Sunday, 31 July 2011

PHP

PHP Tutorial - Learn PHP

If you want to learn the basics of PHP, then you've come to the right place. The goal of this tutorial is to teach you the basics of PHP so that you can:

Customize PHP scripts that you download, so that they better fit your needs.
Begin to understand the working model of PHP, so you may begin to design your own PHP projects.
Give you a solid base in PHP, so as to make you more valuable in the eyes of future employers.

PHP stands for PHP Hypertext Preprocessor.

PHP - What is it?

Taken directly from PHP's home, PHP.net, "PHP is an HTML-embedded scripting language. Much of its syntax is borrowed from C, Java and Perl with a couple of unique PHP-specific features thrown in. The goal of the language is to allow web developers to write dynamically generated pages quickly."

This is generally a good definition of PHP. However, it does contain a lot of terms you may not be used to. Another way to think of PHP is a powerful, behind the scenes scripting language that your visitors won't see!

When someone visits your PHP webpage, your web server processes the PHP code. It then sees which parts it needs to show to visitors(content and pictures) and hides the other stuff(file operations, math calculations, etc.) then translates your PHP into HTML. After the translation into HTML, it sends the webpage to your visitor's web browser.

PHP - What's it do?

It is also helpful to think of PHP in terms of what it can do for you. PHP will allow you to:

Reduce the time to create large websites.
Create a customized user experience for visitors based on information that you have gathered from them.
Open up thousands of possibilities for online tools. Check out PHP - HotScripts for examples of the great things that are possible with PHP.
Allow creation of shopping carts for e-commerce websites.

What You Should Know

Before starting this tutorial it is important that you have a basic understanding and experience in the following:

HTML - Know the syntax and especially HTML Forms.
Basic programming knowledge - This isn't required, but if you have any traditional programming experience it will make learning PHP a great deal easier.

Tutorial Overview

This tutorial is aimed at the PHP novice and will teach you PHP from the ground up. If you want a drive-through PHP tutorial this probably is not the right tutorial for you.

Remember, you should not try to plow through this tutorial in one sitting. Read a couple lessons, take a break, then do some more after the information has had some time to sink in.

PHP - Syntax

Before we talk about PHP's syntax, let us first define what syntax is referring to.

Syntax - The rules that must be followed to write properly structured code.

PHP's syntax and semantics are similar to most other programming languages (C, Java, Perl)
with the addition that all PHP code is contained with a tag, of sorts. All
PHP code must be contained within the following...

PHP Code:

<?php
?>

or the shorthand PHP tag that requires shorthand support to be enabled
on your server...

<?
?>

If you are writing PHP scripts and plan on distributing them, we suggest
that you use the standard form (which includes the ?php) rather than the shorthand
form. This will ensure that your scripts will work, even when running on other
servers with different settings.

How to Save Your PHP Pages

If you have PHP inserted into your HTML and want the
web browser to interpret it correctly, then you must save the file with a .php extension,
instead of the standard .html extension. So be sure to check that you are saving your files
correctly. Instead of index.html, it should be index.php if there
is PHP code in the file.




Example Simple HTML & PHP Page

Below is an example of one of the easiest PHP and HTML page that you
can create and still follow web standards.

PHP and HTML Code:

<html>
<head>
<title>My First PHP Page</title>

</head>
<body>
<?php
echo "Hello World!";
?>
</body>
</html>

Display:

Hello World!

If you save this file (e.g. helloworld.php) and place it on PHP enabled server and load it up in your web browser, then you should see
"Hello World!" displayed. If not, please check that you followed our example
correctly.
We used the PHP command echo to write "Hello World!" and we will be talking in greater depth about how echo is special later on in this tutorial.

The Semicolon!

As you may or may not have noticed in the above example, there was a semicolon after
the line of PHP code. The semicolon signifies the end of a PHP statement and
should never be forgotten. For example, if we repeated our "Hello World!" code several times, then we would
need to place a semicolon at the end of each statement.

PHP and HTML Code:

<html>
<head>
<title>My First PHP Page</title>

</head>
<body>
<?php
echo "Hello World! ";
echo "Hello World! ";
echo "Hello World! ";
echo "Hello World! ";
echo "Hello World! ";
?>
</body>
</html>

Display:

Hello World!
Hello World!
Hello World!
Hello World!
Hello World!

White Space

As with HTML, whitespace is ignored between PHP statements. This means it is OK to have
one line of PHP code, then 20 lines of blank space before the next line of PHP code. You can also
press tab to indent your code and the PHP interpreter will ignore those spaces as well.


