1. PHP: Hypertext Preprocessor

2. PHP An HTML embedded scripting language
JSP, ASP (executes on webserver)
VBScript, Javascript (executes in browser)
PHP is (normally) used on a webserver
Output from a php script is usually HTML
Aim is to allow web developers to write dynamically generated pages quickly
Much syntax borrowed from C, Java and Perl
“Glue” between lots of other programs
Database friendly
Client/Server application friendly
Widely used open source scripting language
Started in 1995, under continual development

3. PHP and HTML PHP is usually part of an HTML page Special HTML tag
<?php php program ?>
Webserver sends html file to php interpreter
Interpreter looks for <?php … ?> tag and interprets code
Output (may be html) replaces php tags
Other html passes through unchanged
Interpreter sends output back to webserver
Page sent to remote browser

4. Basic features
All the usual programming language features (plus some…)
Instruction separation
As in C or PERL, new lines are not important.
instructions end with a semicolon (;) character
Comments
C (/* … */)
C++ (//)
Unix Shell (#)
Variables
Start with a dollar ($) symbol
Programmer needn’t specify datatype
Some special variables from outside PHP

5. More features Arrays Functions Control Structures
Actually an “ordered map”
“map” from a key to a value
Use square brackets [] to access arrays
Value can also be an array
Some predefined arrays for getting information from webserver
Functions
Hundreds of built-in functions
Control Structures
Conditional Statements
If, else, elseif
Loops
while, do-while, for, foreach, switch, break, continue

6. Working with forms Reason PHP was invented! HTML forms
Can use HTTP ‘POST’ or ‘GET’ methods to send data to webserver
PHP predefined variables
$_GET array
$_POST array
Elements are named as in the HTML form

7. Sessions Each request from a browser is independent
Need to keep track of which request comes from which browser
PHP makes this simple with a $_SESSION array variable – any data stored here will be maintained for the browser ‘session’

8. Local filesystem Can read and write to other files on the webserver
Access files using a handle
Lots of functions to access files
fopen – open file and get a handle
ffeof – test for end of file
fgets – read a line from a file
fwrite – write a line to a file
fclose – close a file
flock – test for and lock, or unlock, a file
Writing to a file
Must lock file first
Shouldn’t allow user to interrupt script while we write our data [ignore_user_abort(true);]