xiapply
-------

There are a few settings I must apply to my keyboard when I start X11
(e.g. remapping Caps Lock, setting the repeat rate).  Unfortunately, these
changes are not applied to subsequently added devices.  This means when I
plug a real keyboard into my laptop, or every time I flip the USB switch
it passes through, I have to manually reapply these changes.  (Usually not
before I've sent a scary variety of capital letters to vi.)  Making these
changes permanent by changing the X server's configuration might be
possible, but doing so strikes me as inelegant -- though I consider
these settings a necessity, they are nonetheless user customizations.

xiapply is an X11 client that executes its argument once and then
listens to XInput events [1].  When an event comes in signalling that a
device has been enabled, xiapply's argument is re-executed.  No effort
is made to coalesce related events -- xiapply's argument is expected
to be idempotent.  xiapply will, however, run only one instance of its
argument at a time.

xiapply runs until it encounters an error or the X server goes away.
You will probably want to place it in the background.

Example:

  $ xiapply setxkbmap -option ctrl:nocaps &

Compatibility
-------------

This was written on Linux, but should probably work elsewhere.  One
potential problem is that, frustratingly, one must use glibc-specific
arguments to get POSIX-compliant behavior out of glibc's getopt().
You get what you pay for.


[1] This actually happens in the opposite order to avoid the obvious race.