day/night detection for cron jobs

day-night-detection.cron

# Run every minute and do things IF NOT night.
* * * * * (is_night || do_things) >/dev/null 2>&1

# Run every hour and do things IF night.
0 * * * * (is_night && do_things) >/dev/null 2>&1

is_night

#!/usr/bin/python3
import ephem
import time
import sys

home     = ephem.Observer()
home.lat = '50.5'
home.lon = '8.7'

next_sunrise    = home.next_rising(ephem.Sun()).datetime()
next_sunset     = home.next_setting(ephem.Sun()).datetime()

if next_sunset < next_sunrise:
        print("NOT NIGHT rc=1")
        sys.exit(1)
else:
        print("NIGHT rc=0")
        sys.exit(0)