The basics of php for engeneering students

UNIT-2
PHP
J Vishnu Priyanka
Assistant Professor
Dept of CSE
RGUKT-SRIKAKULAM.

Contents:
 Server Programming: PHP basics: PHP Syntax,
 Variables
 Constants
 Data Types
 Strings
 Conditional and Control Structures.
 PHP GET and POST.
 PHP Advanced: include files, File system
 Parsing directories
 File upload and download
 Sessions
 Form handling
 JSON Parsing

Server Programming: PHP basics
 The PHP Hypertext Pre-processor (PHP) is a programming language
that allows web developers to create dynamic content that interacts with
databases.
 PHP is basically used for developing web based software applications.
 Rasmus Lerdorf unleashed the first version of PHP way back in 1994
 PHP is a recursive acronym for "PHP: Hypertext Pre-processor".
 PHP is a server side scripting language that is embedded in HTML.
 It is used to manage dynamic content, databases, session tracking, even
build entire e-commerce sites.
 It is integrated with a number of popular databases, including MySQL,
PostgreSQL, Oracle, Sybase, Informix, and Microsoft SQL Server
 PHP supports a large number of major protocols such as POP3, IMAP

COMMON USES OF PHP:
 PHP performs system functions, i.e. from files on a system it can create,
open, read, write, and close them.
 PHP can handle forms, i.e. gather data from files, save data to a file, thru
email you can send data, return data to the user.
 You add, delete, modify elements within your database thru PHP.
 Access cookies variables and set cookies.
 Using PHP, you can restrict users to access some pages of your website.
 It can encrypt data.

A PHP script is executed on the server, and the plain HTML result is sent
back to the browser.
Basic PHP Syntax
 A PHP script can be placed anywhere in the document.
A PHP script starts with <?php and ends with ?>:
 <?php
// PHP code goes here
?>
 The default file extension for PHP files is ".php".
 A PHP file normally contains HTML tags, and some PHP scripting code.
 Below, we have an example of a simple PHP file, with a PHP script that
uses a built-in PHP function "echo" to output the text "Hello World!" on a
web page:

Example:
<!DOCTYPE html>
<html>
<body>
<h1>My first PHP page</h1>
<?php
echo "Hello World!";
?>
</body>
</html>
Note: PHP statements end with a semicolon (;).

PHP CASE SENSITIVITY
 In PHP, keywords (e.g. if, else, while, echo, etc.), classes, functions, and
user-defined functions are not case-sensitive.
 In the example below, all three echo statements below are equal and legal:
Example:
<!DOCTYPE html>
<html>
<body>
<?php
ECHO "Hello World!<br>";
echo "Hello World!<br>";
EcHo "Hello World!<br>";
?>
</body>
</html>

However; all variable names are case-sensitive!
Look at the example below;
only the first statement will display the value of the $color variable! This is
because $color, $COLOR, and $coLOR are treated as three different
variables:
Example:
<!DOCTYPE html>
<html>
<body>
<?php
$color = "red";
echo "My car is " . $color . "<br>";
echo "My house is " . $COLOR . "<br>";
echo "My boat is " . $coLOR . "<br>";
?>
</body>
</html>

Comments in PHP
PHP supports several ways of commenting:
Example
 Syntax for single-line comments:
 <!DOCTYPE html>
<html>
<body>
<?php
// This is a single-line comment
# This is also a single-line comment
?>
</body>
</html>

Example
 Syntax for multiple-line comments:
 <!DOCTYPE html>
<html>
<body>
<?php
/*
This is a multiple-lines comment block
that spans over multiple
lines
*/
?>
</body>
</html>

Example
 Using comments to leave out parts of the code:
 <!DOCTYPE html>
<html>
<body>
<?php
// You can also use comments to leave out parts of a code line
$x = 5 /* + 15 */ + 5;
echo $x;
?>
</body>
</html>

PHP VARIABLES
Creating (Declaring) PHP Variables
 In PHP, a variable starts with the $ sign, followed by the name of the
variable:
Example
<?php
$txt = "Hello world!";
$x = 5;
$y = 10.5;
?>

PHP Variables
 A variable can have a short name (like x and y) or a more descriptive
name (age, carname, total_volume).
Rules for PHP variables:
 A variable starts with the $ sign, followed by the name of the variable
 A variable name must start with a letter or the underscore character
 A variable name cannot start with a number
 A variable name can only contain alpha-numeric characters and
underscores (A-z, 0-9, and _ )
 Variable names are case-sensitive ($age and $AGE are two different
variables)

