Shell Tip Of the Day - Interactively Deleting Docker Images

Posted on Fri 08 June 2018 in Posts

![Sometimes when you learn about a hammer, everything looks like a nail....] ({filename}/static/imgs/hammer_nail.jpg)


Sometimes when you learn about a hammer, everything looks like a nail.... In a previous tip I showed off using Bash's select statement to interactively select untracked files in a Git repo.

Today I found another use for the select statement -- deleting local Docker images.

I often will build various Docker images on my machine, and then want to delete selected ones later. In the past, what I'd do is list all images:

$ docker images
REPOSITORY                    TAG                 IMAGE ID            CREATED             SIZE
my-project                    latest              2d0ff261164e        6 hours ago         229MB
ubuntu                        16.04               c9d990395902        8 weeks ago         113MB
nginx                         1.13.11-alpine      2dea9e73d89e        2 months ago        18MB
ruby                          2.3                 9cc35bb87070        2 months ago        723MB

And then copy the IMAGE ID and delete it:

$ docker rmi 2d0ff261164e
Untagged: my-project:latest
Deleted: sha256:2d0ff261164e6caf1024f67e702652ccad040b3031bc56c829d810b3e4a3f72b
Deleted: sha256:0144bb04af73ca7e66420954ef1ebd0355739d932e2b3ce4f0d4e852f1e2cb28
Deleted: sha256:798362db6603c5f680029cfd8ec614cb2a4d7a321a28d222b26a4eb8597371b1

If you have many though this is a lot of tedious copy & pasting. I don't want to delete all images though, just selected ones. Enter the select statement:

select x in `docker images --format '{{.ID}}--{{.Repository}}/{{.Tag}}'` ; do docker rmi `echo $x | awk -F'--' '{print $1}'`; done

Quick dissection: docker images --format '{{.ID}}--{{.Repository}}/{{.Tag}}' will output the list of local Docker images with their ID, followed by two dashes, followed by the repository, followed by a slash, followed by the tag. Ie:

$ docker images --format '{{.ID}}--{{.Repository}}/{{.Tag}}'

etc. Now we select over this output and this displays a menu of them all:

$ select x in `docker images --format '{{.ID}}--{{.Repository}}/{{.Tag}}'` ; do echo "$x" ; done
1) 18bfe820e13a--microsoft/dotnet/1.1-sdk    6) 24ed1c575f81--nginx/1.12.2-alpine
2) c9d990395902--ubuntu/16.04                7) c7fc7faf8c28--alpine/3.4
3) 2dea9e73d89e--nginx/1.13.11-alpine        8) 3fd9065eaf02--alpine/3.7
4) 9cc35bb87070--ruby/2.3                    9) 3fd9065eaf02--alpine/latest
5) 24ed1c575f81--nginx/1.12-alpine          10) cb178ebbf0f2--python/3.6.0-alpine

However, we can't just do a docker rmi $x on a selected item as docker rmi takes an id, not an id followed by two dashes, followed by the image name. However, the argument we need to delete is everything preceding the double-dash. awk to the rescue:

select x in `docker images --format '{{.ID}}--{{.Repository}}/{{.Tag}}'` ;
    docker rmi `echo $x | awk -F'--' '{print $1}'` ;

Dissecting the clunky argument to docker rmi: awk -F'--' '{print $1}' splits the input string on a double dash and then prints just the first column (the ID in our case). We then just echo it back to docker rmi. This works, and I tweeted it at Eric Promislow who was the person who demoed the select statement at Polyglot this year which was where I first saw the trick:

And he replied with a nice simplification of the clunky awk stuff:

select x in `docker images --format '{{.ID}}--{{.Repository}}/{{.Tag}}'` ; do
    docker rmi "${x%--*}";

Much nicer. Final version is also in a gist at: