Extracting a parameter from a URL in WordPress

4 comments

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' );
   

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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.

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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/

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4. In the call back function, use the $request parameter

   $parameters = $request->get_params();
   echo $parameters['ppc'];
   

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