Improve language in git-merge.txt and related docs
[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
0f69be53 42
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'.
3ae854c3 45
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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.
3ae854c3 54
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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
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72 most common case especially when invoked from 'git pull':
73 you are tracking an upstream repository, have committed no local
c0be8aa0 74 changes and now you want to update to a newer upstream revision.
29b802aa 75 Your `HEAD` (and the index) is updated to point at the merged
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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
29b802aa 80 tied together by a merge commit that has both of them as its parents.
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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.
29b802aa 85When things merge cleanly, this is what happens:
ffb1a4be 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
29b802aa 94file matches exactly the current `HEAD` commit; otherwise we
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95will write out your local changes already registered in your
96index file along with the merge result, which is not good.
29b802aa 97Because 1. involves only those paths differing between your
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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
29b802aa 103When there are conflicts, the following happens:
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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 contain the result of the "merge" program; i.e. 3-way
115 merge results 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
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122HOW CONFLICTS ARE PRESENTED
123---------------------------
124
125During a merge, the working tree files are updated to reflect the result
126of the merge. Among the changes made to the common ancestor's version,
127non-overlapping ones (that is, you changed an area of the file while the
128other side left that area intact, or vice versa) are incorporated in the
129final result verbatim. When both sides made changes to the same area,
130however, git cannot randomly pick one side over the other, and asks you to
131resolve it by leaving what both sides did to that area.
132
133By default, git uses the same style as that is used by "merge" program
134from the RCS suite to present such a conflicted hunk, like this:
135
136------------
137Here are lines that are either unchanged from the common
138ancestor, or cleanly resolved because only one side changed.
139<<<<<<< yours:sample.txt
140Conflict resolution is hard;
141let's go shopping.
142=======
143Git makes conflict resolution easy.
144>>>>>>> theirs:sample.txt
145And here is another line that is cleanly resolved or unmodified.
146------------
147
29b802aa 148The area where a pair of conflicting changes happened is marked with markers
3407a7a9 149"`<<<<<<<`", "`=======`", and "`>>>>>>>`". The part before the "`=======`"
29b802aa 150is typically your side, and the part afterwards is typically their side.
70a3f897 151
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152The default format does not show what the original said in the conflicting
153area. You cannot tell how many lines are deleted and replaced with
154Barbie's remark on your side. The only thing you can tell is that your
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155side wants to say it is hard and you'd prefer to go shopping, while the
156other side wants to claim it is easy.
157
158An alternative style can be used by setting the "merge.conflictstyle"
159configuration variable to "diff3". In "diff3" style, the above conflict
160may look like this:
161
162------------
163Here are lines that are either unchanged from the common
164ancestor, or cleanly resolved because only one side changed.
165<<<<<<< yours:sample.txt
166Conflict resolution is hard;
167let's go shopping.
168|||||||
169Conflict resolution is hard.
170=======
171Git makes conflict resolution easy.
172>>>>>>> theirs:sample.txt
173And here is another line that is cleanly resolved or unmodified.
174------------
175
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176In addition to the "`<<<<<<<`", "`=======`", and "`>>>>>>>`" markers, it uses
177another "`|||||||`" marker that is followed by the original text. You can
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178tell that the original just stated a fact, and your side simply gave in to
179that statement and gave up, while the other side tried to have a more
180positive attitude. You can sometimes come up with a better resolution by
181viewing the original.
182
183
184HOW TO RESOLVE CONFLICTS
185------------------------
186
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187After seeing a conflict, you can do two things:
188
29b802aa 189 * Decide not to merge. The only clean-ups you need are to reset
ffb1a4be 190 the index file to the `HEAD` commit to reverse 2. and to clean
c0be8aa0 191 up working tree changes made by 2. and 3.; 'git-reset --hard' can
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192 be used for this.
193
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194 * Resolve the conflicts. Git will mark the conflicts in
195 the working tree. Edit the files into shape and
29b802aa 196 'git-add' them to the index. Use 'git-commit' to seal the deal.
ffb1a4be 197
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198You can work through the conflict with a number of tools:
199
200 * Use a mergetool. 'git mergetool' to launch a graphical
201 mergetool which will work you through the merge.
202
203 * Look at the diffs. 'git diff' will show a three-way diff,
204 highlighting changes from both the HEAD and remote versions.
205
206 * Look at the diffs on their own. 'git log --merge -p <path>'
207 will show diffs first for the HEAD version and then the
208 remote version.
209
210 * Look at the originals. 'git show :1:filename' shows the
211 common ancestor, 'git show :2:filename' shows the HEAD
212 version and 'git show :3:filename' shows the remote version.
ffb1a4be 213
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214SEE ALSO
215--------
5162e697 216linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
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217linkgit:gitattributes[5],
218linkgit:git-reset[1],
219linkgit:git-diff[1], linkgit:git-ls-files[1],
220linkgit:git-add[1], linkgit:git-rm[1],
221linkgit:git-mergetool[1]
3c64314c 222
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223Author
224------
59eb68aa 225Written by Junio C Hamano <gitster@pobox.com>
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226
227
228Documentation
229--------------
230Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
231
232GIT
233---
9e1f0a85 234Part of the linkgit:git[1] suite