merge-recursive: enforce rule that index matches head before merging
[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]
f8246281 12'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
340f2c5e 13 [-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
09c2cb87 14 [--[no-]allow-unrelated-histories]
93e535a5 15 [--[no-]rerere-autoupdate] [-m <msg>] [<commit>...]
35d2fffd 16'git merge' --abort
367ff694 17'git merge' --continue
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18
19DESCRIPTION
20-----------
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21Incorporates changes from the named commits (since the time their
22histories diverged from the current branch) into the current
23branch. This command is used by 'git pull' to incorporate changes
24from another repository and can be used by hand to merge changes
25from one branch into another.
26
27Assume the following history exists and the current branch is
28"`master`":
29
30------------
31 A---B---C topic
32 /
33 D---E---F---G master
34------------
35
36Then "`git merge topic`" will replay the changes made on the
37`topic` branch since it diverged from `master` (i.e., `E`) until
38its current commit (`C`) on top of `master`, and record the result
39in a new commit along with the names of the two parent commits and
40a log message from the user describing the changes.
41
42------------
43 A---B---C topic
44 / \
45 D---E---F---G---H master
46------------
0f69be53 47
b4391657 48The second syntax ("`git merge --abort`") can only be run after the
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49merge has resulted in conflicts. 'git merge --abort' will abort the
50merge process and try to reconstruct the pre-merge state. However,
51if there were uncommitted changes when the merge started (and
52especially if those changes were further modified after the merge
53was started), 'git merge --abort' will in some cases be unable to
54reconstruct the original (pre-merge) changes. Therefore:
55
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56*Warning*: Running 'git merge' with non-trivial uncommitted changes is
57discouraged: while possible, it may leave you in a state that is hard to
e330d8ca 58back out of in the case of a conflict.
dee48c3c 59
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60The fourth syntax ("`git merge --continue`") can only be run after the
61merge has resulted in conflicts.
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62
63OPTIONS
64-------
93d69d86 65include::merge-options.txt[]
0f69be53 66
dee48c3c 67-m <msg>::
0f8a02c6 68 Set the commit message to be used for the merge commit (in
f0ecac2b 69 case one is created).
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70+
71If `--log` is specified, a shortlog of the commits being merged
72will be appended to the specified message.
73+
74The 'git fmt-merge-msg' command can be
75used to give a good default for automated 'git merge'
561d2b79 76invocations. The automated message can include the branch description.
3c64314c 77
0460ed2c 78--[no-]rerere-autoupdate::
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79 Allow the rerere mechanism to update the index with the
80 result of auto-conflict resolution if possible.
81
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82--abort::
83 Abort the current conflict resolution process, and
84 try to reconstruct the pre-merge state.
85+
86If there were uncommitted worktree changes present when the merge
87started, 'git merge --abort' will in some cases be unable to
88reconstruct these changes. It is therefore recommended to always
89commit or stash your changes before running 'git merge'.
90+
91'git merge --abort' is equivalent to 'git reset --merge' when
92`MERGE_HEAD` is present.
93
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94--continue::
95 After a 'git merge' stops due to conflicts you can conclude the
96 merge by running 'git merge --continue' (see "HOW TO RESOLVE
97 CONFLICTS" section below).
98
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99<commit>...::
100 Commits, usually other branch heads, to merge into our branch.
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101 Specifying more than one commit will create a merge with
102 more than two parents (affectionately called an Octopus merge).
103+
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104If no commit is given from the command line, merge the remote-tracking
105branches that the current branch is configured to use as its upstream.
93e535a5 106See also the configuration section of this manual page.
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107+
108When `FETCH_HEAD` (and no other commit) is specified, the branches
109recorded in the `.git/FETCH_HEAD` file by the previous invocation
110of `git fetch` for merging are merged to the current branch.
0f69be53 111
bb73d73c 112
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113PRE-MERGE CHECKS
114----------------
0f69be53 115
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116Before applying outside changes, you should get your own work in
117good shape and committed locally, so it will not be clobbered if
118there are conflicts. See also linkgit:git-stash[1].
119'git pull' and 'git merge' will stop without doing anything when
120local uncommitted changes overlap with files that 'git pull'/'git
121merge' may need to update.
