Android image resizer script

#!/bin/bash

f=$(pwd)
original_width=$(sips -g pixelWidth $f/drawable-xxxhdpi/$1 | grep "pixelWidth" | tr " " "," | cut -d "," -f4)
txw=$((original_width/4))

for i in {1..4}
do
  case $i in
  1*)
    dir="drawable-mdpi"
    scale=1
    ;;
  2*)
    dir="drawable-hdpi"
    scale=1.5
    ;;
  3*)
    dir="drawable-xhdpi"
    scale=2
    ;;
  4*)
    dir="drawable-xxhdpi"
    scale=3
    ;;
  esac

  size=$(bc -l <<< "scale=0; $txw*$scale")
  sips --resampleWidth $size "$f/drawable-xxxhdpi/$1" --out "$f/$dir/$1"
done