Output Variables
 The PHP echo statement is often used to output data to the screen.
 The following example will show how to output text and a variable:
Example
<?php
$txt = “Srikakulam";
echo “RGUKT $txt!";
?>
The following example will output the sum of two variables:
Example
<?php
$x = 5;
$y = 4;
echo $x + $y;
?>

PHP Constants
 A constant is an identifier (name) for a simple value. The value cannot be
changed during the script.
 A valid constant name starts with a letter or underscore (no $ sign before
the constant name).
Create a PHP Constant
 To create a constant, use the define() function.
Syntax
 define(name, value, case-insensitive)
Parameters:
 name: Specifies the name of the constant
 value: Specifies the value of the constant
 case-insensitive: Specifies whether the constant name should be case-
insensitive. Default is false

Example
Create a constant with a case-sensitive name:
<?php
define("GREETING", "Welcome to RGUKT Srikakulam!");
echo GREETING;
?>
Example
Create a constant with a case-insensitive name:
 <?php
define("GREETING", "Welcome to RGUKT Srikakulam!", true);
echo greeting;
?>

PHP Constant Arrays
In PHP7, you can create an Array constant using the define() function.
Example
Create an Array constant:
<?php
define("cars", [
"Alfa Romeo",
"BMW",
"Toyota"
]);
echo cars[0];
?>

Constants are Global
 Constants are automatically global and can be used across the entire
script.
Example
 This example uses a constant inside a function, even if it is defined outside
the function:
<?php
define("GREETING", "Welcome toRGUKT Srikakulam!");
function myTest() {
echo GREETING;
}
myTest();
?>

PHP Data Types
Variables can store data of different types, and different data types can do
different things. PHP supports the following data types:
 String
 Integer
 Float (floating point numbers - also called double)
 Boolean
 Array
 Object
 NULL
 Resource

PHP String
 A string is a sequence of characters, like "Hello world!".
 A string can be any text inside quotes. You can use single or double
quotes:
Example
<?php
$x = "Hello world!";
$y = 'Hello world!';
echo $x;
echo "<br>";
echo $y;
?>

PHP Integer
Rules for integers:
 An integer must have at least one digit
 An integer can be either positive or negative
 Integers can be specified in: decimal (base 10), hexadecimal (base 16),
octal (base 8), or binary (base 2) notation
In the following example $x is an integer. The PHP var_dump() function
returns the data type and value:
Example
 <?php
$x = 5985;
var_dump($x);
?>

PHP Float
 A float (floating point number) is a number with a decimal point or a
number in exponential form.
 In the following example $x is a float. The PHP var_dump() function
Example
<?php
$x = 10.365;
var_dump($x);
?>
PHP Boolean
A Boolean represents two possible states: TRUE or FALSE.
 $x = true;
$y = false;
 Booleans are often used in conditional testing.

PHP Array
 An array stores multiple values in one single variable.
 In the following example $cars is an array. The PHP var_dump() function
Example
<!DOCTYPE html>
<html>
<body>
<?php
$depts = array("Cse","civil","Mech");
var_dump($depts);
?>
</body>
</html>

PHP Objects:
When the individual objects are created, they inherit all the properties and
behaviors from the class, but each object will have different values for the
properties.
 Let's assume we have a class named Car. A Car can have properties like
model, color, etc. We can define variables like $model, $color, and so on,
to hold the values of these properties.
 When the individual objects (Volvo, BMW, Toyota, etc.) are created, they
inherit all the properties and behaviors from the class, but each object will
have different values for the properties.
 If you create a __construct() function, PHP will automatically call this
function when you create an object from a class.