3ae854c3 122
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123To avoid recording unrelated changes in the merge commit,
124'git pull' and 'git merge' will also abort if there are any changes
125registered in the index relative to the `HEAD` commit. (One
126exception is when the changed index entries are in the state that
127would result from the merge already.)
dbddb714 128
30f2bade 129If all named commits are already ancestors of `HEAD`, 'git merge'
7560f547 130will exit early with the message "Already up to date."
3ae854c3 131
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132FAST-FORWARD MERGE
133------------------
134
135Often the current branch head is an ancestor of the named commit.
136This is the most common case especially when invoked from 'git
137pull': you are tracking an upstream repository, you have committed
138no local changes, and now you want to update to a newer upstream
139revision. In this case, a new commit is not needed to store the
140combined history; instead, the `HEAD` (along with the index) is
141updated to point at the named commit, without creating an extra
142merge commit.
143
144This behavior can be suppressed with the `--no-ff` option.
ffb1a4be 145
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146TRUE MERGE
147----------
c0be8aa0 148
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149Except in a fast-forward merge (see above), the branches to be
150merged must be tied together by a merge commit that has both of them
151as its parents.
ffb1a4be 152
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153A merged version reconciling the changes from all branches to be
154merged is committed, and your `HEAD`, index, and working tree are
155updated to it. It is possible to have modifications in the working
156tree as long as they do not overlap; the update will preserve them.
ffb1a4be 157
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158When it is not obvious how to reconcile the changes, the following
159happens:
ffb1a4be 160
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1611. The `HEAD` pointer stays the same.
1622. The `MERGE_HEAD` ref is set to point to the other branch head.
1633. Paths that merged cleanly are updated both in the index file and
ffb1a4be 164 in your working tree.
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1654. For conflicting paths, the index file records up to three
166 versions: stage 1 stores the version from the common ancestor,
167 stage 2 from `HEAD`, and stage 3 from `MERGE_HEAD` (you
b1889c36 168 can inspect the stages with `git ls-files -u`). The working
29b802aa 169 tree files contain the result of the "merge" program; i.e. 3-way
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170 merge results with familiar conflict markers `<<<` `===` `>>>`.
1715. No other changes are made. In particular, the local
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172 modifications you had before you started merge will stay the
173 same and the index entries for them stay as they were,
174 i.e. matching `HEAD`.
175
ed4a6baa 176If you tried a merge which resulted in complex conflicts and
35d2fffd 177want to start over, you can recover with `git merge --abort`.
ed4a6baa 178
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179MERGING TAG
180-----------
181
182When merging an annotated (and possibly signed) tag, Git always
183creates a merge commit even if a fast-forward merge is possible, and
184the commit message template is prepared with the tag message.
185Additionally, if the tag is signed, the signature check is reported
186as a comment in the message template. See also linkgit:git-tag[1].
187
188When you want to just integrate with the work leading to the commit
189that happens to be tagged, e.g. synchronizing with an upstream
190release point, you may not want to make an unnecessary merge commit.
191
192In such a case, you can "unwrap" the tag yourself before feeding it
193to `git merge`, or pass `--ff-only` when you do not have any work on
194your own. e.g.
195
e45bda87 196----
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197git fetch origin
198git merge v1.2.3^0
199git merge --ff-only v1.2.3
e45bda87 200----
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201
202
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203HOW CONFLICTS ARE PRESENTED
204---------------------------
205
206During a merge, the working tree files are updated to reflect the result
207of the merge. Among the changes made to the common ancestor's version,
208non-overlapping ones (that is, you changed an area of the file while the
209other side left that area intact, or vice versa) are incorporated in the
210final result verbatim. When both sides made changes to the same area,
2de9b711 211however, Git cannot randomly pick one side over the other, and asks you to
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212resolve it by leaving what both sides did to that area.
213
2de9b711 214By default, Git uses the same style as the one used by the "merge" program
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215from the RCS suite to present such a conflicted hunk, like this:
216
217------------
218Here are lines that are either unchanged from the common
219ancestor, or cleanly resolved because only one side changed.
220<<<<<<< yours:sample.txt
221Conflict resolution is hard;
222let's go shopping.
223=======
224Git makes conflict resolution easy.
225>>>>>>> theirs:sample.txt
226And here is another line that is cleanly resolved or unmodified.
227------------
228
29b802aa 229The area where a pair of conflicting changes happened is marked with markers
dcb11263 230`<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======`
29b802aa 231is typically your side, and the part afterwards is typically their side.
