How to quote entrypoint argument when updating a docker service - bash

Question

I've a small script to update some services in my docker stack.
The problem is that I'm not able to update the entrypoint of a service.
For example, my script generates the following command :
docker service update --entrypoint 'go run main.go web' myservice:latest
If a run this command in my terminal it works like a charm but when the command is launched by my script I get the following error:
invalid argument "'go" for "--entrypoint" flag: EOF found when expecting closing quote
Here are the interesting lines in my script :
CMD="go run main web"
...
if [ -n "$CMD" ]; then
update="--entrypoint '${CMD}'"
fi
if [ -n "$update" ]; then
docker service update $update $fullname
echo "docker service update $update $fullname" // output => docker service update --entrypoint 'go run main.go web' myservice:latest
fi
Any help is welcome.

Answer 1

The problem is with your script. Using update as you are, you are running the following
docker service update --entrypoint \'go run main web\'
not
docker service update --entrypoint 'go run main web'
Use an array to store the arguments instead
CMD="go run main web"
if [ -n "$CMD" ]; then
update=(--entrypoint "$CMD")
fi
if [ -n "$update" ]; then # Really just checks ${update[0]}, but that's sufficient
docker service update "${update[#]}" "$fullname"
echo "docker service update ${update[*]} $fullname"
fi
Alternatively, you can test CMD directly to decide if you want to run the command with the --entrypoint option at all.
CMD="go run main web"
if [ -n "$CMD" ]; then
docker service update --entrypoint "$CMD" "$fullname"
echo "docker service --entrypoint $CMD $fullname"
fi