.

PHP also has static variables that retain their value across function invocations. Their initialization is only executed on the first invocation, so they’re useful for caching the result of a computation, for example. When used in class methods, static variables are shared amongst all instances of the class and its subclasses.

Operators

The spaceship operator returns -1, 0, or 1 as a result of comparing its operands. Since comparison in PHP works with arrays, sorting by many criteria at once can be expressed succintly with:

usort(
	$arr, 
	fn($a, $b) => [$a->title(), $a->date()] <=> [$b->title(), $b->date()]
);

False friends. The null coalescing operator ?? works similarly to JavaScript: a ?? b is equivalent to isset(a) ? a : b. However the boolean OR operator is unlike the Javascript counterpart: a || b returns a boolean, not either a or b. What you want instead is a ?: b, which is short for a ? a : b.

Strings

$name = 'Dan';
'My name is ' . $name; // Concatenation
"My name is $name"; // Interpolation

Arrays

Arrays in PHP are used for both indexed arrays and associative arrays (dictionaries), with support for int and string keys. String keys holding valid decimal integers will be interpreted as integers, unless the value starts with +.

$fruits = [];
$fruits[] = 'apple'; // Array push

The array push shortcut works for higher dimension arrays as well, creating the necessary objects as needed:

$tasks['Dan'][] = 'Documentation';
$transactions[$a][$b][] = $transaction;

Sorting arrays

To sort the array in descending order, use rsort(), arsort(), and krsort() respectively.

For custom sorting functions, there’s usort(), uasort(), and uksort() respectively.

Functions

Functions in PHP have surprising aspects coming from a JavaScript background. User-defined functions, regardless of the scope in which they were declared, are added to the global scope.

A function declaration, shown below with a default parameter value and a variable-length argument list:

function add($a, $b = 0, ...$rest) {
	return $a + $b;
}

Functions can be invoked with positional arguments or named arguments (or combined):

add(5, 10); // positional arguments
add($b: 10, $a: 5); // named arguments

Arrays can be unpacked (spread) into arguments:

$numbers = [1, 2, 3];
add(...$numbers);

Anonymous functions or closures are defined with:

$add = function($a, $b) {
    return $a + $b;
};

Variables from the outer scope are not available by default and must be explicitly inherited with use:

$padding = 10;

$add = function($a, $b) use ($padding) {
    return $a + $b + $padding;
};

Variables inherited from the outer scope are passed by value. To pass by reference, you can use use(&$var).

Arrow functions:

$add = fn($a, $b) => $a + $b;

Arrow functions have implicit access to variables from the outer scope, roughly equivalent to use($var), so still passed by value. There’s no syntax for passing by reference in arrow functions, so you must use anonymous functions instead.

Classes

class MyClass {

	const SOME_CONSTANT = 10;

	public function __construct() {

	}
}

Dates and times

Comparison and sorting

DateTime objects can be sorted with the spaceship operator:

$arr = [
	new DateTime(…),
	new DateTime(…),
	new DateTime(…)
];
usort($arr, fn($a, $b) => $a <=> $b);

Timezones

The default timezone in PHP is UTC, but can be changed with the date_default_timezone_set() method or with the date.timezone configuration. To update the timezone for a DateTime object:

$date->setTimezone(new DateTimeZone('Europe/Bucharest'));

Internationalization

The intl extension provides locale-aware functions for collation, formatting numbers, dates, etc. On Homebrew it’s distributed separately from core PHP, so you’ll have to install it with:

brew install php php-intl

Type declarations

See Type declarations.

Use declare(strict_types=1); at the top of a PHP file to switch from PHPs default (coercive type checking) to strict type checking.

Development

Composer is the npm of the PHP world. On macOS I install Composer with Homebrew, which despite not being officially advertised seems mostly fine.

The most popular package repository is Packagist.

Miscellaneous

Write to built-in server stdout

Useful for local debugging.

define('STDOUT', fopen('php://stdout', 'w'));
fwrite(STDOUT, $str);

Further reading

Tools, resources