GIT 1.5.3.6
[git/git.git] / Documentation / user-manual.txt
1 Git User's Manual (for version 1.5.3 or newer)
2 ______________________________________________
3
4
5 Git is a fast distributed revision control system.
6
7 This manual is designed to be readable by someone with basic UNIX
8 command-line skills, but no previous knowledge of git.
9
10 <<repositories-and-branches>> and <<exploring-git-history>> explain how
11 to fetch and study a project using git--read these chapters to learn how
12 to build and test a particular version of a software project, search for
13 regressions, and so on.
14
15 People needing to do actual development will also want to read
16 <<Developing-with-git>> and <<sharing-development>>.
17
18 Further chapters cover more specialized topics.
19
20 Comprehensive reference documentation is available through the man
21 pages. For a command such as "git clone", just use
22
23 ------------------------------------------------
24 $ man git-clone
25 ------------------------------------------------
26
27 See also <<git-quick-start>> for a brief overview of git commands,
28 without any explanation.
29
30 Finally, see <<todo>> for ways that you can help make this manual more
31 complete.
32
33
34 [[repositories-and-branches]]
35 Repositories and Branches
36 =========================
37
38 [[how-to-get-a-git-repository]]
39 How to get a git repository
40 ---------------------------
41
42 It will be useful to have a git repository to experiment with as you
43 read this manual.
44
45 The best way to get one is by using the gitlink:git-clone[1] command to
46 download a copy of an existing repository. If you don't already have a
47 project in mind, here are some interesting examples:
48
49 ------------------------------------------------
50 # git itself (approx. 10MB download):
51 $ git clone git://git.kernel.org/pub/scm/git/git.git
52 # the linux kernel (approx. 150MB download):
53 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
54 ------------------------------------------------
55
56 The initial clone may be time-consuming for a large project, but you
57 will only need to clone once.
58
59 The clone command creates a new directory named after the project
60 ("git" or "linux-2.6" in the examples above). After you cd into this
61 directory, you will see that it contains a copy of the project files,
62 together with a special top-level directory named ".git", which
63 contains all the information about the history of the project.
64
65 [[how-to-check-out]]
66 How to check out a different version of a project
67 -------------------------------------------------
68
69 Git is best thought of as a tool for storing the history of a collection
70 of files. It stores the history as a compressed collection of
71 interrelated snapshots of the project's contents. In git each such
72 version is called a <<def_commit,commit>>.
73
74 A single git repository may contain multiple branches. It keeps track
75 of them by keeping a list of <<def_head,heads>> which reference the
76 latest commit on each branch; the gitlink:git-branch[1] command shows
77 you the list of branch heads:
78
79 ------------------------------------------------
80 $ git branch
81 * master
82 ------------------------------------------------
83
84 A freshly cloned repository contains a single branch head, by default
85 named "master", with the working directory initialized to the state of
86 the project referred to by that branch head.
87
88 Most projects also use <<def_tag,tags>>. Tags, like heads, are
89 references into the project's history, and can be listed using the
90 gitlink:git-tag[1] command:
91
92 ------------------------------------------------
93 $ git tag -l
94 v2.6.11
95 v2.6.11-tree
96 v2.6.12
97 v2.6.12-rc2
98 v2.6.12-rc3
99 v2.6.12-rc4
100 v2.6.12-rc5
101 v2.6.12-rc6
102 v2.6.13
103 ...
104 ------------------------------------------------
105
106 Tags are expected to always point at the same version of a project,
107 while heads are expected to advance as development progresses.
108
109 Create a new branch head pointing to one of these versions and check it
110 out using gitlink:git-checkout[1]:
111
112 ------------------------------------------------
113 $ git checkout -b new v2.6.13
114 ------------------------------------------------
115
116 The working directory then reflects the contents that the project had
117 when it was tagged v2.6.13, and gitlink:git-branch[1] shows two
118 branches, with an asterisk marking the currently checked-out branch:
119
120 ------------------------------------------------
121 $ git branch
122 master
123 * new
124 ------------------------------------------------
125
126 If you decide that you'd rather see version 2.6.17, you can modify
127 the current branch to point at v2.6.17 instead, with
128
129 ------------------------------------------------
130 $ git reset --hard v2.6.17
131 ------------------------------------------------
132
133 Note that if the current branch head was your only reference to a
134 particular point in history, then resetting that branch may leave you
135 with no way to find the history it used to point to; so use this command
136 carefully.
137
138 [[understanding-commits]]
139 Understanding History: Commits
140 ------------------------------
141
142 Every change in the history of a project is represented by a commit.
143 The gitlink:git-show[1] command shows the most recent commit on the
144 current branch:
145
146 ------------------------------------------------
147 $ git show
148 commit 17cf781661e6d38f737f15f53ab552f1e95960d7
149 Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)>
150 Date: Tue Apr 19 14:11:06 2005 -0700
151
152 Remove duplicate getenv(DB_ENVIRONMENT) call
153
154 Noted by Tony Luck.
155
156 diff --git a/init-db.c b/init-db.c
157 index 65898fa..b002dc6 100644
158 --- a/init-db.c
159 +++ b/init-db.c
160 @@ -7,7 +7,7 @@
161
162 int main(int argc, char **argv)
163 {
164 - char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
165 + char *sha1_dir, *path;
166 int len, i;
167
168 if (mkdir(".git", 0755) < 0) {
169 ------------------------------------------------
170
171 As you can see, a commit shows who made the latest change, what they
172 did, and why.
173
174 Every commit has a 40-hexdigit id, sometimes called the "object name" or the
175 "SHA1 id", shown on the first line of the "git show" output. You can usually
176 refer to a commit by a shorter name, such as a tag or a branch name, but this
177 longer name can also be useful. Most importantly, it is a globally unique
178 name for this commit: so if you tell somebody else the object name (for
179 example in email), then you are guaranteed that name will refer to the same
180 commit in their repository that it does in yours (assuming their repository
181 has that commit at all). Since the object name is computed as a hash over the
182 contents of the commit, you are guaranteed that the commit can never change
183 without its name also changing.
184
185 In fact, in <<git-concepts>> we shall see that everything stored in git
186 history, including file data and directory contents, is stored in an object
187 with a name that is a hash of its contents.
188
189 [[understanding-reachability]]
190 Understanding history: commits, parents, and reachability
191 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
192
193 Every commit (except the very first commit in a project) also has a
194 parent commit which shows what happened before this commit.
195 Following the chain of parents will eventually take you back to the
196 beginning of the project.
197
198 However, the commits do not form a simple list; git allows lines of
199 development to diverge and then reconverge, and the point where two
200 lines of development reconverge is called a "merge". The commit
201 representing a merge can therefore have more than one parent, with
202 each parent representing the most recent commit on one of the lines
203 of development leading to that point.
204
205 The best way to see how this works is using the gitlink:gitk[1]
206 command; running gitk now on a git repository and looking for merge
207 commits will help understand how the git organizes history.
208
209 In the following, we say that commit X is "reachable" from commit Y
210 if commit X is an ancestor of commit Y. Equivalently, you could say
211 that Y is a descendant of X, or that there is a chain of parents
212 leading from commit Y to commit X.
213
214 [[history-diagrams]]
215 Understanding history: History diagrams
216 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
217
218 We will sometimes represent git history using diagrams like the one
219 below. Commits are shown as "o", and the links between them with
220 lines drawn with - / and \. Time goes left to right:
221
222
223 ................................................
224 o--o--o <-- Branch A
225 /
226 o--o--o <-- master
227 \
228 o--o--o <-- Branch B
229 ................................................
230
231 If we need to talk about a particular commit, the character "o" may
232 be replaced with another letter or number.
233
234 [[what-is-a-branch]]
235 Understanding history: What is a branch?
236 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
237
238 When we need to be precise, we will use the word "branch" to mean a line
239 of development, and "branch head" (or just "head") to mean a reference
240 to the most recent commit on a branch. In the example above, the branch
241 head named "A" is a pointer to one particular commit, but we refer to
242 the line of three commits leading up to that point as all being part of
243 "branch A".
244
245 However, when no confusion will result, we often just use the term
246 "branch" both for branches and for branch heads.
247
248 [[manipulating-branches]]
249 Manipulating branches
250 ---------------------
251
252 Creating, deleting, and modifying branches is quick and easy; here's
253 a summary of the commands:
254
255 git branch::
256 list all branches
257 git branch <branch>::
258 create a new branch named <branch>, referencing the same
259 point in history as the current branch
260 git branch <branch> <start-point>::
261 create a new branch named <branch>, referencing
262 <start-point>, which may be specified any way you like,
263 including using a branch name or a tag name
264 git branch -d <branch>::
265 delete the branch <branch>; if the branch you are deleting
266 points to a commit which is not reachable from the current
267 branch, this command will fail with a warning.
268 git branch -D <branch>::
269 even if the branch points to a commit not reachable
270 from the current branch, you may know that that commit
271 is still reachable from some other branch or tag. In that
272 case it is safe to use this command to force git to delete
273 the branch.
274 git checkout <branch>::
275 make the current branch <branch>, updating the working
276 directory to reflect the version referenced by <branch>
277 git checkout -b <new> <start-point>::
278 create a new branch <new> referencing <start-point>, and
279 check it out.
280
281 The special symbol "HEAD" can always be used to refer to the current
282 branch. In fact, git uses a file named "HEAD" in the .git directory to
283 remember which branch is current:
284
285 ------------------------------------------------
286 $ cat .git/HEAD
287 ref: refs/heads/master
288 ------------------------------------------------
289
290 [[detached-head]]
291 Examining an old version without creating a new branch
292 ------------------------------------------------------
293
294 The git-checkout command normally expects a branch head, but will also
295 accept an arbitrary commit; for example, you can check out the commit
296 referenced by a tag:
297
298 ------------------------------------------------
299 $ git checkout v2.6.17
300 Note: moving to "v2.6.17" which isn't a local branch
301 If you want to create a new branch from this checkout, you may do so
302 (now or later) by using -b with the checkout command again. Example:
303 git checkout -b <new_branch_name>
304 HEAD is now at 427abfa... Linux v2.6.17
305 ------------------------------------------------
306
307 The HEAD then refers to the SHA1 of the commit instead of to a branch,
308 and git branch shows that you are no longer on a branch:
309
310 ------------------------------------------------
311 $ cat .git/HEAD
312 427abfa28afedffadfca9dd8b067eb6d36bac53f
313 $ git branch
314 * (no branch)
315 master
316 ------------------------------------------------
317
318 In this case we say that the HEAD is "detached".
319
320 This is an easy way to check out a particular version without having to
321 make up a name for the new branch. You can still create a new branch
322 (or tag) for this version later if you decide to.
323
324 [[examining-remote-branches]]
325 Examining branches from a remote repository
326 -------------------------------------------
327
328 The "master" branch that was created at the time you cloned is a copy
329 of the HEAD in the repository that you cloned from. That repository
330 may also have had other branches, though, and your local repository
331 keeps branches which track each of those remote branches, which you
332 can view using the "-r" option to gitlink:git-branch[1]:
333
334 ------------------------------------------------
335 $ git branch -r
336 origin/HEAD
337 origin/html
338 origin/maint
339 origin/man
340 origin/master
341 origin/next
342 origin/pu
343 origin/todo
344 ------------------------------------------------
345
346 You cannot check out these remote-tracking branches, but you can
347 examine them on a branch of your own, just as you would a tag:
348
349 ------------------------------------------------
350 $ git checkout -b my-todo-copy origin/todo
351 ------------------------------------------------
352
353 Note that the name "origin" is just the name that git uses by default
354 to refer to the repository that you cloned from.
355
356 [[how-git-stores-references]]
357 Naming branches, tags, and other references
358 -------------------------------------------
359
360 Branches, remote-tracking branches, and tags are all references to
361 commits. All references are named with a slash-separated path name
362 starting with "refs"; the names we've been using so far are actually
363 shorthand:
364
365 - The branch "test" is short for "refs/heads/test".
366 - The tag "v2.6.18" is short for "refs/tags/v2.6.18".
367 - "origin/master" is short for "refs/remotes/origin/master".
368
369 The full name is occasionally useful if, for example, there ever
370 exists a tag and a branch with the same name.
371
372 (Newly created refs are actually stored in the .git/refs directory,
373 under the path given by their name. However, for efficiency reasons
374 they may also be packed together in a single file; see
375 gitlink:git-pack-refs[1]).
376
377 As another useful shortcut, the "HEAD" of a repository can be referred
378 to just using the name of that repository. So, for example, "origin"
379 is usually a shortcut for the HEAD branch in the repository "origin".
380
381 For the complete list of paths which git checks for references, and
382 the order it uses to decide which to choose when there are multiple
383 references with the same shorthand name, see the "SPECIFYING
384 REVISIONS" section of gitlink:git-rev-parse[1].
385
386 [[Updating-a-repository-with-git-fetch]]
387 Updating a repository with git fetch
388 ------------------------------------
389
390 Eventually the developer cloned from will do additional work in her
391 repository, creating new commits and advancing the branches to point
392 at the new commits.
393
394 The command "git fetch", with no arguments, will update all of the
395 remote-tracking branches to the latest version found in her
396 repository. It will not touch any of your own branches--not even the
397 "master" branch that was created for you on clone.
398
399 [[fetching-branches]]
400 Fetching branches from other repositories
401 -----------------------------------------
402
403 You can also track branches from repositories other than the one you
404 cloned from, using gitlink:git-remote[1]:
405
406 -------------------------------------------------
407 $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
408 $ git fetch linux-nfs
409 * refs/remotes/linux-nfs/master: storing branch 'master' ...
410 commit: bf81b46
411 -------------------------------------------------
412
413 New remote-tracking branches will be stored under the shorthand name
414 that you gave "git remote add", in this case linux-nfs:
415
416 -------------------------------------------------
417 $ git branch -r
418 linux-nfs/master
419 origin/master
420 -------------------------------------------------
421
422 If you run "git fetch <remote>" later, the tracking branches for the
423 named <remote> will be updated.
424
425 If you examine the file .git/config, you will see that git has added
426 a new stanza:
427
428 -------------------------------------------------
429 $ cat .git/config
430 ...
431 [remote "linux-nfs"]
432 url = git://linux-nfs.org/pub/nfs-2.6.git
433 fetch = +refs/heads/*:refs/remotes/linux-nfs/*
434 ...
435 -------------------------------------------------
436
437 This is what causes git to track the remote's branches; you may modify
438 or delete these configuration options by editing .git/config with a
439 text editor. (See the "CONFIGURATION FILE" section of
440 gitlink:git-config[1] for details.)
441
442 [[exploring-git-history]]
443 Exploring git history
444 =====================
445
446 Git is best thought of as a tool for storing the history of a
447 collection of files. It does this by storing compressed snapshots of
448 the contents of a file hierarchy, together with "commits" which show
449 the relationships between these snapshots.
450
451 Git provides extremely flexible and fast tools for exploring the
452 history of a project.
453
454 We start with one specialized tool that is useful for finding the
455 commit that introduced a bug into a project.
