Fixes · Checked on 2026-10-03
fatal: Needed a single revision
git rev-parse --short takes one revision at a time.
The error
$ git rev-parse --short HEAD FETCH_HEAD
fatal: Needed a single revisionWhy it happens
--short is --verify with a shorter answer, and --verify takes exactly one
revision. Without --short, rev-parse takes several. The same message also means a ref
that doesn't exist, such as FETCH_HEAD before any fetch.
The fix
One call per ref:
git rev-parse --short HEAD
git rev-parse --short FETCH_HEADOr full hashes for several refs in one call:
git rev-parse HEAD FETCH_HEADHow DMN learned it
It came up, and was fixed, in 2 of our own sessions. DMN kept the fix as one line:
`git rev-parse --short` implies --verify and accepts only one revision; run `git rev-parse --short <ref>`
separately per ref (e.g. FETCH_HEAD, HEAD) to avoid 'Needed a single revision'.
DMN reads your agents' past sessions on your machine. When the same error is fixed the same way in two or more of them, it keeps the fix as a one-line lesson. When the error turns up again, Claude Code is told the fix straight away, and any agent can search what earlier sessions found. How DMN keeps what agents learn.