jq: print key and value for each entry in an object

How do I get jq to take json like this:

{
  "host1": { "ip": "10.1.2.3" },
  "host2": { "ip": "10.1.2.2" },
  "host3": { "ip": "10.1.18.1" }
}

and generate this output:

host1, 10.1.2.3
host2, 10.1.2.2
host3, 10.1.18.1

I'm not interested in the formatting, I just can't figure out how to access the key name and value.

To get the top-level keys as a stream, you can use the built-in function keys[]. So one solution to your particular problem would be:

jq -r 'keys[] as $k | "\($k), \(.[$k] | .ip)"' 

keys produces the key names in sorted order; if you want them in the original order, use keys_unsorted.

Another alternative, which produces keys in the original order, is:

jq -r 'to_entries[] | "\(.key), \(.value | .ip)"'

CSV and TSV output

The @csv and @tsv filters might also be worth considering here, e.g.

jq -r 'to_entries[] | [.key, .value.ip] | @tsv'

produces:

host1   10.1.2.3
host2   10.1.2.2
host3   10.1.18.1

Embedded objects

If the keys of interest are embedded as in the following example, the jq filter would have to be modified along the lines shown.

Input:

{
  "myhosts": {
    "host1": { "ip": "10.1.2.3" },
    "host2": { "ip": "10.1.2.2" },
    "host3": { "ip": "10.1.18.1" }
  }
}

Modification:

jq -r '.myhosts | keys[] as $k | "\($k), \(.[$k] | .ip)"'

Came across very elegant solution

jq 'with_entries(.value |= .ip)'

Which ouputs

{
  "host1": "10.1.2.3",
  "host2": "10.1.2.2",
  "host3": "10.1.18.1"
}

Here is the jqplay snippet to play with: https://jqplay.org/s/Jb_fnBveMQ

The function with_entries converts each object in the list of objects to Key/Value-pair, thus we can access .key or .value respectively, we're updating (overwriting) every KV-item .value with the field .ip by using update |= operator