You specifically need `--patch` since the default output is a raw diff.
Signed-off-by: Kristoffer Haugsbakk <code@khaugsbakk.name>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
The main usecase for this command is to look for likely duplicate commits.
-When dealing with `git diff-tree` output, it takes advantage of
+When dealing with `git diff-tree --patch` output, it takes advantage of
the fact that the patch is prefixed with the object name of the
commit, and outputs two 40-byte hexadecimal strings. The first
string is the patch ID, and the second string is the commit ID.