remove-images.bash

#!/bin/bash

IGNORED_IMAGES=("busybox" "debian:stretch-slim" "dokku/ambassador" "dokku/letsencrypt" "dokku/s3backup" "dokku/wait" "gliderlabs/herokuish:latest")
USED_IMAGES=("${IGNORED_IMAGES[@]}" $(docker container ls -a --format '{{.Image}}' | sort -u | uniq | awk -F ':' '$2{ print $1":"$2 }!$2{ print $1":latest" }'))
USED_IMAGE_IDS=()
ALL_IMAGE_IDS=($(docker image ls --format '{{.ID}}' | sort -u))

for image in "${USED_IMAGES[@]}"; do
  IFS=":" read -a parameters <<<"$image"

  imageName="${parameters[0]}"
  imageVersion="${parameters[1]}"

  if [ "$imageVersion" = "" ]; then
    id=$(docker image ls | grep $imageName | awk '{ print $3 }')
  else
    id=$(docker image ls | grep $imageName | grep $imageVersion | awk '{ print $3 }')
  fi

  USED_IMAGE_IDS=("$id" "${USED_IMAGE_IDS[@]}")
done

for i in "${ALL_IMAGE_IDS[@]}"; do
  unused=true

  for j in "${USED_IMAGE_IDS[@]}"; do
    if [ "$i" = "$j" ]; then
      unused=false
    fi
  done

  if [ "$unused" = true ]; then
    name=($(docker image ls | grep $i | awk '{ print $1":"$2 }'))

    echo "====> Removing ${name[@]}"

    docker image rm ${name[@]} > /dev/null
  fi
done