Sebastian Schuberth [off-list ref] writes:
"--quite" is documented to "Disable all output of the program". Yet
calling diff-tree with a single commit like
$ git diff-tree --quiet c925fe2
was logging
c925fe23684455735c3bb1903803643a24a58d8f
At this point, unfortunately I think we need to call that a
documentation bug. The "output" it refers to is output from the
"diff" portion, not the "poor-man's log" portion, of the program,
where diff-tree was the workhorse behind scripted "git log" that
gave the commit object name as the preamble for each commit it
shows information about.