1GIT-BISECT(1) Git Manual GIT-BISECT(1)
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6 git-bisect - Use binary search to find the commit that introduced a bug
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9 git bisect <subcommand> <options>
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12 The command takes various subcommands, and different options depending
13 on the subcommand:
14 git bisect start [--term-(new|bad)=<term-new> --term-(old|good)=<term-old>]
16 [--no-checkout] [--first-parent] [<bad> [<good>...]] [--] [<paths>...]
17 git bisect (bad|new|<term-new>) [<rev>]
18 git bisect (good|old|<term-old>) [<rev>...]
19 git bisect terms [--term-good | --term-bad]
20 git bisect skip [(<rev>|<range>)...]
21 git bisect reset [<commit>]
22 git bisect (visualize|view)
23 git bisect replay <logfile>
24 git bisect log
25 git bisect run <cmd> [<arg>...]
26 git bisect help
27 This command uses a binary search algorithm to find which commit in
29 your project’s history introduced a bug. You use it by first telling it
30 a "bad" commit that is known to contain the bug, and a "good" commit
31 that is known to be before the bug was introduced. Then git bisect
32 picks a commit between those two endpoints and asks you whether the
33 selected commit is "good" or "bad". It continues narrowing down the
34 range until it finds the exact commit that introduced the change.
35 In fact, git bisect can be used to find the commit that changed any
37 property of your project; e.g., the commit that fixed a bug, or the
38 commit that caused a benchmark’s performance to improve. To support
39 this more general usage, the terms "old" and "new" can be used in place
40 of "good" and "bad", or you can choose your own terms. See section
41 "Alternate terms" below for more information.
42 Basic bisect commands: start, bad, good
44 As an example, suppose you are trying to find the commit that broke a
45 feature that was known to work in version v2.6.13-rc2 of your project.
46 You start a bisect session as follows:
47 $ git bisect start
49 $ git bisect bad # Current version is bad
50 $ git bisect good v2.6.13-rc2 # v2.6.13-rc2 is known to be good
51 Once you have specified at least one bad and one good commit, git
53 bisect selects a commit in the middle of that range of history, checks
54 it out, and outputs something similar to the following:
55 Bisecting: 675 revisions left to test after this (roughly 10 steps)
57 You should now compile the checked-out version and test it. If that
59 version works correctly, type
60 $ git bisect good
62 If that version is broken, type
64 $ git bisect bad
66 Then git bisect will respond with something like
68 Bisecting: 337 revisions left to test after this (roughly 9 steps)
70 Keep repeating the process: compile the tree, test it, and depending on
72 whether it is good or bad run git bisect good or git bisect bad to ask
73 for the next commit that needs testing.
74 Eventually there will be no more revisions left to inspect, and the
76 command will print out a description of the first bad commit. The
77 reference refs/bisect/bad will be left pointing at that commit.
78 Bisect reset
80 After a bisect session, to clean up the bisection state and return to
81 the original HEAD, issue the following command:
82 $ git bisect reset
84 By default, this will return your tree to the commit that was checked
86 out before git bisect start. (A new git bisect start will also do that,
87 as it cleans up the old bisection state.)
88 With an optional argument, you can return to a different commit
90 instead:
91 $ git bisect reset <commit>
93 For example, git bisect reset bisect/bad will check out the first bad
95 revision, while git bisect reset HEAD will leave you on the current
96 bisection commit and avoid switching commits at all.
97 Alternate terms
99 Sometimes you are not looking for the commit that introduced a
100 breakage, but rather for a commit that caused a change between some
101 other "old" state and "new" state. For example, you might be looking
102 for the commit that introduced a particular fix. Or you might be
103 looking for the first commit in which the source-code filenames were
104 finally all converted to your company’s naming standard. Or whatever.
105 In such cases it can be very confusing to use the terms "good" and
107 "bad" to refer to "the state before the change" and "the state after
108 the change". So instead, you can use the terms "old" and "new",
109 respectively, in place of "good" and "bad". (But note that you cannot
110 mix "good" and "bad" with "old" and "new" in a single session.)
111 In this more general usage, you provide git bisect with a "new" commit
113 that has some property and an "old" commit that doesn’t have that
114 property. Each time git bisect checks out a commit, you test if that
115 commit has the property. If it does, mark the commit as "new";
116 otherwise, mark it as "old". When the bisection is done, git bisect
117 will report which commit introduced the property.
118 To use "old" and "new" instead of "good" and bad, you must run git
120 bisect start without commits as argument and then run the following
121 commands to add the commits:
122 git bisect old [<rev>]
124 to indicate that a commit was before the sought change, or
126 git bisect new [<rev>...]
128 to indicate that it was after.
130 To get a reminder of the currently used terms, use
132 git bisect terms
134 You can get just the old (respectively new) term with git bisect terms
136 --term-old or git bisect terms --term-good.
