What are the differences in die() and exit() in PHP?

There's no difference - they are the same.

PHP Manual for exit:

Note: This language construct is equivalent to die().

PHP Manual for die:

This language construct is equivalent to exit().

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As stated before, these two commands produce the same parser token.

BUT

There is a small difference, and that is how long it takes the parser to return the token.

I haven't studied the PHP parser, but if it's a long list of functions starting with "d", and a shorter list starting with "e", then there must be a time penalty looking up the function name for functions starting with "e". And there may be other differences due to how the whole function name are checked.

I doubt it will be measurable unless you have a "perfect" environment dedicated to parsing php, and a lot of requests with different parameters. But there must be a difference, after all, PHP is an interpreted language.

---

As all the other correct answers says, die and exit are identical/aliases.

Although I have a personal convention that when I want to end the execution of a script when it is expected and desired, I use exit;. And when I need to end the execution due to some problems (couldn't connect to db, can't write to file etc.), I use die("Something went wrong."); to "kill" the script.

When I use exit:

header( "Location: http://www.example.com/" ); /* Redirect browser */
/* Make sure that code below does not get executed when we redirect. */
exit; // I would like to end now.

When I use die:

$data = file_get_contents( "file.txt" );
if( $data === false ) {
    die( "Failure." ); // I don't want to end, but I can't continue. Die, script! Die!
}
do_something_important( $data );

This way, when I see exit at some point in my code, I know that at this point I want to exit because the logic ends here. When I see die, I know that I'd like to continue execution, but I can't or shouldn't due to error in previous execution.

Of course this only works when working on a project alone. When there is more people nobody will prevent them to use die or exit where it does not fit my conventions...

---

When using command line,

 die("Error");

Will print to "Error" to STDOUT and exit with error code 0.

if you want to exit with error code 1, you have to:

  fwrite(STDERR, "Error");
    exit(1);

It could be useful while executing php scripts from command line or shell scripts and you want to see if the script terminated with a non zero exit code. 

---

The result of exit() function and die() function is allways same. But as explained in alias manual page (http://php.net/manual/en/aliases.php), it says that die() function calls exit function. I think it is hard coded like below:

function die($msg){
  exit($msg);
}

This is not a performance issue for small, medium and large projects but if project has billions multiply billions multiply billions processes, this happens very important performance optimization state.

But very most of people don't thinks this is a problem, because if you have that much processes, you must think more problem than if a function is master or alias.

But, exact answer is that; allways master function is more faster than alias.

Finally; Alias manual page says that, you may no longer use die. It is only an alias, and it is deprecated.

It is usually a bad idea to use these kind of aliases, as they may be bound to obsolescence or renaming, which will lead to unportable script. This list is provided to help those who want to upgrade their old scripts to newer syntax.

PHP: Redirect Web Page to Another Web Page: PHP Redirect Script

How to redirect from one page to another ? It is a common question from beginner developers in PHP. You can easily transferred to the new page without having to click a link to continue by using a default power of PHP which is also useful for search engines.,
 
header();
PHP Redirect Script

You can easily redirect using following code:

   
/*
|-----------------
| Redirect
|------------------
*/

header ( "Location: https://thiscode4u.blogspot.com" );

/*
|-----------------
| Stop Execution
|------------------
*/

exit;
Stop Execution

It is very important to stop the script after sending header command. “exit” will ensure to stop the execution of next code or algorithm before the completion of header command.

/*
|-----------------
| Stop Execution
|------------------
*/

exit;
Very Important

Remember that header() must be called before any actual output is sent, either by normal HTML tags, blank lines in a file, or from PHP. It is a very common error to read code with include(), or require(), functions, or another file access function, and have spaces or empty lines that are output before header() is called. The same problem exists when using a single PHP/HTML file.

   
/*
|-----------------
| Bad Code Example
| Some output before header()
|------------------
*/

echo "Some Output: Hello World!";

/*
|-----------------
| Redirect
|------------------
*/

header ( "Location: https://thiscode4u.blogspot.com" );

/*
|-----------------
| Stop Execution
|------------------
*/

exit;

PHP: Web concepts in PHP

This session demonstrates how PHP can provide dynamic content according to browser type, randomly generated numbers or User Input. It also demonstrated how the client borwser can be redirected.

