Get key names from JSON file recursively using jq

Question

I can get top-level JSON keys with jq as

jq 'keys'

E.g., see this question: Get key names from JSON file using jq

And I can enable recursion in jq:

jq '..'

As in: Recursive search values by key

But jq '.. | keys' returns jq: error at <stdin> string has no keys.

Answer 1

Just ignore keys when they are absent for some values in JSON:

jq '.. | keys?'