Emacs: What's Hook?
What's a hook?
A hook is a variable, its value is a list of functions (lisp symbols or lambda).
Each hook is designed to “run” when some event happens. When a hook “run”, all functions in that hook are called.
html-modeis loaded, html-mode-hook's functions are run.
- when any command is called, post-command-hook's functions are run.
There are hundreds of hooks. Each major mode usually have at least 1 hook, designed to run when the mode is loaded. 〔►see List of Emacs Hooks〕
A hook is similar to the concept of events in other systems. Adding function to a hook is similar to adding event handlers. (note: emacs lisp manual also uses the term “event”, but that is lower level events to emacs, not events from emacs.)
Examples of Using Hook
Here's example of turning on line number only for some modes:
(add-hook 'emacs-lisp-mode-hook 'linum-mode) (add-hook 'js-mode-hook 'linum-mode) (add-hook 'css-mode-hook 'linum-mode) (add-hook 'html-mode-hook 'linum-mode) (add-hook 'nxml-mode-hook 'linum-mode)
Here's example of use variable-width font for some modes:
;; use variable-width font for some modes (add-hook 'nxml-mode-hook 'variable-pitch-mode) (add-hook 'emacs-lisp-mode-hook 'variable-pitch-mode) (add-hook 'js-mode-hook 'variable-pitch-mode) (add-hook 'css-mode-hook 'variable-pitch-mode) (add-hook 'html-mode-hook 'variable-pitch-mode)
〔►see Emacs: Avoid Lambda in Hook〕
How to List All Hooks?
How to find the name of hook?
Most major modes have a hook. If a mode's name is “xyz-mode”, its hook by convention is named “xyz-mode-hook”.
First, be sure you load the mode first. Some hook many not show when the mode isn't loaded or initialized.
describe-variable, then try to type a name you guessed, press Tab for completion.
- type “-hook”, press Enter ↵.
Note: A major mode may have more than 1 hook.
How to See the Value of a Hook?
describe-variable, then type the hook name, to see its current value.
How to Remove a Function in a Hook?
;; remove a hook (remove-hook 'html-mode-hook 'xyz-function-name)
How to Bind Keys for Major Mode?
Avoid Lambda in Hook
Emacs Customize Topic
- How to Set Emacs's User Interface
- Emacs: How to Install Packages Using ELPA, MELPA
- How to Install Emacs Package Manually
- Emacs: How to Define Keys
- Emacs: M-x customize Tutorial
- Emacs: Set File to Open in a Major Mode
- Organize Emacs Init File in 5 Minutes
- Emacs: Byte Compile Elisp Files
- Emacs: What's Hook?
- Emacs: Set Environment Variables within Emacs