super global variable
What is super global variable ?
- Super global were introduced to PHP of version 4.0 and higher.
- These are specially-defined array variables in PHP that make it easy for you to get information about a request or its context.
- Superglobals are built-in variables that are always available in all scopes
- The superglobals are available throughout your script. These variables can be accessed from any function, class or any file without doing any special task such as declaring any global variable etc.
- They are mainly used to store and get information from one page to another etc in an application.
- the PHP Superglobals represent data coming from URLs, HTML forms, cookies, sessions, and the Web server itself.
Types of super global variables:
The PHP super global variables are:
- 1. $GLOBALS
- 2. $_SERVER
- 3. $_REQUEST
- 4. $_POST
- 5. $_GET
- 6. $_FILES
- 7. $_ENV
- 8. $_COOKIE
- 9. $_SESSION
1.PHP $GLOBALS:
- $GLOBALS is a PHP super global variable which is used to access global variables from anywhere in the PHP script means also from within functions or methods.
- PHP stores all global variables in an array called $GLOBALS[index]. Where the index holds the name of the variable.
Example:
<?php
$x = 75;
$y = 25;
function substraction() {
$GLOBALS['z'] = $GLOBALS['x']
- $GLOBALS['y'];
}
substraction ();
echo $z;
?>
Output:
50
Example2:
<?php
$x = 300;
$y = 200;
function addition (){
$GLOBALS['z'] = $GLOBALS['x'] +
$GLOBALS['y'];
}
addition();
echo $z;
?>
Output:
500
In the above code two global variables are
declared $x and $y which are assigned some value to them.
Then a function addition() is defined to
add the values of $x and $y and store in another
variable $z defined in the GLOBAL array.
2.$_SERVER:
- It is a PHP super global variable that stores the information about headers, paths and script locations.
- Some of these elements are used to get the information from the superglobal variable $_SERVER.
Example:
<?php
echo $_SERVER['PHP_SELF'];
echo "<br>";
echo $_SERVER['SERVER_NAME'];
echo "<br>";
echo $_SERVER['HTTP_HOST'];
echo "<br>";
echo $_SERVER['HTTP_USER_AGENT'];
echo "<br>";
echo $_SERVER['HTTP_REFERER'];
echo "<br>";
echo $_SERVER['SCRIPT_NAME'];
echo "<br>"
?>
In the above code we used the $_SERVER elements to get some information. We get the current file name which is worked on using ‘PHP_SELF’ element. Then we get server name used currently using ‘SERVER_NAME’ element. And then we get the host name through ‘HTTP_HOST’.
Elements
that can use inside $_SERVER:
|
Sl.No. |
Elements |
Description |
|
1 |
$_SERVER['PHP_SELF'] |
Returns the filename of the currently executing
script |
|
2 |
$_SERVER['GATEWAY_INTERFACE'] |
Returns the version of the
Common Gateway Interface (CGI) the server is using |
|
3 |
$_SERVER['SERVER_ADDR'] |
Returns the IP address of the
host server |
|
4 |
$_SERVER['SERVER_NAME'] |
Returns the name of the host
server |
|
5 |
$_SERVER['SERVER_SOFTWARE'] |
Returns the server
identification string (such as Apache/2.2.24) |
|
6 |
$_SERVER['SERVER_PROTOCOL'] |
Returns the name and revision of
the information protocol (such as HTTP/1.1) |
|
7 |
$_SERVER['REQUEST_METHOD'] |
Returns the request method
used to access the page (such as POST) |
|
8 |
$_SERVER['REQUEST_TIME'] |
Returns the timestamp of the
start of the request (such as 1377687496) |
|
9 |
$_SERVER['QUERY_STRING'] |
Returns the query string if
the page is accessed via a query string |
|
10 |
$_SERVER['HTTP_ACCEPT'] |
Returns the Accept header from
the current request |
|
11 |
$_SERVER['HTTP_HOST'] |
Returns the Host header from the
current request |
|
12 |
$_SERVER['HTTP_ACCEPT_CHARSET'] |
Returns the Accept_Charset
header from the current request (such as utf-8,ISO-8859-1) |
|
13 |
$_SERVER['HTTP_REFERER'] |
Returns the complete URL of
the current page (not reliable because not all user-agents support it) |
|
14 |
$_SERVER['HTTPS'] |
Is the script queried through a
secure HTTP protocol |
|
15 |
$_SERVER['REMOTE_ADDR'] |
Returns the IP address from
where the user is viewing the current page |
|
16 |
$_SERVER['REMOTE_HOST'] |
Returns the Host name from where
