learnxinyminutes-docs/php.html.markdown

language	author	author_url	filename
php	Malcolm Fell	http://emarref.net/	learnphp.php

This document describes PHP 5+.

<?php // PHP code must be enclosed with <?php ? > tags

// Two forward slashes start a one-line comment.

# So will a hash (aka pound symbol) but // is more common

/*
     Surrounding text in slash-asterisk and asterisk-slash
     makes it a multi-line comment.
*/

// Use "echo" or "print" to print output
print('Hello '); // Prints "Hello " with no line break

// () are optional for print and echo
echo 'World\n'; // Prints "World" with a line break
// (all statements must end with a semicolon)

// Anything outside <?php tags is echoed automatically
?>Hello World Again!
<?php


/************************************
 * Types & Variables
 */

// Variables begin with the $ symbol.
// A valid variable name starts with a letter or underscore,
// followed by any number of letters, numbers, or underscores.

// Boolean values are case-insensitive
$boolean = true; // or TRUE or True
$boolean = false; // or FALSE or False

// Integers
$int1 = 19; // => 19
$int2 = -19; // => -19
$int3 = 019; // => 15 (a leading 0 denotes an octal number)
$int4 = 0x0F; // => 15 (a leading 0x denotes a hex literal)

// Floats (aka doubles)
$float = 1.234;
$float = 1.2e3;
$float = 7E-10;

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

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

// Strings should be enclosed in single quotes;
$sgl_quotes = '$String'; // => '$String'

// Avoid using double quotes except to embed other variables
$dbl_quotes = "This is a $sgl_quotes."; // => 'This is a $String'

// Special characters are only escaped in double quotes
$escaped = "This contains a \t tab character.";
$unescaped = 'This just contains a slash and a t: \t';

// Enclose a variable in curly braces if needed
$money = "I have $${number} in the bank.";

// Since PHP 5.3, nowdocs can be used for uninterpolated multi-liners
$nowdoc = <<<'END'
Multi line
string
END;

// Heredocs will do string interpolation
$heredoc = <<<END
Multi line
$sgl_quotes
END;

// String concatenation is done with .
echo 'This string ' . 'is concatenated';


/********************************
 * Arrays
 */

// All arrays in PHP are associative arrays (hashmaps),

// Associative arrays, known as hashmaps in some languages.

// Works with all PHP versions
$associative = array('One' => 1, 'Two' => 2, 'Three' => 3);

// PHP 5.4 introduced a new syntax
$associative = ['One' => 1, 'Two' => 2, 'Three' => 3];

echo $associative['One']; // prints "1"

// List literals implicitly assign integer keys
$array = ['One', 'Two', 'Three'];
echo $array[0]; // => "One"


/********************************
 * Output
 */

echo('Hello World!');
// Prints Hello World! to stdout.
// Stdout is the web page if running in a browser.

print('Hello World!'); // The same as echo

// echo is actually a language construct, so you can drop the parentheses.
echo 'Hello World!';
print 'Hello World!'; // So is print

$paragraph = 'paragraph';

echo 100;
echo $paragraph;

// If short open tags are configured, or your PHP version is
// 5.4.0 or greater, you can use the short echo syntax
?>
<p><?= $paragraph ?></p>
<?php

$x = 1;
$y = 2;
$x = $y; // A now contains the same value sa $y
$z = &$y;
// $x now contains a reference to $y. Changing the value of
// $x will change the value of $y also, and vice-versa.

echo $x; // => 2
echo $z; // => 2
$y = 0;
echo $x; // => 2
echo $z; // => 0


/********************************
 * Logic
 */
$a = 0;
$b = '0';
$c = '1';
$d = '1';

// assert throws a warning if its argument is not true

// These comparisons will always be true, even if the types aren't the same.
assert($a == $b); // equality
assert($b != $a); // inequality
assert($a <> $b); // alternative inequality
assert($a < $c);
assert($c > $b);
assert($a <= $b);
assert($c >= $d);

// The following will only be true if the values match and are the same type.
assert($c === $d);
assert($a !== $d);
assert(1 == '1');
assert(1 !== '1');

// Variables can be converted between types, depending on their usage.

