Dynamic wallpaper directories for Ubuntu

seasons.sh

#!/bin/bash
# NAME: season.sh
# PATH: ~/bin
# DATE: December 15, 2018

# NOTE: modified from script given at: https://askubuntu.com/questions/1100934/change-dynamic-wallpaper-directory-every-season/1102084#1102084

# User defined variables, change to suit your needs
# Our directory names, lines indented for cosmetic reasons only
SlideShowDir=$HOME/wallpapers/slideshow
   SpringDir=$HOME/wallpapers/spring
   SummerDir=$HOME/wallpapers/summer
     FallDir=$HOME/wallpapers/fall
   WinterDir=$HOME/wallpapers/winter

# Day of year that seasons start
Spring=$(date --date="March 21" '+%j')
Summer=$(date --date="June 21" '+%j')
Fall=$(date --date="Sep 21" '+%j')
Winter=$(date --date="Dec 21" '+%j')

# Start of Mainline
DOY=$(date '+%j')                     # DOY = Current Day of Year
# Reference: https://stackoverflow.com/questions/10112453/how-to-get-day-of-the-year-in-shell

# For days less than 100, the date function returns as 0XX, which is interpreted as an octal.
# This will force it to be a decimal and avoid the "value too great for base" error.
# Reference: https://stackoverflow.com/questions/12821715/convert-string-into-integer-in-bash-script
DOY=$((10#$DOY))
Spring=$((10#$Spring))
Summer=$((10#$Summer))
Fall=$((10#$Fall))
Winter=$((10#$Winter))

# Reference: https://stackoverflow.com/questions/12614011/using-case-for-a-range-of-numbers-in-bash
if ((DOY>="$Spring" && DOY<"$Summer")) ; then
    ln -sfn "$SpringDir" "$SlideShowDir"          # Spring has sprung!
elif ((DOY>="$Summer" && DOY<"$Fall")) ; then
    ln -sfn "$SummerDir" "$SlideShowDir"          # Hit the beach!
elif ((DOY>="$Fall" && DOY<"$Winter")) ; then
    ln -sfn "$FallDir" "$SlideShowDir"            # Rake those leaves!
else
    ln -sfn "$WinterDir" "$SlideShowDir"          # Shovel the snow!
fi

exit 0 # Command not necessary but good habit to signify no Abend.