What's the difference between git “--track” and “--set-upstream-to”?

Question

As I can see, both git --track and --set-upstream-to modify a branch so it becames a tracking (or upstream) branch. But where is a subtle differenc

Answer 1

$ git checkout foo -b
$ git branch --track origin/retarget

The first two commands instruct git to:

• create a local branch named "origin/retarget" (very bad idea, as it is named as a remote tracking branch", while it is actually a simple local branch with a '/' in its name)
• starting from the current branch ("foo", another local branch)
• to make that new local branch tracking its starting point.

See git branch

--track

When creating a new branch, set up branch..remote and branch..merge configuration entries to mark the start-point branch as "upstream" from the new branch.

You would use track when you create a branch starting from a remote tracking one.

In other word, your first example isn't how you would use --track.
This would work better:

git checkout -b foo --track origin/retarget

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As for the difference between --track and --set-upstream-to:

--set-upstream-to

If specified branch does not exist yet or if --force has been given, acts exactly like --track.
Otherwise sets up configuration like --track would when creating the branch, except that where branch points to is not changed.