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<body class="manpage">
<div id="header">
<h1>git-bisect(1) Manual Page</h1>
<h2 id="_name">NAME</h2>
<div class="sectionbody">
<p>git-bisect - Use binary search to find the commit that introduced a bug</p>
</div>
</div>
<div id="content">
<div class="sect1">
<h2 id="_synopsis">SYNOPSIS</h2>
<div class="sectionbody">
<div class="verseblock">
<pre class="content"><em>git bisect</em> &lt;subcommand&gt; &lt;options&gt;</pre>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_description">DESCRIPTION</h2>
<div class="sectionbody">
<div class="paragraph">
<p>The command takes various subcommands, and different options depending
on the subcommand:</p>
</div>
<div class="literalblock">
<div class="content">
<pre>git bisect start [--term-(bad|new)=&lt;term-new&gt; --term-(good|old)=&lt;term-old&gt;]
	  [--no-checkout] [--first-parent] [&lt;bad&gt; [&lt;good&gt;...]] [--] [&lt;pathspec&gt;...]
git bisect (bad|new|&lt;term-new&gt;) [&lt;rev&gt;]
git bisect (good|old|&lt;term-old&gt;) [&lt;rev&gt;...]
git bisect terms [--term-(good|old) | --term-(bad|new)]
git bisect skip [(&lt;rev&gt;|&lt;range&gt;)...]
git bisect reset [&lt;commit&gt;]
git bisect (visualize|view)
git bisect replay &lt;logfile&gt;
git bisect log
git bisect run &lt;cmd&gt; [&lt;arg&gt;...]
git bisect help</pre>
</div>
</div>
<div class="paragraph">
<p>This command uses a binary search algorithm to find which commit in
your project&#8217;s history introduced a bug. You use it by first telling
it a "bad" commit that is known to contain the bug, and a "good"
commit that is known to be before the bug was introduced. Then <code>git</code>
<code>bisect</code> picks a commit between those two endpoints and asks you
whether the selected commit is "good" or "bad". It continues narrowing
down the range until it finds the exact commit that introduced the
change.</p>
</div>
<div class="paragraph">
<p>In fact, <code>git</code> <code>bisect</code> can be used to find the commit that changed
<strong>any</strong> property of your project; e.g., the commit that fixed a bug, or
the commit that caused a benchmark&#8217;s performance to improve. To
support this more general usage, the terms "old" and "new" can be used
in place of "good" and "bad", or you can choose your own terms. See
section "Alternate terms" below for more information.</p>
</div>
<div class="sect2">
<h3 id="_basic_bisect_commands_start_bad_good">Basic bisect commands: start, bad, good</h3>
<div class="paragraph">
<p>As an example, suppose you are trying to find the commit that broke a
feature that was known to work in version <code>v2.6.13-rc2</code> of your
project. You start a bisect session as follows:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start
$ git bisect bad                 # Current version is bad
$ git bisect good v2.6.13-rc2    # v2.6.13-rc2 is known to be good</pre>
</div>
</div>
<div class="paragraph">
<p>Once you have specified at least one bad and one good commit, <code>git</code>
<code>bisect</code> selects a commit in the middle of that range of history,
checks it out, and outputs something similar to the following:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>Bisecting: 675 revisions left to test after this (roughly 10 steps)</pre>
</div>
</div>
<div class="paragraph">
<p>You should now compile the checked-out version and test it. If that
version works correctly, type</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect good</pre>
</div>
</div>
<div class="paragraph">
<p>If that version is broken, type</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect bad</pre>
</div>
</div>
<div class="paragraph">
<p>Then <code>git</code> <code>bisect</code> will respond with something like</p>
</div>
<div class="listingblock">
<div class="content">
<pre>Bisecting: 337 revisions left to test after this (roughly 9 steps)</pre>
</div>
</div>
<div class="paragraph">
<p>Keep repeating the process: compile the tree, test it, and depending
on whether it is good or bad run <code>git</code> <code>bisect</code> <code>good</code> or <code>git</code> <code>bisect</code> <code>bad</code>
to ask for the next commit that needs testing.</p>
</div>
<div class="paragraph">
<p>Eventually there will be no more revisions left to inspect, and the
command will print out a description of the first bad commit. The
reference <code>refs/bisect/bad</code> will be left pointing at that commit.</p>
</div>
</div>
<div class="sect2">
<h3 id="_bisect_reset">Bisect reset</h3>
<div class="paragraph">
<p>After a bisect session, to clean up the bisection state and return to
the original HEAD, issue the following command:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect reset</pre>
</div>
</div>
<div class="paragraph">
<p>By default, this will return your tree to the commit that was checked
out before <code>git</code> <code>bisect</code> <code>start</code>.  (A new <code>git</code> <code>bisect</code> <code>start</code> will also do
that, as it cleans up the old bisection state.)</p>