456
457 [[using-bisect]]
458 How to use bisect to find a regression
459 --------------------------------------
460
461 Suppose version 2.6.18 of your project worked, but the version at
462 "master" crashes. Sometimes the best way to find the cause of such a
463 regression is to perform a brute-force search through the project's
464 history to find the particular commit that caused the problem. The
465 gitlink:git-bisect[1] command can help you do this:
466
467 -------------------------------------------------
468 $ git bisect start
469 $ git bisect good v2.6.18
470 $ git bisect bad master
471 Bisecting: 3537 revisions left to test after this
472 [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
473 -------------------------------------------------
474
475 If you run "git branch" at this point, you'll see that git has
476 temporarily moved you to a new branch named "bisect". This branch
477 points to a commit (with commit id 65934...) that is reachable from
478 v2.6.19 but not from v2.6.18. Compile and test it, and see whether
479 it crashes. Assume it does crash. Then:
480
481 -------------------------------------------------
482 $ git bisect bad
483 Bisecting: 1769 revisions left to test after this
484 [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
485 -------------------------------------------------
486
487 checks out an older version. Continue like this, telling git at each
488 stage whether the version it gives you is good or bad, and notice
489 that the number of revisions left to test is cut approximately in
490 half each time.
491
492 After about 13 tests (in this case), it will output the commit id of
493 the guilty commit. You can then examine the commit with
494 gitlink:git-show[1], find out who wrote it, and mail them your bug
495 report with the commit id. Finally, run
496
497 -------------------------------------------------
498 $ git bisect reset
499 -------------------------------------------------
500
501 to return you to the branch you were on before and delete the
502 temporary "bisect" branch.
503
504 Note that the version which git-bisect checks out for you at each
505 point is just a suggestion, and you're free to try a different
506 version if you think it would be a good idea. For example,
507 occasionally you may land on a commit that broke something unrelated;
508 run
509
510 -------------------------------------------------
511 $ git bisect visualize
512 -------------------------------------------------
513
514 which will run gitk and label the commit it chose with a marker that
515 says "bisect". Chose a safe-looking commit nearby, note its commit
516 id, and check it out with:
517
518 -------------------------------------------------
519 $ git reset --hard fb47ddb2db...
520 -------------------------------------------------
521
522 then test, run "bisect good" or "bisect bad" as appropriate, and
523 continue.
524
525 [[naming-commits]]
526 Naming commits
527 --------------
528
529 We have seen several ways of naming commits already:
530
531 - 40-hexdigit object name
532 - branch name: refers to the commit at the head of the given
533 branch
534 - tag name: refers to the commit pointed to by the given tag
535 (we've seen branches and tags are special cases of
536 <<how-git-stores-references,references>>).
537 - HEAD: refers to the head of the current branch
538
539 There are many more; see the "SPECIFYING REVISIONS" section of the
540 gitlink:git-rev-parse[1] man page for the complete list of ways to
541 name revisions. Some examples:
542
543 -------------------------------------------------
544 $ git show fb47ddb2 # the first few characters of the object name
545 # are usually enough to specify it uniquely
546 $ git show HEAD^ # the parent of the HEAD commit
547 $ git show HEAD^^ # the grandparent
548 $ git show HEAD~4 # the great-great-grandparent
549 -------------------------------------------------
550
551 Recall that merge commits may have more than one parent; by default,
552 ^ and ~ follow the first parent listed in the commit, but you can
553 also choose:
554
555 -------------------------------------------------
556 $ git show HEAD^1 # show the first parent of HEAD
557 $ git show HEAD^2 # show the second parent of HEAD
558 -------------------------------------------------
559
560 In addition to HEAD, there are several other special names for
561 commits:
562
563 Merges (to be discussed later), as well as operations such as
564 git-reset, which change the currently checked-out commit, generally
565 set ORIG_HEAD to the value HEAD had before the current operation.
566
567 The git-fetch operation always stores the head of the last fetched
568 branch in FETCH_HEAD. For example, if you run git fetch without
569 specifying a local branch as the target of the operation
570
571 -------------------------------------------------
572 $ git fetch git://example.com/proj.git theirbranch
573 -------------------------------------------------
574
575 the fetched commits will still be available from FETCH_HEAD.
576
577 When we discuss merges we'll also see the special name MERGE_HEAD,
578 which refers to the other branch that we're merging in to the current
579 branch.
580
581 The gitlink:git-rev-parse[1] command is a low-level command that is
582 occasionally useful for translating some name for a commit to the object
583 name for that commit:
584
585 -------------------------------------------------
586 $ git rev-parse origin
587 e05db0fd4f31dde7005f075a84f96b360d05984b
588 -------------------------------------------------
589
590 [[creating-tags]]
591 Creating tags
592 -------------
593
594 We can also create a tag to refer to a particular commit; after
595 running
596
597 -------------------------------------------------
598 $ git tag stable-1 1b2e1d63ff
599 -------------------------------------------------
600
601 You can use stable-1 to refer to the commit 1b2e1d63ff.
602
603 This creates a "lightweight" tag. If you would also like to include a
604 comment with the tag, and possibly sign it cryptographically, then you
605 should create a tag object instead; see the gitlink:git-tag[1] man page
606 for details.
607
608 [[browsing-revisions]]
609 Browsing revisions
610 ------------------
611
612 The gitlink:git-log[1] command can show lists of commits. On its
613 own, it shows all commits reachable from the parent commit; but you
614 can also make more specific requests:
615
616 -------------------------------------------------
617 $ git log v2.5.. # commits since (not reachable from) v2.5
618 $ git log test..master # commits reachable from master but not test
619 $ git log master..test # ...reachable from test but not master
620 $ git log master...test # ...reachable from either test or master,
621 # but not both
622 $ git log --since="2 weeks ago" # commits from the last 2 weeks
623 $ git log Makefile # commits which modify Makefile
624 $ git log fs/ # ... which modify any file under fs/
625 $ git log -S'foo()' # commits which add or remove any file data
626 # matching the string 'foo()'
627 -------------------------------------------------
628
629 And of course you can combine all of these; the following finds
630 commits since v2.5 which touch the Makefile or any file under fs:
631
632 -------------------------------------------------
633 $ git log v2.5.. Makefile fs/
634 -------------------------------------------------
635
636 You can also ask git log to show patches:
637
638 -------------------------------------------------
639 $ git log -p
640 -------------------------------------------------
641
642 See the "--pretty" option in the gitlink:git-log[1] man page for more
643 display options.
644
645 Note that git log starts with the most recent commit and works
646 backwards through the parents; however, since git history can contain
647 multiple independent lines of development, the particular order that
648 commits are listed in may be somewhat arbitrary.
649
650 [[generating-diffs]]
651 Generating diffs
652 ----------------
653
654 You can generate diffs between any two versions using
655 gitlink:git-diff[1]:
656
657 -------------------------------------------------
658 $ git diff master..test
659 -------------------------------------------------
660
661 Sometimes what you want instead is a set of patches:
662
663 -------------------------------------------------
664 $ git format-patch master..test
665 -------------------------------------------------
666
667 will generate a file with a patch for each commit reachable from test
668 but not from master. Note that if master also has commits which are
669 not reachable from test, then the combined result of these patches
670 will not be the same as the diff produced by the git-diff example.
671
672 [[viewing-old-file-versions]]
673 Viewing old file versions
674 -------------------------
675
676 You can always view an old version of a file by just checking out the
677 correct revision first. But sometimes it is more convenient to be
678 able to view an old version of a single file without checking
679 anything out; this command does that:
680
681 -------------------------------------------------
682 $ git show v2.5:fs/locks.c
683 -------------------------------------------------
684
685 Before the colon may be anything that names a commit, and after it
686 may be any path to a file tracked by git.
687
688 [[history-examples]]
689 Examples
690 --------
691
692 [[counting-commits-on-a-branch]]
693 Counting the number of commits on a branch
694 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
695
696 Suppose you want to know how many commits you've made on "mybranch"
697 since it diverged from "origin":
698
699 -------------------------------------------------
700 $ git log --pretty=oneline origin..mybranch | wc -l
701 -------------------------------------------------
702
703 Alternatively, you may often see this sort of thing done with the
704 lower-level command gitlink:git-rev-list[1], which just lists the SHA1's
705 of all the given commits:
706
707 -------------------------------------------------
708 $ git rev-list origin..mybranch | wc -l
709 -------------------------------------------------
710
711 [[checking-for-equal-branches]]
712 Check whether two branches point at the same history
713 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
714
715 Suppose you want to check whether two branches point at the same point
716 in history.
717
718 -------------------------------------------------
719 $ git diff origin..master
720 -------------------------------------------------
721
722 will tell you whether the contents of the project are the same at the
723 two branches; in theory, however, it's possible that the same project
724 contents could have been arrived at by two different historical
725 routes. You could compare the object names:
726
727 -------------------------------------------------
728 $ git rev-list origin
729 e05db0fd4f31dde7005f075a84f96b360d05984b
730 $ git rev-list master
731 e05db0fd4f31dde7005f075a84f96b360d05984b
732 -------------------------------------------------
733
734 Or you could recall that the ... operator selects all commits
735 contained reachable from either one reference or the other but not
736 both: so
737
738 -------------------------------------------------
739 $ git log origin...master
740 -------------------------------------------------
741
742 will return no commits when the two branches are equal.
743
744 [[finding-tagged-descendants]]
745 Find first tagged version including a given fix
746 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
747
748 Suppose you know that the commit e05db0fd fixed a certain problem.
749 You'd like to find the earliest tagged release that contains that
750 fix.
751
752 Of course, there may be more than one answer--if the history branched
753 after commit e05db0fd, then there could be multiple "earliest" tagged
754 releases.
755
756 You could just visually inspect the commits since e05db0fd:
757
758 -------------------------------------------------
759 $ gitk e05db0fd..
760 -------------------------------------------------
761
762 Or you can use gitlink:git-name-rev[1], which will give the commit a
763 name based on any tag it finds pointing to one of the commit's
764 descendants:
765
766 -------------------------------------------------
767 $ git name-rev --tags e05db0fd
768 e05db0fd tags/v1.5.0-rc1^0~23
769 -------------------------------------------------
770
771 The gitlink:git-describe[1] command does the opposite, naming the
772 revision using a tag on which the given commit is based:
773
774 -------------------------------------------------
775 $ git describe e05db0fd
776 v1.5.0-rc0-260-ge05db0f
777 -------------------------------------------------
778
779 but that may sometimes help you guess which tags might come after the
780 given commit.
781
782 If you just want to verify whether a given tagged version contains a
783 given commit, you could use gitlink:git-merge-base[1]:
784
785 -------------------------------------------------
786 $ git merge-base e05db0fd v1.5.0-rc1
787 e05db0fd4f31dde7005f075a84f96b360d05984b
788 -------------------------------------------------
789
790 The merge-base command finds a common ancestor of the given commits,
791 and always returns one or the other in the case where one is a
792 descendant of the other; so the above output shows that e05db0fd
793 actually is an ancestor of v1.5.0-rc1.
794
795 Alternatively, note that
796
797 -------------------------------------------------
798 $ git log v1.5.0-rc1..e05db0fd
799 -------------------------------------------------
800
801 will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
802 because it outputs only commits that are not reachable from v1.5.0-rc1.
803
804 As yet another alternative, the gitlink:git-show-branch[1] command lists
805 the commits reachable from its arguments with a display on the left-hand
806 side that indicates which arguments that commit is reachable from. So,
807 you can run something like
808
809 -------------------------------------------------
810 $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
811 ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
812 available
813 ! [v1.5.0-rc0] GIT v1.5.0 preview
814 ! [v1.5.0-rc1] GIT v1.5.0-rc1
815 ! [v1.5.0-rc2] GIT v1.5.0-rc2
816 ...
817 -------------------------------------------------
818
819 then search for a line that looks like
820
821 -------------------------------------------------
822 + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
823 available
824 -------------------------------------------------
825
826 Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
827 from v1.5.0-rc2, but not from v1.5.0-rc0.
828
829 [[showing-commits-unique-to-a-branch]]
830 Showing commits unique to a given branch
831 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
832
833 Suppose you would like to see all the commits reachable from the branch
834 head named "master" but not from any other head in your repository.
835
836 We can list all the heads in this repository with
837 gitlink:git-show-ref[1]:
838
839 -------------------------------------------------
840 $ git show-ref --heads
841 bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
842 db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
843 a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
844 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
845 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
846 -------------------------------------------------
847
848 We can get just the branch-head names, and remove "master", with
849 the help of the standard utilities cut and grep:
850
851 -------------------------------------------------
852 $ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
853 refs/heads/core-tutorial
854 refs/heads/maint
855 refs/heads/tutorial-2
856 refs/heads/tutorial-fixes
857 -------------------------------------------------
858
859 And then we can ask to see all the commits reachable from master
860 but not from these other heads:
861
862 -------------------------------------------------
863 $ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
864 grep -v '^refs/heads/master' )
865 -------------------------------------------------
866
867 Obviously, endless variations are possible; for example, to see all
868 commits reachable from some head but not from any tag in the repository:
869
870 -------------------------------------------------
871 $ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
872 -------------------------------------------------
873
874 (See gitlink:git-rev-parse[1] for explanations of commit-selecting
875 syntax such as `--not`.)
876
877 [[making-a-release]]
878 Creating a changelog and tarball for a software release
879 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
880
881 The gitlink:git-archive[1] command can create a tar or zip archive from
882 any version of a project; for example:
883
884 -------------------------------------------------
885 $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
886 -------------------------------------------------
887
888 will use HEAD to produce a tar archive in which each filename is
889 preceded by "project/".
890
891 If you're releasing a new version of a software project, you may want
892 to simultaneously make a changelog to include in the release
893 announcement.
894
895 Linus Torvalds, for example, makes new kernel releases by tagging them,
896 then running:
897
898 -------------------------------------------------
899 $ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
900 -------------------------------------------------
901
902 where release-script is a shell script that looks like:
903
904 -------------------------------------------------
905 #!/bin/sh
906 stable="$1"
907 last="$2"
908 new="$3"
909 echo "# git tag v$new"
910 echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
911 echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
912 echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
913 echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
914 echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
915 -------------------------------------------------
916
917 and then he just cut-and-pastes the output commands after verifying that
918 they look OK.
919
920 [[Finding-comments-with-given-content]]
921 Finding commits referencing a file with given content
922 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
923
924 Somebody hands you a copy of a file, and asks which commits modified a
925 file such that it contained the given content either before or after the
926 commit. You can find out with this:
927
928 -------------------------------------------------
929 $ git log --raw --abbrev=40 --pretty=oneline -- filename |
930 grep -B 1 `git hash-object filename`
931 -------------------------------------------------
932
933 Figuring out why this works is left as an exercise to the (advanced)
934 student. The gitlink:git-log[1], gitlink:git-diff-tree[1], and
935 gitlink:git-hash-object[1] man pages may prove helpful.
936
937 [[Developing-with-git]]
938 Developing with git
939 ===================
940
941 [[telling-git-your-name]]
942 Telling git your name
943 ---------------------
944
945 Before creating any commits, you should introduce yourself to git. The
946 easiest way to do so is to make sure the following lines appear in a
947 file named .gitconfig in your home directory:
948
949 ------------------------------------------------
950 [user]
951 name = Your Name Comes Here
952 email = you@yourdomain.example.com
953 ------------------------------------------------
954
955 (See the "CONFIGURATION FILE" section of gitlink:git-config[1] for
956 details on the configuration file.)
