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Your First PHP Code

syndicated from planet-php.net on October 31, 2017

The following is a short extract from our new book, PHP & MySQL: Novice to Ninja, 6th Edition, written by Tom Butler and Kevin Yank. It's the ultimate beginner's guide to PHP. SitePoint Premium members get access with their membership, or you can buy a copy in stores worldwide.

Now that you have your virtual server up and running, it’s time to write your first PHP script. PHP is a server-side language. This concept may be a little difficult to grasp, especially if you’ve only ever designed websites using 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 html code of a web page. 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 result takes the place of the PHP code in the page. All the browser sees is standard html code when it receives the page, hence the name “server-side language.” Let’s look at simple example of some PHP that generates a random number between 1 and 10 and then displays it on the screen: 


<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <title>Random Number</title>
    </head>
    <body>
        <p>Generating a random number between 1 and 10:
            <?php

echo rand(1, 10);

?>
        </p>
    </body>
</html>

Most of this is plain html. Only the line between <?php and ?> is PHP code. <?php marks the start of an embedded PHP script and ?> marks its end. The web server is asked to interpret everything between these two delimiters and convert it to regular html code before it sends the web page to the requesting browser. If you right-click inside your browser and choose View Source (the text may be different depending on the browser you’re using) you can see that the browser is presented with the following:


<!DOCTYPE html>
<html lang="en">
    <head>
        <meta charset="utf-8">
        <title>Random Number</title>
    </head>
    <body>
        <p>Generating a random number between 1 and 10:
            5
        </p>
    </body>
</html>

Notice that all signs of the PHP code have disappeared. In its place the output of the script has appeared, and it looks just like standard html. This example demonstrates several advantages of server-side scripting …

  • No browser compatibility issues. PHP scripts are interpreted by the web server alone, so there’s no need to worry about whether the language features you’re using are supported by the visitor’s browser.
  • Access to server-side resources. In the example above, we placed a random number generated by the web server into the web page. If we had inserted the number using JavaScript, the number would be generated in the browser and someone could potentially amend the code to insert a specific number. Granted, there are more impressive examples of the exploitation of server-side resources, such as inserting content pulled out of a MySQL database.
  • Reduced load on the client. JavaScript can delay the display of a web page significantly (especially on mobile devices!) as the browser must run the script before it can display the web page. With server-side code, this burden is passed to the web server, which you can make as beefy as your application requires (and your wallet can afford).
  • Choice. When writing code that’s run in the browser, the browser has to understand how to run the code given to it. All modern browsers understand html, CSS and JavaScript. To write some code that’s run in t

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