The xmodmap program reads a list of expressions and parses them all before attempting to execute any of them. This makes it possible to refer to keysyms that are being redefined in a natural way without having to worry as much about name conflicts.
The list of keysym names may be found in the header file <X11/keysymdef.h> (without the XK_ prefix), supplemented by the keysym database /usr/share/X11/XKeysymDB. Keysyms matching Unicode characters may be specified as "U0020" to "U007E" and "U00A0" to "U10FFFF" for all possible Unicode characters.
- keycode NUMBER = KEYSYMNAME ...
- The list of keysyms is assigned to the indicated keycode (which may be specified in decimal, hex or octal and can be determined by running the xev program). Up to eight keysyms may be attached to a key, however the last four are not used in any major X server implementation. The first keysym is used when no modifier key is pressed in conjunction with this key, the second with Shift, the third when the Mode_switch key is used with this key and the fourth when both the Mode_switch and Shift keys are used.
- keycode any = KEYSYMNAME ...
- If no existing key has the specified list of keysyms assigned to it, a spare key on the keyboard is selected and the keysyms are assigned to it. The list of keysyms may be specified in decimal, hex or octal.
- keysym KEYSYMNAME = KEYSYMNAME ...
- The KEYSYMNAME on the left hand side is translated into matching keycodes used to perform the corresponding set of keycode expressions. Note that if the same keysym is bound to multiple keys, the expression is executed for each matching keycode.
- clear MODIFIERNAME
- This removes all entries in the modifier map for the given modifier, where valid name are: Shift, Lock, Control, Mod1, Mod2, Mod3, Mod4, and Mod5 (case does not matter in modifier names, although it does matter for all other names). For example, ``clear Lock'' will remove all any keys that were bound to the shift lock modifier.
- add MODIFIERNAME = KEYSYMNAME ...
- This adds all keys containing the given keysyms to the indicated modifier map. The keysym names are evaluated after all input expressions are read to make it easy to write expressions to swap keys (see the EXAMPLES section).
- remove MODIFIERNAME = KEYSYMNAME ...
- This removes all keys containing the given keysyms from the indicated modifier map. Unlike add, the keysym names are evaluated as the line is read in. This allows you to remove keys from a modifier without having to worry about whether or not they have been reassigned.
- pointer = default
- This sets the pointer map back to its default settings (button 1 generates a code of 1, button 2 generates a 2, etc.).
- pointer = NUMBER ...
- This sets the pointer map to contain the indicated button codes. The list always starts with the first physical button. Setting a button code to 0 disables events from that button.
Lines that begin with an exclamation point (!) are taken as comments.
If you want to change the binding of a modifier key, you must also remove it from the appropriate modifier map.
Many pointers are designed such that the first button is pressed using the index finger of the right hand. People who are left-handed frequently find that it is more comfortable to reverse the button codes that get generated so that the primary button is pressed using the index finger of the left hand. This could be done on a 3 button pointer as follows:
% xmodmap -e "pointer = 3 2 1"
Many applications support the notion of Meta keys (similar to Control keys except that Meta is held down instead of Control). However, some servers do not have a Meta keysym in the default keymap table, so one needs to be added by hand. The following command will attach Meta to the Multi-language key (sometimes labeled Compose Character). It also takes advantage of the fact that applications that need a Meta key simply need to get the keycode and don't require the keysym to be in the first column of the keymap table. This means that applications that are looking for a Multi_key (including the default modifier map) won't notice any change.
% xmodmap -e "keysym Multi_key = Multi_key Meta_L"
Similarly, some keyboards have an Alt key but no Meta key. In that case the following may be useful:
% xmodmap -e "keysym Alt_L = Meta_L Alt_L"
One of the more simple, yet convenient, uses of xmodmap is to set the keyboard's "rubout" key to generate an alternate keysym. This frequently involves exchanging Backspace with Delete to be more comfortable to the user. If the ttyModes resource in xterm is set as well, all terminal emulator windows will use the same key for erasing characters:
% xmodmap -e "keysym BackSpace = Delete" % echo "XTerm*ttyModes: erase ^?" | xrdb -merge
Some keyboards do not automatically generate less than and greater than characters when the comma and period keys are shifted. This can be remedied with xmodmap by resetting the bindings for the comma and period with the following scripts:
! ! make shift-, be < and shift-. be > ! keysym comma = comma less keysym period = period greater
One of the more irritating differences between keyboards is the location of the Control and CapsLock keys. A common use of xmodmap is to swap these two keys as follows:
! ! Swap Caps_Lock and Control_L ! remove Lock = Caps_Lock remove Control = Control_L keysym Control_L = Caps_Lock keysym Caps_Lock = Control_L add Lock = Caps_Lock add Control = Control_L
This example can be run again to swap the keys back to their previous assignments.
The keycode command is useful for assigning the same keysym to multiple keycodes. Although unportable, it also makes it possible to write scripts that can reset the keyboard to a known state. The following script sets the backspace key to generate Delete (as shown above), flushes all existing caps lock bindings, makes the CapsLock key be a control key, make F5 generate Escape, and makes Break/Reset be a shift lock.
! ! On the HP, the following keycodes have key caps as listed: ! ! 101 Backspace ! 55 Caps ! 14 Ctrl ! 15 Break/Reset ! 86 Stop ! 89 F5 ! keycode 101 = Delete keycode 55 = Control_R clear Lock add Control = Control_R keycode 89 = Escape keycode 15 = Caps_Lock add Lock = Caps_Lock
Every time a keycode expression is evaluated, the server generates a MappingNotify event on every client. This can cause some thrashing. All of the changes should be batched together and done at once. Clients that receive keyboard input and ignore MappingNotify events will not notice any changes made to keyboard mappings.
Xmodmap should generate "add" and "remove" expressions automatically whenever a keycode that is already bound to a modifier is changed.
There should be a way to have the remove expression accept keycodes as well as keysyms for those times when you really mess up your mappings.