Documentation: suggest `reset --merge` in How Merge Works section
[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>]...
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13 [-m <msg>] <commit>...
14'git merge' <msg> HEAD <commit>...
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15
16DESCRIPTION
17-----------
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18Merges the history specified by <commit> into HEAD, optionally using a
19specific merge strategy.
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57bddb11 21The second syntax (<msg> `HEAD` <commit>...) is supported for
dee48c3c 22historical reasons. Do not use it from the command line or in
57bddb11 23new scripts. It is the same as `git merge -m <msg> <commit>...`.
dee48c3c 24
0b444cdb 25*Warning*: Running 'git merge' with uncommitted changes is
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26discouraged: while possible, it leaves you in a state that is hard to
27back out of in the case of a conflict.
28
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29
30OPTIONS
31-------
93d69d86 32include::merge-options.txt[]
0f69be53 33
dee48c3c 34-m <msg>::
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35 Set the commit message to be used for the merge commit (in
36 case one is created). The 'git fmt-merge-msg' command can be
37 used to give a good default for automated 'git merge'
38 invocations.
3c64314c 39
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40<commit>...::
41 Commits, usually other branch heads, to merge into our branch.
42 You need at least one <commit>. Specifying more than one
43 <commit> obviously means you are trying an Octopus.
0f69be53 44
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45include::merge-strategies.txt[]
46
0f69be53 47
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48HOW MERGE WORKS
49---------------
50
51A merge is always between the current `HEAD` and one or more
81646ad2 52commits (usually, branch head or tag), and the index file must
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53match the tree of `HEAD` commit (i.e. the contents of the last commit)
54when it starts out. In other words, `git diff --cached HEAD` must
55report no changes. (One exception is when the changed index
56entries are already in the same state that would result from
57the merge anyway.)
58
59Three kinds of merge can happen:
60
61* The merged commit is already contained in `HEAD`. This is the
62 simplest case, called "Already up-to-date."
63
64* `HEAD` is already contained in the merged commit. This is the
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65 most common case especially when invoked from 'git pull':
66 you are tracking an upstream repository, have committed no local
c0be8aa0 67 changes and now you want to update to a newer upstream revision.
29b802aa 68 Your `HEAD` (and the index) is updated to point at the merged
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69 commit, without creating an extra merge commit. This is
70 called "Fast-forward".
71
72* Both the merged commit and `HEAD` are independent and must be
29b802aa 73 tied together by a merge commit that has both of them as its parents.
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74 The rest of this section describes this "True merge" case.
75
76The chosen merge strategy merges the two commits into a single
77new source tree.
29b802aa 78When things merge cleanly, this is what happens:
ffb1a4be 79
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801. The results are updated both in the index file and in your
81 working tree;
822. Index file is written out as a tree;
833. The tree gets committed; and
844. The `HEAD` pointer gets advanced.
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85
86Because of 2., we require that the original state of the index
29b802aa 87file matches exactly the current `HEAD` commit; otherwise we
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88will write out your local changes already registered in your
89index file along with the merge result, which is not good.
29b802aa 90Because 1. involves only those paths differing between your
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91branch and the branch you are merging
92(which is typically a fraction of the whole tree), you can
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93have local modifications in your working tree as long as they do
94not overlap with what the merge updates.
95
29b802aa 96When there are conflicts, the following happens:
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97
981. `HEAD` stays the same.
99
1002. Cleanly merged paths are updated both in the index file and
101 in your working tree.
102
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1033. For conflicting paths, the index file records up to three
104 versions; stage1 stores the version from the common ancestor,
57bddb11 105 stage2 from `HEAD`, and stage3 from the other branch (you
b1889c36 106 can inspect the stages with `git ls-files -u`). The working
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107 tree files contain the result of the "merge" program; i.e. 3-way
108 merge results with familiar conflict markers `<<< === >>>`.
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109
1104. No other changes are done. In particular, the local
111 modifications you had before you started merge will stay the
112 same and the index entries for them stay as they were,
113 i.e. matching `HEAD`.
114
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115If you tried a merge which resulted in complex conflicts and
116want to start over, you can recover with `git reset --merge`.
117
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118HOW CONFLICTS ARE PRESENTED
119---------------------------
120
121During a merge, the working tree files are updated to reflect the result
122of the merge. Among the changes made to the common ancestor's version,
123non-overlapping ones (that is, you changed an area of the file while the
124other side left that area intact, or vice versa) are incorporated in the
125final result verbatim. When both sides made changes to the same area,
126however, git cannot randomly pick one side over the other, and asks you to
127resolve it by leaving what both sides did to that area.
