PHP

Server-side code.

Normally in public_html
Normally named like: file.php

File contains normal HTML, and PHP code mixed in, delimited as follows:

<html>
<body>

html code

<?php 
php code 
?>

more html code

PHP gets interpreted on server side before resulting HTML stream is returned to client.
Whatever the PHP writes to standard output (stdout) appears in the browser.
Client can't see PHP code: Unlike with Javascript, client can't see the code that generated the HTML.
PHP used for interaction with databases/files on server.

Basics

Debugging can be difficult.
The issue:
- If PHP writes error messages to stdout (to web page), hackers can use this to experiment, and test for server-side vulnerabilities.
- So servers often turn off PHP error output.
Over-ride server defaults: Turn on error output for your own PHP. Include these lines:
```
ini_set ( 'display_errors', true );
ini_set ( 'display_startup_errors', true );
error_reporting ( E_ALL );  
```
and then error messages are displayed.
Comment/uncomment this block.
Exercise:
Put this error in a PHP file:
```
 nonExistentFunction(); 
```
View it with and without those 3 lines above inserted.

You can dump variables to stdout:
```
print "x is $x";
```
To display full structure of a complex object:
```
var_dump($x);
print_r($x);  
```

A multi-line string can be useful. Assign a chunk of HTML to a string, and maybe re-use it in different places.

Strings in PHP shows ways of doing a multi-line string: