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3. PHP Tutorial

In this tutorial we assume that your server has support for PHP activated and that all files ending in .php3 are handled by PHP.

Your first PHP-enabled page: Create a file named hello.php3 and in it put the following lines: 

      <html>< head>< title >PHP Test< /title >< /head >
      < body>
      <?php echo "Hello World<P>"; ?>
      < /body>< /html>

Note that this is not like a CGI script. Think of it as a normal HTML file which happens to have a set of special tags available to you.

If you tried this example and it didn't output anything, chances are that the server you are on does not have PHP enabled. Ask your administrator to enable it for you.

The point of the example is to show the special PHP tag format. In this example we used < ?php to indicate the start of a PHP tag. Then we put the PHP statement and left PHP mode by adding the closing tag, ? > . You may jump in and out of PHP mode in an HTML file like this all you want.

We are going to check what sort of browser the person viewing the page is using. In order to do that we check the user agent string that the browser sends as part of its request. This information is stored in a variable. Variables always start with a dollar-sign in PHP. The variable we are interested in is $HTTP_USER_AGENT. To display this variable we can simply do: 

      <?php echo $HTTP_USER_AGENT; ?>

For the browser that you are using right now to view this page, this displays:

Mozilla/4.0 (compatible; MSIE 4.01; Windows 98)

There are many other variables that are automatically set by your web server. You can get a complete list of them by creating a file that looks like this: 

      <?php phpinfo()?>

Then load up this file in your browser and you will see a page full of information about PHP along with a list of all the variables available to you.

You can put multiple PHP statements inside a PHP tag and create little blocks of code that do more than just a single echo. 

      <?php
      if(strstr($HTTP_USER_AGENT,"MSIE")) {
          echo "You are using Internet Explorer<br>";
      }
      ?>

We can take this a step further and show how you can jump in and out of PHP mode even in the middle of a PHP block: 

        <?php
        if(strstr($HTTP_USER_AGENT,"MSIE")) 
        {
                ?>
                < center>< b>You are using Internet Explorer< /b>< /center>
                <?
        } 
        else 
        {
                ?>
                < center>< b>You are not using Internet Explorer< /b>< /center>
                <?
        }
        ?>
Instead of using a PHP echo statement to output something, we jumped out of PHP mode and just sent straight HTML. The important and powerful point to note here is that the logical flow of the script remain intact. Only one of the HTML blocks will end up getting sent to the viewer. Running this script right now results in:

You are using Internet Explorer

Dealing with Forms

One of the most powerful features of PHP is the way it handles HTML forms. The basic concept that is important to understand is that any form element in a form will automatically result in a variable with the same name as the element being created on the target page. This probably sounds confusing, so here is a simple example. Assume you have a page with a form like this on it: 

      <form action="action.php3" method="POST">
      Your name: <input type=text name=name>
      You age: <input type=text name=age>
      <input type=submit>
      < /form>
There is nothing special about this form. It is a straight HTML form with no special tags of any kind. When the user fills in this form and hits the submit button, the action.php3 page is called. In this file you would have something like this: 
      Hi <?php echo $name?>.  You are <?php echo $age?> years old.
Surprise!! The $name and $age variables are automatically set for you by PHP !!
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