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PHP

Essentials



PHP Essentials

2

© 2009 Techotopia.com

PHP Essentials


Edition 1.0

© 2009 Techotopia
.com. This eBook

is provided for personal use only. Unauthorized use,
reproduction and/or distribution strictly prohibited. All rights reserved.

The content of this book is provided for informational purposes only. Neither the publisher nor
the author offers any warrantie
s or representation, express or implied, with regard to the
accuracy of information contained in this book, nor do they accept any liability for any loss or
damage arising from any errors or omissions.

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PHP Essentials

3

© 2009 Techotopia.com

Table of Contents

Chapter 1.

About PHP Essentials

................................
................................
..............................

10

1.1

Intended Audience

................................
................................
................................
.........

10

Chapter 2.

The History of PHP

................................
................................
................................
..

11

2.1

The Creation of PHP

................................
................................
................................
.......

11

2.2

PHP 3 Hits the Big Time

................................
................................
................................
..

11

2.3

PHP 4
-

Optimization, Scalabilty and More

................................
................................
....

12

2.4

PHP 5
-

Object Orientation, Error Handling and XML

................................
....................

12

2.5

How Popular is PHP?

................................
................................
................................
......

13

Chapter 3.

An Overview of PHP

................................
................................
................................

14

3.
1

What Exactly is PHP?

................................
................................
................................
......

14

3.2

How Does PHP Work?

................................
................................
................................
....

14

3.3

Why is PHP so Useful?

................................
................................
................................
....

16

3.4

Summary

................................
................................
................................
........................

17

Chapter 4.

Creating
a Simple PHP Script

................................
................................
..................

18

4.1

The PHP Code Delimiters

................................
................................
...............................

18

4.2

Testing the PHP Installation

................................
................................
...........................

18

4.3

Emdedding PHP into an HTML File

................................
................................
.................

19

4.4

Embedding HTML into a PHP Script

................................
................................
...............

20

4.5

Summary

................................
................................
................................
........................

21

Chapter 5.

Commenting PHP Code

................................
................................
...........................

22

5.1

PHP Single Line Comments
................................
................................
.............................

22

5.2

PHP Multi
-
line Comments

................................
................................
..............................

23

Summary

................................
................................
................................
..............................

24

Chapter 6.

An Introduction to PHP Variables

................................
................................
...........

25

6.1

Naming and Creating a Variable in PHP

................................
................................
.........

2
5

6.2

Assigning a Value to a PHP Variable

................................
................................
...............

26

6.3

Accessing PHP Variable Values

................................
................................
.......................

26

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6.4

Changing the Type of a PHP Variable

................................
................................
.............

28

6.5

Checking Whether a Variable is Set

................................
................................
...............

28

Chapter 7.

Understanding PHP Variable Types

................................
................................
........

30

7.1

The PHP Integer Variable Type

................................
................................
.......................

30

7.2

The PHP Float Variable Type

................................
................................
..........................

30

7.3

The PHP Boolean Variable Type

................................
................................
.....................

31

7.4

The PHP String Variable

................................
................................
................................
..

31

7.5

Extracting and Writing String Fragments

................................
................................
.......

32

7.6

Creating PHP heredoc Strings

................................
................................
........................

33

Chapter 8.

PHP Constants

................................
................................
................................
.........

34

8.1

Defi
ning a PHP Constant

................................
................................
................................

34

8.2

Checking if a PHP Constant is Defined

................................
................................
...........

35

8.3

Using a Variable as a Constant Name

................................
................................
............

35

8.4

Predefined PHP
Constants

................................
................................
.............................

36

8.4.1

PHP Script and Environment Related Constants

................................
....................

37

8.4.2

PHP Mathematical Constants

................................
................................
.................

37

Chapter 9.

PHP Operators
................................
................................
................................
.........

39

9.1

PHP Assignment Operators

................................
................................
............................

39

9.2

PHP Arithmetic Operators

................................
................................
..............................

40

9.3

PHP Comparison Operators

................................
................................
...........................

41

9.4

PHP Logical Operators

................................
................................
................................
....

42

9.5

PHP Increment and Decrement Operators

................................
................................
....

44

9.6

PHP String Concatenation Operator

................................
................................
..............

45

9.7

Concatenation of Numbers and Strings in PHP

................................
..............................