957
958
959 [[creating-a-new-repository]]
960 Creating a new repository
961 -------------------------
962
963 Creating a new repository from scratch is very easy:
964
965 -------------------------------------------------
966 $ mkdir project
967 $ cd project
968 $ git init
969 -------------------------------------------------
970
971 If you have some initial content (say, a tarball):
972
973 -------------------------------------------------
974 $ tar -xzvf project.tar.gz
975 $ cd project
976 $ git init
977 $ git add . # include everything below ./ in the first commit:
978 $ git commit
979 -------------------------------------------------
980
981 [[how-to-make-a-commit]]
982 How to make a commit
983 --------------------
984
985 Creating a new commit takes three steps:
986
987 1. Making some changes to the working directory using your
988 favorite editor.
989 2. Telling git about your changes.
990 3. Creating the commit using the content you told git about
991 in step 2.
992
993 In practice, you can interleave and repeat steps 1 and 2 as many
994 times as you want: in order to keep track of what you want committed
995 at step 3, git maintains a snapshot of the tree's contents in a
996 special staging area called "the index."
997
998 At the beginning, the content of the index will be identical to
999 that of the HEAD. The command "git diff --cached", which shows
1000 the difference between the HEAD and the index, should therefore
1001 produce no output at that point.
1002
1003 Modifying the index is easy:
1004
1005 To update the index with the new contents of a modified file, use
1006
1007 -------------------------------------------------
1008 $ git add path/to/file
1009 -------------------------------------------------
1010
1011 To add the contents of a new file to the index, use
1012
1013 -------------------------------------------------
1014 $ git add path/to/file
1015 -------------------------------------------------
1016
1017 To remove a file from the index and from the working tree,
1018
1019 -------------------------------------------------
1020 $ git rm path/to/file
1021 -------------------------------------------------
1022
1023 After each step you can verify that
1024
1025 -------------------------------------------------
1026 $ git diff --cached
1027 -------------------------------------------------
1028
1029 always shows the difference between the HEAD and the index file--this
1030 is what you'd commit if you created the commit now--and that
1031
1032 -------------------------------------------------
1033 $ git diff
1034 -------------------------------------------------
1035
1036 shows the difference between the working tree and the index file.
1037
1038 Note that "git add" always adds just the current contents of a file
1039 to the index; further changes to the same file will be ignored unless
1040 you run git-add on the file again.
1041
1042 When you're ready, just run
1043
1044 -------------------------------------------------
1045 $ git commit
1046 -------------------------------------------------
1047
1048 and git will prompt you for a commit message and then create the new
1049 commit. Check to make sure it looks like what you expected with
1050
1051 -------------------------------------------------
1052 $ git show
1053 -------------------------------------------------
1054
1055 As a special shortcut,
1056
1057 -------------------------------------------------
1058 $ git commit -a
1059 -------------------------------------------------
1060
1061 will update the index with any files that you've modified or removed
1062 and create a commit, all in one step.
1063
1064 A number of commands are useful for keeping track of what you're
1065 about to commit:
1066
1067 -------------------------------------------------
1068 $ git diff --cached # difference between HEAD and the index; what
1069 # would be committed if you ran "commit" now.
1070 $ git diff # difference between the index file and your
1071 # working directory; changes that would not
1072 # be included if you ran "commit" now.
1073 $ git diff HEAD # difference between HEAD and working tree; what
1074 # would be committed if you ran "commit -a" now.
1075 $ git status # a brief per-file summary of the above.
1076 -------------------------------------------------
1077
1078 You can also use gitlink:git-gui[1] to create commits, view changes in
1079 the index and the working tree files, and individually select diff hunks
1080 for inclusion in the index (by right-clicking on the diff hunk and
1081 choosing "Stage Hunk For Commit").
1082
1083 [[creating-good-commit-messages]]
1084 Creating good commit messages
1085 -----------------------------
1086
1087 Though not required, it's a good idea to begin the commit message
1088 with a single short (less than 50 character) line summarizing the
1089 change, followed by a blank line and then a more thorough
1090 description. Tools that turn commits into email, for example, use
1091 the first line on the Subject line and the rest of the commit in the
1092 body.
1093
1094 [[ignoring-files]]
1095 Ignoring files
1096 --------------
1097
1098 A project will often generate files that you do 'not' want to track with git.
1099 This typically includes files generated by a build process or temporary
1100 backup files made by your editor. Of course, 'not' tracking files with git
1101 is just a matter of 'not' calling "`git add`" on them. But it quickly becomes
1102 annoying to have these untracked files lying around; e.g. they make
1103 "`git add .`" and "`git commit -a`" practically useless, and they keep
1104 showing up in the output of "`git status`".
1105
1106 You can tell git to ignore certain files by creating a file called .gitignore
1107 in the top level of your working directory, with contents such as:
1108
1109 -------------------------------------------------
1110 # Lines starting with '#' are considered comments.
1111 # Ignore any file named foo.txt.
1112 foo.txt
1113 # Ignore (generated) html files,
1114 *.html
1115 # except foo.html which is maintained by hand.
1116 !foo.html
1117 # Ignore objects and archives.
1118 *.[oa]
1119 -------------------------------------------------
1120
1121 See gitlink:gitignore[5] for a detailed explanation of the syntax. You can
1122 also place .gitignore files in other directories in your working tree, and they
1123 will apply to those directories and their subdirectories. The `.gitignore`
1124 files can be added to your repository like any other files (just run `git add
1125 .gitignore` and `git commit`, as usual), which is convenient when the exclude
1126 patterns (such as patterns matching build output files) would also make sense
1127 for other users who clone your repository.
1128
1129 If you wish the exclude patterns to affect only certain repositories
1130 (instead of every repository for a given project), you may instead put
1131 them in a file in your repository named .git/info/exclude, or in any file
1132 specified by the `core.excludesfile` configuration variable. Some git
1133 commands can also take exclude patterns directly on the command line.
1134 See gitlink:gitignore[5] for the details.
1135
1136 [[how-to-merge]]
1137 How to merge
1138 ------------
1139
1140 You can rejoin two diverging branches of development using
1141 gitlink:git-merge[1]:
1142
1143 -------------------------------------------------
1144 $ git merge branchname
1145 -------------------------------------------------
1146
1147 merges the development in the branch "branchname" into the current
1148 branch. If there are conflicts--for example, if the same file is
1149 modified in two different ways in the remote branch and the local
1150 branch--then you are warned; the output may look something like this:
1151
1152 -------------------------------------------------
1153 $ git merge next
1154 100% (4/4) done
1155 Auto-merged file.txt
1156 CONFLICT (content): Merge conflict in file.txt
1157 Automatic merge failed; fix conflicts and then commit the result.
1158 -------------------------------------------------
1159
1160 Conflict markers are left in the problematic files, and after
1161 you resolve the conflicts manually, you can update the index
1162 with the contents and run git commit, as you normally would when
1163 creating a new file.
1164
1165 If you examine the resulting commit using gitk, you will see that it
1166 has two parents, one pointing to the top of the current branch, and
1167 one to the top of the other branch.
1168
1169 [[resolving-a-merge]]
1170 Resolving a merge
1171 -----------------
1172
1173 When a merge isn't resolved automatically, git leaves the index and
1174 the working tree in a special state that gives you all the
1175 information you need to help resolve the merge.
1176
1177 Files with conflicts are marked specially in the index, so until you
1178 resolve the problem and update the index, gitlink:git-commit[1] will
1179 fail:
1180
1181 -------------------------------------------------
1182 $ git commit
1183 file.txt: needs merge
1184 -------------------------------------------------
1185
1186 Also, gitlink:git-status[1] will list those files as "unmerged", and the
1187 files with conflicts will have conflict markers added, like this:
1188
1189 -------------------------------------------------
1190 <<<<<<< HEAD:file.txt
1191 Hello world
1192 =======
1193 Goodbye
1194 >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1195 -------------------------------------------------
1196
1197 All you need to do is edit the files to resolve the conflicts, and then
1198
1199 -------------------------------------------------
1200 $ git add file.txt
1201 $ git commit
1202 -------------------------------------------------
1203
1204 Note that the commit message will already be filled in for you with
1205 some information about the merge. Normally you can just use this
1206 default message unchanged, but you may add additional commentary of
1207 your own if desired.
1208
1209 The above is all you need to know to resolve a simple merge. But git
1210 also provides more information to help resolve conflicts:
1211
1212 [[conflict-resolution]]
1213 Getting conflict-resolution help during a merge
1214 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1215
1216 All of the changes that git was able to merge automatically are
1217 already added to the index file, so gitlink:git-diff[1] shows only
1218 the conflicts. It uses an unusual syntax:
1219
1220 -------------------------------------------------
1221 $ git diff
1222 diff --cc file.txt
1223 index 802992c,2b60207..0000000
1224 --- a/file.txt
1225 +++ b/file.txt
1226 @@@ -1,1 -1,1 +1,5 @@@
1227 ++<<<<<<< HEAD:file.txt
1228 +Hello world
1229 ++=======
1230 + Goodbye
1231 ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1232 -------------------------------------------------
1233
1234 Recall that the commit which will be committed after we resolve this
1235 conflict will have two parents instead of the usual one: one parent
1236 will be HEAD, the tip of the current branch; the other will be the
1237 tip of the other branch, which is stored temporarily in MERGE_HEAD.
1238
1239 During the merge, the index holds three versions of each file. Each of
1240 these three "file stages" represents a different version of the file:
1241
1242 -------------------------------------------------
1243 $ git show :1:file.txt # the file in a common ancestor of both branches
1244 $ git show :2:file.txt # the version from HEAD, but including any
1245 # nonconflicting changes from MERGE_HEAD
1246 $ git show :3:file.txt # the version from MERGE_HEAD, but including any
1247 # nonconflicting changes from HEAD.
1248 -------------------------------------------------
1249
1250 Since the stage 2 and stage 3 versions have already been updated with
1251 nonconflicting changes, the only remaining differences between them are
1252 the important ones; thus gitlink:git-diff[1] can use the information in
1253 the index to show only those conflicts.
1254
1255 The diff above shows the differences between the working-tree version of
1256 file.txt and the stage 2 and stage 3 versions. So instead of preceding
1257 each line by a single "+" or "-", it now uses two columns: the first
1258 column is used for differences between the first parent and the working
1259 directory copy, and the second for differences between the second parent
1260 and the working directory copy. (See the "COMBINED DIFF FORMAT" section
1261 of gitlink:git-diff-files[1] for a details of the format.)
1262
1263 After resolving the conflict in the obvious way (but before updating the
1264 index), the diff will look like:
1265
1266 -------------------------------------------------
1267 $ git diff
1268 diff --cc file.txt
1269 index 802992c,2b60207..0000000
1270 --- a/file.txt
1271 +++ b/file.txt
1272 @@@ -1,1 -1,1 +1,1 @@@
1273 - Hello world
1274 -Goodbye
1275 ++Goodbye world
1276 -------------------------------------------------
1277
1278 This shows that our resolved version deleted "Hello world" from the
1279 first parent, deleted "Goodbye" from the second parent, and added
1280 "Goodbye world", which was previously absent from both.
1281
1282 Some special diff options allow diffing the working directory against
1283 any of these stages:
1284
1285 -------------------------------------------------
1286 $ git diff -1 file.txt # diff against stage 1
1287 $ git diff --base file.txt # same as the above
1288 $ git diff -2 file.txt # diff against stage 2
1289 $ git diff --ours file.txt # same as the above
1290 $ git diff -3 file.txt # diff against stage 3
1291 $ git diff --theirs file.txt # same as the above.
1292 -------------------------------------------------
1293
1294 The gitlink:git-log[1] and gitk[1] commands also provide special help
1295 for merges:
1296
1297 -------------------------------------------------
1298 $ git log --merge
1299 $ gitk --merge
1300 -------------------------------------------------
1301
1302 These will display all commits which exist only on HEAD or on
1303 MERGE_HEAD, and which touch an unmerged file.
1304
1305 You may also use gitlink:git-mergetool[1], which lets you merge the
1306 unmerged files using external tools such as emacs or kdiff3.
1307
1308 Each time you resolve the conflicts in a file and update the index:
1309
1310 -------------------------------------------------
1311 $ git add file.txt
1312 -------------------------------------------------
1313
1314 the different stages of that file will be "collapsed", after which
1315 git-diff will (by default) no longer show diffs for that file.
1316
1317 [[undoing-a-merge]]
1318 Undoing a merge
1319 ---------------
1320
1321 If you get stuck and decide to just give up and throw the whole mess
1322 away, you can always return to the pre-merge state with
1323
1324 -------------------------------------------------
1325 $ git reset --hard HEAD
1326 -------------------------------------------------
1327
1328 Or, if you've already committed the merge that you want to throw away,
1329
1330 -------------------------------------------------
1331 $ git reset --hard ORIG_HEAD
1332 -------------------------------------------------
1333
1334 However, this last command can be dangerous in some cases--never
1335 throw away a commit you have already committed if that commit may
1336 itself have been merged into another branch, as doing so may confuse
1337 further merges.
1338
1339 [[fast-forwards]]
1340 Fast-forward merges
1341 -------------------
1342
1343 There is one special case not mentioned above, which is treated
1344 differently. Normally, a merge results in a merge commit, with two
1345 parents, one pointing at each of the two lines of development that
1346 were merged.
1347
1348 However, if the current branch is a descendant of the other--so every
1349 commit present in the one is already contained in the other--then git
1350 just performs a "fast forward"; the head of the current branch is moved
1351 forward to point at the head of the merged-in branch, without any new
1352 commits being created.
1353
1354 [[fixing-mistakes]]
1355 Fixing mistakes
1356 ---------------
1357
1358 If you've messed up the working tree, but haven't yet committed your
1359 mistake, you can return the entire working tree to the last committed
1360 state with
1361
1362 -------------------------------------------------
1363 $ git reset --hard HEAD
1364 -------------------------------------------------
1365
1366 If you make a commit that you later wish you hadn't, there are two
1367 fundamentally different ways to fix the problem:
1368
1369 1. You can create a new commit that undoes whatever was done
1370 by the previous commit. This is the correct thing if your
1371 mistake has already been made public.
1372
1373 2. You can go back and modify the old commit. You should
1374 never do this if you have already made the history public;
1375 git does not normally expect the "history" of a project to
1376 change, and cannot correctly perform repeated merges from
1377 a branch that has had its history changed.
1378
1379 [[reverting-a-commit]]
1380 Fixing a mistake with a new commit
1381 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1382
1383 Creating a new commit that reverts an earlier change is very easy;
1384 just pass the gitlink:git-revert[1] command a reference to the bad
1385 commit; for example, to revert the most recent commit:
1386
1387 -------------------------------------------------
1388 $ git revert HEAD
1389 -------------------------------------------------
1390
1391 This will create a new commit which undoes the change in HEAD. You
1392 will be given a chance to edit the commit message for the new commit.
