JQ JSON – How to Keep One Specific Key from Nested Object

jqjson

I have the following config.json file:

{
        "auths": {
                "reg1.io": {
                        "auth": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
                },
                "reg2.io": {
                        "auth": "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
                },
                "reg3.io": {
                        "auth": "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"
                }
        }
}

I want to keep only the reg2.io object to get:

{
        "auths": {
                "reg2.io": {
                        "auth": "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
                }
        }
}

I can delete one specific object with e.g.:

→ jq 'del(.. | ."reg2.io"? )' ./config.json
{
  "auths": {
    "reg1.io": {
      "auth": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"
    },
    "reg3.io": {
      "auth": "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz"
    }
  }
}

but what if i want to keep one specific object? Thanks.

Best Answer

Using select() with with_entries() to select only the key that you want:

$ jq '.auths |= with_entries(select(.key == "reg2.io"))' file
{
  "auths": {
    "reg2.io": {
      "auth": "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
    }
  }
}

Parametrised so that it takes the wanted key from the command line:

$ jq --arg key "reg2.io" '.auths |= with_entries(select(.key == $key))' file
{
  "auths": {
    "reg2.io": {
      "auth": "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy"
    }
  }
}

Change the == to != to delete the named key.

Note that your own attempt does not distinguish where the key is found in the document, which could cause some confusion in the general case.

Just to add a bit more explanation as to what's happening in the jq expression.

Within the with_entries() command, what's visible is the following set of objects, each with a key and a value key:

{
   "key": "reg1.io",
   "value": { "auth": "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" }
}
{
   "key": "reg2.io",
   "value": { "auth": "yyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyyy" }
}
{
   "key": "reg3.io",
   "value": { "auth": "zzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzzz" }
}

The select() call extracts each object for which the given test is true, and discards the rest. Our test is simply "Is the value of the key key the string reg2.io?".

A call to with_entries(expr) is equivalent to to_entries | map(expr) | from_entries.

Related Solutions

JSON Object Removal – How to Remove a Specific JSON Object from a File

To delete the .packages.code key and its value, using jq:

jq 'del(.packages.code)' file.json

To delete any entry under .packages whose .name key has the value code:

jq 'del(.packages[] | select(.name == "code"))' file.json

The same two commands, but they take the code string from a shell variable:

string=code

jq --arg key "$string" 'del(.packages[$key])' file.json

jq --arg key "$string" 'del(.packages[] | select(.name == $key))' file.json

Redirect the output to a new file and replace the old file with that if it looks ok.

Shell – How to Merge Multiple JSON Objects into One Array

Assuming that the input looks like

[1] 14:44:51 [SUCCESS] 1.1.1.1
{"field1":"value11","field2":"value12","field3":"value13"}
[2] 14:44:51 [SUCCESS] 1.1.1.2
{"field1":"value21","field2":"value22","field3":"value23"}

(Note that I have fixed the broken JSON on the lines that have JSON objects.)

... then you can extract the lines that you want with grep:

grep '^{' file

grep -v -F '[SUCCESS]' file

or similar grep command.

You may then parse the stream of JSON objects using jq -s, which will automatically read them into an array. This allows you do the processing of the data like so:

grep '^{' file | jq -s 'map({ alias1: .field1, alias2: .field3 })'

With the input shown above in file, this would generate

[
  {
    "alias1": "value11",
    "alias2": "value13"
  },
  {
    "alias1": "value21",
    "alias2": "value23"
  }
]

If you are uninterested in changing your already existing initial parsing of the input and want to put your output into an array, then it's just a matter of passing it through jq -s .:

$ cat file
{ "alias1": "value11", "alias2": "value13" }
{ "alias1": "value21", "alias2": "value23" }

$ jq -s . file
[
  {
    "alias1": "value11",
    "alias2": "value13"
  },
  {
    "alias1": "value21",
    "alias2": "value23"
  }
]

A hack to read directly from the original file with jq is to read the data as raw strings, try to convert them into valid JSON, and then throw away any errors:

$ cat file
[1] 14:44:51 [SUCCESS] 1.1.1.1
{"field1":"value11","field2":"value12","field3":"value13"}
[2] 14:44:51 [SUCCESS] 1.1.1.2
{"field1":"value21","field2":"value22","field3":"value23"}

$ jq -R 'fromjson | { alias1: .field1, alias2: .field3 }' file 2>/dev/null
{
  "alias1": "value11",
  "alias2": "value13"
}
{
  "alias1": "value21",
  "alias2": "value23"
}

This could then be gathered in an array:

$ jq -R 'fromjson | { alias1: .field1, alias2: .field3 }' file 2>/dev/null | jq -s .
[
  {
    "alias1": "value11",
    "alias2": "value13"
  },
  {
    "alias1": "value21",
    "alias2": "value23"
  }
]

Note that we need the two separate invocations of jq here as the first jq invocation would terminate prematurely if it tried to convert the input into JSON with fromjson into an array (or any other structure other than individual objects).

Best Answer

Related Solutions

JSON Object Removal – How to Remove a Specific JSON Object from a File

Shell – How to Merge Multiple JSON Objects into One Array

Related Question