I am trying to create a custom module that programmatically creates a LESS file.

I created a menu callback that is a file. Here is hook_menu()...

$items['sites/all/themes/universal/less/dynamic.css.less'] = array(
  'page callback' => 'jobs_universal_lessvars',
  'access arguments' => array('access content'),
  'type' => MENU_CALLBACK

Here is the callback.

function jobs_universal_lessvars(){ 
  header('Content-type: text/css');
  $output = '
    @color: #4D926F;
    body.notaclass {
  print $output;

And I call this to add it.

function universal_preprocess_html(&$variables) {

I uploaded a static file to the above ^^ path, disabled the menu callback, and it processed/applied correctly. When I try to run this module, it's not included and I get an error saying

LESS error: load error: failed to find sites/all/themes/universal/less/dynamic.css.less

Before you answer...

  1. I have the LESS module installed
  2. I have the LESS library uploaded correctly
  3. I have tested that I can include a static .less file and have it process
  4. I have tested the menu callback by manually going to the URL
  5. I have tried it with and without calling header('Content-type: text/css');

I get it... it's not a file. But it "is", right? I could just call this function and have it create a new CSS file that's added, but it doesn't fulfil the requirements of the module. Help me? :) Programmatically creating files is very new to me!

  • I believe LESS needs the full server side path to the file. you want something like drupal_add_css(DRUPAL_ROOT . drupal_get_path('theme', 'universal') . '/less/dynamic.css.less');. I'm confused why you need to do this if you already have the LESS module installed; what are you achieving with this ?
    – tenken
    Dec 19, 2013 at 22:54
  • the issue is drupal_add_css() is looking for an actual file in the filesystem of your host/server, while drupal and its menu_hook() send information out via the host's webserver giving the impression that the file exists.
    – Jimajamma
    Dec 19, 2013 at 23:27

1 Answer 1


It may appear like a file to the browser if you were to directly request that path in the browser, but drupal_add_css() and the LESS module deal with the file system directly and does not attempt to resolve file paths through Drupal's menu system.

drupal_add_css() will not add files that do not exist on the file system.

If you are attempting to have programmatically assigned variables within a .less file I would suggest checking out the Variables functionality that is available within the latest version of the LESS CSS Preprocessor module, documentation here: https://drupal.org/node/2139603

If you are truly trying to create a dynamically composed .less file, you first need to create the file in the files directory of the drupal install and then add that file with drupal_add_css().

  • Thank you so much!! Perfect... I had no idea there were less hooks. Thank you :) I would 1 up you if I could! Dec 19, 2013 at 23:06

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