Merge branch 'wk/pull-signoff'
[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>] [<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 fourth 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 --[no-]rerere-autoupdate::
79 Allow the rerere mechanism to update the index with the
80 result of auto-conflict resolution if possible.
81
82 --abort::
83 Abort the current conflict resolution process, and
84 try to reconstruct the pre-merge state.
85 +
86 If there were uncommitted worktree changes present when the merge
87 started, 'git merge --abort' will in some cases be unable to
88 reconstruct these changes. It is therefore recommended to always
89 commit 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
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
99 <commit>...::
100 Commits, usually other branch heads, to merge into our branch.
101 Specifying more than one commit will create a merge with
102 more than two parents (affectionately called an Octopus merge).
103 +
104 If no commit is given from the command line, merge the remote-tracking
105 branches that the current branch is configured to use as its upstream.
106 See also the configuration section of this manual page.
107 +
108 When `FETCH_HEAD` (and no other commit) is specified, the branches
109 recorded in the `.git/FETCH_HEAD` file by the previous invocation
110 of `git fetch` for merging are merged to the current branch.
111
112
113 PRE-MERGE CHECKS
114 ----------------
115
116 Before applying outside changes, you should get your own work in
117 good shape and committed locally, so it will not be clobbered if
118 there are conflicts. See also linkgit:git-stash[1].
119 'git pull' and 'git merge' will stop without doing anything when
120 local uncommitted changes overlap with files that 'git pull'/'git
121 merge' may need to update.
122
123 To avoid recording unrelated changes in the merge commit,
124 'git pull' and 'git merge' will also abort if there are any changes
125 registered in the index relative to the `HEAD` commit. (One
126 exception is when the changed index entries are in the state that
127 would result from the merge already.)
128
129 If all named commits are already ancestors of `HEAD`, 'git merge'
130 will exit early with the message "Already up to date."
131
132 FAST-FORWARD MERGE
133 ------------------
134
135 Often the current branch head is an ancestor of the named commit.
136 This is the most common case especially when invoked from 'git
137 pull': you are tracking an upstream repository, you have committed
138 no local changes, and now you want to update to a newer upstream
139 revision. In this case, a new commit is not needed to store the
140 combined history; instead, the `HEAD` (along with the index) is
141 updated to point at the named commit, without creating an extra
142 merge commit.
143
144 This behavior can be suppressed with the `--no-ff` option.
145
146 TRUE MERGE
147 ----------
148
149 Except in a fast-forward merge (see above), the branches to be
150 merged must be tied together by a merge commit that has both of them
151 as its parents.
152
153 A merged version reconciling the changes from all branches to be
154 merged is committed, and your `HEAD`, index, and working tree are
155 updated to it. It is possible to have modifications in the working
156 tree as long as they do not overlap; the update will preserve them.
157
158 When it is not obvious how to reconcile the changes, the following
159 happens:
160
161 1. The `HEAD` pointer stays the same.
162 2. The `MERGE_HEAD` ref is set to point to the other branch head.
163 3. Paths that merged cleanly are updated both in the index file and
164 in your working tree.
165 4. 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
168 can inspect the stages with `git ls-files -u`). The working
169 tree files contain the result of the "merge" program; i.e. 3-way
170 merge results with familiar conflict markers `<<<` `===` `>>>`.
171 5. No other changes are made. In particular, the local
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
176 If you tried a merge which resulted in complex conflicts and
177 want to start over, you can recover with `git merge --abort`.
178
179 MERGING TAG
180 -----------
181
182 When merging an annotated (and possibly signed) tag, Git always
183 creates a merge commit even if a fast-forward merge is possible, and
184 the commit message template is prepared with the tag message.
185 Additionally, if the tag is signed, the signature check is reported
186 as a comment in the message template. See also linkgit:git-tag[1].
187
188 When you want to just integrate with the work leading to the commit
189 that happens to be tagged, e.g. synchronizing with an upstream
190 release point, you may not want to make an unnecessary merge commit.
191
192 In such a case, you can "unwrap" the tag yourself before feeding it
193 to `git merge`, or pass `--ff-only` when you do not have any work on
194 your own. e.g.
