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.<name>.remote and branch.<name>.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.

Answer 2

Let's assume that you have one master branch which is checked out. Now when you do a

$ git branch --track someBranch

you will create a new branch named someBranch which changes will be tracked according to the master branch. But this branch has no remote branch set. Thus you see remote = . in the git config.

Now that someBranch is tracked it means that changes will appear in git status and git branch -v as if a remote exists.

For example if you make a commit on someBranch git will tell you that you are 1 ahead when you do a git branch -v or when you do a git status it shows you

Your branch is ahead of 'master' by 1 commit.

And this is the interessting part. The branch is tracked and git shows you that it is 1 commit ahead of master (the branch that was checked out when you created someBranch)