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<title>git-bisect(1)</title>
</head>
<body>
<div id="header">
<h1>
git-bisect(1) Manual Page
</h1>
<h2>NAME</h2>
<div class="sectionbody">
<p>git-bisect -
Find the change that introduced a bug by binary search
</p>
</div>
</div>
<h2>SYNOPSIS</h2>
<div class="sectionbody">
<div class="para"><p><em>git bisect</em> &lt;subcommand&gt; &lt;options&gt;</p></div>
</div>
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="para"><p>The command takes various subcommands, and different options depending
on the subcommand:</p></div>
<div class="literalblock">
<div class="content">
<pre><tt>git bisect help
git bisect start [&lt;bad&gt; [&lt;good&gt;...]] [--] [&lt;paths&gt;...]
git bisect bad [&lt;rev&gt;]
git bisect good [&lt;rev&gt;...]
git bisect skip [&lt;rev&gt;...]
git bisect reset [&lt;branch&gt;]
git bisect visualize
git bisect replay &lt;logfile&gt;
git bisect log
git bisect run &lt;cmd&gt;...</tt></pre>
</div></div>
<div class="para"><p>This command uses <em>git-rev-list --bisect</em> to help drive the
binary search process to find which change introduced a bug, given an
old "good" commit object name and a later "bad" commit object name.</p></div>
<h3 id="_getting_help">Getting help</h3><div style="clear:left"></div>
<div class="para"><p>Use "git bisect" to get a short usage description, and "git bisect
help" or "git bisect -h" to get a long usage description.</p></div>
<h3 id="_basic_bisect_commands_start_bad_good">Basic bisect commands: start, bad, good</h3><div style="clear:left"></div>
<div class="para"><p>The way you use it is:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect start
$ git bisect bad # Current version is bad
$ git bisect good v2.6.13-rc2 # v2.6.13-rc2 was the last version
# tested that was good</tt></pre>
</div></div>
<div class="para"><p>When you give at least one bad and one good versions, it will bisect
the revision tree and say something like:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>Bisecting: 675 revisions left to test after this</tt></pre>
</div></div>
<div class="para"><p>and check out the state in the middle. Now, compile that kernel, and
boot it. Now, let's say that this booted kernel works fine, then just
do</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect good # this one is good</tt></pre>
</div></div>
<div class="para"><p>which will now say</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>Bisecting: 337 revisions left to test after this</tt></pre>
</div></div>
<div class="para"><p>and you continue along, compiling that one, testing it, and depending
on whether it is good or bad, you say "git bisect good" or "git bisect
bad", and ask for the next bisection.</p></div>
<div class="para"><p>Until you have no more left, and you'll have been left with the first
bad kernel rev in "refs/bisect/bad".</p></div>
<h3 id="_bisect_reset">Bisect reset</h3><div style="clear:left"></div>
<div class="para"><p>Oh, and then after you want to reset to the original head, do a</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect reset</tt></pre>
</div></div>
<div class="para"><p>to get back to the original branch, instead of being on the bisection
commit ("git bisect start" will do that for you too, actually: it will
reset the bisection state).</p></div>
<h3 id="_bisect_visualize">Bisect visualize</h3><div style="clear:left"></div>
<div class="para"><p>During the bisection process, you can say</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect visualize</tt></pre>
</div></div>
<div class="para"><p>to see the currently remaining suspects in <em>gitk</em>. <tt>visualize</tt> is a bit
too long to type and <tt>view</tt> is provided as a synonym.</p></div>
<div class="para"><p>If <em>DISPLAY</em> environment variable is not set, <em>git-log</em> is used
instead. You can even give command line options such as <tt>-p</tt> and
<tt>--stat</tt>.</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect view --stat</tt></pre>
</div></div>
<h3 id="_bisect_log_and_bisect_replay">Bisect log and bisect replay</h3><div style="clear:left"></div>
<div class="para"><p>The good/bad input is logged, and</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect log</tt></pre>
</div></div>
<div class="para"><p>shows what you have done so far. You can truncate its output somewhere
and save it in a file, and run</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect replay that-file</tt></pre>
</div></div>
<div class="para"><p>if you find later you made a mistake telling good/bad about a
revision.</p></div>
<h3 id="_avoiding_to_test_a_commit">Avoiding to test a commit</h3><div style="clear:left"></div>
<div class="para"><p>If in a middle of bisect session, you know what the bisect suggested
to try next is not a good one to test (e.g. the change the commit
introduces is known not to work in your environment and you know it
does not have anything to do with the bug you are chasing), you may
want to find a near-by commit and try that instead.</p></div>
<div class="para"><p>It goes something like this:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect good/bad # previous round was good/bad.
Bisecting: 337 revisions left to test after this
$ git bisect visualize # oops, that is uninteresting.
