PHP: Hypertext Preprocessor
PHP is a powerful script language for web authors. You write special instructions in the HTML text that the web server interprets before the page is delivered to the browser.
The central web servers www.tu-chemnitz.de and www-user.tu-chemnitz.de
are configured almost identically regarding PHP:
www.tu-chemnitz.de |
PHP-Commands in the central web space | PHP 7 – Configuration |
|---|---|---|
www-user.tu-chemnitz.de |
PHP-Commands in the user's web space | PHP 7 – Configuration |
Introduction, Documentation
Files with PHP commends must have the extensions .html (recommended) or
.php, then the PHP code they contain will also be interpreted.
Files with the extension .phps are not interpreted, but the source text is displayed directly in the browser.
(So be careful with code that contains business logic or internal comments!)
This is how it looks in the web browser – PHP statements are executed.
<html lang="en">
<head>
<title>PHP Example: Simple Statements</title>
</head>
<body>
<main>
<h1>PHP Example: Simple Statements</h1>
<p>Hello, <?php echo $_SERVER['REMOTE_ADDR']; ?></p>
<p>Today's date is the
<?php
# Comment: Output the date, then a character string depending on the month.
$day = date('z') + 1;
echo date('d. m. Y') . ', the ' . $day . '. day of the year. ';
$month = date('m');
if ($month == 1 || $month == 2 || $month == 12) {
echo 'It is winter.';
} else if ($month > 2 && $month < 6) {
echo 'It is spring.';
} else if ($month > 5 && $month < 9){
echo 'It is summer.';
} else {
echo 'It is autumn.';
}
?>
</p>
</main>
</body>
</html>
You can see that the PHP instructions are separated from the HTML text by the tags <?php … ?>. It also becomes clear that PHP features important elements of a programming language – variables, terms,
statements, control elements, classes. For a description, please refer to the following documents:
- PHP handbook: German or English
- PHP homepage (English)
- SELFPHP – Create PHP files yourself
Be sure to read our notes on safe programming with PHP.
Notes
PHP Error Messages (For Development/Troubleshooting)
Display errors on the web page (only during development)
- in file
.htaccess:php_flag display_errors on - Please switch off again after the development phase.
Write errors to a file
-
in file
.htaccess:# write PHP error in file php_value log_errors on # file in own directory, must be writeable for web server: php_value error_log "/afs/tu-chemnitz.de/home/urz/.../public_html/log/php_errors" # which errors: all = -1, most important = 8, the worst = 1 php_value error_reporting -1 # maximum size of the error file in bytes: unlimited = 0 … until memory is full php_value log_errors_max_len 1000000 # Protect log file from web access <Files "php_errors"> Require all denied </Files> - Please switch off again after the development phase.
Start Tag
The web server only interprets PHP instructions that are within special tags:
<?php echo "Hello"; ?>.
So far we also support the short form <? … ?> However, as this is not XML and XHTML compliant, all PHP programmers should use the long form above.
.htaccess file in the PHP script directory:
php_flag short_open_tag off<?xml ... ?>