1GIT-BISECT(1)                     Git Manual                     GIT-BISECT(1)
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NAME

6       git-bisect - Use binary search to find the commit that introduced a bug
7

SYNOPSIS

9       git bisect <subcommand> <options>
10
11

DESCRIPTION

13       The command takes various subcommands, and different options depending
14       on the subcommand:
15
16           git bisect start [--term-{old,good}=<term> --term-{new,bad}=<term>]
17                            [--no-checkout] [<bad> [<good>...]] [--] [<paths>...]
18           git bisect (bad|new|<term-new>) [<rev>]
19           git bisect (good|old|<term-old>) [<rev>...]
20           git bisect terms [--term-good | --term-bad]
21           git bisect skip [(<rev>|<range>)...]
22           git bisect reset [<commit>]
23           git bisect (visualize|view)
24           git bisect replay <logfile>
25           git bisect log
26           git bisect run <cmd>...
27           git bisect help
28
29       This command uses a binary search algorithm to find which commit in
30       your project’s history introduced a bug. You use it by first telling it
31       a "bad" commit that is known to contain the bug, and a "good" commit
32       that is known to be before the bug was introduced. Then git bisect
33       picks a commit between those two endpoints and asks you whether the
34       selected commit is "good" or "bad". It continues narrowing down the
35       range until it finds the exact commit that introduced the change.
36
37       In fact, git bisect can be used to find the commit that changed any
38       property of your project; e.g., the commit that fixed a bug, or the
39       commit that caused a benchmark’s performance to improve. To support
40       this more general usage, the terms "old" and "new" can be used in place
41       of "good" and "bad", or you can choose your own terms. See section
42       "Alternate terms" below for more information.
43
44   Basic bisect commands: start, bad, good
45       As an example, suppose you are trying to find the commit that broke a
46       feature that was known to work in version v2.6.13-rc2 of your project.
47       You start a bisect session as follows:
48
49           $ git bisect start
50           $ git bisect bad                 # Current version is bad
51           $ git bisect good v2.6.13-rc2    # v2.6.13-rc2 is known to be good
52
53
54       Once you have specified at least one bad and one good commit, git
55       bisect selects a commit in the middle of that range of history, checks
56       it out, and outputs something similar to the following:
57
58           Bisecting: 675 revisions left to test after this (roughly 10 steps)
59
60
61       You should now compile the checked-out version and test it. If that
62       version works correctly, type
63
64           $ git bisect good
65
66
67       If that version is broken, type
68
69           $ git bisect bad
70
71
72       Then git bisect will respond with something like
73
74           Bisecting: 337 revisions left to test after this (roughly 9 steps)
75
76
77       Keep repeating the process: compile the tree, test it, and depending on
78       whether it is good or bad run git bisect good or git bisect bad to ask
79       for the next commit that needs testing.
80
81       Eventually there will be no more revisions left to inspect, and the
82       command will print out a description of the first bad commit. The
83       reference refs/bisect/bad will be left pointing at that commit.
84
85   Bisect reset
86       After a bisect session, to clean up the bisection state and return to
87       the original HEAD, issue the following command:
88
89           $ git bisect reset
90
91
92       By default, this will return your tree to the commit that was checked
93       out before git bisect start. (A new git bisect start will also do that,
94       as it cleans up the old bisection state.)
95
96       With an optional argument, you can return to a different commit
97       instead:
98
99           $ git bisect reset <commit>
100
101
102       For example, git bisect reset bisect/bad will check out the first bad
103       revision, while git bisect reset HEAD will leave you on the current
104       bisection commit and avoid switching commits at all.
105
106   Alternate terms
107       Sometimes you are not looking for the commit that introduced a
108       breakage, but rather for a commit that caused a change between some
109       other "old" state and "new" state. For example, you might be looking
110       for the commit that introduced a particular fix. Or you might be
111       looking for the first commit in which the source-code filenames were
112       finally all converted to your company’s naming standard. Or whatever.
113
114       In such cases it can be very confusing to use the terms "good" and
115       "bad" to refer to "the state before the change" and "the state after
116       the change". So instead, you can use the terms "old" and "new",
117       respectively, in place of "good" and "bad". (But note that you cannot
118       mix "good" and "bad" with "old" and "new" in a single session.)
119
120       In this more general usage, you provide git bisect with a "new" commit
121       that has some property and an "old" commit that doesn’t have that
122       property. Each time git bisect checks out a commit, you test if that
123       commit has the property. If it does, mark the commit as "new";
124       otherwise, mark it as "old". When the bisection is done, git bisect
125       will report which commit introduced the property.
126
127       To use "old" and "new" instead of "good" and bad, you must run git
128       bisect start without commits as argument and then run the following
129       commands to add the commits:
130
131           git bisect old [<rev>]
132
133
134       to indicate that a commit was before the sought change, or
135
136           git bisect new [<rev>...]
137
138
139       to indicate that it was after.
140
141       To get a reminder of the currently used terms, use
142
143           git bisect terms
144
145
146       You can get just the old (respectively new) term with git bisect terms
147       --term-old or git bisect terms --term-good.
148
149       If you would like to use your own terms instead of "bad"/"good" or
150       "new"/"old", you can choose any names you like (except existing bisect
151       subcommands like reset, start, ...) by starting the bisection using
152
153           git bisect start --term-old <term-old> --term-new <term-new>
