Shell script to take Android assets exported from Sketch and sort them into resource folders. Adapted from https://medium.com/@lmindler/using-sketch-3-and-a-bit-of-fairy-dust-for-a-better-android-workflow-f667d0048855#.r8qyblpe7.

SortDroidAssets.sh

mkdir drawable-xxhdpi; mkdir drawable-xhdpi; mkdir drawable-hdpi; mkdir drawable-mdpi
for file in $(find . -type f -iname '*-xxhdpi*'); do
  mv "$file" "drawable-xxhdpi/${file/-xxhdpi/}"
done
for file in $(find . -type f -iname '*-xhdpi*'); do
  mv "$file" "drawable-xhdpi/${file/-xhdpi/}"
done
for file in $(find . -type f -iname '*-hdpi*'); do
  mv "$file" "drawable-hdpi/${file/-hdpi/}"
done
for file in $(find . -type f -iname '*-mdpi*'); do
  mv "$file" "drawable-mdpi/${file/-mdpi/}"
done

To make the shell script executable:
sudo chmod +x SortDroidAssets.sh

I add the file to my PATH so I can use it anywhere.