Command composition / machine-readable output

[whatisaphone]

Is there some generalized way to get machine-readable output from commands? Example:

❯ jj duplicate m
Duplicated 6b5c77a987e6 as sqtkpzzm f4de6d68 .

That message shows up on stderr. I could capture stderr and parse it with a regex or something. But it seems saner to do something like this:

❯ jj --json duplicate m
{"change_id":"sqtkpzzm","commit_id":"f4de6d68"}

My use case is scripting/composition. For example, I'd like to be able to write a script that duplicates a commit, and also sets its description:

change_id=$(jj --json duplicate "$1" | jq .change_id)
jj describe "${change_id}" --message="$2"

I don't see a good way to chain commands like this right now. Did I overlook something?

[josephlou5]

This (parsing human output) is currently the recommended and only way to "compose" commands together. Also see #10329 and the discussion linked there. Most of this would be made trivial by the eventual scripting language, but that isn't done yet.