PHP Introduction

The PHP Hypertext Preprocessor (PHP) is a programming language that allows web developers to create dynamic content that interacts with databases.

PHP is basically used for developing web based software applications.  

PHP is probably the most popular scripting language on the web. It is used to enhance web pages. With PHP, you can do things like create username and password login pages, check details from a form, create forums, picture galleries, surveys, and a whole lot more. If you've come across a web page that ends in PHP, then the author has written some programming code to liven up the plain, old HTML.

PHP is known as a server-sided language. That's because the PHP doesn't get executed on your computer, but on the computer you requested the page from. The results are then handed over to you, and displayed in your browser. Other scripting languages you may have heard of are ASP, Python and Perl. (You don't need to know any of these to make a start on PHP. In fact, these tutorials assume that you have no programming experience at all.)

The most popular explanation of just what PHP stands for is "Hypertext Pre-processor". But that would make it HPP, surely? An alternative explanation is that the initials come from the earliest version of the program, which was called Personal Home Page Tools. At least you get the letters "PHP" in the right order!

But PHP is so popular that if you're looking for a career in the web design/web scripting industry then you just have to know it! In these tutorials, we'll get you up and running. And, hopefully, it will be a lot easier than you think

Before you can write and test your PHP scripts, there's one thing you'll need - a server! Fortunately, you don't need to go out and buy one. In fact, you won't be spending any extra money. That's why PHP is so popular! But because PHP is a server-sided scripting language, you either have to get some web space with a hosting company that supports PHP, or make your computer pretend that it has a server installed. This is because PHP is not run on your PC - it's executed on the server. The results are then sent back to the client PC (your computer).

Don't worry if this all sounds a little daunting - we've come across an easier way to get you up and running. We're going to be using some software called Wampserver. This allows you to test your PHP scripts on your own computer. It installs everything you need, if you have a Windows PC. We'll explain how to get it installed in a moment, and where to get it from. But just a word for non-windows users.

Apple Users

If you have OS X, then try these sites to get up and running with PHP:

http://www.onlamp.com/pub/a/mac/2001/12/07/apache.html

http://www.entropy.ch/software/macosx/php/

What you're doing here is getting the apache server up and running, so that you can run PHP scripts offline. Pay particular attention to where files are stored, and to the "localhost" address.
Linux Users

There are quite a few sites out there to help Linux users get up and running with the Apache server and PHP. Here are three sites that are worth checking out:

http://en.wikipedia.org/wiki/LAMP_(software_bundle)

http://www.php-mysql-tutorial.com/wikis/php-tutorial/installing-php-and-mysql.aspx

http://www.phpfreaks.com/tutorials/12/0.php

If you know any better ones, we'd be interested in hearing from you!

Windows Users

OK, back to Wampserver and Windows. First, you need to download the software.


This chapter will give you an idea of very basic syntax of PHP and very important to make your PHP foundation strong.

Escaping to PHP:

The PHP parsing engine needs a way to differentiate PHP code from other elements in the page. The mechanism for doing so is known as 'escaping to PHP.' There are four ways to do this:
Canonical PHP tags:

The most universally effective PHP tag style is:

<?php...?>

If you use this style, you can be positive that your tags will always be correctly interpreted.
Short-open (SGML-style) tags:

Short or short-open tags look like this:

<?...?>

Short tags are, as one might expect, the shortest option You must do one of two things to enable PHP to recognize the tags:

    Choose the --enable-short-tags configuration option when you're building PHP.

    Set the short_open_tag setting in your php.ini file to on. This option must be disabled to parse XML with PHP because the same syntax is used for XML tags.

ASP-style tags:

ASP-style tags mimic the tags used by Active Server Pages to delineate code blocks. ASP-style tags look like this:

<%...%>

To use ASP-style tags, you will need to set the configuration option in your php.ini file.
HTML script tags:

HTML script tags look like this:

<script language="PHP">...</script>

Commenting PHP Code:

A comment is the portion of a program that exists only for the human reader and stripped out before displaying the programs result. There are two commenting formats in PHP:

Single-line comments: They are generally used for short explanations or notes relevant to the local code. Here are the examples of single line comments.

<?
# This is a comment, and
# This is the second line of the comment
// This is a comment too. Each style comments only
print "An example with single line comments";
?>

Multi-lines printing: Here are the examples to print multiple lines in a single print statement:

<?
# First Example
print <<<END
This uses the "here document" syntax to output
multiple lines with $variable interpolation. Note
that the here document terminator must appear on a
line with just a semicolon no extra whitespace!
END;
# Second Example
print "This spans
multiple lines. The newlines will be
output as well";
?>

Multi-lines comments: They are generally used to provide pseudocode algorithms and more detailed explanations when necessary. The multiline style of commenting is the same as in C. Here are the example of multi lines comments.

<?
/* This is a comment with multiline
    Author : Mohammad Mohtashim
    Purpose: Multiline Comments Demo
    Subject: PHP
*/
print "An example with multi line comments";
?>

PHP is whitespace insensitive:

Whitespace is the stuff you type that is typically invisible on the screen, including spaces, tabs, and carriage returns (end-of-line characters).

PHP whitespace insensitive means that it almost never matters how many whitespace characters you have in a row.one whitespace character is the same as many such characters

For example, each of the following PHP statements that assigns the sum of 2 + 2 to the variable $four is equivalent:

$four = 2 + 2; // single spaces
$four <tab>=<tab2<tab>+<tab>2 ; // spaces and tabs
$four =
2+
2; // multiple lines

PHP is case sensitive:

Yeah it is true that PHP is a case sensitive language. Try out following example:

<html>
<body>
<?
$capital = 67;
print("Variable capital is $capital<br>");
print("Variable CaPiTaL is $CaPiTaL<br>");
?>
</body>
</html>

This will produce following result:

Variable capital is 67
Variable CaPiTaL is

Statements are expressions terminated by semicolons:

A statement in PHP is any expression that is followed by a semicolon (;).Any sequence of valid PHP statements that is enclosed by the PHP tags is a valid PHP program. Here is a typical statement in PHP, which in this case assigns a string of characters to a variable called $greeting:

$greeting = "Welcome to PHP!";

Expressions are combinations of tokens:

The smallest building blocks of PHP are the indivisible tokens, such as numbers (3.14159), strings (.two.), variables ($two), constants (TRUE), and the special words that make up the syntax of PHP itself like if, else, while, for and so forth
Braces make blocks:

Although statements cannot be combined like expressions, you can always put a sequence of statements anywhere a statement can go by enclosing them in a set of curly braces.

Here both statements are equivalent:

if (3 == 2 + 1)
  print("Good - I haven't totally lost my mind.<br>");

if (3 == 2 + 1)
{
   print("Good - I haven't totally");
   print("lost my mind.<br>");
}

Running PHP Script from Command Prompt:

Yes you can run your PHP script on your command prompt. Assuming you have following content in test.php file

<?php
   echo "Hello PHP!!!!!";
?>

Now run this script as command prompt as follows:

$ php test.php

It will produce following result:

Hello PHP!!!!!

Hope now you have basic knowledge of PHP Syntax.