How to pretty print a JSON inside a string with jq?

Question

I'm writing a more complex transformation with jq, and one of the things I'd like to do is to have a pretty printed JSON inside a string. For example:

echo '{"foo": "bar"}' | jq '{json: {other: .} | tostring}'

gives

{
  "json": "{\"other\":{\"foo\":\"bar\"}}"
}

while I'd like to get:

{
  "json": "{\n  \"other\": {\n    \"foo\": \"bar\"\n  }\n}"
}

I have also tried tojson and @json, but they give the same result as tostring. Is it possible to do with jq or do I have to resort to some other trickery? Note that I need to have multiple such string with formatted JSON in the output, not just one like in the example.

Answer 1

I ended up writing a simple formatting function:

#   9 = \t
#  10 = \n
#  13 = \r
#  32 = (space)
#  34 = "
#  44 = ,
#  58 = :
#  91 = [
#  92 = \
#  93 = ]
# 123 = {
# 125 = }

def pretty:
  explode | reduce .[] as $char (
    {out: [], indent: [], string: false, escape: false};
    if .string == true then
      .out += [$char]
      | if $char == 34 and .escape == false then .string = false else . end
      | if $char == 92 and .escape == false then .escape = true else .escape = false end
    elif $char == 91 or $char == 123 then
      .indent += [32, 32] | .out += [$char, 10] + .indent
    elif $char == 93 or $char == 125 then
      .indent = .indent[2:] | .out += [10] + .indent + [$char]
    elif $char == 34 then
      .out += [$char] | .string = true
    elif $char == 58 then
      .out += [$char, 32]
    elif $char == 44 then
      .out += [$char, 10] + .indent
    elif $char == 9 or $char == 10 or $char == 13 or $char == 32 then
      .
    else
      .out += [$char]
    end
  ) | .out | implode;

It adds unnecessary empty lines inside empty objects and arrays, but it's good enough for my purpose. For example (used on its own):

jq -Rr 'include "pretty"; pretty' test.json

where the function is saved in pretty.jq and test.json file is:

{"type":"FeatureCollection","features":[{"type":"Feature","properties":{"key":"string with \"quotes\" and \\"},"geometry":{"type":"Polygon","coordinates":[[[24.2578125,55.178867663281984],[22.67578125,50.958426723359935],[28.125,50.62507306341435],[30.322265625000004,53.80065082633023],[24.2578125,55.178867663281984]]]}}]}

gives:

{
  "type": "FeatureCollection",
  "features": [
    {
      "type": "Feature",
      "properties": {
        "key": "string with \"quotes\" and \\"
      },
      "geometry": {
        "type": "Polygon",
        "coordinates": [
          [
            [
              24.2578125,
              55.178867663281984
            ],
            [
              22.67578125,
              50.958426723359935
            ],
            [
              28.125,
              50.62507306341435
            ],
            [
              30.322265625000004,
              53.80065082633023
            ],
            [
              24.2578125,
              55.178867663281984
            ]
          ]
        ]
      }
    }
  ]
}

Answer 2

This:

echo '{"foo": "bar"}' | jq '{other: .}' | jq -Rs '{json: .}'

produces:

{
  "json": "{\n  \"other\": {\n    \"foo\": \"bar\"\n  }\n}\n"
}

One way to remove the terminating "\n" would be to strip it:

echo '{"foo": "bar"}' | jq '{other: .}' | jq -Rs '{json: .[:-1]}'