Makefile remove stopped Docker containers - makefile

Question

I'm new to Makefiles, I'm trying to use one to help me automate the build of my docker images.
I'm struggling to write, what feels like, a simple recipe that does the following:
Check to see if there are running containers (docker ps -a -q)
If running containers exist remove them (docker rm $(docker ps -a -q))
This is what I've manage to cobble together so far through various Google searches:
DOCKER_CONTAINER_LIST := $(shell docker ps -a -q)
clean-docker:
if [[ ! $(DOCKER_CONTAINER_LIST) == "" ]];then \
docker rm $$(docker ps -a -q) \
fi
Which yields the following output:
if [[ de6e694da4f9 == "" ]];then \
/bin/sh: -c: line 0: conditional binary operator expected
/bin/sh: -c: line 0: syntax error near 'de6e694da4f9'
/bin/sh: -c: line 0: 'if [[ de6e694da4f9 == "" ]];then \ '
make: *** [clean-docker] Error 2
Would be great if someone could show me how to achieve this please
UPDATE
Thank #I0b0 for your answer, I think I'm almost there now. The Makefile now looks like this:
DOCKER_CONTAINER_LIST := $(shell docker ps -a -q)
clean-docker:
if [ -n "$(DOCKER_CONTAINER_LIST)" ] \
then \
docker rm "$(DOCKER_CONTAINER_LIST)" \
fi
But I get the following error when running it:
if [ -n "6778d35e5c95" ] \
then \
docker rm "6778d35e5c95" \
fi
/usr/bin/sh: -c: line 4: syntax error: unexpected end of file
make: *** [clean-docker] Error 1
I had a look at this answer regarding line endings, but that made no difference. I am using Makefile on both Mac and Windows.

Answer 1

It can be done with:
# for images
docker rmi $(shell docker images -a -q)
# for containers
docker rm $(shell docker ps -a -q)
# for volumes
docker volume rm $(shell docker volume ls -q)
PS. macOS

Answer 2

if [ -n "$(DOCKER_CONTAINER_LIST)" ] should do it:
-n is the standard test for a non-empty string
Use More Quotes™ never gets old
[[ is a bashism, but sh is not bash
Bonus points for reusing the variable with docker rm "$(DOCKER_CONTAINER_LIST)".
After the update the problem is related to a fundamental difference between scripts and makefiles: the latter cannot be broken into lines in the exact same way as scripts by just adding backslashes before the end of line. What you've ended up with is a single line if [ -n "$(DOCKER_CONTAINER_LIST)" ] then docker rm "$(DOCKER_CONTAINER_LIST)" fi. Because newlines in a makefile don't work like ; in a shell script you have to add two:
if [ -n "$(DOCKER_CONTAINER_LIST)" ]; \
then \
docker rm "$(DOCKER_CONTAINER_LIST)"; \
fi

Answer 3

I couldn't figure out how to divide those commands into multiple lines either, but ugly oneliners work for me.
So what you were asking about would be something like this
DOCKER_CONTAINER_LIST := $(shell docker ps -a -q)
clean_docker:
#if [ -n "$(DOCKER_CONTAINER_LIST)" ]; then echo "Removing docker containers" && docker rm "$(DOCKER_CONTAINER_LIST)"; else echo "No containers found"; fi;