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Introduction to PHP

PHP stands for PHP: Hypertext Preprocessor. It is a free and popular scripting language used mainly for making websites interactive. You write PHP code inside HTML pages, and when a user visits your page, the server runs the PHP code and sends back the result as a web page.

PHP is great for making websites that change based on user actions — like forms, logins, or displaying data from a database.

Key Features of PHP

  • Free and works on Windows, Linux, and Mac computers.
  • Works with popular web servers like Apache and Nginx.
  • Can create dynamic content that changes as users interact.
  • Can connect to databases like MySQL to store or get information.
  • Can handle file operations (create, read, update, delete files).
  • Can read data from web forms like text boxes and buttons.
  • Manages sessions and cookies to remember users.
  • Supports security features like encryption and access control.
  • PHP files end with .php and can have HTML, CSS, JavaScript, and PHP code together.

php server

How PHP Works

  • User opens a website or submits a form.
  • Server checks if PHP code needs to run.
  • PHP code runs on the server.
  • If needed, PHP talks to a database to get or save data.
  • Server sends back a webpage with HTML to the user.

This makes websites smart and personal for every user.

Basic PHP Syntax

PHP code is put between <?php and ?> tags inside an HTML file. Every PHP command ends with a semicolon ;.

Example:

<!DOCTYPE html>
<html>
<body>
<?php
echo "Hello, this is my first PHP script!";
?>
</body>
</html>

Output:
Hello, this is my first PHP script!

PHP Comments

Comments help explain your code. PHP ignores comments when running the script.

Types of comments:

  • Single line: starts with // or #
  • Multi-line: between /* and */

Example:

<?php
// This is a single-line comment
# This is also a single-line comment
/*
This is a
multi-line comment
*/
echo "Comments in PHP!";
?>

Case Sensitivity in PHP

  • Keywords and function names are not case-sensitive.
  • Variable names are case-sensitive.

Example:

<?php
$color = "red";
echo "Car color: " . $color . "<br>";
echo "House color: " . $COLOR . "<br>";
?>

Output:
Car color: red
House color:

Reading Data from Web Forms

You can collect user input using $_GET or $_POST in PHP.

HTML Form Example:

<form method="post" action="process.php">
  Name: <input type="text" name="username"><br>
  Gender:  
  <input type="radio" name="gender" value="Male"> Male  
  <input type="radio" name="gender" value="Female"> Female<br>
  <input type="submit" value="Submit">
</form>

PHP to handle form data:

<?php
$username = $_POST['username'];
$gender = $_POST['gender'];
echo "Name: " . $username . "<br>";
echo "Gender: " . $gender;
?>

Connecting to MySQL Database

PHP can connect to MySQL to store or get data easily.

Example:

<?php
$conn = new mysqli("localhost", "username", "password", "database");
if ($conn->connect_error) {
    die("Connection failed: " . $conn->connect_error);
}

$sql = "SELECT id, name FROM users";
$result = $conn->query($sql);

if ($result->num_rows > 0) {
    while($row = $result->fetch_assoc()) {
        echo "ID: " . $row["id"]. " - Name: " . $row["name"]. "<br>";
    }
} else {
    echo "No results found";
}
$conn->close();
?>

Handling File Uploads

PHP can upload files from user computers and save them on your server.

HTML form example:

<form action="upload.php" method="post" enctype="multipart/form-data">
  Select file:  
  <input type="file" name="fileToUpload"><br>  
  <input type="submit" value="Upload">
</form>

PHP upload code:

<?php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);

if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file)) {
    echo "File ". htmlspecialchars(basename($_FILES["fileToUpload"]["name"])) . " uploaded successfully.";
} else {
    echo "Error uploading your file.";
}
?>

Managing Sessions and Cookies

Sessions and cookies help remember users on your site.

Start a session and set a variable:

<?php
session_start();
$_SESSION["username"] = "JohnDoe";
echo "Session started for " . $_SESSION["username"];
?>

Set a cookie:

<?php
setcookie("user", "JohnDoe", time() + (86400 * 30), "/");  // expires in 30 days
?>++