1393
1394 You can also revert an earlier change, for example, the next-to-last:
1395
1396 -------------------------------------------------
1397 $ git revert HEAD^
1398 -------------------------------------------------
1399
1400 In this case git will attempt to undo the old change while leaving
1401 intact any changes made since then. If more recent changes overlap
1402 with the changes to be reverted, then you will be asked to fix
1403 conflicts manually, just as in the case of <<resolving-a-merge,
1404 resolving a merge>>.
1405
1406 [[fixing-a-mistake-by-editing-history]]
1407 Fixing a mistake by editing history
1408 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1409
1410 If the problematic commit is the most recent commit, and you have not
1411 yet made that commit public, then you may just
1412 <<undoing-a-merge,destroy it using git-reset>>.
1413
1414 Alternatively, you
1415 can edit the working directory and update the index to fix your
1416 mistake, just as if you were going to <<how-to-make-a-commit,create a
1417 new commit>>, then run
1418
1419 -------------------------------------------------
1420 $ git commit --amend
1421 -------------------------------------------------
1422
1423 which will replace the old commit by a new commit incorporating your
1424 changes, giving you a chance to edit the old commit message first.
1425
1426 Again, you should never do this to a commit that may already have
1427 been merged into another branch; use gitlink:git-revert[1] instead in
1428 that case.
1429
1430 It is also possible to edit commits further back in the history, but
1431 this is an advanced topic to be left for
1432 <<cleaning-up-history,another chapter>>.
1433
1434 [[checkout-of-path]]
1435 Checking out an old version of a file
1436 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1437
1438 In the process of undoing a previous bad change, you may find it
1439 useful to check out an older version of a particular file using
1440 gitlink:git-checkout[1]. We've used git checkout before to switch
1441 branches, but it has quite different behavior if it is given a path
1442 name: the command
1443
1444 -------------------------------------------------
1445 $ git checkout HEAD^ path/to/file
1446 -------------------------------------------------
1447
1448 replaces path/to/file by the contents it had in the commit HEAD^, and
1449 also updates the index to match. It does not change branches.
1450
1451 If you just want to look at an old version of the file, without
1452 modifying the working directory, you can do that with
1453 gitlink:git-show[1]:
1454
1455 -------------------------------------------------
1456 $ git show HEAD^:path/to/file
1457 -------------------------------------------------
1458
1459 which will display the given version of the file.
1460
1461 [[interrupted-work]]
1462 Temporarily setting aside work in progress
1463 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1464
1465 While you are in the middle of working on something complicated, you
1466 find an unrelated but obvious and trivial bug. You would like to fix it
1467 before continuing. You can use gitlink:git-stash[1] to save the current
1468 state of your work, and after fixing the bug (or, optionally after doing
1469 so on a different branch and then coming back), unstash the
1470 work-in-progress changes.
1471
1472 ------------------------------------------------
1473 $ git stash "work in progress for foo feature"
1474 ------------------------------------------------
1475
1476 This command will save your changes away to the `stash`, and
1477 reset your working tree and the index to match the tip of your
1478 current branch. Then you can make your fix as usual.
1479
1480 ------------------------------------------------
1481 ... edit and test ...
1482 $ git commit -a -m "blorpl: typofix"
1483 ------------------------------------------------
1484
1485 After that, you can go back to what you were working on with
1486 `git stash apply`:
1487
1488 ------------------------------------------------
1489 $ git stash apply
1490 ------------------------------------------------
1491
1492
1493 [[ensuring-good-performance]]
1494 Ensuring good performance
1495 -------------------------
1496
1497 On large repositories, git depends on compression to keep the history
1498 information from taking up to much space on disk or in memory.
1499
1500 This compression is not performed automatically. Therefore you
1501 should occasionally run gitlink:git-gc[1]:
1502
1503 -------------------------------------------------
1504 $ git gc
1505 -------------------------------------------------
1506
1507 to recompress the archive. This can be very time-consuming, so
1508 you may prefer to run git-gc when you are not doing other work.
1509
1510
1511 [[ensuring-reliability]]
1512 Ensuring reliability
1513 --------------------
1514
1515 [[checking-for-corruption]]
1516 Checking the repository for corruption
1517 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1518
1519 The gitlink:git-fsck[1] command runs a number of self-consistency checks
1520 on the repository, and reports on any problems. This may take some
1521 time. The most common warning by far is about "dangling" objects:
1522
1523 -------------------------------------------------
1524 $ git fsck
1525 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1526 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1527 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1528 dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1529 dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1530 dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1531 dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1532 dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1533 ...
1534 -------------------------------------------------
1535
1536 Dangling objects are not a problem. At worst they may take up a little
1537 extra disk space. They can sometimes provide a last-resort method for
1538 recovering lost work--see <<dangling-objects>> for details. However, if
1539 you wish, you can remove them with gitlink:git-prune[1] or the --prune
1540 option to gitlink:git-gc[1]:
1541
1542 -------------------------------------------------
1543 $ git gc --prune
1544 -------------------------------------------------
1545
1546 This may be time-consuming. Unlike most other git operations (including
1547 git-gc when run without any options), it is not safe to prune while
1548 other git operations are in progress in the same repository.
1549
1550 [[recovering-lost-changes]]
1551 Recovering lost changes
1552 ~~~~~~~~~~~~~~~~~~~~~~~
1553
1554 [[reflogs]]
1555 Reflogs
1556 ^^^^^^^
1557
1558 Say you modify a branch with gitlink:git-reset[1] --hard, and then
1559 realize that the branch was the only reference you had to that point in
1560 history.
1561
1562 Fortunately, git also keeps a log, called a "reflog", of all the
1563 previous values of each branch. So in this case you can still find the
1564 old history using, for example,
1565
1566 -------------------------------------------------
1567 $ git log master@{1}
1568 -------------------------------------------------
1569
1570 This lists the commits reachable from the previous version of the head.
1571 This syntax can be used to with any git command that accepts a commit,
1572 not just with git log. Some other examples:
1573
1574 -------------------------------------------------
1575 $ git show master@{2} # See where the branch pointed 2,
1576 $ git show master@{3} # 3, ... changes ago.
1577 $ gitk master@{yesterday} # See where it pointed yesterday,
1578 $ gitk master@{"1 week ago"} # ... or last week
1579 $ git log --walk-reflogs master # show reflog entries for master
1580 -------------------------------------------------
1581
1582 A separate reflog is kept for the HEAD, so
1583
1584 -------------------------------------------------
1585 $ git show HEAD@{"1 week ago"}
1586 -------------------------------------------------
1587
1588 will show what HEAD pointed to one week ago, not what the current branch
1589 pointed to one week ago. This allows you to see the history of what
1590 you've checked out.
1591
1592 The reflogs are kept by default for 30 days, after which they may be
1593 pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn
1594 how to control this pruning, and see the "SPECIFYING REVISIONS"
1595 section of gitlink:git-rev-parse[1] for details.
1596
1597 Note that the reflog history is very different from normal git history.
1598 While normal history is shared by every repository that works on the
1599 same project, the reflog history is not shared: it tells you only about
1600 how the branches in your local repository have changed over time.
1601
1602 [[dangling-object-recovery]]
1603 Examining dangling objects
1604 ^^^^^^^^^^^^^^^^^^^^^^^^^^
1605
1606 In some situations the reflog may not be able to save you. For example,
1607 suppose you delete a branch, then realize you need the history it
1608 contained. The reflog is also deleted; however, if you have not yet
1609 pruned the repository, then you may still be able to find the lost
1610 commits in the dangling objects that git-fsck reports. See
1611 <<dangling-objects>> for the details.
1612
1613 -------------------------------------------------
1614 $ git fsck
1615 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1616 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1617 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1618 ...
1619 -------------------------------------------------
1620
1621 You can examine
1622 one of those dangling commits with, for example,
1623
1624 ------------------------------------------------
1625 $ gitk 7281251ddd --not --all
1626 ------------------------------------------------
1627
1628 which does what it sounds like: it says that you want to see the commit
1629 history that is described by the dangling commit(s), but not the
1630 history that is described by all your existing branches and tags. Thus
1631 you get exactly the history reachable from that commit that is lost.
1632 (And notice that it might not be just one commit: we only report the
1633 "tip of the line" as being dangling, but there might be a whole deep
1634 and complex commit history that was dropped.)
1635
1636 If you decide you want the history back, you can always create a new
1637 reference pointing to it, for example, a new branch:
1638
1639 ------------------------------------------------
1640 $ git branch recovered-branch 7281251ddd
1641 ------------------------------------------------
1642
1643 Other types of dangling objects (blobs and trees) are also possible, and
1644 dangling objects can arise in other situations.
1645
1646
1647 [[sharing-development]]
1648 Sharing development with others
1649 ===============================
1650
1651 [[getting-updates-with-git-pull]]
1652 Getting updates with git pull
1653 -----------------------------
1654
1655 After you clone a repository and make a few changes of your own, you
1656 may wish to check the original repository for updates and merge them
1657 into your own work.
1658
1659 We have already seen <<Updating-a-repository-with-git-fetch,how to
1660 keep remote tracking branches up to date>> with gitlink:git-fetch[1],
1661 and how to merge two branches. So you can merge in changes from the
1662 original repository's master branch with:
1663
1664 -------------------------------------------------
1665 $ git fetch
1666 $ git merge origin/master
1667 -------------------------------------------------
1668
1669 However, the gitlink:git-pull[1] command provides a way to do this in
1670 one step:
1671
1672 -------------------------------------------------
1673 $ git pull origin master
1674 -------------------------------------------------
1675
1676 In fact, if you have "master" checked out, then by default "git pull"
1677 merges from the HEAD branch of the origin repository. So often you can
1678 accomplish the above with just a simple
1679
1680 -------------------------------------------------
1681 $ git pull
1682 -------------------------------------------------
1683
1684 More generally, a branch that is created from a remote branch will pull
1685 by default from that branch. See the descriptions of the
1686 branch.<name>.remote and branch.<name>.merge options in
1687 gitlink:git-config[1], and the discussion of the --track option in
1688 gitlink:git-checkout[1], to learn how to control these defaults.
1689
1690 In addition to saving you keystrokes, "git pull" also helps you by
1691 producing a default commit message documenting the branch and
1692 repository that you pulled from.
1693
1694 (But note that no such commit will be created in the case of a
1695 <<fast-forwards,fast forward>>; instead, your branch will just be
1696 updated to point to the latest commit from the upstream branch.)
1697
1698 The git-pull command can also be given "." as the "remote" repository,
1699 in which case it just merges in a branch from the current repository; so
1700 the commands
1701
1702 -------------------------------------------------
1703 $ git pull . branch
1704 $ git merge branch
1705 -------------------------------------------------
1706
1707 are roughly equivalent. The former is actually very commonly used.
1708
1709 [[submitting-patches]]
1710 Submitting patches to a project
1711 -------------------------------
1712
1713 If you just have a few changes, the simplest way to submit them may
1714 just be to send them as patches in email:
1715
1716 First, use gitlink:git-format-patch[1]; for example:
1717
1718 -------------------------------------------------
1719 $ git format-patch origin
1720 -------------------------------------------------
1721
1722 will produce a numbered series of files in the current directory, one
1723 for each patch in the current branch but not in origin/HEAD.
1724
1725 You can then import these into your mail client and send them by
1726 hand. However, if you have a lot to send at once, you may prefer to
1727 use the gitlink:git-send-email[1] script to automate the process.
1728 Consult the mailing list for your project first to determine how they
1729 prefer such patches be handled.
1730
1731 [[importing-patches]]
1732 Importing patches to a project
1733 ------------------------------
1734
1735 Git also provides a tool called gitlink:git-am[1] (am stands for
1736 "apply mailbox"), for importing such an emailed series of patches.
1737 Just save all of the patch-containing messages, in order, into a
1738 single mailbox file, say "patches.mbox", then run
1739
1740 -------------------------------------------------
1741 $ git am -3 patches.mbox
1742 -------------------------------------------------
1743
1744 Git will apply each patch in order; if any conflicts are found, it
1745 will stop, and you can fix the conflicts as described in
1746 "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1747 git to perform a merge; if you would prefer it just to abort and
1748 leave your tree and index untouched, you may omit that option.)
1749
1750 Once the index is updated with the results of the conflict
1751 resolution, instead of creating a new commit, just run
1752
1753 -------------------------------------------------
1754 $ git am --resolved
1755 -------------------------------------------------
1756
1757 and git will create the commit for you and continue applying the
1758 remaining patches from the mailbox.
1759
1760 The final result will be a series of commits, one for each patch in
1761 the original mailbox, with authorship and commit log message each
1762 taken from the message containing each patch.
1763
1764 [[public-repositories]]
1765 Public git repositories
1766 -----------------------
1767
1768 Another way to submit changes to a project is to tell the maintainer
1769 of that project to pull the changes from your repository using
1770 gitlink:git-pull[1]. In the section "<<getting-updates-with-git-pull,
1771 Getting updates with git pull>>" we described this as a way to get
1772 updates from the "main" repository, but it works just as well in the
1773 other direction.
1774
1775 If you and the maintainer both have accounts on the same machine, then
1776 you can just pull changes from each other's repositories directly;
1777 commands that accept repository URLs as arguments will also accept a
1778 local directory name:
1779
1780 -------------------------------------------------
1781 $ git clone /path/to/repository
1782 $ git pull /path/to/other/repository
1783 -------------------------------------------------
1784
1785 or an ssh url:
1786
1787 -------------------------------------------------
1788 $ git clone ssh://yourhost/~you/repository
1789 -------------------------------------------------
1790
1791 For projects with few developers, or for synchronizing a few private
1792 repositories, this may be all you need.
1793
1794 However, the more common way to do this is to maintain a separate public
1795 repository (usually on a different host) for others to pull changes
1796 from. This is usually more convenient, and allows you to cleanly
1797 separate private work in progress from publicly visible work.
1798
1799 You will continue to do your day-to-day work in your personal
1800 repository, but periodically "push" changes from your personal
1801 repository into your public repository, allowing other developers to
1802 pull from that repository. So the flow of changes, in a situation
1803 where there is one other developer with a public repository, looks
1804 like this:
1805
1806 you push
1807 your personal repo ------------------> your public repo
1808 ^ |
1809 | |
1810 | you pull | they pull
1811 | |
1812 | |
1813 | they push V
1814 their public repo <------------------- their repo
1815
1816 We explain how to do this in the following sections.
1817
1818 [[setting-up-a-public-repository]]
1819 Setting up a public repository
1820 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1821
1822 Assume your personal repository is in the directory ~/proj. We
1823 first create a new clone of the repository and tell git-daemon that it
1824 is meant to be public:
1825
1826 -------------------------------------------------
1827 $ git clone --bare ~/proj proj.git
1828 $ touch proj.git/git-daemon-export-ok
1829 -------------------------------------------------
1830
1831 The resulting directory proj.git contains a "bare" git repository--it is
1832 just the contents of the ".git" directory, without any files checked out
1833 around it.
1834
1835 Next, copy proj.git to the server where you plan to host the
1836 public repository. You can use scp, rsync, or whatever is most
1837 convenient.
