Add item to list in yq if it doesn't already exist

Question

Using mikefarah's yq v4 I want to conditionally add an IP address to a list within a yml file if it does not exist in the list already.

Given a file like:

servers:
  web:
    - 1.1.1.1
  jobs:
    - 2.2.2.2

If 1.1.1.1 was attempted to be added it should not change, if 3.3.3.3 was added to web then it should become

servers:
  web:
    - 1.1.1.1
    - 3.3.3.3
  jobs:
    - 2.2.2.2

I tried a couple of options, hoping to find something that went along the lines of append if not exists but didn't see that option.

I eventually settled on an update with append & unique.

yq '.servers.web = (.servers.web + ["3.3.3.3"]  | unique)' test.yml

And for removal I have:

yq '.servers.web = (.servers.web - ["3.3.3.3"])' test.yml

Which seems to work fine.

Any yq experts have some advice on a more clear way of describing the first one, or is that the most clear way of doing it?

Answer 1

That's basically how you'd do it. Iterating through the items and processing them directly could be a tad more efficient, but unnecessarily complicated to write, and with negligible benefit for such short arrays.

A thing to optimize, though: You could use the update operator |=, so the context is already set, removing some duplicate code. When using the mikefarah implementation, you could even remove the array brackets as yq will automatically add items to arrays correctly (it might, however, be counter-intuitive wrt the - case, where this is not possible, at least as of version v4.44.1):

yq '.servers.web |= (. + ["1.1.1.1"]  | unique)'

# or (only for mikefarah/yq)
yq '.servers.web |= (. + "1.1.1.1"  | unique)'

In the - case, you could reduce the analogous .servers.web |= (. - ["1.1.1.1"]) even further by using the -= shortcut, as there is no other function to process before the assignment (like there was with unique in the + case):

yq '.servers.web -= ["1.1.1.1"]'