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authorJunio C Hamano <junkio@cox.net>2007-01-17 18:43:50 (GMT)
committerJunio C Hamano <junkio@cox.net>2007-01-17 18:43:50 (GMT)
commit5e1a2e8c61b31410fd0c2e5a67c45bf6b373f4c3 (patch)
tree4888a74f13f6b2a664323549fe57fa9d6f2085da
parent23bfbb815d7d71ff20c014f4610732597f0a75db (diff)
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Documentation: detached HEAD
Add discussion section to git-checkout documentation and mention detached HEAD in repository-layout document. Signed-off-by: Junio C Hamano <junkio@cox.net>
-rw-r--r--Documentation/git-checkout.txt54
-rw-r--r--Documentation/repository-layout.txt6
2 files changed, 58 insertions, 2 deletions
diff --git a/Documentation/git-checkout.txt b/Documentation/git-checkout.txt
index fbdbadc..c44a4a8 100644
--- a/Documentation/git-checkout.txt
+++ b/Documentation/git-checkout.txt
@@ -9,7 +9,7 @@ SYNOPSIS
--------
[verse]
'git-checkout' [-f] [-b <new_branch> [-l]] [-m] [<branch>]
-'git-checkout' [-m] [<branch>] <paths>...
+'git-checkout' [<branch>] <paths>...
DESCRIPTION
-----------
@@ -63,7 +63,57 @@ and mark the resolved paths with `git update-index`.
<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
diff --git a/Documentation/repository-layout.txt b/Documentation/repository-layout.txt
index 0fdd366..7c8c141 100644
--- a/Documentation/repository-layout.txt
+++ b/Documentation/repository-layout.txt
@@ -91,6 +91,12 @@ HEAD::
'name' does not (yet) exist. In some legacy setups, it is
a symbolic link instead of a symref that points at the current
branch.
++
+HEAD can also record a specific commit directly, instead of
+being a symref to point at the current branch. Such a state
+is often called 'detached HEAD', and almost all commands work
+identically as normal. See gitlink:git-checkout[1] for
+details.
branches::
A slightly deprecated way to store shorthands to be used