45

9.8

PHP Execution Operator
-

Executing Server Side Commands
................................
........

46

Chapter 10.

PHP Flow Control and Looping

................................
................................
...............

48

10.1

PHP Conditional Statements

................................
................................
..........................

48

10.1.1

The PHP
if

Statement

................................
................................
..............................

49

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© 2009 Techotopia.com

10.1.2

The PHP
if ... else

Statements

................................
................................
.................

50

10.2

PHP Looping Statements

................................
................................
................................

51

10.2
.1

PHP
for

loops

................................
................................
................................
...........

51

10.3

PHP
while

loops

................................
................................
................................
..............

53

10.3.1

PHP
do ... while

loops

................................
................................
..............................

54

10.4

PHP
switch

Statements

................................
................................
................................
..

55

10.5

B
reaking a Loop

................................
................................
................................
..............

58

10.5.1

Breaking Out of Nested Loops

................................
................................
................

58

10.6

Skipping Statements in Current Loop Iteration

................................
.............................

59

Chapter 11.

PHP Functions

................................
................................
................................
.........

60

11.1

What is a PHP Function?

................................
................................
................................

60

11.2

How to Write a PHP Function

................................
................................
........................

60

11.3

Returning a Value from a PHP Function

................................
................................
.........

61

11.4

Passing Parameters to a PHP Function

................................
................................
..........

61

11.5

Calling PHP Functions

................................
................................
................................
.....

62

11.6

Passing Parameters by Reference

................................
................................
..................

62

11.7

Returning Values by Reference

................................
................................
......................

64

11.8

Functions and Variable Scope

................................
................................
........................

64

Chapter 12.

PHP Arrays

................................
................................
................................
...............

67

12.1

Create a PHP Array

................................
................................
................................
.........

67

12.2

Accessing Elements in a PHP Array

................................
................................
................

68

12.3

Creating an Associative Array

................................
................................
........................

68

12.4

Accessing Elements of an Associative Array

................................
................................
..

68

12.5

Creating Multidimensional PHP Arrays

................................
................................
..........

69

12.6

Accessing Elements in a Multidimensional PHP Array

................................
...................

69

12.7

Using PHP Array Pointers

................................
................................
...............................

70

12
.8

Changing, Adding and Removing PHP Array Elements

................................
..................

71

12.9

Looping through PHP Array Elements

................................
................................
............

72

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12.10

Replacing Sections of an Array

................................
................................
...................

73

12.11

Sorting a PHP Array
................................
................................
................................
.....

74

12.12

Sorting Associative Arrays

................................
................................
..........................

74

12.13

Getting Information About PHP Arrays & other Array Functions

..............................

74

12.14

Summary

................................
................................
................................
.....................

75

Chapter 13.

Workin
g with Strings and Text in PHP

................................
................................
....

76

13.1

Converting to and from ASCII Values

................................
................................
.............

77

13.2

Printing Formatted Strings in PHP

................................
................................
..................

78

13.2.1

PHP printf
Formatting Specifiers

................................
................................
............

78

13.3

Finding the Length of a PHP String

................................
................................
.................

80

13.4

Converting a String into a PHP Array

................................
................................
.............

81

13.5

Removing Leading an
d Trailing Whitespace from a PHP String

................................
.....

82

13.6

Comparing Strings in PHP

................................
................................
...............................

82

13.6.1

String Comparison Functions Return Value

................................
............................

83

13.7

Accessing and Modifying Characters in String

................................
...............................

83

13.8

Searching for Characters and Substrings in a PHP String

................................
...............

84

13.9

Extracting and Replacing Substrings in PHP

................................
................................
...

84

13.10

Replacing All Instances of a Word in a PHP String

................................
.....................

85

Chapter 14.

PHP, Filesystems and File I/O

................................
................................
..................

87

14.1

Opening and Creating Files in PHP

................................
................................
.................

87

14.2

Closing Files in PHP

................................
................................
................................
.........

87

14.3

Writing to a File using PHP

................................
................................
.............................

88

14.4

Reading From a File using PHP

................................
................................
.......................

89

14.5

Checking Whether a File Exists

................................
................................
......................

90

14.6

Moving, Copying and Deleting Files with PHP

................................
...............................

90

14.7

Accessing File Attributes

................................
................................
................................