Example:
<!DOCTYPE html>
<html>
<body>
<?php
class Car {
public $color;
public $model;
public function __construct($color, $model) {
$this->color = $color;
$this->model = $model;
}
public function message() {
return "My car is a " . $this->color . " " . $this->model . "!";
}
}

$myCar = new Car("black", "Volvo");
echo $myCar -> message();
echo "<br>";
$myCar = new Car("red", "Toyota");
echo $myCar -> message();
?>
</body>
</html>

PHP NULL Value
 Null is a special data type which can have only one value: NULL.
 A variable of data type NULL is a variable that has no value assigned to it.
Example:
<!DOCTYPE html>
<html>
<body>
<?php
$x = "Hello world!";
$x = null;
var_dump($x);
?>
</body>
</html>

PHP Resource
 The special resource type is not an actual data type. It is the storing of a
reference to functions and resources external to PHP.
 A common example of using the resource data type is a database call.
PHP String Functions
strlen() - Return the Length of a String
The PHP strlen() function returns the length of a string.
Example
Return the length of the string "Hello world!":
<?php
echo strlen("Hello world!"); // outputs 12
?>

str_word_count() - Count Words in a String
The PHP str_word_count() function counts the number of words in a string.
Example
Count the number of word in the string "Hello world!":
<?php
echo str_word_count("Hello world!"); // outputs 2
?>
strrev() - Reverse a String
The PHP strrev() function reverses a string.
Example
Reverse the string "Hello world!":
<?php
echo strrev("Hello world!"); // outputs !dlrow olleH
?>

strpos() - Search For a Text Within a String
The PHP strpos() function searches for a specific text within a string. If a
match is found, the function returns the character position of the first match.
If no match is found, it will return FALSE.
Example
Search for the text "world" in the string "Hello world!":
<?php
echo strpos("Hello world!", "world"); // outputs 6
?>
str_replace() - Replace Text Within a String
The PHP str_replace() function replaces some characters with some other
characters in a string.
Example
Replace the text "world" with "Dolly":
<?php
echo str_replace("world", "Dolly", "Hello world!"); // outputs Hello
Dolly!
?>

PHP Conditional Statements
In PHP we have the following conditional statements:
 if statement - executes some code if one condition is true
 if...else statement - executes some code if a condition is true and
another code if that condition is false
 if...elseif...else statement - executes different codes for more than two
conditions
 switch statement - selects one of many blocks of code to be executed
PHP - The if Statement
The if statement executes some code if one condition is true.
Syntax
if (condition) {
code to be executed if condition is true;
}

Example:
<?php
$t = date("H");
if ($t < "20") {
echo "Have a good day!";
}
?>
PHP - The if...else Statement
The if...else statement executes some code if a condition is true and another
code if that condition is false.
Syntax
if (condition) {
code to be executed if condition is true;
} else {
code to be executed if condition is false;
}

Example:
<?php
$t = date("H");
if ($t < "20") {
} else {
echo "Have a good night!";
}
?>
PHP - The if...elseif...else Statement
The if...elseif...else statement executes different codes for more than two
conditions.
Syntax
if (condition) {
code to be executed if this condition is true;
} elseif (condition) {
code to be executed if first condition is false and this condition is true;
} else {
code to be executed if all conditions are false;
}

<?php
$t = date("H");
if ($t < "10") {
echo "Have a good morning!";
} elseif ($t < "20") {
} else {
echo "Have a good night!";
}
?>

The PHP switch Statement
Use the switch statement to select one of many blocks of code to be
executed.
Syntax
switch (n) {
case label1:
code to be executed if n=label1;
break;
case label2:
break;
case label3:
break;
...
default:
code to be executed if n is different from all labels;
}

<?php
$favcolor = "red";
switch ($favcolor) {
case "red":
echo "Your favorite color is red!";
break;
case "blue":
echo "Your favorite color is blue!";
break;
case "green":
echo "Your favorite color is green!";
break;
default:
echo "Your favorite color is neither red, blue, nor green!";
}
?>

PHP Loops
 Loops are used to execute the same block of code again and again, as
long as a certain condition is true.
 In PHP, we have the following loop types:
 while - loops through a block of code as long as the specified condition is
true
 do...while - loops through a block of code once, and then repeats the loop
as long as the specified condition is true
 for - loops through a block of code a specified number of times
 foreach - loops through a block of code for each element in an array
The PHP while Loop
The while loop executes a block of code as long as the specified condition is
true.
Syntax
while (condition is true) {
code to be executed;
}

Example:
The example below displays the numbers from 1 to 5:
<?php
$x = 1;
while($x <= 5) {
echo "The number is: $x <br>";
$x++;
}
?>
Example Explained
 $x = 1; - Initialize the loop counter ($x), and set the start value to 1
 $x <= 5 - Continue the loop as long as $x is less than or equal to 5
 $x++; - Increase the loop counter value by 1 for each iteration

