PHP cheat sheet

Hello World

<?php // begin with a PHP open tag.

echo "Hello World\n";
print("Hello cheatsheets.one");

?>

PHP run command

$ php hello.php

Syntax

• <?php - You need to have the opening tag to start PHP code
• ?> - Closing tag, only need if you mix PHP code with HTML.
• Only variables are case-sensitive (e.g., $message and $MESSAGE are different variables.)
• A statement always ends with a semicolon (;).
• Whitespace and line breaks don’t matter in PHP.

Variables

$boolean1 = true;
$boolean2 = True;

$int = 12;
$float = 3.1415926;
unset($float);  // Delete variable

$str1 = "How are you?";
$str2 = 'Fine, thanks';

See: Types

Strings

$url = "cheatsheets.one";
echo "I'm learning PHP at $url";

// Concatenate strings
echo "I'm learning PHP at " . $url;

$hello = "Hello, ";
$hello .= "World!";
echo $hello;   # => Hello, World!

See: Strings

Arrays

$num = [1, 3, 5, 7, 9];
$num[5] = 11;
unset($num[2]);    // Delete variable
print_r($num);     # => 1 3 7 9 11
echo count($num);  # => 5

See: Arrays

Operators

$x = 1;
$y = 2;

$sum = $x + $y;
echo $sum;   # => 3

See: Operators

Include

vars.php

<?php // begin with a PHP open tag.
$fruit = 'apple';
echo "I was imported";
return 'Anything you like.';
?>

test.php

<?php
include 'vars.php';
echo $fruit . "\n";   # => apple

/* Same as include,
cause an error if cannot be included*/
require 'vars.php';

// Also works
include('vars.php');
require('vars.php');

// Include through HTTP
include 'http://x.com/file.php';

// Include and the return statement
$result = include 'vars.php';
echo $result;  # => Anything you like.
?>

Functions

function add($num1, $num2 = 1) {
    return $num1 + $num2;
}
echo add(10);    # => 11
echo add(10, 5); # => 15

See: Functions

Comments

# This is a one line shell-style comment

// This is a one line c++ style comment

/* This is a multi line comment
   yet another line of comment */

Constants

const MY_CONST = "hello";

echo MY_CONST;   # => hello

# => MY_CONST is: hello
echo 'MY_CONST is: ' . MY_CONST; 

Classes

class Student {
    public function __construct($name) {
        $this->name = $name;
    }
}
$alex = new Student("Alex");

See: Classes

Boolean

$boolean1 = true;
$boolean2 = TRUE;
$boolean3 = false;
$boolean4 = FALSE;

$boolean5 = (boolean) 1;   # => true
$boolean6 = (boolean) 0;   # => false

Boolean are case-insensitive

Integer

$int1 = 28;    # => 28
$int2 = -32;   # => -32
$int3 = 012;   # => 10 (octal)
$int4 = 0x0F;  # => 15 (hex)
$int5 = 0b101; # => 5  (binary)

# => 2000100000 (decimal, PHP 7.4.0)
$int6 = 2_000_100_000;

See also: Integers

Strings

echo 'this is a simple string';

See: Strings

Arrays

$arr = array("hello", "world", "!");

See: Arrays

Float (Double)

$float1 = 1.234;
$float2 = 1.2e7;
$float3 = 7E-10;

$float4 = 1_234.567;  // as of PHP 7.4.0
var_dump($float4);    // float(1234.567)

$float5 = 1 + "10.5";   # => 11.5
$float6 = 1 + "-1.3e3"; # => -1299

Null

$a = null;
$b = 'Hello php!';
echo $a ?? 'a is unset'; # => a is unset
echo $b ?? 'b is unset'; # => Hello php

$a = array();
$a == null    # => true
$a === null   # => false
is_null($a)   # => false

Iterables

function bar(): iterable {
    return [1, 2, 3];
}
function gen(): iterable {
    yield 1;
    yield 2;
    yield 3;
}
foreach (bar() as $value) {
    echo $value;   # => 123
} 

