docker inspect getting various fields for key:value and elements of list
various docker inspect examples
I find that the examples in the docker inspect documentation seem magic, but do not explain much.
Docker inspect is important because it is the clean way to extract information from a running container
docker inspect -f ... container_id
(or all running container)
docker inspect -f ... $(docker ps -q)
avoiding some unreliable
docker command | grep or awk | tr or cut
When you launch a docker inspect you can get the values from the “top-level” easily, with a basic syntax like, for a container running htop (from https://hub.docker.com/r/jess/htop/) with a pid ae1
docker inspect -f '{{.Created}}' ae1
can show
2016-07-14T17:44:14.159094456Z
or
docker inspect -f '{{.Path}}' ae1
can show
htop
Now if I extract a part of my docker inspect
I see
"State": {
"Status": "running",
"Running": true,
"Paused": false,
"Restarting": false,
"OOMKilled": false,
"Dead": false,
"Pid": 4525,
"ExitCode": 0,
"Error": "",
"StartedAt": "2016-07-14T17:44:14.406286293Z",
"FinishedAt": "0001-01-01T00:00:00Z"
So I get a dictionary, as it has { ...} and a lot of key:values
So the command
docker inspect -f '{{.State}}' ae1
will return a list, such as
{running true false false false false 4525 0 2016-07-14T17:44:14.406286293Z 0001-01-01T00:00:00Z}
I can get the value of State.Pid easily
docker inspect -f '{{ .State.Pid }}' ae1
I get
4525
Sometimes docker inspect gives a list as it begins with [ and ends with ]
another example, with another container
docker inspect -f ‘{{ .Config.Env }}’ 7a7
gives
[DISPLAY=:0 PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin LANG=fr_FR.UTF-8 LANGUAGE=fr_FR:en LC_ALL=fr_FR.UTF-8 DEBIAN_FRONTEND=noninteractive HOME=/home/gg WINEARCH=win32 WINEPREFIX=/home/gg/.wine_captvty]
In order to get the first element of the list, we add index before the required field and 0 (as first element) after, so
docker inspect -f ‘{{ index ( .Config.Env) 0 }}’ 7a7
gives
DISPLAY=:0
We get the next element with 1 instead of 0 using the same syntax
docker inspect -f ‘{{ index ( .Config.Env) 1 }}’ 7a7
gives
PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin
We can get the number of elements of this list
docker inspect -f ‘{{ len .Config.Env }}’ 7a7
gives
9
and we can get the last element of the list, the syntax is not easy
docker inspect -f “{{ index .Config.Cmd $[$(docker inspect –format ‘{{ len .Config.Cmd }}’ $CID)-1]}}” 7a7