Biren: January 2014

Tuesday, 7 January 2014

PHP Tutorial

Before we can start coding you first need to know some basics. In this PHP language introduction tutorial you’ll find some descriptions of words you should know before you can start coding. Of course we will also look at where you can download PHP, MySQL and Apache.

What is PHP?

The PHP programming language is a server-side HTML embedded scripting language.

Let‘s depict the sentence. The PHP language runs on the server-side. This means that the execution (read starting) of the scripts are done on the server where the web-site is hosted. HTML embedded means that you can use PHP statements (read a piece of PHP code) from within an HTML code. PHP files are returned to the browser as plain HTML.

The last piece of the sentence – scripting language – is a little harder to explain, but we will give it a go. A scripting language is a form of programming language that is usually interpreted rather than compiled. In programming languages such C or C++ you compile the program (permanently) into an executable file, before you can execute the program. A program that is written in a scripting language, is interpreted one command at a time by a command interpreter (Command interpreter is in most cases an executable written in another language (for instance C/C++) than the scripting language.) Some other examples of scripting languages are Perl, Phyton, Java and Ruby.

A last note: scripting languages are also often used by applications as control or configure language. An example: Firefox is written in C/C++ and can be controlled with JavaScript.
Things You Should Know

Because PHP is an HTML embedded language you should have a basic understanding of HTML/XHTML and (a little) JavaScript. In the coming tutorials we will explain the PHP code, but we won’t explain the HTML code (at least not in great detail.)

What is PHP?

PHP stands for PHP: Hypertext Preprocessor.
As we said before it is a server-side scripting language.
PHP is free and is an open source software product.
The PHP scripts are executed on the server.
PHP supports many databases (MySQL, Sybase, Oracle and many others.)
PHP runs on different platforms (Unix, Linux, Windows.)
PHP is compatible with almost all web-servers used today (Apache, IIS, etc.)
A PHP file can contain plain text, HTML tags and scripts
The PHP files can have one of the following extensions: php, php3 or phtml.
What do you need?

Before you can follow the coming PHP tutorials you need to have the following:

Access to a web server (like Apache)
PHP and MySQL should be installed on the web server.
The easiest way is to find a cheap web hosting plan that support PHP and MySQL (most of the web-hosting providers do.) For a couple of bucks a month you can get a virtual host. The advantage is that everything is already installed and that you can share your program (that you are going to write) with the rest of the world.

If you don’t want to spend money, you can also install everything on your local machine. The easiest way is to install WAMP if you have a Windows machine and LAMP if you have a Linux machine. (WAMP = Windows Apache MySQL PHP and LAMP = Linux Apache MySQL PHP.) These packages install everything you need. Read the install manual of these packages for instructions. After installation you should have access to http://localhost in your browser.

The examples on this Site

To keep things small we will not place every example between <html> <body> some piece of PHP code </body></html>. In most cases you need to add it yourself if you cut/paste some piece of code.

That is all for this PHP language introduction tutorial. We hope that you will learn something from the coming PHP tutorials and as always we hope that you will let us know if something is wrong by leaving us a comment.

Introduction

Introduction

PHP supports eight primitive types.

Four scalar types:

boolean
integer
float (floating-point number, aka double)
string
Two compound types:

array
object
And finally two special types:

resource
NULL
This manual also introduces some pseudo-types for readability reasons:

mixed
number
callback
And the pseudo-variable $....

Some references to the type "double" may remain in the manual. Consider double the same as float; the two names exist only for historic reasons.

The type of a variable is not usually set by the programmer; rather, it is decided at runtime by PHP depending on the context in which that variable is used.

Note: To check the type and value of an expression, use the var_dump() function.
To get a human-readable representation of a type for debugging, use the gettype() function. To check for a certain type, do not use gettype(), but rather the is_type functions. Some examples:
<?php
$a_bool = TRUE; // a boolean
$a_str = "foo"; // a string
$a_str2 = 'foo'; // a string
$an_int = 12; // an integer

echo gettype($a_bool); // prints out: boolean
echo gettype($a_str); // prints out: string

// If this is an integer, increment it by four
if (is_int($an_int)) {
$an_int += 4;
}

// If $a_bool is a string, print it out
// (does not print out anything)
if (is_string($a_bool)) {
echo "String: $a_bool";
}
?>

PHP Types

Types

Table of Contents

Introduction
Booleans
Integers
Floating point numbers
Strings
Arrays
Objects
Resources
NULL
Callbacks
Pseudo-types and variables used in this documentation
Type Juggling