The PHP do...while Loop
 The do...while loop will always execute the block of code once, it will then
check the condition, and repeat the loop while the specified condition is
true.
Syntax
do {
} while (condition is true);
Example:
<?php
$x = 1;
do {
$x++;
} while ($x <= 5);
?>

The PHP for Loop
The for loop is used when you know in advance how many times the script
should run.
Syntax
for (init counter; test counter; increment counter) {
code to be executed for each iteration;
}
Parameters:
init counter: Initialize the loop counter value
test counter: Evaluated for each loop iteration. If it evaluates to TRUE, the
loop continues. If it evaluates to FALSE, the loop ends.
increment counter: Increases the loop counter value
Example:
<?php
for ($x = 0; $x <= 10; $x++) {
}
?>

The PHP foreach Loop
The foreach loop works only on arrays, and is used to loop through each
key/value pair in an array.
Syntax
foreach ($array as $value) {
}
For every loop iteration, the value of the current array element is assigned to
$value and the array pointer is moved by one, until it reaches the last array
element.
Example
 <?php
$colors = array("red", "green", "blue", "yellow");
foreach ($colors as $value) {
echo "$value <br>";
}
?>

PHP GET and POST
There are two ways the browser client can send information to the web
server.
 The GET Method
 The POST Method
 Before the browser sends the information, it encodes it using a scheme
called URL encoding. In this scheme, name/value pairs are joined with
equal signs and different pairs are separated by the ampersand.
name1=value1&name2=value2&name3=value3
The GET Method
 The GET method sends the encoded user information appended to the
page request. The page and the encoded information are separated by
the ? character.
http://www.test.com/index.htm?name1=value1&name2=value2

 The GET method produces a long string that appears in your server logs, in
the browser's Location: box.
 The GET method is restricted to send upto 1024 characters only.
 Never use GET method if you have password or other sensitive information
to be sent to the server.
 GET can't be used to send binary data, like images or word documents, to
the server.
 The data sent by GET method can be accessed using QUERY_STRING
environment variable.
 The PHP provides $_GET associative array to access all the sent
information using GET method.

Example:
<?php
if( $_GET["name"] || $_GET["age"] ) {
echo "Welcome ". $_GET['name']. "<br />";
echo "You are ". $_GET['age']. " years old.";
exit();
}
?>
<html>
<body>
<form action = "<?php $_PHP_SELF ?>" method = "GET">
Name: <input type = "text" name = "name" />
Age: <input type = "text" name = "age" />
<input type = "submit" />
</form>
</body>
</html>

The POST Method
 The POST method transfers information via HTTP headers. The
information is encoded as described in case of GET method and put into a
header called QUERY_STRING.
 The POST method does not have any restriction on data size to be sent.
 The POST method can be used to send ASCII as well as binary data.
 The data sent by POST method goes through HTTP header so security
depends on HTTP protocol. By using Secure HTTP you can make sure
that your information is secure.
 The PHP provides $_POST associative array to access all the sent
information using POST method.
Example:
<?php
if( $_POST["name"] || $_POST["age"] ) {
if (preg_match("/[^A-Za-z'-]/",$_POST['name'] )) {
die ("invalid name and name should be alpha");
}

echo "Welcome ". $_POST['name']. "<br />";
echo "You are ". $_POST['age']. " years old.";
exit();
}
?>
<html>
<body>
<form action = "<?php $_PHP_SELF ?>" method = "POST">
</form>
</body>
</html>

The $_REQUEST variable
 The PHP $_REQUEST variable contains the contents of both $_GET,
$_POST, and $_COOKIE
 The PHP $_REQUEST variable can be used to get the result from form
data sent with both the GET and POST methods.
Example:
<?php
if( $_REQUEST["name"] || $_REQUEST["age"] ) {
echo "Welcome ". $_REQUEST['name']. "<br />";
echo "You are ". $_REQUEST['age']. " years old.";
exit();
}
?>
<html>
<body>
<form action = "<?php $_PHP_SELF ?>" method = "POST">

</form>
</body>
</html>

PHP - A Simple HTML Form
The example below displays a simple HTML form with two input fields and a
submit button:
Example
<html>
<body>
<form action="welcome.php" method="post">
Name: <input type="text" name="name"><br>
E-mail: <input type="text" name="email"><br>
<input type="submit">
</form>
</body>
</html>
 When the user fills out the form above and clicks the submit button, the
form data is sent for processing to a PHP file named "welcome.php". The
form data is sent with the HTTP POST method.

