Action Hook Inside Wordpress Plugin Shortcode

Question

I'm developing a Wordpress plugin and I'm having trouble getting $_POST data using an action inside my shortcode. The form I'm parsing is on a page that I've added my shortcode to.

Here's what I've got:

function wpd_post_parse() {

$string = 'wp hook: ' . var_dump($_POST) . "\r\n";

//$string = 'wp hook: first name: ' . $_POST["first_name"] . "\r\n";
//$string .= 'wp hook: last name: ' . $_POST["last_name"] . "\r\n";
//$string .= 'wp hook: email: ' . $_POST["email"] . "\r\n";

$fileName = dirname(__FILE__) . '/log.txt';     

file_put_contents($fileName, $string, FILE_APPEND | LOCK_EX);
//file_put_contents($fileName, $string, FILE_APPEND);

/*
if (!empty($_POST)){

    $string = 'wp hook: ' . var_dump($_POST) . "\r\n";

    $fileName = dirname(__FILE__) . '/log.txt';     

    file_put_contents($fileName, $string, FILE_APPEND | LOCK_EX);
    //file_put_contents($fileName, $string, FILE_APPEND);

}else{

    $string = 'wp hook: POST empty' . "\r\n";

    $fileName = dirname(__FILE__) . '/log.txt';     

    file_put_contents($fileName, $string, FILE_APPEND | LOCK_EX);
}
*/

}

function mgc_init(){

   $htmlStr = 'Hello World!' . "\r\n";

   $fileName = dirname(__FILE__) . '/log.txt';

   file_put_contents($fileName, $htmlStr, FILE_APPEND | LOCK_EX);
  //file_put_contents($fileName, $htmlStr, FILE_APPEND);  

  //Add hook to capture $_POST data
  add_action( 'parse_request', 'wpd_post_parse' );

}

add_shortcode('mgc','mgc_init'); //put this shortcode [mgc] on page in Wordpress 

UPDATE: Thanks for your help so far. I'm trying to get a $_POST value (first name) on form submit but the value isn't inside $_POST["first_name"]. All that gets printed to the file is "wp hook: first name: " Here's how the code looks now:

//Capture the $_POST data
function wpd_post_parse() {

  //$string = 'wp hook: ' . var_dump($_POST) . "\r\n";

  $string = 'wp hook: first name: ' . $_POST["first_name"] . "\r\n";
  //$string .= 'wp hook: last name: ' . $_POST["last_name"] . "\r\n";
  //$string .= 'wp hook: email: ' . $_POST["email"] . "\r\n";

  $fileName = dirname(__FILE__) . '/log.txt';       

  file_put_contents($fileName, $string, FILE_APPEND | LOCK_EX);
  //file_put_contents($fileName, $string, FILE_APPEND);

  /*
  if (!empty($_POST)){

    $string = 'wp hook: ' . var_dump($_POST) . "\r\n";

    $fileName = dirname(__FILE__) . '/log.txt';     

    file_put_contents($fileName, $string, FILE_APPEND | LOCK_EX);
    //file_put_contents($fileName, $string, FILE_APPEND);

  }else{

    $string = 'wp hook: POST empty' . "\r\n";

    $fileName = dirname(__FILE__) . '/log.txt';     

    file_put_contents($fileName, $string, FILE_APPEND | LOCK_EX);
}
*/

//exit;
}

function mgc_init(){


  $htmlStr = 'Hello World!' . "\r\n";

  $fileName = dirname(__FILE__) . '/log.txt';

  file_put_contents($fileName, $htmlStr, FILE_APPEND | LOCK_EX);
  //file_put_contents($fileName, $htmlStr, FILE_APPEND);    

  do_action( 'wpd_post_parse' );

}

add_shortcode('mgc','mgc_init'); //put this shortcode [mgc] page in Wordpress 

add_action( 'parse_request', 'wpd_post_parse' );

Answer 1

It's not entirely clear what your ultimate goal is, but a simple way to catch a form submission is to hook init and check if something is set:

function wpd_check_post_vars(){
    if( isset( $_POST['first_name'] ) ){
        // do something
    }
}
add_action( 'init', 'wpd_check_post_vars' );

There's no connection here between the action and your Shortcode, it's not really necessary. An important point to remember is that actions don't persist beyond the request they're added on. If you add_action after its corresponding do_action is triggered, nothing will happen.

You should also probably use something more unique than first_name.