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Simple public domain library and application that shows sunset and sunrise based on your latitude,longitude. The application can also be used with cron to run a script, see section Goal below.

The library, which can be used entirely stand-alone, is based on the excellent code by Paul Schlyter.

Without any arguments the sun goes dumpster diving in system files /etc/timezone and /usr/share/zoneinfo/zone.tab to figure out your latitude and longitude.

On my system, in mid December here in Sweden, the result is:

$ cat /etc/timezone
Europe/Stockholm
$ sun
Sun rises 07:31, sets 13:49 UTC

You can set the environment variable TZ to check other locations:

$ TZ="Africa/Luanda" sun
Sun rises 04:42, sets 17:18 UTC

For more precision, you can of course provide your exact latitude and longitude. See the built-in usage text for more help: sun -h

To launch applications at sunrise/sunset using cron, simply:

$ crontab -e
01 00 * * * sun -r -w -o -30m; play english.au

This plays Linus Torvalds' classic audio file 30 minutes before sunrise.

NOTE: You may want to set the $PATH in your crontab, or use an absolute path to your programs, otherwise cron will not find them.

Usage:
  sun [-ahirsw] [-o OFFSET] [+/-latitude +/-longitude]

Options:
  -a      Show all relevant times and exit
  -l      Increased verbosity, enable log messages
  -h      This help text
  -i      Interactive mode
  -r      Sunrise mode
  -s      Sunset mode
  -u      Use UTC everywhere, not local time
  -v      Show program version and exit
  -w      Wait until sunset or sunrise
  -o ARG  Time offset to adjust wait, e.g. -o -30m
          maximum allowed offset: +/- 6h

Bug report address: https://github.com/troglobit/sun/issues

The goal of this project is to provide just enough intelligence to my home automation system so it can control the indoor lights, which are operated using 433 MHz outlet switches.

The sun is built with the GNU configure and build system. Simply run the following commands to build and install:

$ ./configure
$ make
$ sudo make install

The sunriset.c code can be built as a library, use --enable-library with the configure script to enable this optional feature.

If you built from GIT, or have modified any of the .ac or .am files, you have to run the following to (re-)create the configure script:

.$ /autogen.sh

For that to work you need to have autoconf, automake, and libtool installed. These tools are not needed when building from an official released tarball.