154
155
156       For example, if you are looking for a commit that introduced a
157       performance regression, you might use
158
159           git bisect start --term-old fast --term-new slow
160
161
162       Or if you are looking for the commit that fixed a bug, you might use
163
164           git bisect start --term-new fixed --term-old broken
165
166
167       Then, use git bisect <term-old> and git bisect <term-new> instead of
168       git bisect good and git bisect bad to mark commits.
169
170   Bisect visualize/view
171       To see the currently remaining suspects in gitk, issue the following
172       command during the bisection process (the subcommand view can be used
173       as an alternative to visualize):
174
175           $ git bisect visualize
176
177
178       If the DISPLAY environment variable is not set, git log is used
179       instead. You can also give command-line options such as -p and --stat.
180
181           $ git bisect visualize --stat
182
183
184   Bisect log and bisect replay
185       After having marked revisions as good or bad, issue the following
186       command to show what has been done so far:
187
188           $ git bisect log
189
190
191       If you discover that you made a mistake in specifying the status of a
192       revision, you can save the output of this command to a file, edit it to
193       remove the incorrect entries, and then issue the following commands to
194       return to a corrected state:
195
196           $ git bisect reset
197           $ git bisect replay that-file
198
199
200   Avoiding testing a commit
201       If, in the middle of a bisect session, you know that the suggested
202       revision is not a good one to test (e.g. it fails to build and you know
203       that the failure does not have anything to do with the bug you are
204       chasing), you can manually select a nearby commit and test that one
205       instead.
206
207       For example:
208
209           $ git bisect good/bad                   # previous round was good or bad.
210           Bisecting: 337 revisions left to test after this (roughly 9 steps)
211           $ git bisect visualize                  # oops, that is uninteresting.
212           $ git reset --hard HEAD~3               # try 3 revisions before what
213                                                   # was suggested
214
215
216       Then compile and test the chosen revision, and afterwards mark the
217       revision as good or bad in the usual manner.
218
219   Bisect skip
220       Instead of choosing a nearby commit by yourself, you can ask Git to do
221       it for you by issuing the command:
222
223           $ git bisect skip                 # Current version cannot be tested
224
225
226       However, if you skip a commit adjacent to the one you are looking for,
227       Git will be unable to tell exactly which of those commits was the first
228       bad one.
229
230       You can also skip a range of commits, instead of just one commit, using
231       range notation. For example:
232
233           $ git bisect skip v2.5..v2.6
234
235
236       This tells the bisect process that no commit after v2.5, up to and
237       including v2.6, should be tested.
238
239       Note that if you also want to skip the first commit of the range you
240       would issue the command:
241
242           $ git bisect skip v2.5 v2.5..v2.6
243
244
245       This tells the bisect process that the commits between v2.5 and v2.6
246       (inclusive) should be skipped.
247
248   Cutting down bisection by giving more parameters to bisect start
249       You can further cut down the number of trials, if you know what part of
250       the tree is involved in the problem you are tracking down, by
251       specifying path parameters when issuing the bisect start command:
252
253           $ git bisect start -- arch/i386 include/asm-i386
254
255
256       If you know beforehand more than one good commit, you can narrow the
257       bisect space down by specifying all of the good commits immediately
258       after the bad commit when issuing the bisect start command:
259
260           $ git bisect start v2.6.20-rc6 v2.6.20-rc4 v2.6.20-rc1 --
261                              # v2.6.20-rc6 is bad
262                              # v2.6.20-rc4 and v2.6.20-rc1 are good
263
264
265   Bisect run
266       If you have a script that can tell if the current source code is good
267       or bad, you can bisect by issuing the command:
268
269           $ git bisect run my_script arguments
270
271
272       Note that the script (my_script in the above example) should exit with
273       code 0 if the current source code is good/old, and exit with a code
274       between 1 and 127 (inclusive), except 125, if the current source code
275       is bad/new.
276
277       Any other exit code will abort the bisect process. It should be noted
278       that a program that terminates via exit(-1) leaves $? = 255, (see the
279       exit(3) manual page), as the value is chopped with & 0377.
280
281       The special exit code 125 should be used when the current source code
282       cannot be tested. If the script exits with this code, the current
283       revision will be skipped (see git bisect skip above). 125 was chosen as
284       the highest sensible value to use for this purpose, because 126 and 127
285       are used by POSIX shells to signal specific error status (127 is for
286       command not found, 126 is for command found but not executable—these
287       details do not matter, as they are normal errors in the script, as far
288       as bisect run is concerned).
289
290       You may often find that during a bisect session you want to have
291       temporary modifications (e.g. s/#define DEBUG 0/#define DEBUG 1/ in a
292       header file, or "revision that does not have this commit needs this
293       patch applied to work around another problem this bisection is not
294       interested in") applied to the revision being tested.
295
296       To cope with such a situation, after the inner git bisect finds the
297       next revision to test, the script can apply the patch before compiling,
298       run the real test, and afterwards decide if the revision (possibly with
299       the needed patch) passed the test and then rewind the tree to the
300       pristine state. Finally the script should exit with the status of the
301       real test to let the git bisect run command loop determine the eventual
302       outcome of the bisect session.
303