Identifying Browser & Platform

PHP creates some useful environment variables that can be seen in the phpinfo.php page that was used to setup the PHP environment.
One of the environemnt variables set by PHP is HTTP_USER_AGENT which identifies the user's browser and operating system.
PHP provides a function getenv() to access the value of all the environment variables. The information contained in the HTTP_USER_AGENT environment variable can be used to create dynamic content appropriate to the borwser.
Following example demonstrates how you can identify a client borwser and operating system.
NOTE: The function preg_match()is discussed in PHP Regular expression session.

<html> <body> <?php $viewer = getenv( "HTTP_USER_AGENT" ); $browser = "An unidentified browser"; if( preg_match( "/MSIE/i", "$viewer" ) ) { $browser = "Internet Explorer"; } else if( preg_match( "/Netscape/i", "$viewer" ) ) { $browser = "Netscape"; } else if( preg_match( "/Mozilla/i", "$viewer" ) ) { $browser = "Mozilla"; } $platform = "An unidentified OS!"; if( preg_match( "/Windows/i", "$viewer" ) ) { $platform = "Windows!"; } else if ( preg_match( "/Linux/i", "$viewer" ) ) { $platform = "Linux!"; } echo("You are using $browser on $platform"); ?> </body> </html>

This is producing following result on my machine. This result may be different for your computer depnding on what you are using.

You are using Mozilla! on Windows!

Display Images Randomly

The PHP rand() function is used to generate a random number.i This function can generate numbers with-in a given range. The random number generator should be seeded to prevent a regular pattern of numbers being generated. This is achieved using the srand() function that specifiies the seed number as its argument.
Following example demonstrates how you can display different image each time out of four images:

<html> <body> <?php srand( microtime() * 1000000 ); $num = rand( 1, 4 ); switch( $num ) { case 1: $image_file = "/home/images/alfa.jpg"; break; case 2: $image_file = "/home/images/ferrari.jpg"; break; case 3: $image_file = "/home/images/jaguar.jpg"; break; case 4: $image_file = "/home/images/porsche.jpg"; break; } echo "Random Image : <img src=$image_file />"; ?> </body> </html>

Using HTML Forms

The most important thing to notice when dealing with HTML forms and PHP is that any form element in an HTML page will automatically be available to your PHP scripts.
Try out following example by putting the source code in test.php script.

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

• The PHP default variable $_PHP_SELF is used for the PHP script name and when you click "submit" button then same PHP script will be called and will produce following result:
• The method = "POST" is used to post user data to the server script. There are two methods of posting data to the server script which are discussed in PHP GET & POST chapter.

Browser Redirection

The PHP header() function supplies raw HTTP headers to the browser and can be used to redirect it to another location. The redirection script should be at the very top of the page to prevent any other part of the page from loading.
The target is specified by the Location: header as the argument to the header() function. After calling this function the exit() function can be used to halt parsing of rest of the code.
Following example demonstrates how you can redirect a borwser request to another web page. Try out this example by puttingthe source code in test.php script.

<?php if( $_POST["location"] ) { $location = $_POST["location"]; header( "Location:$location" ); exit(); } ?> <html> <body> <p>Choose a site to visit :</p> <form action="<?php $_PHP_SELF ?>" method="POST"> <select name="location"> <option value="http://w3c.org"> World Wise Web Consortium </option> <option value="http://www.google.com"> Google Search Page </option> </select> <input type="submit" /> </form> </body> </html>

Displaying "File Download" Dialog Box

Sometime it is desired that you want to give option where a use will click a link and it will pop up a "File Download" box to the user in stead of displaying actual content. This is very easy and will be achived through HTTP header.
The HTTP header will be different from the actual header where we send Content-Type as text/html\n\n. In this case content type will be application/octet-stream and actual file name will be concatenated alongwith it.
For example,if you want make a FileName file downloadable from a given link then its syntax will be as follows.

#!/usr/bin/perl

# HTTP Header
print "Content-Type:application/octet-stream; name=\"FileName\"\r\n";
print "Content-Disposition: attachment; filename=\"FileName\"\r\n\n";

# Actual File Content
open( FILE, "<FileName" );
while(read(FILE, $buffer, 100) )
{
   print("$buffer");
}