the user is viewing the current page |
|
17 |
$_SERVER['REMOTE_PORT'] |
Returns the port being used on
the user's machine to communicate with the web server |
|
18 |
$_SERVER['SCRIPT_FILENAME'] |
Returns the absolute pathname of
the currently executing script |
|
19 |
$_SERVER[SERVER_ADMIN'] |
Returns the value given to the
SERVER_ADMIN directive in the web server configuration file (if your script
runs on a virtual host, it will be the value defined for that virtual host)
(such as someone@w3schools.com) |
|
20 |
$_SERVER[SERVER_PORT'] |
Returns the port on the server
machine being used by the web server for communication (such as 80) |
|
21 |
$_SERVER[SERVER_SIGNATURE'] |
Returns the server version and
virtual host name which are added to server-generated pages |
|
22 |
$_SERVER[PATH_TRANSLATED'] |
Returns the file system based
path to the current script |
|
23 |
$_SERVER[SCRIPT_NAME'] |
Returns the path of the
current script |
|
24 |
$_SERVER[SCRIPT_URI'] |
Returns the URI of the current page |
3.PHP $_REQUEST
PHP $_REQUEST is a superglobal variable which
is used to collect the data after submitting a HTML form.But $_REQUEST is
not used mostly.
Example:
<!DOCTYPE html>
<html>
<body>
<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
NAME: <input type="text" name="fname">
<button type="submit">SUBMIT</button>
</form>
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
$name = htmlspecialchars($_REQUEST['fname']);
if(empty($name)){
echo "Name is empty";
} else {
echo $name;
}
}
?>
</body>
</html>
In the above code we have created a form that takes the name as input from the user and prints it’s name on clicking of submit button. We transport the data accepted in the form to the same page using $_SERVER[‘PHP_SELF’] element as specified in the action attribute, because we manipulate the data in the same page using the PHP code.
The data is
retrieved using the $_REQUEST super global array variable.
4.PHP $_POST
- PHP $_POST is widely used to collect form data after submitting an HTML form with method="post". $_POST is also widely used to pass variables.
- It is a super global variable used to collect data from the HTML form after submitting the HTML form. When form uses method post to transfer data, the data is not visible in the query string, security levels are maintained in this method.
Example:
<html>
<body>
<form method="post" action="<?php echo $_SERVER['PHP_SELF'];?>">
Name: <input type="text" name="fname">
<input type="submit">
</form>
<?php
if ($_SERVER["REQUEST_METHOD"] == "POST") {
// collect value of input field
$name = $_POST['fname'];
if (empty($name)) {
echo "Name is
empty";
} else {
echo $name;
}
}
?>
</body>
</html>
Here in this example below shows a form with an
input field and a submit button. When a user submits the data by clicking on
"Submit", the form data is sent to the file specified in the action
attribute of the <form> tag. In this example, we point to the file itself
for processing form data. If you wish to use another PHP file to process form
data, replace that with the filename of your choice. Then, we can use the super
global variable $_POST to collect the value of the input field.
5.PHP $_GET
- PHP $_GET can also be used to collect form data after submitting an HTML form with method="get".
- When form uses method get to transfer data, the data is visible in the query string, therefore the values are not hidden. $_GET super global array variable stores the values that come in the URL.
Example:
<html>
<body>
<?php
echo "Study " . $_GET['subject'] . " at
" . $_GET['web'];
?>
</body>
</html>
5.PHP $_FILES
- PHP $_FILES is also a super global variable .
- This variable is an associate double dimension array and keeps all the information related to uploaded file. So if the value assigned to the input's name attribute in uploading form was file, then PHP would create following five variables −
· $_FILES['file']['name'] −
the actual name of the uploaded file.
· $_FILES['file']['size'] −
the size in bytes of the uploaded file.
· $_FILES['file']['type'] −
the MIME type of the uploaded file.
· $_FILES['file']['error'] −
the error code associated with this file upload.
