Documentation/git-bisect.txt - jrn/git - Git at Google

 git-bisect(1)
 =============

 NAME
 ----
 git-bisect - Find the change that introduced a bug by binary search


 SYNOPSIS
 --------
 'git bisect' <subcommand> <options>

 DESCRIPTION
 -----------
 The command takes various subcommands, and different options depending
 on the subcommand:

  git bisect help
  git bisect start [<bad> [<good>...]] [--] [<paths>...]
  git bisect bad [<rev>]
  git bisect good [<rev>...]
  git bisect skip [<rev>...]
  git bisect reset [<branch>]
  git bisect visualize
  git bisect replay <logfile>
  git bisect log
  git bisect run <cmd>...

 This command uses 'git-rev-list --bisect' option 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.

 Getting help
 ~~~~~~~~~~~~

 Use "git bisect" to get a short usage description, and "git bisect
 help" or "git bisect -h" to get a long usage description.

 Basic bisect commands: start, bad, good
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 The way you use it is:

 ------------------------------------------------
 $ 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
 ------------------------------------------------

 When you give at least one bad and one good versions, it will bisect
 the revision tree and say something like:

 ------------------------------------------------
 Bisecting: 675 revisions left to test after this
 ------------------------------------------------

 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

 ------------------------------------------------
 $ git bisect good			# this one is good
 ------------------------------------------------

 which will now say

 ------------------------------------------------
 Bisecting: 337 revisions left to test after this
 ------------------------------------------------

 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.

 Until you have no more left, and you'll have been left with the first
 bad kernel rev in "refs/bisect/bad".

 Bisect reset
 ~~~~~~~~~~~~

 Oh, and then after you want to reset to the original head, do a

 ------------------------------------------------
 $ git bisect reset
 ------------------------------------------------

 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).

 Bisect visualize
 ~~~~~~~~~~~~~~~~

 During the bisection process, you can say

 ------------
 $ git bisect visualize
 ------------

 to see the currently remaining suspects in `gitk`.  `visualize` is a bit
 too long to type and `view` is provided as a synonym.

 If `DISPLAY` environment variable is not set, `git log` is used
 instead.  You can even give command line options such as `-p` and
 `--stat`.

 ------------
 $ git bisect view --stat
 ------------

 Bisect log and bisect replay
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 The good/bad input is logged, and

 ------------
 $ git bisect log
 ------------

 shows what you have done so far. You can truncate its output somewhere
 and save it in a file, and run

 ------------
 $ git bisect replay that-file
 ------------

 if you find later you made a mistake telling good/bad about a
 revision.

 Avoiding to test a commit
 ~~~~~~~~~~~~~~~~~~~~~~~~~

 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.

 It goes something like this:

 ------------
 $ 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
 ------------

 Then compile and test the one you chose to try. After that, tell
 bisect what the result was as usual.

 Bisect skip
 ~~~~~~~~~~~~

 Instead of choosing by yourself a nearby commit, you may just want git
 to do it for you using:

 ------------
 $ git bisect skip                 # Current version cannot be tested
 ------------

 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.

 Cutting down bisection by giving more parameters to bisect start
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

 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 `bisect start`, like this:

 ------------
 $ git bisect start -- arch/i386 include/asm-i386
 ------------

 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 `start`
 and then you give all the good revisions you have:

 ------------
 $ 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
 ------------

 Bisect run
 ~~~~~~~~~~

 If you have a script that can tell if the current source code is good
 or bad, you can automatically bisect using:

 ------------
 $ git bisect run my_script
 ------------

 Note that the "run" script (`my_script` 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.

 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 "& 0377".)

 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 `git bisect skip` above.

 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.

 To cope with such a situation, after the inner git-bisect 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 "git bisect run" command loop to
 know the outcome.

 EXAMPLES
 --------

 * Automatically bisect a broken build between v1.2 and HEAD:
 +
 ------------
 $ git bisect start HEAD v1.2 --      # HEAD is bad, v1.2 is good
 $ git bisect run make                # "make" builds the app
 ------------

 * Automatically bisect a broken test suite:
 +
 ------------
 $ 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
 ------------
 +
 Here we use a "test.sh" custom script. In this script, if "make"
 fails, we "skip" the current commit.
 +
 It's safer to use a custom script outside the repo to prevent
 interactions between the bisect, make and test processes and the
 script.
 +
 And "make test" should "exit 0", if the test suite passes, and
 "exit 1" (for example) otherwise.

 * Automatically bisect a broken test case:
 +
 ------------
 $ 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
 ------------
 +
 Here "check_test_case.sh" should "exit 0", if the test case passes,
 and "exit 1" (for example) otherwise.
 +
 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.

