[thirdparty/git.git] / Documentation / git-merge.txt

git-merge(1)
============

NAME
----
git-merge - Grand Unified Merge Driver


SYNOPSIS
--------
'git-merge' [-n] [--no-commit] [-s <strategy>]... <msg> <head> <remote> <remote>...


DESCRIPTION
-----------
This is the top-level user interface to the merge machinery
which drives multiple merge strategy scripts.


OPTIONS
-------
include::merge-options.txt[]

<msg>::
	The commit message to be used for the merge commit (in case
	it is created). The `git-fmt-merge-msg` script can be used
	to give a good default for automated `git-merge` invocations.

<head>::
	our branch head commit.

<remote>::
	other branch head merged into our branch.  You need at
	least one <remote>.  Specifying more than one <remote>
	obviously means you are trying an Octopus.

include::merge-strategies.txt[]


If you tried a merge which resulted in a complex conflicts and
would want to start over, you can recover with
gitlink:git-reset[1].


HOW MERGE WORKS
---------------

A merge is always between the current `HEAD` and one or more
remote branch heads, and the index file must exactly match the
tree of `HEAD` commit (i.e. the contents of the last commit) when
it happens.  In other words, `git-diff --cached HEAD` must
report no changes.

[NOTE]
This is a bit of lie.  In certain special cases, your index are
allowed to be different from the tree of `HEAD` commit.  The most
notable case is when your `HEAD` commit is already ahead of what
is being merged, in which case your index can have arbitrary
difference from your `HEAD` commit.  Otherwise, your index entries
are allowed have differences from your `HEAD` commit that match
the result of trivial merge (e.g. you received the same patch
from external source to produce the same result as what you are
merging).  For example, if a path did not exist in the common
ancestor and your head commit but exists in the tree you are
merging into your repository, and if you already happen to have
that path exactly in your index, the merge does not have to
fail.

Otherwise, merge will refuse to do any harm to your repository
(that is, it may fetch the objects from remote, and it may even
update the local branch used to keep track of the remote branch
with `git pull remote rbranch:lbranch`, but your working tree,
`.git/HEAD` pointer and index file are left intact).

You may have local modifications in the working tree files.  In
other words, `git-diff` is allowed to report changes.
However, the merge uses your working tree as the working area,
and in order to prevent the merge operation from losing such
changes, it makes sure that they do not interfere with the
merge. Those complex tables in read-tree documentation define
what it means for a path to "interfere with the merge".  And if
your local modifications interfere with the merge, again, it
stops before touching anything.

So in the above two "failed merge" case, you do not have to
worry about lossage of data --- you simply were not ready to do
a merge, so no merge happened at all.  You may want to finish
whatever you were in the middle of doing, and retry the same
pull after you are done and ready.

When things cleanly merge, these things happen:

1. the results are updated both in the index file and in your
   working tree,
2. index file is written out as a tree,
3. the tree gets committed, and 
4. the `HEAD` pointer gets advanced.

Because of 2., we require that the original state of the index
file to match exactly the current `HEAD` commit; otherwise we
will write out your local changes already registered in your
index file along with the merge result, which is not good.
Because 1. involves only the paths different between your
branch and the remote branch you are pulling from during the
merge (which is typically a fraction of the whole tree), you can
have local modifications in your working tree as long as they do
not overlap with what the merge updates.

When there are conflicts, these things happen:

1. `HEAD` stays the same.

2. Cleanly merged paths are updated both in the index file and
   in your working tree.

3. For conflicting paths, the index file records up to three
   versions; stage1 stores the version from the common ancestor,
   stage2 from `HEAD`, and stage3 from the remote branch (you
   can inspect the stages with `git-ls-files -u`).  The working
   tree files have the result of "merge" program; i.e. 3-way
   merge result with familiar conflict markers `<<< === >>>`.

4. No other changes are done.  In particular, the local
   modifications you had before you started merge will stay the
   same and the index entries for them stay as they were,
   i.e. matching `HEAD`.

After seeing a conflict, you can do two things:

 * Decide not to merge.  The only clean-up you need are to reset
   the index file to the `HEAD` commit to reverse 2. and to clean
   up working tree changes made by 2. and 3.; `git-reset` can
   be used for this.

 * Resolve the conflicts.  `git-diff` would report only the
   conflicting paths because of the above 2. and 3..  Edit the
   working tree files into a desirable shape, `git-update-index`
   them, to make the index file contain what the merge result
   should be, and run `git-commit` to commit the result.


SEE ALSO
--------
gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1]