Comments

Comments

PHP supports 'C', 'C++' and Unix shell-style (Perl style) comments. For example:

<?php
echo 'This is a test'; // This is a one-line c++ style comment
/* This is a multi line comment
yet another line of comment */
echo 'This is yet another test';
echo 'One Final Test'; # This is a one-line shell-style comment
?>
The "one-line" comment styles only comment to the end of the line or the current block of PHP code, whichever comes first. This means that HTML code after // ... ?> or # ... ?> WILL be printed: ?> breaks out of PHP mode and returns to HTML mode, and // or # cannot influence that. If the asp_tags configuration directive is enabled, it behaves the same with // %> and # %>. However, the </script> tag doesn't break out of PHP mode in a one-line comment.

<h1>This is an <?php # echo 'simple';?> example</h1>
<p>The header above will say 'This is an example'.</p>
'C' style comments end at the first */ encountered. Make sure you don't nest 'C' style comments. It is easy to make this mistake if you are trying to comment out a large block of code.

<?php
/*
echo 'This is a test'; /* This comment will cause a problem */
*/
?>

Instruction separation

As in C or Perl, PHP requires instructions to be terminated with a semicolon at the end of each statement. The closing tag of a block of PHP code automatically implies a semicolon; you do not need to have a semicolon terminating the last line of a PHP block. The closing tag for the block will include the immediately trailing newline if one is present.

<?php
echo 'This is a test';
?>

<?php echo 'This is a test' ?>

<?php echo 'We omitted the last closing tag';

Escaping from HTML

Everything outside of a pair of opening and closing tags is ignored by the PHP parser which allows PHP files to have mixed content. This allows PHP to be embedded in HTML documents, for example to create templates.

<p>This is going to be ignored by PHP and displayed by the browser.</p>
<?php echo 'While this is going to be parsed.'; ?>
<p>This will also be ignored by PHP and displayed by the browser.</p>
This works as expected, because when the PHP interpreter hits the ?> closing tags, it simply starts outputting whatever it finds (except for an immediately following newline - see instruction separation) until it hits another opening tag unless in the middle of a conditional statement in which case the interpreter will determine the outcome of the conditional before making a decision of what which to skip over. See the next example.
Using structures with conditions

Example #1 Advanced escaping using conditions

<?php if ($expression == true): ?>
This will show if the expression is true.
<?php else: ?>
Otherwise this will show.
<?php endif; ?>
In this example PHP will skip the blocks where the condition is not met, even though they are outside of the PHP open/close tags, PHP skips them according to the condition since the PHP interpreter will jump over blocks contained within a condition what is not met.
For outputting large blocks of text, dropping out of PHP parsing mode is generally more efficient than sending all of the text through echo or print.

There are four different pairs of opening and closing tags which can be used in PHP. Two of those, <?php ?> and <script language="php"> </script>, are always available. The other two are short tags and ASP style tags, and can be turned on and off from the php.ini configuration file. As such, while some people find short tags and ASP style tags convenient, they are less portable, and generally not recommended.

Note:
Also note that if you are embedding PHP within XML or XHTML you will need to use the <?php ?> tags to remain compliant with standards.
Example #2 PHP Opening and Closing Tags

1. <?php echo 'if you want to serve XHTML or XML documents, do it like this'; ?>

2. <script language="php">
echo 'some editors (like FrontPage) don\'t
like processing instructions';
</script>

3. <? echo 'this is the simplest, an SGML processing instruction'; ?>
<?= expression ?> This is a shortcut for "<? echo expression ?>"

4. <% echo 'You may optionally use ASP-style tags'; %>
<%= $variable; # This is a shortcut for "<% echo . . ." %>
While the tags seen in examples one and two are both always available, example one is the most commonly used, and recommended, of the two.

Short tags (example three) are only available when they are enabled via the short_open_tag php.ini configuration file directive, or if PHP was configured with the --enable-short-tags option.

ASP style tags (example four) are only available when they are enabled via the asp_tags php.ini configuration file directive.