Example:
<?php
$currentDir = getcwd();
$uploadDirectory = "/uploads/";
$errors = []; // Store all foreseen and unforseen errors here
$fileExtensions = ['jpeg','jpg','png']; // Get all the file extensions
$fileName = $_FILES['myfile']['name'];
$fileSize = $_FILES['myfile']['size'];
$fileTmpName = $_FILES['myfile']['tmp_name'];
$fileType = $_FILES['myfile']['type'];
$fileExtension = strtolower(end(explode('.',$fileName)));
$uploadPath = $currentDir . $uploadDirectory . basename($fileName);
if (isset($_POST['submit']))
{
if (! in_array($fileExtension,$fileExtensions)) {
$errors[] = "This file extension
is not allowed. Please upload a JPEG or PNG file";
}
if ($fileSize > 2000000) {
$errors[] = "This file is more than 2MB. Sorry, it has to be less
than or equal to 2MB";
}
if (empty($errors)) {
$didUpload = move_uploaded_file($fileTmpName, $uploadPath);
if ($didUpload) {
echo "The
file " . basename($fileName) . " has been
uploaded";
} else {
echo "An
error occurred somewhere. Try again or contact the admin";
}
} else {
foreach ($errors as $error)
{
echo $error
. "These are the errors" . "\n";
}
}
}
?>
Look at the code above.
1.
· $fileName
= $_FILES['myfile']['name']; This refers to the real name of the
uploaded file.
2.
· $fileSize
= $_FILES['myfile']['size']; This refers to the size of the file.
3.
· $fileTmpName
= $_FILES['myfile']['tmp_name']; This is the temporary uploaded file
that resides in the tmp/ directory of the web server.
4.
· $fileType
= $_FILES['myfile']['type']; This refers to the type of the file. Is
it a jpeg or png or mp3 file?
5.
· $fileExtension
= strtolower(end(explode('.',$fileName))); This grabs the extension of
the file.
6.
· $uploadPath
= $currentDir . $uploadDirectory . basename($fileName); This is the
path where the files will be stored on the server. We grabbed the current
working directory.
7. $_ENV:
$_ENV is a
superglobal that contains environment variables.
Environment variables are provided by the shell under which PHP is running, so
they may vary according to different shells.
To display an environment variable you can also
use getenv()
Example:
<?php
echo "<pre>";
print_r($_ENV);
echo "</pre>";
/* ****environment variables on a mac machine****
Array
(
[SHELL] => ***
[TMPDIR] => ***
[Apple_PubSub_Socket_Render] => ***
[USER] => ***
[SSH_AUTH_SOCK] => ***
[__CF_USER_TEXT_ENCODING] => ***
[PATH] => ***
[PWD] => ***
[HOME] => ***
[SHLVL] => ***
[DYLD_LIBRARY_PATH] => ***
[LOGNAME] => ***
[__LAUNCHD_FD] => ***
[DISPLAY] => ***
[_] => ***
[COMMAND_MODE] => ***
)
*/
?>
Example:
<?php
Echo ‘My username is’.$_ENV[“USER”].’!’;
?>
8.$_COOKIE Variable
$_COOKIE is used to create cookie.
Example:
<?php
$cookie_name=”user”;
$cookie_value=”Lopa”;
Setcookie($cookie_name,$ cookie_value,time()
+(86400 * 30),”/”);
?>
<html>
<body>
<?php
If(!isset($_COOKIE[$cookie_name]))
{
echo “Cookie name ‘ “.$cookie_name.” ’is not set
!”;
}
else
{
echo “Cookie name ‘ “.$cookie_name.” ’is set !”;
echo “Value is : “.$_COOKIE[$cookie_name];
}
?>
</body>
</html>
9.$_SESSION Variable
- $_SESSION Variable is used to create session. It is a type of super global variable which is used to set the session variables.
- Session variables contain data about the current user, and all pages contained in a single web application .
Example:
<?php
Session_start();
?>
<html>
<body>
<?php
$_SESSION[“favcolor”]=”green”;
$_SESSION[“favanimal”]=”cat”;
echo “Session variable are set “;
?>
</body>
</html>
In addition to that the $_SESSION variable holds
all of the session data declared in your files: