SYNOPSIS
--------
[verse]
-'git-checkout' [-f] [-b <new_branch>] [-m] [<branch>]
-'git-checkout' [
-m] [<branch>] <paths>...
+'git-checkout' [-q] [-f] [-b <new_branch> [-l]] [-m] [<branch>]
+'git-checkout' [
<tree-ish>] <paths>...
DESCRIPTION
-----------
When <paths> are given, this command does *not* switch
branches. It updates the named paths in the working tree from
-the index file (i.e. it runs `git-checkout-index -f -u`). In
+the index file (i.e. it runs `git-checkout-index -f -u`), or a
+named commit. In
this case, `-f` and `-b` options are meaningless and giving
-either of them results in an error. <branch> argument can be
-used to specify a specific tree-ish to update the index for the
-given paths before updating the working tree.
+either of them results in an error. <tree-ish> argument can be
+used to specify a specific tree-ish (i.e. commit, tag or tree)
+to update the index for the given paths before updating the
+working tree.
OPTIONS
-------
+-q::
+ Quiet, supress feedback messages.
+
-f::
Force a re-read of everything.
-b::
- Create a new branch and start it at <branch>.
+ Create a new branch named <new_branch> and start it at
+ <branch>. The new branch name must pass all checks defined
+ by gitlink:git-check-ref-format[1]. Some of these checks
+ may restrict the characters allowed in a branch name.
+
+-l::
+ Create the new branch's ref log. This activates recording of
+ all changes to made the branch ref, enabling use of date
+ based sha1 expressions such as "<branchname>@{yesterday}".
-m::
If you have local modifications to one or more files that
<branch>::
Branch to checkout; may be any object ID that resolves to a
- commit. Defaults to HEAD.
+ commit. Defaults to HEAD.
++
+When this parameter names a non-branch (but still a valid commit object),
+your HEAD becomes 'detached'.
+
+
+Detached HEAD
+-------------
+
+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:
+
+------------
+$ git checkout v2.6.18
+------------
+
+Earlier versions of git did not allow this and asked you to
+create a temporary branch using `-b` option, but starting from
+version 1.5.0, the above command 'detaches' your HEAD from the
+current branch and directly point at the commit named by the tag
+(`v2.6.18` in the above example).
+
+You can use usual 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`.
+
+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.
+
+The command would refuse to switch back to make sure that you do
+not discard your temporary state by mistake when your detached
+HEAD is not pointed at by any existing ref. If you did want to
+save your state (e.g. "I was interested in the fifth commit from
+the top of 'master' branch", or "I made two commits to fix minor
+bugs while on a detached HEAD" -- and if you do not want to lose
+these facts), you can create a new branch and switch to it with
+`git checkout -b newbranch` so that you can keep building on
+that state, or tag it first so that you can come back to it
+later and switch to the branch you wanted to switch to with `git
+tag that_state; git checkout master`. On the other hand, if you
+did want to discard the temporary state, you can give `-f`
+option (e.g. `git checkout -f master`) to override this
+behaviour.
EXAMPLES