List all Docker images in a Shell-friendly format (optionally, JSON too)

grep-images.py

#!/usr/bin/env python
#
# Created by M. Massenzio (c) 2017.

# The output of `docker images` is easy on the eye, but not
# terribly helpful if you want to pipe it into further shell
# commands; and using `cut` only gets you so far (in fact,
# not very far at all).
#
# This script emits the list of Docker images on your system
# in a format that is suitable for piping to further commands,
# (probably, with a `grep` in there, to pick only the one(s)
# you seek) and additional tooling.
#
# There are two optional arguments: `--json` and `--id` if you
# need, respectively, the output to be well-formed JSON, or
# just the images' IDs.
#
# Example:
#   ./grep-images.py
#
#   massenz/kafka:0.10.1.1
#   cassandra:3.7
#   cassandra:latest
#   mongo:latest
#   massenz/spark:2.0.0
#   massenz/voldemort:1.10.14
#   ...

import itertools
import json
import sh
import sys

is_json = '--json' in sys.argv
only_ids = '--id' in sys.argv

images_cmd = sh.docker('images')
lines = images_cmd.stdout.decode().splitlines()

images = list()
keys = lines[0].split()
keys.remove('IMAGE')

for img in lines[1:]:
    if not img.startswith('<none>'):
        if only_ids:
            print(img.split()[2])
        else:
            images.append(dict(itertools.zip_longest(keys[:3], img.split()[:3])))

if not only_ids:
    if is_json:
        print(json.dumps(images, indent=4))
    else:
        for img in images:
            print("{rep}:{tag}".format(rep=img['REPOSITORY'], tag=img['TAG']))