Drupal hook

When sending e-mails or newsletters from your website, you might want to inject some information like website name, disclaimer, copy right information, unsubscribe link and such. Just like hook_form_alter, you can use hook_mail_alter to virtually alter anything in the mail just before Drupal sends the e-mail. You can even change the mime type of the email, for example, from plain text to HTML and vice versa.
Here is the syntax/signature of the hook

• Drupal 5: hook_mail_alter(&$mailkey, &$to, &$subject, &$body, &$from, &$headers)
• Drupal 6, 7: hook_mail_alter(&$message)

$message has the following key-value pairs:

• 'id': Unique id of the mail being sent.
• 'to': The destination e-mail address(es)

Blocks are the one of the basic and most fascinating features of Drupal. With block you can display information in the form of block by saving and utilizing the screen area. Here is an example of implementation of hook_block

<?php
/**
* Implementation of hook_block
*
* @param $op
* @param $delta
* @param $edit
* @return $block
* @author Drupal Developer
*/
function browse_info_block($op = 'list', $delta = 0, $edit = array()) {
switch ($op) {
case 'list':
$blocks[1] = array(
'info' => t("Browse information by category"),
'status' => 1,
'region' => 'content',
'weight' => 0,
);

return $blocks;
case 'configure':
$am__vocabulary = _get_vocabulary();
$am__imagecache = _get_imagecache();

hook_install() creates tables in the database for the module to which its associated. hook_install not just restricted creating tables but it also creates vocabularies, terms in the vocabularies and sets variables to be used by modules. The hook_install set ups the basic requirement for a module to function properly. Not all the modules require to implement hook_install but which saves data to own tables and for providing extra features for which there are no tables or fields exists from where information can be fetched.

• Drupal 5: Table definition and all other required set up for the module
• Drupal 6, 7: drupal_install_schema('[hook]')

Here is an example of hook_install()

<?php
/**
* Implementation of hook_install
*

When Developing a custom module for Drupal, we need to use Drupal APIs and we need to make use of Drupal hooks. There are many Drupal hooks available and different hooks go in different files.

In this section we will learn about all those required hooks which should be written when developing a custom Drupal module.

First we will look at the hooks which are written in .install file.

I'd like to make a note here that don't mistaken the .module as the Drupal module. A Drupal module is consist of one or more .module file, one or more .info file and optionally, one or more .install file.

So, first we look at the hooks in .install file.

hook_install()

• Drupal 5.x - Table structure and other items like vocabulary and its terms to be used by the module.