 Author
 ------
 Written by Linus Torvalds <torvalds@osdl.org>

 Documentation
 -------------
 Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

 GIT
 ---
 Part of the linkgit:git[1] suite
	git-bisect(1)
	=============

	NAME
	----
	git-bisect - Find the change that introduced a bug by binary search


	SYNOPSIS
	--------
	'git bisect' <subcommand> <options>

	DESCRIPTION
	-----------
	The command takes various subcommands, and different options depending
	on the subcommand:

	git bisect help
	git bisect start [<bad> [<good>...]] [--] [<paths>...]
	git bisect bad [<rev>]
	git bisect good [<rev>...]
	git bisect skip [<rev>...]
	git bisect reset [<branch>]
	git bisect visualize
	git bisect replay <logfile>
	git bisect log
	git bisect run <cmd>...

	This command uses 'git-rev-list --bisect' option 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.

	Getting help
	~~~~~~~~~~~~

	Use "git bisect" to get a short usage description, and "git bisect
	help" or "git bisect -h" to get a long usage description.

	Basic bisect commands: start, bad, good
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	The way you use it is:

	------------------------------------------------
	$ 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
	------------------------------------------------

	When you give at least one bad and one good versions, it will bisect
	the revision tree and say something like:

	------------------------------------------------
	Bisecting: 675 revisions left to test after this
	------------------------------------------------

	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

	------------------------------------------------
	$ git bisect good # this one is good
	------------------------------------------------

	which will now say

	------------------------------------------------
	Bisecting: 337 revisions left to test after this
	------------------------------------------------

	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.

	Until you have no more left, and you'll have been left with the first
	bad kernel rev in "refs/bisect/bad".

	Bisect reset
	~~~~~~~~~~~~

	Oh, and then after you want to reset to the original head, do a

	------------------------------------------------
	$ git bisect reset
	------------------------------------------------

	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).

	Bisect visualize
	~~~~~~~~~~~~~~~~

	During the bisection process, you can say

	------------
	$ git bisect visualize
	------------

	to see the currently remaining suspects in `gitk`. `visualize` is a bit
	too long to type and `view` is provided as a synonym.

	If `DISPLAY` environment variable is not set, `git log` is used
	instead. You can even give command line options such as `-p` and
	`--stat`.

	------------
	$ git bisect view --stat
	------------

	Bisect log and bisect replay
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	The good/bad input is logged, and

	------------
	$ git bisect log
	------------

	shows what you have done so far. You can truncate its output somewhere
	and save it in a file, and run

	------------
	$ git bisect replay that-file
	------------

	if you find later you made a mistake telling good/bad about a
	revision.

	Avoiding to test a commit
	~~~~~~~~~~~~~~~~~~~~~~~~~

	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.

	It goes something like this:

	------------
	$ 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
	------------

	Then compile and test the one you chose to try. After that, tell
	bisect what the result was as usual.

	Bisect skip
	~~~~~~~~~~~~

	Instead of choosing by yourself a nearby commit, you may just want git
	to do it for you using:

	------------
	$ git bisect skip # Current version cannot be tested
	------------

	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.

	Cutting down bisection by giving more parameters to bisect start
	~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

	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 `bisect start`, like this:

	------------
	$ git bisect start -- arch/i386 include/asm-i386
	------------

	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 `start`
	and then you give all the good revisions you have:

	------------
	$ 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
	------------

	Bisect run
	~~~~~~~~~~

	If you have a script that can tell if the current source code is good
	or bad, you can automatically bisect using:

	------------
	$ git bisect run my_script
	------------

	Note that the "run" script (`my_script` 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.

	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 "& 0377".)

	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 `git bisect skip` above.

	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.

	To cope with such a situation, after the inner git-bisect 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 "git bisect run" command loop to
	know the outcome.

	EXAMPLES
	--------

	* Automatically bisect a broken build between v1.2 and HEAD:
	+
	------------
	$ git bisect start HEAD v1.2 -- # HEAD is bad, v1.2 is good
	$ git bisect run make # "make" builds the app
	------------

	* Automatically bisect a broken test suite:
	+
	------------
	$ 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
	------------
	+
	Here we use a "test.sh" custom script. In this script, if "make"
	fails, we "skip" the current commit.
	+
	It's safer to use a custom script outside the repo to prevent
	interactions between the bisect, make and test processes and the
	script.
	+
	And "make test" should "exit 0", if the test suite passes, and
	"exit 1" (for example) otherwise.

	* Automatically bisect a broken test case:
	+
	------------
	$ 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
	------------
	+
	Here "check_test_case.sh" should "exit 0", if the test case passes,
	and "exit 1" (for example) otherwise.
	+
	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.

	Author
	------
	Written by Linus Torvalds <torvalds@osdl.org>

	Documentation
	-------------
	Documentation by Junio C Hamano and the git-list <git@vger.kernel.org>.

	GIT
	---
	Part of the linkgit:git[1] suite