$integer = 1;
echo $integer + $integer; // => 2

$string = '1';
echo $string + $string; // => 2 (strings are coerced to integers)

$string = 'one';
echo $string + $string; // => 0
// Outputs 0 because the + operator cannot cast the string 'one' to a number

// Type casting can be used to treat a variable as another type

$boolean = (boolean) 1; // => true

$zero = 0;
$boolean = (boolean) $zero; // => false

// There are also dedicated functions for casting most types
$integer = 5;
$string = strval($integer);

$var = null; // Null value


/********************************
 * Control Structures
 */

if (true) {
    print 'I get printed';
}

if (false) {
    print "I don't";
} else {
    print 'I get printed';
}

if (false) {
    print 'Does not get printed';
} elseif(true) {
    print 'Does';
}

$x = 0;
if ($x === '0') {
    print 'Does not print';
} elseif($x == '1') {
    print 'Does not print';
} else {
    print 'Does print';
}

// This alternative syntax is useful for templates:
?>

<?php if ($x): ?>
This is displayed if the test is truthy.
<?php else: ?>
This is displayed otherwise.
<?php endif; ?>

<?php

// Use switch to save some logic.
switch ($x) {
    case '0':
        print 'Switch does type coercion';
        break; // You must include a break, or you will fall through
    case 'two':
    case 'three':
        // Do something if $variable is either 'two' or 'three'
        break;
    default:
        // Do something by default
}

// While, do...while and for loops are probably familiar
$i = 0;
while ($i < 5) {
    echo $i++;
}; // Prints "01234"

echo "\n";

$i = 0;
do {
    echo $i++;
} while ($i < 5); // Prints "01234"

echo "\n";

for ($x = 0; $x < 10; $x++) {
    echo $x; // Will echo 0 - 9
}// Prints "0123456789"

echo "\n";

$wheels = ['bicycle' => 2, 'car' => 4];

// Foreach loops can iterate over arrays
foreach ($wheels as $wheel_count){
    echo "$wheel_count";
} // Prints "24"

echo "\n";

// You can iterate over the keys as well as the values
foreach ($wheels as $vehicle => $wheel_count) {
    echo "A $vehicle has $wheel_count wheels";
}

echo "\n";

$i = 0;
while ($i < 5) {
    if ($i === 3) {
        break; // Exit out of the while loop
    }
    echo $i++;
}// Prints "012"

for($i = 0; $i < 5; $i++){
    if ($i === 3) {
        continue; // Skip this iteration of the loop
    }
    echo $i;
} // Prints "0124"


/********************************
 * Functions
 */

// Define a function with "function":
function my_function() {
  return 'Hello';
}

echo my_function(); // => "Hello"

// A valid function name starts with a letter or underscore, followed by any
// number of letters, numbers, or underscores.

function add($x, $y = 1) { // $y is optional, and defaults to 2
  $result = $x + $y;
  return $result;
}

echo add(4); // => 5
echo add(4, 2); // => 6

// $result is not accessible outside the function
// print $result; // Gives a warning.

// Since PHP 5.3 you can declare anonymous functions;
$inc = function($x){
  return $x + 1;
};

echo $inc(2); // => 3

function foo ($x, $y, $z) {
  echo "$x - $y - $z";
}

// Functions can return functions
function bar ($x, $y) {
  // Use 'use' to bring in outside variables
  return function ($z) use ($x, $y) {
    foo($x, $y, $z);
  };
}

$bar = bar('A', 'B');
$bar('C');

// You can call named functions using strings
$function_name = 'add';
echo $function_name(1, 2); // => 3
// But, you should probably use anonymous functions instead.

