xcape(1) use a modifier key as another key


xcape [-d] [-t timeout] [-e map-expression]


xcape allows a modifier key to be used as another key when it is pressed and released on its own. The default behaviour is to generate the Escape key in place of Control_L (Left Control).


Debug mode. Will run as a foreground process.
-t timeout
Give a timeout in milliseconds. If you hold a key longer than timeout a key event will not be generated.
-e map-expression
Use map-expression as the expression(s).


Expression syntax is 'ModKey=Key[|OtherKey]'. Multiple expressions can be passed, delimited by semi-colons (;).

A list of keysyms can be found in the header file <X11/keysymdef.h> (without the XK_ prefix).

Note that 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.


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'

In conjugation with xmodmap it is possible to make an ordinary key act as an extra modifier. First map the key to the modifier with xmodmap and then the modifier back to the key with xcape. As an example, we can make the space bar work as an additional ctrl key when held with the following sequence of commands:

First, map an unused modifier's keysym to the spacebar's keycode and make it a control modifier. It needs to be an existing key so that emacs won't spazz out when you press it. Hyper_L is a good candidate.

xmoadmap -e "keycode 65 = $spare_modifier"
xmoadmap -e "remove mod4 = $spare_modifier"
# hyper_l is mod4 by default
xmoadmap -e "add Control = $spare_modifier"

Next, map space to an unused keycode (to keep it around for xcape to use).

xmodmap -e "keycode any = space"

Finally use xcape to cause the space bar to generate a space when tapped.

xcape -e "$spare_modifier=space"


xcape was written by Albin Olsson (albin dot olsson at gmail dot com)