The PHP file (.php)

The basics

What is a PHP file?

Anatomy

What's inside a PHP file

A PHP file is a text file in which <?php … ?> tags mark the code. PHP runs the code and sends everything outside the tags as it is. Here is a small page that lists products from PHP objects, part by part.

<?php
declare(strict_types=1);

require __DIR__ . '/vendor/autoload.php';

use App\Shop\Product;

$products = [
    new Product('Notebook', 4.50),
    new Product('Pencil', 0.80),
];

function h(string $text): string
{
    return htmlspecialchars($text, ENT_QUOTES, 'UTF-8');
}
?>
<!DOCTYPE html>
<html lang="en">
<head><meta charset="utf-8"><title>Shop</title></head>
<body>
  <h1>Products</h1>
  <ul>
  <?php foreach ($products as $product): ?>
    <li><?= h($product->name) ?>: €<?= number_format($product->price, 2) ?></li>
  <?php endforeach; ?>
  </ul>
</body>
</html>

1. 1<?php

   The opening tag

   Switches from output to code. It must be followed by a space, tab or newline. Anything before it, even one blank line or an invisible byte order mark, is sent to the browser.

2. 2declare(strict_types=1);

   Strict types

   Must be the first statement in the file. With it, passing a number where a function expects a string is a TypeError instead of a silent conversion.

3. 3require __DIR__ . '/vendor/autoload.php';

   The Composer autoloader

   Loads the packages installed with Composer and lets PHP find your own classes by name. __DIR__ is this file's folder, so the path works whichever folder the request started from.

4. 4use App\Shop\Product;

   A namespace import

   Lets the code say Product instead of App\Shop\Product. Under the PSR-4 convention, that class lives in a file called Product.php in a Shop folder.

5. 5$products = [ … ];

   Variables and arrays

   Variables start with $. Square brackets make an array, PHP's all-purpose list and dictionary.

6. 6htmlspecialchars($text, ENT_QUOTES, 'UTF-8')

   Escaping output

   Turns <, >, & and quotes into HTML entities, so text from a database or a visitor can't add HTML or scripts to the page (cross-site scripting).

7. 7?>

   The closing tag

   Switches back to output. Everything until the next <?php goes to the browser unchanged. A file that is all PHP should leave this tag out, as the next section explains.

8. 8<!DOCTYPE html> …

   Plain HTML

   Sent as it is. The browser only ever receives HTML like this: it never sees the PHP code, only what the code printed.

9. 9<?php foreach (…): ?> … <?php endforeach; ?>

   A loop around HTML

   The alternative syntax (a colon and endforeach) is made for templates: the HTML between the tags is sent once per product.

10. 10<?= h($product->name) ?>

    The short echo tag

    <?= is short for <?php echo, and is always available. -> reads a property of an object.

Under the hood

What happens when a server runs a PHP file

The big gotcha

Why a PHP file downloads or shows its code instead of running

How to

How to run, edit and check a PHP file

# In the folder that holds your PHP files:
php -S localhost:8000

# then open http://localhost:8000/sample-page.php in a browser.
# Serve a subfolder as the document root instead:
php -S localhost:8000 -t public/

The rules

Tags, encodings, file names and project layout

my-site/
  composer.json         dependencies and autoload rules
  composer.lock         exact versions Composer installed: commit it
  vendor/               installed packages; vendor/autoload.php loads them
  public/               the web server's document root, the only folder online
    index.php           the entry point: every request starts here
    style.css
  src/
    Shop/
      Product.php       class App\Shop\Product (PSR-4: one class per file)
  config/
    database.php        settings and passwords, outside public/

Versions

PHP versions and which ones are still supported

Related formats

PHP files and their neighbours

Troubleshooting

PHP errors you'll meet on a server, and what they mean

Security

Is it safe to open a PHP file, and what goes wrong on servers

Free downloads

Sample PHP files to download

Free sample PHP files for testing servers, editors, syntax highlighters, linters and upload filters. All pass php -l and run with PHP 8.2 or later, except sample-syntax-error.php, which fails on purpose.

