Extend "checkout --track" DWIM to support more cases
[git/git.git] / Documentation / git-merge.txt
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1git-merge(1)
2============
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3
4NAME
5----
c3f0baac 6git-merge - Join two or more development histories together
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7
8
9SYNOPSIS
10--------
17bcdad3 11[verse]
b1889c36 12'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
1e8b0d48 13 [-m <msg>] <remote> <remote>...
b1889c36 14'git merge' <msg> HEAD <remote>...
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15
16DESCRIPTION
17-----------
17bcdad3 18This is the top-level interface to the merge machinery
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19which drives multiple merge strategy scripts.
20
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21The second syntax (<msg> `HEAD` <remote>) is supported for
22historical reasons. Do not use it from the command line or in
23new scripts. It is the same as `git merge -m <msg> <remote>`.
24
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25
26OPTIONS
27-------
93d69d86 28include::merge-options.txt[]
0f69be53 29
dee48c3c 30-m <msg>::
3c64314c 31 The commit message to be used for the merge commit (in case
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32 it is created). The 'git-fmt-merge-msg' script can be used
33 to give a good default for automated 'git-merge' invocations.
3c64314c 34
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35<remote>...::
36 Other branch heads to merge into our branch. You need at
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37 least one <remote>. Specifying more than one <remote>
38 obviously means you are trying an Octopus.
39
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40include::merge-strategies.txt[]
41
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3ae854c3 43If you tried a merge which resulted in a complex conflicts and
ba020ef5 44would want to start over, you can recover with 'git-reset'.
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46CONFIGURATION
47-------------
f5a84c37 48include::merge-config.txt[]
dbddb714 49
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50branch.<name>.mergeoptions::
51 Sets default options for merging into branch <name>. The syntax and
ba020ef5 52 supported options are equal to that of 'git-merge', but option values
aec7b362 53 containing whitespace characters are currently not supported.
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55HOW MERGE WORKS
56---------------
57
58A merge is always between the current `HEAD` and one or more
81646ad2 59commits (usually, branch head or tag), and the index file must
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60match the tree of `HEAD` commit (i.e. the contents of the last commit)
61when it starts out. In other words, `git diff --cached HEAD` must
62report no changes. (One exception is when the changed index
63entries are already in the same state that would result from
64the merge anyway.)
65
66Three kinds of merge can happen:
67
68* The merged commit is already contained in `HEAD`. This is the
69 simplest case, called "Already up-to-date."
70
71* `HEAD` is already contained in the merged commit. This is the
72 most common case especially when involved through 'git pull':
73 you are tracking an upstream repository, committed no local
74 changes and now you want to update to a newer upstream revision.
75 Your `HEAD` (and the index) is updated to at point the merged
76 commit, without creating an extra merge commit. This is
77 called "Fast-forward".
78
79* Both the merged commit and `HEAD` are independent and must be
80 tied together by a merge commit that has them both as its parents.
81 The rest of this section describes this "True merge" case.
82
83The chosen merge strategy merges the two commits into a single
84new source tree.
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85When things cleanly merge, these things happen:
86
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871. The results are updated both in the index file and in your
88 working tree;
892. Index file is written out as a tree;
903. The tree gets committed; and
914. The `HEAD` pointer gets advanced.
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92
93Because of 2., we require that the original state of the index
94file to match exactly the current `HEAD` commit; otherwise we
95will write out your local changes already registered in your
96index file along with the merge result, which is not good.
97Because 1. involves only the paths different between your
98branch and the remote branch you are pulling from during the
99merge (which is typically a fraction of the whole tree), you can
100have local modifications in your working tree as long as they do
101not overlap with what the merge updates.
102
103When there are conflicts, these things happen:
104
1051. `HEAD` stays the same.
106
1072. Cleanly merged paths are updated both in the index file and
108 in your working tree.
109
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1103. For conflicting paths, the index file records up to three
111 versions; stage1 stores the version from the common ancestor,
112 stage2 from `HEAD`, and stage3 from the remote branch (you
b1889c36 113 can inspect the stages with `git ls-files -u`). The working
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114 tree files have the result of "merge" program; i.e. 3-way
115 merge result with familiar conflict markers `<<< === >>>`.
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116
1174. No other changes are done. In particular, the local
118 modifications you had before you started merge will stay the
119 same and the index entries for them stay as they were,
120 i.e. matching `HEAD`.
121
122After seeing a conflict, you can do two things:
123
124 * Decide not to merge. The only clean-up you need are to reset
125 the index file to the `HEAD` commit to reverse 2. and to clean
c0be8aa0 126 up working tree changes made by 2. and 3.; 'git-reset --hard' can
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127 be used for this.
128
b1889c36 129 * Resolve the conflicts. `git diff` would report only the
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130 conflicting paths because of the above 2. and 3.
131 Edit the working tree files into a desirable shape
132 ('git mergetool' can ease this task), 'git-add' or 'git-rm'
ffb1a4be 133 them, to make the index file contain what the merge result
ba020ef5 134 should be, and run 'git-commit' to commit the result.
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135
136
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137SEE ALSO
138--------
5162e697 139linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
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140linkgit:gitattributes[5],
141linkgit:git-reset[1],
142linkgit:git-diff[1], linkgit:git-ls-files[1],
143linkgit:git-add[1], linkgit:git-rm[1],
144linkgit:git-mergetool[1]
3c64314c 145
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146Author
147------
59eb68aa 148Written by Junio C Hamano <gitster@pobox.com>
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149
150
151Documentation
152--------------
153Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
154
155GIT
156---
9e1f0a85 157Part of the linkgit:git[1] suite