beepy-bl.service

# this file goes in $HOME/.config/systemd/user
[Unit]
Description=beepy backlight controller

[Service]
Type=simple
# adjust this path to where you wrote the script out
ExecStart=/home/rj/bin/noarch/beepy-bl.sh
Restart=on-failure

[Install]
WantedBy=default.target

beepy-bl.sh

#!/usr/bin/env bash

# I created this file in $HOME/bin/noarch/beepy-bl.sh (you will need to adjust unit paths, see above)

# beepy keyboard device to watch for events
DEVICE=/dev/input/by-path/platform-3f804000.i2c-event

# time (in seconds) before we shut the backlight off
IDLE=10

# keyboard brightness (0..255)
BRIGHT=255
DARK=0

# check for keyboard backlight
backlight=/sys/firmware/beepy/keyboard_backlight
[[ -f "${backlight}" ]] || { printf 'could not find backlight control %s\n' "${backlight}" 1>&2 ; exit 1 ; } 

# this is going to loop on events from our device
# it will immediately flip the backlight to on
# and output the letter k
evemu_event() {
  local event_ready=0
  # output an event *before* we get going
  printf '%s\n' 'k'
  while read -r line ; do
    case "${line}" in
      ################################) : ;;
      *"Waiting for events"*) event_ready=1 ;;
      *)
       [[ "${event_ready}" -eq 1 ]] || continue
       printf '%s\n' "${BRIGHT}" | sudo tee "${backlight}" >/dev/null
       printf '%s\n' 'k'
      ;;
    esac
  done < <(evemu-record "${DEVICE}")
}

# start the coprocs now
coproc watch { evemu_event ; }

# main loop
ce="${IDLE}"
light="${BRIGHT}"

# initial read flags - raw, 1sec timeout
def_rflags=('-t' '1' '-r')
rflags=("${def_rflags[@]}")

while true ; do
  # the read with a timeout is actually what helps us
  read "${rflags[@]}" -u "${watch[0]}" event
  # get event - reset idle counter
  [[ "${event}" ]] && { ce="${IDLE}" ; light="${BRIGHT}" ; rflags=("${def_rflags[@]}") ; continue ; }
  # waiting out the idle counter
  [[ "${ce}" -gt 0 ]] && { ce=$((ce -= 1)) ; continue ; }
  # okay, sleep the thing
  [[ "${light}" -ne "${DARK}" ]] && {
    printf '%s\n' "${DARK}" | sudo tee "${backlight}" >/dev/null
    light="${DARK}"
    # pause the loop by removing the read timeout
    rflags=('-r')
  }
done

commands

systemctl --user enable beepy-bl
systemctl --user start beepy-bl
systemctl --user status beepy-bl