gistfile1.aw

<?php

/**
 * Invokes hook_greeting() to collect greetings from all other modules.
 * Located in greeting.module.
 */
function greetings_init() {
  $greetings = array();
  // Invoke hook_greeting() to collect all greetings, keyed by module name. 
  // Can also use module_invoke_all() to achieve the same.
  foreach (module_impelements('greeting') as $module) {
    //$modules == array('hello', 'howdy');
    $function = $module . '_' . 'greeting';
    $greetings[$module] = $function(); 
  }
  // Allow modules to implement hook_greeting_alter().
  drupal_alter('greeting', $greetings);
  // Render greetings
  foreach ($greetings as $module => $greeting) { 
    drupal_set_message("Greeting from $module: $greeting");
  }
}

/* Implementation of hook_greeting. Located in hello.module. */
function hello_greeting() {
  return "Hello there!";
}

/* Implementation of hook_greeting. Located in howdy.module. */
function howdy_greeting() {
  return "Howdy, partner!";
}

/* Implementation of hook_greeting_alter(). Located in nasty.module. */
function nasty_greeting_alter(&$greetings) {
 $greetings['howdy'] = "Howdy, jerk!";
}