I. Overview
II. How PHP works
III. "Hello PHP!" - Attempt #1
VI. Adding HTML tags
VII. Creating a valid HTML page with PHP
VIII. phpinfo() - Getting information about a web server's PHP install
XI. Review Questions
XI. Resources
I. Overview
PHP (recursive acronym for PHP: Hypertext Preprocessor) is a widely-used open source general-purpose scripting language that is especially suited for web development and can be embedded into HTML. It was originally created by Rasmus Lerdorf.
What distinguishes PHP from client-side technologies like JavaScript is that the code is executed on the server, generating HTML which is then sent to the client. The client receives the results of running that script, but will not see the underlying code or data. This makes PHP code much more secure than code that is run on the client-side.
We will be taking a look at both PHP 5 and PHP 7 in this class, as there is not an official "PHP 6": https://www.phproundtable.com/episode/what-happened-to-php-6
II. How PHP works
First, lets look at what a web server does when a regular HTML file (named index.html for example) is requested by a web browser:
- The web browser (the client) creates a socket connection to a web server
- The web browser requests a file from the web server over the socket connection by sending a request line, followed by 1 or more request headers
- The web server receives the request, and locates the file
- The web server sends the requested file to the client application
- The client application parses the returned file and displays it to the user
Now let's see what happens on banjo.rit.edu when a web file ends in the .php file extension (named index.php for example):
- The web browser (the client) creates a socket connection to a web server
- The web browser requests a file from the web server over the socket connection by sending a request line, followed by 1 or more request headers
- The web server receives the request, and locates the file
- The web server scans the web page for PHP directives, and runs any PHP code through a PHP parser, and replaces that code with the results of the parsing.
- The web server sends the requested file to the client application
- The client application parses the returned file and displays it to the user
We now have a new step #4, where the web server first "runs" any PHP code that is found on the page before sending the HTML file back to the web browser.
Let's get started! Using a text editor, type the following program into a file named hello-1.php:
hello-1.php
<?PHP
echo "Hello!"; // the echo statement prints out strings
?>- All of the executable PHP code must be contained in a special markup tag -
<?PHP /* Code goes here... */ ?>- the lettersPHPmay be captitalized, or not. - Now open the file up in a web browser - you should see the following - just the source code - FAIL!
- The code was not executed because PHP is run as a module in a web server, but here we are attempting to "run" the code off of our computer hard drive.
- Because the browser does not know how to parse the PHP code, it will be unable to execute the code and will instead simply display it.
- Go ahead and post hello.php to a web viewable directory on
banjo.rit.edu(and don't forget to set the file permissions to644) - Navigate to the file in a web browser and open it up
- Now the PHP code should run, and you will see the following:
- If you right-click in Chrome and "view page source" of hello-1.php in the web browser, you will only see the word
Hello!because the PHP source code properly executes on the server, and will not be visible anywhere in the browser. SUCCESS! - So when we use "view page source" in a browser, we should always be seeing only HTML/CSS/JavaScript, and should NEVER see the PHP source code.
IMPORTANT: Your PHP source code should run on your web server and NEVER be visible in any users web browser. If it is, you have really messed something up!
Now try this one - here we've added another echo statement.
hello-2.php
<?PHP
echo "Hello!\n\n";
echo "Hello Again!";
?>The \n gives us a carriage return and a line feed, as you probably already know. So here we're hoping that we get a line separating the two "Hello's".
But we probably don't. (Firefox and Safari don't show the line feeds, Chrome probably does, although it really shouldn't :-|)
Although the lines are always visible in the HTML source when we "view source".
The reason we don't see the line feeds in the browser window is that the browser will ignore extra white space characters beyond a single space. What do we do if we want spacing? Add HTML tags!
