docker ps -f should return nonzero exit status for no matches
Nobody has claimed this yet.
Assessment
- Difficulty
- 4/5
- Estimated time
- 3-5 days
- Newbie friendliness
- 35/100
Research direction
Start at the docker ps command and its filter handling, then trace how an empty result currently determines the process exit status. The change is done when docker ps -f returns a nonzero status for no matching containers while retaining the expected output and integration behavior.
Written by the indexing model from the issue text.
Description
Description
As per vdemeester comment, re-opening https://github.com/moby/moby/issues/35057.
Reason to close was command will return zero even when "docker ps" returns no containers.
If instead docker ps returns ie 1 or not zero when container is not running, it then enables better integration with other tooling:
# Conventional Exit Code Use - ls command on folder exists, not-exists
if [[ $( ls /tmp 2>/dev/null ) ]]; then echo "folder exists"; else echo "folder does not exist"; fi
folder exists
if [[ $( ls /tmpXX 2>/dev/null ) ]]; then echo "folder exists"; else echo "folder does not exist"; fi
folder does not exist
# Docker ps - Less Useful Zero Exit Code
if [[ $( docker ps --filter label=runningimage=no 2>/dev/null ) ]]; then echo "container is running"; else echo "container is not running"; fi
container is running
??? WHY
eg, docker ps - no containers are running
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
....
Another closer example, "pgrep" - listing processes by process matching, clearly explains rationale:
...
-c, --count
Suppress normal output; instead print a count of matching processes. When count does not match anything, e.g. returns zero, the command will return
non-zero value. Note that for pkill and pidwait, the count is the number of matching processes, not the processes that were successfully signaled or
waited for.
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