days-countdown: generate a png showing the number of days remaining until a specified date

days-countdown.sh

#!/usr/bin/env bash
#####
# usage: just run days-countdown.sh to get a countdown until the default date of October 25
# or specify "from" (e.g. today) and "to" (your target date) in this terrible, terrible format:
# days-countdown.sh "$(gdate)" "$(gdate -d 25-Dec)"
# result is ~/tmp/days-countdown.png
# the png's text color is the hex interpretation of the three-digit days-remaining number ;)
# I use Geektool to position the png on my desktop, and run the script in crontab every hour:
## 44 * * * * /Users/andrewrich/Documents/scripts/days-countdown.sh >/dev/null 2>&1
#
# added terminal-notifier so you get a gentle alert when the script fires; comment that if you don't want it
#
# requires: 
# * gdate (brew install coreutils)
# * imagemagick (brew install imagemagick)
# * terminal-notifier (brew install terminal-notifier)
#####

set -euo pipefail
PATH=/usr/local/bin:/usr/local/sbin:$PATH

THIS=$(basename "$0") || THIS="days-countdown"
THIS_FILENAME="${THIS%.*}"

FROM="${1:-$(gdate)}"
TO="${2:-$(gdate -d 25-Oct)}"

DAYNUM_FROM=$(gdate -d "${FROM}" +%j)
DAYNUM_TO=$(gdate -d "${TO}" +%j)

DAY_DIFF=$((DAYNUM_TO - DAYNUM_FROM))

DAY_COLOR="#$( printf '%03d' "${DAY_DIFF}" )"

DAY_DIFF_PNG="$HOME/tmp/${THIS_FILENAME}.png"
convert -background transparent -fill "${DAY_COLOR}" -family Monaco -pointsize 72 label:"${DAY_DIFF}" "${DAY_DIFF_PNG}"
terminal-notifier -title "${THIS}" -message "${DAY_DIFF}" -contentImage "${DAY_DIFF_PNG}"