e3c611dd0e5a7564c087d8d09eea8943dc509d08
1 git-merge(1)
2 ============
4 NAME
5 ----
6 git-merge - Join two or more development histories together
9 SYNOPSIS
10 --------
11 [verse]
12 'git merge' [-n] [--stat] [--no-commit] [--squash] [-s <strategy>]...
13 [-m <msg>] <commit>...
14 'git merge' <msg> HEAD <commit>...
16 DESCRIPTION
17 -----------
18 Incorporates changes from the named commits (since the time their
19 histories diverged from the current branch) into the current
20 branch. This command is used by 'git pull' to incorporate changes
21 from another repository and can be used by hand to merge changes
22 from one branch into another.
24 Assume the following history exists and the current branch is
25 "`master`":
27 ------------
28 A---B---C topic
29 /
30 D---E---F---G master
31 ------------
33 Then "`git merge topic`" will replay the changes made on the
34 `topic` branch since it diverged from `master` (i.e., `E`) until
35 its current commit (`C`) on top of `master`, and record the result
36 in a new commit along with the names of the two parent commits and
37 a log message from the user describing the changes.
39 ------------
40 A---B---C topic
41 / \
42 D---E---F---G---H master
43 ------------
45 The second syntax (<msg> `HEAD` <commit>...) is supported for
46 historical reasons. Do not use it from the command line or in
47 new scripts. It is the same as `git merge -m <msg> <commit>...`.
49 *Warning*: Running 'git merge' with uncommitted changes is
50 discouraged: while possible, it leaves you in a state that is hard to
51 back out of in the case of a conflict.
54 OPTIONS
55 -------
56 include::merge-options.txt[]
58 -m <msg>::
59 Set the commit message to be used for the merge commit (in
60 case one is created). The 'git fmt-merge-msg' command can be
61 used to give a good default for automated 'git merge'
62 invocations.
64 <commit>...::
65 Commits, usually other branch heads, to merge into our branch.
66 You need at least one <commit>. Specifying more than one
67 <commit> obviously means you are trying an Octopus.
70 HOW MERGE WORKS
71 ---------------
73 A merge is always between the current `HEAD` and one or more
74 commits (usually, branch head or tag), and the index file must
75 match the tree of `HEAD` commit (i.e. the contents of the last commit)
76 when it starts out. In other words, `git diff --cached HEAD` must
77 report no changes. (One exception is when the changed index
78 entries are already in the same state that would result from
79 the merge anyway.)
81 Three kinds of merge can happen:
83 * The merged commit is already contained in `HEAD`. This is the
84 simplest case, called "Already up-to-date."
86 * `HEAD` is already contained in the merged commit. This is the
87 most common case especially when invoked from 'git pull':
88 you are tracking an upstream repository, have committed no local
89 changes and now you want to update to a newer upstream revision.
90 Your `HEAD` (and the index) is updated to point at the merged
91 commit, without creating an extra merge commit. This is
92 called "Fast-forward".
94 * Both the merged commit and `HEAD` are independent and must be
95 tied together by a merge commit that has both of them as its parents.
96 The rest of this section describes this "True merge" case.
98 The chosen merge strategy merges the two commits into a single
99 new source tree.
100 When things merge cleanly, this is what happens:
102 1. The results are updated both in the index file and in your
103 working tree;
104 2. Index file is written out as a tree;
105 3. The tree gets committed; and
106 4. The `HEAD` pointer gets advanced.
108 Because of 2., we require that the original state of the index
109 file matches exactly the current `HEAD` commit; otherwise we
110 will write out your local changes already registered in your
111 index file along with the merge result, which is not good.
112 Because 1. involves only those paths differing between your
113 branch and the branch you are merging
114 (which is typically a fraction of the whole tree), you can
115 have local modifications in your working tree as long as they do
116 not overlap with what the merge updates.
118 When there are conflicts, the following happens:
120 1. `HEAD` stays the same.
122 2. Cleanly merged paths are updated both in the index file and
123 in your working tree.
125 3. For conflicting paths, the index file records up to three
126 versions; stage1 stores the version from the common ancestor,
127 stage2 from `HEAD`, and stage3 from the other branch (you
128 can inspect the stages with `git ls-files -u`). The working
129 tree files contain the result of the "merge" program; i.e. 3-way
130 merge results with familiar conflict markers `<<< === >>>`.
132 4. No other changes are done. In particular, the local
133 modifications you had before you started merge will stay the
134 same and the index entries for them stay as they were,
135 i.e. matching `HEAD`.
137 If you tried a merge which resulted in complex conflicts and
138 want to start over, you can recover with `git reset --merge`.
140 HOW CONFLICTS ARE PRESENTED
141 ---------------------------
143 During a merge, the working tree files are updated to reflect the result
144 of the merge. Among the changes made to the common ancestor's version,
145 non-overlapping ones (that is, you changed an area of the file while the
146 other side left that area intact, or vice versa) are incorporated in the
147 final result verbatim. When both sides made changes to the same area,
148 however, git cannot randomly pick one side over the other, and asks you to
149 resolve it by leaving what both sides did to that area.