1838
1839 [[exporting-via-git]]
1840 Exporting a git repository via the git protocol
1841 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1842
1843 This is the preferred method.
1844
1845 If someone else administers the server, they should tell you what
1846 directory to put the repository in, and what git:// url it will appear
1847 at. You can then skip to the section
1848 "<<pushing-changes-to-a-public-repository,Pushing changes to a public
1849 repository>>", below.
1850
1851 Otherwise, all you need to do is start gitlink:git-daemon[1]; it will
1852 listen on port 9418. By default, it will allow access to any directory
1853 that looks like a git directory and contains the magic file
1854 git-daemon-export-ok. Passing some directory paths as git-daemon
1855 arguments will further restrict the exports to those paths.
1856
1857 You can also run git-daemon as an inetd service; see the
1858 gitlink:git-daemon[1] man page for details. (See especially the
1859 examples section.)
1860
1861 [[exporting-via-http]]
1862 Exporting a git repository via http
1863 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1864
1865 The git protocol gives better performance and reliability, but on a
1866 host with a web server set up, http exports may be simpler to set up.
1867
1868 All you need to do is place the newly created bare git repository in
1869 a directory that is exported by the web server, and make some
1870 adjustments to give web clients some extra information they need:
1871
1872 -------------------------------------------------
1873 $ mv proj.git /home/you/public_html/proj.git
1874 $ cd proj.git
1875 $ git --bare update-server-info
1876 $ chmod a+x hooks/post-update
1877 -------------------------------------------------
1878
1879 (For an explanation of the last two lines, see
1880 gitlink:git-update-server-info[1], and the documentation
1881 link:hooks.html[Hooks used by git].)
1882
1883 Advertise the url of proj.git. Anybody else should then be able to
1884 clone or pull from that url, for example with a command line like:
1885
1886 -------------------------------------------------
1887 $ git clone http://yourserver.com/~you/proj.git
1888 -------------------------------------------------
1889
1890 (See also
1891 link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1892 for a slightly more sophisticated setup using WebDAV which also
1893 allows pushing over http.)
1894
1895 [[pushing-changes-to-a-public-repository]]
1896 Pushing changes to a public repository
1897 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1898
1899 Note that the two techniques outlined above (exporting via
1900 <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1901 maintainers to fetch your latest changes, but they do not allow write
1902 access, which you will need to update the public repository with the
1903 latest changes created in your private repository.
1904
1905 The simplest way to do this is using gitlink:git-push[1] and ssh; to
1906 update the remote branch named "master" with the latest state of your
1907 branch named "master", run
1908
1909 -------------------------------------------------
1910 $ git push ssh://yourserver.com/~you/proj.git master:master
1911 -------------------------------------------------
1912
1913 or just
1914
1915 -------------------------------------------------
1916 $ git push ssh://yourserver.com/~you/proj.git master
1917 -------------------------------------------------
1918
1919 As with git-fetch, git-push will complain if this does not result in
1920 a <<fast-forwards,fast forward>>. Normally this is a sign of
1921 something wrong. However, if you are sure you know what you're
1922 doing, you may force git-push to perform the update anyway by
1923 proceeding the branch name by a plus sign:
1924
1925 -------------------------------------------------
1926 $ git push ssh://yourserver.com/~you/proj.git +master
1927 -------------------------------------------------
1928
1929 Note that the target of a "push" is normally a
1930 <<def_bare_repository,bare>> repository. You can also push to a
1931 repository that has a checked-out working tree, but the working tree
1932 will not be updated by the push. This may lead to unexpected results if
1933 the branch you push to is the currently checked-out branch!
1934
1935 As with git-fetch, you may also set up configuration options to
1936 save typing; so, for example, after
1937
1938 -------------------------------------------------
1939 $ cat >>.git/config <<EOF
1940 [remote "public-repo"]
1941 url = ssh://yourserver.com/~you/proj.git
1942 EOF
1943 -------------------------------------------------
1944
1945 you should be able to perform the above push with just
1946
1947 -------------------------------------------------
1948 $ git push public-repo master
1949 -------------------------------------------------
1950
1951 See the explanations of the remote.<name>.url, branch.<name>.remote,
1952 and remote.<name>.push options in gitlink:git-config[1] for
1953 details.
1954
1955 [[setting-up-a-shared-repository]]
1956 Setting up a shared repository
1957 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1958
1959 Another way to collaborate is by using a model similar to that
1960 commonly used in CVS, where several developers with special rights
1961 all push to and pull from a single shared repository. See
1962 link:cvs-migration.html[git for CVS users] for instructions on how to
1963 set this up.
1964
1965 However, while there is nothing wrong with git's support for shared
1966 repositories, this mode of operation is not generally recommended,
1967 simply because the mode of collaboration that git supports--by
1968 exchanging patches and pulling from public repositories--has so many
1969 advantages over the central shared repository:
1970
1971 - Git's ability to quickly import and merge patches allows a
1972 single maintainer to process incoming changes even at very
1973 high rates. And when that becomes too much, git-pull provides
1974 an easy way for that maintainer to delegate this job to other
1975 maintainers while still allowing optional review of incoming
1976 changes.
1977 - Since every developer's repository has the same complete copy
1978 of the project history, no repository is special, and it is
1979 trivial for another developer to take over maintenance of a
1980 project, either by mutual agreement, or because a maintainer
1981 becomes unresponsive or difficult to work with.
1982 - The lack of a central group of "committers" means there is
1983 less need for formal decisions about who is "in" and who is
1984 "out".
1985
1986 [[setting-up-gitweb]]
1987 Allowing web browsing of a repository
1988 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1989
1990 The gitweb cgi script provides users an easy way to browse your
1991 project's files and history without having to install git; see the file
1992 gitweb/INSTALL in the git source tree for instructions on setting it up.
1993
1994 [[sharing-development-examples]]
1995 Examples
1996 --------
1997
1998 [[maintaining-topic-branches]]
1999 Maintaining topic branches for a Linux subsystem maintainer
2000 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2001
2002 This describes how Tony Luck uses git in his role as maintainer of the
2003 IA64 architecture for the Linux kernel.
2004
2005 He uses two public branches:
2006
2007 - A "test" tree into which patches are initially placed so that they
2008 can get some exposure when integrated with other ongoing development.
2009 This tree is available to Andrew for pulling into -mm whenever he
2010 wants.
2011
2012 - A "release" tree into which tested patches are moved for final sanity
2013 checking, and as a vehicle to send them upstream to Linus (by sending
2014 him a "please pull" request.)
2015
2016 He also uses a set of temporary branches ("topic branches"), each
2017 containing a logical grouping of patches.
2018
2019 To set this up, first create your work tree by cloning Linus's public
2020 tree:
2021
2022 -------------------------------------------------
2023 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2024 $ cd work
2025 -------------------------------------------------
2026
2027 Linus's tree will be stored in the remote branch named origin/master,
2028 and can be updated using gitlink:git-fetch[1]; you can track other
2029 public trees using gitlink:git-remote[1] to set up a "remote" and
2030 gitlink:git-fetch[1] to keep them up-to-date; see
2031 <<repositories-and-branches>>.
2032
2033 Now create the branches in which you are going to work; these start out
2034 at the current tip of origin/master branch, and should be set up (using
2035 the --track option to gitlink:git-branch[1]) to merge changes in from
2036 Linus by default.
2037
2038 -------------------------------------------------
2039 $ git branch --track test origin/master
2040 $ git branch --track release origin/master
2041 -------------------------------------------------
2042
2043 These can be easily kept up to date using gitlink:git-pull[1]
2044
2045 -------------------------------------------------
2046 $ git checkout test && git pull
2047 $ git checkout release && git pull
2048 -------------------------------------------------
2049
2050 Important note! If you have any local changes in these branches, then
2051 this merge will create a commit object in the history (with no local
2052 changes git will simply do a "Fast forward" merge). Many people dislike
2053 the "noise" that this creates in the Linux history, so you should avoid
2054 doing this capriciously in the "release" branch, as these noisy commits
2055 will become part of the permanent history when you ask Linus to pull
2056 from the release branch.
2057
2058 A few configuration variables (see gitlink:git-config[1]) can
2059 make it easy to push both branches to your public tree. (See
2060 <<setting-up-a-public-repository>>.)
2061
2062 -------------------------------------------------
2063 $ cat >> .git/config <<EOF
2064 [remote "mytree"]
2065 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2066 push = release
2067 push = test
2068 EOF
2069 -------------------------------------------------
2070
2071 Then you can push both the test and release trees using
2072 gitlink:git-push[1]:
2073
2074 -------------------------------------------------
2075 $ git push mytree
2076 -------------------------------------------------
2077
2078 or push just one of the test and release branches using:
2079
2080 -------------------------------------------------
2081 $ git push mytree test
2082 -------------------------------------------------
2083
2084 or
2085
2086 -------------------------------------------------
2087 $ git push mytree release
2088 -------------------------------------------------
2089
2090 Now to apply some patches from the community. Think of a short
2091 snappy name for a branch to hold this patch (or related group of
2092 patches), and create a new branch from the current tip of Linus's
2093 branch:
2094
2095 -------------------------------------------------
2096 $ git checkout -b speed-up-spinlocks origin
2097 -------------------------------------------------
2098
2099 Now you apply the patch(es), run some tests, and commit the change(s). If
2100 the patch is a multi-part series, then you should apply each as a separate
2101 commit to this branch.
2102
2103 -------------------------------------------------
2104 $ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2105 -------------------------------------------------
2106
2107 When you are happy with the state of this change, you can pull it into the
2108 "test" branch in preparation to make it public:
2109
2110 -------------------------------------------------
2111 $ git checkout test && git pull . speed-up-spinlocks
2112 -------------------------------------------------
2113
2114 It is unlikely that you would have any conflicts here ... but you might if you
2115 spent a while on this step and had also pulled new versions from upstream.
2116
2117 Some time later when enough time has passed and testing done, you can pull the
2118 same branch into the "release" tree ready to go upstream. This is where you
2119 see the value of keeping each patch (or patch series) in its own branch. It
2120 means that the patches can be moved into the "release" tree in any order.
2121
2122 -------------------------------------------------
2123 $ git checkout release && git pull . speed-up-spinlocks
2124 -------------------------------------------------
2125
2126 After a while, you will have a number of branches, and despite the
2127 well chosen names you picked for each of them, you may forget what
2128 they are for, or what status they are in. To get a reminder of what
2129 changes are in a specific branch, use:
2130
2131 -------------------------------------------------
2132 $ git log linux..branchname | git-shortlog
2133 -------------------------------------------------
2134
2135 To see whether it has already been merged into the test or release branches
2136 use:
2137
2138 -------------------------------------------------
2139 $ git log test..branchname
2140 -------------------------------------------------
2141
2142 or
2143
2144 -------------------------------------------------
2145 $ git log release..branchname
2146 -------------------------------------------------
2147
2148 (If this branch has not yet been merged you will see some log entries.
2149 If it has been merged, then there will be no output.)
2150
2151 Once a patch completes the great cycle (moving from test to release,
2152 then pulled by Linus, and finally coming back into your local
2153 "origin/master" branch) the branch for this change is no longer needed.
2154 You detect this when the output from:
2155
2156 -------------------------------------------------
2157 $ git log origin..branchname
2158 -------------------------------------------------
2159
2160 is empty. At this point the branch can be deleted:
2161
2162 -------------------------------------------------
2163 $ git branch -d branchname
2164 -------------------------------------------------
2165
2166 Some changes are so trivial that it is not necessary to create a separate
2167 branch and then merge into each of the test and release branches. For
2168 these changes, just apply directly to the "release" branch, and then
2169 merge that into the "test" branch.
2170
2171 To create diffstat and shortlog summaries of changes to include in a "please
2172 pull" request to Linus you can use:
2173
2174 -------------------------------------------------
2175 $ git diff --stat origin..release
2176 -------------------------------------------------
2177
2178 and
2179
2180 -------------------------------------------------
2181 $ git log -p origin..release | git shortlog
2182 -------------------------------------------------
2183
2184 Here are some of the scripts that simplify all this even further.
2185
2186 -------------------------------------------------
2187 ==== update script ====
2188 # Update a branch in my GIT tree. If the branch to be updated
2189 # is origin, then pull from kernel.org. Otherwise merge
2190 # origin/master branch into test|release branch
2191
2192 case "$1" in
2193 test|release)
2194 git checkout $1 && git pull . origin
2195 ;;
2196 origin)
2197 before=$(git rev-parse refs/remotes/origin/master)
2198 git fetch origin
2199 after=$(git rev-parse refs/remotes/origin/master)
2200 if [ $before != $after ]
2201 then
2202 git log $before..$after | git shortlog
2203 fi
2204 ;;
2205 *)
2206 echo "Usage: $0 origin|test|release" 1>&2
2207 exit 1
2208 ;;
2209 esac
2210 -------------------------------------------------
2211
2212 -------------------------------------------------
2213 ==== merge script ====
2214 # Merge a branch into either the test or release branch
2215
2216 pname=$0
2217
2218 usage()
2219 {
2220 echo "Usage: $pname branch test|release" 1>&2
2221 exit 1
2222 }
2223
2224 git show-ref -q --verify -- refs/heads/"$1" || {
2225 echo "Can't see branch <$1>" 1>&2
2226 usage
2227 }
2228
2229 case "$2" in
2230 test|release)
2231 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2232 then
2233 echo $1 already merged into $2 1>&2
2234 exit 1
2235 fi
2236 git checkout $2 && git pull . $1
2237 ;;
2238 *)
2239 usage
2240 ;;
2241 esac
2242 -------------------------------------------------
2243
2244 -------------------------------------------------
2245 ==== status script ====
2246 # report on status of my ia64 GIT tree
2247
2248 gb=$(tput setab 2)
2249 rb=$(tput setab 1)
2250 restore=$(tput setab 9)
2251
2252 if [ `git rev-list test..release | wc -c` -gt 0 ]
2253 then
2254 echo $rb Warning: commits in release that are not in test $restore
2255 git log test..release
2256 fi
2257
2258 for branch in `git show-ref --heads | sed 's|^.*/||'`
2259 do
2260 if [ $branch = test -o $branch = release ]
2261 then
2262 continue
2263 fi
2264
2265 echo -n $gb ======= $branch ====== $restore " "
2266 status=
2267 for ref in test release origin/master
2268 do
2269 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2270 then
2271 status=$status${ref:0:1}
2272 fi
2273 done
2274 case $status in
2275 trl)
2276 echo $rb Need to pull into test $restore
2277 ;;
2278 rl)
2279 echo "In test"
2280 ;;
2281 l)
2282 echo "Waiting for linus"
2283 ;;
2284 "")
2285 echo $rb All done $restore
2286 ;;
2287 *)
2288 echo $rb "<$status>" $restore
2289 ;;
2290 esac
2291 git log origin/master..$branch | git shortlog
2292 done
2293 -------------------------------------------------
2294
2295
2296 [[cleaning-up-history]]
2297 Rewriting history and maintaining patch series
2298 ==============================================
2299
2300 Normally commits are only added to a project, never taken away or
2301 replaced. Git is designed with this assumption, and violating it will
2302 cause git's merge machinery (for example) to do the wrong thing.
