Merge branch 'pw/rerere-autoupdate'
[git/git.git] / Documentation / git-merge.txt
1 git-merge(1)
2 ============
3
4 NAME
5 ----
6 git-merge - Join two or more development histories together
7
8
9 SYNOPSIS
10 --------
11 [verse]
12 'git merge' [-n] [--stat] [--no-commit] [--squash] [--[no-]edit]
13 [-s <strategy>] [-X <strategy-option>] [-S[<keyid>]]
14 [--[no-]allow-unrelated-histories]
15 [--[no-]rerere-autoupdate] [-m <msg>] [-F <file>] [<commit>...]
16 'git merge' --abort
17 'git merge' --continue
18
19 DESCRIPTION
20 -----------
21 Incorporates changes from the named commits (since the time their
22 histories diverged from the current branch) into the current
23 branch. This command is used by 'git pull' to incorporate changes
24 from another repository and can be used by hand to merge changes
25 from one branch into another.
26
27 Assume 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
36 Then "`git merge topic`" will replay the changes made on the
37 `topic` branch since it diverged from `master` (i.e., `E`) until
38 its current commit (`C`) on top of `master`, and record the result
39 in a new commit along with the names of the two parent commits and
40 a log message from the user describing the changes.
41
42 ------------
43 A---B---C topic
44 / \
45 D---E---F---G---H master
46 ------------
47
48 The second syntax ("`git merge --abort`") can only be run after the
49 merge has resulted in conflicts. 'git merge --abort' will abort the
50 merge process and try to reconstruct the pre-merge state. However,
51 if there were uncommitted changes when the merge started (and
52 especially if those changes were further modified after the merge
53 was started), 'git merge --abort' will in some cases be unable to
54 reconstruct the original (pre-merge) changes. Therefore:
55
56 *Warning*: Running 'git merge' with non-trivial uncommitted changes is
57 discouraged: while possible, it may leave you in a state that is hard to
58 back out of in the case of a conflict.
59
60 The third syntax ("`git merge --continue`") can only be run after the
61 merge has resulted in conflicts.
62
63 OPTIONS
64 -------
65 include::merge-options.txt[]
66
67 -m <msg>::
68 Set the commit message to be used for the merge commit (in
69 case one is created).
70 +
71 If `--log` is specified, a shortlog of the commits being merged
72 will be appended to the specified message.
73 +
74 The 'git fmt-merge-msg' command can be
75 used to give a good default for automated 'git merge'
76 invocations. The automated message can include the branch description.
77
78 -F <file>::
79 --file=<file>::
80 Read the commit message to be used for the merge commit (in
81 case one is created).
82 +
83 If `--log` is specified, a shortlog of the commits being merged
84 will be appended to the specified message.
85
86 --rerere-autoupdate::
87 --no-rerere-autoupdate::
88 Allow the rerere mechanism to update the index with the
89 result of auto-conflict resolution if possible.
90
91 --abort::
92 Abort the current conflict resolution process, and
93 try to reconstruct the pre-merge state.
94 +
95 If there were uncommitted worktree changes present when the merge
96 started, 'git merge --abort' will in some cases be unable to
97 reconstruct these changes. It is therefore recommended to always
98 commit or stash your changes before running 'git merge'.
99 +
100 'git merge --abort' is equivalent to 'git reset --merge' when
101 `MERGE_HEAD` is present.
102
103 --continue::
104 After a 'git merge' stops due to conflicts you can conclude the
105 merge by running 'git merge --continue' (see "HOW TO RESOLVE
106 CONFLICTS" section below).
107
108 <commit>...::
109 Commits, usually other branch heads, to merge into our branch.
110 Specifying more than one commit will create a merge with
111 more than two parents (affectionately called an Octopus merge).
112 +
113 If no commit is given from the command line, merge the remote-tracking
114 branches that the current branch is configured to use as its upstream.
115 See also the configuration section of this manual page.
116 +
117 When `FETCH_HEAD` (and no other commit) is specified, the branches
118 recorded in the `.git/FETCH_HEAD` file by the previous invocation
119 of `git fetch` for merging are merged to the current branch.
120
121
122 PRE-MERGE CHECKS
123 ----------------
124
125 Before applying outside changes, you should get your own work in
126 good shape and committed locally, so it will not be clobbered if
127 there are conflicts. See also linkgit:git-stash[1].