$ git reset --hard HEAD~3 # try 3 revs before what
# was suggested</tt></pre>
</div></div>
<div class="para"><p>Then compile and test the one you chose to try. After that, tell
bisect what the result was as usual.</p></div>
<h3 id="_bisect_skip">Bisect skip</h3><div style="clear:left"></div>
<div class="para"><p>Instead of choosing by yourself a nearby commit, you may just want git
to do it for you using:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect skip # Current version cannot be tested</tt></pre>
</div></div>
<div class="para"><p>But computing the commit to test may be slower afterwards and git may
eventually not be able to tell the first bad among a bad and one or
more "skip"ped commits.</p></div>
<h3 id="_cutting_down_bisection_by_giving_more_parameters_to_bisect_start">Cutting down bisection by giving more parameters to bisect start</h3><div style="clear:left"></div>
<div class="para"><p>You can further cut down the number of trials if you know what part of
the tree is involved in the problem you are tracking down, by giving
paths parameters when you say <tt>bisect start</tt>, like this:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect start -- arch/i386 include/asm-i386</tt></pre>
</div></div>
<div class="para"><p>If you know beforehand more than one good commits, you can narrow the
bisect space down without doing the whole tree checkout every time you
give good commits. You give the bad revision immediately after <tt>start</tt>
and then you give all the good revisions you have:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
# v2.6.20-rc6 is bad
# v2.6.20-rc4 and v2.6.20-rc1 are good</tt></pre>
</div></div>
<h3 id="_bisect_run">Bisect run</h3><div style="clear:left"></div>
<div class="para"><p>If you have a script that can tell if the current source code is good
or bad, you can automatically bisect using:</p></div>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect run my_script</tt></pre>
</div></div>
<div class="para"><p>Note that the "run" script (<tt>my_script</tt> in the above example) should
exit with code 0 in case the current source code is good. Exit with a
code between 1 and 127 (inclusive), except 125, if the current
source code is bad.</p></div>
<div class="para"><p>Any other exit code will abort the automatic bisect process. (A
program that does "exit(-1)" leaves $? = 255, see exit(3) manual page,
the value is chopped with "&amp; 0377".)</p></div>
<div class="para"><p>The special exit code 125 should be used when the current source code
cannot be tested. If the "run" script exits with this code, the current
revision will be skipped, see <tt>git bisect skip</tt> above.</p></div>
<div class="para"><p>You may often find that during bisect you want to have near-constant
tweaks (e.g., s/#define DEBUG 0/#define DEBUG 1/ in a header file, or
"revision that does not have this commit needs this patch applied to
work around other problem this bisection is not interested in")
applied to the revision being tested.</p></div>
<div class="para"><p>To cope with such a situation, after the inner <em>git-bisect</em> finds the
next revision to test, with the "run" script, you can apply that tweak
before compiling, run the real test, and after the test decides if the
revision (possibly with the needed tweaks) passed the test, rewind the
tree to the pristine state. Finally the "run" script can exit with
the status of the real test to let the "git bisect run" command loop to
determine the outcome.</p></div>
</div>
<h2 id="_examples">EXAMPLES</h2>
<div class="sectionbody">
<div class="ilist"><ul>
<li>
<p>
Automatically bisect a broken build between v1.2 and HEAD:
</p>
<div class="listingblock">
<div class="content">
<pre><tt>$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good
$ git bisect run make # "make" builds the app</tt></pre>
</div></div>
</li>
<li>
<p>
Automatically bisect a broken test suite:
</p>
<div class="listingblock">
<div class="content">
<pre><tt>$ cat ~/test.sh
#!/bin/sh
make || exit 125 # this "skip"s broken builds
make test # "make test" runs the test suite
$ git bisect start v1.3 v1.1 -- # v1.3 is bad, v1.1 is good
$ git bisect run ~/test.sh</tt></pre>
</div></div>
<div class="para"><p>Here we use a "test.sh" custom script. In this script, if "make"
fails, we "skip" the current commit.</p></div>
<div class="para"><p>It's safer to use a custom script outside the repo to prevent
interactions between the bisect, make and test processes and the
script.</p></div>
<div class="para"><p>And "make test" should "exit 0", if the test suite passes, and
"exit 1" (for example) otherwise.</p></div>
</li>
<li>
<p>
Automatically bisect a broken test case:
</p>
<div class="listingblock">
<div class="content">
<pre><tt>$ cat ~/test.sh
#!/bin/sh
make || exit 125 # this "skip"s broken builds
~/check_test_case.sh # does the test case passes ?
$ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
$ git bisect run ~/test.sh</tt></pre>
</div></div>
<div class="para"><p>Here "check_test_case.sh" should "exit 0", if the test case passes,
and "exit 1" (for example) otherwise.</p></div>
<div class="para"><p>It's safer if both "test.sh" and "check_test_case.sh" scripts are
outside the repo to prevent interactions between the bisect, make and
test processes and the scripts.</p></div>
</li>
</ul></div>
</div>
<h2 id="_author">Author</h2>
<div class="sectionbody">
<div class="para"><p>Written by Linus Torvalds &lt;torvalds@osdl.org&gt;</p></div>
</div>
<h2 id="_documentation">Documentation</h2>
<div class="sectionbody">
<div class="para"><p>Documentation by Junio C Hamano and the git-list &lt;git@vger.kernel.org&gt;.</p></div>
</div>
<h2 id="_git">GIT</h2>
<div class="sectionbody">
<div class="para"><p>Part of the <a href="git.html">git(1)</a> suite</p></div>
</div>
<div id="footer">
<div id="footer-text">
Last updated 2008-07-06 05:16:35 UTC
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