HTML Goodies: PHP Tutorial - Duplicate

By Vince Barnes

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This very first page you make that includes some PHP code deserves to be something really useful.  Don't let the simplicity of this little page fool you!  This is a very useful tool -- as you will see when you try it.   This page is going to verify the availability of PHP on your server, and provide you with a lot of information about the PHP itself and the server it's running on.  Here's the code:

<title>PHP Test</title>
<?php phpinfo(); ?>

That's it!  Small, but then so are diamonds!  Let's break this little gem down.

Almost all of this is instantly recognizable to you as plain old HTML code -- all except that one curious line in the middle:   <?php phpinfo(); ?>   That's the PHP code.

A PHP code snippet is surrounded by an opening and a closing delimiter.  The opening delimiter is <?php and the closing is ?>  the code in between is PHP code.  In this example we are calling the PHP function "phpinfo".  The function name is followed by opening and closing parentheses which surround any parameters being passed to the function -- in this case there are none.  The function call is terminated with a semicolon.

Go ahead and create a file containing this code -- the file name should end with a .php suffix -- send it up to your server and pull it up in your web browser just like you would any other web page.  you should see lots of interesting info about the server system and PHP itself.  Take a look at the source of the resulting page (View Source).  You'll notice that the HTML from your original page is still there, but the PHP code has been replaced by all the information you see.  That's basically how the engine works.  The PHP code you write is replace in the resulting web page by the results of running the PHP code.  Nobody gets to see your actual PHP code -- only the result of it running.  That's significant, as I imagine you already realize!

For a little further note about PHP syntax; the code snippet above, contained between the beginning and ending delimiters is similar to HTML tags in appearance.  It is in fact called a PHP tag.  There are four forms of PHP tags.  The one we've used here is called an XML style tag and is the one we will continue to use throughout this tutorial.  It is the most common form. another style is called script style and will also look somewhat familiar to you if you have written any other script code such as JavaScript.  This example is exactly equivalent to our snippet above:

<script language=php>

The other two forms are called the short style of tag and the ASP style.  Both of these require special settings in the PHP configuration files.  They are less commonly used and I will only provide this one example of each in this series.  Here is the same code in the Short style and ASP style, respectively:

<? phpinfo(); ?>

<% phpinfo(); %>

As I previously mentioned, each statement in your PHP code is ended with a semicolon.  Leaving this semicolon off is a common syntax error and when something isn't working the way you expect it to should be one of the first things you check.

Whitespace (spaces, tabs and newlines) are ignored in the syntax of PHP.  These three examples are completely equivalent:

<?php phpinfo(); ?>

<?php     phpinfo();     ?>


As in all forms of programming, adding comments to you code is a very useful idea.  Make your code self-documenting and you will love yourself later when you come back to if after having forgotten why you did things a certain way!  You can also add comments to you code in a variety of ways similar to some other language syntaxes.  You can use /* multi-line comment here */ like in C, or add comments to individual lines like in C++ or shell scripts with // and # respectively.  Here are some examples:

/*  This is a
     multi-line comment following
     the C language style of comments.

<?php  // this is a C++ style comment on the one code line

<?php  # this is a shell script style comment on the one code line

That's it!  You have now (or should have!) created your first PHP page and learned the basic syntax requirements of PHP code.  You are well on your way!


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