70a3f897 232
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233The default format does not show what the original said in the conflicting
234area. You cannot tell how many lines are deleted and replaced with
235Barbie's remark on your side. The only thing you can tell is that your
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236side wants to say it is hard and you'd prefer to go shopping, while the
237other side wants to claim it is easy.
238
da0005b8 239An alternative style can be used by setting the "merge.conflictStyle"
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240configuration variable to "diff3". In "diff3" style, the above conflict
241may look like this:
242
243------------
244Here are lines that are either unchanged from the common
245ancestor, or cleanly resolved because only one side changed.
246<<<<<<< yours:sample.txt
247Conflict resolution is hard;
248let's go shopping.
249|||||||
250Conflict resolution is hard.
251=======
252Git makes conflict resolution easy.
253>>>>>>> theirs:sample.txt
254And here is another line that is cleanly resolved or unmodified.
255------------
256
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257In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
258another `|||||||` marker that is followed by the original text. You can
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259tell that the original just stated a fact, and your side simply gave in to
260that statement and gave up, while the other side tried to have a more
261positive attitude. You can sometimes come up with a better resolution by
262viewing the original.
263
264
265HOW TO RESOLVE CONFLICTS
266------------------------
267
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268After seeing a conflict, you can do two things:
269
29b802aa 270 * Decide not to merge. The only clean-ups you need are to reset
ffb1a4be 271 the index file to the `HEAD` commit to reverse 2. and to clean
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272 up working tree changes made by 2. and 3.; `git merge --abort`
273 can be used for this.
ffb1a4be 274
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275 * Resolve the conflicts. Git will mark the conflicts in
276 the working tree. Edit the files into shape and
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277 'git add' them to the index. Use 'git commit' or
278 'git merge --continue' to seal the deal. The latter command
279 checks whether there is a (interrupted) merge in progress
280 before calling 'git commit'.
ffb1a4be 281
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282You can work through the conflict with a number of tools:
283
ca768288 284 * Use a mergetool. `git mergetool` to launch a graphical
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285 mergetool which will work you through the merge.
286
ca768288 287 * Look at the diffs. `git diff` will show a three-way diff,
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288 highlighting changes from both the `HEAD` and `MERGE_HEAD`
289 versions.
34ad1afa 290
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291 * Look at the diffs from each branch. `git log --merge -p <path>`
292 will show diffs first for the `HEAD` version and then the
293 `MERGE_HEAD` version.
34ad1afa 294
ca768288 295 * Look at the originals. `git show :1:filename` shows the
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296 common ancestor, `git show :2:filename` shows the `HEAD`
297 version, and `git show :3:filename` shows the `MERGE_HEAD`
298 version.
ffb1a4be 299
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300
301EXAMPLES
302--------
303
304* Merge branches `fixes` and `enhancements` on top of
305 the current branch, making an octopus merge:
306+
307------------------------------------------------
308$ git merge fixes enhancements
309------------------------------------------------
310
311* Merge branch `obsolete` into the current branch, using `ours`
312 merge strategy:
313+
314------------------------------------------------
315$ git merge -s ours obsolete
316------------------------------------------------
317
318* Merge branch `maint` into the current branch, but do not make
319 a new commit automatically:
320+
321------------------------------------------------
322$ git merge --no-commit maint
323------------------------------------------------
324+
325This can be used when you want to include further changes to the
326merge, or want to write your own merge commit message.
327+
328You should refrain from abusing this option to sneak substantial
329changes into a merge commit. Small fixups like bumping
330release/version name would be acceptable.
331
332
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333include::merge-strategies.txt[]
334
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335CONFIGURATION
336-------------
337include::merge-config.txt[]
338
da0005b8 339branch.<name>.mergeOptions::
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340 Sets default options for merging into branch <name>. The syntax and
341 supported options are the same as those of 'git merge', but option
342 values containing whitespace characters are currently not supported.
343
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344SEE ALSO
345--------
5162e697 346linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
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347linkgit:gitattributes[5],
348linkgit:git-reset[1],
349linkgit:git-diff[1], linkgit:git-ls-files[1],
350linkgit:git-add[1], linkgit:git-rm[1],
351linkgit:git-mergetool[1]
3c64314c 352
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353GIT
354---
9e1f0a85 355Part of the linkgit:git[1] suite