Dynamically get docker image id from its name - bash

Question

I need to dynamically delete all docker images in a server, except for the postgres image and container.
Now I need a dynamic way to get the id of that docker image so i will know to avoid it, using:
docker rmi $(docker images -q | grep -v $<id_of_postgres_container>)
For the container part, i managed to find this:
docker ps -aqf "name=postgres"
which returns only the id of the postgres container. Is there any way to do the same with images without getting too deep into bash scripting?
or any better suggestions?

Answer 1

docker images --format="{{.Repository}} {{.ID}}" |
grep "^postgres " |
cut -d' ' -f2
Get docker images in the format repository<space>id, then filter lines starting with postgres<space>, then leave only id.
docker images --format="{{.Repository}} {{.ID}}" |
grep "^postgres " |
cut -d' ' -f2 |
xargs docker rmi
But, if the postgres container and image is currently running or used, you can just:
docker system prune --force --all

Answer 2

You can just use:
$ docker images -q [image_name]
Where image_name can contain tags (appended after :), registry username with / (if applicable), etc.
The image has to be downloaded for this to work, for example:
$ docker pull hello-world
...
Status: Downloaded newer image for hello-world:latest
docker.io/library/hello-world:latest
$ docker images -q hello-world
d1165f221234
$ docker images -q hello-world:latest
d1165f221234
If the image is not locally available, the only alternative I can think of is to manually query the registry, e.g. like this.

Answer 3

docker rmi will never delete an image that corresponds to a running container. So if you have a container based on postgres running, and you want to delete every other image on your system, the age-old incantations will do what you want; I’m too old-school for docker system but the “get all of the image IDs, then try to delete them all” I know is
docker images -q | xargs docker rmi
Which will print out some errors, but will delete all of the images it can.