Introduction to PHP

PHP is a scripting language designed for building websites. It runs on the server: when someone visits a PHP page, the server runs the PHP code and sends back the resulting HTML. PHP powers WordPress, which alone runs a large share of all websites, plus Wikipedia, Facebook's early versions and countless online shops.

How PHP works

Browser asks for page.php
   → server runs the PHP code
   → PHP produces HTML
   → the browser receives plain HTML (never the PHP source)

Built with PHP

Project	What it is
WordPress	the site builder behind a large share of all websites
Laravel	a popular framework for web apps
Symfony	a framework whose components many projects reuse
Composer	PHP's package manager, for adding libraries

Your first script

<?php
echo "Hello, PHP!\n";
echo "Today's lucky number is " . rand(1, 100) . "\n";

• PHP code goes between <?php and ?> (the closing tag can be left off when a file is pure PHP).
• echo outputs text.
• . joins strings.
• Statements end with a semicolon.

PHP mixed with HTML

PHP was built to sit inside HTML pages:

<h1>Welcome</h1>
<p>The year is <?php echo date("Y"); ?>.</p>
<ul>
<?php foreach (["Python", "PHP", "SQL"] as $lang): ?>
  <li><?php echo $lang; ?></li>
<?php endforeach; ?>
</ul>

Run it: the output is plain HTML, which the playground also renders in its Preview tab.