128 'git pull' and 'git merge' will stop without doing anything when
129 local uncommitted changes overlap with files that 'git pull'/'git
130 merge' may need to update.
131
132 To avoid recording unrelated changes in the merge commit,
133 'git pull' and 'git merge' will also abort if there are any changes
134 registered in the index relative to the `HEAD` commit. (Special
135 narrow exceptions to this rule may exist depending on which merge
136 strategy is in use, but generally, the index must match HEAD.)
137
138 If all named commits are already ancestors of `HEAD`, 'git merge'
139 will exit early with the message "Already up to date."
140
141 FAST-FORWARD MERGE
142 ------------------
143
144 Often the current branch head is an ancestor of the named commit.
145 This is the most common case especially when invoked from 'git
146 pull': you are tracking an upstream repository, you have committed
147 no local changes, and now you want to update to a newer upstream
148 revision. In this case, a new commit is not needed to store the
149 combined history; instead, the `HEAD` (along with the index) is
150 updated to point at the named commit, without creating an extra
151 merge commit.
152
153 This behavior can be suppressed with the `--no-ff` option.
154
155 TRUE MERGE
156 ----------
157
158 Except in a fast-forward merge (see above), the branches to be
159 merged must be tied together by a merge commit that has both of them
160 as its parents.
161
162 A merged version reconciling the changes from all branches to be
163 merged is committed, and your `HEAD`, index, and working tree are
164 updated to it. It is possible to have modifications in the working
165 tree as long as they do not overlap; the update will preserve them.
166
167 When it is not obvious how to reconcile the changes, the following
168 happens:
169
170 1. The `HEAD` pointer stays the same.
171 2. The `MERGE_HEAD` ref is set to point to the other branch head.
172 3. Paths that merged cleanly are updated both in the index file and
173 in your working tree.
174 4. For conflicting paths, the index file records up to three
175 versions: stage 1 stores the version from the common ancestor,
176 stage 2 from `HEAD`, and stage 3 from `MERGE_HEAD` (you
177 can inspect the stages with `git ls-files -u`). The working
178 tree files contain the result of the "merge" program; i.e. 3-way
179 merge results with familiar conflict markers `<<<` `===` `>>>`.
180 5. No other changes are made. In particular, the local
181 modifications you had before you started merge will stay the
182 same and the index entries for them stay as they were,
183 i.e. matching `HEAD`.
184
185 If you tried a merge which resulted in complex conflicts and
186 want to start over, you can recover with `git merge --abort`.
187
188 MERGING TAG
189 -----------
190
191 When merging an annotated (and possibly signed) tag, Git always
192 creates a merge commit even if a fast-forward merge is possible, and
193 the commit message template is prepared with the tag message.
194 Additionally, if the tag is signed, the signature check is reported
195 as a comment in the message template. See also linkgit:git-tag[1].
196
197 When you want to just integrate with the work leading to the commit
198 that happens to be tagged, e.g. synchronizing with an upstream
199 release point, you may not want to make an unnecessary merge commit.
200
201 In such a case, you can "unwrap" the tag yourself before feeding it
202 to `git merge`, or pass `--ff-only` when you do not have any work on
203 your own. e.g.
204
205 ----
206 git fetch origin
207 git merge v1.2.3^0
208 git merge --ff-only v1.2.3
209 ----
210
211
212 HOW CONFLICTS ARE PRESENTED
213 ---------------------------
214
215 During a merge, the working tree files are updated to reflect the result
216 of the merge. Among the changes made to the common ancestor's version,
217 non-overlapping ones (that is, you changed an area of the file while the
218 other side left that area intact, or vice versa) are incorporated in the
219 final result verbatim. When both sides made changes to the same area,
220 however, Git cannot randomly pick one side over the other, and asks you to
221 resolve it by leaving what both sides did to that area.
222
223 By default, Git uses the same style as the one used by the "merge" program
224 from the RCS suite to present such a conflicted hunk, like this:
225
226 ------------
227 Here are lines that are either unchanged from the common
228 ancestor, or cleanly resolved because only one side changed.
229 <<<<<<< yours:sample.txt
230 Conflict resolution is hard;
231 let's go shopping.
232 =======
233 Git makes conflict resolution easy.
234 >>>>>>> theirs:sample.txt
235 And here is another line that is cleanly resolved or unmodified.
236 ------------
237
238 The area where a pair of conflicting changes happened is marked with markers
239 `<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======`
240 is typically your side, and the part afterwards is typically their side.