2303
2304 However, there is a situation in which it can be useful to violate this
2305 assumption.
2306
2307 [[patch-series]]
2308 Creating the perfect patch series
2309 ---------------------------------
2310
2311 Suppose you are a contributor to a large project, and you want to add a
2312 complicated feature, and to present it to the other developers in a way
2313 that makes it easy for them to read your changes, verify that they are
2314 correct, and understand why you made each change.
2315
2316 If you present all of your changes as a single patch (or commit), they
2317 may find that it is too much to digest all at once.
2318
2319 If you present them with the entire history of your work, complete with
2320 mistakes, corrections, and dead ends, they may be overwhelmed.
2321
2322 So the ideal is usually to produce a series of patches such that:
2323
2324 1. Each patch can be applied in order.
2325
2326 2. Each patch includes a single logical change, together with a
2327 message explaining the change.
2328
2329 3. No patch introduces a regression: after applying any initial
2330 part of the series, the resulting project still compiles and
2331 works, and has no bugs that it didn't have before.
2332
2333 4. The complete series produces the same end result as your own
2334 (probably much messier!) development process did.
2335
2336 We will introduce some tools that can help you do this, explain how to
2337 use them, and then explain some of the problems that can arise because
2338 you are rewriting history.
2339
2340 [[using-git-rebase]]
2341 Keeping a patch series up to date using git-rebase
2342 --------------------------------------------------
2343
2344 Suppose that you create a branch "mywork" on a remote-tracking branch
2345 "origin", and create some commits on top of it:
2346
2347 -------------------------------------------------
2348 $ git checkout -b mywork origin
2349 $ vi file.txt
2350 $ git commit
2351 $ vi otherfile.txt
2352 $ git commit
2353 ...
2354 -------------------------------------------------
2355
2356 You have performed no merges into mywork, so it is just a simple linear
2357 sequence of patches on top of "origin":
2358
2359 ................................................
2360 o--o--o <-- origin
2361 \
2362 o--o--o <-- mywork
2363 ................................................
2364
2365 Some more interesting work has been done in the upstream project, and
2366 "origin" has advanced:
2367
2368 ................................................
2369 o--o--O--o--o--o <-- origin
2370 \
2371 a--b--c <-- mywork
2372 ................................................
2373
2374 At this point, you could use "pull" to merge your changes back in;
2375 the result would create a new merge commit, like this:
2376
2377 ................................................
2378 o--o--O--o--o--o <-- origin
2379 \ \
2380 a--b--c--m <-- mywork
2381 ................................................
2382
2383 However, if you prefer to keep the history in mywork a simple series of
2384 commits without any merges, you may instead choose to use
2385 gitlink:git-rebase[1]:
2386
2387 -------------------------------------------------
2388 $ git checkout mywork
2389 $ git rebase origin
2390 -------------------------------------------------
2391
2392 This will remove each of your commits from mywork, temporarily saving
2393 them as patches (in a directory named ".dotest"), update mywork to
2394 point at the latest version of origin, then apply each of the saved
2395 patches to the new mywork. The result will look like:
2396
2397
2398 ................................................
2399 o--o--O--o--o--o <-- origin
2400 \
2401 a'--b'--c' <-- mywork
2402 ................................................
2403
2404 In the process, it may discover conflicts. In that case it will stop
2405 and allow you to fix the conflicts; after fixing conflicts, use "git
2406 add" to update the index with those contents, and then, instead of
2407 running git-commit, just run
2408
2409 -------------------------------------------------
2410 $ git rebase --continue
2411 -------------------------------------------------
2412
2413 and git will continue applying the rest of the patches.
2414
2415 At any point you may use the --abort option to abort this process and
2416 return mywork to the state it had before you started the rebase:
2417
2418 -------------------------------------------------
2419 $ git rebase --abort
2420 -------------------------------------------------
2421
2422 [[modifying-one-commit]]
2423 Modifying a single commit
2424 -------------------------
2425
2426 We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the
2427 most recent commit using
2428
2429 -------------------------------------------------
2430 $ git commit --amend
2431 -------------------------------------------------
2432
2433 which will replace the old commit by a new commit incorporating your
2434 changes, giving you a chance to edit the old commit message first.
2435
2436 You can also use a combination of this and gitlink:git-rebase[1] to edit
2437 commits further back in your history. First, tag the problematic commit with
2438
2439 -------------------------------------------------
2440 $ git tag bad mywork~5
2441 -------------------------------------------------
2442
2443 (Either gitk or git-log may be useful for finding the commit.)
2444
2445 Then check out that commit, edit it, and rebase the rest of the series
2446 on top of it (note that we could check out the commit on a temporary
2447 branch, but instead we're using a <<detached-head,detached head>>):
2448
2449 -------------------------------------------------
2450 $ git checkout bad
2451 $ # make changes here and update the index
2452 $ git commit --amend
2453 $ git rebase --onto HEAD bad mywork
2454 -------------------------------------------------
2455
2456 When you're done, you'll be left with mywork checked out, with the top
2457 patches on mywork reapplied on top of your modified commit. You can
2458 then clean up with
2459
2460 -------------------------------------------------
2461 $ git tag -d bad
2462 -------------------------------------------------
2463
2464 Note that the immutable nature of git history means that you haven't really
2465 "modified" existing commits; instead, you have replaced the old commits with
2466 new commits having new object names.
2467
2468 [[reordering-patch-series]]
2469 Reordering or selecting from a patch series
2470 -------------------------------------------
2471
2472 Given one existing commit, the gitlink:git-cherry-pick[1] command
2473 allows you to apply the change introduced by that commit and create a
2474 new commit that records it. So, for example, if "mywork" points to a
2475 series of patches on top of "origin", you might do something like:
2476
2477 -------------------------------------------------
2478 $ git checkout -b mywork-new origin
2479 $ gitk origin..mywork &
2480 -------------------------------------------------
2481
2482 And browse through the list of patches in the mywork branch using gitk,
2483 applying them (possibly in a different order) to mywork-new using
2484 cherry-pick, and possibly modifying them as you go using commit --amend.
2485 The gitlink:git-gui[1] command may also help as it allows you to
2486 individually select diff hunks for inclusion in the index (by
2487 right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
2488
2489 Another technique is to use git-format-patch to create a series of
2490 patches, then reset the state to before the patches:
2491
2492 -------------------------------------------------
2493 $ git format-patch origin
2494 $ git reset --hard origin
2495 -------------------------------------------------
2496
2497 Then modify, reorder, or eliminate patches as preferred before applying
2498 them again with gitlink:git-am[1].
2499
2500 [[patch-series-tools]]
2501 Other tools
2502 -----------
2503
2504 There are numerous other tools, such as StGIT, which exist for the
2505 purpose of maintaining a patch series. These are outside of the scope of
2506 this manual.
2507
2508 [[problems-with-rewriting-history]]
2509 Problems with rewriting history
2510 -------------------------------
2511
2512 The primary problem with rewriting the history of a branch has to do
2513 with merging. Suppose somebody fetches your branch and merges it into
2514 their branch, with a result something like this:
2515
2516 ................................................
2517 o--o--O--o--o--o <-- origin
2518 \ \
2519 t--t--t--m <-- their branch:
2520 ................................................
2521
2522 Then suppose you modify the last three commits:
2523
2524 ................................................
2525 o--o--o <-- new head of origin
2526 /
2527 o--o--O--o--o--o <-- old head of origin
2528 ................................................
2529
2530 If we examined all this history together in one repository, it will
2531 look like:
2532
2533 ................................................
2534 o--o--o <-- new head of origin
2535 /
2536 o--o--O--o--o--o <-- old head of origin
2537 \ \
2538 t--t--t--m <-- their branch:
2539 ................................................
2540
2541 Git has no way of knowing that the new head is an updated version of
2542 the old head; it treats this situation exactly the same as it would if
2543 two developers had independently done the work on the old and new heads
2544 in parallel. At this point, if someone attempts to merge the new head
2545 in to their branch, git will attempt to merge together the two (old and
2546 new) lines of development, instead of trying to replace the old by the
2547 new. The results are likely to be unexpected.
2548
2549 You may still choose to publish branches whose history is rewritten,
2550 and it may be useful for others to be able to fetch those branches in
2551 order to examine or test them, but they should not attempt to pull such
2552 branches into their own work.
2553
2554 For true distributed development that supports proper merging,
2555 published branches should never be rewritten.
2556
2557 [[advanced-branch-management]]
2558 Advanced branch management
2559 ==========================
2560
2561 [[fetching-individual-branches]]
2562 Fetching individual branches
2563 ----------------------------
2564
2565 Instead of using gitlink:git-remote[1], you can also choose just
2566 to update one branch at a time, and to store it locally under an
2567 arbitrary name:
2568
2569 -------------------------------------------------
2570 $ git fetch origin todo:my-todo-work
2571 -------------------------------------------------
2572
2573 The first argument, "origin", just tells git to fetch from the
2574 repository you originally cloned from. The second argument tells git
2575 to fetch the branch named "todo" from the remote repository, and to
2576 store it locally under the name refs/heads/my-todo-work.
2577
2578 You can also fetch branches from other repositories; so
2579
2580 -------------------------------------------------
2581 $ git fetch git://example.com/proj.git master:example-master
2582 -------------------------------------------------
2583
2584 will create a new branch named "example-master" and store in it the
2585 branch named "master" from the repository at the given URL. If you
2586 already have a branch named example-master, it will attempt to
2587 <<fast-forwards,fast-forward>> to the commit given by example.com's
2588 master branch. In more detail:
2589
2590 [[fetch-fast-forwards]]
2591 git fetch and fast-forwards
2592 ---------------------------
2593
2594 In the previous example, when updating an existing branch, "git
2595 fetch" checks to make sure that the most recent commit on the remote
2596 branch is a descendant of the most recent commit on your copy of the
2597 branch before updating your copy of the branch to point at the new
2598 commit. Git calls this process a <<fast-forwards,fast forward>>.
2599
2600 A fast forward looks something like this:
2601
2602 ................................................
2603 o--o--o--o <-- old head of the branch
2604 \
2605 o--o--o <-- new head of the branch
2606 ................................................
2607
2608
2609 In some cases it is possible that the new head will *not* actually be
2610 a descendant of the old head. For example, the developer may have
2611 realized she made a serious mistake, and decided to backtrack,
2612 resulting in a situation like:
2613
2614 ................................................
2615 o--o--o--o--a--b <-- old head of the branch
2616 \
2617 o--o--o <-- new head of the branch
2618 ................................................
2619
2620 In this case, "git fetch" will fail, and print out a warning.
2621
2622 In that case, you can still force git to update to the new head, as
2623 described in the following section. However, note that in the
2624 situation above this may mean losing the commits labeled "a" and "b",
2625 unless you've already created a reference of your own pointing to
2626 them.
2627
2628 [[forcing-fetch]]
2629 Forcing git fetch to do non-fast-forward updates
2630 ------------------------------------------------
2631
2632 If git fetch fails because the new head of a branch is not a
2633 descendant of the old head, you may force the update with:
2634
2635 -------------------------------------------------
2636 $ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2637 -------------------------------------------------
2638
2639 Note the addition of the "+" sign. Alternatively, you can use the "-f"
2640 flag to force updates of all the fetched branches, as in:
2641
2642 -------------------------------------------------
2643 $ git fetch -f origin
2644 -------------------------------------------------
2645
2646 Be aware that commits that the old version of example/master pointed at
2647 may be lost, as we saw in the previous section.
2648
2649 [[remote-branch-configuration]]
2650 Configuring remote branches
2651 ---------------------------
2652
2653 We saw above that "origin" is just a shortcut to refer to the
2654 repository that you originally cloned from. This information is
2655 stored in git configuration variables, which you can see using
2656 gitlink:git-config[1]:
2657
2658 -------------------------------------------------
2659 $ git config -l
2660 core.repositoryformatversion=0
2661 core.filemode=true
2662 core.logallrefupdates=true
2663 remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2664 remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2665 branch.master.remote=origin
2666 branch.master.merge=refs/heads/master
2667 -------------------------------------------------
2668
2669 If there are other repositories that you also use frequently, you can
2670 create similar configuration options to save typing; for example,
2671 after
2672
2673 -------------------------------------------------
2674 $ git config remote.example.url git://example.com/proj.git
2675 -------------------------------------------------
2676
2677 then the following two commands will do the same thing:
2678
2679 -------------------------------------------------
2680 $ git fetch git://example.com/proj.git master:refs/remotes/example/master
2681 $ git fetch example master:refs/remotes/example/master
2682 -------------------------------------------------
2683
2684 Even better, if you add one more option:
2685
2686 -------------------------------------------------
2687 $ git config remote.example.fetch master:refs/remotes/example/master
2688 -------------------------------------------------
2689
2690 then the following commands will all do the same thing:
2691
2692 -------------------------------------------------
2693 $ git fetch git://example.com/proj.git master:refs/remotes/example/master
2694 $ git fetch example master:refs/remotes/example/master
2695 $ git fetch example
2696 -------------------------------------------------
2697
2698 You can also add a "+" to force the update each time:
2699
2700 -------------------------------------------------
2701 $ git config remote.example.fetch +master:ref/remotes/example/master
2702 -------------------------------------------------
2703
2704 Don't do this unless you're sure you won't mind "git fetch" possibly
2705 throwing away commits on mybranch.
2706
2707 Also note that all of the above configuration can be performed by
2708 directly editing the file .git/config instead of using
2709 gitlink:git-config[1].
2710
2711 See gitlink:git-config[1] for more details on the configuration
2712 options mentioned above.
2713
2714
2715 [[git-concepts]]
2716 Git concepts
2717 ============
2718
2719 Git is built on a small number of simple but powerful ideas. While it
2720 is possible to get things done without understanding them, you will find
2721 git much more intuitive if you do.
2722
2723 We start with the most important, the <<def_object_database,object
2724 database>> and the <<def_index,index>>.
2725
2726 [[the-object-database]]
2727 The Object Database
2728 -------------------
2729
2730
2731 We already saw in <<understanding-commits>> that all commits are stored
2732 under a 40-digit "object name". In fact, all the information needed to
2733 represent the history of a project is stored in objects with such names.
2734 In each case the name is calculated by taking the SHA1 hash of the
2735 contents of the object. The SHA1 hash is a cryptographic hash function.
2736 What that means to us is that it is impossible to find two different
2737 objects with the same name. This has a number of advantages; among
2738 others:
2739
2740 - Git can quickly determine whether two objects are identical or not,
2741 just by comparing names.
2742 - Since object names are computed the same way in ever repository, the
2743 same content stored in two repositories will always be stored under
2744 the same name.
2745 - Git can detect errors when it reads an object, by checking that the
2746 object's name is still the SHA1 hash of its contents.
2747
2748 (See <<object-details>> for the details of the object formatting and
2749 SHA1 calculation.)
2750
2751 There are four different types of objects: "blob", "tree", "commit", and
2752 "tag".
2753
2754 - A <<def_blob_object,"blob" object>> is used to store file data.
2755 - A <<def_tree_object,"tree" object>> is an object that ties one or more
2756 "blob" objects into a directory structure. In addition, a tree object
2757 can refer to other tree objects, thus creating a directory hierarchy.
