Technical Interview Questions & Answers: PHP Tutorial

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Difference between PHP Validating filters and PHP Sanitizing filters

Validating filters:

Are used to validate user input
Strict format rules (like URL or E-Mail validating)
Returns the expected type on success or FALSE on failure

Sanitizing filters:

Are used to allow or disallow specified characters in a string
No data format rules
Always return the string

PHP Filter

A PHP filter is used to validate and filter data coming from insecure sources.

To test, validate and filter user input or custom data is an important part of any web application.

The PHP filter extension is designed to make data filtering easier and quicker.

PHP code -Create a Custom Exception Class

<?php
class customException extends Exception
{
public function errorMessage()
{
//error message
$errorMsg = 'Error on line '.$this->getLine().' in '.$this->getFile()
.': '.$this->getMessage().' is not a valid E-Mail address';
return $errorMsg;
}
}

$email = "someone@example...com";

try
{
//check if
if(filter_var($email, FILTER_VALIDATE_EMAIL) === FALSE)
{
//throw exception if email is not valid
throw new customException($email);
}
}

catch (customException $e)
{
//display custom message
echo $e->errorMessage();
}
?>

PHP Error Handling -Try, throw and catch

Proper exception code should include:

Try - A function using an exception should be in a "try" block. If the exception does not trigger, the code will continue as normal. However if the exception triggers, an exception is "thrown"
Throw - This is how you trigger an exception. Each "throw" must have at least one "catch"
Catch - A "catch" block retrieves an exception and creates an object containing the exception information

Lets try to trigger an exception with valid code:

<?php
//create function with an exception
function checkNum($number)
{
if($number>1)
{
throw new Exception("Value must be 1 or below");
}
return true;
}

//trigger exception in a "try" block
try
{
checkNum(2);
//If the exception is thrown, this text will not be shown
echo 'If you see this, the number is 1 or below';
}

//catch exception
catch(Exception $e)
{
echo 'Message: ' .$e->getMessage();
}
?>

How to send mail in PHP

Code for send mail in PHP

<?php

$to = "someone@example.com";
$subject = "Test mail";
$message = "Hello! This is a simple email message.";
$from = "someonelse@example.com";
$headers = "From: $from";
mail($to,$subject,$message,$headers);
echo "Mail Sent.";

?>

PHP mail() Function

The PHP mail() function is used to send emails from inside a script.

Syntax

mail(to,subject,message,headers,parameters)

to Required. Specifies the receiver / receivers of the email
subject Required. Specifies the subject of the email. Note: This parameter cannot contain any newline characters
message Required. Defines the message to be sent. Each line should be separated with a LF (\n). Lines should not exceed 70 characters
headers Optional. Specifies additional headers, like From, Cc, and Bcc. The additional headers should be separated with a CRLF (\r\n)
parameters Optional. Specifies an additional parameter to the sendmail program

How to destroy a Session in PHP

You can use the unset() or the session_destroy() function.

The unset() function is used to free the specified session variable:

<?php
unset($_SESSION['views']);
?>

You can also completely destroy the session by calling the session_destroy() function:

<?php
session_destroy();
?>

How to store a Session Variable in PHP

The correct way to store and retrieve session variables is to use the PHP $_SESSION variable:

Code for store a session in pHP

<?php
session_start();
// store session data
$_SESSION['views']=1;
?>

<html>
<body>

<?php
//retrieve session data
echo "Pageviews=". $_SESSION['views'];
?>

</body>
</html>

Output:

Pageviews=1

How to start a PHP Session

Start a PHP Session

Before you can store user information in your PHP session, you must first start up the session.

Note: The session_start() function must appear BEFORE the <html> tag:

<?php session_start(); ?>

<html>
<body>

</body>
</html>

In PHP, How to Delete a Cookie?

Deleting a cookie you should assure that the expiration date is in the past.

example:

<?php
// set the expiration date to one hour ago
setcookie("user", "", time()-3600);
?>

In PHP, How to get a Cookie Value?

PHP isset() function to find out if a cookie has been set:

<html>
<body>

<?php
if (isset($_COOKIE["user"]))
echo "Welcome " . $_COOKIE["user"] . "! ";
else
echo "Welcome guest! ";
?>

</body>
</html>

In PHP, How to Retrieve a Cookie Value?

PHP $_COOKIE variable is used to retrieve a cookie value.

