Thorough docker cleanup script

docker-cleanup

#!/bin/sh
# Cleanup docker files: untagged containers and images.
#
# Use `docker-cleanup -n` for a dry run to see what would be deleted.

exited_containers() {
  docker ps -a -q -f status=exited
}

untagged_containers() {
    # Print containers using untagged images: $1 is used with awk's print: 0=line, 1=column 1.
    # NOTE: "[0-9a-f]{12}" does not work with GNU Awk 3.1.7 (RHEL6).
    # Ref: https://github.com/blueyed/dotfiles/commit/a14f0b4b#commitcomment-6736470
    docker ps -a | tail -n +2 | awk '$2 ~ "^[0-9a-f]+$" {print $'$1'}'
}

untagged_images() {
    # Print untagged images: $1 is used with awk's print: 0=line, 3=column 3.
    # NOTE: intermediate images (via -a) seem to only cause
    # "Error: Conflict, foobarid wasn't deleted" messages.
    # Might be useful sometimes when Docker messed things up?!
    # docker images -a | awk '$1 == "<none>" {print $'$1'}'
    docker images | tail -n +2 | awk '$1 == "<none>" {print $'$1'}'
}

untagged_volumes() {
    docker volume ls -qf dangling=true
}

# Dry-run.
if [ "$1" = "-n" ]; then
    echo "=== Exited containers: ==="
    exited_containers
    echo
    echo "=== Containers with uncommitted images: ==="
    untagged_containers 0
    echo
    echo "=== Uncommitted images: ==="
    untagged_images 0
    echo
    echo "=== Untagged volumes: ==="
    untagged_volumes
    exit
fi
if [ -n "$1" ]; then
    echo "Cleanup docker files: remove untagged containers and images."
    echo "Usage: ${0##*/} [-n]"
    echo " -n: dry run: display what would get removed."
    exit 1
fi

# Remove exited containers
echo "Removing exited containers:" >&2
exited_containers | xargs --no-run-if-empty docker rm -v

# Remove containers with untagged images.
echo "Removing containers:" >&2
untagged_containers 1 | xargs --no-run-if-empty docker rm --volumes=true

# Remove untagged images
echo "Removing images:" >&2
untagged_images 3 | xargs --no-run-if-empty docker rmi

# Remove untagged volumes
echo "Removing volumes:" >&2
untagged_volumes | xargs --no-run-if-empty docker volume rm