2758 - A <<def_commit_object,"commit" object>> ties such directory hierarchies
2759 together into a <<def_DAG,directed acyclic graph>> of revisions - each
2760 commit contains the object name of exactly one tree designating the
2761 directory hierarchy at the time of the commit. In addition, a commit
2762 refers to "parent" commit objects that describe the history of how we
2763 arrived at that directory hierarchy.
2764 - A <<def_tag_object,"tag" object>> symbolically identifies and can be
2765 used to sign other objects. It contains the object name and type of
2766 another object, a symbolic name (of course!) and, optionally, a
2767 signature.
2768
2769 The object types in some more detail:
2770
2771 [[commit-object]]
2772 Commit Object
2773 ~~~~~~~~~~~~~
2774
2775 The "commit" object links a physical state of a tree with a description
2776 of how we got there and why. Use the --pretty=raw option to
2777 gitlink:git-show[1] or gitlink:git-log[1] to examine your favorite
2778 commit:
2779
2780 ------------------------------------------------
2781 $ git show -s --pretty=raw 2be7fcb476
2782 commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2783 tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2784 parent 257a84d9d02e90447b149af58b271c19405edb6a
2785 author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2786 committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2787
2788 Fix misspelling of 'suppress' in docs
2789
2790 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2791 ------------------------------------------------
2792
2793 As you can see, a commit is defined by:
2794
2795 - a tree: The SHA1 name of a tree object (as defined below), representing
2796 the contents of a directory at a certain point in time.
2797 - parent(s): The SHA1 name of some number of commits which represent the
2798 immediately prevoius step(s) in the history of the project. The
2799 example above has one parent; merge commits may have more than
2800 one. A commit with no parents is called a "root" commit, and
2801 represents the initial revision of a project. Each project must have
2802 at least one root. A project can also have multiple roots, though
2803 that isn't common (or necessarily a good idea).
2804 - an author: The name of the person responsible for this change, together
2805 with its date.
2806 - a committer: The name of the person who actually created the commit,
2807 with the date it was done. This may be different from the author, for
2808 example, if the author was someone who wrote a patch and emailed it
2809 to the person who used it to create the commit.
2810 - a comment describing this commit.
2811
2812 Note that a commit does not itself contain any information about what
2813 actually changed; all changes are calculated by comparing the contents
2814 of the tree referred to by this commit with the trees associated with
2815 its parents. In particular, git does not attempt to record file renames
2816 explicitly, though it can identify cases where the existence of the same
2817 file data at changing paths suggests a rename. (See, for example, the
2818 -M option to gitlink:git-diff[1]).
2819
2820 A commit is usually created by gitlink:git-commit[1], which creates a
2821 commit whose parent is normally the current HEAD, and whose tree is
2822 taken from the content currently stored in the index.
2823
2824 [[tree-object]]
2825 Tree Object
2826 ~~~~~~~~~~~
2827
2828 The ever-versatile gitlink:git-show[1] command can also be used to
2829 examine tree objects, but gitlink:git-ls-tree[1] will give you more
2830 details:
2831
2832 ------------------------------------------------
2833 $ git ls-tree fb3a8bdd0ce
2834 100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
2835 100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
2836 100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
2837 040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
2838 100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
2839 100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
2840 100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
2841 100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
2842 ...
2843 ------------------------------------------------
2844
2845 As you can see, a tree object contains a list of entries, each with a
2846 mode, object type, SHA1 name, and name, sorted by name. It represents
2847 the contents of a single directory tree.
2848
2849 The object type may be a blob, representing the contents of a file, or
2850 another tree, representing the contents of a subdirectory. Since trees
2851 and blobs, like all other objects, are named by the SHA1 hash of their
2852 contents, two trees have the same SHA1 name if and only if their
2853 contents (including, recursively, the contents of all subdirectories)
2854 are identical. This allows git to quickly determine the differences
2855 between two related tree objects, since it can ignore any entries with
2856 identical object names.
2857
2858 (Note: in the presence of submodules, trees may also have commits as
2859 entries. See <<submodules>> for documentation.)
2860
2861 Note that the files all have mode 644 or 755: git actually only pays
2862 attention to the executable bit.
2863
2864 [[blob-object]]
2865 Blob Object
2866 ~~~~~~~~~~~
2867
2868 You can use gitlink:git-show[1] to examine the contents of a blob; take,
2869 for example, the blob in the entry for "COPYING" from the tree above:
2870
2871 ------------------------------------------------
2872 $ git show 6ff87c4664
2873
2874 Note that the only valid version of the GPL as far as this project
2875 is concerned is _this_ particular version of the license (ie v2, not
2876 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
2877 ...
2878 ------------------------------------------------
2879
2880 A "blob" object is nothing but a binary blob of data. It doesn't refer
2881 to anything else or have attributes of any kind.
2882
2883 Since the blob is entirely defined by its data, if two files in a
2884 directory tree (or in multiple different versions of the repository)
2885 have the same contents, they will share the same blob object. The object
2886 is totally independent of its location in the directory tree, and
2887 renaming a file does not change the object that file is associated with.
2888
2889 Note that any tree or blob object can be examined using
2890 gitlink:git-show[1] with the <revision>:<path> syntax. This can
2891 sometimes be useful for browsing the contents of a tree that is not
2892 currently checked out.
2893
2894 [[trust]]
2895 Trust
2896 ~~~~~
2897
2898 If you receive the SHA1 name of a blob from one source, and its contents
2899 from another (possibly untrusted) source, you can still trust that those
2900 contents are correct as long as the SHA1 name agrees. This is because
2901 the SHA1 is designed so that it is infeasible to find different contents
2902 that produce the same hash.
2903
2904 Similarly, you need only trust the SHA1 name of a top-level tree object
2905 to trust the contents of the entire directory that it refers to, and if
2906 you receive the SHA1 name of a commit from a trusted source, then you
2907 can easily verify the entire history of commits reachable through
2908 parents of that commit, and all of those contents of the trees referred
2909 to by those commits.
2910
2911 So to introduce some real trust in the system, the only thing you need
2912 to do is to digitally sign just 'one' special note, which includes the
2913 name of a top-level commit. Your digital signature shows others
2914 that you trust that commit, and the immutability of the history of
2915 commits tells others that they can trust the whole history.
2916
2917 In other words, you can easily validate a whole archive by just
2918 sending out a single email that tells the people the name (SHA1 hash)
2919 of the top commit, and digitally sign that email using something
2920 like GPG/PGP.
2921
2922 To assist in this, git also provides the tag object...
2923
2924 [[tag-object]]
2925 Tag Object
2926 ~~~~~~~~~~
2927
2928 A tag object contains an object, object type, tag name, the name of the
2929 person ("tagger") who created the tag, and a message, which may contain
2930 a signature, as can be seen using the gitlink:git-cat-file[1]:
2931
2932 ------------------------------------------------
2933 $ git cat-file tag v1.5.0
2934 object 437b1b20df4b356c9342dac8d38849f24ef44f27
2935 type commit
2936 tag v1.5.0
2937 tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
2938
2939 GIT 1.5.0
2940 -----BEGIN PGP SIGNATURE-----
2941 Version: GnuPG v1.4.6 (GNU/Linux)
2942
2943 iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
2944 nLE/L9aUXdWeTFPron96DLA=
2945 =2E+0
2946 -----END PGP SIGNATURE-----
2947 ------------------------------------------------
2948
2949 See the gitlink:git-tag[1] command to learn how to create and verify tag
2950 objects. (Note that gitlink:git-tag[1] can also be used to create
2951 "lightweight tags", which are not tag objects at all, but just simple
2952 references whose names begin with "refs/tags/").
2953
2954 [[pack-files]]
2955 How git stores objects efficiently: pack files
2956 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2957
2958 Newly created objects are initially created in a file named after the
2959 object's SHA1 hash (stored in .git/objects).
2960
2961 Unfortunately this system becomes inefficient once a project has a
2962 lot of objects. Try this on an old project:
2963
2964 ------------------------------------------------
2965 $ git count-objects
2966 6930 objects, 47620 kilobytes
2967 ------------------------------------------------
2968
2969 The first number is the number of objects which are kept in
2970 individual files. The second is the amount of space taken up by
2971 those "loose" objects.
2972
2973 You can save space and make git faster by moving these loose objects in
2974 to a "pack file", which stores a group of objects in an efficient
2975 compressed format; the details of how pack files are formatted can be
2976 found in link:technical/pack-format.txt[technical/pack-format.txt].
2977
2978 To put the loose objects into a pack, just run git repack:
2979
2980 ------------------------------------------------
2981 $ git repack
2982 Generating pack...
2983 Done counting 6020 objects.
2984 Deltifying 6020 objects.
2985 100% (6020/6020) done
2986 Writing 6020 objects.
2987 100% (6020/6020) done
2988 Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
2989 Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
2990 ------------------------------------------------
2991
2992 You can then run
2993
2994 ------------------------------------------------
2995 $ git prune
2996 ------------------------------------------------
2997
2998 to remove any of the "loose" objects that are now contained in the
2999 pack. This will also remove any unreferenced objects (which may be
3000 created when, for example, you use "git reset" to remove a commit).
3001 You can verify that the loose objects are gone by looking at the
3002 .git/objects directory or by running
3003
3004 ------------------------------------------------
3005 $ git count-objects
3006 0 objects, 0 kilobytes
3007 ------------------------------------------------
3008
3009 Although the object files are gone, any commands that refer to those
3010 objects will work exactly as they did before.
3011
3012 The gitlink:git-gc[1] command performs packing, pruning, and more for
3013 you, so is normally the only high-level command you need.
3014
3015 [[dangling-objects]]
3016 Dangling objects
3017 ~~~~~~~~~~~~~~~~
3018
3019 The gitlink:git-fsck[1] command will sometimes complain about dangling
3020 objects. They are not a problem.
3021
3022 The most common cause of dangling objects is that you've rebased a
3023 branch, or you have pulled from somebody else who rebased a branch--see
3024 <<cleaning-up-history>>. In that case, the old head of the original
3025 branch still exists, as does everything it pointed to. The branch
3026 pointer itself just doesn't, since you replaced it with another one.
3027
3028 There are also other situations that cause dangling objects. For
3029 example, a "dangling blob" may arise because you did a "git add" of a
3030 file, but then, before you actually committed it and made it part of the
3031 bigger picture, you changed something else in that file and committed
3032 that *updated* thing - the old state that you added originally ends up
3033 not being pointed to by any commit or tree, so it's now a dangling blob
3034 object.
3035
3036 Similarly, when the "recursive" merge strategy runs, and finds that
3037 there are criss-cross merges and thus more than one merge base (which is
3038 fairly unusual, but it does happen), it will generate one temporary
3039 midway tree (or possibly even more, if you had lots of criss-crossing
3040 merges and more than two merge bases) as a temporary internal merge
3041 base, and again, those are real objects, but the end result will not end
3042 up pointing to them, so they end up "dangling" in your repository.
3043
3044 Generally, dangling objects aren't anything to worry about. They can
3045 even be very useful: if you screw something up, the dangling objects can
3046 be how you recover your old tree (say, you did a rebase, and realized
3047 that you really didn't want to - you can look at what dangling objects
3048 you have, and decide to reset your head to some old dangling state).
3049
3050 For commits, you can just use:
3051
3052 ------------------------------------------------
3053 $ gitk <dangling-commit-sha-goes-here> --not --all
3054 ------------------------------------------------
3055
3056 This asks for all the history reachable from the given commit but not
3057 from any branch, tag, or other reference. If you decide it's something
3058 you want, you can always create a new reference to it, e.g.,
3059
3060 ------------------------------------------------
3061 $ git branch recovered-branch <dangling-commit-sha-goes-here>
3062 ------------------------------------------------
3063
3064 For blobs and trees, you can't do the same, but you can still examine
3065 them. You can just do
3066
3067 ------------------------------------------------
3068 $ git show <dangling-blob/tree-sha-goes-here>
3069 ------------------------------------------------
3070
3071 to show what the contents of the blob were (or, for a tree, basically
3072 what the "ls" for that directory was), and that may give you some idea
3073 of what the operation was that left that dangling object.
3074
3075 Usually, dangling blobs and trees aren't very interesting. They're
3076 almost always the result of either being a half-way mergebase (the blob
3077 will often even have the conflict markers from a merge in it, if you
3078 have had conflicting merges that you fixed up by hand), or simply
3079 because you interrupted a "git fetch" with ^C or something like that,
3080 leaving _some_ of the new objects in the object database, but just
3081 dangling and useless.
3082
3083 Anyway, once you are sure that you're not interested in any dangling
3084 state, you can just prune all unreachable objects:
3085
3086 ------------------------------------------------
3087 $ git prune
3088 ------------------------------------------------
3089
3090 and they'll be gone. But you should only run "git prune" on a quiescent
3091 repository - it's kind of like doing a filesystem fsck recovery: you
3092 don't want to do that while the filesystem is mounted.
3093
3094 (The same is true of "git-fsck" itself, btw - but since
3095 git-fsck never actually *changes* the repository, it just reports
3096 on what it found, git-fsck itself is never "dangerous" to run.
3097 Running it while somebody is actually changing the repository can cause
3098 confusing and scary messages, but it won't actually do anything bad. In
3099 contrast, running "git prune" while somebody is actively changing the
3100 repository is a *BAD* idea).
3101
3102 [[the-index]]
3103 The index
3104 -----------
3105
3106 The index is a binary file (generally kept in .git/index) containing a
3107 sorted list of path names, each with permissions and the SHA1 of a blob
3108 object; gitlink:git-ls-files[1] can show you the contents of the index:
3109
3110 -------------------------------------------------
3111 $ git ls-files --stage
3112 100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore
3113 100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap
3114 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING
3115 100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore
3116 100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile
3117 ...
3118 100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h
3119 100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c
3120 100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h
3121 -------------------------------------------------
3122
3123 Note that in older documentation you may see the index called the
3124 "current directory cache" or just the "cache". It has three important
3125 properties:
3126
3127 1. The index contains all the information necessary to generate a single
3128 (uniquely determined) tree object.
3129 +
3130 For example, running gitlink:git-commit[1] generates this tree object
3131 from the index, stores it in the object database, and uses it as the
3132 tree object associated with the new commit.
3133
3134 2. The index enables fast comparisons between the tree object it defines
3135 and the working tree.
3136 +
3137 It does this by storing some additional data for each entry (such as
3138 the last modified time). This data is not displayed above, and is not
3139 stored in the created tree object, but it can be used to determine
3140 quickly which files in the working directory differ from what was
3141 stored in the index, and thus save git from having to read all of the
3142 data from such files to look for changes.
3143
3144 3. It can efficiently represent information about merge conflicts
3145 between different tree objects, allowing each pathname to be
3146 associated with sufficient information about the trees involved that
3147 you can create a three-way merge between them.
3148 +
3149 We saw in <<conflict-resolution>> that during a merge the index can
3150 store multiple versions of a single file (called "stages"). The third
3151 column in the gitlink:git-ls-files[1] output above is the stage
3152 number, and will take on values other than 0 for files with merge
3153 conflicts.
