Improve language in git-merge.txt and related docs
[git/git.git] / Documentation / git-merge-base.txt
1 git-merge-base(1)
2 =================
3
4 NAME
5 ----
6 git-merge-base - Find as good common ancestors as possible for a merge
7
8
9 SYNOPSIS
10 --------
11 'git merge-base' [--all] <commit> <commit>...
12
13 DESCRIPTION
14 -----------
15
16 'git-merge-base' finds best common ancestor(s) between two commits to use
17 in a three-way merge. One common ancestor is 'better' than another common
18 ancestor if the latter is an ancestor of the former. A common ancestor
19 that does not have any better common ancestor is a 'best common
20 ancestor', i.e. a 'merge base'. Note that there can be more than one
21 merge base for a pair of commits.
22
23 Among the two commits to compute the merge base from, one is specified by
24 the first commit argument on the command line; the other commit is a
25 (possibly hypothetical) commit that is a merge across all the remaining
26 commits on the command line. As the most common special case, specifying only
27 two commits on the command line means computing the merge base between
28 the given two commits.
29
30 OPTIONS
31 -------
32 --all::
33 Output all merge bases for the commits, instead of just one.
34
35 DISCUSSION
36 ----------
37
38 Given two commits 'A' and 'B', `git merge-base A B` will output a commit
39 which is reachable from both 'A' and 'B' through the parent relationship.
40
41 For example, with this topology:
42
43 o---o---o---B
44 /
45 ---o---1---o---o---o---A
46
47 the merge base between 'A' and 'B' is '1'.
48
49 Given three commits 'A', 'B' and 'C', `git merge-base A B C` will compute the
50 merge base between 'A' and a hypothetical commit 'M', which is a merge
51 between '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
59 the result of `git merge-base A B C` is '1'. This is because the
60 equivalent 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
69 and the result of `git merge-base A M` is '1'. Commit '2' is also a
70 common ancestor between 'A' and 'M', but '1' is a better common ancestor,
71 because '2' is an ancestor of '1'. Hence, '2' is not a merge base.
72
73 When the history involves criss-cross merges, there can be more than one
74 'best' common ancestor for two commits. For example, with this topology:
75
76 ---1---o---A
77 \ /
78 X
79 / \
80 ---2---o---o---B
81
82 both '1' and '2' are merge-bases of A and B. Neither one is better than
83 the other (both are 'best' merge bases). When the `--all` option is not given,
84 it is unspecified which best one is output.
85
86 Author
87 ------
88 Written by Linus Torvalds <torvalds@osdl.org>
89
90 Documentation
91 --------------
92 Documentation by David Greaves, Junio C Hamano and the git-list <git@vger.kernel.org>.
93
94 GIT
95 ---
96 Part of the linkgit:git[1] suite