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429 lines
15 KiB
XML
429 lines
15 KiB
XML
<?xml version="1.0" encoding="iso-8859-1"?>
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<!-- $Revision: 1.5 $ -->
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<chapter id="tutorial">
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<title>A simple tutorial</title>
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<para>
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Here we would like to show the very basics of PHP in a short simple
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tutorial. This text only deals with dynamic webpage creation with
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PHP, though PHP is not only capable of creating webpages. See
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the section titled <link linkend="intro-whatcando">What can PHP
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do</link> for more information.
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</para>
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<para>
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PHP-enabled web pages are treated just like regular HTML pages and
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you can create and edit them the same way you normally create
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regular HTML pages.
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</para>
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<sect1 id="tutorial.requirements">
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<title>What do I need?</title>
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<para>
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In this tutorial we assume that your server has support for PHP
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activated and that all files ending in <filename>.php</filename>
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are handled by PHP. On most servers this is the default extension
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for PHP files, but ask your server administrator to be sure. If
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your server supports PHP then you don't need to do anything. Just
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create your <filename>.php</filename> files and put them in your
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web directory and the server will magically parse them for you.
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There is no need to compile anything nor do you need to install
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any extra tools. Think of these PHP-enabled files as simple HTML
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files with a whole new family of magical tags that let you do all
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sorts of things.
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</para>
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</sect1>
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<sect1 id="tutorial.firstpage">
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<title>Your first PHP-enabled page</title>
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<para>
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Create a file named <filename>hello.php</filename> under your
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webserver root directory with the following content:
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</para>
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<para>
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<example>
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<title>Our first PHP script: <filename>hello.php</filename></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>PHP Test</title>
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</head>
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<body>
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<?php echo "Hello World<p>"; ?>
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</body>
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</html>
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]]>
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</programlisting>
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<para>
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The output of this script will be:
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<screen role="html">
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<![CDATA[
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<html>
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<head>
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<title>PHP Test</title>
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</head>
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<body>
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Hello World<p>
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</body>
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</html>
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]]>
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</screen>
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</para>
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</example>
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</para>
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<para>
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Note that this is not like a CGI script. The file does not need to be
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executable or special in any way. Think of it as a normal HTML
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file which happens to have a set of special tags available to you
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that do a lot of interesting things.
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</para>
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<para>
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This program is extremely simple and you really didn't need to use
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PHP to create a page like this. All it does is display:
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<literal>Hello World</literal> using the PHP <function>echo</function>
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statement.
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</para>
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<para>
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If you tried this example and it didn't output anything, or it prompted
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for download, or you see the whole file as text, chances are that the
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server you are on does not have PHP enabled. Ask your administrator
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to enable it for you using the
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<link linkend="installation">Installation</link> chapter
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of the manual. If you want to develop PHP scripts locally, see
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the <ulink url="&url.php.downloads;">downloads</ulink> section.
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You can develop locally on any Operating system, be sure to
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install an appropriate web server too.
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</para>
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<para>
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The point of the example is to show the special PHP tag format.
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In this example we used <literal><?php</literal> to indicate the
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start of a PHP tag. Then we put the PHP statement and left PHP mode by
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adding the closing tag, <literal>?></literal>. You may jump in
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and out of PHP mode in an HTML file like this all you want.
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</para>
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</sect1>
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<sect1 id="tutorial.useful">
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<title>Something Useful</title>
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<para>
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Let's do something a bit more useful now. We are going to check
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what sort of browser the person viewing the page is using.
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In order to do that we check the user agent string that the browser
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sends as part of its HTTP request. This information is stored in a <link
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linkend="language.variables">variable</link>. Variables always start
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with a dollar-sign in PHP. The variable we are interested in right now
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is <varname>$_SERVER["HTTP_USER_AGENT"]</varname>.
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</para>
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<note>
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<title>PHP Autoglobals Note</title>
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<para>
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<link linkend="reserved.variables.server">$_SERVER</link> is a
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special reserved PHP variable that contains all web server information.
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It's known as an Autoglobal. See the related manual page on
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<link linkend="language.variables.superglobals">Autoglobals</link>
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(also known as Superglobals) for more information. These special
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variables were introduced in PHP 4.1.0. Before this time, we used
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the older <varname>$HTTP_*_VARS</varname> arrays instead,
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such as <varname>$HTTP_SERVER_VARS</varname>. Although deprecated,
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these older variables still exist.
