Check if all Docker containers are running

Question

I want to check if all Docker containers on a host are in "running" state. My naive approach was to print JSON output and then process that with jq:

docker ps -a --format json | jq -r 'map(.State=="running")|all'

However, docker ps apparently produces individual JSON objects per container, not an array of JSON objects, so the above produces the following errors:

jq: error (at :1): Cannot index string with string "State"
jq: error (at :2): Cannot index string with string "State"
...

How can I make docker ps produce a proper JSON array?

Answer 1

AFAIK the docker command doesn't support this and will always output individual objects. But you can tell jq to ingest a series of input objects into an array before processing them:

... | jq -sr 'map(.State=="running")|all'

From the documentation:

• --slurp/-s:
  Instead of running the filter for each JSON object in the input, read the entire input stream into a large array and run the filter just once.