1GIT-MERGE-BASE(1)                 Git Manual                 GIT-MERGE-BASE(1)
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NAME

6       git-merge-base - Find as good common ancestors as possible for a merge
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SYNOPSIS

9       git merge-base [-a|--all] <commit> <commit>...
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DESCRIPTION

12       git merge-base finds best common ancestor(s) between two commits to use
13       in a three-way merge. One common ancestor is better than another common
14       ancestor if the latter is an ancestor of the former. A common ancestor
15       that does not have any better common ancestor is a best common
16       ancestor, i.e. a merge base. Note that there can be more than one merge
17       base for a pair of commits.
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19       Among the two commits to compute the merge base from, one is specified
20       by the first commit argument on the command line; the other commit is a
21       (possibly hypothetical) commit that is a merge across all the remaining
22       commits on the command line. As the most common special case,
23       specifying only two commits on the command line means computing the
24       merge base between the given two commits.
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26       As a consequence, the merge base is not necessarily contained in each
27       of the commit arguments if more than two commits are specified. This is
28       different from git-show-branch(1) when used with the --merge-base
29       option.
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OPTIONS

32       -a, --all
33           Output all merge bases for the commits, instead of just one.
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DISCUSSION

36       Given two commits A and B, git merge-base A B will output a commit
37       which is reachable from both A and B through the parent relationship.
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39       For example, with this topology:
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41                    o---o---o---B
42                   /
43           ---o---1---o---o---o---A
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45       the merge base between A and B is 1.
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47       Given three commits A, B and C, git merge-base A B C will compute the
48       merge base between A and a hypothetical commit M, which is a merge
49       between B and C. For example, with this topology:
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51                  o---o---o---o---C
52                 /
53                /   o---o---o---B
54               /   /
55           ---2---1---o---o---o---A
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57       the result of git merge-base A B C is 1. This is because the equivalent
58       topology with a merge commit M between B and C is:
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60                  o---o---o---o---o
61                 /                 \
62                /   o---o---o---o---M
63               /   /
64           ---2---1---o---o---o---A
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66       and the result of git merge-base A M is 1. Commit 2 is also a common
67       ancestor between A and M, but 1 is a better common ancestor, because 2
68       is an ancestor of 1. Hence, 2 is not a merge base.
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70       When the history involves criss-cross merges, there can be more than
71       one best common ancestor for two commits. For example, with this
72       topology:
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74           ---1---o---A
75               \ /
76                X
77               / \
78           ---2---o---o---B
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80       both 1 and 2 are merge-bases of A and B. Neither one is better than the
81       other (both are best merge bases). When the --all option is not given,
82       it is unspecified which best one is output.
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AUTHOR

85       Written by Linus Torvalds <torvalds@osdl.org[1]>
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DOCUMENTATION

88       Documentation by David Greaves, Junio C Hamano and the git-list
89       <git@vger.kernel.org[2]>.
90

GIT

92       Part of the git(1) suite
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NOTES

95        1. torvalds@osdl.org
96           mailto:torvalds@osdl.org
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98        2. git@vger.kernel.org
99           mailto:git@vger.kernel.org
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103Git 1.7.1                         08/16/2017                 GIT-MERGE-BASE(1)
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