Improve language in git-merge.txt and related docs
[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] [-s <strategy>]...
13 [-m <msg>] <remote> <remote>...
14 'git merge' <msg> HEAD <remote>...
15
16 DESCRIPTION
17 -----------
18 This is the top-level interface to the merge machinery
19 which drives multiple merge strategy scripts.
20
21 The second syntax (<msg> `HEAD` <remote>) is supported for
22 historical reasons. Do not use it from the command line or in
23 new scripts. It is the same as `git merge -m <msg> <remote>`.
24
25
26 OPTIONS
27 -------
28 include::merge-options.txt[]
29
30 -m <msg>::
31 The commit message to be used for the merge commit (in case
32 it is created). The 'git-fmt-merge-msg' script can be used
33 to give a good default for automated 'git-merge' invocations.
34
35 <remote>...::
36 Other branch heads to merge into our branch. You need at
37 least one <remote>. Specifying more than one <remote>
38 obviously means you are trying an Octopus.
39
40 include::merge-strategies.txt[]
41
42
43 If you tried a merge which resulted in a complex conflicts and
44 would want to start over, you can recover with 'git-reset'.
45
46 CONFIGURATION
47 -------------
48 include::merge-config.txt[]
49
50 branch.<name>.mergeoptions::
51 Sets default options for merging into branch <name>. The syntax and
52 supported options are equal to that of 'git-merge', but option values
53 containing whitespace characters are currently not supported.
54
55 HOW MERGE WORKS
56 ---------------
57
58 A merge is always between the current `HEAD` and one or more
59 commits (usually, branch head or tag), and the index file must
60 match the tree of `HEAD` commit (i.e. the contents of the last commit)
61 when it starts out. In other words, `git diff --cached HEAD` must
62 report no changes. (One exception is when the changed index
63 entries are already in the same state that would result from
64 the merge anyway.)
65
66 Three kinds of merge can happen:
67
68 * The merged commit is already contained in `HEAD`. This is the
69 simplest case, called "Already up-to-date."
70
71 * `HEAD` is already contained in the merged commit. This is the
72 most common case especially when invoked from 'git pull':
73 you are tracking an upstream repository, have committed no local
74 changes and now you want to update to a newer upstream revision.
75 Your `HEAD` (and the index) is updated to point at the merged
76 commit, without creating an extra merge commit. This is
77 called "Fast-forward".
78
79 * Both the merged commit and `HEAD` are independent and must be
80 tied together by a merge commit that has both of them as its parents.
81 The rest of this section describes this "True merge" case.
82
83 The chosen merge strategy merges the two commits into a single
84 new source tree.
85 When things merge cleanly, this is what happens:
86
87 1. The results are updated both in the index file and in your
88 working tree;
89 2. Index file is written out as a tree;
90 3. The tree gets committed; and
91 4. The `HEAD` pointer gets advanced.
92
93 Because of 2., we require that the original state of the index
94 file matches exactly the current `HEAD` commit; otherwise we
95 will write out your local changes already registered in your
96 index file along with the merge result, which is not good.
97 Because 1. involves only those paths differing between your
98 branch and the remote branch you are pulling from during the
99 merge (which is typically a fraction of the whole tree), you can
100 have local modifications in your working tree as long as they do
101 not overlap with what the merge updates.
102
103 When there are conflicts, the following happens:
104
105 1. `HEAD` stays the same.
106
107 2. Cleanly merged paths are updated both in the index file and
108 in your working tree.
109
110 3. For conflicting paths, the index file records up to three
111 versions; stage1 stores the version from the common ancestor,
112 stage2 from `HEAD`, and stage3 from the remote branch (you
113 can inspect the stages with `git ls-files -u`). The working
114 tree files contain the result of the "merge" program; i.e. 3-way
115 merge results with familiar conflict markers `<<< === >>>`.
116
117 4. No other changes are done. In particular, the local
118 modifications you had before you started merge will stay the
119 same and the index entries for them stay as they were,
120 i.e. matching `HEAD`.
