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

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.

A HTML form should be build before uploading the file. The following HTML code is used for selecting the file that is to be uploaded. The type attribute of input must be “file”.

<form enctype="multipart/form-data" action="uploader.php" method="POST">

<input type="hidden" name="MAX_FILE_SIZE" value="100000" />

Choose a file to upload: <input name="uploadedfile" type="file" /><br />

<input type="submit" value="Upload File" />

</form>

At the time of executing uploader.php, the uploaded file will be stored in a temporary storage are on the webserver. An associative array $_FILES['uploadedfile']['name'] is used for uploading. The ‘name’ is the original file that is to be uploaded. Another associative array $_FILES['uploadedfile']['tmp_name'] is used for placing the uploaded file in a temporary location on the server and the file should be empty and should exist with the tmp_name.

The following code snippet is used for uploading the file.

$target_path = "uploads/"; // the target location of the file

$target_path = $target_path . basename( $_FILES['uploadedfile']['name']);

if(move_uploaded_file($_FILES['uploadedfile']['tmp_name'], $target_path)) 

{

       echo "The file ". basename( $_FILES['uploadedfile']['name']). 

        " has been uploaded";

}

else

{

      echo “There was an error while uploading the file”;

}

The function move_uploaded_file()is used to place the source file into the destination folder, which resides on the server.

If the uploading is successful, the message “The file filename has been uploaded. Otherwise the error message “There was an error while uploading the file” would be displayed.

To pass the information into the script from outside, help can be taken from the PHP CLI (Command line interface) method. Suppose addition of two numbers has to be passed to PHP then it can be passed like this on the command line:

php add.php 2 3

Here the script name is add.php, and 2 and 3 are the numbers that has to be added by the script. These numbers are available inside the script in an array called $argv. This array contains all the information on the command line; the statement is stored as follows:

$argv[0]=add.php

$argv[1]=2

$argv[2]=3

So, $argv always contains at least one element — the script name.

Then, in your script, you can use the following statements:

$sum = $argv[1] + $argv[2];

echo $sum;

$argc is a variable that stores the numbers of elements in $argv. $argc is equal to at least 1, which is saved for the name of the script. Example is $argc=3 using the above statements.

$_SERVER and $_ENV arrays contain different information. The information depends on the server and operating system being used. Most of the information can be seen of an array for a particular server and operating system. The syntax is as follows:

foreach($_SERVER as $key =>$value)

{ echo “Key=$key, Value=$value\n”; }

Super global arrays are the built in arrays that can be used anywhere. They are also called as auto-global as they can be used inside a function as well. The arrays with the longs names such as $HTTP_SERVER_VARS, must be made global before they can be used in an array. This $HTTP_SERVER_VARS check your php.ini setting for long arrays.