git-merge-base.html

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 404 <div id="header">
 405 <h1>
 406 git-merge-base(1) Manual Page
 407 </h1>
 408 <h2>NAME</h2>
 409 <div class="sectionbody">
 410 <p>git-merge-base -
 411    Find as good common ancestors as possible for a merge
 412 </p>
 413 </div>
 414 </div>
 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] [--octopus] &lt;commit&gt; &lt;commit&gt;&#8230;
 419 <em>git merge-base</em> --independent &lt;commit&gt;&#8230;</div>
 420 <div class="verseblock-attribution">
 421 </div></div>
 422 </div>
 423 <h2 id="_description">DESCRIPTION</h2>
 424 <div class="sectionbody">
 425 <div class="paragraph"><p><em>git merge-base</em> finds best common ancestor(s) between two commits to use
 426 in a three-way merge.  One common ancestor is <em>better</em> than another common
 427 ancestor if the latter is an ancestor of the former.  A common ancestor
 428 that does not have any better common ancestor is a <em>best common
 429 ancestor</em>, i.e. a <em>merge base</em>.  Note that there can be more than one
 430 merge base for a pair of commits.</p></div>
 431 <div class="paragraph"><p>Unless <tt>--octopus</tt> is given, among the two commits to compute the merge
 432 base from, one is specified by the first commit argument on the command
 433 line; the other commit is a (possibly hypothetical) commit that is a merge
 434 across all the remaining commits on the command line.  As the most common
 435 special case, specifying only two commits on the command line means
 436 computing the merge base between the given two commits.</p></div>
 437 <div class="paragraph"><p>As a consequence, the <em>merge base</em> is not necessarily contained in each of the
 438 commit arguments if more than two commits are specified. This is different
 439 from <a href="git-show-branch.html">git-show-branch(1)</a> when used with the <tt>--merge-base</tt> option.</p></div>
 440 </div>
 441 <h2 id="_options">OPTIONS</h2>
 442 <div class="sectionbody">
 443 <div class="dlist"><dl>
 444 <dt class="hdlist1">
 445 -a
 446 </dt>
 447 <dt class="hdlist1">
 448 --all
 449 </dt>
 450 <dd>
 451 <p>
 452         Output all merge bases for the commits, instead of just one.
 453 </p>
 454 </dd>
 455 <dt class="hdlist1">
 456 --octopus
 457 </dt>
 458 <dd>
 459 <p>
 460         Compute the best common ancestors of all supplied commits,
 461         in preparation for an n-way merge.  This mimics the behavior
 462         of <em>git show-branch --merge-base</em>.
 463 </p>
 464 </dd>
 465 <dt class="hdlist1">
 466 --independent
 467 </dt>
 468 <dd>
 469 <p>
 470         Instead of printing merge bases, print a minimal subset of
 471         the supplied commits with the same ancestors.  In other words,
 472         among the commits given, list those which cannot be reached
 473         from any other.  This mimics the behavior of <em>git show-branch
 474         --independent</em>.
 475 </p>
 476 </dd>
 477 </dl></div>
 478 </div>
 479 <h2 id="_discussion">DISCUSSION</h2>
 480 <div class="sectionbody">
 481 <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
 482 which is reachable from both <em>A</em> and <em>B</em> through the parent relationship.</p></div>
 483 <div class="paragraph"><p>For example, with this topology:</p></div>
 484 <div class="literalblock">
 485 <div class="content">
 486 <pre><tt>         o---o---o---B
 487         /
 488 ---o---1---o---o---o---A</tt></pre>
 489 </div></div>
 490 <div class="paragraph"><p>the merge base between <em>A</em> and <em>B</em> is <em>1</em>.</p></div>
 491 <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
 492 merge base between <em>A</em> and a hypothetical commit <em>M</em>, which is a merge
 493 between <em>B</em> and <em>C</em>.  For example, with this topology:</p></div>
 494 <div class="literalblock">
 495 <div class="content">
 496 <pre><tt>       o---o---o---o---C
 497       /
 498      /   o---o---o---B
 499     /   /
 500 ---2---1---o---o---o---A</tt></pre>
 501 </div></div>
 502 <div class="paragraph"><p>the result of <tt>git merge-base A B C</tt> is <em>1</em>.  This is because the
 503 equivalent topology with a merge commit <em>M</em> between <em>B</em> and <em>C</em> is:</p></div>
 504 <div class="literalblock">
 505 <div class="content">
 506 <pre><tt>       o---o---o---o---o
 507       /                 \
 508      /   o---o---o---o---M
 509     /   /
 510 ---2---1---o---o---o---A</tt></pre>
 511 </div></div>
 512 <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
 513 common ancestor between <em>A</em> and <em>M</em>, but <em>1</em> is a better common ancestor,
 514 because <em>2</em> is an ancestor of <em>1</em>.  Hence, <em>2</em> is not a merge base.</p></div>
 515 <div class="paragraph"><p>When the history involves criss-cross merges, there can be more than one
 516 <em>best</em> common ancestor for two commits.  For example, with this topology:</p></div>
 517 <div class="literalblock">
 518 <div class="content">
 519 <pre><tt>---1---o---A
 520     \ /
 521      X
 522     / \
 523 ---2---o---o---B</tt></pre>
 524 </div></div>
 525 <div class="paragraph"><p>both <em>1</em> and <em>2</em> are merge-bases of A and B.  Neither one is better than
 526 the other (both are <em>best</em> merge bases).  When the <tt>--all</tt> option is not given,
 527 it is unspecified which best one is output.</p></div>
 528 </div>
 529 <h2 id="_author">Author</h2>
 530 <div class="sectionbody">
 531 <div class="paragraph"><p>Written by Linus Torvalds &lt;<a href="mailto:torvalds@osdl.org">torvalds@osdl.org</a>&gt;</p></div>
 532 </div>
 533 <h2 id="_documentation">Documentation</h2>
 534 <div class="sectionbody">
 535 <div class="paragraph"><p>Documentation by David Greaves, Junio C Hamano and the git-list &lt;<a href="mailto:git@vger.kernel.org">git@vger.kernel.org</a>&gt;.</p></div>
 536 </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>
 542 </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>
 546 </div>
 547 <div id="footer">
 548 <div id="footer-text">
 549 Last updated 2010-09-03 21:29:54 UTC
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