current_moon_phase.md

Calculate the phase of the moon in bash and get the appropriate icon. This can be used to put a picture of the phase of the moon in your bash prompt.

I used the "Simple" lunar phase calculator from here:

http://www.ben-daglish.net/moon.shtml

It seems to work well on OSX. The call to date that I use is not portable to linux or solaris since date is one of the most infuriatingly inconsistent utilities.

current_moon_phase.sh

#!/bin/bash

get_phase_day () {
  local lp=2551443
  local now=$(date -ju +"%s")
  local newmoon=592500
  local phase=$((($now - $newmoon) % $lp))
  echo $(((phase / 86400) + 1))
}


get_moon_icon () {
  local phase_number=$(get_phase_day)
  # Multiply by 100000 so we can do integer comparison.  Go Bash!
  local phase_number_biggened=$((phase_number * 100000))

  if   [ $phase_number_biggened -lt 184566 ];  then phase_icon="🌑"  # new
  elif [ $phase_number_biggened -lt 553699 ];  then phase_icon="🌒"  # waxing crescent
  elif [ $phase_number_biggened -lt 922831 ];  then phase_icon="🌓"  # first quarter
  elif [ $phase_number_biggened -lt 1291963 ]; then phase_icon="🌔"  # waxing gibbous
  elif [ $phase_number_biggened -lt 1661096 ]; then phase_icon="🌕"  # full
  elif [ $phase_number_biggened -lt 2030228 ]; then phase_icon="🌖"  # waning gibbous
  elif [ $phase_number_biggened -lt 2399361 ]; then phase_icon="🌗"  # last quarter
  elif [ $phase_number_biggened -lt 2768493 ]; then phase_icon="🌘"  # waning crescent
  else                                     phase_icon="🌑"  # new
  fi
  echo $phase_icon

}

get_moon_icon

I wonder why you turn a small int into a big int to do comparisons instead of rounding the phase numbers to int size? Say phase_number is 15. You save a step by just asking if 15 is < 16 instead of multiplying 15 by 100000 and asking if 1500000 < 1661096. Though perhaps I'm not fully grasping what's going on :)