 To display the submitted data you could simply echo all the variables. The
"welcome.php" looks like this:
<html>
<body>
Welcome <?php echo $_POST["name"]; ?><br>
Your email address is: <?php echo $_POST["email"]; ?>
</body>
</html>
The output could be something like this:
Welcome John
Your email address is john.doe@example.com
https://tryphp.w3schools.com/showphp.php?filename=demo_form_post

PHP - File Inclusion
You can include the content of a PHP file into another PHP file before the
server executes it. There are two PHP functions which can be used to
included one PHP file into another PHP file.
 The include() Function
 The require() Function
The include() Function
 The include() function takes all the text in a specified file and copies it into
the file that uses the include function. If there is any problem in loading a
file then the include() function generates a warning but the script will
continue execution.
Syntax
 include 'filename';
or
require 'filename';

Example
Assume we have a standard footer file called "footer.php", that looks like this:
 <?php
echo "<p>Copyright © 1999-" . date("Y") . " Rgukt.com</p>";
?>
To include the footer file in a page, use the include statement:
<html>
<body>
<h1>Welcome to my home page!</h1>
<p>Some text.</p>
<p>Some more text.</p>
<?php include 'footer.php';?>
</body>
</html>

Example
Assume we have a standard menu file called "menu.php":
 <?php
echo '<a href="/default.asp">Home</a> -
<a href="/html/default.asp">HTML Tutorial</a> -
<a href="/css/default.asp">CSS Tutorial</a> -
<a href="/js/default.asp">JavaScript Tutorial</a> -
<a href="default.asp">PHP Tutorial</a>';
?>
<html>
<body>
<div class="menu">
<?php include 'menu.php';?>
</div>
<p>Some text.</p>
<p>Some more text.</p>
</body>
</html>

Example
Assume we have a file called “cars.php", with some variables defined:
<?php
$color='red';
$car='BMW';
?>
Then, if we include the "vars.php" file, the variables can be used in the calling
file:
Example
<html>
<body>
<?php include 'vars.php';
echo "I have a $color $car.";
?>
</body>
</html>

PHP require() Function: The require() function in PHP is basically used to
include the contents/code/data of one PHP file to another PHP file. During
this process if there are any kind of errors then this require() function will
pop up a warning along with a fatal error and it will immediately stop the
execution of the script.
PHP include vs. require
 The require statement is also used to include a file into the PHP code.
 However, there is one big difference between include and require; when a
file is included with the include statement and PHP cannot find it, the
script will continue to execute:
<html>
<body>
<?php include 'noFileExists.php';
?>
</body>
</html>

Using the require statement, the echo statement will not be executed
because the script execution dies after the require statement returned a fatal
error:
<html>
<body>
<?php require 'noFileExists.php';
?>
</body>
</html>

PHP File Handling
PHP has several functions for creating, reading, uploading, and editing files.
PHP readfile() Function
 The readfile() function reads a file and writes it to the output buffer.
 Assume we have a text file called "webdictionary.txt", stored on the
server, that looks like this:
 AJAX = Asynchronous JavaScript and XML
CSS = Cascading Style Sheets
HTML = Hyper Text Markup Language
PHP = PHP Hypertext Preprocessor
SQL = Structured Query Language
SVG = Scalable Vector Graphics
XML = EXtensible Markup Language

 The PHP code to read the file and write it to the output buffer is as follows
(the readfile() function returns the number of bytes read on success):
Example
 <?php
echo readfile("webdictionary.txt");
?>
 Opening a file
 Reading a file
 Writing a file
 Closing a file
Opening and Closing Files
 The PHP fopen() function is used to open a file. It requires two arguments
stating first the file name and then mode in which to operate.
 Files modes can be specified as one of the six options in this table.

Sr.No Mode & Purpose
1 r
Opens the file for reading only.
Places the file pointer at the beginning of the file.
2 r+
Opens the file for reading and writing.
3 w
Opens the file for writing only.
and truncates the file to zero length. If files does not
exist then it attempts to create a file.

4 w+
Opens the file for reading and writing only.
and truncates the file to zero length. If files does not
exist then it attempts to create a file.
5 a
Opens the file for writing only.
Places the file pointer at the end of the file.
If files does not exist then it attempts to create a file.
6 a+
Opens the file for reading and writing only.
Places the file pointer at the end of the file.
If files does not exist then it attempts to create a file.