/********************************
 * Classes
 */

//Classes are defined with the class keyword

class MyClass {
    const MY_CONST = 'value'; // A constant
    static $staticVar = 'static';
    public $property = 'public'; // Properties must declare their visibility
    private $privprop = 'private'; // Accessible within the class only
    protected $protprop = 'protected'; // Accessible within the class and subclasses
    public $instanceProp;

    // Create a constructor with __construct
    public function __construct($instanceProp){
        // Access instance variables with $this
        $this->instanceProp = $instanceProp;
    }
    // Methods are declared as functions inside a class
    public function myMethod() {
        print "MyClass";
    }

    final function youCannotOverrideMe() {
    }

    public static function myStaticMethod() {
        print "I am static";
    }
}

echo MyClass::MY_CONST; // Outputs "value";
echo MyClass::$staticVar; // Outputs 'static';
MyClass::myStaticMethod(); // Outputs "I am static";

// Access class members using ->.
$my_class = new MyClass("An instance property"); // The parentheses are optional.
echo $my_class->property; // => "public"
echo $my_class->instanceProp; // => "An instance property"
$my_class->myMethod(); // => "MyClass"


// Extend classes using "extends"
class MyOtherClass extends MyClass{
    function printProtectedProperty(){
        echo $this->protprop;
    }

    // Override a method
    function myMethod() {
        parent::myMethod();
        print " > MyOtherClass";
    }
}

$my_other_class = new MyOtherClass("Instance prop");
$my_other_class->printProtectedProperty(); // => Prints "protected"
$my_other_class->myMethod(); // Prints "MyClass > MyOtherClass"

final class YouCannotExtendMe {
}

// You can use "magic methods" to create getters and setters
class MyMapClass {
    private $property;

    public function __get($key)
    {
        return $this->$key;
    }

    public function __set($key, $value)
    {
        $this->$key = $value;
    }
}

$x = new MyMapClass();
echo $x->property; // Will use the __get() method
$x->property = 'Something'; // Will use the __set() method

// Classes can be abstract (using the abstract keyword) or
// implement interfaces (using the implements keyword).
// An interface is declared with the interface keyword.

interface InterfaceOne
{
    public function doSomething();
}

interface InterfaceTwo
{
    public function doSomethingElse();
}

abstract class MyAbstractClass implements InterfaceOne
{
    public $x = "doSomething";
}

class MyConcreteClass extends MyAbstractClass implements InterfaceTwo
{
    public function doSomething(){
        echo $x;
    }
    public function doSomethingElse(){
        echo "doSomethingElse";
    }
}


// Classes can implement more than one interface
class SomeOtherClass implements InterfaceOne, InterfaceTwo
{
    public function doSomething(){
        echo "doSomething";
    }
    public function doSomethingElse(){
        echo "doSomethingElse";
    }
}


/********************************
 * Traits
 */

//Traits are available since PHP 5.4.0 and are declared using the trait keyword.

trait MyTrait {
    public function myTraitMethod()
    {
        print "I have MyTrait";
    }
}

class MyTraitfulClass
{
    use MyTrait;
}

$cls = new MyTraitfulClass();
$cls->myTraitMethod(); // Prints "I have MyTrait"


/********************************
 * Namespaces
 */

// This section is separate, because a namespace declaration
// must be the first statement in a file. Let's pretend that is not the case

/*

<?php

// By default, classes exist in the global namespace, and can
// be explicitly called with a backslash.

$cls = new \MyClass();



// Set the namespace for a file
namespace My\Namespace;

class MyClass
{
}

// (from another file)
$cls = new My\Namespace\MyClass;

//Or from within another namespace.
namespace My\Other\Namespace;

use My\Namespace\MyClass;

$cls = new MyClass();

// Or you can alias the namespace;

namespace My\Other\Namespace;

use My\Namespace as SomeOtherNamespace;

$cls = new SomeOtherNamespace\MyClass();

*/

More Information

Visit the official PHP documentation for reference and community input.

If you're interested in up-to-date best practices, visit PHP The Right Way.

If you're coming from a language with good package management, check out Composer.