Question

I was trying to convert this into a Drupal module so that I can check PHP code instantly on my site for debugging purposes. I saw this Firefox add on which allows you to execute PHP on the fly but admin log in is necessary, so far I did everything , have one form and set up ajax calls , but if I pass a string like:

preg_match($pat,$str,$matches);
print_r($matches);

How to execute this in backend?

EDIT

To load the form:

$items['localphp'] = array(
  'page callback' => 'executePHP',
  'access callback' => TRUE,
  'type' => MENU_CALLBACK,
);

function executePHP(){
  $output = drupal_get_form('executePHP_form');
  return $output;
}

Ajax callback function:

$items['runPHP'] = array(
  'page callback' => 'getResult',
  'access callback' => TRUE,
  'type' => MENU_CALLBACK,
);
function getResult(){
  $code = $_POST['code'];
  //I need help here how to execute $code i.e the php code and return back result
  echo $code;
}

JS function

function executePHP(baseurl){
  var code = $("#edit-code").val();
  $.ajax({
      type : "POST",
      url : baseurl+'runPHP',
      data : 'code='+code,
      async : true,
      cache : false,
      success : function (res) {
        $("#edit-result").html(res);
      },
      error : function (res) {
        alert("error");
      }
  });
  return false;
}

Answer 1

FYI, the Devel module has a feature that allows admins to run custom PHP code from their page. The Devel module has a block with a ton of features useful for debugging.

For a custom module, without seeing any of your other code, I can tell you what I have done to achieve AJAX in a Drupal module:

In JavaScript make an AJAX request to a url on your site. Add a menu item with the specified path inside of hook_menu() as 'type' => MENU_CALLBACK that points to a function in your module. This function should do all the processing you need, then return the results to JavaScript to do what you want with it there.