151 By default, git uses the same style as that is used by "merge" program
152 from the RCS suite to present such a conflicted hunk, like this:
154 ------------
155 Here are lines that are either unchanged from the common
156 ancestor, or cleanly resolved because only one side changed.
157 <<<<<<< yours:sample.txt
158 Conflict resolution is hard;
159 let's go shopping.
160 =======
161 Git makes conflict resolution easy.
162 >>>>>>> theirs:sample.txt
163 And here is another line that is cleanly resolved or unmodified.
164 ------------
166 The area where a pair of conflicting changes happened is marked with markers
167 `<<<<<<<`, `=======`, and `>>>>>>>`. The part before the `=======`
168 is typically your side, and the part afterwards is typically their side.
170 The default format does not show what the original said in the conflicting
171 area. You cannot tell how many lines are deleted and replaced with
172 Barbie's remark on your side. The only thing you can tell is that your
173 side wants to say it is hard and you'd prefer to go shopping, while the
174 other side wants to claim it is easy.
176 An alternative style can be used by setting the "merge.conflictstyle"
177 configuration variable to "diff3". In "diff3" style, the above conflict
178 may look like this:
180 ------------
181 Here are lines that are either unchanged from the common
182 ancestor, or cleanly resolved because only one side changed.
183 <<<<<<< yours:sample.txt
184 Conflict resolution is hard;
185 let's go shopping.
186 |||||||
187 Conflict resolution is hard.
188 =======
189 Git makes conflict resolution easy.
190 >>>>>>> theirs:sample.txt
191 And here is another line that is cleanly resolved or unmodified.
192 ------------
194 In addition to the `<<<<<<<`, `=======`, and `>>>>>>>` markers, it uses
195 another `|||||||` marker that is followed by the original text. You can
196 tell that the original just stated a fact, and your side simply gave in to
197 that statement and gave up, while the other side tried to have a more
198 positive attitude. You can sometimes come up with a better resolution by
199 viewing the original.
202 HOW TO RESOLVE CONFLICTS
203 ------------------------
205 After seeing a conflict, you can do two things:
207 * Decide not to merge. The only clean-ups you need are to reset
208 the index file to the `HEAD` commit to reverse 2. and to clean
209 up working tree changes made by 2. and 3.; `git-reset --hard` can
210 be used for this.
212 * Resolve the conflicts. Git will mark the conflicts in
213 the working tree. Edit the files into shape and
214 'git add' them to the index. Use 'git commit' to seal the deal.
216 You can work through the conflict with a number of tools:
218 * Use a mergetool. `git mergetool` to launch a graphical
219 mergetool which will work you through the merge.
221 * Look at the diffs. `git diff` will show a three-way diff,
222 highlighting changes from both the HEAD and their versions.
224 * Look at the diffs on their own. `git log --merge -p <path>`
225 will show diffs first for the HEAD version and then
226 their version.
228 * Look at the originals. `git show :1:filename` shows the
229 common ancestor, `git show :2:filename` shows the HEAD
230 version and `git show :3:filename` shows their version.
233 EXAMPLES
234 --------
236 * Merge branches `fixes` and `enhancements` on top of
237 the current branch, making an octopus merge:
238 +
239 ------------------------------------------------
240 $ git merge fixes enhancements
241 ------------------------------------------------
243 * Merge branch `obsolete` into the current branch, using `ours`
244 merge strategy:
245 +
246 ------------------------------------------------
247 $ git merge -s ours obsolete
248 ------------------------------------------------
250 * Merge branch `maint` into the current branch, but do not make
251 a new commit automatically:
252 +
253 ------------------------------------------------
254 $ git merge --no-commit maint
255 ------------------------------------------------
256 +
257 This can be used when you want to include further changes to the
258 merge, or want to write your own merge commit message.
259 +
260 You should refrain from abusing this option to sneak substantial
261 changes into a merge commit. Small fixups like bumping
262 release/version name would be acceptable.
265 include::merge-strategies.txt[]
267 CONFIGURATION
268 -------------
269 include::merge-config.txt[]
271 branch.<name>.mergeoptions::
272 Sets default options for merging into branch <name>. The syntax and
273 supported options are the same as those of 'git merge', but option
274 values containing whitespace characters are currently not supported.
276 SEE ALSO
277 --------
278 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
279 linkgit:gitattributes[5],
280 linkgit:git-reset[1],
281 linkgit:git-diff[1], linkgit:git-ls-files[1],
282 linkgit:git-add[1], linkgit:git-rm[1],
283 linkgit:git-mergetool[1]
285 Author
286 ------
287 Written by Junio C Hamano <gitster@pobox.com>
290 Documentation
291 --------------
292 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
294 GIT
295 ---
296 Part of the linkgit:git[1] suite