如何在drupal中以编程方式访问模块？

based on some condition i want to give access to a module.

if(abc == abc) {
  //give access to module xyz.
}

There's no such concept as giving access to a whole module in Drupal, only pages that a module would define. Usually this is done by implementing hook_menu() to define the page(s) and then providing either an access callback or access arguments.

The first defines a function that will be called to make your access decision:

function mymodule_menu() {
  $items['some/path'] = array(
    'title' => 'Some Title',
    'page callback' => 'mymodule_callback',
    'access callback' => 'mymodule_some_path_access'
  );

  return $items;
}

function mymodule_some_path_access() {
  global $user;

  if ($user->foo == 'bar') {
    // Access allowed, return TRUE
    return TRUE;
  }

  // Access not allowed, return FALSE
  return FALSE;
}

The second defines arguments that will be passed to the user_access function. This will usually be based on permissions your module provides:

function mymodule_menu() {
  $items['some/path'] = array(
    'title' => 'Some Title',
    'page callback' => 'mymodule_callback',
    'access arguments' => array('access mymodule')
  );

  return $items;
}

function mymodule_perm() {
  return array(
    'access mymodule'
  );
}

In the second example a user will be denied access unless they have the permission 'access mymodule' (as defined in the permissions admin area of Drupal).

Hope that helps