intro.xml

<?xml version="1.0" encoding="utf-8"?>
<!-- $Revision$ -->
 <chapter xml:id="introduction" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
  <info><title>Introduction</title></info>

  <section xml:id="intro-whatis">
   <info><title>What is PHP?</title></info>
   <para>
    <acronym>PHP</acronym> (recursive acronym for <literal>PHP: Hypertext
    Preprocessor</literal>) 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>
    Nice, but what does that mean? An example:
   </para>
   <para>
    <example>
     <info><title>An introductory example</title></info>
     <programlisting role="php">
<![CDATA[
<!DOCTYPE html>
<html>
    <head>
        <title>Example</title>
    </head>
    <body>

        <?php
            echo "Hi, I'm a PHP script!";
        ?>

    </body>
</html>
]]>
     </programlisting>
    </example>
   </para>
   <para>
    Instead of lots of commands to output HTML (as seen in C or Perl),
    PHP pages contain HTML with embedded code that does
    "something" (in this case, output "Hi, I'm a PHP script!").
    The PHP code is enclosed in special <link
    linkend="language.basic-syntax.phpmode">start and end processing
    instructions <code>&lt;?php</code> and <code>?&gt;</code></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, generating HTML which
    is then sent to the client. The client would receive
    the results of running that script, but would not know
    what the underlying code was. 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>
  </section>

  <section xml:id="intro-whatcando">
   <info><title>What can PHP do?</title></info>
   <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 web server and a web browser. You need to
       run the web server, 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 <link xlink:href="&url.php.gtk;">its
       own website</link>.
      </simpara>
     </listitem>
    </itemizedlist>
   </para>
   <para>
    PHP can be <link linkend="install">used</link> on all major operating systems, including
    Linux, many Unix variants (including HP-UX, Solaris and OpenBSD),
    Microsoft Windows, macOS, RISC OS, and probably others.
    PHP also has support for most of the web servers today. This
    includes Apache, IIS, and many others. And this includes any
    web server that can utilize the FastCGI PHP binary, like lighttpd
    and nginx. PHP works as either a module, or 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 (OOP), or a mixture of them both.
   </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 <link linkend="refs.database">wide range of databases</link>.
    Writing a database-enabled web page is incredibly simple using one of
    the database specific extensions (e.g., for <link linkend="book.mysqli">mysql</link>),
    or using an abstraction layer like <link linkend="book.pdo">PDO</link>, or connect
    to any database supporting the Open Database Connection standard via the
    <link linkend="book.uodbc">ODBC</link> extension. Other databases may utilize
    <link linkend="book.curl">cURL</link> or <link linkend="book.sockets">sockets</link>,
    like CouchDB.
   </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.
   </para>
   <para>
    PHP has useful <link linkend="refs.basic.text">text processing</link> features,
    which includes the Perl compatible regular expressions (<link linkend="book.pcre">PCRE</link>),
    and many extensions and tools to <link linkend="refs.xml">parse and access XML documents</link>.
    PHP standardizes all of the XML extensions on the solid base of <link linkend="book.libxml">libxml2</link>,
    and extends the feature set adding <link linkend="book.simplexml">SimpleXML</link>,
    <link linkend="book.xmlreader">XMLReader</link> and <link linkend="book.xmlwriter">XMLWriter</link> support.
   </para>
   <para>
    And many other interesting extensions exist, which are categorized both
    <link linkend="extensions">alphabetically</link> and by <link linkend="funcref">category</link>.
    And there are additional PECL extensions that may or may not be documented
    within the PHP manual itself, like <link xlink:href="&url.xdebug;">XDebug</link>.
   </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>
  </section>

 </chapter>

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	<?xml version="1.0" encoding="utf-8"?>
	<!-- $Revision$ -->
	<chapter xml:id="introduction" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
	<info><title>Introduction</title></info>

	<section xml:id="intro-whatis">
	<info><title>What is PHP?</title></info>
	<para>
	<acronym>PHP</acronym> (recursive acronym for <literal>PHP: Hypertext
	Preprocessor</literal>) 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>
	Nice, but what does that mean? An example:
	</para>
	<para>
	<example>
	<info><title>An introductory example</title></info>
	<programlisting role="php">
	<![CDATA[
	<!DOCTYPE html>
	<html>
	<head>
	<title>Example</title>
	</head>
	<body>

	<?php
	echo "Hi, I'm a PHP script!";
	?>

	</body>
	</html>
	]]>
	</programlisting>
	</example>
	</para>
	<para>
	Instead of lots of commands to output HTML (as seen in C or Perl),
	PHP pages contain HTML with embedded code that does
	"something" (in this case, output "Hi, I'm a PHP script!").
	The PHP code is enclosed in special <link
	linkend="language.basic-syntax.phpmode">start and end processing
	instructions <code><?php</code> and <code>?></code></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, generating HTML which
	is then sent to the client. The client would receive
	the results of running that script, but would not know
	what the underlying code was. 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>
	</section>

	<section xml:id="intro-whatcando">
	<info><title>What can PHP do?</title></info>
	<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 web server and a web browser. You need to
	run the web server, 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 <link xlink:href="&url.php.gtk;">its
	own website</link>.
	</simpara>
	</listitem>
	</itemizedlist>
	</para>
	<para>
	PHP can be <link linkend="install">used</link> on all major operating systems, including
	Linux, many Unix variants (including HP-UX, Solaris and OpenBSD),
	Microsoft Windows, macOS, RISC OS, and probably others.
	PHP also has support for most of the web servers today. This
	includes Apache, IIS, and many others. And this includes any
	web server that can utilize the FastCGI PHP binary, like lighttpd
	and nginx. PHP works as either a module, or 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 (OOP), or a mixture of them both.
	</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 <link linkend="refs.database">wide range of databases</link>.
	Writing a database-enabled web page is incredibly simple using one of
	the database specific extensions (e.g., for <link linkend="book.mysqli">mysql</link>),
	or using an abstraction layer like <link linkend="book.pdo">PDO</link>, or connect
	to any database supporting the Open Database Connection standard via the
	<link linkend="book.uodbc">ODBC</link> extension. Other databases may utilize
	<link linkend="book.curl">cURL</link> or <link linkend="book.sockets">sockets</link>,
	like CouchDB.
	</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.
	</para>
	<para>
	PHP has useful <link linkend="refs.basic.text">text processing</link> features,
	which includes the Perl compatible regular expressions (<link linkend="book.pcre">PCRE</link>),
	and many extensions and tools to <link linkend="refs.xml">parse and access XML documents</link>.
	PHP standardizes all of the XML extensions on the solid base of <link linkend="book.libxml">libxml2</link>,
	and extends the feature set adding <link linkend="book.simplexml">SimpleXML</link>,
	<link linkend="book.xmlreader">XMLReader</link> and <link linkend="book.xmlwriter">XMLWriter</link> support.
	</para>
	<para>
	And many other interesting extensions exist, which are categorized both
	<link linkend="extensions">alphabetically</link> and by <link linkend="funcref">category</link>.
	And there are additional PECL extensions that may or may not be documented
	within the PHP manual itself, like <link xlink:href="&url.xdebug;">XDebug</link>.
	</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>
	</section>

	</chapter>

	<!-- Keep this comment at the end of the file
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	sgml-omittag:t
	sgml-shorttag:t
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	End:
	vim600: syn=xml fen fdm=syntax fdl=2 si
	vim: et tw=78 syn=sgml
	vi: ts=1 sw=1
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