Reading a file
 Once a file is opened using fopen() function it can be read with a function
called fread(). This function requires two arguments. These must be the
file pointer and the length of the file expressed in bytes.
 The files length can be found using the filesize() function which takes the
file name as its argument and returns the size of the file expressed in
bytes.
So here are the steps required to read a file with PHP.
 Open a file using fopen() function.
 Get the file's length using filesize() function.
 Read the file's content using fread() function.
 Close the file with fclose() function.

<html>
<head>
<title>Reading a file using PHP</title>
</head>
<body>
<?php
$filename = "tmp.txt";
$file = fopen( $filename, "r" );
if( $file == false ) {
echo ( "Error in opening file" );
exit();
}
$filesize = filesize( $filename );
$filetext = fread( $file, $filesize );
fclose( $file );
echo ( "File size : $filesize bytes" );
echo ( "<pre>$filetext</pre>" ); </body></html>

The basics of php for engeneering students

Writing a file
 A new file can be written or text can be appended to an existing file using
the PHP fwrite() function. This function requires two arguments specifying
a file pointer and the string of data that is to be written
<?php
$filename = "/home/user/guest/newfile.txt";
$file = fopen( $filename, "w" );
if( $file == false )
{
echo ( "Error in opening new file" );
exit();
}
fwrite( $file, "This is a simple testn" );
fclose( $file );?>

<html>
<head>
<title>Writing a file using PHP</title>
</head>
<body>
<?php
$filename = "newfile.txt";
$file = fopen( $filename, "r" );
if( $file == false ) {
echo ( "Error in opening file" );
exit();
}
$filesize = filesize( $filename );
$filetext = fread( $file, $filesize );
fclose( $file );
echo ( "File size : $filesize bytes" );
echo ( "$filetext" );
echo("file name: $filename");
?>
</body></html>

Parsing directories
PHP scandir( ) Function
 The scandir() function in PHP is an inbuilt function that is used to return
an array of files and directories of the specified directory.
 The scandir() function lists the files and directories which are present
inside a specified path.
 The directory, stream behavior, and sorting_order of the files and
directories are passed as a parameter to the scandir() function and it
returns an array of filenames on success, or false on failure.
Syntax:
scandir(directory, sorting_order, context);
Parameters: The scandir() function in PHP accepts 3 parameters that are
listed below:
 directory: It is a mandatory parameter that specifies the path.

 sorting_order: It is an optional parameter that specifies the sorting order.
Alphabetically ascending order (0) is the default sort order. It can be set to
SCANDIR_SORT_DESCENDING or 1 to sort in alphabetically descending
order, or SCANDIR_SORT_NONE to return the result unsorted.
 context: It is an optional parameter that specifies the behavior of the
stream.
Return Value: It returns an array of filenames on success, or false on failure.
Errors And Exceptions:
 The scandir() function throws an error of level E_WARNING if the directory
specified is not a directory.
 Doing a recursive scandir will on a directory that has many files will likely
either slow down your application or cause a high rise in RAM
consumption due to the large size of the generated array.

<?php
$dir = "/images/";
// Sort in ascending order - this is default
$a = scandir($dir);
// Sort in descending order
$b = scandir($dir,1);
print_r($a);
print_r($b);
?>

Create The HTML Form
 Next, create an HTML form that allow users to choose the image file they
want to upload:
<!DOCTYPE html>
<html>
<body>
<form action="upload.php" method="post" enctype="multipart/form-data">
Select image to upload:
<input type="file" name="fileToUpload" id="fileToUpload">
<input type="submit" value="Upload Image" name="submit">
</form>
</body>
</html>

Some rules to follow for the HTML form above:
 Make sure that the form uses method="post"
 The form also needs the following attribute: enctype="multipart/form-
data". It specifies which content-type to use when submitting the form
Without the requirements above, the file upload will not work.
Other things to notice:
 The type="file" attribute of the <input> tag shows the input field as a file-
select control, with a "Browse" button next to the input control
 The form above sends data to a file called "upload.php", which we will
create next.
Create The Upload File PHP Script
The "upload.php" file contains the code for uploading a file:

<?php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType
= strtolower(pathinfo($target_file,PATHINFO_EXTENSION));
// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
$check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
if($check !== false) {
echo "File is an image - " . $check["mime"] . ".";
$uploadOk = 1;
} else {
echo "File is not an image.";
$uploadOk = 0;
}
}
?>

