Friday, September 9, 2011

PHP Introduction


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

What is PHP?

ñ PHP stands for PHP: Hypertext Preprocessor
ñ PHP is a server-side scripting language, like ASP
ñ PHP scripts are executed on the server
ñ PHP supports many databases (MySQL, Informix, Oracle, Sybase, Solid, PostgreSQL, Generic ODBC, etc.)
ñ PHP is an open source software
ñ PHP is free to download and use

What is a PHP File?

ñ PHP files can contain text, HTML tags and scripts
ñ PHP files are returned to the browser as plain HTML 
ñ PHP files have a file extension of ".php", ".php3", or ".phtml"

Why PHP?

ñ PHP runs on different platforms (Windows, Linux, Unix, etc.)
ñ PHP is compatible with almost all servers used today (Apache, IIS, etc.)
ñ PHP is FREE to download from the official PHP resource:
ñ PHP is easy to learn and runs efficiently on the server side

Where to Start?

To get access to a web server with PHP support, you can:
ñ Install Apache (or IIS) on your own server, install PHP, and MySQL
ñ Or find a web hosting plan with PHP and MySQL support

PHP Syntax

PHP code is executed on the server, and the plain HTML result is sent to the browser.

Basic PHP Syntax

A PHP scripting block always starts with <?php and ends with ?>. A PHP scripting block can be placed anywhere in the document.
On servers with shorthand support enabled you can start a scripting block with <? and end with ?>.
Each code line in PHP must end with a semicolon. The semicolon is a separator and is used to distinguish one set of instructions from another.

Simple “Hello World” Program


echo "Hello World";


Note: The file must have a .php extension. If the file has a .html extension, the PHP code will not be executed.

PHP Variables

Variables are used for storing values, like text strings, numbers or arrays.
When a variable is declared, it can be used over and over again in your script.
All variables in PHP start with a $ sign symbol.
The correct way of declaring a variable in PHP:
$var_name = value;

PHP is a Loosely Typed Language

In PHP, a variable does not need to be declared before adding a value to it.
In the example above, you see that you do not have to tell PHP which data type the variable is.
PHP automatically converts the variable to the correct data type, depending on its value.
In a strongly typed programming language, you have to declare (define) the type and name of the variable before using it.
In PHP, the variable is declared automatically when you use it.

The Concatenation Operator

There is only one string operator in PHP.
The concatenation operator (.)  is used to put two string values together.
To concatenate two string variables together, use the concatenation operator:

$txt1="Hello World!";
$txt2="What a nice day!";
echo $txt1 . " " . $txt2;

The output of the code above will be:
Hello World! What a nice day!

PHP Forms and User Input

The PHP $_GET and $_POST variables are used to retrieve information from forms, like user input.

PHP Form Handling

The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts.


The example below contains an HTML form with two input fields and a submit button:

<form action="welcome.php" method="post">
Name: <input type="text" name="fname" />
Age: <input type="text" name="age" />
<input type="submit" />

When a user fills out the form above and click on the submit button, the form data is sent to a PHP file, called "welcome.php":
"welcome.php" looks like this:

Welcome <?php echo $_POST["fname"]; ?>!<br />
You are <?php echo $_POST["age"]; ?> years old.

Output could be something like this:
Welcome John!
You are 28 years old.

Note: Highlighted $_POST[“ “] specifies how the input value passed from another form or page is get into new PHP scripting page.

PHP $_GET Function

The built-in $_GET function is used to collect values in a form with method="get".

When using method="get" in HTML forms, all variable names and values are displayed in the URL.

PHP $_POST Function

The built-in $_POST function is used to collect values in a form with method="post".

Information sent from a form with the POST method is invisible to others and has no limits on the amount of information to send.

Deploying our PHP Application

Windows :
                        Install WAMP Web-Server Software and deploy all your applications.

               (Refer this sites for “How to use?”)

Fedora :
                    Save your php files into “\var\www\html\” folder. To place your files first we have to set access permissions.
                        Follow the steps
1.      Open the Terminal.
2.      Log in as Super User. Type “su” command it will ask for root password ( ask the technicians or respective faculties).
3.      Next step is to change our current working location.
4.      Type “cd ..” as many times until your present working directory(can be found by using pwd command) reaches “/”.
5.      Type cd var/www.
6.      Type “ls” it will list all the files & directories present in that directory. We have to deploy our php files under HTML.
ñ  To set access permission to HTML folder use chmod command
ñ  type chmod 777 html.
ñ  Now you have set the access permissions to that folder. We can paste any files in under that folder.

            To display our PHP files in Browser,

            Before opening browser, ensure that apache services is running or not.
            (In Browser) Type “localhost” in url and press enter. If the apache services is running correctly, it will shows fedora test page as shown below.

                        If it shows “Problems on page load error” means, the apache services is not running.          open terminal (enter as super user (“su”))
ñ  Type apchectl start – to start the apache server.
ñ  Type  apchectl stop – to stop the apache server. (its not mandatory to stop).

Creating separate folders for your PHP applications

            You can create any number of folders under that HTML  folder and deploy your projects without any choas by placing it under single folder.
            If you put your projects in a folder named “test”, then while running it through browser, you should specify clearly as follows,

            in url type, localhost/test/yourphpfilename along with .php extension


       MySQL is the most popular open-source database system.
            In MySQL we can create any number of databases under particular databases we can create any number of tables.
            Log in as super user in terminal by using “su” command.
            Then type mysql.

            To lists all existing databases, type show databases;
            Note: Tables can be created only by selecting a database first.

            To select a database, type use database_name;

            to lists all tables exists under that database, type show tables;
            PHP MySQL Connect to a Database

             Before you can access data in a database, you must create a connection to the database. In PHP, this is done with the mysql_connect() function.

            Ex :-)
            $con = mysql_connect("localhost","root","");
            if (!$con)
              die('Could not connect: ' . mysql_error());

            // some code

            The connection will be closed automatically when the script ends. To close the connection before, use the mysql_close() function.

            mysql_select_db() -> Sets the current active database on the server that's associated with the specified link identifier. Every subsequent call to mysql_query() will be made on the active database.

            mysql_query() -> executes the INSERT INTO statement, and a new record will be added to the  table.

            mysql_num_rows() -> Retrieves the number of rows from a result set. This command is only valid for statements like SELECT or SHOW that return an actual result set. To retrieve the number of rows affected by a INSERT, UPDATE, REPLACE or DELETE query, use mysql_affected_rows().

            mysql_fetch_array() -> return the first row from the recordset as an array. Each call to mysql_fetch_array() returns the next row in the recordset.

Select data from database :


$result = mysql_query("SELECT * FROM Persons");

while($row = mysql_fetch_array($result))
  echo $row['FirstName'] . " " . $row['LastName'];
  echo "<br />";

The while loop loops through all the records in the recordset. To print the value of each row, we use the PHP $row variable ($row['FirstName'] and $row['LastName']).

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