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<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.43 $ -->
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<chapter id="introduction">
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<title>Introduction</title>
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<sect1 id="intro-whatis">
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<title>What is PHP?</title>
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<para>
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<acronym>PHP</acronym> (recursive acronym for "PHP: Hypertext
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Preprocessor") is a widely-used Open Source general-purpose
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scripting language that is especially suited for Web
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development and can be embedded into HTML.
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</para>
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<para>
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Simple answer, but what does that mean? An example:
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</para>
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<para>
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<example>
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<title>An introductory example</title>
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<programlisting role="php">
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<![CDATA[
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<html>
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<head>
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<title>Example</title>
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</head>
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<body>
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<?php
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echo "Hi, I'm a PHP script!";
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?>
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</body>
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</html>
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]]>
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</programlisting>
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</example>
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</para>
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<para>
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Notice how this is different from a script written in other
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languages like Perl or C -- instead of writing a program with lots
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of commands to output HTML, you write an HTML script with some
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embedded code to do something (in this case, output some
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text). The PHP code is enclosed in special <link
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linkend="language.basic-syntax.phpmode">start and end tags</link>
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that allow you to jump into and out of "PHP mode".
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</para>
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<para>
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What distinguishes PHP from something like client-side JavaScript
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is that the code is executed on the server. If you were to have a
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script similar to the above on your server, the client would receive
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the results of running that script, with no way of determining what
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the underlying code may be. You can even configure your web server
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to process all your HTML files with PHP, and then there's really no
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way that users can tell what you have up your sleeve.
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</para>
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<para>
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The best things in using PHP are that it is extremely simple
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for a newcomer, but offers many advanced features for
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a professional programmer. Don't be afraid reading the long
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list of PHP's features. You can jump in, in a short time, and
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start writing simple scripts in a few hours.
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</para>
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<para>
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Although PHP's development is focused on server-side scripting,
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you can do much more with it. Read on, and see more in the
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<link linkend="intro-whatcando">What can PHP do?</link> section,
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or go right to the <link linkend="tutorial">introductory
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tutorial</link> if you are only interested in web programming.
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</para>
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</sect1>
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<sect1 id="intro-whatcando">
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<title>What can PHP do?</title>
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<para>
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Anything. PHP is mainly focused on server-side scripting,
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so you can do anything any other CGI program can do, such
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as collect form data, generate dynamic page content, or
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send and receive cookies. But PHP can do much more.
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</para>
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<para>
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There are three main areas where PHP scripts are used.
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<itemizedlist>
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<listitem>
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<simpara>
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Server-side scripting. This is the most traditional
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and main target field for PHP. You need three things
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to make this work. The PHP parser (CGI or server
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module), a web server and a web browser. You need to
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run the web server, with a connected PHP installation.
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You can access the PHP program output with a web browser,
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viewing the PHP page through the server. All these can
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run on your home machine if you are just experimenting
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with PHP programming. See the
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<link linkend="install">installation instructions</link>
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section for more information.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Command line scripting. You can make a PHP script
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to run it without any server or browser.
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You only need the PHP parser to use it this way.
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This type of usage is ideal for scripts regularly
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executed using cron (on *nix or Linux) or Task Scheduler (on
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Windows). These scripts can also be used for simple text
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processing tasks. See the section about
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<link linkend="features.commandline">Command line usage of PHP</link>
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for more information.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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Writing desktop applications. PHP is probably
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not the very best language to create a desktop
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application with a graphical user interface, but if
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you know PHP very well, and would like to use some
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advanced PHP features in your client-side applications
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you can also use PHP-GTK to write such programs. You also
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have the ability to write cross-platform applications this
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way. PHP-GTK is an extension to PHP, not available in
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the main distribution. If you are interested
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in PHP-GTK, visit <ulink url="&url.php.gtk;">its
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own website</ulink>.
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</simpara>
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</listitem>
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</itemizedlist>
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</para>
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<para>
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PHP can be used on all major operating systems, including
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Linux, many Unix variants (including HP-UX, Solaris and OpenBSD),
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Microsoft Windows, Mac OS X, RISC OS, and probably others.
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PHP has also support for most of the web servers today. This
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includes Apache, Microsoft Internet Information Server,
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Personal Web Server, Netscape and iPlanet servers, Oreilly
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Website Pro server, Caudium, Xitami, OmniHTTPd, and many
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others. For the majority of the servers PHP has a module,
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for the others supporting the CGI standard, PHP can work
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as a CGI processor.
