Is there a "git pull --dry-run" option in Git?

I have always relied on the inherent abilities of Git to get me back if a merge fails.

To estimate how the merge might occur, you can start like you did with:

$ git fetch origin branch  # Fetch changes, but don't merge
$ git diff HEAD..origin/branch # Diff your current head to the fetched commit

... personal judgement of potential merge conflicts ...

$ git merge origin/branch # merge with the fetched commit

If things did not go as planned, look at your reflog and reset back to your desired state:

$ git reflog
...
abc987  HEAD@{0}: merge activity
b58aae8 HEAD@{1}: fetch origin/branch
8f3a362 HEAD@{2}: activity before the fetch
...
$ git reset --hard HEAD{2}

You will need to fetch first to update your local origin/master

git fetch origin

Then you can do:

git diff --name-only origin/master

Will list the files that have changed.

git diff origin/master directory_foo/file_bar.m

Will list the line by line diff of file directory_foo/file_bar.m.

You can get the effect you want by creating a new throw-away branch from your current one and doing the git pull there. If you're unhappy with the results, the original branch is intact.