121
122 HOW CONFLICTS ARE PRESENTED
123 ---------------------------
124
125 During a merge, the working tree files are updated to reflect the result
126 of the merge. Among the changes made to the common ancestor's version,
127 non-overlapping ones (that is, you changed an area of the file while the
128 other side left that area intact, or vice versa) are incorporated in the
129 final result verbatim. When both sides made changes to the same area,
130 however, git cannot randomly pick one side over the other, and asks you to
131 resolve it by leaving what both sides did to that area.
132
133 By default, git uses the same style as that is used by "merge" program
134 from the RCS suite to present such a conflicted hunk, like this:
135
136 ------------
137 Here are lines that are either unchanged from the common
138 ancestor, or cleanly resolved because only one side changed.
139 <<<<<<< yours:sample.txt
140 Conflict resolution is hard;
141 let's go shopping.
142 =======
143 Git makes conflict resolution easy.
144 >>>>>>> theirs:sample.txt
145 And here is another line that is cleanly resolved or unmodified.
146 ------------
147
148 The area where a pair of conflicting changes happened is marked with markers
149 "`<<<<<<<`", "`=======`", and "`>>>>>>>`". The part before the "`=======`"
150 is typically your side, and the part afterwards is typically their side.
151
152 The default format does not show what the original said in the conflicting
153 area. You cannot tell how many lines are deleted and replaced with
154 Barbie's remark on your side. The only thing you can tell is that your
155 side wants to say it is hard and you'd prefer to go shopping, while the
156 other side wants to claim it is easy.
157
158 An alternative style can be used by setting the "merge.conflictstyle"
159 configuration variable to "diff3". In "diff3" style, the above conflict
160 may look like this:
161
162 ------------
163 Here are lines that are either unchanged from the common
164 ancestor, or cleanly resolved because only one side changed.
165 <<<<<<< yours:sample.txt
166 Conflict resolution is hard;
167 let's go shopping.
168 |||||||
169 Conflict resolution is hard.
170 =======
171 Git makes conflict resolution easy.
172 >>>>>>> theirs:sample.txt
173 And here is another line that is cleanly resolved or unmodified.
174 ------------
175
176 In addition to the "`<<<<<<<`", "`=======`", and "`>>>>>>>`" markers, it uses
177 another "`|||||||`" marker that is followed by the original text. You can
178 tell that the original just stated a fact, and your side simply gave in to
179 that statement and gave up, while the other side tried to have a more
180 positive attitude. You can sometimes come up with a better resolution by
181 viewing the original.
182
183
184 HOW TO RESOLVE CONFLICTS
185 ------------------------
186
187 After seeing a conflict, you can do two things:
188
189 * Decide not to merge. The only clean-ups you need are to reset
190 the index file to the `HEAD` commit to reverse 2. and to clean
191 up working tree changes made by 2. and 3.; 'git-reset --hard' can
192 be used for this.
193
194 * Resolve the conflicts. Git will mark the conflicts in
195 the working tree. Edit the files into shape and
196 'git-add' them to the index. Use 'git-commit' to seal the deal.
197
198 You can work through the conflict with a number of tools:
199
200 * Use a mergetool. 'git mergetool' to launch a graphical
201 mergetool which will work you through the merge.
202
203 * Look at the diffs. 'git diff' will show a three-way diff,
204 highlighting changes from both the HEAD and remote versions.
205
206 * Look at the diffs on their own. 'git log --merge -p <path>'
207 will show diffs first for the HEAD version and then the
208 remote version.
209
210 * Look at the originals. 'git show :1:filename' shows the
211 common ancestor, 'git show :2:filename' shows the HEAD
212 version and 'git show :3:filename' shows the remote version.
213
214 SEE ALSO
215 --------
216 linkgit:git-fmt-merge-msg[1], linkgit:git-pull[1],
217 linkgit:gitattributes[5],
218 linkgit:git-reset[1],
219 linkgit:git-diff[1], linkgit:git-ls-files[1],
220 linkgit:git-add[1], linkgit:git-rm[1],
221 linkgit:git-mergetool[1]
222
223 Author
224 ------
225 Written by Junio C Hamano <gitster@pobox.com>
226
227
228 Documentation
229 --------------
230 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.
231
232 GIT
233 ---
234 Part of the linkgit:git[1] suite