In the example below, we retrieve the value of the cookie named "user" and display it on a page:

<?php
// Print a cookie
echo $_COOKIE["user"];

// A way to view all cookies
print_r($_COOKIE);
?>

PHP setcookie() function

The setcookie() function is used to set a cookie.

Note: The setcookie() function must appear BEFORE the <html> tag.

Syntax
setcookie(name, value, expire, path, domain);

In PHP how to Create a Cookie?

The setcookie() function is used to set a cookie.

Note: The setcookie() function must appear BEFORE the <html> tag.
Syntax

setcookie(name, value, expire, path, domain);

Example

In the example below, we will create a cookie named "user" and assign the value "Alex Porter" to it. We also specify that the cookie should expire after one hour:

<?php
setcookie("user", "Alex Porter", time()+3600);
?>

<html>
<body>

</body>
</html>

PHP - Saving the Uploaded File

The examples above create a temporary copy of the uploaded files in
the PHP temp folder on the server.

The temporary copied files disappears when the script ends. To store
the uploaded file we need to copy it to a different location:

<?php
if ((($_FILES["file"]["type"] == "image/gif")
|| ($_FILES["file"]["type"] == "image/jpeg")
|| ($_FILES["file"]["type"] == "image/pjpeg"))
&& ($_FILES["file"]["size"] < 20000))
{
if ($_FILES["file"]["error"] > 0)
{
echo "Return Code: " . $_FILES["file"]["error"] . " ";
}
else
{
echo "Upload: " . $_FILES["file"]["name"] . " ";
echo "Type: " . $_FILES["file"]["type"] . " ";
echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb ";
echo "Temp file: " . $_FILES["file"]["tmp_name"] . " ";

if (file_exists("upload/" . $_FILES["file"]["name"]))
{
echo $_FILES["file"]["name"] . " already exists. ";
}
else
{
move_uploaded_file($_FILES["file"]["tmp_name"],
"upload/" . $_FILES["file"]["name"]);
echo "Stored in: " . "upload/" . $_FILES["file"]["name"];
}
}
}
else
{
echo "Invalid file";
}
?>

PHP Upload Script

<?php
if ($_FILES["file"]["error"] > 0)
{
 echo "Error: " . $_FILES["file"]["error"] . " ";
}
else
{
 echo "Upload: " . $_FILES["file"]["name"] . " ";
 echo "Type: " . $_FILES["file"]["type"] . " ";
 echo "Size: " . ($_FILES["file"]["size"] / 1024) . " Kb ";
 echo "Stored in: " . $_FILES["file"]["tmp_name"];
}
?>

By using the global PHP $_FILES array you can upload files from a client computer to the remote server.

The first parameter is the form's input name and the second index can be either "name", "type", "size", "tmp_name" or "error". Like this:

$_FILES["file"]["name"] - the name of the uploaded file
$_FILES["file"]["type"] - the type of the uploaded file
$_FILES["file"]["size"] - the size in bytes of the uploaded file
$_FILES["file"]["tmp_name"] - the name of the temporary copy of the file stored on the server
$_FILES["file"]["error"] - the error code resulting from the file upload

This is a very simple way of uploading files. For security reasons, you should add restrictions on what the user is allowed to upload.

PHP fgetc() function

fgetc() function : Reading a File Character by Character

The fgetc() function is used to read a single character from a file.

Note: After a call to this function the file pointer moves to the next character.

Example

The example below reads a file character by character, until the end of file is reached:

<?php
$file=fopen("welcome.txt","r") or exit("Unable to open file!");
while (!feof($file))
{
echo fgetc($file);
}
fclose($file);
?>

PHP fgets() function

Reading a File Line by Line

The fgets() function is used to read a single line from a file.

Note: After a call to this function the file pointer has moved to the next line.

Example

The example below reads a file line by line, until the end of file is reached:

<?php
$file = fopen("welcome.txt", "r") or exit("Unable to open file!");
//Output a line of the file until the end is reached
while(!feof($file))
{
echo fgets($file). " ";
}
fclose($file);
?>

PHP feof() function

Check End-of-file
The feof() function checks if the "end-of-file" (EOF) has been reached.

The feof() function is useful for looping through data of unknown length.

if (feof($file)) echo "End of file";

PHP fclose() Function

The fclose() function is used to close an open file:

<?php
$file = fopen("test.txt","r");

//some code to be executed

fclose($file);
?>