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<?xml version="1.0" encoding="iso-8859-1"?>
<!-- $Revision: 1.42 $ -->
<chapter id="introduction">
<title>Introduction</title>
<sect1 id="intro-whatis">
<title>What is PHP?</title>
<para>
<acronym>PHP</acronym> (recursive acronym for "PHP: Hypertext
Preprocessor") is a widely-used Open Source general-purpose
scripting language that is especially suited for Web
development and can be embedded into HTML.
</para>
<para>
Simple answer, but what does that mean? An example:
</para>
<para>
<example>
<title>An introductory example</title>
<programlisting role="php">
<![CDATA[
<html>
<head>
<title>Example</title>
</head>
<body>
<?php
echo "Hi, I'm a PHP script!";
?>
</body>
</html>
]]>
</programlisting>
</example>
</para>
<para>
Notice how this is different from a script written in other
languages like Perl or C -- instead of writing a program with lots
of commands to output HTML, you write an HTML script with some
embedded code to do something (in this case, output some
text). The PHP code is enclosed in special <link
linkend="language.basic-syntax.phpmode">start and end tags</link>
that allow you to jump into and out of "PHP mode".
</para>
<para>
What distinguishes PHP from something like client-side JavaScript
is that the code is executed on the server. If you were to have a
script similar to the above on your server, the client would receive
the results of running that script, with no way of determining what
the underlying code may be. You can even configure your web server
to process all your HTML files with PHP, and then there's really no
way that users can tell what you have up your sleeve.
</para>
<para>
The best things in using PHP are that it is extremely simple
for a newcomer, but offers many advanced features for
a professional programmer. Don't be afraid reading the long
list of PHP's features. You can jump in, in a short time, and
start writing simple scripts in a few hours.
</para>
<para>
Although PHP's development is focused on server-side scripting,
you can do much more with it. Read on, and see more in the
<link linkend="intro-whatcando">What can PHP do?</link> section,
or go right to the <link linkend="tutorial">introductory
tutorial</link> if you are only interested in web programming.
</para>
</sect1>
<sect1 id="intro-whatcando">
<title>What can PHP do?</title>
<para>
Anything. PHP is mainly focused on server-side scripting,
so you can do anything any other CGI program can do, such
as collect form data, generate dynamic page content, or
send and receive cookies. But PHP can do much more.
</para>
<para>
There are three main areas where PHP scripts are used.
<itemizedlist>
<listitem>
<simpara>
Server-side scripting. This is the most traditional
and main target field for PHP. You need three things
to make this work. The PHP parser (CGI or server
module), a webserver and a web browser. You need to
run the webserver, with a connected PHP installation.
You can access the PHP program output with a web browser,
viewing the PHP page through the server. All these can
run on your home machine if you are just experimenting
with PHP programming. See the
<link linkend="install">installation instructions</link>
section for more information.
</simpara>
</listitem>
<listitem>
<simpara>
Command line scripting. You can make a PHP script
to run it without any server or browser.
You only need the PHP parser to use it this way.
This type of usage is ideal for scripts regularly
executed using cron (on *nix or Linux) or Task Scheduler (on
Windows). These scripts can also be used for simple text
processing tasks. See the section about
<link linkend="features.commandline">Command line usage of PHP</link>
for more information.
</simpara>
</listitem>
<listitem>
<simpara>
Writing desktop applications. PHP is probably
not the very best language to create a desktop
application with a graphical user interface, but if
you know PHP very well, and would like to use some
advanced PHP features in your client-side applications
you can also use PHP-GTK to write such programs. You also
have the ability to write cross-platform applications this
way. PHP-GTK is an extension to PHP, not available in
the main distribution. If you are interested
in PHP-GTK, visit <ulink url="&url.php.gtk;">its
own website</ulink>.
</simpara>
</listitem>
</itemizedlist>
</para>
<para>
PHP can be used on all major operating systems, including
Linux, many Unix variants (including HP-UX, Solaris and OpenBSD),
Microsoft Windows, Mac OS X, RISC OS, and probably others.
PHP has also support for most of the web servers today. This
includes Apache, Microsoft Internet Information Server,
Personal Web Server, Netscape and iPlanet servers, Oreilly
Website Pro server, Caudium, Xitami, OmniHTTPd, and many
others. For the majority of the servers PHP has a module,
for the others supporting the CGI standard, PHP can work
as a CGI processor.
</para>
<para>
So with PHP, you have the freedom of choosing an operating
system and a web server. Furthermore, you also have the choice
of using procedural programming or object oriented
programming, or a mixture of them. Although not every
standard OOP feature is implemented in PHP 4,
many code libraries and large applications (including
the PEAR library) are written only using OOP code. PHP 5 fixes the
OOP related weaknesses of PHP 4, and introduces a complete object
model.
</para>
<para>
With PHP you are not limited to output HTML. PHP's abilities
includes outputting images, PDF files and even Flash movies
(using libswf and Ming) generated on the fly. You can also
output easily any text, such as XHTML and any other XML file.
PHP can autogenerate these files, and save them in the file
system, instead of printing it out, forming a server-side
cache for your dynamic content.
</para>
<para>
One of the strongest and most significant features in PHP is its
support for a wide range of databases. Writing a database-enabled
web page is incredibly simple. The following databases are currently
supported:
<blockquote>
<simplelist columns="3">
<member>Adabas D</member>
<member>dBase</member>
<member>Empress</member>
<member>FilePro (read-only)</member>
<member>Hyperwave</member>
<member>IBM DB2</member>
<member>Informix</member>
<member>Ingres</member>
<member>InterBase</member>
<member>FrontBase</member>
<member>mSQL</member>
<member>Direct MS-SQL</member>
<member>MySQL</member>
<member>ODBC</member>
<member>Oracle (OCI7 and OCI8)</member>
<member>Ovrimos</member>
<member>PostgreSQL</member>
<member>SQLite</member>
<member>Solid</member>
<member>Sybase</member>
<member>Velocis</member>
<member>Unix dbm</member>
</simplelist>
</blockquote>
We also have a database abstraction extension (named PDO) allowing you
to transparently use any database supported by that extension.
Additionally PHP supports ODBC, the Open Database Connection
standard, so you can connect to any other database supporting
this world standard.
</para>
<para>
PHP also has support for talking to other services using protocols
such as LDAP, IMAP, SNMP, NNTP, POP3, HTTP, COM (on Windows) and
countless others. You can also open raw network sockets and
interact using any other protocol. PHP has support for the WDDX
complex data exchange between virtually all Web programming
languages. Talking about interconnection, PHP has support for
instantiation of Java objects and using them transparently
as PHP objects. You can also use our CORBA extension to
access remote objects.
</para>
<para>
PHP has extremely useful text processing features, from the
POSIX Extended or Perl regular expressions to parsing XML
documents. For parsing and accessing XML documents, PHP 4
supports the SAX and DOM standards, and you can also use the
XSLT extension to transform XML documents. PHP 5 standardizes
all the XML extensions on the solid base of libxml2 and extends
the feature set adding SimpleXML and XMLReader support.
</para>
<para>
At last but not least, we have many other interesting
extensions, the mnoGoSearch search engine functions,
the IRC Gateway functions, many compression utilities
(gzip, bz2, zip), calendar conversion, translation...
</para>
<para>
As you can see this page is not enough to list all
the features and benefits PHP can offer. Read on in
the sections about <link linkend="install">installing
PHP</link>, and see the <link linkend="funcref">function
reference</link> part for explanation of the extensions
mentioned here.
</para>
</sect1>
</chapter>
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