[FEATURE] Add PPL support to access values in array

[A-Gray-Cat]

Is your feature request related to a problem?
Currently, PPL doesn't support accessing values inside an array. For example,

{
    "items": ["a", "b", "c"]
}

Users can't select value a, b, or c using PPL.

What solution would you like?
Users can access the first element of the array by using syntax like eval first_item = items[0], or it can be retrieved directly using the fields command, e.g. fields items[0].

[YANG-DB]

@A-Gray-Cat thanks - we will review !

[dblock]

[Catch All Triage - 1, 2, 3, 4]

[LantaoJin]

With #780 , we can access the first element in a array by

| eval first_elem = json_extract('{"items": ["a", "b", "c"]}', '$.items[0]') // json object string

or

| eval first_elem = json_extract('["a", "b", "c"]', '$.[0]') // json array string

But it requires the input is a json string. If the input is json array (ArrayType), I think we need a new function such as array_get:

| eval first_elem = array_get(json_array("a", "b", "c"), 0)

But as a workaround, we could rewrite by

| eval first_elem = json_extract(to_json_string(json_array("a", "b", "c")), '$.[0]')

From the issue's description, it seems the input is a json string and json_extract should work as the solution. @A-Gray-Cat

[YANG-DB]

@A-Gray-Cat we are closing this since we have a workaround as described above