PHP script explained:
 $target_dir = "uploads/" - specifies the directory where the file is going to
be placed
 $target_file specifies the path of the file to be uploaded
 $uploadOk=1 is not used yet (will be used later)
 $imageFileType holds the file extension of the file (in lower case)
 Next, check if the image file is an actual image or a fake image
You will need to create a new directory called "uploads" in the directory
where "upload.php" file resides. The uploaded files will be saved there.
Check if File Already Exists
First, we will check if the file already exists in the "uploads" folder. If it does,
an error message is displayed, and $uploadOk is set to 0:
 // Check if file already exists
if (file_exists($target_file)) {
echo "Sorry, file already exists.";
$uploadOk = 0;
}

Limit File Size
 The file input field in our HTML form above is named "fileToUpload".
 Now, we want to check the size of the file. If the file is larger than 500KB,
an error message is displayed, and $uploadOk is set to 0:
 // Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
echo "Sorry, your file is too large.";
$uploadOk = 0;
}
Limit File Type
 The code below only allows users to upload JPG, JPEG, PNG, and GIF
files. All other file types gives an error message before setting $uploadOk
to 0:
 // Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" &&
$imageFileType != "jpeg"
&& $imageFileType != "gif" ) {
echo "Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
$uploadOk = 0;
}

Complete Upload File PHP Script
<?php
$target_dir = "uploads/";
$target_file = $target_dir . basename($_FILES["fileToUpload"]["name"]);
$uploadOk = 1;
$imageFileType
= strtolower(pathinfo($target_file,PATHINFO_EXTENSION));
// Check if image file is a actual image or fake image
if(isset($_POST["submit"])) {
$check = getimagesize($_FILES["fileToUpload"]["tmp_name"]);
if($check !== false) {
echo "File is an image - " . $check["mime"] . ".";
$uploadOk = 1;
} else {
echo "File is not an image.";
$uploadOk = 0;
}
}

// Check if file already exists
if (file_exists($target_file)) {
echo "Sorry, file already exists.";
$uploadOk = 0;
}
// Check file size
if ($_FILES["fileToUpload"]["size"] > 500000) {
echo "Sorry, your file is too large.";
$uploadOk = 0;
}
// Allow certain file formats
if($imageFileType != "jpg" && $imageFileType != "png" && $imageFileType
!= "jpeg"
&& $imageFileType != "gif" ) {
echo "Sorry, only JPG, JPEG, PNG & GIF files are allowed.";
$uploadOk = 0;
}

// Check if $uploadOk is set to 0 by an error
if ($uploadOk == 0) {
echo "Sorry, your file was not uploaded.";
// if everything is ok, try to upload file
} else {
if (move_uploaded_file($_FILES["fileToUpload"]["tmp_name"], $target_file))
{
echo "The file ". htmlspecialchars(
basename( $_FILES["fileToUpload"]["name"])). " has been uploaded.";
} else {
echo "Sorry, there was an error uploading your file.";
}
}
?>

File Download
Image-gallery.php
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<title>Simple Image Gallery</title>
<style type="text/css">
.img-box{
display: inline-block;
text-align: center;
margin: 0 15px;
}
</style>
</head>
<body>

<?php
// Array containing sample image file names
$images=array("kites.jpg","balloons.jpg");
// Loop through array to create image gallery
foreach($images as $image){
echo '<div class="img-box">';
echo '<img src="images/'. $image . '"width="200" alt="' .
pathinfo($image, PATHINFO_FILENAME).'">';
echo '<p><a href="download.php?file=' . urlencode($image)
. '">Download</a></p>';
echo '<div>';
}
?>
</body>
</html>

Download.php
<?php
if(isset($_REQUEST["file"])){
// Get parameters
$file = urldecode($_REQUEST["file"]); //Decode URL-encodestring
$filepath = "images/" . $file;
// Process download
if(file_exists($filepath)) {
header('Content-Description: File Transfer');
header('Content-Type: application/octet-stream');
header('Content-Disposition: File Transfer');
header('Expires: 0');
header('Cache-Control: must-revalidate');
header('Pragma: public');
header('content-Length: ' . filesize($filepath));
flush(); //flush system output buffer
readfile($filepath);
exit;
}
}
?>

