title: How to debug variable not posting to MYSQL database
body: <p>I'm trying to figure out how to debug an issue with the posting of a variable to my database. Everything is being posted, but the username. Any tips on how to debug this would be much  appreciated.</p>
  
  <p>The username does run through a couple of functions first.  I'm not getting any errors with the script itself, but I'm also not getting anything to post to the database.</p>
  
  <pre><code>&lt;?php
  
  // Check to see there are posted variables coming into the script
  if ($_SERVER['REQUEST_METHOD'] != "POST") die ("No Post Variables");
  // Initialize the $req variable and add CMD key value pair
  $req = 'cmd=_notify-validate';
  // Read the post from PayPal
  foreach ($_POST as $key =&gt; $value) {
      $value = urlencode(stripslashes($value));
      $req .= "&amp;$key=$value";
  }
  // Now Post all of that back to PayPal's server using curl, and validate everything with PayPal
  // We will use CURL instead of PHP for this for a more universally operable script (fsockopen has issues on some environments)
  //$url = "https://www.sandbox.paypal.com/cgi-bin/webscr";
  $url = "https://www.paypal.com/cgi-bin/webscr";
  $curl_result=$curl_err='';
  $ch = curl_init();
  curl_setopt($ch, CURLOPT_URL,$url);
  curl_setopt($ch, CURLOPT_RETURNTRANSFER,1);
  curl_setopt($ch, CURLOPT_POST, 1);
  curl_setopt($ch, CURLOPT_POSTFIELDS, $req);
  curl_setopt($ch, CURLOPT_HTTPHEADER, array("Content-Type: application/x-www-form-urlencoded", "Content-Length: " . strlen($req)));
  curl_setopt($ch, CURLOPT_HEADER , 0);   
  curl_setopt($ch, CURLOPT_VERBOSE, 1);
  curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, FALSE);
  curl_setopt($ch, CURLOPT_TIMEOUT, 30);
  $curl_result = @curl_exec($ch);
  $curl_err = curl_error($ch);
  curl_close($ch);
  
  $req = str_replace("&amp;", "\n", $req);  // Make it a nice list in case we want to email it to ourselves for reporting
  
  // Check that the result verifies
  if (strpos($curl_result, "VERIFIED") !== false) {
      $req .= "\n\nPaypal Verified OK";
  } else {
      $req .= "\n\nData NOT verified from Paypal!";
      mail(".com", "IPN interaction not verified", "$req", "From: .com" );
      exit();
  }
  
  /* CHECK THESE 4 THINGS BEFORE PROCESSING THE TRANSACTION, HANDLE THEM AS YOU WISH
  1. Make sure that business email returned is your business email
  2. Make sure that the transaction’s payment status is “completed”
  3. Make sure there are no duplicate txn_id
  4. Make sure the payment amount matches what you charge for items. (Defeat Price-Jacking) */
  
  // Check Number 1 ------------------------------------------------------------------------------------------------------------
  $receiver_email = $_POST['receiver_email'];
  if ($receiver_email != ".com") {
      $message = "Investigate why and how receiver email is wrong. Email = " . $_POST['receiver_email'] . "\n\n\n$req";
      mail(".com", "Receiver Email is incorrect", $message, "From: .com" );
      exit(); // exit script
  }
  // Check number 2 ------------------------------------------------------------------------------------------------------------
  if ($_POST['payment_status'] != "Completed") {
      // Handle how you think you should if a payment is not complete yet, a few scenarios can cause a transaction to be incomplete
  }
  // Connect to database ------------------------------------------------------------------------------------------------------
  require_once 'connect_to_mysql.php';
  // Check number 3 ------------------------------------------------------------------------------------------------------------
  $this_txn = $_POST['txn_id'];
  $sql = mysql_query("SELECT id FROM transactions WHERE txn_id='$this_txn' LIMIT 1");
  $numRows = mysql_num_rows($sql);
  if ($numRows &gt; 0) {
      $message = "Duplicate transaction ID occured so we killed the IPN script. \n\n\n$req";
      mail(".com", "Duplicate txn_id in the IPN system", $message, "From: .com" );
      exit(); // exit script
  } 
  // Check number 4 ------------------------------------------------------------------------------------------------------------
  $product_id_string = $_POST['custom'];
  $product_id_string = rtrim($product_id_string, ","); // remove last comma
  // Explode the string, make it an array, then query all the prices out, add them up, and make sure they match the payment_gross amount
  $id_str_array = explode(",", $product_id_string); // Uses Comma(,) as delimiter(break point)
  $fullAmount = 0;
  foreach ($id_str_array as $key =&gt; $value) {
  
