Use jq to turn x=y pairs into key/value pairs

Question

I'm trying to parse environment variables from the JSON output of docker inspect. Annoyingly, those environment variables aren't returned as useful key-value pairs. They're just an array of x=y strings. Here's a relevant snippet of the output:

[
    {
        "Config": {
            "Env": [
                "JENKINS_HOST=1.2.3.4",
                "JENKINS_INSTANCE=tea",
                "JENKINS_NAME=Enterprise Architecture Tools",
                "JENKINS_VERSION=2.46.2",
                "JENKINS_PROTOCOL=http"
            ]
        }
    }
]

I would like to convert that array into something like this:

{
  "Config": {
    "Env": {
      "JENKINS_HOST": "1.2.3.4",
      "JENKINS_INSTANCE": "tea",
      "JENKINS_NAME": "Enterprise Architecture Tools",
      "JENKINS_VERSION": "2.46.2",
      "JENKINS_PROTOCOL": "http"
    }
  }
}

That way, I can use a command like jq '.[] | .Config.Env.JENKINS_HOST' to get the values that I care about. I can't figure out how to accomplish this.

It's relatively easy to select the data and even split the key and value into separate elements. For instance, if I use jq '.[] | .Config.Env | .[] | split("=")', I get data like this:

[
  "JENKINS_HOST",
  "1.2.3.4"
]
[
  "JENKINS_INSTANCE",
  "tea"
]
[
  "JENKINS_NAME",
  "Enterprise Architecture Tools"
]
[
  "JENKINS_VERSION",
  "2.46.2"
]
[
  "JENKINS_PROTOCOL",
  "http"
]

However, I can't figure out how to turn that data into an object assignment. It seems like it should probably be some combination of map or reduce, but I'm stumped. Can anyone point me in the right direction?

Answer 1

Given collection of items to convert to a single object, I generally would opt to using reduce for this purpose. Turn those items to their constituent keys and values, then assign to the result object.

reduce (.[] | split("=")) as [$key, $value] ({}; .[$key] = $value)

Though using from_entries is also useful here as well, instead you'd create an array of the key/value objects that it expects.

map(split("=") as [$key, $value] | {$key, $value}) | from_entries

Then put it all together with the update of the Env property using whichever method you choose.

.[].Config.Env |= reduce (.[] | split("=")) as [$key, $value] ({}; .[$key] = $value)
#or
.[].Config.Env |= (map(split("=") as [$key, $value] | {$key, $value}) | from_entries)

https://jqplay.org/s/qfItW5U-Tf

Answer 2

To convert an array of two strings (e.g. ["k", "v"]) to an object, you can write:

{ (.[0]) : .[1] }

So you'll want to write something like:

 map(.Config.Env |= (map( split("=") | { (.[0]) : .[1] } ) | add))

a2o

Abstracting out the array-to-object functionality makes the solution a bit more digestible:

def a2o: map( split("=") | { (.[0]) : .[1] } ) | add;

map(.Config.Env |= a2o)

Using match or capture instead of split

Since it is possible for an "=" character to appear in the "value" part of each var=value string, using split naively might not be such a great idea. Here is a more robust alternative, assuming your jq supports regular expressions:

match("([^=]*)=(.*)") | .captures | {(.[0].string) : .[1].string}

Or, slightly more succinctly and perhaps elegantly:

[capture( "(?<key>[^:]*):(?<value>.*)" )] | from_entries

index/1

If your jq does not have regex support, you could use index/1, along these lines:

index("=") as $ix | {(.[:$ix]) : .[$ix+1:]}