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</para>
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<para>
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So with PHP, you have the freedom of choosing an operating
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system and a web server. Furthermore, you also have the choice
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of using procedural programming or object oriented
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programming, or a mixture of them. Although not every
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standard OOP feature is implemented in PHP 4,
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many code libraries and large applications (including
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the PEAR library) are written only using OOP code. PHP 5 fixes the
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OOP related weaknesses of PHP 4, and introduces a complete object
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model.
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</para>
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<para>
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With PHP you are not limited to output HTML. PHP's abilities
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includes outputting images, PDF files and even Flash movies
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(using libswf and Ming) generated on the fly. You can also
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output easily any text, such as XHTML and any other XML file.
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PHP can autogenerate these files, and save them in the file
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system, instead of printing it out, forming a server-side
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cache for your dynamic content.
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</para>
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<para>
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One of the strongest and most significant features in PHP is its
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support for a wide range of databases. Writing a database-enabled
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web page is incredibly simple. The following databases are currently
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supported:
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<blockquote>
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<simplelist columns="3">
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<member>Adabas D</member>
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<member>dBase</member>
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<member>Empress</member>
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<member>FilePro (read-only)</member>
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<member>Hyperwave</member>
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<member>IBM DB2</member>
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<member>Informix</member>
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<member>Ingres</member>
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<member>InterBase</member>
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<member>FrontBase</member>
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<member>mSQL</member>
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<member>Direct MS-SQL</member>
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<member>MySQL</member>
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<member>ODBC</member>
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<member>Oracle (OCI7 and OCI8)</member>
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<member>Ovrimos</member>
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<member>PostgreSQL</member>
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<member>SQLite</member>
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<member>Solid</member>
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<member>Sybase</member>
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<member>Velocis</member>
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<member>Unix dbm</member>
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</simplelist>
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</blockquote>
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We also have a database abstraction extension (named PDO) allowing you
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to transparently use any database supported by that extension.
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Additionally PHP supports ODBC, the Open Database Connection
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standard, so you can connect to any other database supporting
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this world standard.
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</para>
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<para>
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PHP also has support for talking to other services using protocols
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such as LDAP, IMAP, SNMP, NNTP, POP3, HTTP, COM (on Windows) and
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countless others. You can also open raw network sockets and
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interact using any other protocol. PHP has support for the WDDX
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complex data exchange between virtually all Web programming
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languages. Talking about interconnection, PHP has support for
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instantiation of Java objects and using them transparently
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as PHP objects. You can also use our CORBA extension to
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access remote objects.
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</para>
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<para>
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PHP has extremely useful text processing features, from the
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POSIX Extended or Perl regular expressions to parsing XML
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documents. For parsing and accessing XML documents, PHP 4
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supports the SAX and DOM standards, and you can also use the
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XSLT extension to transform XML documents. PHP 5 standardizes
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all the XML extensions on the solid base of libxml2 and extends
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the feature set adding SimpleXML and XMLReader support.
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</para>
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<para>
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At last but not least, we have many other interesting
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extensions, the mnoGoSearch search engine functions,
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the IRC Gateway functions, many compression utilities
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(gzip, bz2, zip), calendar conversion, translation...
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</para>
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<para>
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As you can see this page is not enough to list all
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the features and benefits PHP can offer. Read on in
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the sections about <link linkend="install">installing
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PHP</link>, and see the <link linkend="funcref">function
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reference</link> part for explanation of the extensions
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mentioned here.
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</para>
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</sect1>
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</chapter>
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<!-- Keep this comment at the end of the file
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Local variables:
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mode: sgml
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sgml-minimize-attributes:nil
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sgml-always-quote-attributes:t
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sgml-indent-step:1
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sgml-indent-data:t
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indent-tabs-mode:nil
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sgml-parent-document:nil
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sgml-default-dtd-file:"../../manual.ced"
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sgml-exposed-tags:nil
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sgml-local-catalogs:nil
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sgml-local-ecat-files:nil
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End:
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vim600: syn=xml fen fdm=syntax fdl=2 si
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vim: et tw=78 syn=sgml
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vi: ts=1 sw=1
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-->
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