Loading…

What's inside sample-page.php

The preview shows the file as source, the way a static host serves it. Open it in a text editor to follow the numbered comments, or run php -S localhost:8000 in its folder and open /sample-page.php to see the page PHP builds from it.

1. Comments 1 and 2: the opening tag and strict types

   <?php on the first line, a comment explaining how to run the file, then declare(strict_types=1) as the first statement.

2. Comment 3: data

   An array with string keys holding a week of opening hours, with null for a closed day.

3. Comment 4: an escaping function

   h() wraps htmlspecialchars() so every value printed into the page is safe against cross-site scripting.

4. Comments 5 and 6: input and dates

   $_GET['name'] ?? '' reads an optional ?name= from the address, and a DateTimeImmutable with a named time zone works out today's day.

5. Comment 7: the closing tag

   PHP stops and the HTML that follows is sent as it is, up to each <?= or <?php tag inside it.

6. Comments 8 and 9: templates

   Short echo tags print values, and a foreach … endforeach loop writes one table row per day, marking today's row with a class.

7. Comments 10 and 11: a form and constants

   A GET form that sends a name back to the same file, and PHP_VERSION in the footer, so you can see which PHP built the page.

All sample PHP files

• Commented PHP page

  sample-page.php · 3.4 KB (3,473 bytes)

  A web page mixing PHP and HTML: opening hours with today highlighted, a greeting form and escaped output, with numbered comments explaining each part.

  • Checking whether a server runs PHP or serves it as text
  • Teaching how PHP and HTML mix
  DownloadOpen

• Command-line script

  sample-cli.php · 2.1 KB (2,169 bytes)

  A pure-PHP length converter with a #!/usr/bin/env php shebang and no closing tag. Uses an enum, match, $argv, STDERR and exit codes: php sample-cli.php 5 km mi.

  • Testing PHP on the command line and in CI
  • An example of a file with the closing tag left out
  DownloadOpen

• UTF-8 encoding test

  sample-utf8.php · 1.9 KB (1,946 bytes)

  Greetings in 12 languages plus symbols and emoji, comparing strlen() with mb_strlen(), strtoupper() with mb_strtoupper(), and JSON with and without escaped Unicode.

  • Spotting encoding bugs in editors and pipelines
  • Checking that the mbstring and intl extensions are installed
  DownloadOpen

• UTF-8 with a byte order mark

  sample-bom.php · 1.0 KB (1,034 bytes)

  Starts with the bytes EF BB BF before <?php. When run, it reports that output had already started at line 1, which is what breaks header() and sessions.

  • Reproducing "headers already sent" problems
  • Checking whether an editor or pipeline adds or strips a BOM
  DownloadOpen

• Missing semicolon (deliberate syntax error)

  sample-syntax-error.php · 541 bytes

  An echo without a semicolon. Clearly labelled; php -l reports unexpected token "echo" on line 16 and exits with status 255.

  • Testing how editors, linters and CI report parse errors
  • Showing that PHP reports the line after the mistake
  DownloadOpen

• 100 KB PHP file

  sample-100kb.php · 100 KB (102,400 bytes)

  A constant array of Roman numerals from 1 to 3,999 and a function that checks every one, padded with a comment to exactly 102,400 bytes.

  • Upload and size-limit tests
  • Parser, highlighter and OPcache tests
  DownloadOpen

Ways to test with them

• Does the server run PHP? Upload sample-page.php and open it. A page with an opening-hours table means PHP ran; the source code means it didn't.
• Lint in CI: php -l should pass for every sample except sample-syntax-error.php, which must fail with exit status 255.
• BOM handling: run sample-bom.php; if it no longer reports output at line 1, something on the way removed the BOM.
• Upload filters: many upload forms rightly refuse .php files. Use the samples to confirm yours does, including the exactly 102,400-byte sample-100kb.php for size limits.

Free to use for testing, teaching and demos, commercially or not, with no attribution needed. A link back to this page is always appreciated.

Questions

PHP files, frequently asked