Get the last element of a docker image path using Go templates - docker

Question

I would like to generate a synthetic docker ps table but my docker image paths are very long. The solution I am trying to do is to display only the last part of the image name:
This is what I have:
docker ps --format "table {{.Names}}\\t{{.Image}}\\t{{.Status}}\\t{{.Command}}"
NAMES IMAGE STATUS COMMAND
a_container a_local_image Up 36 minutes "python…"
another_container registry.example.com/group/subgroup/project/my_image:latest Up 38 minutes "go…"
I would like:
docker ps --format "table {{.Names}}\\t{{ <magic .Image> }}\\t{{.Status}}\\t{{.Command}}"
NAMES IMAGE STATUS COMMAND
a_container a_local_image Up 36 minutes "python…"
another_container my_image:latest Up 38 minutes "go…"
so basically, get what is after the last /, like basename does.
This is what I tried:
# No fixed length
docker ps --format "table {{ slice .Image 0 10}}"
# No last index available
docker ps --format 'table {{ (split "/" .Image) }}'
Any help or workaround is appreciated.
p.s.: since I use docker cli, I don't think I can define custom functions to use in the template expression.

Answer 1

There is no good way to get the last element of a template array. Even though you can use index and len built-ins, you can't use arithmetic to get len - 1.
This is a template-only trick:
{{ $image := "" }}{{ range split .Image "/" }}{{ $image = . }}{{ end }}{{ $image }}
Basically it does the following:
declare a var $image
split the .Image on /
iterate over the array string and just assign to $image
at the end of the range, $image will hold the value of the last element
print $image
Full command (with enclosing apex ' so you don't have to escape quotes):
docker ps --format 'table {{.Names}}\t{{ $image := "" }}{{ range split .Image "/" }}{{ $image = . }}{{ end }}{{ $image }}\t{{.Status}}\t{{.Command}}'

Answer 2

You may could use next workaround, I put it in a shell file just because it's too long, but you are ok to call it directly in shell.
test.sh
paste <(docker ps --format 'table {{.ID}}') \
<(docker ps --format 'table {{.Image}}' | awk -F '/' '{print $NF}') \
<(docker ps --format 'table {{.Command}} {{.CreatedAt}} {{.Status}} {{.Ports}} {{.Names}}')
Explain:
docker ps --format 'table {{.ID}}' get the ID column of docker ps
docker ps --format 'table {{.Image}}' | awk -F '/' '{print $NF}'), frist get the Image column, then use awk to split /, get the last sub column as you required.
the left is used to get remained columns as you needed of docker ps
Finally, use paste command to combine the output of above command.