PHP and HTML Code:

<html>
<head>
<title>My First PHP Page</title>
</head>
<body>

<?php
echo "Hello World!";        



 echo "Hello World!";


?>
</body>
</html>

Display:

Hello World!Hello World!

This is perfectly legal PHP code.

PHP - Variables

If you have never had any programming, Algebra, or scripting experience, then the concept of variables might be a new concept to you. A detailed explanation of variables is beyond the scope of this tutorial, but we've included a refresher crash course to guide you.

A variable is a means of storing a value, such as text string "Hello World!"
or the integer value 4. A variable can then be reused throughout
your code, instead of having to type out the actual value over and over again. In PHP you define a variable with the following form:
  • $variable_name = Value;

If you forget that dollar sign at the beginning, it will not work. This is a common
mistake for new PHP programmers!

Note: Also, variable names are case-sensitive, so use the exact same capitalization when using a variable. The variables $a_number and $A_number are different variables in PHP's eyes.

A Quick Variable Example

Say that we wanted to store the values that we talked about in the above paragraph.
How would we go about doing this? We would first want to make a variable name and then
set that equal to the value we want. See our example below for the correct way to do this.

PHP Code:

<?php
$hello = "Hello World!";
$a_number = 4;
$anotherNumber = 8;
?>

Note for programmers: PHP does not require variables to be declared before
being initialized.

PHP Variable Naming Conventions

There are a few rules that you need to follow when choosing a name for your
PHP variables.
  • PHP variables must start with a letter or underscore "_".
  • PHP variables may only be comprised of alpha-numeric characters and underscores. a-z, A-Z, 0-9, or _ .
  • Variables with more than one word should be separated with underscores. $my_variable
  • Variables with more than one word can also be distinguished with capitalization. $myVariable
  • PHP - Echo As you saw in the previous lesson, the PHP command echo is a means of outputting text to the web browser. Throughout your PHP career you will be using the echo command more than any other. So let's give it a solid perusal!

    Outputting a String

    To output a string, like we have done in previous lessons, use PHP echo. You can place either a string variable or you can use quotes, like we do below, to create a string that the echo function will output.

    PHP Code:

    <?php
    $myString = "Hello!";
    echo $myString;
    echo "<h5>I love using PHP!</h5>";
    ?>
    
    

    Display:

    Hello!
    I love using PHP!
    In the above example we output "Hello!" without a hitch. The text we are outputting is being sent to the user in the form of a web page, so it is important that we use proper HTML syntax!
    In our second echo statement we use echo to write a valid Header 5 HTML statement. To do this we simply put the <h5> at the beginning of the string and closed it at the end of the string. Just because you're using PHP to make web pages does not mean you can forget about HTML syntax!

    Careful When Echoing Quotes!

    It is pretty cool that you can output HTML with PHP. However, you must be careful when using HTML code or any other string that includes quotes! Echo uses quotes to define the beginning and end of the string, so you must use one of the following tactics if your string contains quotations:
    • Don't use quotes inside your string
    • Escape your quotes that are within the string with a backslash. To escape a quote
      just place a backslash directly before the quotation mark, i.e. \"
    • Use single quotes (apostrophes) for quotes inside your string.
    See our example below for the right and wrong use of echo:

    PHP Code:

    <?php
    // This won't work because of the quotes around specialH5!
    echo "<h5 class="specialH5">I love using PHP!</h5>";  
    
    // OK because we escaped the quotes!
    echo "<h5 class=\"specialH5\">I love using PHP!</h5>";  
    
    // OK because we used an apostrophe '
    echo "<h5 class='specialH5'>I love using PHP!</h5>";  
    ?>
    
    
    If you want to output a string that includes quotations, either use an apostrophe ( ' ) or escape the quotations by placing a backslash in front of it ( \" ). The backslash will tell PHP that you want the quotation to be used within the string and NOT to be used to end echo's string.

    Echoing Variables

    Echoing variables is very easy. The PHP developers put in some extra work to make the common task of echoing all variables nearly foolproof! No quotations are required, even if the variable does not hold a string. Below is the correct format for echoing a variable.

    PHP Code:

    <?php
    $my_string = "Hello Bob.  My name is: ";
    $my_number = 4;
    $my_letter = a;
    echo $my_string;
    echo $my_number;
    echo $my_letter;
    ?>
    

    Display:

    Hello Bob. My name is: 4a

    Echoing Variables and Text Strings

    You can also place variables inside of double-quoted strings (e.g. "string here and a $variable"). By putting a variable inside the quotes (" ") you are telling PHP that you want it to grab the string value of that variable and use it in the string. The example below shows an example of this cool feature.

