refs.c: off-by-one fix.
[git/git.git] / Documentation / git-merge.txt
CommitLineData
0f69be53
JH
1git-merge(1)
2============
0f69be53
JH
3
4NAME
5----
6git-merge - Grand Unified Merge Driver
7
8
9SYNOPSIS
10--------
37465016 11'git-merge' [-n] [--no-commit] [-s <strategy>]... <msg> <head> <remote> <remote>...
0f69be53
JH
12
13
14DESCRIPTION
15-----------
16This is the top-level user interface to the merge machinery
17which drives multiple merge strategy scripts.
18
19
20OPTIONS
21-------
93d69d86 22include::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
37include::merge-strategies.txt[]
38
0f69be53 39
ffb1a4be
JH
40HOW MERGE WORKS
41---------------
42
43A merge is always between the current `HEAD` and one or more
44remote branch heads, and the index file must exactly match the
45tree of `HEAD` commit (i.e. the contents of the last commit) when
46it happens. In other words, `git-diff --cached HEAD` must
47report no changes.
48
49[NOTE]
50This is a bit of lie. In certain special cases, your index are
51allowed to be different from the tree of `HEAD` commit. The most
52notable case is when your `HEAD` commit is already ahead of what
53is being merged, in which case your index can have arbitrary
54difference from your `HEAD` commit. Otherwise, your index entries
55are allowed have differences from your `HEAD` commit that match
56the result of trivial merge (e.g. you received the same patch
57from external source to produce the same result as what you are
58merging). For example, if a path did not exist in the common
59ancestor and your head commit but exists in the tree you are
60merging into your repository, and if you already happen to have
61that path exactly in your index, the merge does not have to
62fail.
63
64Otherwise, merge will refuse to do any harm to your repository
65(that is, it may fetch the objects from remote, and it may even
66update the local branch used to keep track of the remote branch
67with `git pull remote rbranch:lbranch`, but your working tree,
68`.git/HEAD` pointer and index file are left intact).
69
70You may have local modifications in the working tree files. In
71other words, `git-diff` is allowed to report changes.
72However, the merge uses your working tree as the working area,
73and in order to prevent the merge operation from losing such
74changes, it makes sure that they do not interfere with the
75merge. Those complex tables in read-tree documentation define
76what it means for a path to "interfere with the merge". And if
77your local modifications interfere with the merge, again, it
78stops before touching anything.
79
80So in the above two "failed merge" case, you do not have to
81worry about lossage of data --- you simply were not ready to do
82a merge, so no merge happened at all. You may want to finish
83whatever you were in the middle of doing, and retry the same
84pull after you are done and ready.
85
86When things cleanly merge, these things happen:
87
881. the results are updated both in the index file and in your
89 working tree,
902. index file is written out as a tree,
913. the tree gets committed, and
924. the `HEAD` pointer gets advanced.
93
94Because of 2., we require that the original state of the index
95file to match exactly the current `HEAD` commit; otherwise we
96will write out your local changes already registered in your
97index file along with the merge result, which is not good.
98Because 1. involves only the paths different between your
99branch and the remote branch you are pulling from during the
100merge (which is typically a fraction of the whole tree), you can
101have local modifications in your working tree as long as they do
102not overlap with what the merge updates.
103
104When there are conflicts, these things happen:
105
1061. `HEAD` stays the same.
107
1082. Cleanly merged paths are updated both in the index file and
109 in your working tree.
110
3ace1fe3
JH
1113. For conflicting paths, the index file records up to three
112 versions; stage1 stores the version from the common ancestor,
113 stage2 from `HEAD`, and stage3 from the remote branch (you
114 can inspect the stages with `git-ls-files -u`). The working
115 tree files have the result of "merge" program; i.e. 3-way
116 merge result with familiar conflict markers `<<< === >>>`.
ffb1a4be
JH
117
1184. No other changes are done. In particular, the local
119 modifications you had before you started merge will stay the
120 same and the index entries for them stay as they were,
121 i.e. matching `HEAD`.
122
123After seeing a conflict, you can do two things:
124
125 * Decide not to merge. The only clean-up you need are to reset
126 the index file to the `HEAD` commit to reverse 2. and to clean
127 up working tree changes made by 2. and 3.; `git-reset` can
128 be used for this.
129
130 * Resolve the conflicts. `git-diff` would report only the
131 conflicting paths because of the above 2. and 3.. Edit the
132 working tree files into a desirable shape, `git-update-index`
133 them, to make the index file contain what the merge result
134 should be, and run `git-commit` to commit the result.
135
136
3c64314c
PB
137SEE ALSO
138--------
fdd08979 139gitlink:git-fmt-merge-msg[1], gitlink:git-pull[1]
3c64314c
PB
140
141
0f69be53
JH
142Author
143------
144Written by Junio C Hamano <junkio@cox.net>
145
146
147Documentation
148--------------
149Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
150
151GIT
152---
a7154e91 153Part of the gitlink:git[7] suite