learnxinyminutes-docs/php.html.markdown

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---
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language: PHP
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contributors:
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- ["Malcolm Fell", "http://emarref.net/"]
- ["Trismegiste", "https://github.com/Trismegiste"]
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filename: learnphp.php
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---
This document describes PHP 5+.
```php
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<?php // PHP code must be enclosed with <?php tags
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// If your php file only contains PHP code, it is best practice
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// to omit the php closing tag to prevent accidental output.
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// 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.
*/
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// Use "echo" or "print" to print output
print('Hello '); // Prints "Hello " with no line break
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// () are optional for print and echo
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echo "World\n"; // Prints "World" with a line break
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// (all statements must end with a semicolon)
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// Anything outside <?php tags is echoed automatically
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?>
Hello World Again!
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<?php
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/************************************
* 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.
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// Boolean values are case-insensitive
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$boolean = true; // or TRUE or True
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$boolean = false; // or FALSE or False
// Integers
$int1 = 12; // => 12
$int2 = -12; // => -12
$int3 = 012; // => 10 (a leading 0 denotes an octal number)
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$int4 = 0x0F; // => 15 (a leading 0x denotes a hex literal)
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// Binary integer literals are available since PHP 5.4.0.
$int5 = 0b11111111; // 255 (a leading 0b denotes a binary number)
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// Floats (aka doubles)
$float = 1.234;
$float = 1.2e3;
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$float = 7E-10;
// Delete variable
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unset($int1);
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// Arithmetic
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$sum = 1 + 1; // 2
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$difference = 2 - 1; // 1
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$product = 2 * 2; // 4
$quotient = 2 / 1; // 2
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// Shorthand arithmetic
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$number = 0;
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$number += 1; // Increment $number by 1
echo $number++; // Prints 1 (increments after evaluation)
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echo ++$number; // Prints 3 (increments before evaluation)
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$number /= $float; // Divide and assign the quotient to $number
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// Strings should be enclosed in single quotes;
$sgl_quotes = '$String'; // => '$String'
// Avoid using double quotes except to embed other variables
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$dbl_quotes = "This is a $sgl_quotes."; // => 'This is a $String.'
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// Special characters are only escaped in double quotes
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$escaped = "This contains a \t tab character.";
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$unescaped = 'This just contains a slash and a t: \t';
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// Enclose a variable in curly braces if needed
$apples = "I have {$number} apples to eat.";
$oranges = "I have ${number} oranges to eat.";
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$money = "I have $${number} in the bank.";
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// Since PHP 5.3, nowdocs can be used for uninterpolated multi-liners
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$nowdoc = <<<'END'
Multi line
string
END;
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// Heredocs will do string interpolation
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$heredoc = <<<END
Multi line
$sgl_quotes
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END;
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// String concatenation is done with .
echo 'This string ' . 'is concatenated';
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// Strings can be passed in as parameters to echo
echo 'Multiple', 'Parameters', 'Valid'; // Returns 'MultipleParametersValid'
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/********************************
* Constants
*/
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// A constant is defined by using define()
// and can never be changed during runtime!
// a valid constant name starts with a letter or underscore,
// followed by any number of letters, numbers, or underscores.
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define("FOO", "something");
// access to a constant is possible by calling the choosen name without a $
echo FOO; // Returns 'something'
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echo 'This outputs ' . FOO; // Returns 'This ouputs something'
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/********************************
* Arrays
*/
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// All arrays in PHP are associative arrays (hashmaps in some languages)
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// Works with all PHP versions
$associative = array('One' => 1, 'Two' => 2, 'Three' => 3);
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// PHP 5.4 introduced a new syntax
$associative = ['One' => 1, 'Two' => 2, 'Three' => 3];
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echo $associative['One']; // prints 1
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// Add an element to an associative array
$associative['Four'] = 4;
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// List literals implicitly assign integer keys
$array = ['One', 'Two', 'Three'];
echo $array[0]; // => "One"
// Add an element to the end of an array
$array[] = 'Four';
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// or
array_push($array, 'Five');
// Remove element from array
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unset($array[3]);
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/********************************
* Output
*/
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echo('Hello World!');
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// Prints Hello World! to stdout.
// Stdout is the web page if running in a browser.
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print('Hello World!'); // The same as echo
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// echo and print are language constructs too, so you can drop the parentheses
echo 'Hello World!';
print 'Hello World!';
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$paragraph = 'paragraph';
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echo 100; // Echo scalar variables directly
echo $paragraph; // or variables
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// If short open tags are configured, or your PHP version is
// 5.4.0 or greater, you can use the short echo syntax
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?>
<p><?= $paragraph ?></p>
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<?php
$x = 1;
$y = 2;
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$x = $y; // $x now contains the same value as $y
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$z = &$y;
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// $z now contains a reference to $y. Changing the value of
// $z will change the value of $y also, and vice-versa.
