Do you need to create a branch to check out a specific git revision?

Question

A common thing I'd like to do is revert my working copy to a particular revision, do some testing, and then bring it back to the head of my current master. In the past I have naively done a "git checkout hash" only to lose my head. I've since learned I can create a branch and check that out, switch back and delete the branch, but it feels like too many steps for a simple check. In SVN parlance, is there a way to quickly revert and then quickly go back to the tip of trunk in git?

Edit: I think my confusion stems from the fact that when I checkout a hash and then git log, I don't see the changes that happened after the checked out hash (which is reasonable, when you think of it). But the accepted answer is correct; "git checkout branch" will restore the head to the previous branch.

Answer 1

If you want Git to show the tip of some line of changes, you need to have it branched or tagged. But even if you do not make a branch, none of the commits is lost. It stays in the repository as a garbage node (i.e. not reachable through any branch or tag), and is removed only some days/weeks later when you do "git gc".

So if you want to have an easy access to the changes, it's best to create a temporary branch and work there. If you do commits outside a branch and then checkout another branch, then you will need to use the command "git reflog" or look into the logs (".git/logs" directory) to find out what was the hash of the changes that you lost. When you know the hash, you can do "git checkout hash" or "git checkout -b new_branch hash" and recover the tip.

Answer 2

Yes, you can visit any arbitrary revision with "git checkout" as you describe. If you ask for an arbitrary revision rather than a branch, git will not have any obvious way to keep track of what changes you make, though. You can see where you were before by consulting the reflog ("git reflog show") - but in general, you would have been on a branch before so presumably just want to change back to that with "git checkout master" or similar.

Note that this method won't automatically deal with uncommitted changes in your workspace--- either commit or stash your changes before moving between branches, or use "git checkout -m" to carry them around as you move (and be prepared to deal with merge conflicts if the changes you're carrying aren't trivial).

I think recent git versions have introduced the shorthand "@{-1}" for "where I was before I last moved", which might actually be what you want in this case. (I haven't used it, just read about it in the release notes).

Answer 3

Assuming you're already on a branch (which you always should be for changes you want to keep), you can just do

git checkout <revision to check out>

This will take you off the topic branch you were working on into (no branch), in which the working copy refers directly to a commit ID rather than a branch name as normal.

Then to move back, simply:

git checkout <old branch name>

A helpful way to think of it is this: git checkout never alters branches; it merely changes what your working copy is currently looking at (ie, HEAD), which might either be a branch (in which case commits will update the branch) or a random commit hash.

As such, as long as the changes you want to keep are on a branch, you don't have to worry about git checkout losing them.