How do I format embedded JSON strings

[ChipWolf]

Describe the bug
When attempting to apply style="literal" to JSON string values in a YAML file using yq, the transformation unexpectedly affects all string values, not just the targeted JSON strings, even when using select() to distinguish between JSON and non-JSON values.

This behavior makes it difficult to pretty-print JSON strings without inadvertently modifying other strings in the document.

Version of yq: 4.44.5
Operating system: linux
Installed via: binary release

---

Input Yaml
data.yml:

json_value: '{"key1": "value1", "key2": [1, 2, 3]}'
non_json_value: "This is a plain string."

---

Command
The command I ran:

yq eval-all '
  .. |= (select(tag == "!!str" and test("^{.*}$")) |= (fromjson | tojson | . style="literal"))
' data.yml

---

Actual behavior

json_value: "{\n  \"key1\": \"value1\",\n  \"key2\": [\n    1,\n    2,\n    3\n  ]\n}"
non_json_value: "This is a plain string."

---

Expected behavior

json_value: |-
  {
    "key1": "value1",
    "key2": [
      1,
      2,
      3
    ]
  }
non_json_value: "This is a plain string."

---

Workaround
A two-step yq command works as expected:

yq eval-all '
  .. |= (select(tag == "!!str" and test("^{.*}$")) |= (fromjson | tojson | . style="literal"))
' data.yml | yq eval-all '
  .. |= (select(tag == "!!str" and (test("^{.*}$") | not)) |= . style="")
'

This outputs:

json_value: |-
  {
    "key1": "value1",
    "key2": [
      1,
      2,
      3
    ]
  }
non_json_value: This is a plain string.

---

Additional context
Is it possible to achieve this in a single eval-all command? Or is this a limitation of how style="literal" and select() interact within a single evaluation pass? If this is intended behavior, I’d love to understand more about why it happens.

I've also attempted to use with(), with similar results.

[mikefarah]

Hey - you don't quite have the right expression; I think you're mixing up |= which updates value w.r.t themselves, and | which pipes the output of one filter into the next. You can do it like this:

yq 'with(.. | select(tag == "!!str" and test("^{.*}$")); 
    . |= (fromjson | . style="literal" | tojson ) | 
    . style = "literal"
)' data1.yaml

Explanation:

• We want to match all the strings that appear to be json; so we match all nodes then filter using select: .. | select(tag == "!!str" and test("^{.*}$")
• There are two updates we need to do, one to the value (format the stringified JSON) and another to the string style (to make it a block instead of single quotes. So we'll use with to allow us to make both those updates
• . |= exp updates the node value w.r.t itself, we'll use that to decode the json, reformat using style and re-encode back into a string
• then we can also apply a literal style to the string node itself, to make it a block

Hope that made sense!