git-commit-vandalism/Documentation/git-checkout.txt

git-checkout(1)
===============

NAME
----
git-checkout - Checkout and switch to a branch

SYNOPSIS
--------
[verse]
'git-checkout' [-f] [-b <new_branch> [-l]] [-m] [<branch>]
'git-checkout' [<branch>] <paths>...

DESCRIPTION
-----------

When <paths> are not given, this command switches branches by
updating the index and working tree to reflect the specified
branch, <branch>, and updating HEAD to be <branch> or, if
specified, <new_branch>.  Using -b will cause <new_branch> to
be created.

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
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.


OPTIONS
-------
-f::
	Force a re-read of everything.

-b::
	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
	are different between the current branch and the branch to
	which you are switching, the command refuses to switch
	branches in order to preserve your modifications in context.
	However, with this option, a three-way merge between the current
	branch, your working tree contents, and the new branch
	is done, and you will be on the new branch.
+
When a merge conflict happens, the index entries for conflicting
paths are left unmerged, and you need to resolve the conflicts
and mark the resolved paths with `git update-index`.

<new_branch>::
	Name for the new branch.

<branch>::
	Branch to checkout; may be any object ID that resolves to a
	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
--------

. The following sequence checks out the `master` branch, reverts
the `Makefile` to two revisions back, deletes hello.c by
mistake, and gets it back from the index.
+
------------
$ git checkout master             <1>
$ git checkout master~2 Makefile  <2>
$ rm -f hello.c
$ git checkout hello.c            <3>
------------
+
<1> switch branch
<2> take out a file out of other commit
<3> restore hello.c from HEAD of current branch
+
If you have an unfortunate branch that is named `hello.c`, this
step would be confused as an instruction to switch to that branch.
You should instead write:
+
------------
$ git checkout -- hello.c
------------

. After working in a wrong branch, switching to the correct
branch would be done using:
+
------------
$ git checkout mytopic
------------
+
However, your "wrong" branch and correct "mytopic" branch may
differ in files that you have locally modified, in which case,
the above checkout would fail like this:
+
------------
$ git checkout mytopic
fatal: Entry 'frotz' not uptodate. Cannot merge.
------------
+
You can give the `-m` flag to the command, which would try a
three-way merge:
+
------------
$ git checkout -m mytopic
Auto-merging frotz
------------
+
After this three-way merge, the local modifications are _not_
registered in your index file, so `git diff` would show you what
changes you made since the tip of the new branch.

. When a merge conflict happens during switching branches with
the `-m` option, you would see something like this:
+
------------
$ git checkout -m mytopic
Auto-merging frotz
merge: warning: conflicts during merge
ERROR: Merge conflict in frotz
fatal: merge program failed
------------
+
At this point, `git diff` shows the changes cleanly merged as in
the previous example, as well as the changes in the conflicted
files.  Edit and resolve the conflict and mark it resolved with
`git update-index` as usual:
+
------------
$ edit frotz
$ git update-index frotz
------------


Author
------
Written by Linus Torvalds <torvalds@osdl.org>

Documentation
--------------
Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

GIT
---
Part of the gitlink:git[7] suite