Top Forums Shell Programming and Scripting Poll Wacom input from "libinput debug-events" in Bash Post 303039686 by mrjpaxton on Saturday 12th of October 2019 12:43:42 AM
Poll Wacom input from "libinput debug-events" in Bash


I am making a Bash shell script to grab input from libinput. There's a few reasons why I am doing it this way:
  1. Using Python with python-libinput does not work. I installed version 0.1.0 with pip, and it complains about "ContextType" not existing. So that's a no-go.
  2. I am trying to get away from my dependence on Xorg-related stuff, such as xsetwacom and xserver-input-wacom, and do things that are more compatible with Wayland.
  3. Both methods above do not have support for the four different modes when you press the center ring button on the ExpressKey pad. I plan to eventually support all of these events.

Without explaining my entire plan of this script, I figured I could ask the question that's harder for me to understand, and figure out the rest as I go along.

I want to poll the outputs from "libinput debug-events" in an infinite loop Bash script that will run in the background. This polling will happen, say, every 1 second.

This pseudocode down below can help explain what I am looking to do to start out my script:

while true; do
  sleep 1
  OUTPUT=$(libinput debug-events | grep "TABLET_PAD_BUTTON")
  case ${OUTPUT} in
  "4 pressed (mode 0)")
    echo "Button 4"
    # Etc . . .

My big problem is figuring out how to do this.

The thing is, "libinput debug-devices" works a lot like showkey or xev, but not exactly. For some reason, stdin for "TABLET_PAD_BUTTON" is "frozen" until I move the mouse around. Why this is, I have no idea. Regardless to say, I feel like I may be overcomplicating my problem, or I just don't really see a clear cut solution. Doing it this way just doesn't work right, as it is.

The libinput binary program will need to somehow exit after a period of time, because by default it is left running, so some sort of control implementation needs to exist there. Also, I notice that when it loops back to "OUTPUT=xyz" the existing variable data should be replaced by new input data again, which is great. That's exactly how it should work in that case.

Finally, this is a script that needs to run in the background (like a daemon process), and also accept input from libinput/udev devices at all times. And I'm not sure if Bash is powerful enough to tell the libinput binary to do that, is the thing.... If this really needs to be written in C, then perhaps there's no good solution here, and the thread can be closed if that's the case.

Anybody have any idea how I could approach this problem, or could even possibly provide a good bash script solution? Thank you very much in advance!

Last edited by mrjpaxton; 10-12-2019 at 02:55 AM..
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SCRIPT(1)						    BSD General Commands Manual 						 SCRIPT(1)

script -- make typescript of terminal session SYNOPSIS
script [-a] [-k] [-q] [-t time] [file [command ...]] DESCRIPTION
The script utility makes a typescript of everything printed on your terminal. It is useful for students who need a hardcopy record of an interactive session as proof of an assignment, as the typescript file can be printed out later with lpr(1). If the argument file is given, script saves all dialogue in file. If no file name is given, the typescript is saved in the file typescript. If the argument command ... is given, script will run the specified command with an optional argument vector instead of an interactive shell. Options: -a Append the output to file or typescript, retaining the prior contents. -k Log keys sent to program as well as output. -q Run in quiet mode, omit the start and stop status messages. -t time Specify time interval between flushing script output file. A value of 0 causes script to flush for every character I/O event. The default interval is 30 seconds. The script ends when the forked shell (or command) exits (a control-D to exit the Bourne shell (sh(1)), and exit, logout or control-d (if ignoreeof is not set) for the C-shell, csh(1)). Certain interactive commands, such as vi(1), create garbage in the typescript file. The script utility works best with commands that do not manipulate the screen. The results are meant to emulate a hardcopy terminal, not an addressable one. ENVIRONMENT
The following environment variable is utilized by script: SHELL If the variable SHELL exists, the shell forked by script will be that shell. If SHELL is not set, the Bourne shell is assumed. (Most shells set this variable automatically). SEE ALSO
csh(1) (for the history mechanism). HISTORY
The script command appeared in 3.0BSD. BUGS
The script utility places everything in the log file, including linefeeds and backspaces. This is not what the naive user expects. It is not possible to specify a command without also naming the script file because of argument parsing compatibility issues. When running in -k mode, echo cancelling is far from ideal. The slave terminal mode is checked for ECHO mode to check when to avoid manual echo logging. This does not work when in a raw mode where the program being run is doing manual echo. BSD
June 6, 1993 BSD

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