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PHP is a server side scripting language. Now you may have thought that PHP was a programming language. Well, technically speaking, it's not. So how's a scripting language different from a programming language? The distinction between them is largely artificial, and the lines can get a bit blurry. But we can do a general comparison. A script only runs in response to an event.
It also usually runs a set of instructions by working down the page from the start to the end. It has little or no user interaction after that initial event. So PHP script does not run until a web page is requested. Then it launches, follows its instructions from top to bottom, and then quits until another action launches the script again. On the other hand, a program, runs even when not responding to events. It continues to run, and to wait for interaction.
Whether that interaction comes from a user, making choices, or from other programs or input. A programs also jumps around with instructions a lot more. So that there's often not a clear start and end point. And it often involves lots of user interaction. Photoshop is a good example of an application. After you launch it, it keeps running, waiting for more interactions or for you to tell it to quit. The task that it performs are not a linear set of instructions. It jumps around based on the task that you want to do at that particular moment. But as I said, the lines get blurry as scripts get more complex, they start to resemble programs.
And the simplest programs are basically just scripts. So you could say it's a distinction without a difference. But we still call PHP a scripting language. Now what does it mean when we say PHP is server side. When we talk about server side and its opposite, client side. What we're talking about is where the code does its work. Does the code run on our web server, which is server-side, or on the user's computer, which is client-side? The client-side, when we're working with web pages, is the user's browser.
As a contrast, JavaScript is an example of another popular scripting language, but JavaScript is a client-side scripting language. JavaScript code is sent to the user's browser and then it does its work there. PHP code is never sent to the user. It runs entirely on the web server, and the results of that code is what's sent to the user's browser. That's an important difference. Because PHP runs on a web server that means it generally can't run on its own. We'll need to have a running web server in order to use PHP. PHP code does not need to be compiled. It's executed by the web server exactly as it's written. Other programming languages, such as C or Java, require the code to be compiled or translated into another form before it can be used.
We'll be able to just write our PHP, put it where our web server can find it, and then we can load up the web page and see the results. PHP is designed for use with HTML. It can be embedded in our HTML. And we can use it to generate HTML. In the end PHP is going to return HTML to the browser. PHP code is going to be our input and web pages are going to be our output. Now if you've been working with HTML you're already familiar with having .htm or .html at the end of your file names.
PHP is going to work exactly the same but we're going to put php at the end. The php is going to tell the web server that this file contains php codes that needs to be executed. PHP is going to provide more flexibility than html does on it own. HTML pages are static by their nature. So all visitors to a web page see that same page all the time. A PHP lets us create dynamic pages. And page content can change based on conditions. Such as interactions with the user, or data stored in a database.
You can think of PHP as turbo charging your html. PHP syntax is going to be very similar to C, Java, and Perl. The small details are going to vary quite a bit, but the structure of logical expressions and loops, those kinds of things will be kind of familiar to anyone with programming experience in one of these languages.
Categories: Learn PHP
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