Emacs: Toggle Letter Case

By Xah Lee. Date: . Last updated: .

Emacs has these commands for changing letter case. They are:

There are also “region” versions for each:

(Note: for elisp programing, there are also these functions: upcase, capitalize, downcase, upcase-initials.)

One problem with these commands is that you need to move your cursor to the beginning of the word first. For example, if you have the text “THat”, and your cursor is on the “a”, and you call downcase-word, but it doesn't do anything because it only start at the cursor point to end of word. It would be nice if it'll just automatically perform the operation on the whole word.

Another problem is that it does not consider the final result. For example, if you have “oncE upon a time …”, and you select the whole sentence and call upcase-initials-region, it becomes “OncE Upon A Time …”. Note the capital E is not automatically lowered. For elisp programing, the orthogonal precision is nice, but as user commands, it is better to change the whole sentence.

Also, these commands have a “-word” and “-region” variants. You have to chose which one to use. It would be nice if emacs automatically choose the right command depending whether there is text selection.


Here's a command that combines letter-case commands into one.

(defun xah-toggle-letter-case ()
  "Toggle the letter case of current word or text selection.
Always cycle in this order: Init Caps, ALL CAPS, all lower.

URL `http://ergoemacs.org/emacs/modernization_upcase-word.html'
Version 2017-04-19"
  (let (
        (deactivate-mark nil)
        -p1 -p2)
    (if (use-region-p)
        (setq -p1 (region-beginning)
              -p2 (region-end))
        (skip-chars-backward "[:alnum:]-_")
        (setq -p1 (point))
        (skip-chars-forward "[:alnum:]-_")
        (setq -p2 (point))))
    (when (not (eq last-command this-command))
      (put this-command 'state 0))
     ((equal 0 (get this-command 'state))
      (upcase-initials-region -p1 -p2)
      (put this-command 'state 1))
     ((equal 1  (get this-command 'state))
      (upcase-region -p1 -p2)
      (put this-command 'state 2))
     ((equal 2 (get this-command 'state))
      (downcase-region -p1 -p2)
      (put this-command 'state 0)))))

Give it a easy key, such as Ctrl+9. 〔►see Emacs: How to Define Keys

This command is also in ErgoEmacs Keybinding and Emacs: Xah Fly Keys.

Toggle Previous Letter Case

Another issue, not related to emacs, but related to efficiency of ⇧ Shift key, is that the conventional way of typing capital letter using the ⇧ Shift key is inefficient. You have to hold it, type a letter, then release it. (For detail about the Shift key problem, see Banish Shift Key.)

A better way to type capital letters, is to have a designated key, so that, when pressed, the previous letter is capitalized. (alternatively, press this key first, then next letter key pressed is capitalized. This is like a ⎄ Compose key. 〔►see Keyboard: What's the Difference Between Alt Graph Key, Compose Key, Dead Key?〕 )

This is better because:

Here's the emacs command.

(defun xah-toggle-previous-letter-case ()
  "Toggle the letter case of the letter to the left of cursor.
URL `http://ergoemacs.org/emacs/modernization_upcase-word.html'
Version 2015-12-22"
  (let ((case-fold-search nil))
    (left-char 1)
     ((looking-at "[[:lower:]]") (upcase-region (point) (1+ (point))))
     ((looking-at "[[:upper:]]") (downcase-region (point) (1+ (point)))))

For this to work, you need to assign a easy key for this. For example, if you have a ergodox keyboard 〔►see Best Keyboard for Emacs〕, set it to a thumb key.

If you have a normal PC keyboard, you could set the right ⇧ Shift to something such as F20, then bind F20 to the command.

For how to remap keys in OS, see: Keyboard Tutorial: Layout, Keybinding, Key Macro ⌨.

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