String

# => '$String'
$sgl_quotes = '$String';

# => 'This is a $String.'
$dbl_quotes = "This is a $sgl_quotes.";

# => a   tab character.
$escaped   = "a \t tab character.";

# => a slash and a t: \t
$unescaped = 'a slash and a t: \t';

Multi-line

$str = "foo";

// Uninterpolated multi-liners
$nowdoc = <<<'END'
Multi line string
$str
END;

// Will do string interpolation
$heredoc = <<<END
Multi line
$str
END;

Manipulation

$s = "Hello Phper";
echo strlen($s);       # => 11

echo substr($s, 0, 3); # => Hel
echo substr($s, 1);    # => ello Phper
echo substr($s, -4, 3);# => hpe

echo strtoupper($s);   # => HELLO PHPER
echo strtolower($s);   # => hello phper

echo strpos($s, "l");      # => 2
var_dump(strpos($s, "L")); # => false

See: String Functions

Defining

$a1 = ["hello", "world", "!"]
$a2 = array("hello", "world", "!");
$a3 = explode(",", "apple,pear,peach");

Mixed int and string keys

$array = array(
    "foo" => "bar",
    "bar" => "foo",
    100   => -100,
    -100  => 100,
);
var_dump($array);

Short array syntax

$array = [
    "foo" => "bar",
    "bar" => "foo",
];

Multi array

$multiArray = [ 
    [1, 2, 3],
    [4, 5, 6],
    [7, 8, 9],
];

print_r($multiArray[0][0]) # => 1
print_r($multiArray[0][1]) # => 2
print_r($multiArray[0][2]) # => 3

Multi type

$array = array(
    "foo" => "bar",
    42    => 24,
    "multi" => array(
         "dim" => array(
             "a" => "foo"
         )
    )
);

# => string(3) "bar"
var_dump($array["foo"]);

# => int(24)
var_dump($array[42]);    

# =>  string(3) "foo"
var_dump($array["multi"]["dim"]["a"]);

manipulation

$arr = array(5 => 1, 12 => 2);
$arr[] = 56;      // Append
$arr["x"] = 42;   // Add with key
sort($arr);       // Sort
unset($arr[5]);   // Remove
unset($arr);      // Remove all

See: Array Functions

Indexing iteration

$array = array('a', 'b', 'c');
$count = count($array);

for ($i = 0; $i < $count; $i++) {
    echo "i:{$i}, v:{$array[$i]}\n";
}

Value iteration

$colors = array('red', 'blue', 'green');

foreach ($colors as $color) {
    echo "Do you like $color?\n";
}

Key iteration

$arr = ["foo" => "bar", "bar" => "foo"];

foreach ( $arr as $key => $value )
{
    echo "key: " . $key . "\n";
    echo "val: {$arr[$key]}\n";
}

Concatenate arrays

$a = [1, 2];
$b = [3, 4];

// PHP 7.4 later
# => [1, 2, 3, 4]
$result = [...$a, ...$b];

Into functions

$array = [1, 2];

function foo(int $a, int $b) {
    echo $a; # => 1
    echo $b; # => 2
}
foo(...$array);

Splat Operator

function foo($first, ...$other) {
    var_dump($first); # => a
    var_dump($other); # => ['b', 'c']
}
foo('a', 'b', 'c' /*, ...*/ );
// or
function foo($first, string ...$other){}

Arithmetic

Assignment

Comparison

Logical

Arithmetic

// Arithmetic
$sum        = 1 + 1; // 2
$difference = 2 - 1; // 1
$product    = 2 * 2; // 4
$quotient   = 2 / 1; // 2

// Shorthand arithmetic
$num = 0;
$num += 1;       // Increment $num by 1
echo $num++;     // Prints 1 (increments after evaluation)
echo ++$num;     // Prints 3 (increments before evaluation)
$num /= $float;  // Divide and assign the quotient to $num

