Starts a GUI application if not running. If it is running, it switches to it. It is unlikely to work well with multiwindow applications without modification because it focuses all of application's windows. Does not work well with "minimize to tray", because it can't find the app's window.

run-once-gui

#!/bin/bash
set -u
set -e
set -o pipefail


# Settings
NAME=GQueues
COMMAND=firefox-gqueues


PREFIX="$HOME/.cache/$NAME-$(id -u)"
LOCKFILE="$PREFIX.lock"
PIDFILE="$PREFIX.pid"

subpids () {
	echo $1
	for i in $( ps --no-headers --ppid $1 -o pid); do
		subpids $i
	done
}

umask 007

if
	( # TODO: Add trap(s) for kill&cleanup
		flock -n 9 || exit 5
		echo critical section: enter
		$COMMAND &
		child_pid=$!
		echo PID: $child_pid
		echo -n $child_pid > "$PIDFILE"
		echo -n "Waiting…"
		wait "$child_pid"
		echo DONE
		rm "$PIDFILE" "$LOCKFILE"
		echo critical section: exit
	) 9> "$LOCKFILE";
	RET=$?;
	[ "$RET" != 0 ]
then
	if [ "$RET" == 5 ]; then
		echo "Can't lock"
		focused=0
		main_pid=$(cat "$PIDFILE")
		for pid in $(subpids "$main_pid"); do
			for winid in $(xdotool search --pid "$pid"); do
				echo "winid: $winid"
				xdotool windowraise "$winid"
				xdotool windowfocus "$winid" || true
				echo "focused: $focused"
				focused=1
			done
		done
		if [ "$focused" != 1 ]; then
			notify-send "Can't focus $NAME!"
			exit 2
		fi
	else
		echo unknown error: $RET
		exit 1
	fi
else
	echo 0
fi

$PREFIX should NOT be in tmpdir, since it would be vulnerable to symlink race condition: https://en.wikipedia.org/wiki/Symlink_race