VI. Adding HTML tags
Let's go ahead and wrap our text in HTML tags:
hello-3.php
<?PHP
echo "<h1>Hello!</h1>";
echo "<p>Hello Again!</p>";
?>Which gives you this in the browser window:
And this when you view source:
- In hello-3.php write PHP code that:
- add a
titleattribute to the <h1> with a value of"Hello! Hello!" - create a clickable link to
http://www.amazon.com, wrap it inside of a <p> tag.
- add a
To handle the quoting, you can either use single quotes (') inside of double quotes, or escape the double-quotes with a backslash like this: \"
When you are done it should look like this:
Our first two attempts at dynamic PHP pages would never validate because they are missing tags like <html>, <head>, <title>, <body> and so on. It would also be nice to have a <style> tag so that we could add some CSS styles to the page.
Below, you can see that we can mix HTML and PHP quite easily, and that all 3 of the PHP directives on this page will be executed by the PHP parser.
hello-4.php
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="utf-8" />
<?PHP
$pageTitle = "Hello-4"; // here we are declaring a variable
?>
<title>
<?PHP
echo $pageTitle; // and we use that variable here
?>
</title>
</head>
<body>
<?PHP
echo "<h1>$pageTitle</h1>"; // and we use that variable a second time here
echo "<div>Content goes here!</div>";
echo "<hr>";
echo "Page accessed on: ";
echo date("Y-m-d H:i:s"); // date() is a built-in PHP function
?>
</body>
</html>When you are done it should look like this:
- When you "view source" in the browser, you will see that all of the PHP directives have been replaced by the results of the processing.
- Paste the URL to this page into the HTML validator at https://validator.w3.org - it should validate as legal HTML5.
- Did you see the String Interpolation technique we used on the <h1> line? When we place variable names inside of double-quoted strings, PHP will place the contents of that variable in the string for us.
- In hello-4.php write code that:
- adds a <style> tag to the page - it should make the default font on the entire page
sans-serif. Just use HTML and CSS to do this, not PHP. - wraps the "page accessed on" text into a <footer> tag. Change the "date string" to something different - see the documentation here: http://php.net/manual/en/function.date.php
- adds a <style> tag to the page - it should make the default font on the entire page
The built-in phpinfo() function outputs information about PHP's configuration: compilation options and extensions, the PHP version, server information and environment, OS version information, paths, master and local values of configuration options, HTTP headers, and the PHP License.
Go ahead and create the following script and post it to your web server.
info.php
<?php
phpinfo();
?>If you are running your code on banjo.rit.edu, you should see something like this in your web browser:
If you keep scrolling, you will see that the information you are given runs on for 20+ pages! Be sure to look over the contents of this web page - it basically tells you what this installed version of PHP can "do".
If the PHP version number at the top is 7.1 or greater, you don't need to do anything. If it is an earlier version, you will need to upgrade to version 7 (see the homework assignment below).
IX. Review Questions
- Look up the original creator of PHP on Wikipedia. Where doe he work now?
- What is the special "tag" that contains PHP code?
- If everything is working properly, will a web browser ever "see" this tag?
- What usually happens if use a web browser to open up a PHP file on your computer's desktop?
- Which PHP statement is used to print strings?
- Which PHP function will tell the developer which version and which modules of of PHP are installed?
- Upgrade your banjo account to at least PHP 7+ - to do so involves editing a file named
phpthat already exists on your banjo web account atabc1234/php_data/php- you can find instructions here: https://www.rit.edu/webdev/php-7 - the instructions tell you to modify this file via the command line, but you can also "download it/modify it/upload it back to banjo" if you wish. - Post the info.php to your web account. Also verify that it shows you are running PHP 7.
- Do the section VII. "Try This", rename the file to php-1-HW.php, and post it to the web with your changes.
XI. Resources
Here are some links you might find helpful:
- http://php.net/manual/en/ - best source for PHP API documentation.
- http://php.net/manual/en/tutorial.php
- https://www.tutorialspoint.com/php/
- https://www.w3schools.com/php/
- https://feryn.eu/blog/php-7-is-now-available-new-features-improvements/