NAME
----
-git-bisect - Find the change that introduced a bug
+git-bisect - Find the change that introduced a bug by binary search
SYNOPSIS
--------
-'git bisect' start
-'git bisect' bad <rev>
-'git bisect' good <rev>
-'git bisect' reset [<branch>]
-'git bisect' visualize
-'git bisect' replay <logfile>
-'git bisect' log
+'git bisect' <subcommand> <options>
DESCRIPTION
-----------
+The command takes various subcommands, and different options
+depending on the subcommand:
+
+ git bisect start [<paths>...]
+ git bisect bad <rev>
+ git bisect good <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
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
+$ 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
it. Now, let's say that this booted kernel works fine, then just do
------------------------------------------------
-git bisect good # this one is good
+$ git bisect good # this one is good
------------------------------------------------
which will now say
Oh, and then after you want to reset to the original head, do a
------------------------------------------------
-git bisect reset
+$ git bisect reset
------------------------------------------------
to get back to the master branch, instead of being in one of the bisection
During the bisection process, you can say
- git bisect visualize
+------------
+$ git bisect visualize
+------------
to see the currently remaining suspects in `gitk`.
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
+------------
+$ git bisect replay that-file
+------------
if you find later you made a mistake telling good/bad about a
revision.
+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.
+
+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 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 and with a code between 1 and 127
+(included) in case the current source code is bad.
+
+Any other exit code (a program that does "exit(-1)" leaves $? = 255,
+see exit(3) manual page, the value is chopped with "& 0377") will
+abort the automatic bisect process.
+
+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.
Author
------