137 If you would like to use your own terms instead of "bad"/"good" or
139 "new"/"old", you can choose any names you like (except existing bisect
140 subcommands like reset, start, ...) by starting the bisection using
141 git bisect start --term-old <term-old> --term-new <term-new>
143 For example, if you are looking for a commit that introduced a
145 performance regression, you might use
146 git bisect start --term-old fast --term-new slow
148 Or if you are looking for the commit that fixed a bug, you might use
150 git bisect start --term-new fixed --term-old broken
152 Then, use git bisect <term-old> and git bisect <term-new> instead of
154 git bisect good and git bisect bad to mark commits.
155 Bisect visualize/view
157 To see the currently remaining suspects in gitk, issue the following
158 command during the bisection process (the subcommand view can be used
159 as an alternative to visualize):
160 $ git bisect visualize
162 Git detects a graphical environment through various environment
164 variables: DISPLAY, which is set in X Window System environments on
165 Unix systems. SESSIONNAME, which is set under Cygwin in interactive
166 desktop sessions. MSYSTEM, which is set under Msys2 and Git for
167 Windows. SECURITYSESSIONID, which may be set on macOS in interactive
168 desktop sessions.
169 If none of these environment variables is set, git log is used instead.
171 You can also give command-line options such as -p and --stat.
172 $ git bisect visualize --stat
174 Bisect log and bisect replay
176 After having marked revisions as good or bad, issue the following
177 command to show what has been done so far:
178 $ git bisect log
180 If you discover that you made a mistake in specifying the status of a
182 revision, you can save the output of this command to a file, edit it to
183 remove the incorrect entries, and then issue the following commands to
184 return to a corrected state:
185 $ git bisect reset
187 $ git bisect replay that-file
188 Avoiding testing a commit
190 If, in the middle of a bisect session, you know that the suggested
191 revision is not a good one to test (e.g. it fails to build and you know
192 that the failure does not have anything to do with the bug you are
193 chasing), you can manually select a nearby commit and test that one
194 instead.
195 For example:
197 $ git bisect good/bad # previous round was good or bad.
199 Bisecting: 337 revisions left to test after this (roughly 9 steps)
200 $ git bisect visualize # oops, that is uninteresting.
201 $ git reset --hard HEAD~3 # try 3 revisions before what
202 # was suggested
203 Then compile and test the chosen revision, and afterwards mark the
205 revision as good or bad in the usual manner.
206 Bisect skip
208 Instead of choosing a nearby commit by yourself, you can ask Git to do
209 it for you by issuing the command:
210 $ git bisect skip # Current version cannot be tested
212 However, if you skip a commit adjacent to the one you are looking for,
214 Git will be unable to tell exactly which of those commits was the first
215 bad one.
216 You can also skip a range of commits, instead of just one commit, using
218 range notation. For example:
219 $ git bisect skip v2.5..v2.6
221 This tells the bisect process that no commit after v2.5, up to and
223 including v2.6, should be tested.
224 Note that if you also want to skip the first commit of the range you
226 would issue the command:
227 $ git bisect skip v2.5 v2.5..v2.6
229 This tells the bisect process that the commits between v2.5 and v2.6
231 (inclusive) should be skipped.
232 Cutting down bisection by giving more parameters to bisect start
234 You can further cut down the number of trials, if you know what part of
235 the tree is involved in the problem you are tracking down, by
236 specifying path parameters when issuing the bisect start command:
237 $ git bisect start -- arch/i386 include/asm-i386
239 If you know beforehand more than one good commit, you can narrow the
241 bisect space down by specifying all of the good commits immediately
242 after the bad commit when issuing the bisect start command:
243 $ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
245 # v2.6.20-rc6 is bad
246 # v2.6.20-rc4 and v2.6.20-rc1 are good
247 Bisect run
249 If you have a script that can tell if the current source code is good
250 or bad, you can bisect by issuing the command:
251 $ git bisect run my_script arguments
253 Note that the script (my_script in the above example) should exit with
255 code 0 if the current source code is good/old, and exit with a code
256 between 1 and 127 (inclusive), except 125, if the current source code
257 is bad/new.
258 Any other exit code will abort the bisect process. It should be noted
260 that a program that terminates via exit(-1) leaves $? = 255, (see the
261 exit(3) manual page), as the value is chopped with & 0377.
262 The special exit code 125 should be used when the current source code
264 cannot be tested. If the script exits with this code, the current
265 revision will be skipped (see git bisect skip above). 125 was chosen as
266 the highest sensible value to use for this purpose, because 126 and 127
267 are used by POSIX shells to signal specific error status (127 is for
268 command not found, 126 is for command found but not executable—these
269 details do not matter, as they are normal errors in the script, as far
270 as bisect run is concerned).
271 You may often find that during a bisect session you want to have
273 temporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a
274 header file, or "revision that does not have this commit needs this
275 patch applied to work around another problem this bisection is not
276 interested in") applied to the revision being tested.
