$ LANG=C xinput --test-xi2 --root | awk '
/RawKeyPress/ { relevant=1 }
relevant==1 && /detail/ { print $2; relevant=0 }
'

The most obvious application of this is a keylogger (https://github.com/bdantas/keylogger), but the keylogger itself may just be a stepping stone to something more useful (e.g., https://github.com/bdantas/iksilo).

$ master_id=$(LANG=C xinput list | grep -i 'master keyboard' | egrep -o 'id=[0-9]+' | egrep -o '[0-9]+')
$ keyboard_id=$(LANG=C xinput list $master_id | grep 'XIKeyClass' | egrep -o '[0-9]+')

This version is easier for my pea brain to grasp.

So how can it be done without asking the user to install xinput?

Chris

eileen@vaio:~$ xinput list --id-only | xargs -n 1 -I+ sh -c "xinput list + | grep -wv + | grep XIKeyClass" | egrep -o '[0-9]+'
12

Wow, ralph.ronnquist. Very impressive. Thank you!

I understand the logic of the command, but don't understand how you figured out that it was the necessary logic. Will chew on it.

BTW, I had also found that nugget on stackexchange, but do not want to give users anything in addition to the shell script I've created. The script is here if you are curious:
https://github.com/bdantas/iksilo

xinput list --id-only | \
    xargs -n 1 -I+ sh -c "xinput list + | grep -wv + | grep XIKeyClass" | \
    grep -oE "[0-9]+"

I.e., in words: for each of the available ids, check the details for the id, but ignoring lines containing the id, for a XIKeyClass line, and then reduce resulting lines to the number they contains. Ideally there should be only one resulting line, but if there are more... well.

Then you might want to check out https://unix.stackexchange.com/question … ress-a-key on how to "really" do this

$ LANG=C xinput --list | grep -i keyboard | egrep -iv 'virtual|video|button|bus'
    ↳ Sony Vaio Keys                          	id=7	[slave  keyboard (3)]
    ↳ USB 2.0 Camera: USB 2.0 Camera          	id=10	[slave  keyboard (3)]
    ↳ AT Translated Set 2 keyboard            	id=12	[slave  keyboard (3)]
    ↳ Sony Vaio Jogdial                       	id=14	[slave  keyboard (3)]

This is tough.

It's also a guess that the label XIKeyClass is a code label without i18n, and that no i18n of that detail line will morph the id number, or add any other digits into the mix.

It works while it works

Eventually someone with direct insight into the source might pass by, to confirm or refute.

ralph.ronnquist's suggestion works in Devuan, in Tiny Core Linux (which uses BusyBox instead of coreutils), and even in OpenBSD. I modified it slightly to something that does same thing but makes more sense to me:

xinput --list --long | grep XIKeyClass | head -n 1 | egrep -o '[0-9]+'

There's no way I would have figured this out on my own. Thanks again, ralph. You're a wizard!

The only thing I don't understand is why the entry of interest always happens to be the first match.

LANG=C xinput --list --long

Or similar?

xinput --list --long | grep -Fwm1 XIKeyClass | egrep -oE '[0-9]*'

which would allow almost any i18n of the sought line, merely expecting XIKeyClass to be present, and the id being the only number on the line.

That method should find at least one of the currently available keyboards; I think it'll pick "the last one" if you connect additional USB or Bluetooth keyboards. Or possibly it's "the last one used".