241
242 The default format does not show what the original said in the conflicting
243 area. You cannot tell how many lines are deleted and replaced with
244 Barbie's remark on your side. The only thing you can tell is that your
245 side wants to say it is hard and you'd prefer to go shopping, while the
246 other side wants to claim it is easy.
247
248 An alternative style can be used by setting the "merge.conflictStyle"
249 configuration variable to "diff3". In "diff3" style, the above conflict
250 may look like this:
251
252 ------------
253 Here are lines that are either unchanged from the common
254 ancestor, or cleanly resolved because only one side changed.
255 <<<<<<< yours:sample.txt
256 Conflict resolution is hard;
257 let's go shopping.
258 |||||||
259 Conflict resolution is hard.
260 =======
261 Git makes conflict resolution easy.
262 >>>>>>> theirs:sample.txt
263 And here is another line that is cleanly resolved or unmodified.
264 ------------
265
266 In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
267 another `|||||||` marker that is followed by the original text. You can
268 tell that the original just stated a fact, and your side simply gave in to
269 that statement and gave up, while the other side tried to have a more
270 positive attitude. You can sometimes come up with a better resolution by
271 viewing the original.
272
273
274 HOW TO RESOLVE CONFLICTS
275 ------------------------
276
277 After seeing a conflict, you can do two things:
278
279 * Decide not to merge. The only clean-ups you need are to reset
280 the index file to the `HEAD` commit to reverse 2. and to clean
281 up working tree changes made by 2. and 3.; `git merge --abort`
282 can be used for this.
283
284 * Resolve the conflicts. Git will mark the conflicts in
285 the working tree. Edit the files into shape and
286 'git add' them to the index. Use 'git commit' or
287 'git merge --continue' to seal the deal. The latter command
288 checks whether there is a (interrupted) merge in progress
289 before calling 'git commit'.
290
291 You can work through the conflict with a number of tools:
292
293 * Use a mergetool. `git mergetool` to launch a graphical
294 mergetool which will work you through the merge.
295
296 * Look at the diffs. `git diff` will show a three-way diff,
297 highlighting changes from both the `HEAD` and `MERGE_HEAD`
298 versions.
299
300 * Look at the diffs from each branch. `git log --merge -p <path>`
301 will show diffs first for the `HEAD` version and then the
302 `MERGE_HEAD` version.
303
304 * Look at the originals. `git show :1:filename` shows the
305 common ancestor, `git show :2:filename` shows the `HEAD`
306 version, and `git show :3:filename` shows the `MERGE_HEAD`
307 version.
308
309
310 EXAMPLES
311 --------
312
313 * Merge branches `fixes` and `enhancements` on top of
314 the current branch, making an octopus merge:
315 +
316 ------------------------------------------------
317 $ git merge fixes enhancements
318 ------------------------------------------------
319
320 * Merge branch `obsolete` into the current branch, using `ours`
321 merge strategy:
322 +
323 ------------------------------------------------
324 $ git merge -s ours obsolete
325 ------------------------------------------------
326
327 * Merge branch `maint` into the current branch, but do not make
328 a new commit automatically:
329 +
330 ------------------------------------------------
331 $ git merge --no-commit maint
332 ------------------------------------------------
333 +
334 This can be used when you want to include further changes to the
335 merge, or want to write your own merge commit message.
336 +
337 You should refrain from abusing this option to sneak substantial
338 changes into a merge commit. Small fixups like bumping
339 release/version name would be acceptable.
340
341
342 include::merge-strategies.txt[]
343
344 CONFIGURATION
345 -------------
346 include::config/merge.txt[]
347
348 branch.<name>.mergeOptions::
349 Sets default options for merging into branch <name>. The syntax and
350 supported options are the same as those of 'git merge', but option
351 values containing whitespace characters are currently not supported.
352
353 SEE ALSO
354 --------
355 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
356 linkgit:gitattributes[5],
357 linkgit:git-reset[1],
358 linkgit:git-diff[1], linkgit:git-ls-files[1],
359 linkgit:git-add[1], linkgit:git-rm[1],
360 linkgit:git-mergetool[1]
361
362 GIT
363 ---
364 Part of the linkgit:git[1] suite