277 To cope with such a situation, after the inner git bisect finds the
279 next revision to test, the script can apply the patch before compiling,
280 run the real test, and afterwards decide if the revision (possibly with
281 the needed patch) passed the test and then rewind the tree to the
282 pristine state. Finally the script should exit with the status of the
283 real test to let the git bisect run command loop determine the eventual
284 outcome of the bisect session.
285
287 --no-checkout
288 Do not checkout the new working tree at each iteration of the
289 bisection process. Instead just update a special reference named
290 BISECT_HEAD to make it point to the commit that should be tested.
291 This option may be useful when the test you would perform in each
293 step does not require a checked out tree.
294 If the repository is bare, --no-checkout is assumed.
296 --first-parent
298 Follow only the first parent commit upon seeing a merge commit.
299 In detecting regressions introduced through the merging of a
301 branch, the merge commit will be identified as introduction of the
302 bug and its ancestors will be ignored.
303 This option is particularly useful in avoiding false positives when
305 a merged branch contained broken or non-buildable commits, but the
306 merge itself was OK.
307
309 • Automatically bisect a broken build between v1.2 and HEAD:
310 $ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good
312 $ git bisect run make # "make" builds the app
313 $ git bisect reset # quit the bisect session
314 • Automatically bisect a test failure between origin and HEAD:
316 $ git bisect start HEAD origin -- # HEAD is bad, origin is good
318 $ git bisect run make test # "make test" builds and tests
319 $ git bisect reset # quit the bisect session
320 • Automatically bisect a broken test case:
322 $ cat ~/test.sh
324 #!/bin/sh
325 make || exit 125 # this skips broken builds
326 ~/check_test_case.sh # does the test case pass?
327 $ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
328 $ git bisect run ~/test.sh
329 $ git bisect reset # quit the bisect session
330 Here we use a test.sh custom script. In this script, if make fails,
332 we skip the current commit. check_test_case.sh should exit 0 if
333 the test case passes, and exit 1 otherwise.
334 It is safer if both test.sh and check_test_case.sh are outside the
336 repository to prevent interactions between the bisect, make and
337 test processes and the scripts.
338 • Automatically bisect with temporary modifications (hot-fix):
340 $ cat ~/test.sh
342 #!/bin/sh
343 # tweak the working tree by merging the hot-fix branch
345 # and then attempt a build
346 if git merge --no-commit --no-ff hot-fix &&
347 make
348 then
349 # run project specific test and report its status
350 ~/check_test_case.sh
351 status=$?
352 else
353 # tell the caller this is untestable
354 status=125
355 fi
356 # undo the tweak to allow clean flipping to the next commit
358 git reset --hard
359 # return control
361 exit $status
362 This applies modifications from a hot-fix branch before each test
364 run, e.g. in case your build or test environment changed so that
365 older revisions may need a fix which newer ones have already. (Make
366 sure the hot-fix branch is based off a commit which is contained in
367 all revisions which you are bisecting, so that the merge does not
368 pull in too much, or use git cherry-pick instead of git merge.)
369 • Automatically bisect a broken test case:
371 $ git bisect start HEAD HEAD~10 -- # culprit is among the last 10
373 $ git bisect run sh -c "make || exit 125; ~/check_test_case.sh"
374 $ git bisect reset # quit the bisect session
375 This shows that you can do without a run script if you write the
377 test on a single line.
378 • Locate a good region of the object graph in a damaged repository
380 $ git bisect start HEAD <known-good-commit> [ <boundary-commit> ... ] --no-checkout
382 $ git bisect run sh -c '
383 GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &&
384 git rev-list --objects BISECT_HEAD --not $GOOD >tmp.$$ &&
385 git pack-objects --stdout >/dev/null <tmp.$$
386 rc=$?
387 rm -f tmp.$$
388 test $rc = 0'
389 $ git bisect reset # quit the bisect session
391 In this case, when git bisect run finishes, bisect/bad will refer
393 to a commit that has at least one parent whose reachable graph is
394 fully traversable in the sense required by git pack objects.
395 • Look for a fix instead of a regression in the code
397 $ git bisect start
399 $ git bisect new HEAD # current commit is marked as new
400 $ git bisect old HEAD~10 # the tenth commit from now is marked as old
401 or:
403 $ git bisect start --term-old broken --term-new fixed
405 $ git bisect fixed
406 $ git bisect broken HEAD~10
407 Getting help
409 Use git bisect to get a short usage description, and git bisect help or
410 git bisect -h to get a long usage description.
411
413 Fighting regressions with git bisect[1], git-blame(1).
414
416 Part of the git(1) suite
417
419 1. Fighting regressions with git bisect
420 file:///usr/share/doc/git/git-bisect-lk2009.html
421Git 2.43.0 11/20/2023 GIT-BISECT(1)