</div>
<div class="paragraph">
<p>With an optional argument, you can return to a different commit
instead:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect reset &lt;commit&gt;</pre>
</div>
</div>
<div class="paragraph">
<p>For example, <code>git</code> <code>bisect</code> <code>reset</code> <code>bisect/bad</code> will check out the first
bad revision, while <code>git</code> <code>bisect</code> <code>reset</code> <code>HEAD</code> will leave you on the
current bisection commit and avoid switching commits at all.</p>
</div>
</div>
<div class="sect2">
<h3 id="_alternate_terms">Alternate terms</h3>
<div class="paragraph">
<p>Sometimes you are not looking for the commit that introduced a
breakage, but rather for a commit that caused a change between some
other "old" state and "new" state. For example, you might be looking
for the commit that introduced a particular fix. Or you might be
looking for the first commit in which the source-code filenames were
finally all converted to your company&#8217;s naming standard. Or whatever.</p>
</div>
<div class="paragraph">
<p>In such cases it can be very confusing to use the terms "good" and
"bad" to refer to "the state before the change" and "the state after
the change". So instead, you can use the terms "old" and "new",
respectively, in place of "good" and "bad". (But note that you cannot
mix "good" and "bad" with "old" and "new" in a single session.)</p>
</div>
<div class="paragraph">
<p>In this more general usage, you provide <code>git</code> <code>bisect</code> with a "new"
commit that has some property and an "old" commit that doesn&#8217;t have that
property. Each time <code>git</code> <code>bisect</code> checks out a commit, you test if that
commit has the property. If it does, mark the commit as "new";
otherwise, mark it as "old". When the bisection is done, <code>git</code> <code>bisect</code>
will report which commit introduced the property.</p>
</div>
<div class="paragraph">
<p>To use "old" and "new" instead of "good" and bad, you must run <code>git</code>
<code>bisect</code> <code>start</code> without commits as argument and then run the following
commands to add the commits:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>git bisect old [&lt;rev&gt;]</pre>
</div>
</div>
<div class="paragraph">
<p>to indicate that a commit was before the sought change, or</p>
</div>
<div class="listingblock">
<div class="content">
<pre>git bisect new [&lt;rev&gt;...]</pre>
</div>
</div>
<div class="paragraph">
<p>to indicate that it was after.</p>
</div>
<div class="paragraph">
<p>To get a reminder of the currently used terms, use</p>
</div>
<div class="listingblock">
<div class="content">
<pre>git bisect terms</pre>
</div>
</div>
<div class="paragraph">
<p>You can get just the old term with <code>git</code> <code>bisect</code> <code>terms</code> <code>--term-old</code>
or <code>git</code> <code>bisect</code> <code>terms</code> <code>--term-good</code>; <code>git</code> <code>bisect</code> <code>terms</code> <code>--term-new</code>
and <code>git</code> <code>bisect</code> <code>terms</code> <code>--term-bad</code> can be used to learn how to call
the commits more recent than the sought change.</p>
</div>
<div class="paragraph">
<p>If you would like to use your own terms instead of "bad"/"good" or
"new"/"old", you can choose any names you like (except existing bisect
subcommands like <code>reset</code>, <code>start</code>, &#8230;&#8203;) by starting the
bisection using</p>
</div>
<div class="listingblock">
<div class="content">
<pre>git bisect start --term-old &lt;term-old&gt; --term-new &lt;term-new&gt;</pre>
</div>
</div>
<div class="paragraph">
<p>For example, if you are looking for a commit that introduced a
performance regression, you might use</p>
</div>
<div class="listingblock">
<div class="content">
<pre>git bisect start --term-old fast --term-new slow</pre>
</div>
</div>
<div class="paragraph">
<p>Or if you are looking for the commit that fixed a bug, you might use</p>
</div>
<div class="listingblock">
<div class="content">
<pre>git bisect start --term-new fixed --term-old broken</pre>
</div>
</div>
<div class="paragraph">
<p>Then, use <code>git</code> <code>bisect</code> <em>&lt;term-old&gt;</em> and <code>git</code> <code>bisect</code> <em>&lt;term-new&gt;</em> instead
of <code>git</code> <code>bisect</code> <code>good</code> and <code>git</code> <code>bisect</code> <code>bad</code> to mark commits.</p>
</div>
</div>
<div class="sect2">
<h3 id="_bisect_visualizeview">Bisect visualize/view</h3>
<div class="paragraph">
<p>To see the currently remaining suspects in <em>gitk</em>, issue the following
command during the bisection process (the subcommand <code>view</code> can be used
as an alternative to <code>visualize</code>):</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect visualize</pre>
</div>
</div>
<div class="paragraph">
<p>Git detects a graphical environment through various environment variables:
<code>DISPLAY</code>, which is set in X Window System environments on Unix systems.
