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