What are good custom keybindings in emacs?

Question

Emacs seems to have all the possible keyboard combinations already randomly distributed among it's commands. :p

If I am to define new keyboard shortcuts, where should I put them? Which prefixes should I use?

For instance: I want to define shortcuts for the following functions:

• indent-buffer (C-c i, after I got the answer)
• comment-or-uncomment-region (C-c C)
• rdebug (ruby debugger) (C-c R)
• rsense-complete (ruby autocomplete) (C-c e)

Where would you put these? Why?

Answer 1

I have an unconventional approach to this that I recommend highly. I have redefined the C-l ('ell') key to be a prefix key, and I use that to prefix my favorite commands. This key is very easy to type and it is bound to a function ('recenter) that isn't used that much.

Well, I don't use 'recenter much, but even if you did, it can be assigned to C-l C-l which is almost as easy to type, and a small price to pay for the possibilities opened up by the Ctrl-L-map . (Actually I prefer 'redraw-display to 'recenter, so I gave that the place of honor.)

I don't remember where I got the magic incantation that makes it work:

(global-unset-key "\C-l")
(defvar ctl-l-map (make-keymap)
     "Keymap for local bindings and functions, prefixed by (^L)")
(define-key global-map "\C-l" 'Control-L-prefix)
(fset 'Control-L-prefix ctl-l-map)

Then you can define keys to your heart's content. C-l is a great place to put bindings for your own commands, as well as functions that are not bound to keys, or are bound to keys you can't remember or find hard to type. Here are some sample bindings to standard functions:

(define-key ctl-l-map "\C-l"  'redraw-display)
(define-key ctl-l-map "l"  'recenter)

(define-key ctl-l-map "g"  'goto-line)
(define-key ctl-l-map "r"  'replace-string)
(define-key ctl-l-map "R"  'replace-regexp)
(define-key ctl-l-map "q"  'query-replace)
(define-key ctl-l-map "Q"  'query-replace-regexp)
(define-key ctl-l-map "o"  'overwrite-mode)
(define-key ctl-l-map "\C-w"  'kill-rectangle)
(define-key ctl-l-map "\C-y"  'yank-rectangle)
(define-key ctl-l-map "h"  'command-history)
(define-key ctl-l-map "w"  'write-region)
(define-key ctl-l-map "r" 'electric-replace-string)
(define-key ctl-l-map "\er" 'replace-string)
(define-key ctl-l-map "T"  'delete-trailing-whitespace)
(define-key ctl-l-map "C"  'describe-char)
(define-key ctl-l-map "W"  'ediff-regions-wordwise)
(define-key ctl-l-map "L"  'ediff-regions-linewise)
(define-key ctl-l-map "\C-f" 'facemenu-remove-all)
(define-key ctl-l-map "\C-c" 'calendar)
(define-key ctl-l-map "m"  'not-modified)   ;; already at M-~
(define-key ctl-l-map "\C-q" 'fill-region)
(define-key ctl-l-map "u" 'set-buffer-file-coding-system)
(define-key ctl-l-map [?\C-2] 'transient-mark-mode)
(define-key ctl-l-map "\C-@"  'transient-mark-mode)
(define-key ctl-l-map "\C-n"  'linum-mode)
(define-key ctl-l-map "\C-s" 'isearch-forward-regexp)
(define-key ctl-l-map "\C-r" 'isearch-backward-regexp)a
(define-key ctl-l-map "U" 'browse-url)
(define-key ctl-l-map "F" 'browse-url-of-file)
(define-key ctl-l-map "\C-u" 'undo-only)

Answer 2

Emacs actually has a very definite pattern to its bindings, this answer shows some.

As far as where you should define keys, if you take a look at the documentation for conventions, you'll see that C-c a (where a is any lower or upper case character) is reserved for users.

Plus, if you're defining a key that really only makes sense in a particular mode, then you should define it in that keymap.

For example, M-/ is bound to dabbrev-expand, which is a handy way of autocompleting the word you're typing. It might very well make sense to use rsense-complete instead, but only when you're in ruby. In which case, you can do this:

(add-hook 'ruby-mode-hook
     (lambda () (define-key ruby-mode-map (kbd "M-/") 'rsense-complete)))

That will override the binding for M-/ only when you're in ruby-mode, and leave it unchanged (or available) for the rest of the modes.