Pips for Jonathan (also now partly BY Jonathan)

pips.sh

#!/bin/bash -e

# you need to run this file at startup.
# copy it to your system, make it executable (chmod +x pips.sh), then use /etc/rc.local or whatever to start it up once at boot.
# shouldn't really ever crash, there's nothing to go wrong, as long as the audio player never fails. Then you might
# want some error checking.

while true; do
	# get time now in nanoseconds since 1970-01-01 00:00:00
	now=$(date +%s%N)
	
	# get time at the top of the next hour in nanoseconds since 1970
	# nexthour=$(date -d $(date -d 'next hour' '+%H:00:00') +%s%N) # this broke at 23:00
	# this should be safer:
	thishour=$(date -d $(date '+%H:00:00') +%s%N)
        nexthour=$(($thishour + 3600000000000))

	nexthalfhour=$(($nexthour-1800000000000))
	nextquarterhour=$(($nexthour-2700000000000))
	nextthreequarterhour=$(($nexthour-900000000000))

	
	# take 6 seconds (6000000000 nanoseconds) off that to find next xx:59:54
	next59=$(($nexthour-6000000000))
	next29=$(($nexthalfhour-6000000000))
	next44=$(($nextthreequarterhour-6000000000))
	next14=$(($nextquarterhour-6000000000))


	
	# for debugging, keep these commented out
	#echo Nanoseconds to next hour: $(($nexthour - $now))
	echo Nanoseconds to next hh:59:54: $(($next59 - $now))
	echo Nanoseconds to next hh:29:54: $(($next29 - $now))	
	echo Nanoseconds to next hh:44:54: $(($next44 - $now))
	echo Nanoseconds to next hh:14:54: $(($next14 - $now))


	# if it is later than xx:29:54 BUT BEFORE xx:30:00
	if [ "$now" -gt "$next29" ] && [ "$now" -lt "$nexthalfhour" ]
	then
		# yep, play the pips
		aplay /home/pi/pips.wav # something with aplay or whatever. Note, the command must NOT return 
		                                                       # until the file has finished playing the audio file, and the file must 
															   # be > 5s long, otherwise this will trigger multiple times.
		#sleep 6 # this pretends to play file, remove it when the above echo statement is replaced with a command that plays audio
		#echo "Back to clock-watching"
	else
		# nope, it's elsewhere in the hour.
		sleep 0.005 # stops you from pegging the CPU. Don't need to check time more than maybe every 5ms. 
		            # experiment to find a value that is accurate enough for you, but doesn't thrash the CPU.
	fi

	# if it is later than xx:44:54 BUT BEFORE xx:45:00
	if [ "$now" -gt "$next44" ] && [ "$now" -lt "$nextthreequarterhour" ]
	then
		# yep, play the pips
		aplay /home/pi/pips.wav # something with aplay or whatever. Note, the command must NOT return 
		                                                       # until the file has finished playing the audio file, and the file must 
															   # be > 5s long, otherwise this will trigger multiple times.
		#sleep 6 # this pretends to play file, remove it when the above echo statement is replaced with a command that plays audio
		#echo "Back to clock-watching"
	else
		# nope, it's elsewhere in the hour.
		sleep 0.005 # stops you from pegging the CPU. Don't need to check time more than maybe every 5ms. 
		            # experiment to find a value that is accurate enough for you, but doesn't thrash the CPU.
	fi

	# if it is later than xx:59:54
	if [ "$now" -gt "$next59" ]
	then
		# yep, play the pips
		aplay /home/pi/pips.wav # something with aplay or whatever. Note, the command must NOT return 
		                                                       # until the file has finished playing the audio file, and the file must 
															   # be > 5s long, otherwise this will trigger multiple times.
		#sleep 6 # this pretends to play file, remove it when the above echo statement is replaced with a command that plays audio
		#echo "Back to clock-watching"
	else
		# nope, it's elsewhere in the hour.
		sleep 0.005 # stops you from pegging the CPU. Don't need to check time more than maybe every 5ms. 
		            # experiment to find a value that is accurate enough for you, but doesn't thrash the CPU.
	fi


	# if it is later than xx:14:54 BUT BEFORE xx:15:00
	if [ "$now" -gt "$next14" ] && [ "$now" -lt "$nextquarterhour" ]
	then
		# yep, play the pips
		aplay /home/pi/pips.wav # something with aplay or whatever. Note, the command must NOT return 
		                                                       # until the file has finished playing the audio file, and the file must 
															   # be > 5s long, otherwise this will trigger multiple times.
		#sleep 6 # this pretends to play file, remove it when the above echo statement is replaced with a command that plays audio
		#echo "Back to clock-watching"
	else
		# nope, it's elsewhere in the hour.
		sleep 0.005 # stops you from pegging the CPU. Don't need to check time more than maybe every 5ms. 
		            # experiment to find a value that is accurate enough for you, but doesn't thrash the CPU.
	fi


done