Extracting certain fields to manipulate them individually and combine into line by line output

[manuelgrabowski]

Given the following YAML:

- name: Bob Blob
  start_date: 2022-11-05
  slack:
    id: 0123
    username: BOB
  hobbies: []
- name: Jane Doe
  start_date: 2022-12-12
  slack:
    id: 1234
    username: Jane

My desired output is:

Bob Blob | `@bob`
Jane Doe | `@jane`

But I'm unable to figure out how to achieve this, even after going through the docs many times and reading plenty of other examples in here. I'm guessing my approach must be rather fundamentally wrong? Please let me know if I missed this in the docs, it feels like such a basic thing to do.

This is what I tried:

cat test.yml | yq '.[] | (.name + " | `@" + .slack.username | downcase + "`")'

Which results in this:

bob blob | `@bob`
jane doe | `@jane`

So downcase is applied to the entire line rather than just the .slack.username field.

[mikefarah]

Just need brackets:

cat test.yml | yq '.[] | (.name + " | `@" + (.slack.username | downcase) + "`")'

[mikefarah]

Bob Blob | `@bob`
Jane Doe | `@jane`

[manuelgrabowski]

Thank you very much! Could have sworn I tried that as well, but must have done something wrong… my actual use case was a fair bit more complex, so maybe I messed up the ordering somehow – but it definitely works on the complex case as well now.

Not to downplay my own inability, but it's rather counterintuitive behavior to me. I guess the reason is that the Add operater has higher precedence than Pipe, so it first merges everything before into one string and then applies downcase to that?