What is PHP

PHP (Hypertext Preprocessor)

  • Just like other script language, using variables, loop, etc.
  • It runs on the server side and is embedded directly into HTML. Used to create dynamic, interactive websites.
  • PHP powers many popular platforms like WordPress and Laravel.
  • All php scripts start with <?php and with ?>
  • PHP can be placed directly inside HTML

Example

<?php
$author = "John Smiths";
$message = "How are you?";
echo $author . " says " . $message;
?>

PHP - Forms

  • <form method="post" action="process.php" >
    • Method specifies how the data will be sent
    • Action specifies the file to send to. E.g. process.php
  • Post method sends all contents of a form with basically hidden headers (not easily visible to users)
  • Get method sends all form input in the URL requested using name=value pairs separated by ampersands (&)
    • E.g. process.php?name=John&number=345
    • Is visible in the URL shown in the browser
  • All form values are placed into an array
  • Assume a form contains one textbox called “lastname” and the form is submitted using the post method, invoking process.php
  • process.php could access the form data using:
    • $_POST[‘lastname’] or
    • Use extract($_POST) to imports form fields as variables
  • If the form used the get method, the form data would be available as:
    • $_GET[‘lastname’]

PHP Session handling

Session handling is a way to make the data available across all pages of aweb application for a user. A session creates a file in a temporary directory on the server where registered session variables and their values are stored.

Using Seesion Steps

  • The session_start() function is used to start a new session or, resume an existing one.
  • Session variables are stored in associative array called $_SESSION[].
    • session_start() ;
    • $_SESSION['username'] = $username;
    • $_SESSION['total_amount'] = 2000;
  • Make use of isset() function to check if a session variable is already set or not.

Common functions

empty()

The empty() function checks whether a variable is empty or not. For exampel: empty($_POST)

header(“Location:myphp.php”)

  • The header() function sends a raw HTTP header to a client.
  • The header location can be used to redirect a user to another page. 
    header("Location:myphp.php")
header("Location: https://www.google.com/")

isset()

  • The function isset() is used to determine is a variable is set/declared and is not null.
  • This function returns true if variable exists and has any value other than null.
session_start();
if (!isset($_SESSION['username'])){
  header("Location:login.php");
}

PHP Exceptions

<?php
try {
throw new Exception("This is an exception");
} catch(Exception $e) {
echo $e->getMessage();
}
?>