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.
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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.
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