<code>SESSIONNAME</code>, which is set under Cygwin in interactive desktop sessions.
<code>MSYSTEM</code>, which is set under Msys2 and Git for Windows.
<code>SECURITYSESSIONID</code>, which may be set on macOS in interactive desktop sessions.</p>
</div>
<div class="paragraph">
<p>If none of these environment variables is set, <em>git log</em> is used instead.
You can also give command-line options such as <code>-p</code> and <code>--stat</code>.</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect visualize --stat</pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_bisect_log_and_bisect_replay">Bisect log and bisect replay</h3>
<div class="paragraph">
<p>After having marked revisions as good or bad, issue the following
command to show what has been done so far:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect log</pre>
</div>
</div>
<div class="paragraph">
<p>If you discover that you made a mistake in specifying the status of a
revision, you can save the output of this command to a file, edit it to
remove the incorrect entries, and then issue the following commands to
return to a corrected state:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect reset
$ git bisect replay that-file</pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_avoiding_testing_a_commit">Avoiding testing a commit</h3>
<div class="paragraph">
<p>If, in the middle of a bisect session, you know that the suggested
revision is not a good one to test (e.g. it fails to build and you
know that the failure does not have anything to do with the bug you
are chasing), you can manually select a nearby commit and test that
one instead.</p>
</div>
<div class="paragraph">
<p>For example:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect good/bad                   # previous round was good or bad.
Bisecting: 337 revisions left to test after this (roughly 9 steps)
$ git bisect visualize                  # oops, that is uninteresting.
$ git reset --hard HEAD~3               # try 3 revisions before what
                                        # was suggested</pre>
</div>
</div>
<div class="paragraph">
<p>Then compile and test the chosen revision, and afterwards mark
the revision as good or bad in the usual manner.</p>
</div>
</div>
<div class="sect2">
<h3 id="_bisect_skip">Bisect skip</h3>
<div class="paragraph">
<p>Instead of choosing a nearby commit by yourself, you can ask Git to do
it for you by issuing the command:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect skip                 # Current version cannot be tested</pre>
</div>
</div>
<div class="paragraph">
<p>However, if you skip a commit adjacent to the one you are looking for,
Git will be unable to tell exactly which of those commits was the
first bad one.</p>
</div>
<div class="paragraph">
<p>You can also skip a range of commits, instead of just one commit,
using range notation. For example:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect skip v2.5..v2.6</pre>
</div>
</div>
<div class="paragraph">
<p>This tells the bisect process that no commit after <code>v2.5</code>, up to and
including <code>v2.6</code>, should be tested.</p>
</div>
<div class="paragraph">
<p>Note that if you also want to skip the first commit of the range you
would issue the command:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect skip v2.5 v2.5..v2.6</pre>
</div>
</div>
<div class="paragraph">
<p>This tells the bisect process that the commits between <code>v2.5</code> and
<code>v2.6</code> (inclusive) should be skipped.</p>
</div>
</div>
<div class="sect2">
<h3 id="_cutting_down_bisection_by_giving_more_parameters_to_bisect_start">Cutting down bisection by giving more parameters to bisect start</h3>
<div class="paragraph">
<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 specifying
pathspec parameters when issuing the <code>bisect</code> <code>start</code> command:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start -- arch/i386 include/asm-i386</pre>
</div>
</div>
<div class="paragraph">
<p>If you know beforehand more than one good commit, you can narrow the
bisect space down by specifying all of the good commits immediately after
the bad commit when issuing the <code>bisect</code> <code>start</code> command:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ 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</pre>
</div>
</div>
</div>
<div class="sect2">
<h3 id="_bisect_run">Bisect run</h3>
<div class="paragraph">