Bitwise

If elseif else

$a = 10;
$b = 20;

if ($a > $b) {
    echo "a is bigger than b";
} elseif ($a == $b) {
    echo "a is equal to b";
} else {
    echo "a is smaller than b";
}

Switch

$x = 0;
switch ($x) {
    case '0':
        print "it's zero";
        break; 
    case 'two':
    case 'three':
        // do something
        break;
    default:
        // do something
}

Ternary operator

# => Does
print (false ? 'Not' : 'Does');

$x = false;
# => Does
print($x ?: 'Does');

$a = null;
$b = 'Does print';
# => a is unset
echo $a ?? 'a is unset';
# => print
echo $b ?? 'b is unset';

Match

$statusCode = 500;
$message = match($statusCode) {
  200, 300 => null,
  400 => 'not found',
  500 => 'server error',
  default => 'known status code',
};
echo $message; # => server error

See: Match

Match expressions

$age = 23;

$result = match (true) {
    $age >= 65 => 'senior',
    $age >= 25 => 'adult',
    $age >= 18 => 'young adult',
    default => 'kid',
};

echo $result; # => young adult

while

$i = 1;
# => 12345
while ($i <= 5) {
    echo $i++;
}

do while

$i = 1;
# => 12345
do {
    echo $i++;
} while ($i <= 5);

for i

# => 12345
for ($i = 1; $i <= 5; $i++) {
    echo $i;
}

break

# => 123
for ($i = 1; $i <= 5; $i++) {
    if ($i === 4) {
        break;
    }
    echo $i;
}

continue

# => 1235
for ($i = 1; $i <= 5; $i++) {
    if ($i === 4) {
        continue;
    }
    echo $i;
}

foreach

$a = ['foo' => 1, 'bar' => 2];
# => 12
foreach ($a as $k) {
    echo $k;
}

See: Array iteration

Returning values

function square($x)
{
    return $x * $x;
}

echo square(4);  # => 16

Return types

// Basic return type declaration
function sum($a, $b): float {/*...*/}
function get_item(): string {/*...*/}

class C {}
// Returning an object
function getC(): C { return new C; }

Nullable return types

// Available in PHP 7.1
function nullOrString(int $v) : ?string
{
    return $v % 2 ? "odd" : null;
}
echo nullOrString(3);       # => odd
var_dump(nullOrString(4));  # => NULL

See: Nullable types

Void functions

// Available in PHP 7.1
function voidFunction(): void
{
    echo 'Hello';
    return;
}

voidFunction();  # => Hello

Variable functions

function bar($arg = '')
{
    echo "In bar(); arg: '$arg'.\n";
}

$func = 'bar';
$func('test'); # => In bar(); arg: test

Anonymous functions

$greet = function($name)
{
    printf("Hello %s\r\n", $name);
};

$greet('World'); # => Hello World
$greet('PHP');   # => Hello PHP

Recursive functions

function recursion($x)
{
    if ($x < 5) {
        echo "$x";
        recursion($x + 1);
    }
}
recursion(1);  # => 1234

Default parameters

function coffee($type = "cappuccino")
{
    return "Making a cup of $type.\n";
}
# => Making a cup of cappuccino.
echo coffee();
# => Making a cup of .
echo coffee(null);
# => Making a cup of espresso.
echo coffee("espresso");

Arrow Functions

$y = 1;

$fn1 = fn($x) => $x + $y;

// equivalent to using $y by value:
$fn2 = function ($x) use ($y) {
    return $x + $y;
};
echo $fn1(5);   # => 6
echo $fn2(5);   # => 6

Constructor

class Student {
    public function __construct($name) {
        $this->name = $name;
    }
    public function print() {
        echo "Name: " . $this->name;
    }
}
$alex = new Student("Alex");
$alex->print();    # => Name: Alex

Inheritance

class ExtendClass extends SimpleClass
{
    // Redefine the parent method
    function displayVar()
    {
        echo "Extending class\n";
        parent::displayVar();
    }
}