      $id_quantity_pair = explode("-", $value); // Uses Hyphen(-) as delimiter to separate product ID from its quantity
      $product_id = $id_quantity_pair[0]; // Get the product ID
      $product_quantity = $id_quantity_pair[1]; // Get the quantity
      $sql = mysql_query("SELECT price FROM products WHERE id='$product_id' LIMIT 1");
      while($row = mysql_fetch_array($sql)){
          $product_price = $row["price"];
      }
      $product_price = $product_price * $product_quantity;
      $fullAmount = $fullAmount + $product_price;
  }
  $fullAmount = number_format($fullAmount, 2);
  $grossAmount = $_POST['mc_gross']; 
  if ($fullAmount != $grossAmount) {
          $message = "Possible Price Jack: " . $_POST['payment_gross'] . " != $fullAmount \n\n\n$req";
          mail(".com", "Price Jack or Bad Programming", $message, "From: .com" );
          exit(); // exit script
  } 
  
  //
  //
  require_once 'connect_to_mysql.php';
  
  //now to always get unique username
  $username = substr($payer_email, 0, strpos($payer_email, '@'));
  if ( ! uniqueName($username))
  {
      $username = makeUniqueName($username);
  }
  
  
  //function to check if is the existing username
  function uniqueName($username)
  {
      $sql = mysql_query("SELECT username FROM transactions WHERE username='$username'");
      $numRows = mysql_num_rows($sql);
      if ($numRows &gt; 0)
      {
          return false;
      }
  
      return true;
  }
  
  
  //function to generate new unique username
  function makeUniqueName($username)
  {
      //serch username string for number at the end
      //regexp makes sure all preceeding zeroes go to first match group
      if (preg_match('/^(\S*?0*)?(\d+?)$/', $username, $match))
      {
          //we got digit from the end of string, just add 1 to the digit
          $username = $match[1] . ($match[2] + 1);
      }
      else
      {
          //no digit at the end of string, just add digit 1 at the end
          $username = $username . 1;
      }
  
  if (uniqueName($username))
  {
      return $username;
  }
  
      return makeUniqueName($username);
  }
  
  // END ALL SECURITY CHECKS NOW IN THE DATABASE IT GOES ------------------------------------
  ////////////////////////////////////////////////////
  // Homework - Examples of assigning local variables from the POST variables
  $txn_id = $_POST['txn_id'];
  $payer_email = $_POST['payer_email'];
  $custom = $_POST['custom'];
  $first_name = $_POST['first_name'];
  $last_name = $_POST['last_name'];
  $payment_date = $_POST['payment_date'];
  $mc_gross = $_POST['mc_gross'];
  $payment_currency = $_POST['payment_currency'];
  $txn_id = $_POST['txn_id'];
  $receiver_email = $_POST['receiver_email'];
  $payment_type = $_POST['payment_type'];
  $payment_status = $_POST['payment_status'];
  $txn_type = $_POST['txn_type'];
  $payer_status = $_POST['payer_status'];
  $address_street = $_POST['address_street'];
  $address_city = $_POST['address_city'];
  $address_state = $_POST['address_state'];
  $address_zip = $_POST['address_zip'];
  $address_country = $_POST['address_country'];
  $address_status = $_POST['address_status'];
  $notify_version = $_POST['notify_version'];
  $verify_sign = $_POST['verify_sign'];
  $payer_id = $_POST['payer_id'];
  $mc_currency = $_POST['mc_currency'];
  $mc_fee = $_POST['mc_fee'];
  $password = mt_rand(1000, 9999); 
  $p_hash = md5($password);
  $username = $_POST['username'];
   //
  
  // Place the transaction into the database
  $sql = mysql_query("INSERT INTO transactions (product_id_array, payer_email, first_name, last_name, payment_date, mc_gross, payment_currency, txn_id, receiver_email, payment_type, payment_status, txn_type, payer_status, address_street, address_city, address_state, address_zip, address_country, address_status, notify_version, verify_sign, payer_id, mc_currency, mc_fee, password, ip, username) 
     VALUES('$custom','$payer_email','$first_name','$last_name','$payment_date','$mc_gross','$payment_currency','$txn_id','$receiver_email','$payment_type','$payment_status','$txn_type','$payer_status','$address_street','$address_city','$address_state','$address_zip','$address_country','$address_status','$notify_version','$verify_sign','$payer_id','$mc_currency','$mc_fee','$p_hash','$ip','$username')") or die ("unable to execute the query");
  $to      = $payer_email;  
  $subject = 'Learn  | Login Credentials';  
  $message = ' 
  
  Your officially all ready to go. To login use the information below.
  
  Your account login information 
  ------------------------- 
  Email: '.$payer_email.' 
  Password: '.$password.' 
  ------------------------- 
  
  You can now login at https://www..com/signin.php';  
  $headers = 'From:noreply@.com' . "\r\n";  
  
  mail($to, $subject, $message, $headers);  
  mysql_close();
  // Mail yourself the details
  mail(".com", "NORMAL IPN RESULT YAY MONEY!", $req, "From: ");
  
  ?&gt;
  </code></pre>