<p>If you have a script that can tell if the current source code is good
or bad, you can bisect by issuing the command:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect run my_script arguments</pre>
</div>
</div>
<div class="paragraph">
<p>Note that the script (<code>my_script</code> in the above example) should exit
with code 0 if the current source code is good/old, and exit with a
code between 1 and 127 (inclusive), except 125, if the current source
code is bad/new.</p>
</div>
<div class="paragraph">
<p>Any other exit code will abort the bisect process. It should be noted
that a program that terminates via <code>exit</code>(<code>-1</code>) leaves $? = 255, (see the
exit(3) manual page), as the value is chopped with &amp; <code>0377</code>.</p>
</div>
<div class="paragraph">
<p>The special exit code 125 should be used when the current source code
cannot be tested. If the script exits with this code, the current
revision will be skipped (see <code>git</code> <code>bisect</code> <code>skip</code> above). 125 was chosen
as the highest sensible value to use for this purpose, because 126 and 127
are used by POSIX shells to signal specific error status (127 is for
command not found, 126 is for command found but not executable&#8212;&#8203;these
details do not matter, as they are normal errors in the script, as far as
<code>bisect</code> <code>run</code> is concerned).</p>
</div>
<div class="paragraph">
<p>You may often find that during a bisect session you want to have
temporary modifications (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 another problem this bisection is not
interested in") applied to the revision being tested.</p>
</div>
<div class="paragraph">
<p>To cope with such a situation, after the inner <em>git bisect</em> finds the
next revision to test, the script can apply the patch
before compiling, run the real test, and afterwards decide if the
revision (possibly with the needed patch) passed the test and then
rewind the tree to the pristine state.  Finally the script should exit
with the status of the real test to let the <code>git</code> <code>bisect</code> <code>run</code> command loop
determine the eventual outcome of the bisect session.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_options">OPTIONS</h2>
<div class="sectionbody">
<div class="dlist">
<dl>
<dt class="hdlist1">--no-checkout</dt>
<dd>
<div class="paragraph">
<p>Do not checkout the new working tree at each iteration of the bisection
process. Instead just update the reference named <code>BISECT_HEAD</code> to make
it point to the commit that should be tested.</p>
</div>
<div class="paragraph">
<p>This option may be useful when the test you would perform in each step
does not require a checked out tree.</p>
</div>
<div class="paragraph">
<p>If the repository is bare, <code>--no-checkout</code> is assumed.</p>
</div>
</dd>
<dt class="hdlist1">--first-parent</dt>
<dd>
<div class="paragraph">
<p>Follow only the first parent commit upon seeing a merge commit.</p>
</div>
<div class="paragraph">
<p>In detecting regressions introduced through the merging of a branch, the merge
commit will be identified as introduction of the bug and its ancestors will be
ignored.</p>
</div>
<div class="paragraph">
<p>This option is particularly useful in avoiding false positives when a merged
branch contained broken or non-buildable commits, but the merge itself was OK.</p>
</div>
</dd>
</dl>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_examples">EXAMPLES</h2>
<div class="sectionbody">
<div class="ulist">
<ul>
<li>
<p>Automatically bisect a broken build between v1.2 and HEAD:</p>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start HEAD v1.2 --      # HEAD is bad, v1.2 is good
$ git bisect run make                # "make" builds the app
$ git bisect reset                   # quit the bisect session</pre>
</div>
</div>
</li>
<li>
<p>Automatically bisect a test failure between origin and HEAD:</p>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start HEAD origin --    # HEAD is bad, origin is good
$ git bisect run make test           # "make test" builds and tests
$ git bisect reset                   # quit the bisect session</pre>
</div>
</div>
</li>
<li>
<p>Automatically bisect a broken test case:</p>
<div class="listingblock">
<div class="content">
<pre>$ cat ~/test.sh
#!/bin/sh
make || exit 125                     # this skips broken builds
~/check_test_case.sh                 # does the test case pass?
$ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
$ git bisect run ~/test.sh
$ git bisect reset                   # quit the bisect session</pre>
</div>
</div>
<div class="paragraph">
<p>Here we use a <code>test.sh</code> custom script. In this script, if <code>make</code>
fails, we skip the current commit.
<code>check_test_case.sh</code> should <code>exit</code> <code>0</code> if the test case passes,
and <code>exit</code> <code>1</code> otherwise.</p>
</div>
<div class="paragraph">
<p>It is safer if both <code>test.sh</code> and <code>check_test_case.sh</code> are
outside the repository to prevent interactions between the bisect,
make and test processes and the scripts.</p>
</div>
</li>
<li>
<p>Automatically bisect with temporary modifications (hot-fix):</p>
<div class="listingblock">
<div class="content">
<pre>$ cat ~/test.sh
#!/bin/sh

# tweak the working tree by merging the hot-fix branch
# and then attempt a build
if      git merge --no-commit --no-ff hot-fix &amp;&amp;
        make
then
        # run project specific test and report its status
        ~/check_test_case.sh
        status=$?
else
        # tell the caller this is untestable
        status=125
fi

# undo the tweak to allow clean flipping to the next commit
git reset --hard

# return control
exit $status</pre>
</div>
</div>
<div class="paragraph">
<p>This applies modifications from a hot-fix branch before each test run,
e.g. in case your build or test environment changed so that older
revisions may need a fix which newer ones have already. (Make sure the
hot-fix branch is based off a commit which is contained in all revisions
which you are bisecting, so that the merge does not pull in too much, or
use <code>git</code> <code>cherry-pick</code> instead of <code>git</code> <code>merge</code>.)</p>
</div>
</li>
<li>
<p>Automatically bisect a broken test case:</p>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
$ git bisect run sh -c "make || exit 125; ~/check_test_case.sh"
$ git bisect reset                   # quit the bisect session</pre>
</div>
</div>
<div class="paragraph">
<p>This shows that you can do without a run script if you write the test
on a single line.</p>
</div>
</li>
<li>
<p>Locate a good region of the object graph in a damaged repository</p>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start HEAD &lt;known-good-commit&gt; [ &lt;boundary-commit&gt; ... ] --no-checkout
$ git bisect run sh -c '
        GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &amp;&amp;
        git rev-list --objects BISECT_HEAD --not $GOOD &gt;tmp.$$ &amp;&amp;
        git pack-objects --stdout &gt;/dev/null &lt;tmp.$$
        rc=$?
        rm -f tmp.$$
        test $rc = 0'

$ git bisect reset                   # quit the bisect session</pre>
</div>
</div>
<div class="paragraph">
<p>In this case, when <em>git bisect run</em> finishes, bisect/bad will refer to a commit that
has at least one parent whose reachable graph is fully traversable in the sense
required by <em>git pack objects</em>.</p>
</div>
</li>
<li>
<p>Look for a fix instead of a regression in the code</p>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start
$ git bisect new HEAD    # current commit is marked as new
$ git bisect old HEAD~10 # the tenth commit from now is marked as old</pre>
</div>
</div>
<div class="paragraph">
<p>or:</p>
</div>
<div class="listingblock">
<div class="content">
<pre>$ git bisect start --term-old broken --term-new fixed
$ git bisect fixed
$ git bisect broken HEAD~10</pre>
</div>
</div>
</li>
</ul>
</div>
<div class="sect2">
<h3 id="_getting_help">Getting help</h3>
<div class="paragraph">
<p>Use <code>git</code> <code>bisect</code> to get a short usage description, and <code>git</code> <code>bisect</code>
<code>help</code> or <code>git</code> <code>bisect</code> <code>-h</code> to get a long usage description.</p>
</div>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_see_also">SEE ALSO</h2>
<div class="sectionbody">
<div class="paragraph">
<p><a href="git-bisect-lk2009.html">Fighting regressions with git bisect</a>,
<a href="git-blame.html">git-blame(1)</a>.</p>
</div>
</div>
</div>
<div class="sect1">
<h2 id="_git">GIT</h2>
<div class="sectionbody">
<div class="paragraph">
<p>Part of the <a href="git.html">git(1)</a> suite</p>
</div>
</div>
</div>
</div>
<div id="footer">
<div id="footer-text">
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