How to get the value via Linux command 'grep'

Question

I want to get some specific information with docker api. In this case, I want to get the IMAGE ID that correspond to <none> of REPOSITORY with command docker images

$ docker images
REPOSITORY          TAG                 IMAGE ID            CREATED             SIZE
<none>              <none>              ebeb5aebbeef        5 minutes ago       479MB
build-embed         latest              80636e4726f8        10 minutes ago      479MB
<none>              <none>              a2abf2e07bc3        About an hour ago   1.38GB
ubuntu              18.04               4e5021d210f6        5 weeks ago         64.2MB

I tried the command as below:

$ docker images | grep `<none>'

And get results:

<none>              <none>              ebeb5aebbeef        2 minutes ago       479MB
<none>              <none>              a2abf2e07bc3        58 minutes ago      1.38GB

How can I just only get the IMAGE ID ? (like ebeb5aebbeef a2abf2e07bc3 )

The purpose of this question is that I want to remove <none> images with docker api, like docker rmi $(docker images | grep <none>

Thank you all

Answer 1

Use awk to get just the third field of the matching lines.

docker images | awk '$1 == "<none>" { print $3 }'

Don't use grep '<none>' since that can match in fields other than the REPOSITORY .

Answer 2

Use --filter option with -q option, instead of listing all images and filtering them using grep

docker images -f "dangling=true" -q

Answer 3

The docker images command has a couple of options to do this more directly, without trying to parse apart its output.

docker images -f can filter the list of images presented on a minimal set of conditions. One of those conditions is "dangling", which is exactly those images with <none> labels. This can replace your grep command.

docker images -q prints out only the image IDs and not the rest of the line. This can replace the awk command from @Barmar's answer .

This would leave you with

docker images -f dangling=true -q

to print out the image IDs of <none> images, which is what you're after; and thereby

docker images -f dangling=true -q | xargs docker rmi

to remove them.

Also consider docker system prune which will remove dangling images, and also stopped containers and unused networks.