// $x will remain unchanged as the original value of $y
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echo $x; // => 2
echo $z; // => 2
$y = 0;
echo $x; // => 2
echo $z; // => 0
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// Dumps type and value of variable to stdout
var_dump($z); // prints int(0)
// Prints variable to stdout in human-readable format
print_r($array); // prints: Array ( [0] => One [1] => Two [2] => Three )
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/********************************
* Logic
*/
$a = 0;
$b = '0';
$c = '1';
$d = '1';
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// assert throws a warning if its argument is not true
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// These comparisons will always be true, even if the types aren't the same.
assert($a == $b); // equality
assert($c != $a); // inequality
assert($c <> $a); // alternative inequality
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assert($a < $c);
assert($c > $b);
assert($a <= $b);
assert($c >= $d);
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// The following will only be true if the values match and are the same type.
assert($c === $d);
assert($a !== $d);
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assert(1 === '1');
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assert(1 !== '1');
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// 'Spaceship' operator (since PHP 7)
// Returns 0 if values on either side are equal
// Returns 1 if value on the left is greater
// Returns -1 if the value on the right is greater
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$a = 100;
$b = 1000;
echo $a <=> $a; // 0 since they are equal
echo $a <=> $b; // -1 since $a < $b
echo $b <=> $a; // 1 since $b > $a
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// Variables can be converted between types, depending on their usage.
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$integer = 1;
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echo $integer + $integer; // => 2
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$string = '1';
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echo $string + $string; // => 2 (strings are coerced to integers)
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$string = 'one';
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echo $string + $string; // => 0
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// Outputs 0 because the + operator cannot cast the string 'one' to a number
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// Type casting can be used to treat a variable as another type
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$boolean = (boolean) 1; // => true
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$zero = 0;
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$boolean = (boolean) $zero; // => false
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// There are also dedicated functions for casting most types
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$integer = 5;
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$string = strval($integer);
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$var = null; // Null value
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/********************************
* Control Structures
*/
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if (true) {
print 'I get printed';
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}
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if (false) {
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print 'I don\'t';
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} else {
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print 'I get printed';
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}
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if (false) {
print 'Does not get printed';
} elseif (true) {
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print 'Does';
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}
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// ternary operator
print (false ? 'Does not get printed' : 'Does');
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// ternary shortcut operator since PHP 5.3
// equivalent of "$x ? $x : 'Does'""
$x = false;
print($x ?: 'Does');
// null coalesce operator since php 7
$a = null;
$b = 'Does print';
echo $a ?? 'a is not set'; // prints 'a is not set'
echo $b ?? 'b is not set'; // prints 'Does print'
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$x = 0;
if ($x === '0') {
print 'Does not print';
} elseif ($x == '1') {
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print 'Does not print';
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} else {
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print 'Does print';
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}
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// This alternative syntax is useful for templates:
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?>
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<?php if ($x): ?>
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This is displayed if the test is truthy.
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<?php else: ?>
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This is displayed otherwise.
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<?php endif; ?>
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<?php
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// Use switch to save some logic.
switch ($x) {
case '0':
print 'Switch does type coercion';
break; // You must include a break, or you will fall through
// to cases 'two' and 'three'
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case 'two':
case 'three':
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// Do something if $variable is either 'two' or 'three'
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break;
default:
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// Do something by default
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}
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// While, do...while and for loops are probably familiar
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$i = 0;
while ($i < 5) {
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echo $i++;
} // Prints "01234"
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echo "\n";
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$i = 0;
do {
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echo $i++;
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} while ($i < 5); // Prints "01234"
echo "\n";
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for ($x = 0; $x < 10; $x++) {
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echo $x;
} // Prints "0123456789"
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echo "\n";
$wheels = ['bicycle' => 2, 'car' => 4];
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// Foreach loops can iterate over arrays
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foreach ($wheels as $wheel_count) {
echo $wheel_count;
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} // Prints "24"
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echo "\n";
// You can iterate over the keys as well as the values
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foreach ($wheels as $vehicle => $wheel_count) {
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echo "A $vehicle has $wheel_count wheels";
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}
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echo "\n";
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$i = 0;
while ($i < 5) {
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if ($i === 3) {
break; // Exit out of the while loop
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}
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echo $i++;
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} // Prints "012"
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for ($i = 0; $i < 5; $i++) {
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if ($i === 3) {
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continue; // Skip this iteration of the loop
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}
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echo $i;
} // Prints "0124"
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/********************************
* Functions
*/
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// Define a function with "function":
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function my_function () {
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return 'Hello';
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}
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echo my_function(); // => "Hello"
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// A valid function name starts with a letter or underscore, followed by any
// number of letters, numbers, or underscores.
