List out some hook function in drupal

hook_access->Define access restrictions.

hook_auth->Verify authentication of a user.

hook_block->Declare a block or set of blocks.

hook_comment ->Act on comments.

hook_cron->Perform periodic actions.

hook_db_rewrite_sql ->Add JOIN and WHERE statements to queries and decide whether the primary_field shall be made DISTINCT. For node objects, primary field is always called nid. For taxonomy terms, it is tid and for vocabularies it is vid. For comments, it is cid. Primary...

hook_delete->Respond to node deletion.

hook_elements->Allows modules to declare their own form element types and specify their default values.

hook_exit->Perform cleanup tasks.

hook_file_download ->Allow file downloads.

hook_filter->Define content filters.

hook_filter_tips->Provide tips for using filters.

hook_footer->Insert closing HTML.

hook_form->Display a node editing form.

hook_form_alter->Perform alterations before a form is rendered. One popular use of this hook is to add form elements to the node form.

hook_help->Provide online user help.

hook_info->Declare authentication scheme information.

hook_init->Perform setup tasks.

hook_insert->Respond to node insertion.

hook_install->Install the current version of the database schema.

hook_link->Define internal Drupal links.

hook_load->Load node-type-specific information.

hook_menu->Define menu items and page callbacks.

hook_nodeapi ->Act on nodes defined by other modules.

hook_node_grants->Grant access to nodes.

hook_node_info->Define the human-readable name of a node type.

hook_perm->Define user permissions.

hook_ping->Ping another server.

hook_prepare ->This is a hook used by node modules. It is called after load but before the node is shown on the add/edit form.

hook_search->Define a custom search routine.

hook_search_preprocess->Preprocess text for the search index.

hook_settings->Declare administrative settings for a module.

hook_submit->This is a hook used by node modules. It is called after validation has succeeded and before insert/update. It is used to for actions which must happen only if the node is to be saved. Usually, $node is changed in some way and then the actual saving of...

hook_taxonomy->Act on taxonomy changes.

hook_update->Respond to node updating.

hook_update_index->Update Drupal's full-text index for this module.

hook_update_N->Perform a single update. For each patch which requires a database change add a new hook_update_N() which will be called by update.php.

hook_user->Act on user account actions.

hook_validate ->Verify a node editing form.

hook_view->Display a node.

hook_xmlrpc->Register XML-RPC callbacks.

module_hook->Determine whether a module implements a hook.

module_implements->Determine which modules are implementing a hook.

module_invoke->Invoke a hook in a particular module.

module_invoke_all->Invoke a hook in all enabled modules that implement it.