90

14
.8

PHP Output Buffering

................................
................................
................................
.....

92

Chapter 15.

Working with Directories in PHP

................................
................................
............

93

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© 2009 Techotopia.com

15.1

Creating Directories in PHP

................................
................................
............................

93

15.2

Deleting a Directory

................................
................................
................................
.......

93

15.3

F
inding and Changing the Current Working Directory

................................
...................

93

15.4

Listing Files in a Directory

................................
................................
...............................

94

Chapter 16.

An Overview of HTML Forms

................................
................................
..................

95

16.1

Creating HTML Forms

................................
................................
................................
.....

95

16.2

HTML Text Object

................................
................................
................................
...........

96

16.3

HTML TextArea Object

................................
................................
................................
...

97

16.4

The HTML Button Object

................................
................................
................................

97

16.5

HTML Check Boxes

................................
................................
................................
.........

99

16.6

HTML Radio Buttons
................................
................................
................................
.......

99

16.7

HTML Drop
-
down / Select Object

................................
................................
................

101

16.8

HTML Password Object

................................
................................
................................

102

16.9

S
ummary

................................
................................
................................
......................

103

Chapter 17.

PHP and HTML Forms

................................
................................
...........................

104

17.1

Creating the Form

................................
................................
................................
........

104

17.2

Processing Form Data Using PHP

................................
................................
.................

105

17.3

Processing Multiple Selections with PHP

................................
................................
.....

107

17.4

Summary

................................
................................
................................
......................

108

Chapter 18.

PHP and Cookies
-

Creating, Reading and Writing

................................
................

109

18.1

The Difference Between Cookies and PHP Sessions

................................
....................

109

18.2

The Structure of a Cookie

................................
................................
.............................

110

18.2.1

Cookie Name / Value Pair

................................
................................
.....................

110

18.2.2

Cookie Expiration Setting

................................
................................
......................

110

18.2.3

Cookie
path

Setting

................................
................................
...............................

110

18.2.4

Cookie
domain

Setting

................................
................................
..........................

110

18.2.5

Cookie Security Setting

................................
................................
.........................

111

18.3

Creating a Cookie in PHP

................................
................................
..............................

111

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© 2009 Techotopia.com

18.4

Reading a Cookie in PHP

................................
................................
..............................

111

18.5

Deleting a Cookie

................................
................................
................................
.........

112

Chapter 19.

Understanding PHP Sessions

................................
................................
................

113

19.1

What is a PHP Session?

................................
................................
................................

1
13

19.2

Creating a PHP Session

................................
................................
................................
.

113

19.3

Creating and Reading PHP Session Variables

................................
...............................

114

19.4

Writing PHP Session Data to a File

................................
................................
...............

115

19.5

Reading a Saved PHP Session

................................
................................
.......................

116

Chapter 20.

PHP Object Oriented Programming

................................
................................
......

117

20.1

What is an Object?

................................
................................
................................
.......

117

20.2

What is a Class?

................................
................................
................................
............

117

20.3

How is an Object Created from a Class?

................................
................................
......

117

20.4

What is sub
-
classing?

................................
................................
................................
...

117

20.5

Defining a PHP Class

................................
................................
................................
.....

118

20.6

PHP Class Constructors and Destructors

................................
................................
......

118

20.7

Creating Members in a PHP Class

................................
................................
................

119

20.8

Defining and Calling Methods

................................
................................
......................

120

20.9

Subclassing in PHP

................................
................................
................................
........

123

20.10

PHP Object Serialization

................................
................................
...........................

125

20.11

Getting Information about a PHP Object

................................
................................
.

127

Chapter 21.

Using PHP with MySQL

................................
................................
.........................

128

21.1

Creating a MySQL User Account

................................
................................
..................

128

21.2

Creating and Select MySQL Database

................................
................................
..........

129

21.3

Creating a MySQL Database Table

................................
................................
...............

130

21.4

Inserting Data into a MySQL Database Table

................................
...............................

130

21.5

Connecting with PHP to a MySQL Server

................................
................................
.....

131

21.6

Selecting Records from a MySQL Database Using PHP

................................
................

132

21.7

Adding Records to MySQL Database using PHP

................................
...........................

133

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21.8

Modifying and Deleting MySQL Records using PHP
................................
.....................

