XCAPE

xcape allows you to use a modifier key as another key when pressed and released on its own. Note that it is slightly slower than pressing the original key, because the pressed event does not occur until the key is released. The default behaviour is to generate the Escape key when Left Control is pressed and released on its own. (If you don't understand why anybody would want this, I'm guessing that Vim is not your favourite text editor ;)

Minimal building instructions

$ sudo apt-get install git gcc make libx11-dev libxtst-dev pkg-config
$ mkdir xcape
$ cd xcape
$ git clone https://github.com/alols/xcape.git .
$ make

Usage

$ xcape [-d] [-t <timeout ms>] [-e <map-expression>]

-d

Debug mode. Does not fork into the background.

-t <timeout ms>

If you hold a key longer than this timeout, xcape will not generate a key event. Default is 50 ms.

-e <map-expression>

The expression has the grammar 'ModKey=Key[|OtherKey][;NextExpression]'

The list of key names is found in the header file X11/keysymdef.h (remove the XK_ prefix). Note that due to limitations of X11 shifted keys must be specified as a shift key followed by the key to be pressed rather than the actual name of the character. For example to generate "{" the expression 'ModKey=Shift_L|bracketleft' could be used (assuming that you have a key with "{" above "[").

You can also specify ModKey in decimal (prefix #), octal (#0), or hexadecimal (#0x). It will be interpreted as a keycode unless no corresponding key name is found.

Examples

1. This will make Left Shift generate Escape when pressed and released on it's own, and Left Control generate Ctrl-O combination when pressed and released on it's own.

   xcape -e 'Shift_L=Escape;Control_L=Control_L|O'
   

2. If your s key has the code 42 and your l key 43 and you have set both to AltGr (a.k.a. ISO_Level3_Shift) with xmodmap, then this will generate the ordinary letters when pressed and released on their own. But pressed together with another key, the s or l key will produce AltGr. So, depending on your keyboard layout, you can compose e.g. @, { or ³ easily when touch-typing.

   xcape -e '#42=s;#43=l'
   

3. We can make the space bar work as an additional ctrl key when held (similar to Space2ctrl) with the following sequence of commands.

   # Map a new (currently non-existant) keysym to the spacebar's
   # keycode and make it a control modifier.
   xmodmap -e 'keycode 65 = 0x1234'
   xmodmap -e 'add control = 0x1234'
   
   # Map space to a new keycode which has no corresponding key (to
   # keep it around for xcape to use).
   xmodmap -e 'keycode any = space'
   
   # Finally use xcape to cause our new keysym to generate a space
   # when tapped.
   ./xcape -e '0x1234=space'
   

   This is particularly useful for emacs users.

Note regarding xmodmap

If you are in the habit of remapping keycodes to keysyms (eg, using xmodmap), there are two issues you may encounter.

1. You will need to restart xcape after every time you modify the mapping from keycodes to keysyms (eg, with xmodmap), or xcape will still use the old mapping.

2. The key you wish to send must have a defined keycode. So for example, with the default mapping Control_L=Escape, you still need an escape key defined in your xmodmap mapping. (I get around this by using 255, which my keyboard cannot send).

Contact

Find the latest version at https://github.com/alols/xcape

The author can be reached at albin dot olsson at gmail dot com