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function add ($x, $y = 1) { // $y is optional and defaults to 1
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$result = $x + $y;
return $result;
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}
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echo add(4); // => 5
echo add(4, 2); // => 6
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// $result is not accessible outside the function
// print $result; // Gives a warning.
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// Since PHP 5.3 you can declare anonymous functions;
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$inc = function ($x) {
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return $x + 1;
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};
echo $inc(2); // => 3
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function foo ($x, $y, $z) {
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echo "$x - $y - $z";
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}
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// Functions can return functions
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function bar ($x, $y) {
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// Use 'use' to bring in outside variables
return function ($z) use ($x, $y) {
foo($x, $y, $z);
};
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}
$bar = bar('A', 'B');
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$bar('C'); // Prints "A - B - C"
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// You can call named functions using strings
$function_name = 'add';
echo $function_name(1, 2); // => 3
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// Useful for programatically determining which function to run.
// Or, use call_user_func(callable $callback [, $parameter [, ... ]]);
// You can get the all the parameters passed to a function
function parameters() {
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$numargs = func_num_args();
if ($numargs > 0) {
echo func_get_arg(0) . ' | ';
}
$args_array = func_get_args();
foreach ($args_array as $key => $arg) {
echo $key . ' - ' . $arg . ' | ';
}
}
parameters('Hello', 'World'); // Hello | 0 - Hello | 1 - World |
// Since PHP 5.6 you can get a variable number of arguments
function variable($word, ...$list) {
echo $word . " || ";
foreach ($list as $item) {
echo $item . ' | ';
}
}
variable("Separate", "Hello", "World"); // Separate || Hello | World |
/********************************
* Includes
*/
<?php
// PHP within included files must also begin with a PHP open tag.
include 'my-file.php';
// The code in my-file.php is now available in the current scope.
// If the file cannot be included (e.g. file not found), a warning is emitted.
include_once 'my-file.php';
// If the code in my-file.php has been included elsewhere, it will
// not be included again. This prevents multiple class declaration errors
require 'my-file.php';
require_once 'my-file.php';
// Same as include(), except require() will cause a fatal error if the
// file cannot be included.
// Contents of my-include.php:
<?php
return 'Anything you like.';
// End file
// Includes and requires may also return a value.
$value = include 'my-include.php';
// Files are included based on the file path given or, if none is given,
// the include_path configuration directive. If the file isn't found in
// the include_path, include will finally check in the calling script's
// own directory and the current working directory before failing.
/* */
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/********************************
* Classes
*/
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// Classes are defined with the class keyword
class MyClass
{
const MY_CONST = 'value'; // A constant
static $staticVar = 'static';
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// Static variables and their visibility
public static $publicStaticVar = 'publicStatic';
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// Accessible within the class only
private static $privateStaticVar = 'privateStatic';
// Accessible from the class and subclasses
protected static $protectedStaticVar = 'protectedStatic';
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// Properties must declare their visibility
public $property = 'public';
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public $instanceProp;
protected $prot = 'protected'; // Accessible from the class and subclasses
private $priv = 'private'; // Accessible within the class only
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// Create a constructor with __construct
public function __construct($instanceProp)
{
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// Access instance variables with $this
$this->instanceProp = $instanceProp;
}
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// Methods are declared as functions inside a class
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public function myMethod()
{
print 'MyClass';
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}
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// final keyword would make a function unoverridable
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final function youCannotOverrideMe()
{
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}
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// Magic Methods
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// what to do if Object is treated as a String
public function __toString()
{
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return $property;
}
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// opposite to __construct()
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// called when object is no longer referenced
public function __destruct()
{
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print "Destroying";
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}
/*
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* Declaring class properties or methods as static makes them accessible without
* needing an instantiation of the class. A property declared as static can not
* be accessed with an instantiated class object (though a static method can).
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*/
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public static function myStaticMethod()
{
print 'I am static';
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}
}
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// Class constants can always be accessed statically
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echo MyClass::MY_CONST; // Outputs 'value';
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echo MyClass::$staticVar; // Outputs 'static';
MyClass::myStaticMethod(); // Outputs 'I am static';
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// Instantiate classes using new
$my_class = new MyClass('An instance property');
// The parentheses are optional if not passing in an argument.
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// Access class members using ->
echo $my_class->property; // => "public"
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echo $my_class->instanceProp; // => "An instance property"
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$my_class->myMethod(); // => "MyClass"
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// Extend classes using "extends"
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class MyOtherClass extends MyClass
{
function printProtectedProperty()
{
echo $this->prot;
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}
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// Override a method
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function myMethod()
{
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parent::myMethod();
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print ' > MyOtherClass';
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}
}
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$my_other_class = new MyOtherClass('Instance prop');
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$my_other_class->printProtectedProperty(); // => Prints "protected"
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$my_other_class->myMethod(); // Prints "MyClass > MyOtherClass"
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final class YouCannotExtendMe
{
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}
// You can use "magic methods" to create getters and setters
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class MyMapClass
{
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private $property;
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public function __get($key)
{
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return $this->$key;
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}
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public function __set($key, $value)
{
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$this->$key = $value;
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}
}
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$x = new MyMapClass();
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echo $x->property; // Will use the __get() method
$x->property = 'Something'; // Will use the __set() method
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// Classes can be abstract (using the abstract keyword) or
// implement interfaces (using the implements keyword).