135

21.9

Using PHP to get Information about a MySQL Database

................................
.............

135

21.10

Summary

................................
................................
................................
...................

136

Chapter 22.

PHP and SQLite
................................
................................
................................
......

138

22.1

Creating an SQLite Database with PHP

................................
................................
........

138

22.2

Using PHP to Add Records to an SQLite Database

................................
.......................

139

22.3

Using PHP to Select Records from an SQLite Database

................................
...............

139

22.4

Summary

................................
................................
................................
......................

141





PHP Essentials

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© 2009 Techotopia.com

Chapter 1.

About PHP Essentials

Any attempt to gauge the popularity of PHP on the internet results in statistics which prove
difficult for the human mind to comp
rehend. As of April 2007 there we
re an estimated 20
million unique web domains actively using PHP to generate and deliver content. While it is hard
to conceptualize 20 million web servers using PHP, it is not hard to inf
er from this number that
PHP has taken the web design and development community by storm since humble beginnings
in 1995.

The purpose of this book is bring the power and ease of use of PHP to anyone with a desire to
learn PHP, and in doing so, join the te
ns of thousands of web developers who have already
discovered the flexibility and productivity that comes with using PHP.

The book is intended to cover all aspects of PHP. It begins by covering the history of PHP before
providing a high level overview of
how PHP works and why it is so useful to web developers. It
then moves on to cover each area of PHP in detail, from the basics of the scripting language
through to object oriented programming, file and file

system handling and MySQL and SQLite
database acc
ess. In addition, chapters are also provided covering the creation and handling of
HTML based forms and maintaining state using cookies and PHP sessions. All topics are
accompanied by extensive real world examples intended to bring theory to life.

1.1

Intende
d Audience

It is anticipated that the typical reader already has some web based experience at least in terms
of understanding the concepts of a web server and creating HTML based content. While prior
programming and scripting experience will be benefici
al to the reader, this book is designed
such that even the non
-
programmer can quickly get up to speed with PHP.



PHP Essentials

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© 2009 Techotopia.com

Chapter 2.

The History of PHP

Every once in a while a person faces a particular problem or requirement to which there
appears to be no existing solution. Faced with this problem the person decides to create a
solution to provide the needed functionality.

Having developed the solution
to their problem it then occurs to them that others may need to
solve the same problem, and they decide to make their solution freely available to others who,
in turn, can use and improve on it. Within a short period of time many people adopt the
technolog
y and work on it, adding new features they feel will be useful. Th
e

solution soon
grows beyond expectations in terms of features and is adopted by more people than the
original creator could ever have imagined.

The history of PHP is just such a story.

2.1

Th
e Creation of PHP

The first version of what came to be known as PHP was created in 1995 by a man named
Rasmus Lerdof. Rasmus, now an engineer at Yahoo!, needed something to make it easier to
create content on his web site, something that would work well w
ith HTML, yet give him power
and flexibility beyond what HTML could offer him. Essentially, what he needed was an easy way
to write scripts that would run on his web server both to create content, and handle data being
passed back to the server from the we
b browser. Using the Perl language, he created some
technology that gave him what he needed and decided to call this technology "Personal Home
Page/Forms Interpreter". The technology provided a convenient way to process web forms and
create content.

The n
ame "Personal Home Page/Forms Interpreter" was later shortened to PHP/FI and
eventually renamed to represent "PHP: Hypertext Preprocessor". The name is said to be
recursive because the full name also includes the acronym "PHP"
-

an odd geeky joke that is
c
ommon in technology circles when people have trouble naming things. GNU is another
recursive name that represents "GNU's Not Unix".

PHP/FI version 1.0 was never really used outside of Rasmus' own web site. With the
introduction of PHP/FI 2.0 this began to

change. When PHP 3 was released in 1997, adoption of
PHP exploded beyond all belief.

2.2

PHP 3 Hits the Big Time

By the time 1997 arrived the number of web sites on the internet was growing exponentially
and most of these web sites were being implemented
using the Apache web server. It was
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© 2009 Techotopia.com

around this time that Andy Gutmans and Zeev Suraski launched the PHP 3 project, a project
designed to take PHP to the next level. One of the key achievements of the PHP 3 project was
to implement PHP as a robust Apache M
odule.

