home | O'Reilly's CD bookshelfs | FreeBSD | Linux | Cisco | Cisco Exam    

Programming PHPProgramming PHPSearch this book

2.7. Embedding PHP in Web Pages

Although it is possible to write and run standalone PHP programs, most PHP code is embedded in HTML or XML files. This is, after all, why it was created in the first place. Processing such documents involves replacing each chunk of PHP source code with the output it produces when executed.

Because a single file contains PHP and non-PHP source code, we need a way to identify the regions of PHP code to be executed. PHP provides four different ways to do this.

As you'll see, the first, and preferred, method looks like XML. The second method looks like SGML. The third method is based on ASP tags. The fourth method uses the standard HTML <script> tag; this makes it easy to edit pages with enabled PHP using a regular HTML editor.

2.7.1. XML Style

Because of the advent of the eXtensible Markup Language (XML) and the migration of HTML to an XML language (XHTML), the currently preferred technique for embedding PHP uses XML-compliant tags to denote PHP instructions.

Coming up with tags to demark PHP commands in XML was easy, because XML allows the definition of new tags. To use this style, surround your PHP code with <?php and ?>. Everything between these markers is interpreted as PHP, and everything outside the markers is not. Although it is not necessary to include spaces between the markers and the enclosed text, doing so improves readability. For example, to get PHP to print "Hello, world", you can insert the following line in a web page:

<?php echo "Hello, world"; ?>

The trailing semicolon on the statement is optional, because the end of the block also forces the end of the expression. Embedded in a complete HTML file, this looks like:

<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<head>
  <title>This is my first PHP program!</title>
</head>
<body>
<p>
  Look, ma! It's my first PHP program:<br />
  <?php echo "Hello, world"; ?><br />
  How cool is that?
</p>
</body>
</html>

Of course, this isn't very exciting—we could have done it without PHP. The real value of PHP comes when we put dynamic information from sources such as databases and form values into the web page. That's for a later chapter, though. Let's get back to our "Hello, world" example. When a user visits this page and views its source, it looks like this:

<!doctype html public "-//w3c//dtd html 4.0 transitional//en">
<html>
<head>
  <title>This is my first PHP program!</title>
</head>
<body>
<p>
  Look, ma! It's my first PHP program:<br />
  Hello, world!<br />
  How cool is that?
</p>
</body>
</html>

Notice that there's no trace of the PHP source code from the original file. The user sees only its output.

Also notice that we switched between PHP and non-PHP, all in the space of a single line. PHP instructions can be put anywhere in a file, even within valid HTML tags. For example:

<input type="text" name="first_name"
       value="<?php echo "Rasmus"; ?>" />

When PHP is done with this text, it will read:

<input type="text" name="first_name"
       value="Rasmus" />

The PHP code within the opening and closing markers does not have to be on the same line. If the closing marker of a PHP instruction is the last thing on a line, the line break following the closing tag is removed as well. Thus, we can replace the PHP instructions in the "Hello, world" example with:

<?php
 echo "Hello, world"; ?>
<br />

with no change in the resulting HTML.



Library Navigation Links

Copyright © 2003 O'Reilly & Associates. All rights reserved.











??????????????@Mail.ru