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. |