Author
------
Written by Junio C Hamano <junkio@cox.net>


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

GIT
---
Part of the gitlink:git[7] suite
Commit	Line	Data
0f69be53 JH	1	git-merge(1)
0f69be53 JH	2	============
0f69be53 JH	3
	4	NAME
	5	----
	6	git-merge - Grand Unified Merge Driver
	7
	8
	9	SYNOPSIS
	10	--------
37465016	11	'git-merge' [-n] [--no-commit] [-s <strategy>]... <msg> <head> <remote> <remote>...
0f69be53 JH	12
	13
	14	DESCRIPTION
	15	-----------
	16	This is the top-level user interface to the merge machinery
	17	which drives multiple merge strategy scripts.
	18
	19
	20	OPTIONS
	21	-------
93d69d86	22	include::merge-options.txt[]
0f69be53	23
3c64314c PB	24	<msg>::
	25	The commit message to be used for the merge commit (in case
	26	it is created). The `git-fmt-merge-msg` script can be used
	27	to give a good default for automated `git-merge` invocations.
	28
0f69be53 JH	29	<head>::
	30	our branch head commit.
	31
	32	<remote>::
	33	other branch head merged into our branch. You need at
	34	least one <remote>. Specifying more than one <remote>
	35	obviously means you are trying an Octopus.
	36
bb73d73c JL	37	include::merge-strategies.txt[]
bb73d73c JL	38
0f69be53	39
3ae854c3 JH	40	If you tried a merge which resulted in a complex conflicts and
	41	would want to start over, you can recover with
	42	gitlink:git-reset[1].
	43
	44
ffb1a4be JH	45	HOW MERGE WORKS
	46	---------------
	47
	48	A merge is always between the current `HEAD` and one or more
	49	remote branch heads, and the index file must exactly match the
	50	tree of `HEAD` commit (i.e. the contents of the last commit) when
	51	it happens. In other words, `git-diff --cached HEAD` must
	52	report no changes.
	53
	54	[NOTE]
	55	This is a bit of lie. In certain special cases, your index are
	56	allowed to be different from the tree of `HEAD` commit. The most
	57	notable case is when your `HEAD` commit is already ahead of what
	58	is being merged, in which case your index can have arbitrary
	59	difference from your `HEAD` commit. Otherwise, your index entries
	60	are allowed have differences from your `HEAD` commit that match
	61	the result of trivial merge (e.g. you received the same patch
	62	from external source to produce the same result as what you are
	63	merging). For example, if a path did not exist in the common
	64	ancestor and your head commit but exists in the tree you are
	65	merging into your repository, and if you already happen to have
	66	that path exactly in your index, the merge does not have to
	67	fail.
	68
	69	Otherwise, merge will refuse to do any harm to your repository
	70	(that is, it may fetch the objects from remote, and it may even
	71	update the local branch used to keep track of the remote branch
	72	with `git pull remote rbranch:lbranch`, but your working tree,
	73	`.git/HEAD` pointer and index file are left intact).
	74
	75	You may have local modifications in the working tree files. In
	76	other words, `git-diff` is allowed to report changes.
	77	However, the merge uses your working tree as the working area,
	78	and in order to prevent the merge operation from losing such
	79	changes, it makes sure that they do not interfere with the
	80	merge. Those complex tables in read-tree documentation define
	81	what it means for a path to "interfere with the merge". And if
	82	your local modifications interfere with the merge, again, it
	83	stops before touching anything.
	84
	85	So in the above two "failed merge" case, you do not have to
	86	worry about lossage of data --- you simply were not ready to do
	87	a merge, so no merge happened at all. You may want to finish
	88	whatever you were in the middle of doing, and retry the same
	89	pull after you are done and ready.
	90
	91	When things cleanly merge, these things happen:
	92
	93	1. the results are updated both in the index file and in your
	94	working tree,
	95	2. index file is written out as a tree,
	96	3. the tree gets committed, and
	97	4. the `HEAD` pointer gets advanced.
	98
	99	Because of 2., we require that the original state of the index
	100	file to match exactly the current `HEAD` commit; otherwise we
	101	will write out your local changes already registered in your
	102	index file along with the merge result, which is not good.
	103	Because 1. involves only the paths different between your
	104	branch and the remote branch you are pulling from during the
	105	merge (which is typically a fraction of the whole tree), you can
	106	have local modifications in your working tree as long as they do
	107	not overlap with what the merge updates.
	108
109	When there are conflicts, these things happen:
110
111	1. `HEAD` stays the same.
112
113	2. Cleanly merged paths are updated both in the index file and
114	in your working tree.
115
3ace1fe3 JH	116	3. For conflicting paths, the index file records up to three
	117	versions; stage1 stores the version from the common ancestor,
	118	stage2 from `HEAD`, and stage3 from the remote branch (you
	119	can inspect the stages with `git-ls-files -u`). The working
	120	tree files have the result of "merge" program; i.e. 3-way
	121	merge result with familiar conflict markers `<<< === >>>`.
ffb1a4be JH	122
	123	4. No other changes are done. In particular, the local
	124	modifications you had before you started merge will stay the
	125	same and the index entries for them stay as they were,
	126	i.e. matching `HEAD`.
	127
	128	After seeing a conflict, you can do two things:
	129
	130	* Decide not to merge. The only clean-up you need are to reset
	131	the index file to the `HEAD` commit to reverse 2. and to clean
	132	up working tree changes made by 2. and 3.; `git-reset` can
	133	be used for this.
	134
	135	* Resolve the conflicts. `git-diff` would report only the
	136	conflicting paths because of the above 2. and 3.. Edit the
	137	working tree files into a desirable shape, `git-update-index`
	138	them, to make the index file contain what the merge result
	139	should be, and run `git-commit` to commit the result.
	140
	141
3c64314c PB	142	SEE ALSO
3c64314c PB	143	--------
fdd08979	144	gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1]
3c64314c PB	145
3c64314c PB	146
0f69be53 JH	147	Author
	148	------
	149	Written by Junio C Hamano <junkio@cox.net>
	150
	151
	152	Documentation
	153	--------------
	154	Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
	155
	156	GIT
	157	---
a7154e91	158	Part of the gitlink:git[7] suite