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</para>
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</note>
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<para>
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To display this variable, we can simply do:
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</para>
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<para>
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<example>
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<title>Printing a variable (Array element)</title>
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<programlisting role="php">
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<![CDATA[
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<?php echo $_SERVER["HTTP_USER_AGENT"]; ?>
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]]>
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</programlisting>
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<para>
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A sample output of this script may be:
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<screen role="html">
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Mozilla/4.0 (compatible; MSIE 5.01; Windows NT 5.0)
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</screen>
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</para>
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</example>
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</para>
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<para>
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There are many <link linkend="language.types">types</link> of
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variables available in PHP. In the above example we printed
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an <link linkend="language.types.array">Array</link> element.
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Arrays can be very useful.
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</para>
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<para>
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<varname>$_SERVER</varname> is just one variable that's automatically
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made available to you by PHP. A list can be seen in the
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<link linkend="reserved.variables">Reserved Variables</link> section
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of the manual or you can get a complete list of them by creating
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a file that looks like this:
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</para>
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<para>
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<example>
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<title>Show all predefined variables with <function>phpinfo</function></title>
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<programlisting role="php">
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<![CDATA[
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<?php phpinfo(); ?>
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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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If you load up this file in your browser you will see a page
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full of information about PHP along with a list of all the
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variables available to you.
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</para>
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<para>
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You can put multiple PHP statements inside a PHP tag and create
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little blocks of code that do more than just a single echo.
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For example, if we wanted to check for Internet Explorer we
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could do something like this:
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</para>
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<para>
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<example>
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<title>Example using <link linkend="control-structures">control
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structures</link> and <link linkend="functions">functions</link></title>
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<programlisting role="php">
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<![CDATA[
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<?php
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if (strstr($_SERVER["HTTP_USER_AGENT"], "MSIE")) {
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echo "You are using Internet Explorer<br />";
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}
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?>
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]]>
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</programlisting>
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<para>
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A sample output of this script may be:
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<screen role="html">
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<![CDATA[
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You are using Internet Explorer<br />
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]]>
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</screen>
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</para>
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</example>
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</para>
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<para>
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Here we introduce a couple of new concepts. We have an
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<link linkend="control-structures.if">if</link> statement.
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If you are familiar with the basic syntax used by the C
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language this should look logical to you. If you don't know enough
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C or some other language where the syntax used above is used, you
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should probably pick up any introductory PHP book and read the first
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couple of chapters, or read the <link linkend="langref">Language
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Reference</link> part of the manual. You can find a list of PHP books
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at <ulink url="&url.php.books;">&url.php.books;</ulink>.
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</para>
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<para>
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The second concept we introduced was the <function>strstr</function>
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function call. <function>strstr</function> is a function built into
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PHP which searches a string for another string. In this case we are
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looking for <literal>"MSIE"</literal> inside
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<varname>$_SERVER["HTTP_USER_AGENT"]</varname>. If the string is found,
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the function returns &true; and if it isn't, it returns &false;. If
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it returns &true;, the <link linkend="control-structures.if">if</link>
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statement evaluates to &true; and the code within its {braces} is
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executed. Otherwise, it's not. Feel free to create similar examples,
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with <link linkend="control-structures.if">if</link>,
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<link linkend="control-structures.else">else</link>, and other
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functions such as <function>strtoupper</function> and
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<function>strlen</function>. Each related manual page contains examples
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too.
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</para>
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<para>
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We can take this a step further and show how you can jump in and out
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of PHP mode even in the middle of a PHP block:
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</para>
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<para>
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<example>
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<title>Mixing both HTML and PHP modes</title>
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<programlisting role="php">
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<![CDATA[
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<?php
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if (strstr($_SERVER["HTTP_USER_AGENT"], "MSIE")) {
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?>
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<h3>strstr must have returned true</h3>
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<center><b>You are using Internet Explorer</b></center>
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<?php
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} else {
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?>
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<h3>strstr must have returned false</h3>
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<center><b>You are not using Internet Explorer</b></center>
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<?php
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}
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?>
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]]>
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</programlisting>
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<para>
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A sample output of this script may be:
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<screen role="html">
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<![CDATA[
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<h3>strstr must have returned true</h3>
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<center><b>You are using Internet Explorer</b></center>
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]]>
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</screen>
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</para>
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</example>
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</para>
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<para>
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Instead of using a PHP echo statement to output something, we jumped out of PHP
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mode and just sent straight HTML. The important and powerful point to note here
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is that the logical flow of the script remains intact. Only one of the HTML blocks
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will end up getting sent to the viewer depending on if
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<function>strstr</function> returned &true; or &false; In other words,
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if the string <literal>MSIE</literal> was found or not.
