Get the current phase of the moon and use it to print an emoji moon phase image. OS X only, requires some shell knowledge. (Emoji moon phases will not show up here, but they will when you copy and paste or download the file.)

.bash_prompt

# Get the current phase of the moon for use as prompt
# Adapted from: http://wan.pengganas.net/entry/calculating-phase-of-moon-in-ruby
function moonphase() {
/usr/bin/env ruby <<-EORUBY
  # Convert a date to Julian.
  def julian(year, month, day)
    a = (14-month)/12
    y = year+4800-a
    m = (12*a)-3+month

    return day + (153*m+2)/5 + (365*y) + y/4 - y/100 + y/400 - 32045
  end

  Define the phases of the moon.
  def phase(year, month, day)
    p = (julian(year, month, day) - julian(2000, 1, 6)) % 29.530588853

    if    p < 1.84566 then  return "🌑"  # new
    elsif p < 5.53699 then  return "🌒"  # waxing crescent
    elsif p < 9.22831 then  return "🌓"  # first quarter
    elsif p < 12.91963 then return "🌔"  # waxing gibbous
    elsif p < 16.61096 then return "🌕"  # full
    elsif p < 20.30228 then return "🌖"  # waning gibbous
    elsif p < 23.99361 then return "🌗"  # last quarter
    elsif p < 27.68493 then return "🌘"  # waning crescent
    else                    return "🌑"  # new
    end
  end

  # Get today's phase.
  today = Time.new
  print "#{phase(today.year, today.month, today.day)}"
EORUBY
}

# Set the prompt.
PS1="\$(moonphase)  "

comments.md

Note the two spaces after the emoji moon; it leaves a decent space between prompt and your command.

This is the simplest possible prompt; just a moon phase. You will probably want to incorporate this into something fancier. My .bash_prompt file has its own line for the current path, Git smarts, and more.

Line 14 of the above script is not commented out, which will result in an error when copy-pasting into a .bash_prompt or elsewhere in the shell. Otherwise lookin' good and thanks! 🌝

Hi, This one should work for you - it's changed a little - now printing the name of the phase rather than the icon, used a bit of bc to do the math and also running it as a ksh script (not sure if that is important!)

!/bin/ksh

Convert a date to Julian.

function convert_to_julian {

let year=$1
let month=$2
let day=$3

let a=$year/100
let b=$a/4
let c=2-$a+$b
let e=365.25_($year+4716)
let e=$(echo "$e/1" |bc)
let f=30.6001_($month+1)
let f=$(echo "$f/1" |bc)
let converted_date=$c+$day+$e+$f-1524.5

}

Define the phases of the moon.

function get_moon_phase {
let year=$1
let month=$2
let day=$3
convert_to_julian $year $month $day
today=$converted_date

convert_to_julian 2000 1 6
converter=$converted_date

echo today is $today
echo converter is $converter

let phase_number=$today-$converter
let phase_number=$(echo "$phase_number%29.530588853" |bc)

phase_number=$(($(($today - $converter))/29))

echo the phase number is $phase_number

if [ $phase_number -lt "1.84566" ]; then phase_icon="new"
elif [ $phase_number -lt "5.53699" ]; then phase_icon="waxing crescent"
elif [ $phase_number -lt "9.22831" ]; then phase_icon="first quarter"
elif [ $phase_number -lt "12.91963" ]; then phase_icon="waxing gibbous"
elif [ $phase_number -lt "16.61096" ]; then phase_icon="full"
elif [ $phase_number -lt "20.30228" ]; then phase_icon="waning gibbous"
elif [ $phase_number -lt "23.99361" ]; then phase_icon="last quarter"
elif [ $phase_number -lt "27.68493" ]; then phase_icon="waning crescent"
else phase_icon="new"
fi
}

now the main line

let year=$1
let month=$2
let day=$3

get_moon_phase $year $month $day
echo $phase_icon

Oh and to use - run ./moonPhase.sh yyyy mm dd

where moonPhase.sh is the name of your script!