Extracting a parameter from a URL in WordPress - php

Question

I am trying to pass a parameter to a WordPress site using a URL - for instance:
www.fioriapts.com/?ppc=1 will be the URL.
I am intending to write a function in the functions.php file but the mechanics of how to extract a parameter in WordPress is beyond me. How can it be done?
I am finding a lot of examples on how to add a parameter to a URL using the function add_query_arg() but have found nothing on how to extract a parameter.

Answer 1

Why not just use the WordPress get_query_var() function? WordPress Code Reference
// Test if the query exists at the URL
if ( get_query_var('ppc') ) {
// If so echo the value
echo get_query_var('ppc');
}
Since get_query_var can only access query parameters available to WP_Query, in order to access a custom query var like 'ppc', you will also need to register this query variable within your plugin or functions.php by adding an action during initialization:
add_action('init','add_get_val');
function add_get_val() {
global $wp;
$wp->add_query_var('ppc');
}
Or by adding a hook to the query_vars filter:
function add_query_vars_filter( $vars ){
$vars[] = "ppc";
return $vars;
}
add_filter( 'query_vars', 'add_query_vars_filter' );

Answer 2

When passing parameters through the URL you're able to retrieve the values as GET parameters.
Use this:
$variable = $_GET['param_name'];
//Or as you have it
$ppc = $_GET['ppc'];
It is safer to check for the variable first though:
if (isset($_GET['ppc'])) {
$ppc = $_GET['ppc'];
} else {
//Handle the case where there is no parameter
}
Here's a bit of reading on GET/POST params you should look at: http://php.net/manual/en/reserved.variables.get.php
EDIT: I see this answer still gets a lot of traffic years after making it. Please read comments attached to this answer, especially input from #emc who details a WordPress function which accomplishes this goal securely.

Answer 3

You can try this function
/**
* Gets the request parameter.
*
* #param string $key The query parameter
* #param string $default The default value to return if not found
*
* #return string The request parameter.
*/
function get_request_parameter( $key, $default = '' ) {
// If not request set
if ( ! isset( $_REQUEST[ $key ] ) || empty( $_REQUEST[ $key ] ) ) {
return $default;
}
// Set so process it
return strip_tags( (string) wp_unslash( $_REQUEST[ $key ] ) );
}
Here is what is happening in the function
Here three things are happening.
First we check if the request key is present or not. If not, then just return a default value.
If it is set, then we first remove slashes by doing wp_unslash. Read here why it is better than stripslashes_deep.
Then we sanitize the value by doing a simple strip_tags. If you expect rich text from parameter, then run it through wp_kses or similar functions.
All of this information plus more info on the thinking behind the function can be found on this link https://www.intechgrity.com/correct-way-get-url-parameter-values-wordpress/

Answer 4

In the call back function, use the $request parameter
$parameters = $request->get_params();
echo $parameters['ppc'];