Is there a way to create a new commit, get its change id in a machine-readable way, and not switch to it?

[AZMCode]

Something like

$ jj new -r <change-id> --no-edit -T 'change_id'
<new-change-id>

Not sure if this is a missing feature, if I'm using an old version, or if there's another way to do it.

It would be really useful for merging within a larger script, for example.

[PhilipMetzger]

This is not possible as jj new provides no templates. This would be something for multi-command aliases, see #3673.

[AZMCode]

Should I maybe post this under Ideas then?

[josephlou5]

This would be something for multi-command aliases, see #3673.

How could this be handled by multi-command aliases? There's no way to guarantee to get the output / state of a previous command without some scripting on the op log (--at-op @- is subject to races on the latest operation, so you'd need to go back and look for the relevant operation). You would probably need some way to figure out the exact operation where jj new ran, which currently isn't possible (without scripting), and seems unrelated to aliases.

[josephlou5]

You can hack around it:

$ jj --config templates.commit_summary=change_id --color never new --no-edit
Created new commit nzsnlovownltwxntvmvlvvsmpuvqyotq
# If you only want the change ID, make sure to redirect stderr to stdout.
$ jj ... new --no-edit 2>&1 | grep -o '[k-z]\+$'
zutzttmzlrvmvmmwrryossxqszovnzvk

# If you're not passing `--no-edit`, it's a little tricky:
$ jj --config templates.commit_summary=change_id --color never new
Working copy  (@) now at: uoqlkuusqlyskywuttosoovnmpxxtoml
Parent commit (@-)      : ttrqtskotmnzvtvpvvwrrosnqzxzmrrs
$ jj ... new 2>&1 | head -n 1 | grep -o '[k-z]\+$'
nnqkqqpyxppmupsuvuzvnmoyptwqvwss

# Or maybe:
$ jj --config 'templates.commit_summary=if(current_working_copy,change_id)' --color never new
Working copy  (@) now at: slmvkolvxzusqyuwxolpnkrywrzzmxms
Parent commit (@-)      : 
# But you'd still need the `head -n 1`, so 🤷

There was a question in the Discord some months ago where I answered this, but I can't find it anymore so unfortunately can't link it. The OP there opted to put null bytes ("\0" with double quotes in templating language) around the change_id as well, just to be extra sure they could parse it out of the output. Maybe that could help with peace of mind if you're not using --no-edit.

Btw, this also works for jj duplicate:

$ jj --config templates.commit_summary=change_id --color never duplicate
Duplicated 51ad3766f1c2 as ruyqwyuvnlnrzpwvyzqmnsowmzquypmm
$ jj --config templates.commit_summary=change_id --color never duplicate tt:: 2>&1 | grep -o '[k-z]\+$'
rkwtvpozmkysyymwzltwuzqvznsmuprs
pwvrtptyulwqqnxkkxwzvtprruxtrzxn
ruumrylzuslyrxtxmuwvqnvwlupnmomu
mllwysutnqvuslommkxkopqrwkpnzoww
owwtyupqvwruwowssznvorqzpxvqwluv