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Commit | Line | Data |
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2cf565c5 DG |
1 | git-merge-base(1) |
2 | ================= | |
2cf565c5 DG |
3 | |
4 | NAME | |
5 | ---- | |
c3f0baac | 6 | git-merge-base - Find as good common ancestors as possible for a merge |
2cf565c5 DG |
7 | |
8 | ||
9 | SYNOPSIS | |
10 | -------- | |
a1e0ad78 | 11 | [verse] |
57294824 VR |
12 | 'git merge-base' [-a|--all] <commit> <commit>... |
13 | 'git merge-base' [-a|--all] --octopus <commit>... | |
a1e0ad78 | 14 | 'git merge-base' --independent <commit>... |
2cf565c5 DG |
15 | |
16 | DESCRIPTION | |
17 | ----------- | |
2aa83961 | 18 | |
995bdc73 | 19 | 'git merge-base' finds best common ancestor(s) between two commits to use |
99f1c04b JH |
20 | in a three-way merge. One common ancestor is 'better' than another common |
21 | ancestor if the latter is an ancestor of the former. A common ancestor | |
29b802aa | 22 | that does not have any better common ancestor is a 'best common |
99f1c04b | 23 | ancestor', i.e. a 'merge base'. Note that there can be more than one |
29b802aa | 24 | merge base for a pair of commits. |
2aa83961 | 25 | |
ded7e049 JN |
26 | OPERATION MODE |
27 | -------------- | |
28 | ||
29 | As the most common special case, specifying only two commits on the | |
30 | command line means computing the merge base between the given two commits. | |
31 | ||
32 | More generally, among the two commits to compute the merge base from, | |
33 | one is specified by the first commit argument on the command line; | |
34 | the other commit is a (possibly hypothetical) commit that is a merge | |
35 | across all the remaining commits on the command line. | |
2cf565c5 | 36 | |
f621a845 MG |
37 | As a consequence, the 'merge base' is not necessarily contained in each of the |
38 | commit arguments if more than two commits are specified. This is different | |
39 | from linkgit:git-show-branch[1] when used with the `--merge-base` option. | |
40 | ||
aa8f98c1 JN |
41 | --octopus:: |
42 | Compute the best common ancestors of all supplied commits, | |
43 | in preparation for an n-way merge. This mimics the behavior | |
44 | of 'git show-branch --merge-base'. | |
45 | ||
a1e0ad78 JN |
46 | --independent:: |
47 | Instead of printing merge bases, print a minimal subset of | |
48 | the supplied commits with the same ancestors. In other words, | |
49 | among the commits given, list those which cannot be reached | |
50 | from any other. This mimics the behavior of 'git show-branch | |
51 | --independent'. | |
52 | ||
ded7e049 JN |
53 | OPTIONS |
54 | ------- | |
55 | -a:: | |
56 | --all:: | |
57 | Output all merge bases for the commits, instead of just one. | |
58 | ||
99f1c04b JH |
59 | DISCUSSION |
60 | ---------- | |
61 | ||
62 | Given two commits 'A' and 'B', `git merge-base A B` will output a commit | |
63 | which is reachable from both 'A' and 'B' through the parent relationship. | |
64 | ||
65 | For example, with this topology: | |
66 | ||
67 | o---o---o---B | |
68 | / | |
69 | ---o---1---o---o---o---A | |
70 | ||
71 | the merge base between 'A' and 'B' is '1'. | |
72 | ||
73 | Given three commits 'A', 'B' and 'C', `git merge-base A B C` will compute the | |
29b802aa | 74 | merge base between 'A' and a hypothetical commit 'M', which is a merge |
99f1c04b JH |
75 | between 'B' and 'C'. For example, with this topology: |
76 | ||
77 | o---o---o---o---C | |
78 | / | |
79 | / o---o---o---B | |
80 | / / | |
81 | ---2---1---o---o---o---A | |
82 | ||
83 | the result of `git merge-base A B C` is '1'. This is because the | |
84 | equivalent topology with a merge commit 'M' between 'B' and 'C' is: | |
85 | ||
86 | ||
87 | o---o---o---o---o | |
88 | / \ | |
89 | / o---o---o---o---M | |
90 | / / | |
91 | ---2---1---o---o---o---A | |
92 | ||
93 | and the result of `git merge-base A M` is '1'. Commit '2' is also a | |
94 | common ancestor between 'A' and 'M', but '1' is a better common ancestor, | |
95 | because '2' is an ancestor of '1'. Hence, '2' is not a merge base. | |
96 | ||
57294824 VR |
97 | The result of `git merge-base --octopus A B C` is '2', because '2' is |
98 | the best common ancestor of all commits. | |
99 | ||
99f1c04b | 100 | When the history involves criss-cross merges, there can be more than one |
29b802aa | 101 | 'best' common ancestor for two commits. For example, with this topology: |
99f1c04b JH |
102 | |
103 | ---1---o---A | |
104 | \ / | |
105 | X | |
106 | / \ | |
107 | ---2---o---o---B | |
108 | ||
29b802aa RW |
109 | both '1' and '2' are merge-bases of A and B. Neither one is better than |
110 | the other (both are 'best' merge bases). When the `--all` option is not given, | |
99f1c04b | 111 | it is unspecified which best one is output. |
2cf565c5 | 112 | |
1846e9ed JN |
113 | See also |
114 | -------- | |
115 | linkgit:git-rev-list[1], | |
116 | linkgit:git-show-branch[1], | |
117 | linkgit:git-merge[1] | |
118 | ||
2cf565c5 DG |
119 | GIT |
120 | --- | |
9e1f0a85 | 121 | Part of the linkgit:git[1] suite |