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406 git-merge-base(
1) Manual Page
409 <div class=
"sectionbody">
411 Find as good common ancestors as possible for a merge
415 <h2 id=
"_synopsis">SYNOPSIS
</h2>
416 <div class=
"sectionbody">
417 <div class=
"verseblock">
418 <div class=
"verseblock-content"><em>git merge-base
</em> [-a|--all]
<commit
> <commit
>…
419 <em>git merge-base
</em> [-a|--all] --octopus
<commit
>…
420 <em>git merge-base
</em> --independent
<commit
>…</div>
421 <div class=
"verseblock-attribution">
424 <h2 id=
"_description">DESCRIPTION
</h2>
425 <div class=
"sectionbody">
426 <div class=
"paragraph"><p><em>git merge-base
</em> finds best common ancestor(s) between two commits to use
427 in a three-way merge. One common ancestor is
<em>better
</em> than another common
428 ancestor if the latter is an ancestor of the former. A common ancestor
429 that does not have any better common ancestor is a
<em>best common
430 ancestor
</em>, i.e. a
<em>merge base
</em>. Note that there can be more than one
431 merge base for a pair of commits.
</p></div>
433 <h2 id=
"_operation_mode">OPERATION MODE
</h2>
434 <div class=
"sectionbody">
435 <div class=
"paragraph"><p>As the most common special case, specifying only two commits on the
436 command line means computing the merge base between the given two commits.
</p></div>
437 <div class=
"paragraph"><p>More generally, among the two commits to compute the merge base from,
438 one is specified by the first commit argument on the command line;
439 the other commit is a (possibly hypothetical) commit that is a merge
440 across all the remaining commits on the command line.
</p></div>
441 <div class=
"paragraph"><p>As a consequence, the
<em>merge base
</em> is not necessarily contained in each of the
442 commit arguments if more than two commits are specified. This is different
443 from
<a href=
"git-show-branch.html">git-show-branch(
1)
</a> when used with the
<tt>--merge-base
</tt> option.
</p></div>
444 <div class=
"dlist"><dl>
450 Compute the best common ancestors of all supplied commits,
451 in preparation for an n-way merge. This mimics the behavior
452 of
<em>git show-branch --merge-base
</em>.
460 Instead of printing merge bases, print a minimal subset of
461 the supplied commits with the same ancestors. In other words,
462 among the commits given, list those which cannot be reached
463 from any other. This mimics the behavior of
<em>git show-branch
469 <h2 id=
"_options">OPTIONS
</h2>
470 <div class=
"sectionbody">
471 <div class=
"dlist"><dl>
480 Output all merge bases for the commits, instead of just one.
485 <h2 id=
"_discussion">DISCUSSION
</h2>
486 <div class=
"sectionbody">
487 <div class=
"paragraph"><p>Given two commits
<em>A
</em> and
<em>B
</em>,
<tt>git merge-base A B
</tt> will output a commit
488 which is reachable from both
<em>A
</em> and
<em>B
</em> through the parent relationship.
</p></div>
489 <div class=
"paragraph"><p>For example, with this topology:
</p></div>
490 <div class=
"literalblock">
491 <div class=
"content">
492 <pre><tt> o---o---o---B
494 ---o---
1---o---o---o---A
</tt></pre>
496 <div class=
"paragraph"><p>the merge base between
<em>A
</em> and
<em>B
</em> is
<em>1</em>.
</p></div>
497 <div class=
"paragraph"><p>Given three commits
<em>A
</em>,
<em>B
</em> and
<em>C
</em>,
<tt>git merge-base A B C
</tt> will compute the
498 merge base between
<em>A
</em> and a hypothetical commit
<em>M
</em>, which is a merge
499 between
<em>B
</em> and
<em>C
</em>. For example, with this topology:
</p></div>
500 <div class=
"literalblock">
501 <div class=
"content">
502 <pre><tt> o---o---o---o---C
506 ---
2---
1---o---o---o---A
</tt></pre>
508 <div class=
"paragraph"><p>the result of
<tt>git merge-base A B C
</tt> is
<em>1</em>. This is because the
509 equivalent topology with a merge commit
<em>M
</em> between
<em>B
</em> and
<em>C
</em> is:
</p></div>
510 <div class=
"literalblock">
511 <div class=
"content">
512 <pre><tt> o---o---o---o---o
516 ---
2---
1---o---o---o---A
</tt></pre>
518 <div class=
"paragraph"><p>and the result of
<tt>git merge-base A M
</tt> is
<em>1</em>. Commit
<em>2</em> is also a
519 common ancestor between
<em>A
</em> and
<em>M
</em>, but
<em>1</em> is a better common ancestor,
520 because
<em>2</em> is an ancestor of
<em>1</em>. Hence,
<em>2</em> is not a merge base.
</p></div>
521 <div class=
"paragraph"><p>The result of
<tt>git merge-base --octopus A B C
</tt> is
<em>2</em>, because
<em>2</em> is
522 the best common ancestor of all commits.
</p></div>
523 <div class=
"paragraph"><p>When the history involves criss-cross merges, there can be more than one
524 <em>best
</em> common ancestor for two commits. For example, with this topology:
</p></div>
525 <div class=
"literalblock">
526 <div class=
"content">
527 <pre><tt>---
1---o---A
531 ---
2---o---o---B
</tt></pre>
533 <div class=
"paragraph"><p>both
<em>1</em> and
<em>2</em> are merge-bases of A and B. Neither one is better than
534 the other (both are
<em>best
</em> merge bases). When the
<tt>--all
</tt> option is not given,
535 it is unspecified which best one is output.
</p></div>
537 <h2 id=
"_see_also">See also
</h2>
538 <div class=
"sectionbody">
539 <div class=
"paragraph"><p><a href=
"git-rev-list.html">git-rev-list(
1)
</a>,
540 <a href=
"git-show-branch.html">git-show-branch(
1)
</a>,
541 <a href=
"git-merge.html">git-merge(
1)
</a></p></div>
543 <h2 id=
"_git">GIT
</h2>
544 <div class=
"sectionbody">
545 <div class=
"paragraph"><p>Part of the
<a href=
"git.html">git(
1)
</a> suite
</p></div>
548 <div id=
"footer-text">
549 Last updated
2011-
05-
05 01:
29:
54 UTC