PHP Sessions
Session variables hold information about one single user, and are available
to all pages in
Start a PHP Session
 A session is started with the session_start() function.
 Session variables are set with the PHP global variable: $_SESSION.
 Now, let's create a new page called "demo_session1.php". In this page,
we start a new PHP session and set some session variables:
one application.
<?php
// Start the session
session_start();
?>
<!DOCTYPE html>
<html>
<body>

<?php
// Set session variables
$_SESSION["favcolor"] = "green";
$_SESSION["favanimal"] = "cat";
echo "Session variables are set.";
?>
</body>
</html>
Get PHP Session Variable Values
 Next, we create another page called "demo_session2.php". And from this
page it access the session information we set on the first page
("demo_session1.php").
 Notice that session variables are not passed individually to each new
page, instead they are retrieved from the session we open at the
beginning of each page (session_start()).
 Also notice that all session variable values are stored in the global
$_SESSION variable:

<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>
<?php
// Echo session variables that were set on previous page
echo "Favorite color is " . $_SESSION["favcolor"] . ".<br>";
echo "Favorite animal is " . $_SESSION["favanimal"] . ".";
?>
</body>
</html>

Modify a PHP Session Variable
To change a session variable, just overwrite it:
Example
 <?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>
<?php
// to change a session variable, just overwrite it
$_SESSION["favcolor"] = "yellow";
print_r($_SESSION);
?>
</body>
</html>

Destroy a PHP Session
To remove all global session variables and destroy the session,
use session_unset() and session_destroy():
Example
<?php
session_start();
?>
<!DOCTYPE html>
<html>
<body>
<?php
// remove all session variables
session_unset();
// destroy the session
session_destroy();
?>
</body>
</html>

JSON
 JSON stands for JavaScript Object Notation, and is a syntax for storing
and exchanging data.
 Since the JSON format is a text-based format, it can easily be sent to and
from a server, and used as a data format by any programming language.
PHP and JSON
PHP has some built-in functions to handle JSON.
First, we will look at the following two functions:
 json_encode()
 json_decode()
PHP - json_encode()
 The json_encode() function is used to encode a value to JSON format.
Example
 This example shows how to encode an associative array into a JSON
object:

<!DOCTYPE html>
<html>
<body>
<?php
$age = array("Peter"=>35, "Ben"=>37, "Joe"=>43);
echo json_encode($age);
?>
</body>
</html>
Example
 This example shows how to encode an indexed array into a JSON array:

<!DOCTYPE html>
<html>
<body>
<?php
$cars = array("Volvo", "BMW", "Toyota");
echo json_encode($cars);
?>
</body>
</html>
PHP - json_decode()
 The json_decode() function is used to decode a JSON object into a PHP
object or an associative array.
Example
 This example decodes JSON data into a PHP object:

<!DOCTYPE html>
<html>
<body>
<?php
$jsonobj = '{"Peter":35,"Ben":37,"Joe":43}';
var_dump(json_decode($jsonobj));
?>
</body>
</html>

JSON.parse()
 A common use of JSON is to exchange data to/from a web server.
 When receiving data from a web server, the data is always a string.
 Parse the data with JSON.parse(), and the data becomes a JavaScript
object.
Example - Parsing JSON
 Text from a web server:
 '{"name":"John", "age":30, "city":"New York"}'
Use the JavaScript function JSON.parse() to convert text into a JavaScript
object:
 const obj = JSON.parse('{"name":"John", "age":30, "city":"New
York"}');

<!DOCTYPE html>
<html>
<body>
<h2>Creating an Object from a JSON String</h2>
<p id="demo"></p>
<script>
const txt = '{"name":"John", "age":30, "city":"New York"}'
const obj = JSON.parse(txt);
document.getElementById("demo").innerHTML = obj.name + ", " + obj.age;
</script>
</body>
</html>

Exceptions
 Parsing Dates
 Date objects are not allowed in JSON.
 If you need to include a date, write it as a string.
<!DOCTYPE html>
<html>
<body>
<h2>Convert a string into a date object.</h2>
<p id="demo"></p>
<script>
const text = '{"name":"John", "birth":"1986-12-14", "city":"New York"}';
const obj = JSON.parse(text);
obj.birth = new Date(obj.birth);
document.getElementById("demo").innerHTML = obj.name + ", " + obj.birth;
</script>
</body>
</html>

Thank you
For queries
(vishnupriya.javvadi@rguktsklm.ac.in)

The basics of php for engeneering students

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