PHP 3 was implemented using a modular approach that made it easy for others to extend
functionality, and also introduced the first elements of object
-
orientation that would continue
to evolve through subsequent releases.

The combination of PHP 3 a
nd Apache quickly lead to the widespread adoption of PHP, and it is
commonly estimated that, at its peak adoption level, PHP3 was used to power over 10% of all
web sites on the internet.

2.3

PHP 4
-

Optimization, Scalabil
i
ty and More

With PHP 4 Andi Gutmans
and Zeev Suraski once again re
-
architected PHP from the ground up.
PHP 4 was built upon a piece of technology called the Zend Engine. The move to the Zend
Engine brought about a number of key improvements in PHP:



Support for other web servers (Microsoft's

Internet Information Server (IIS) being of
particular significance).



Improved memory handling to avoid memory leaks (one of the most difficult types of
problems to isolate in a program).



Improved efficiency and performance to support large scale, comple
x, mission critical
enterprise application development using PHP.

In addition PHP 4 also built on the earlier Object Oriented Programming features of PHP 3 with
the introduction of classes.

2.4

PHP 5
-

Object Orientation, Error Handling and XML

The main,
though far from only, feature of PHP 5 is the improved support for Object Oriented
Programming (OOP). In addition, PHP 5 introduced som
e features common in other lang
u
a
ges
such as Java like try/catch error and exception handling.

PHP 5 also introduced new

extensions aimed at easing the storage and manipulation of data.
Significant new features include SimpleXML for handling XML documents, and SQLite, an
embedded basic and easy to use database interface.

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© 2009 Techotopia.com

2.5

How
Popular

is PHP?

A quick review of some statisti
cs gives a very clear indication of the phenomenal
ly

widespread
use of PHP. A company called Netcraft specializes in recording data about the types of web
servers and web server modules that are used on the internet. A
s of April 2007 Netcraft
reported that

PHP wa
s used on over 20,000,000 distinct web domains.

A web survey by SecuritySpace also lists PHP as the most widely deployed Apache module. It is
safe to say that PHP has taken the internet by storm.

As if that wasn't enough one of the world

s most po
pular web sites, Wikipedia, is build primarily
using PHP.


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Chapter 3.

An Overvie
w

of PHP

Having covered
the h
istory of PHP

in the previous chapter it is now time to provide some detail
as to what PHP actually is. In this chapter we will take a high level look at PHP

and provide a
basic understanding of what it is, what is does and how it does it.

3.1

What Exactly is PHP?

PHP is an intuitive, server side scripting language
. Like any other scripting lang
u
a
ge it allows
devel
o
pers to build logic into the creation of web pa
ge content and handle data returned from
a web browser. PHP also contains a number of extensions that make it easy to interact with
databases, extracting data to be displayed on a web page and storing information entered by a
web site visitor back into the

database.

PHP consists of a scripting language and an interpreter. Like other scripting languages, PHP
enables web developers to define the behavior and logic they need in a web page. These scripts
are embedded into the HTML documents that are served by
the web server. The interpreter
takes the form of a module that integrates into the web server, converting the scripts into
commands the computer then executes to achieve the results defined in the script by the web
developer.

3.2

How Does PHP Work?

To develop an understanding of how PHP works it is helpful to first explore what happens when
a web page is served to a user's browser.

When a user visits a web site or clicks on a link on a page the browser sends a request to the
web server hosting the s
ite asking for a cop
y of the web page. The web serv
er receives the
request, finds the corresponding web page file on the file system and sends it back, over the
internet, to the user's browser.

Typically the web server doesn't pay any attention to the con
tent of the file it has just
transmitted to the web browser. As far as the web server is concerned the web browser
understands the content of the web page file and knows how to interpret and render it so that
it appears as the web designer intended.

Now l
et's consider what kind of web page content a web browser understands. These days a
web page is likely to consist of HTML, XHTML and JavaScript. The web browser contains code
that tells it what to do with these types of content. For example, it understands

the structure
HTML

in terms of rendering the page

and it has a JavaScript interpreter built in that knows how
to execute the instructions in a JavaScript script. A web browser, however, knows absolutely
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© 2009 Techotopia.com

nothing about
any PHP script that may be embed
ded in

an HTML do
cument. If a browser was
serv
ed

a web page containing PHP it would not know how to interpret that code.