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</para>
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</sect1>
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<sect1 id="tutorial.forms">
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<title>Dealing with Forms</title>
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<para>
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One of the most powerful features of PHP is the way it handles HTML
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forms. The basic concept that is important to understand is that any
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form element in a form will automatically be available to your PHP
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scripts. Please read the manual section on
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<link linkend="language.variables.external">Variables from outside
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of PHP</link> for more information and examples on using forms
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with PHP. Here's an example HTML form:
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</para>
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<para>
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<example>
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<title>A simple HTML form</title>
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<programlisting role="html">
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<![CDATA[
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<form action="action.php" method="POST">
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Your name: <input type="text" name="name" />
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Your age: <input type="text" name="age" />
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<input type="submit">
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</form>
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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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There is nothing special about this form. It is a straight HTML form
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with no special tags of any kind. When the user fills in this form
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and hits the submit button, the <filename>action.php</filename> page
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is called. In this file you would have something like this:
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</para>
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<para>
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<example>
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<title>Printing data from our form</title>
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<programlisting role="php">
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<![CDATA[
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Hi <?php echo $_POST["name"]; ?>.
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You are <?php echo $_POST["age"]; ?> years old.
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]]>
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</programlisting>
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<para>
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A sample output of this script may be:
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<screen role="html">
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<![CDATA[
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Hi Joe.
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You are 22 years old.
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]]>
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</screen>
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</para>
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</example>
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</para>
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<para>
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It should be obvious what this does. There is nothing more to it.
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The <varname>$_POST["name"]</varname> and <varname>$_POST["age"]</varname>
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variables are automatically set for you by PHP. Earlier we
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used the <varname>$_SERVER</varname> autoglobal, now above we just
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introduced the <link linkend="reserved.variables.post">$_POST</link>
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autoglobal which contains all POST data. Notice how the
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<emphasis>method</emphasis> of our form is POST. If we used the
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method <emphasis>GET</emphasis> then our form information would live in
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the <link linkend="reserved.variables.get">$_GET</link> autoglobal instead.
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You may also use the <link linkend="reserved.variables.request">$_REQUEST</link>
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autoglobal if you don't care the source of your request data. It
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contains a mix of GET, POST, COOKIE and FILE data. See also the
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<function>import_request_variables</function> function.
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</para>
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</sect1>
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<sect1 id="tutorial.oldcode">
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<title>Using old code with new versions of PHP</title>
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<para>
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Now that PHP has grown to be a popular scripting language, there are
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more resources out there that have listings of code you can reuse
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in your own scripts. For the most part the developers of the PHP
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language have tried to be backwards compatible, so a script written
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for an older version should run (ideally) without changes in a newer
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version of PHP, in practice some changes will usually be needed.
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</para>
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<para>
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Two of the most important recent changes that affect old code are:
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<itemizedlist>
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<listitem>
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<simpara>
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The deprecation of the old <varname>$HTTP_*_VARS</varname> arrays
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(which need to be indicated as global when used inside a function or
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method). The following
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<link linkend="language.variables.superglobals">autoglobal arrays</link>
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were introduced in PHP 4.1.0. They are:
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<varname>$_GET</varname>, <varname>$_POST</varname>,
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<varname>$_COOKIE</varname>, <varname>$_SERVER</varname>,
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<varname>$_ENV</varname>, <varname>$_REQUEST</varname>, and
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<varname>$_SESSION</varname>. The older <varname>$HTTP_*_VARS</varname>
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arrays, such as $HTTP_POST_VARS, still exist and have since PHP 3.
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</simpara>
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</listitem>
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<listitem>
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<simpara>
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External variables are no longer registered in the global scope by
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default. In other words, as of PHP
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<ulink url="&url.php.release4.2.0;">4.2.0</ulink> the PHP directive
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<link linkend="ini.register-globals">register_globals</link> is
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<emphasis>off</emphasis> by default in &php.ini;. The preferred
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method of accessing these values is via the autoglobal arrays mentioned
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above. Older scripts, books, and tutorials may rely on this
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directive being on. If on, for example, one could use
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<varname>$id</varname> from the URL
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<literal>http://www.example.com/foo.php?id=42</literal>. Whether on
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or off, <varname>$_GET['id']</varname> is available.
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</simpara>
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</listitem>
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</itemizedlist>
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For more details on these changes, see the section on
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<link linkend="language.variables.predefined">predefined variables</link>
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and links therein.
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</para>
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</sect1>
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<sect1 id="tutorial.whatsnext">
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<title>What's next?</title>
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<para>
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With what you know now you should be able to understand most of
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the manual and also the various example scripts available in the
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example archives. You can also find other examples on the php.net
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websites in the links section:
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<ulink url="&url.php.links;">&url.php.links;</ulink>.
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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-omittag:t
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sgml-shorttag:t
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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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