$extended = new ExtendClass();
$extended->displayVar();

Classes variables

class MyClass
{
    const MY_CONST       = 'value';
    static $staticVar    = 'static';

    // Visibility
    public static $var1  = 'pubs';

    // Class only
    private static $var2 = 'pris';

    // The class and subclasses
    protected static $var3 = 'pros';

    // The class and subclasses
    protected $var6      = 'pro';

    // The class only
    private $var7        = 'pri';  
}

Access statically

echo MyClass::MY_CONST;   # => value
echo MyClass::$staticVar; # => static

Magic Methods

class MyClass
{
    // Object is treated as a String
    public function __toString()
    {
        return $property;
    }
    // opposite to __construct()
    public function __destruct()
    {
        print "Destroying";
    }
}

Interface

interface Foo 
{
    public function doSomething();
}
interface Bar
{
    public function doSomethingElse();
}
class Cls implements Foo, Bar 
{
    public function doSomething() {}
    public function doSomethingElse() {}
}

Basic error handling

try {
    // Do something
} catch (Exception $e) {
    // Handle exception
} finally {
    echo "Always print!";
}

Exception in PHP 8.0

$nullableValue = null;

try {
    $value = $nullableValue ?? throw new InvalidArgumentException();
} catch (InvalidArgumentException) { // Variable is optional
    // Handle my exception
    echo "print me!";
}

Custom exception

class MyException extends Exception {
    // do something
}

Usage

try {
    $condition = true;
    if ($condition) {
        throw new MyException('bala');
    }
} catch (MyException $e) {
    // Handle my exception
}

Nullsafe Operator

// As of PHP 8.0.0, this line:
$result = $repo?->getUser(5)?->name;

// Equivalent to the following code:
if (is_null($repo)) {
    $result = null;
} else {
    $user = $repository->getUser(5);
    if (is_null($user)) {
        $result = null;
    } else {
        $result = $user->name;
    }
}

See also: Nullsafe Operator

Regular expressions

$str = "Visit Quickref.me";
echo preg_match("/qu/i", $str); # => 1

See: Regex in PHP

fopen() mode

Runtime defined Constants

define("CURRENT_DATE", date('Y-m-d'));

// One possible representation
echo CURRENT_DATE;   # => 2021-01-05

# => CURRENT_DATE is: 2021-01-05
echo 'CURRENT_DATE is: ' . CURRENT_DATE; 

Tips

1. Use Single Quotes for Strings When You Don't Need Interpolation: PHP allows you to use both single (') and double (") quotes for strings. When your string does not require variable interpolation, it's a good practice to use single quotes. This is slightly faster as PHP doesn't have to parse the string for variables.
2. Leverage PHP Built-in Server for Development: Starting with PHP 5.4.0, you can use PHP's built-in server for development purposes. This is incredibly useful for quickly testing scripts without needing a full server setup. You can start the server using the PHP command line interface (CLI) with php -S localhost:8000 in your project's root directory.
3. Array Destructuring for List Assignment: PHP 7.1 introduced array destructuring, which allows you to assign variables from an array using a list-like syntax. This can simplify your code and make it more readable, especially when working with functions that return arrays. For example: [$first, $second] = explode(',', 'hello,world'); 4. Use Null Coalescing Operator for Default Values: The null coalescing operator (??) is a concise syntax for the common case of needing to use a default value when a variable is null. Instead of using isset(), you can write $username = $_GET['user'] ?? 'guest'; to easily assign a default value.
4. Utilize Composer for Dependency Management: While not directly a PHP language feature, using Composer as a dependency manager for PHP projects can greatly simplify managing libraries and frameworks. Composer helps you declare, manage, and install dependencies of PHP projects, ensuring you have the right versions and simplifying autoloading of classes.

Useful Links

• PHP Docs
• W3 School: PHP Tutorial
• PHP Tutorial