Given that a web browser knows nothing about PHP in a web page, then clearly something has
to be done with any PHP script in the page before

it reaches the browser. This is where the PHP
pre
-
processing module comes in. The PHP module is, as mentioned previously, integrated into
the web server. The module tells the web server that when a page is to be served which
contains PHP script (identifie
d by special markers) that it is to pass that script to the PHP pre
-
processing module and wait for the PHP module to send it some content to replace that script
fragment. The PHP processing module understands PHP, executes the PHP script written by the
web

developer and, based on the script instructions, creates output that the browser will
understand. The web server substitutes the content provided by the PHP pre
-
processor m
o
dule
in place of the PHP script in the web page and sends it to the browser where
it is rendered for
the user to view.

To help understand this concept let's take a quick look at a before and after scenario. The
following HTML contains some PHP script that is designed to output an HTML paragraph tag:

<html>

<head>

<title>A PHP Example<
/title>

</head>

<body>

<?php


echo '<p>This line of HTML was generated by a PHP script embedded into
an HTML document</p>';

?>

</body>

</html>

The above example looks very much like standard HTML until you reach the part surrounded by
<?php

and
?>
. These are markers that designate where the embedded PHP script begins and
ends. When the web server finds this it sends it to the PHP module. The PHP module interprets
it, converts it to HTML and sends it back to the web server. The web server, in turn,
sends the
following to the browser:

<html>

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© 2009 Techotopia.com

<head>

<title>A PHP Example</title>

</head>

<body>


<p>This line of HTML was generated by a PHP script embedded into an HTML
document</p>

</body>

</html>

Once loaded into the browser,

it is rendered just like any

other web page. The fact that the web
page originally contained PHP is completely transparent to the web browser.

The above example is certainly an oversimplification of the p
o
wer of PHP. Some may question
why one would use PHP to output some static text

that could have been achieved more easily
using an HTML tag. The fact is, however, HTML only makes sense if you know
beforehand

exactly what needs to be displayed in the web page. Imagine instead, that you are developing
an online banking application. One

of the pages you need to display must contain the
customer's bank account number combined with the current balance. Obviously this
information is going to be different for each customer. In this scenario you would develop an
HTML page that essentially ser
ves as a template for the page, and then embed PHP into the
page to extract the account and balance information from a database. Once processed by the
PHP module integrated into the web server, this customer specific content will then appear in
the HTML pa
ge in place of the PHP script when the page is loaded into the browser.

3.3

Why is PHP so Useful?

In terms of web page content we have two extremes. At one extreme we have HTML which is
completely static. There is very little that can be done with HTML to cr
eate dynamic content in
a web page. At the other extreme we have scripting languages like JavaScript. JavaScript
provides a powerful mechanism for creating interactive and dynamic web pages.

When talking about JavaScript it is important to understand that

it is, by design, a client side
scripting language. By this we mean that the script gets executed inside the user's browser and
not on the web server on which the web page originated. Whilst this is fine for many situations
it is often the case that by th
e time a script reaches the browser it is then either too late, or
inefficient, to do what is needed. A prime example of this involves displaying a web page which
contains some data from a database table. Since the database resides on a server (either the
PHP Essentials

17

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same physical server which runs the web server or on the same network as the web server
connected by a high speed
fiber

network connection) it makes sense for any script that needs
to extract data from the database to be executed on the server, rather than

waiting until it
reaches the browser. It is for this kind of task that PHP is perfectly suited. It is also fast and
efficient (because the script is executed on the server it gets to take advantage of mu
lt
i
-
processing, large scale memory and other such en
terprise level hardware features.

In addition to the advantages of being a server side scripting language PHP is easy to learn and
use. The fact that PHP works
seamlessly

with HTML makes it accessible to a broad
community

of web designers.

Perhaps one of

the most significant advantages of PHP to some is the ease with which it
interacts with the MySQL database to retrieve and store data.

3.4

Summary

In summary, PHP has many advantages, and those listed here are just some of the reasons for
the success of PHP
. Many people will offer their own reasons for using PHP
-

and this fact alone
is testament to the power and flexibility of PHP.

Now that we know a little about
the h
istory of PHP

and have an overview of how it works we
can start looking at how to develop

PHP based web sites, beginning with
creating a simple PHP
s
cript
.