PHP

History

The web in 1993

PHP in 1994

Introduction

Today, PHP is an interpreted language mostly used server-side in web applications.

<?php
// date.php
echo "It is ".date('H:i:s')."!\n";

$ php date.php
It is 17:25:12!

Template language

A peculiarity of the language is that it only interprets the content of PHP tags, which start with <?php and end with ?>.

For example:

Hello world

<?php
echo "Hello world";

Hello <?php echo "World"; ?>

This technique makes it convenient to generate text formats such as HTML:

<h1>Welcome <?= $name ?></h1>

You have <?= count($messages) ?> new messages:

<ul class="messages-list">
<?php foreach ($messages as $message) { ?>
    <li><?= $message['title'] ?></li>
<?php } ?>
</ul>

Language principles

The basics

<?php
$a = 123;
$b = "456";
echo "a+b=".($a+$b)."\n";
$a = true;

• Variables are prefixed with $
• The + operator is addition, and . is concatenation, so there is no ambiguity
• Typing is weak: $a can hold values of different types during execution

var_dump()

A handy PHP function: var_dump(), which displays the content of any variable:

<?php
$a = 123;
var_dump($a);
// int(123)
$a = [1, 2];
var_dump($a);
// array(2) {
//     [0]=>
//     int(1)
//     [1]=>
//     int(2)
// }

Arrays

<?php
// Array of elements
$fruits = ['apple', 'apricot', 'strawberry'];
// $fruits[0] is "apple" etc.

// Associative array
$colors = [
    'apple' => 'green',
    'apricot' => 'orange',
    'strawberry' => 'red'
];
// $colors['apple'] is 'green' etc.

// Iteration
foreach ($fruits as $fruit) {
    echo "The fruit ".$fruit." has the color: ";
    echo $colors[$fruit]."\n";
}

Arrays with implicit keys

<?php
// Creating an empty array
$numbers = [];

// Creating a non-empty array
$numbers = [1, 2, 3];

// Appending the element 4
$numbers[] = 4;

// Displaying the size of the array
echo "There are ".count($numbers)." elements:\n";

// Iterating and displaying the elements
foreach ($numbers as $number) {
    echo "- $number\n";
}

// Removing from the head or the tail
array_pop($numbers); // Removes the last element
array_shift($numbers); // Removes the first element

Associative arrays

<?php
// Creating an empty array
$nameToAge = [];

// Creating an array that already contains elements
$nameToAge = ['Ryan' => 30, 'Nina' => 12];

// Associating an element
$nameToAge['Gilbert'] = 56;

// Removing an element
unset($nameToAge['Ryan']);

// Checking for existence
if (isset($nameToAge['Ryan']))
    echo "Ryan is here!\n";

// Iterating
foreach ($nameToAge as $name => $age)
    echo "$name is $age years old!\n";

HTTP gateway

When used as a server, PHP gives access to a set of information about the current request.

Built-in server

You can use PHP's built-in server, which lets you start a server directly from the command line:

php -S 127.0.0.1:8080

GET parameters

GET parameters are passed in the request URL, for example:

<?php
// index.php
if (isset($_GET['first_name']) && isset($_GET['last_name'])) {
    echo "Hello ".$_GET['first_name']." ".$_GET['last_name']."!";
}

POST parameters

POST parameters are passed in the request body; they can for example come from a form:

<form method="post" action="hello.php">
    First name:
    <input type="text" name="first_name"/><br />
    Last name:
    <input type="text" name="last_name"/><br/>
    <hr />
    <input type="submit" value="Send" />
</form>

Once the form is submitted, these parameters will be available in the PHP $_POST array:

<?php
// hello.php
if ($_SERVER['REQUEST_METHOD'] == 'POST') {
    echo "Hello ".$_POST['first_name']." ".$_POST['last_name']."!";
}

Functions

Database

PHP's PDO interface is today a uniform way to access many different databases.

You connect by instantiating an object of type PDO:

<?php
$pdo = new PDO($dsn, $user, $password)

Where:

• $dsn, for data source name, is the database connection string
• $user is the user's login
• $password is the user's password

For example:

<?php
$dsn = "mysql:dbname=shows;host=info-titania";
$user = 'user';
$password = 'password';
$pdo = new PDO($dsn, $user, $password);

Will connect to the department's database.

• mysql is the name of the driver, since the database is of type MySQL/MariaDB,
• info-titania is the hostname of the server on the network,
• shows is the database on the server.

Simple query

The PDO::query() method lets you run a simple query on the database:

<?php
$sql = "SELECT title FROM series WHERE year_start < 2005";
$query = $pdo->query($sql);
foreach ($query as $row) {
    echo 'Name: ' . $row['title']. "\n";
}

The object returned by PDO::query() is iterable, and provides associative arrays mapping column names to values.

Iterating over a query vs fetch()

Iterating over the query ($query) is actually equivalent to calling $query->fetch() repeatedly until it returns FALSE:

<?php
foreach ($query as $row) {
}
// Is equivalent to
while ($row = $query->fetch()) {
}

Parameterized query

The PDO::prepare() method lets you create a prepared statement, that is, a query containing a parameter.

For example:

$sql = "SELECT * FROM series WHERE title = :title";
$query = $pdo->prepare($sql);
if ($query->execute(['title' => 'Dexter'])) {
    foreach ($query as $row) {
        echo 'Name: ' . $row['title']. ", start year: " . $row['year_start'] . "\n";
    }
}

Here, :title is a prepared parameter of the query, which is provided at execution time with PDO::execute().

Another option is to leave the parameters unnamed, and use the ? symbol:

$sql = "SELECT * FROM series WHERE title = ?";
$query = $pdo->prepare($sql);
$success = $query->execute(['Dexter']);
// ...

In this case, the order of the elements in the array passed to PDO::execute() is what matters

Number of results

You can use the rowCount() method on a PDOStatement object (obtained with query() or prepare()) to know how many rows were returned:

<?php

$query = $pdo->query('SELECT title FROM series');
echo "There are ".$query->rowCount()." results";

<?php

$query = $pdo->query('SELECT COUNT(*) as nb FROM series');
$result = $query->fetch();
echo "There are ".$result['nb']." results";

Cookies and sessions

Cookies

Cookies are data stored by the browser at the request of the web server.

In PHP, you can create them using setcookie:

<?php
// Creates a "name" cookie whose value is "bob"
setcookie('name', 'bob');

<?php
// Was the name cookie provided?
if (isset($_COOKIE['name'])) {
    echo "Hello ".$_COOKIE['name'];
}

Sessions

To do this, we randomly generate a "token" that uniquely identifies a user, for example 0E28B4E12, and store it in a cookie, for example ID.

This mechanism is called a session, and is implemented in PHP:

<?php
// Initializes the session system
session_start();

if (isset($_SESSION['user'])) {
    echo "Welcome ".$_SESSION['user']."!";
} else {
    header('location: login.php');
}

Here, you can read, write and check for values in the $_SESSION array, which is stored server-side.

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