Note:
Using short tags should be avoided when developing applications or libraries that are meant for redistribution, or deployment on PHP servers which are not under your control, because short tags may not be supported on the target server. For portable, redistributable code, be sure not to use short tags.
Note:
In PHP 5.2 and earlier, the parser does not allow the <?php opening tag to be the only thing in a file. This is allowed as of PHP 5.3 provided there are one or more whitespace characters after the opening tag.
Note:
Starting with PHP 5.4, short echo tag <?= is always recognized and valid, regardless of the short_open_tag setting.
add a note add a note
User Contributed Notes 6 notes

up
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63 quickfur at quickfur dot ath dot cx ¶3 years ago
When the documentation says that the PHP parser ignores everything outside the <?php ... ?> tags, it means literally EVERYTHING. Including things you normally wouldn't consider "valid", such as the following:

<html><body>
<p<?php if ($highlight): ?> class="highlight"<?php endif;?>>This is a paragraph.</p>
</body></html>

Notice how the PHP code is embedded in the middle of an HTML opening tag. The PHP parser doesn't care that it's in the middle of an opening tag, and doesn't require that it be closed. It also doesn't care that after the closing ?> tag is the end of the HTML opening tag. So, if $highlight is true, then the output will be:

<html><body>
<p class="highlight">This is a paragraph.</p>
</body></html>

Otherwise, it will be:

<html><body>
<p>This is a paragraph.</p>
</body></html>

Using this method, you can have HTML tags with optional attributes, depending on some PHP condition. Extremely flexible and useful!
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14 ravenswd at gmail dot com ¶4 years ago
One aspect of PHP that you need to be careful of, is that ?> will drop you out of PHP code and into HTML even if it appears inside a // comment. (This does not apply to /* */ comments.) This can lead to unexpected results. For example, take this line:

<?php
$file_contents = '<?php die(); ?>' . "\n";
?>

If you try to remove it by turning it into a comment, you get this:

<?php
// $file_contents = '<?php die(); ?>' . "\n";
?>

Which results in ' . "\n"; (and whatever is in the lines following it) to be output to your HTML page.

The cure is to either comment it out using /* */ tags, or re-write the line as:

<?php
$file_contents = '<' . '?php die(); ?' . '>' . "\n";
?>
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10 mike at clove dot com ¶3 years ago
It's possible to write code to create php escapes which can be processed later by substituting \x3f for '?' - as in echo "<\x3fphp echo 'foo'; \x3f>";

This is useful for creating a template parser which later is rendered by PHP.
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8 snor_007 at hotmail dot com ¶3 years ago
Playing around with different open and close tags I discovered you can actually mix different style open/close tags

some examples

<%
//your php code here
?>

or

<script language="php">
//php code here
%>
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7 david dot jarry at gmail dot com ¶4 years ago
Shorts tags and ASP tags are unportables and should be avoided.

<script /> tags are a waste of time and simply inefficient in some simple cases :
<body>
<p style="color: <script language="php"> echo $text_color </script>;">
(...) VERY long text (...)
</p>
</body>
To render this example in a basic XHTML editor, you need to "echo()" all the content or break the XML rules.

The solution seems obvious to me : Why not add the shortcut "<?php= ?>" to be used within XML and XHTML documents ?
<?php='example1'?>
<?php=$example2?>
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4 admin at furutsuzeru dot net ¶5 years ago
These methods are just messy. Short-opening tags and ASP-styled tags are not always enabled on servers. The <script language="php"></script> alternative is just out there. You should just use the traditional tag opening:

<?php?>

Coding islands, for example:

<?php
$me = 'Pyornide';
?>
<?=$me;?> is happy.
<?php
$me = strtoupper($me);
?>
<?=$me;?> is happier.

Lead to something along the lines of messy code. Writing your application like this can just prove to be more of an
inconvenience when it comes to maintenance.

If you have to deal chunks of HTML, then consider having a templating system do the job for you. It is a poor idea to rely on the coding islands method as a template system in any way, and for reasons listed above.

PHP TAGS

When PHP parses a file, it looks for opening and closing tags, which are <?php and ?> which tell PHP to start and stop interpreting the code between them. Parsing in this manner allows PHP to be embedded in all sorts of different documents, as everything outside of a pair of opening and closing tags is ignored by the PHP parser.

PHP also allows for short open tags <? and ?> (which are discouraged because they are only available if enabled with short_open_tag php.ini configuration file directive, or if PHP was configured with the --enable-short-tags option.

If a file is pure PHP code, it is preferable to omit the PHP closing tag at the end of the file. This prevents accidental whitespace or new lines being added after the PHP closing tag, which may cause unwanted effects because PHP will start output buffering when there is no intention from the programmer to send any output at that point in the script.

Wednesday, 1 January 2014

Biren PHP web developer

PHP is a server scripting language, and is a powerful tool for making dynamic and interactive Web pages quickly.
PHP is a widely-used, free, and efficient alternative to competitors such as Microsoft's ASP.

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