195
196 ----
197 git fetch origin
198 git merge v1.2.3^0
199 git merge --ff-only v1.2.3
200 ----
201
202
203 HOW CONFLICTS ARE PRESENTED
204 ---------------------------
205
206 During a merge, the working tree files are updated to reflect the result
207 of the merge. Among the changes made to the common ancestor's version,
208 non-overlapping ones (that is, you changed an area of the file while the
209 other side left that area intact, or vice versa) are incorporated in the
210 final result verbatim. When both sides made changes to the same area,
211 however, Git cannot randomly pick one side over the other, and asks you to
212 resolve it by leaving what both sides did to that area.
213
214 By default, Git uses the same style as the one used by the "merge" program
215 from the RCS suite to present such a conflicted hunk, like this:
216
217 ------------
218 Here are lines that are either unchanged from the common
219 ancestor, or cleanly resolved because only one side changed.
220 <<<<<<< yours:sample.txt
221 Conflict resolution is hard;
222 let's go shopping.
223 =======
224 Git makes conflict resolution easy.
225 >>>>>>> theirs:sample.txt
226 And here is another line that is cleanly resolved or unmodified.
227 ------------
228
229 The area where a pair of conflicting changes happened is marked with markers
230 `<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======`
231 is typically your side, and the part afterwards is typically their side.
232
233 The default format does not show what the original said in the conflicting
234 area. You cannot tell how many lines are deleted and replaced with
235 Barbie's remark on your side. The only thing you can tell is that your
236 side wants to say it is hard and you'd prefer to go shopping, while the
237 other side wants to claim it is easy.
238
239 An alternative style can be used by setting the "merge.conflictStyle"
240 configuration variable to "diff3". In "diff3" style, the above conflict
241 may look like this:
242
243 ------------
244 Here are lines that are either unchanged from the common
245 ancestor, or cleanly resolved because only one side changed.
246 <<<<<<< yours:sample.txt
247 Conflict resolution is hard;
248 let's go shopping.
249 |||||||
250 Conflict resolution is hard.
251 =======
252 Git makes conflict resolution easy.
253 >>>>>>> theirs:sample.txt
254 And here is another line that is cleanly resolved or unmodified.
255 ------------
256
257 In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
258 another `|||||||` marker that is followed by the original text. You can
259 tell that the original just stated a fact, and your side simply gave in to
260 that statement and gave up, while the other side tried to have a more
261 positive attitude. You can sometimes come up with a better resolution by
262 viewing the original.
263
264
265 HOW TO RESOLVE CONFLICTS
266 ------------------------
267
268 After seeing a conflict, you can do two things:
269
270 * Decide not to merge. The only clean-ups you need are to reset
271 the index file to the `HEAD` commit to reverse 2. and to clean
272 up working tree changes made by 2. and 3.; `git merge --abort`
273 can be used for this.
274
275 * Resolve the conflicts. Git will mark the conflicts in
276 the working tree. Edit the files into shape and
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'.
281
282 You can work through the conflict with a number of tools:
283
284 * Use a mergetool. `git mergetool` to launch a graphical
285 mergetool which will work you through the merge.
286
287 * Look at the diffs. `git diff` will show a three-way diff,
288 highlighting changes from both the `HEAD` and `MERGE_HEAD`
289 versions.
290
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.
294
295 * Look at the originals. `git show :1:filename` shows the
296 common ancestor, `git show :2:filename` shows the `HEAD`
297 version, and `git show :3:filename` shows the `MERGE_HEAD`
298 version.
299
300
301 EXAMPLES
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 +
325 This can be used when you want to include further changes to the
326 merge, or want to write your own merge commit message.
327 +
328 You should refrain from abusing this option to sneak substantial
329 changes into a merge commit. Small fixups like bumping
330 release/version name would be acceptable.
331
332
333 include::merge-strategies.txt[]
334
335 CONFIGURATION
336 -------------
337 include::merge-config.txt[]
338
339 branch.<name>.mergeOptions::
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
344 SEE ALSO
345 --------
346 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
347 linkgit:gitattributes[5],
348 linkgit:git-reset[1],
349 linkgit:git-diff[1], linkgit:git-ls-files[1],
350 linkgit:git-add[1], linkgit:git-rm[1],
351 linkgit:git-mergetool[1]
352
353 GIT
354 ---
355 Part of the linkgit:git[1] suite