What is PHP?
PHP is a server-side scripting language for creating dynamic Web pages. You create pages with PHP and
HTML. When a visitor opens the page, the server processes the PHP commands and then sends the results
to the visitor's browser, just as with ASP or ColdFusion. Unlike ASP or ColdFusion, however, PHP is
Open Source and cross-platform. PHP runs on Windows NT and many Unix versions, and it can be built as
an Apache module and as a binary that can run as a CGI. When built as an Apache module, as on our
servers, PHP is especially lightweight and speedy. Without any process creation overhead, it can return
results quickly, but it doesn't require the tuning of mod_perl to keep your server's memory image
small.
In addition to manipulating the content of your pages, PHP can also send HTTP headers. You can set
cookies, manage authentication, and redirect users. It offers integration with various external
libraries that let you do everything from generating PDF documents to parsing XML.
PHP goes right into your Web pages, so there's no need for a special development environment or IDE.
You start a block of PHP code with <?php and end it with
?>. (You can also configure PHP to use ASP-style
<% %> tags or even <SCRIPT
LANGUAGE="php"></SCRIPT>.) The PHP engine processes everything between those tags.
PHP's language syntax is similar to C's and Perl's. You don't have to declare variables before you use
them, and it's easy to create arrays and hashes (associative arrays). PHP even has some rudimentary
object-oriented features, providing a helpful way to organize and encapsulate your code.
PHP files should have an identifying extension so the server will know to execute the
code - .phtml or .php
Check out our Sample Scripts and Sources
page for links to PHP tutorials, sites and sample PHP code.
Writing Dynamic Web Pages with PHP
Let's start with the simple Hello World example. Here's the code:
<html>
<head>
<title>Hello World</title>
</head>
<body>
<?php
echo "Hello World";
?>
</body>
</html>
This is a somewhat silly example, but it can be used to teach you a few things
anyway.
Most of the code is just plain HTML. Only the part between <?php and
?> is PHP-code. You use either <?php or just <? to start the
code and ?> to stop it again. The parser works within these two tags. Between the <?php
and ?> you put a number of statements, which all must be ended by a ;.
Between the two tags there is one statement, echo "Hello World";. This
statement just prints the string "Hello World" into the webpage, which is then sent to the
browser. After the parser has processed the page, the final output that is sent to the browser looks
this way:
<html>
<head>
<title>Hello World</title>
</head>
<body>
Hello World
</body>
</html>
As you can see, there's no trace of the PHP-code left in the final output. You should think of a
PHP-script as a normal webpage written in HTML, since most of the page is still just plain-old HTML.
But between the start- and end-tags (<?php or < and ?>) the
PHP-parsed spices the page up with possibly dynamic content.
