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David Greaves2cf565c2005-05-10 22:32:30 +01001git-merge-base(1)
2=================
David Greaves2cf565c2005-05-10 22:32:30 +01003
4NAME
5----
Junio C Hamanoc3f0baa2007-01-18 15:53:37 -08006git-merge-base - Find as good common ancestors as possible for a merge
David Greaves2cf565c2005-05-10 22:32:30 +01007
8
9SYNOPSIS
10--------
Junio C Hamano99f1c042008-07-30 07:04:43 +020011'git merge-base' [--all] <commit> <commit>...
David Greaves2cf565c2005-05-10 22:32:30 +010012
13DESCRIPTION
14-----------
Fredrik Kuivinen2aa83962006-05-16 07:58:15 +020015
Junio C Hamano99f1c042008-07-30 07:04:43 +020016'git-merge-base' finds best common ancestor(s) between two commits to use
17in a three-way merge. One common ancestor is 'better' than another common
18ancestor if the latter is an ancestor of the former. A common ancestor
Ralf Wildenhues29b802a2008-12-09 07:23:51 +010019that does not have any better common ancestor is a 'best common
Junio C Hamano99f1c042008-07-30 07:04:43 +020020ancestor', i.e. a 'merge base'. Note that there can be more than one
Ralf Wildenhues29b802a2008-12-09 07:23:51 +010021merge base for a pair of commits.
Fredrik Kuivinen2aa83962006-05-16 07:58:15 +020022
Ralf Wildenhues29b802a2008-12-09 07:23:51 +010023Among the two commits to compute the merge base from, one is specified by
Junio C Hamano99f1c042008-07-30 07:04:43 +020024the first commit argument on the command line; the other commit is a
25(possibly hypothetical) commit that is a merge across all the remaining
Ralf Wildenhues29b802a2008-12-09 07:23:51 +010026commits on the command line. As the most common special case, specifying only
27two commits on the command line means computing the merge base between
Junio C Hamano99f1c042008-07-30 07:04:43 +020028the given two commits.
David Greaves2cf565c2005-05-10 22:32:30 +010029
Fredrik Kuivinen2aa83962006-05-16 07:58:15 +020030OPTIONS
31-------
32--all::
Junio C Hamano99f1c042008-07-30 07:04:43 +020033 Output all merge bases for the commits, instead of just one.
34
35DISCUSSION
36----------
37
38Given two commits 'A' and 'B', `git merge-base A B` will output a commit
39which is reachable from both 'A' and 'B' through the parent relationship.
40
41For example, with this topology:
42
43 o---o---o---B
44 /
45 ---o---1---o---o---o---A
46
47the merge base between 'A' and 'B' is '1'.
48
49Given three commits 'A', 'B' and 'C', `git merge-base A B C` will compute the
Ralf Wildenhues29b802a2008-12-09 07:23:51 +010050merge base between 'A' and a hypothetical commit 'M', which is a merge
Junio C Hamano99f1c042008-07-30 07:04:43 +020051between 'B' and 'C'. For example, with this topology:
52
53 o---o---o---o---C
54 /
55 / o---o---o---B
56 / /
57 ---2---1---o---o---o---A
58
59the result of `git merge-base A B C` is '1'. This is because the
60equivalent topology with a merge commit 'M' between 'B' and 'C' is:
61
62
63 o---o---o---o---o
64 / \
65 / o---o---o---o---M
66 / /
67 ---2---1---o---o---o---A
68
69and the result of `git merge-base A M` is '1'. Commit '2' is also a
70common ancestor between 'A' and 'M', but '1' is a better common ancestor,
71because '2' is an ancestor of '1'. Hence, '2' is not a merge base.
72
73When the history involves criss-cross merges, there can be more than one
Ralf Wildenhues29b802a2008-12-09 07:23:51 +010074'best' common ancestor for two commits. For example, with this topology:
Junio C Hamano99f1c042008-07-30 07:04:43 +020075
76 ---1---o---A
77 \ /
78 X
79 / \
80 ---2---o---o---B
81
Ralf Wildenhues29b802a2008-12-09 07:23:51 +010082both '1' and '2' are merge-bases of A and B. Neither one is better than
83the other (both are 'best' merge bases). When the `--all` option is not given,
Junio C Hamano99f1c042008-07-30 07:04:43 +020084it is unspecified which best one is output.
David Greaves2cf565c2005-05-10 22:32:30 +010085
86Author
87------
88Written by Linus Torvalds <torvalds@osdl.org>
89
90Documentation
91--------------
92Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
93
94GIT
95---
Christian Couder9e1f0a82008-06-06 09:07:32 +020096Part of the linkgit:git[1] suite