PHP is a server-side language. This concept may be a little difficult to grasp, especially if you’re used to designing pages using only client-side languages like HTML, CSS, and JavaScript. A server-side language is similar to JavaScript in that it allows you to embed little programs(scripts) into the HTMLcode of a webpage.When executed,these programs give you greater control over what appears in the browser window than HTML alone can provide. The key difference between JavaScript and PHP is the stage of loading the web page at which these embedded programs are executed.
Client-side languages like JavaScript are read and executed by the web browser, after downloading the web page (embedded programs and all) from the web server. In contrast, server-side languages like PHP are run by the web server, before sending the web page to the browser. Whereas client-side languages give you control over how a page behaves once it’s displayed by the browser, server-side languages let you generate customized pages on the fly before they’re even sent to the browser. Once the web server has executed the PHP code embedded in a web page, the results of that code’s execution take the place of the PHP code in the page. When the browser receives the page, all it sees is standard HTML code, hence the name: server-side language.
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd">
<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en">
<head>
<title>Today’s Date</title>
<meta http-equiv="content-type"
content="text/html; charset=utf-8"/>
</head>
<body>
<p>Today’s date (according to this web server) is
<?php
echo date('l, F dS Y.');
?>
</p>
</body>
</html>
Most of this is plain HTML; however, the line between <?php and ?> is PHP code.
<?php marks the start of an embedded PHP script and ?> marks the end of such a
script. The web server is asked to interpret everything between these two delimiters,
and to convert it to regular HTML code before it sends the web page to the requesting
browser.
