Insert empty value

[sylvainbx]

What I want

Using yq V4, how to insert a key with an empty value in a yaml document?

For example, I have the following document:

a:
  b:
    c: "lorem ipsum"

I would like to add a.d with no value. Here's the expected result:

a:
  b:
    c: "lorem ipsum"
  d:

Using yq v3

With V3, I used to accomplish this with:

yq w -i sample.yml a.d ''

Using yq v4

But, with V4, if I specify an empty string:

yq -i eval '.a.d = ""' sample.yml

I'll get something like this, which is not what I was expecting, because it inserts a string instead of a map:

a:
  b:
    c: "lorem ipsum"
  d: ""

Is there a special operator to accomplish that? e.g.

yq -i eval '.a.d = <empty>' sample.yml

[mikefarah]

That empty value is null in yaml (one of the many ways you can represent null in yaml).

Whereas setting .a.d to "" sets it to the empty string.

To set it to null you can:

yq -i eval '.a.d = null' sample.yml

But then you will see null in .a.d's value. To get an empty (null) value, you can do this:

yq e -n '.a.d = "" | .a.d tag="!!null"'

Not as clean as v3 admittedly.

[sylvainbx]

Thanks for your answer!

[sylvainbx]

Using

yq e -n '.a.d = "" | .a.d tag="!!null"' sample.yml

This ends up with the following message:

Error: Cannot pass files in when using null-input flag

[mikefarah]

remove the -n as that flag means you are not going to pass in any files