// An interface is declared with the interface keyword.
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interface InterfaceOne
{
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public function doSomething();
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}
interface InterfaceTwo
{
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public function doSomethingElse();
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}
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// interfaces can be extended
interface InterfaceThree extends InterfaceTwo
{
public function doAnotherContract();
}
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abstract class MyAbstractClass implements InterfaceOne
{
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public $x = 'doSomething';
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}
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class MyConcreteClass extends MyAbstractClass implements InterfaceTwo
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{
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public function doSomething()
{
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echo $x;
}
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public function doSomethingElse()
{
echo 'doSomethingElse';
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}
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}
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// Classes can implement more than one interface
class SomeOtherClass implements InterfaceOne, InterfaceTwo
{
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public function doSomething()
{
echo 'doSomething';
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}
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public function doSomethingElse()
{
echo 'doSomethingElse';
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}
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}
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/********************************
* Traits
*/
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// Traits are available from PHP 5.4.0 and are declared using "trait"
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trait MyTrait
{
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public function myTraitMethod()
{
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print 'I have MyTrait';
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}
}
class MyTraitfulClass
{
use MyTrait;
}
$cls = new MyTraitfulClass();
$cls->myTraitMethod(); // Prints "I have MyTrait"
/********************************
* Namespaces
*/
// This section is separate, because a namespace declaration
// must be the first statement in a file. Let's pretend that is not the case
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<?php
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// By default, classes exist in the global namespace, and can
// be explicitly called with a backslash.
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$cls = new \MyClass();
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// Set the namespace for a file
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namespace My\Namespace;
class MyClass
{
}
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// (from another file)
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$cls = new My\Namespace\MyClass;
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//Or from within another namespace.
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namespace My\Other\Namespace;
use My\Namespace\MyClass;
$cls = new MyClass();
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// Or you can alias the namespace;
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namespace My\Other\Namespace;
use My\Namespace as SomeOtherNamespace;
$cls = new SomeOtherNamespace\MyClass();
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/**********************
* Late Static Binding
*
*/
class ParentClass
{
public static function who()
{
echo "I'm a " . __CLASS__ . "\n";
}
public static function test()
{
// self references the class the method is defined within
self::who();
// static references the class the method was invoked on
static::who();
}
}
ParentClass::test();
/*
I'm a ParentClass
I'm a ParentClass
*/
class ChildClass extends ParentClass
{
public static function who()
{
echo "But I'm " . __CLASS__ . "\n";
}
}
ChildClass::test();
/*
I'm a ParentClass
But I'm ChildClass
*/
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/**********************
* Magic constants
*
*/
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// Get current class name. Must be used inside a class declaration.
echo "Current class name is " . __CLASS__;
// Get full path directory of a file
echo "Current directory is " . __DIR__;
// Typical usage
require __DIR__ . '/vendor/autoload.php';
// Get full path of a file
echo "Current file path is " . __FILE__;
// Get current function name
echo "Current function name is " . __FUNCTION__;
// Get current line number
echo "Current line number is " . __LINE__;
// Get the name of the current method. Only returns a value when used inside a trait or object declaration.
echo "Current method is " . __METHOD__;
// Get the name of the current namespace
echo "Current namespace is " . __NAMESPACE__;
// Get the name of the current trait. Only returns a value when used inside a trait or object declaration.
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echo "Current trait is " . __TRAIT__;
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/**********************
* Error Handling
*
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*/
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// Simple error handling can be done with try catch block
try {
// Do something
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} catch (Exception $e) {
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// Handle exception
}
// When using try catch blocks in a namespaced enviroment use the following
try {
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// Do something
} catch (\Exception $e) {
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// Handle exception
}
// Custom exceptions
class MyException extends Exception {}
try {
$condition = true;
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if ($condition) {
throw new MyException('Something just happend');
}
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} catch (MyException $e) {
// Handle my exception
}
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```
## More Information
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Visit the [official PHP documentation](http://www.php.net/manual/) for reference
and community input.
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If you're interested in up-to-date best practices, visit
[PHP The Right Way](http://www.phptherightway.com/).
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If you're coming from a language with good package management, check out
[Composer](http://getcomposer.org/).
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For common standards, visit the PHP Framework Interoperability Group's
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[PSR standards](https://github.com/php-fig/fig-standards).