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Docker tip : inspect and jq

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Docker inspect and jq

This isn’t so much a docker tip, as it is a jq tip. If you haven’t heard of jq, it is a great tool for parsing JSON from the command line. This also makes it a great tool to see what is happening in a container instead of having to use the –format specifier which I can never remember how to use exactly:

Get network information:

    $ docker inspect 4c45aea49180 | jq '.[].NetworkSettings.Networks'

The output is:

    {
      "bridge": {
        "EndpointID": "ba1b6efba16de99f260e0fa8892fd4685dbe2f79cba37ac0114195e9fad66075",
        "Gateway": "172.17.0.1",
        "IPAddress": "172.17.0.2",
        "IPPrefixLen": 16,
        "IPv6Gateway": "",
        "GlobalIPv6Address": "",
        "GlobalIPv6PrefixLen": 0,
        "MacAddress": "02:42:ac:11:00:02"
      }
    }
    

I could have achieved the same thing using grep. I have detailed how to extract data from docker command using grep in the blog post.

Get the arguments with which the container was started

    $ docker inspect 4c45aea49180 | jq '.[].Args'

The output is:

    [
    "-server",
    "-advertise",
    "192.168.99.100",
    "-bootstrap-expect",
    "1"
    ]

Get all the mounted volumes

$ docker inspect 4c45aea49180 | jq '.[].Mounts'

Output


    [
    {
    "Name": "a8125ffdf6c4be1db4464345ba36b0417a18aaa3a025267596e292249ca4391f",
    "Source": "/mnt/sda1/var/lib/docker/volumes/a8125ffdf6c4be1db4464345ba36b0417a18aaa3a025267596e292249ca4391f/_data",
    "Destination": "/data",
    "Driver": "local",
    "Mode": "",
    "RW": true
    }
    ]

And of course also works great for querying other kinds of (docker-esque) APIs that produce JSON (e.g Marathon, Mesos, Consul etc.). JQ provides a very extensive API for accessing and processing JSON. More information can be found here: https://stedolan.github.io/jq/

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