128
129By default, git uses the same style as that is used by "merge" program
130from the RCS suite to present such a conflicted hunk, like this:
131
132------------
133Here are lines that are either unchanged from the common
134ancestor, or cleanly resolved because only one side changed.
135<<<<<<< yours:sample.txt
136Conflict resolution is hard;
137let's go shopping.
138=======
139Git makes conflict resolution easy.
140>>>>>>> theirs:sample.txt
141And here is another line that is cleanly resolved or unmodified.
142------------
143
29b802aa 144The area where a pair of conflicting changes happened is marked with markers
dcb11263 145`<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======`
29b802aa 146is typically your side, and the part afterwards is typically their side.
70a3f897 147
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148The default format does not show what the original said in the conflicting
149area. You cannot tell how many lines are deleted and replaced with
150Barbie's remark on your side. The only thing you can tell is that your
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151side wants to say it is hard and you'd prefer to go shopping, while the
152other side wants to claim it is easy.
153
154An alternative style can be used by setting the "merge.conflictstyle"
155configuration variable to "diff3". In "diff3" style, the above conflict
156may look like this:
157
158------------
159Here are lines that are either unchanged from the common
160ancestor, or cleanly resolved because only one side changed.
161<<<<<<< yours:sample.txt
162Conflict resolution is hard;
163let's go shopping.
164|||||||
165Conflict resolution is hard.
166=======
167Git makes conflict resolution easy.
168>>>>>>> theirs:sample.txt
169And here is another line that is cleanly resolved or unmodified.
170------------
171
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172In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
173another `|||||||` marker that is followed by the original text. You can
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174tell that the original just stated a fact, and your side simply gave in to
175that statement and gave up, while the other side tried to have a more
176positive attitude. You can sometimes come up with a better resolution by
177viewing the original.
178
179
180HOW TO RESOLVE CONFLICTS
181------------------------
182
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183After seeing a conflict, you can do two things:
184
29b802aa 185 * Decide not to merge. The only clean-ups you need are to reset
ffb1a4be 186 the index file to the `HEAD` commit to reverse 2. and to clean
ca768288 187 up working tree changes made by 2. and 3.; `git-reset --hard` can
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188 be used for this.
189
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190 * Resolve the conflicts. Git will mark the conflicts in
191 the working tree. Edit the files into shape and
0b444cdb 192 'git add' them to the index. Use 'git commit' to seal the deal.
ffb1a4be 193
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194You can work through the conflict with a number of tools:
195
ca768288 196 * Use a mergetool. `git mergetool` to launch a graphical
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197 mergetool which will work you through the merge.
198
ca768288 199 * Look at the diffs. `git diff` will show a three-way diff,
57bddb11 200 highlighting changes from both the HEAD and their versions.
34ad1afa 201
ca768288 202 * Look at the diffs on their own. `git log --merge -p <path>`
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203 will show diffs first for the HEAD version and then
204 their version.
34ad1afa 205
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206 * Look at the originals. `git show :1:filename` shows the
207 common ancestor, `git show :2:filename` shows the HEAD
208 version and `git show :3:filename` shows their version.
ffb1a4be 209
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210
211EXAMPLES
212--------
213
214* Merge branches `fixes` and `enhancements` on top of
215 the current branch, making an octopus merge:
216+
217------------------------------------------------
218$ git merge fixes enhancements
219------------------------------------------------
220
221* Merge branch `obsolete` into the current branch, using `ours`
222 merge strategy:
223+
224------------------------------------------------
225$ git merge -s ours obsolete
226------------------------------------------------
227
228* Merge branch `maint` into the current branch, but do not make
229 a new commit automatically:
230+
231------------------------------------------------
232$ git merge --no-commit maint
233------------------------------------------------
234+
235This can be used when you want to include further changes to the
236merge, or want to write your own merge commit message.
237+
238You should refrain from abusing this option to sneak substantial
239changes into a merge commit. Small fixups like bumping
240release/version name would be acceptable.
241
242
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243CONFIGURATION
244-------------
245include::merge-config.txt[]
246
247branch.<name>.mergeoptions::
248 Sets default options for merging into branch <name>. The syntax and
249 supported options are the same as those of 'git merge', but option
250 values containing whitespace characters are currently not supported.
251
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252SEE ALSO
253--------
5162e697 254linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
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255linkgit:gitattributes[5],
256linkgit:git-reset[1],
257linkgit:git-diff[1], linkgit:git-ls-files[1],
258linkgit:git-add[1], linkgit:git-rm[1],
259linkgit:git-mergetool[1]
3c64314c 260
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261Author
262------
59eb68aa 263Written by Junio C Hamano <gitster@pobox.com>
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264
265
266Documentation
267--------------
268Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
269
270GIT
271---
9e1f0a85 272Part of the linkgit:git[1] suite