php-doc-en/chapters/intro.sgml

 <chapter id="introduction">
  <title>Introduction</title>
  <simpara></simpara>

  <sect1 id="intro-whatis">
   <title>What is PHP?</title>
   <simpara>
    PHP is a server-side HTML-embedded scripting language.

   <para>
    Simple answer, but what does that mean? An example:
   <example>
    <title>An introductory example</title>
    <programlisting>
&lt;html>&lt;head>&lt;title>Example&lt;/title>
&lt;body>
&lt;?php echo "Hi, I'm a PHP script!"; ?>
&lt;/body>&lt;/html>
    </programlisting>
   </example>

   <para>
    Notice how this is different from a CGI 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 a some
    embedded code to do something (in this case, output some text). The
    PHP code is enclosed in special start and end tags that allow you
    to jump into and out of "PHP mode".

   <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.

  <sect1 id="intro-whatcando">
   <title>What can PHP do?</title>

   <para>
    At the most basic level, PHP can do anything any other CGI
    program can do, such as collect form data, generate dynamic
    page content, or send and receive cookies.

   <para>
    Perhaps the strongest and most significant feature 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</member>
      <member>Informix</member>
      <member>InterBase</member>
      <member>mSQL</member>
      <member>MySQL</member>
      <member>Oracle</member>
      <member>PostgreSQL</member>
      <member>Solid</member>
      <member>Sybase</member>
      <member>Velocis</member>
      <member>Unix dbm</member>
     </simplelist>
    </blockquote>

   <para>
    PHP also has support for talking to other services using protocols
    such as IMAP, SNMP, NNTP, POP3, or even HTTP. You can even open raw
    network sockets and interact using other protocols.

  <sect1 id="intro-history">
   <title>A Brief History of PHP</title>
   <simpara>
    PHP was conceived sometime in the fall of 1994 by Rasmus Lerdorf.
    Early non-released versions were used on his home page to keep track
    of who was looking at his online resume.  The first version used
    by others was available sometime in early 1995 and was known as
    the Personal Home Page Tools.  It consisted of a very simplistic
    parser engine that only understood a few special macros and a
    number of utilities that were in common use on home pages back then.
    A guestbook, a counter and some other stuff.  The parser was rewritten
    in mid-1995 and named PHP/FI Version 2.  The FI came from another package
    Rasmus had written which interpreted html form data.  He combined
    the Personal Home Page tools scripts with the Form Interpreter and
    added mSQL support and PHP/FI was born.  PHP/FI grew at an amazing
    pace and people started contributing code to it.

   <simpara>
    It is hard to give any hard statistics, but it is estimated that
    by late 1996 PHP/FI was in use on at least 15,000 web sites around
    the world.  By mid-1997 this number had grown to over 50,000.
    Mid-1997 also saw a change in the development of PHP.  It changed
    from being Rasmus' own pet project that a handful of people had
    contributed to, to being a much more organized team effort. The
    parser was rewritten from scratch by Zeev Suraski and Andi Gutmans
    and this new parser formed the basis for PHP Version 3.  A lot of
    the utility code from PHP/FI was ported over to PHP3 and a lot of
    it was completely rewritten.

   <simpara>
    Today (mid-1999) either PHP/FI or PHP3 ships with a number of
    commercial products such as C2's StrongHold web server and RedHat
    Linux and a conservative estimate based on an extrapolation from
    numbers provided by NetCraft would be that PHP is in use on over
    150,000 sites around the world.  To put that in perspective, that
    is more sites than run Netscape's flagship Enterprise server on
    the Internet.

   <simpara>
    Also as of this writing, work is underway on the next generation of
    PHP that will utilize the powerful Zend scripting engine to deliver
    higher performance, and will also support running under webservers
    other than Apache as a native server module.

 </chapter>

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