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121 lines
3.6 KiB
121 lines
3.6 KiB
git-merge-base(1) |
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================= |
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NAME |
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---- |
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git-merge-base - Find as good common ancestors as possible for a merge |
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SYNOPSIS |
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-------- |
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[verse] |
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'git merge-base' [-a|--all] <commit> <commit>... |
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'git merge-base' [-a|--all] --octopus <commit>... |
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'git merge-base' --independent <commit>... |
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DESCRIPTION |
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----------- |
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'git merge-base' finds best common ancestor(s) between two commits to use |
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in a three-way merge. One common ancestor is 'better' than another common |
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ancestor if the latter is an ancestor of the former. A common ancestor |
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that does not have any better common ancestor is a 'best common |
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ancestor', i.e. a 'merge base'. Note that there can be more than one |
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merge base for a pair of commits. |
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OPERATION MODE |
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-------------- |
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As the most common special case, specifying only two commits on the |
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command line means computing the merge base between the given two commits. |
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More generally, among the two commits to compute the merge base from, |
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one is specified by the first commit argument on the command line; |
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the other commit is a (possibly hypothetical) commit that is a merge |
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across all the remaining commits on the command line. |
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As a consequence, the 'merge base' is not necessarily contained in each of the |
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commit arguments if more than two commits are specified. This is different |
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from linkgit:git-show-branch[1] when used with the `--merge-base` option. |
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--octopus:: |
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Compute the best common ancestors of all supplied commits, |
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in preparation for an n-way merge. This mimics the behavior |
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of 'git show-branch --merge-base'. |
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--independent:: |
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Instead of printing merge bases, print a minimal subset of |
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the supplied commits with the same ancestors. In other words, |
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among the commits given, list those which cannot be reached |
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from any other. This mimics the behavior of 'git show-branch |
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--independent'. |
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OPTIONS |
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------- |
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-a:: |
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--all:: |
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Output all merge bases for the commits, instead of just one. |
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DISCUSSION |
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---------- |
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Given two commits 'A' and 'B', `git merge-base A B` will output a commit |
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which is reachable from both 'A' and 'B' through the parent relationship. |
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For example, with this topology: |
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o---o---o---B |
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/ |
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---o---1---o---o---o---A |
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the merge base between 'A' and 'B' is '1'. |
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Given three commits 'A', 'B' and 'C', `git merge-base A B C` will compute the |
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merge base between 'A' and a hypothetical commit 'M', which is a merge |
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between 'B' and 'C'. For example, with this topology: |
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o---o---o---o---C |
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/ |
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/ o---o---o---B |
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/ / |
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---2---1---o---o---o---A |
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the result of `git merge-base A B C` is '1'. This is because the |
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equivalent topology with a merge commit 'M' between 'B' and 'C' is: |
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o---o---o---o---o |
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/ \ |
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/ o---o---o---o---M |
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/ / |
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---2---1---o---o---o---A |
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and the result of `git merge-base A M` is '1'. Commit '2' is also a |
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common ancestor between 'A' and 'M', but '1' is a better common ancestor, |
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because '2' is an ancestor of '1'. Hence, '2' is not a merge base. |
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The result of `git merge-base --octopus A B C` is '2', because '2' is |
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the best common ancestor of all commits. |
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When the history involves criss-cross merges, there can be more than one |
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'best' common ancestor for two commits. For example, with this topology: |
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---1---o---A |
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\ / |
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X |
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/ \ |
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---2---o---o---B |
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both '1' and '2' are merge-bases of A and B. Neither one is better than |
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the other (both are 'best' merge bases). When the `--all` option is not given, |
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it is unspecified which best one is output. |
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See also |
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-------- |
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linkgit:git-rev-list[1], |
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linkgit:git-show-branch[1], |
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linkgit:git-merge[1] |
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GIT |
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--- |
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Part of the linkgit:git[1] suite
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