    PHP Code:

    <?php
    $my_string = "Hello Bob.  My name is: ";
    echo "$my_string Bobettta <br />";
    echo "Hi, I'm Bob.  Who are you? $my_string <br />";
    echo "Hi, I'm Bob.  Who are you? $my_string Bobetta";
    ?>
    

    Display:

    Hello Bob. My name is: Bobetta
    Hi, I'm Bob. Who are you? Hello Bob. My name is:
    Hi, I'm Bob. Who are you? Hello Bob. My name is: Bobetta
    By placing variables inside a string you can save yourself some time and make your code easier to read, though it does take some getting used to. Remember to use double-quotes, single-quotes will not grab the value of the string. Single-quotes will just output the variable name to the string, like )$my_string), rather than (Hello Bob. My name is: ).

    PHP Echo - Not a Function

    Echo is not a function, rather it is a language construct. When you use functions in PHP, they have a very particular form, which we will be going over later. For now, just know that echo is a special tool that you'll come to know and love!
    PHP - Strings In the last lesson, PHP Echo, we used strings a bit, but didn't talk about them in depth. Throughout your PHP career you will be using strings a great deal, so it is important to have a basic understanding of PHP strings.

    PHP - String Creation

    Before you can use a string you have to create it! A string can be used directly in a function or it can be stored in a variable. Below we create the exact same string twice: first storing it into a variable and in the second case we send the string directly to echo.

    PHP Code:

    $my_string = "Tizag - Unlock your potential!";
    echo "Tizag - Unlock your potential!";
    echo $my_string;
    
    In the above example the first string will be stored into the variable $my_string, while the second string will be used in the echo and not be stored. Remember to save your strings into variables if you plan on using them more than once! Below is the output from our example code. They look identical just as we thought.

    Display:

    Tizag - Unlock your potential! Tizag - Unlock your potential!

    PHP - String Creation Single Quotes

    Thus far we have created strings using double-quotes, but it is just as correct to create a string using single-quotes, otherwise known as apostrophes.

    PHP Code:

    $my_string = 'Tizag - Unlock your potential!';
    echo 'Tizag - Unlock your potential!';
    echo $my_string;
    
    If you want to use a single-quote within the string you have to escape the single-quote with a backslash \ . Like this: \' !

    PHP Code:

    echo 'Tizag - It\'s Neat!';
    

    PHP - String Creation Double-Quotes

    We have used double-quotes and will continue to use them as the primary method for forming strings. Double-quotes allow for many special escaped characters to be used that you cannot do with a single-quote string. Once again, a backslash is used to escape a character.

    PHP Code:

    $newline = "A newline is \n";
    $return = "A carriage return is \r";
    $tab = "A tab is \t";
    $dollar = "A dollar sign is \$";
    $doublequote = "A double-quote is \"";
    
    Note: If you try to escape a character that doesn't need to be, such as an apostrophe, then the backslash will show up when you output the string.
    These escaped characters are not very useful for outputting to a web page because HTML ignore extra white space. A tab, newline, and carriage return are all examples of extra (ignorable) white space. However, when writing to a file that may be read by human eyes these escaped characters are a valuable tool!

    PHP - String Creation Heredoc

    The two methods above are the traditional way to create strings in most programming languages. PHP introduces a more robust string creation tool called heredoc that lets the programmer create multi-line strings without using quotations. However, creating a string using heredoc is more difficult and can lead to problems if you do not properly code your string! Here's how to do it:

    PHP Code:

    $my_string = <<<TEST
    Tizag.com
    Webmaster Tutorials
    Unlock your potential!
    TEST;
    
    echo $my_string;
    
    There are a few very important things to remember when using heredoc.
    • Use <<< and some identifier that you choose to begin the heredoc. In this example we chose TEST as our
      identifier.
    • Repeat the identifier followed by a semicolon to end the heredoc string creation. In this example that was
      TEST;
    • The closing sequence TEST; must occur on a line by itself and cannot be indented!
    Another thing to note is that when you output this multi-line string to a web page, it will not span multiple lines because we did not have any <br /> tags contained inside our string! Here is the output made from the code above.

    Display:

    Tizag.com Webmaster Tutorials Unlock your potential!
    Once again, take great care in following the heredoc creation guidelines to avoid any headaches.

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