Q:

Git diff with -m

I've a merge conflict, and when I do a git diff I'm shown diff in combined format. The documentation for git help diff, where it explains the combined diff format, it's mentioned that I could use -m with any of the diff commands. But git diff wouldn't take a -m option. git help diff-tree however documents -m option.
I'm trying to look at diffs of the file between each merge parent, one at a time, potentially using the -m switch. Yes, I could use commands like git diff :{1,2}:/path/to/file or git diff :{1,3}:/path/to/file, but given a combined diff output, how do I use the -m switch?

A:

To clarify my own question: the -m flag to git diff or git show, when applied to a merge commit, individually lists how that merge commit differs from each of its parent, one by one.
Say, if you've a layout as below:
--X--A--,
         \
  --X--B--M--
         /
--X--C--'

git show -m M concatenates outputs of git diff A M, then git diff B M and git diff C M. git show M shows the diff information, but in a combined diff format. The -m flag is also useful in cases where git omits diff output completely

