printbar-watch

#!/usr/bin/env bash
# printbar-watch — refresh Waybar's printbar module(s) instantly on CUPS print events.
#
# It subscribes (via the CUPS `dbus` notifier) to job/printer events for every local
# queue, then listens on the system bus and sends SIGRTMIN+N to Waybar on each event so
# the printbar module re-runs immediately (no waiting for its poll interval).
#
# N defaults to 15; override with PRINTBAR_WAYBAR_SIGNAL to match your module's "signal".
set -uo pipefail

SIGNAL="${PRINTBAR_WAYBAR_SIGNAL:-15}"
DEBOUNCE_NS=700000000 # 0.7s

subtest="$(mktemp "${TMPDIR:-/tmp}/printbar-sub.XXXXXX")" || exit 1
trap 'rm -f "$subtest"' EXIT
cat > "$subtest" <<'IPPT'
{
  OPERATION Create-Printer-Subscriptions
  GROUP operation-attributes-tag
  ATTR charset attributes-charset utf-8
  ATTR naturalLanguage attributes-natural-language en
  ATTR uri printer-uri $uri
  ATTR name requesting-user-name $user
  GROUP subscription-attributes-tag
  ATTR uri notify-recipient-uri dbus://
  ATTR keyword notify-events job-created job-completed job-state-changed printer-state-changed printer-stopped
  ATTR integer notify-lease-duration 0
}
IPPT

subscribe() {
  local p
  for p in $(lpstat -e 2>/dev/null); do
    ipptool -tv -d user="$USER" "ipp://localhost/printers/$p" "$subtest" >/dev/null 2>&1
  done
}

# Re-subscribe periodically so a cupsd restart (which drops subscriptions) is tolerated.
( while true; do subscribe; sleep 300; done ) &
trap 'rm -f "$subtest"; kill %1 2>/dev/null' EXIT

# Refresh on each CUPS notifier signal, debounced.
last=0
dbus-monitor --system "type='signal',interface='org.cups.cupsd.Notifier'" 2>/dev/null |
  while read -r line; do
    case "$line" in
      *"member=Job"* | *"member=Printer"*)
        now=$(date +%s%N)
        if ((now - last > DEBOUNCE_NS)); then
          pkill -RTMIN+"$SIGNAL" waybar 2>/dev/null
          printf 'printbar-watch: CUPS event → Waybar refreshed (RTMIN+%s)\n' "$SIGNAL" >&2
          last=$now
        fi
        ;;
    esac
  done