$_GET contains the keys / values that are passed to your script in the URL.

If you have the following URL :

http://www.example.com/test.php?a=10&b=plop

Then $_GET will contain :

array
  'a' => string '10' (length=2)
  'b' => string 'plop' (length=4)

Of course, as $_GET is not read-only, you could also set some values from your PHP code, if needed :

$_GET['my_value'] = 'test';

But this doesn't seem like good practice, as $_GET is supposed to contain data from the URL requested by the client.

$_GET is not a function or language construct—it's just a variable (an array). Try:

<?php
echo $_GET['link'];

In particular, it's a superglobal: a built-in variable that's populated by PHP and is available in all scopes (you can use it from inside a function without the global keyword).

Since the variable might not exist, you could (and should) ensure your code does not trigger notices with:

<?php
if (isset($_GET['link'])) {
    echo $_GET['link'];
} else {
    // Fallback behaviour goes here
}

Alternatively, if you want to skip manual index checks and maybe add further validations you can use the filter extension:

<?php
echo filter_input(INPUT_GET, 'link', FILTER_SANITIZE_URL);

Last but not least, you can use the null coalescing operator (available since PHP/7.0) to handle missing parameters:

echo $_GET['link'] ?? 'Fallback value';

Hi there, You haven't specified the $product_id variable on your page.php. Therefore, your conditional will always return false. However what you can do instead is use a conditional to see if $_GET['id'] has been set, and if so return the product id into a variable. Here's how you'd do it: php However there is a case where the product ID could actually be an empty string. So let's add another part to our conditional to check that the product ID is not an empty string. php Now, you can actually improve this code even further. Let's assume that you only want to return a page with the product ID if and only if the product ID entered is a valid number, and if it exists in the page. Else, just go to the main products page. You can do this with your header function like this: ```php GET['id'] : 0); // This is a ternary operator, something very powerful i think you should get to know :) echo $productid; ?> ``` This will mean that a product has to be specified with a number in order to assign the product id. If not, it will redirect the user to pages.php and assign the ID to 0.

1) Use $_GET if you know that data is coming via URL parameter

if (isset($_GET['htmlVariable'] && $_GET['htmlVariable'] != '') {
  $htmlVariable = $_GET['htmlVariable'];
}

2) Use $_POST if you know that data is coming via HTTP POST method

if (isset($_POST['htmlVariable'] && $_POST['htmlVariable'] != '') {
    $htmlVariable = $_GET['htmlVariable'];
}

3) If you don't know use $_REQUEST

if (isset($_REQUEST['htmlVariable'] && $_REQUEST['htmlVariable'] != '') {
    $htmlVariable = $_GET['htmlVariable'];
}

get_query_var() only works with the Core WP_Query object:

Retrieve public query variable in the WP_Query class of the global $wp_query object.

https://codex.wordpress.org/Function_Reference/get_query_var

Your mistake is a simple PHP one: The key is foo, not bar.

$foo = $_GET['foo'];
echo $foo;

But please do not echo user supplied data to the page without sanitizing it.

Which PHP binary are you using? The CLI or CGI? I suspect you need a CGI version of the binary for PHP to properly handle accept the environment variables and POST data if you pass that.

The php-cgi binary implements the CGI interface, which allows you to pass parameters on the command line:

php-cgi -f index.php left=1058 right=1067 class=A language=English

Which end up in $_GET:

Array
(
    [left] => 1058
    [right] => 1067
    [class] => A
    [language] => English
)

You may want to read up on how CGI works so you can implement that in your web server.

Ref: RFC3875

You can, but the variable in your last include will overwrite the variable in your first one:

myfile.php

$var = 'test';

mysecondfile.php

$var = 'tester';

test.php

include 'myfile.php';
echo $var;

include 'mysecondfile.php';
echo $var;

Output:

test

tester

I suggest using different variable names.

You can print the PHP variable into your javascript while your page is created.

<script type="text/javascript">
    var MyJSStringVar = "<?php Print($MyPHPStringVar); ?>";
    var MyJSNumVar = <?php Print($MyPHPNumVar); ?>;
</script>

Of course this is for simple variables and not objects.