diff options
Diffstat (limited to 'Documentation/git-checkout.txt')
| -rw-r--r-- | Documentation/git-checkout.txt | 159 |
1 files changed, 133 insertions, 26 deletions
diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt index 22d36114df..396f4cc15b 100644 --- a/Documentation/git-checkout.txt +++ b/Documentation/git-checkout.txt @@ -9,6 +9,7 @@ SYNOPSIS -------- [verse] 'git checkout' [-q] [-f] [-m] [<branch>] +'git checkout' [-q] [-f] [-m] [--detach] [<commit>] 'git checkout' [-q] [-f] [-m] [[-b|-B|--orphan] <new_branch>] [<start_point>] 'git checkout' [-f|--ours|--theirs|-m|--conflict=<style>] [<tree-ish>] [--] <paths>... 'git checkout' --patch [<tree-ish>] [--] [<paths>...] @@ -22,9 +23,10 @@ branch. 'git checkout' [<branch>]:: 'git checkout' -b|-B <new_branch> [<start point>]:: +'git checkout' [--detach] [<commit>]:: This form switches branches by updating the index, working - tree, and HEAD to reflect the specified branch. + tree, and HEAD to reflect the specified branch or commit. + If `-b` is given, a new branch is created as if linkgit:git-branch[1] were called and then checked out; in this case you can @@ -98,7 +100,7 @@ entries; instead, unmerged entries are ignored. "--track" in linkgit:git-branch[1] for details. + If no '-b' option is given, the name of the new branch will be -derived from the remote branch. If "remotes/" or "refs/remotes/" +derived from the remote-tracking branch. If "remotes/" or "refs/remotes/" is prefixed it is stripped away, and then the part up to the next slash (which would be the nickname of the remote) is removed. This would tell us to use "hack" as the local branch when branching @@ -115,6 +117,13 @@ explicitly give a name with '-b' in such a case. Create the new branch's reflog; see linkgit:git-branch[1] for details. +--detach:: + Rather than checking out a branch to work on it, check out a + commit for inspection and discardable experiments. + This is the default behavior of "git checkout <commit>" when + <commit> is not a branch name. See the "DETACHED HEAD" section + below for details. + --orphan:: Create a new 'orphan' branch, named <new_branch>, started from <start_point> and switch to it. The first commit made on this @@ -204,42 +213,140 @@ leave out at most one of `A` and `B`, in which case it defaults to `HEAD`. -Detached HEAD +DETACHED HEAD ------------- +HEAD normally refers to a named branch (e.g. 'master'). Meanwhile, each +branch refers to a specific commit. Let's look at a repo with three +commits, one of them tagged, and with branch 'master' checked out: + +------------ + HEAD (refers to branch 'master') + | + v +a---b---c branch 'master' (refers to commit 'c') + ^ + | + tag 'v2.0' (refers to commit 'b') +------------ -It is sometimes useful to be able to 'checkout' a commit that is -not at the tip of one of your branches. The most obvious -example is to check out the commit at a tagged official release -point, like this: +When a commit is created in this state, the branch is updated to refer to +the new commit. Specifically, 'git commit' creates a new commit 'd', whose +parent is commit 'c', and then updates branch 'master' to refer to new +commit 'd'. HEAD still refers to branch 'master' and so indirectly now refers +to commit 'd': ------------ -$ git checkout v2.6.18 +$ edit; git add; git commit + + HEAD (refers to branch 'master') + | + v +a---b---c---d branch 'master' (refers to commit 'd') + ^ + | + tag 'v2.0' (refers to commit 'b') ------------ -Earlier versions of git did not allow this and asked you to -create a temporary branch using the `-b` option, but starting from -version 1.5.0, the above command 'detaches' your HEAD from the -current branch and directly points at the commit named by the tag -(`v2.6.18` in the example above). +It is sometimes useful to be able to checkout a commit that is not at +the tip of any named branch, or even to create a new commit that is not +referenced by a named branch. Let's look at what happens when we +checkout commit 'b' (here we show two ways this may be done): -You can use all git commands while in this state. You can use -`git reset --hard $othercommit` to further move around, for -example. You can make changes and create a new commit on top of -a detached HEAD. You can even create a merge by using `git -merge $othercommit`. +------------ +$ git checkout v2.0 # or +$ git checkout master^^ + + HEAD (refers to commit 'b') + | + v +a---b---c---d branch 'master' (refers to commit 'd') + ^ + | + tag 'v2.0' (refers to commit 'b') +------------ -The state you are in while your HEAD is detached is not recorded -by any branch (which is natural --- you are not on any branch). -What this means is that you can discard your temporary commits -and merges by switching back to an existing branch (e.g. `git -checkout master`), and a later `git prune` or `git gc` would -garbage-collect them. If you did this by mistake, you can ask -the reflog for HEAD where you were, e.g. +Notice that regardless of which checkout command we use, HEAD now refers +directly to commit 'b'. This is known as being in detached HEAD state. +It means simply that HEAD refers to a specific commit, as opposed to +referring to a named branch. Let's see what happens when we create a commit: ------------ -$ git log -g -2 HEAD +$ edit; git add; git commit + + HEAD (refers to commit 'e') + | + v + e + / +a---b---c---d branch 'master' (refers to commit 'd') + ^ + | + tag 'v2.0' (refers to commit 'b') +------------ + +There is now a new commit 'e', but it is referenced only by HEAD. We can +of course add yet another commit in this state: + +------------ +$ edit; git add; git commit + + HEAD (refers to commit 'f') + | + v + e---f + / +a---b---c---d branch 'master' (refers to commit 'd') + ^ + | + tag 'v2.0' (refers to commit 'b') +------------ + +In fact, we can perform all the normal git operations. But, let's look +at what happens when we then checkout master: + +------------ +$ git checkout master + + HEAD (refers to branch 'master') + e---f | + / v +a---b---c---d branch 'master' (refers to commit 'd') + ^ + | + tag 'v2.0' (refers to commit 'b') ------------ +It is important to realize that at this point nothing refers to commit +'f'. Eventually commit 'f' (and by extension commit 'e') will be deleted +by the routine git garbage collection process, unless we create a reference +before that happens. If we have not yet moved away from commit 'f', +any of these will create a reference to it: + +------------ +$ git checkout -b foo <1> +$ git branch foo <2> +$ git tag foo <3> +------------ + +<1> creates a new branch 'foo', which refers to commit 'f', and then +updates HEAD to refer to branch 'foo'. In other words, we'll no longer +be in detached HEAD state after this command. + +<2> similarly creates a new branch 'foo', which refers to commit 'f', +but leaves HEAD detached. + +<3> creates a new tag 'foo', which refers to commit 'f', +leaving HEAD detached. + +If we have moved away from commit 'f', then we must first recover its object +name (typically by using git reflog), and then we can create a reference to +it. For example, to see the last two commits to which HEAD referred, we +can use either of these commands: + +------------ +$ git reflog -2 HEAD # or +$ git log -g -2 HEAD +------------ EXAMPLES -------- |