OPTIONS

305       --no-checkout
306           Do not checkout the new working tree at each iteration of the
307           bisection process. Instead just update a special reference named
308           BISECT_HEAD to make it point to the commit that should be tested.
309
310           This option may be useful when the test you would perform in each
311           step does not require a checked out tree.
312
313           If the repository is bare, --no-checkout is assumed.
314

EXAMPLES

316       ·   Automatically bisect a broken build between v1.2 and HEAD:
317
318               $ git bisect start HEAD v1.2 --      # HEAD is bad, v1.2 is good
319               $ git bisect run make                # "make" builds the app
320               $ git bisect reset                   # quit the bisect session
321
322
323       ·   Automatically bisect a test failure between origin and HEAD:
324
325               $ git bisect start HEAD origin --    # HEAD is bad, origin is good
326               $ git bisect run make test           # "make test" builds and tests
327               $ git bisect reset                   # quit the bisect session
328
329
330       ·   Automatically bisect a broken test case:
331
332               $ cat ~/test.sh
333               #!/bin/sh
334               make || exit 125                     # this skips broken builds
335               ~/check_test_case.sh                 # does the test case pass?
336               $ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
337               $ git bisect run ~/test.sh
338               $ git bisect reset                   # quit the bisect session
339
340           Here we use a test.sh custom script. In this script, if make fails,
341           we skip the current commit.  check_test_case.sh should exit 0 if
342           the test case passes, and exit 1 otherwise.
343
344           It is safer if both test.sh and check_test_case.sh are outside the
345           repository to prevent interactions between the bisect, make and
346           test processes and the scripts.
347
348       ·   Automatically bisect with temporary modifications (hot-fix):
349
350               $ cat ~/test.sh
351               #!/bin/sh
352
353               # tweak the working tree by merging the hot-fix branch
354               # and then attempt a build
355               if      git merge --no-commit hot-fix &&
356                       make
357               then
358                       # run project specific test and report its status
359                       ~/check_test_case.sh
360                       status=$?
361               else
362                       # tell the caller this is untestable
363                       status=125
364               fi
365
366               # undo the tweak to allow clean flipping to the next commit
367               git reset --hard
368
369               # return control
370               exit $status
371
372           This applies modifications from a hot-fix branch before each test
373           run, e.g. in case your build or test environment changed so that
374           older revisions may need a fix which newer ones have already. (Make
375           sure the hot-fix branch is based off a commit which is contained in
376           all revisions which you are bisecting, so that the merge does not
377           pull in too much, or use git cherry-pick instead of git merge.)
378
379       ·   Automatically bisect a broken test case:
380
381               $ git bisect start HEAD HEAD~10 --   # culprit is among the last 10
382               $ git bisect run sh -c "make || exit 125; ~/check_test_case.sh"
383               $ git bisect reset                   # quit the bisect session
384
385           This shows that you can do without a run script if you write the
386           test on a single line.
387
388       ·   Locate a good region of the object graph in a damaged repository
389
390               $ git bisect start HEAD <known-good-commit> [ <boundary-commit> ... ] --no-checkout
391               $ git bisect run sh -c '
392                       GOOD=$(git for-each-ref "--format=%(objectname)" refs/bisect/good-*) &&
393                       git rev-list --objects BISECT_HEAD --not $GOOD >tmp.$$ &&
394                       git pack-objects --stdout >/dev/null <tmp.$$
395                       rc=$?
396                       rm -f tmp.$$
397                       test $rc = 0'
398
399               $ git bisect reset                   # quit the bisect session
400
401           In this case, when git bisect run finishes, bisect/bad will refer
402           to a commit that has at least one parent whose reachable graph is
403           fully traversable in the sense required by git pack objects.
404
405       ·   Look for a fix instead of a regression in the code
406
407               $ git bisect start
408               $ git bisect new HEAD    # current commit is marked as new
409               $ git bisect old HEAD~10 # the tenth commit from now is marked as old
410
411           or:
412
413           $ git bisect start --term-old broken --term-new fixed
414           $ git bisect fixed
415           $ git bisect broken HEAD~10
416
417
418   Getting help
419       Use git bisect to get a short usage description, and git bisect help or
420       git bisect -h to get a long usage description.
421

SEE ALSO

423       Fighting regressions with git bisect[1], git-blame(1).
424

GIT

426       Part of the git(1) suite
427

NOTES

429        1. Fighting regressions with git bisect
430           file:///usr/share/doc/git/git-bisect-lk2009.html
431
432
433
434Git 2.20.1                        12/15/2018                     GIT-BISECT(1)
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