Using yq to traverse a list in Almquist shell

Question

I have this example of a YAML file, which includes a variable number of elements in the 'containers' list and in the 'networks' list of each container.

lab_name: practica0
containers:
- name: vm1
  image: rys
  networks:
  - 1
- name: router
  image: rys
  networks:
  - 1
  - 2
- name: vm2
  image: rys
  networks:
  - 2

I wanna loop through the 'containers' and the 'networks' arrays getting all the values, but I don't know exactly how to do it. I tried using a for loop and a shell variable, like this yq eval '.containers[$i].name' example.yaml, but it didn't work. I tried enclosing $i between double quotes and escaping them as specified here https://github.com/mikefarah/yq/issues/468#issuecomment-752114840, but still no luck. I'm using Go yq by the way, and I have to use Almquist Shell instead of bash so I can't use things like readarray. Thank you

EDIT: For example, my desired output would be something as simple as this:

vm1
rys
1

router
rys
1
2

vm2
rys
2

Answer 1

You can use something like

yq e '.containers | map([ .name, .image, .networks[] ])' input

to create a list of values you desire:

- - vm1
  - rys
  - 1
- - router
  - rys
  - 1
  - 2
- - vm2
  - rys
  - 2

---

Not sure what the prevered way is to convert this into a new-line separated string. But with some additional logic, we can get the desired output using the sed and tr utilities.

Use @tsv to let yq create a tab separated value, then we use some common shell utilities to convert that to the desired output

1. sed G places a newline after each line
2. tr '\t' '\n' replaces the tab with an other newline

yq e '.containers | map([ .name, .image, .networks[] ]) | @tsv' input | sed G | tr '\t' '\n'

vm1
rys
1

router
rys
1
2

vm2
rys
2