listing-labels-of-an-image.md

Listing the labels of an image (or container or task)

Docker leverages Go templates to display information about an image (or a container or a task). I find Go templates to be somewhat tricky, perhaps because I'm not familiar with the Go language, at least not yet (circa 2016).

As I work up the Docker learning curve I've accumulated a large and growing set of images. I decided to start adding labels to some of my docker images so that I could use a --filter to reduce the list of images to just the few I'm interested in.

To see the set of labels attached to a specific image you must use the docker inspect command. Unqualified, that command will spew out a long nested JSON object. To just display the bits you are interested in, you have to use the --format option, and that obliges you to learn about Go templates.

After an unsettling amount of trial and and error, and reading and re-reading the documenation, I finally settled on these two variations:

docker inspect --format='{{range $k, $v := .ContainerConfig.Labels}} {{- $k}}={{$v}}{{printf "\n" -}} {{end}}' datihein/rsync-alpine

docker inspect --format='{{range $k, $v := .ContainerConfig.Labels}} {{- printf "%s = \"%s\"\n" $k $v -}} {{end}}' datihein/rsync-alpine

I like the second one best. It outputs something like this:

net.develves.distro = "alpine"
net.develves.distro-version = "alpine 3.4"
net.develves.examples = "flask-web-development-book"

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© 2016 Dave Hein

This work by Dave Hein is licensed under a Creative Commons Attribution 4.0 International License.