Opendir():- It opens the directory. This function returns a directory stream on success and FALSE and an error on failure.

Syntax:

Opendir(directory, context)

Context is a set of options that can modify the behavior of a stream

Example: opens sample directory.

$dir = opendir("directory");

Readdir(): It returns an entry from a directory handle opened by opendir().

Syntax:

Readdir(dir_stream)

Example:

$file = readdir($dir);

closedir(): It closes a directory handle opened by opendir().

Syntax:

closedir(dir_stream)

Example:

$file = close($dir);

Chmod() is used for changing permissions on a file.

Syntax:

Chmod(file, mode)

Mode here specifies the permissions as follows:

The first number is always zero

The second number specifies permissions for the owner

The third number specifies permissions for the owner's user group

The fourth number specifies permissions for everybody else

Possible values (to set multiple permissions, add up the following numbers)

1 = execute permissions

2 = write permissions

4 = read permissions

Example:

// everything for owner, read for owner's group

chmod("test.txt",0740);

User names and passwords in PHP can be encrypted using md5 function.

MD5 function calculates the md5 hash of a string. It is basically used for encryption. It is also used for digital signature applications, where a large file must be "compressed" in a secure manner.

Example:

Md5($str);

Crypt() function can also be used to encrypt a string,. It used MD5, DES or blow fish algorithms for encryption.

Syntax:

Crypt(str, salt)

Salt is an optional parameter used to increase the number of characters encoded, to make the encoding more secure

A PHP Session persist the user information to be used later. For example, user name, password, shopping item details. The session is temporary and will be removed soon after the user has left the web site. The session can be persisted for long term usage on databases like MySQL. Each session is identified by a unique Id number for every visitor. The first step to use PHP session is to start the session. The starting session must precede the operations like HTML or the other.

The statement session_start() starts the PHP session and registers the user’s information on the server.

The function setcookie() is used to define a cookie that is to be sent along with HTTP headers. The cookie must be sent prior to any output from the script as is the protocol restriction. After setting the cookies, they can be used when the next page is loaded by using $_COOKIE or $HTTP_COOKIE_VARS arrays.

Both GET and POST are used to collect data from a form. However, when security is desired $_POST should be used. When the $_ POST variable is used, all variables used are NOT displayed in the URL. Also, they have no restrictions to the length of the variables. GET should be used when the interaction with the form is more like a question. For e.g. firing a query etc. POST should be used more often when the interaction is more like an order or the interaction changes the state of the resource.

POST example:

<form action="sample.php" method="post">

Name: <input type="text" name="name" />

Age: <input type="text" name="age" />

<input type="submit" />

</form>

On clicking submit the URL resembles to: https://www.mysamplesite.com/sample.php

The sample.php file can be used for catching the form data using $_POST 

Hello <?php echo $_POST["name"]; ?>.<br />

You are <?php echo $_POST["age"]; ?> years old!

GET EXAMPLE

<form action="sample.php" method="get">

Name: <input type="text" name="name" />

Age: <input type="text" name="age" />

<input type="submit" />

</form>

On clicking submit the URL resembles to : https://www.mysamplesite.com/sample.php?name=jim&age=37

The sample.php file can be used for catching the form data using $_GET 

Hello <?php echo $_GET["name"]; ?>.<br />

You are <?php echo $_GET["age"]; ?> years old!

PHP supports single level inheritance.

Inheriting a class would mean creating a new class with all functionality of the existing class in addition to some more. The created class is called as a subclass of the parent class. Parent is a keyword which we use to access members of a parent class. Inheritance is usually defined by using the keyword “Extend”. $this is used a reference to the calling object. Inheritance avoids redundancy of code.

Example:

Class employee extends manager : Here Employee is a subclass of manager.

Echo $this->name can be used to echo variable name of the parent class.

Generating random passwords in PHP can be done in multiple ways depending on how much security the application demands:-

Md5 function can be passed one parameter as uniqid() function which in turn generates a random number. Passing the parameter as TRUE in uniqid() adds additional uniqueness.

<?php
   $passwd = md5(uniqid(rand(), true));
   Echo $passwd;
?>