3154
3155 The index is thus a sort of temporary staging area, which is filled with
3156 a tree which you are in the process of working on.
3157
3158 If you blow the index away entirely, you generally haven't lost any
3159 information as long as you have the name of the tree that it described.
3160
3161 [[submodules]]
3162 Submodules
3163 ==========
3164
3165 Large projects are often composed of smaller, self-contained modules. For
3166 example, an embedded Linux distribution's source tree would include every
3167 piece of software in the distribution with some local modifications; a movie
3168 player might need to build against a specific, known-working version of a
3169 decompression library; several independent programs might all share the same
3170 build scripts.
3171
3172 With centralized revision control systems this is often accomplished by
3173 including every module in one single repository. Developers can check out
3174 all modules or only the modules they need to work with. They can even modify
3175 files across several modules in a single commit while moving things around
3176 or updating APIs and translations.
3177
3178 Git does not allow partial checkouts, so duplicating this approach in Git
3179 would force developers to keep a local copy of modules they are not
3180 interested in touching. Commits in an enormous checkout would be slower
3181 than you'd expect as Git would have to scan every directory for changes.
3182 If modules have a lot of local history, clones would take forever.
3183
3184 On the plus side, distributed revision control systems can much better
3185 integrate with external sources. In a centralized model, a single arbitrary
3186 snapshot of the external project is exported from its own revision control
3187 and then imported into the local revision control on a vendor branch. All
3188 the history is hidden. With distributed revision control you can clone the
3189 entire external history and much more easily follow development and re-merge
3190 local changes.
3191
3192 Git's submodule support allows a repository to contain, as a subdirectory, a
3193 checkout of an external project. Submodules maintain their own identity;
3194 the submodule support just stores the submodule repository location and
3195 commit ID, so other developers who clone the containing project
3196 ("superproject") can easily clone all the submodules at the same revision.
3197 Partial checkouts of the superproject are possible: you can tell Git to
3198 clone none, some or all of the submodules.
3199
3200 The gitlink:git-submodule[1] command is available since Git 1.5.3. Users
3201 with Git 1.5.2 can look up the submodule commits in the repository and
3202 manually check them out; earlier versions won't recognize the submodules at
3203 all.
3204
3205 To see how submodule support works, create (for example) four example
3206 repositories that can be used later as a submodule:
3207
3208 -------------------------------------------------
3209 $ mkdir ~/git
3210 $ cd ~/git
3211 $ for i in a b c d
3212 do
3213 mkdir $i
3214 cd $i
3215 git init
3216 echo "module $i" > $i.txt
3217 git add $i.txt
3218 git commit -m "Initial commit, submodule $i"
3219 cd ..
3220 done
3221 -------------------------------------------------
3222
3223 Now create the superproject and add all the submodules:
3224
3225 -------------------------------------------------
3226 $ mkdir super
3227 $ cd super
3228 $ git init
3229 $ for i in a b c d
3230 do
3231 git submodule add ~/git/$i
3232 done
3233 -------------------------------------------------
3234
3235 NOTE: Do not use local URLs here if you plan to publish your superproject!
3236
3237 See what files `git submodule` created:
3238
3239 -------------------------------------------------
3240 $ ls -a
3241 . .. .git .gitmodules a b c d
3242 -------------------------------------------------
3243
3244 The `git submodule add` command does a couple of things:
3245
3246 - It clones the submodule under the current directory and by default checks out
3247 the master branch.
3248 - It adds the submodule's clone path to the gitlink:gitmodules[5] file and
3249 adds this file to the index, ready to be committed.
3250 - It adds the submodule's current commit ID to the index, ready to be
3251 committed.
3252
3253 Commit the superproject:
3254
3255 -------------------------------------------------
3256 $ git commit -m "Add submodules a, b, c and d."
3257 -------------------------------------------------
3258
3259 Now clone the superproject:
3260
3261 -------------------------------------------------
3262 $ cd ..
3263 $ git clone super cloned
3264 $ cd cloned
3265 -------------------------------------------------
3266
3267 The submodule directories are there, but they're empty:
3268
3269 -------------------------------------------------
3270 $ ls -a a
3271 . ..
3272 $ git submodule status
3273 -d266b9873ad50488163457f025db7cdd9683d88b a
3274 -e81d457da15309b4fef4249aba9b50187999670d b
3275 -c1536a972b9affea0f16e0680ba87332dc059146 c
3276 -d96249ff5d57de5de093e6baff9e0aafa5276a74 d
3277 -------------------------------------------------
3278
3279 NOTE: The commit object names shown above would be different for you, but they
3280 should match the HEAD commit object names of your repositories. You can check
3281 it by running `git ls-remote ../a`.
3282
3283 Pulling down the submodules is a two-step process. First run `git submodule
3284 init` to add the submodule repository URLs to `.git/config`:
3285
3286 -------------------------------------------------
3287 $ git submodule init
3288 -------------------------------------------------
3289
3290 Now use `git submodule update` to clone the repositories and check out the
3291 commits specified in the superproject:
3292
3293 -------------------------------------------------
3294 $ git submodule update
3295 $ cd a
3296 $ ls -a
3297 . .. .git a.txt
3298 -------------------------------------------------
3299
3300 One major difference between `git submodule update` and `git submodule add` is
3301 that `git submodule update` checks out a specific commit, rather than the tip
3302 of a branch. It's like checking out a tag: the head is detached, so you're not
3303 working on a branch.
3304
3305 -------------------------------------------------
3306 $ git branch
3307 * (no branch)
3308 master
3309 -------------------------------------------------
3310
3311 If you want to make a change within a submodule and you have a detached head,
3312 then you should create or checkout a branch, make your changes, publish the
3313 change within the submodule, and then update the superproject to reference the
3314 new commit:
3315
3316 -------------------------------------------------
3317 $ git checkout master
3318 -------------------------------------------------
3319
3320 or
3321
3322 -------------------------------------------------
3323 $ git checkout -b fix-up
3324 -------------------------------------------------
3325
3326 then
3327
3328 -------------------------------------------------
3329 $ echo "adding a line again" >> a.txt
3330 $ git commit -a -m "Updated the submodule from within the superproject."
3331 $ git push
3332 $ cd ..
3333 $ git diff
3334 diff --git a/a b/a
3335 index d266b98..261dfac 160000
3336 --- a/a
3337 +++ b/a
3338 @@ -1 +1 @@
3339 -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b
3340 +Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24
3341 $ git add a
3342 $ git commit -m "Updated submodule a."
3343 $ git push
3344 -------------------------------------------------
3345
3346 You have to run `git submodule update` after `git pull` if you want to update
3347 submodules, too.
3348
3349 Pitfalls with submodules
3350 ------------------------
3351
3352 Always publish the submodule change before publishing the change to the
3353 superproject that references it. If you forget to publish the submodule change,
3354 others won't be able to clone the repository:
3355
3356 -------------------------------------------------
3357 $ cd ~/git/super/a
3358 $ echo i added another line to this file >> a.txt
3359 $ git commit -a -m "doing it wrong this time"
3360 $ cd ..
3361 $ git add a
3362 $ git commit -m "Updated submodule a again."
3363 $ git push
3364 $ cd ~/git/cloned
3365 $ git pull
3366 $ git submodule update
3367 error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.
3368 Did you forget to 'git add'?
3369 Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'
3370 -------------------------------------------------
3371
3372 You also should not rewind branches in a submodule beyond commits that were
3373 ever recorded in any superproject.
3374
3375 It's not safe to run `git submodule update` if you've made and committed
3376 changes within a submodule without checking out a branch first. They will be
3377 silently overwritten:
3378
3379 -------------------------------------------------
3380 $ cat a.txt
3381 module a
3382 $ echo line added from private2 >> a.txt
3383 $ git commit -a -m "line added inside private2"
3384 $ cd ..
3385 $ git submodule update
3386 Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'
3387 $ cd a
3388 $ cat a.txt
3389 module a
3390 -------------------------------------------------
3391
3392 NOTE: The changes are still visible in the submodule's reflog.
3393
3394 This is not the case if you did not commit your changes.
3395
3396 [[low-level-operations]]
3397 Low-level git operations
3398 ========================
3399
3400 Many of the higher-level commands were originally implemented as shell
3401 scripts using a smaller core of low-level git commands. These can still
3402 be useful when doing unusual things with git, or just as a way to
3403 understand its inner workings.
3404
3405 [[object-manipulation]]
3406 Object access and manipulation
3407 ------------------------------
3408
3409 The gitlink:git-cat-file[1] command can show the contents of any object,
3410 though the higher-level gitlink:git-show[1] is usually more useful.
3411
3412 The gitlink:git-commit-tree[1] command allows constructing commits with
3413 arbitrary parents and trees.
3414
3415 A tree can be created with gitlink:git-write-tree[1] and its data can be
3416 accessed by gitlink:git-ls-tree[1]. Two trees can be compared with
3417 gitlink:git-diff-tree[1].
3418
3419 A tag is created with gitlink:git-mktag[1], and the signature can be
3420 verified by gitlink:git-verify-tag[1], though it is normally simpler to
3421 use gitlink:git-tag[1] for both.
3422
3423 [[the-workflow]]
3424 The Workflow
3425 ------------
3426
3427 High-level operations such as gitlink:git-commit[1],
3428 gitlink:git-checkout[1] and git-reset[1] work by moving data between the
3429 working tree, the index, and the object database. Git provides
3430 low-level operations which perform each of these steps individually.
3431
3432 Generally, all "git" operations work on the index file. Some operations
3433 work *purely* on the index file (showing the current state of the
3434 index), but most operations move data between the index file and either
3435 the database or the working directory. Thus there are four main
3436 combinations:
3437
3438 [[working-directory-to-index]]
3439 working directory -> index
3440 ~~~~~~~~~~~~~~~~~~~~~~~~~~
3441
3442 The gitlink:git-update-index[1] command updates the index with
3443 information from the working directory. You generally update the
3444 index information by just specifying the filename you want to update,
3445 like so:
3446
3447 -------------------------------------------------
3448 $ git update-index filename
3449 -------------------------------------------------
3450
3451 but to avoid common mistakes with filename globbing etc, the command
3452 will not normally add totally new entries or remove old entries,
3453 i.e. it will normally just update existing cache entries.
3454
3455 To tell git that yes, you really do realize that certain files no
3456 longer exist, or that new files should be added, you
3457 should use the `--remove` and `--add` flags respectively.
3458
3459 NOTE! A `--remove` flag does 'not' mean that subsequent filenames will
3460 necessarily be removed: if the files still exist in your directory
3461 structure, the index will be updated with their new status, not
3462 removed. The only thing `--remove` means is that update-cache will be
3463 considering a removed file to be a valid thing, and if the file really
3464 does not exist any more, it will update the index accordingly.
3465
3466 As a special case, you can also do `git-update-index --refresh`, which
3467 will refresh the "stat" information of each index to match the current
3468 stat information. It will 'not' update the object status itself, and
3469 it will only update the fields that are used to quickly test whether
3470 an object still matches its old backing store object.
3471
3472 The previously introduced gitlink:git-add[1] is just a wrapper for
3473 gitlink:git-update-index[1].
3474
3475 [[index-to-object-database]]
3476 index -> object database
3477 ~~~~~~~~~~~~~~~~~~~~~~~~
3478
3479 You write your current index file to a "tree" object with the program
3480
3481 -------------------------------------------------
3482 $ git write-tree
3483 -------------------------------------------------
3484
3485 that doesn't come with any options - it will just write out the
3486 current index into the set of tree objects that describe that state,
3487 and it will return the name of the resulting top-level tree. You can
3488 use that tree to re-generate the index at any time by going in the
3489 other direction:
3490
3491 [[object-database-to-index]]
3492 object database -> index
3493 ~~~~~~~~~~~~~~~~~~~~~~~~
3494
3495 You read a "tree" file from the object database, and use that to
3496 populate (and overwrite - don't do this if your index contains any
3497 unsaved state that you might want to restore later!) your current
3498 index. Normal operation is just
3499
3500 -------------------------------------------------
3501 $ git-read-tree <sha1 of tree>
3502 -------------------------------------------------
3503
3504 and your index file will now be equivalent to the tree that you saved
3505 earlier. However, that is only your 'index' file: your working
3506 directory contents have not been modified.
3507
3508 [[index-to-working-directory]]
3509 index -> working directory
3510 ~~~~~~~~~~~~~~~~~~~~~~~~~~
3511
3512 You update your working directory from the index by "checking out"
3513 files. This is not a very common operation, since normally you'd just
3514 keep your files updated, and rather than write to your working
3515 directory, you'd tell the index files about the changes in your
3516 working directory (i.e. `git-update-index`).
3517
3518 However, if you decide to jump to a new version, or check out somebody
3519 else's version, or just restore a previous tree, you'd populate your
3520 index file with read-tree, and then you need to check out the result
3521 with
3522
3523 -------------------------------------------------
3524 $ git-checkout-index filename
3525 -------------------------------------------------
3526
3527 or, if you want to check out all of the index, use `-a`.
3528
3529 NOTE! git-checkout-index normally refuses to overwrite old files, so
3530 if you have an old version of the tree already checked out, you will
3531 need to use the "-f" flag ('before' the "-a" flag or the filename) to
3532 'force' the checkout.
3533
3534
3535 Finally, there are a few odds and ends which are not purely moving
3536 from one representation to the other:
3537
3538 [[tying-it-all-together]]
3539 Tying it all together
3540 ~~~~~~~~~~~~~~~~~~~~~
3541
3542 To commit a tree you have instantiated with "git-write-tree", you'd
3543 create a "commit" object that refers to that tree and the history
3544 behind it - most notably the "parent" commits that preceded it in
3545 history.
3546
3547 Normally a "commit" has one parent: the previous state of the tree
3548 before a certain change was made. However, sometimes it can have two
3549 or more parent commits, in which case we call it a "merge", due to the
3550 fact that such a commit brings together ("merges") two or more
3551 previous states represented by other commits.
3552
3553 In other words, while a "tree" represents a particular directory state
3554 of a working directory, a "commit" represents that state in "time",
3555 and explains how we got there.
3556
3557 You create a commit object by giving it the tree that describes the
3558 state at the time of the commit, and a list of parents:
3559
3560 -------------------------------------------------
3561 $ git-commit-tree <tree> -p <parent> [-p <parent2> ..]
3562 -------------------------------------------------
3563
3564 and then giving the reason for the commit on stdin (either through
3565 redirection from a pipe or file, or by just typing it at the tty).
3566
3567 git-commit-tree will return the name of the object that represents
3568 that commit, and you should save it away for later use. Normally,
3569 you'd commit a new `HEAD` state, and while git doesn't care where you
3570 save the note about that state, in practice we tend to just write the
3571 result to the file pointed at by `.git/HEAD`, so that we can always see
3572 what the last committed state was.
3573
3574 Here is an ASCII art by Jon Loeliger that illustrates how
3575 various pieces fit together.
3576
3577 ------------
3578
3579 commit-tree
3580 commit obj
3581 +----+
3582 | |
3583 | |
3584 V V
3585 +-----------+
3586 | Object DB |
3587 | Backing |
3588 | Store |
3589 +-----------+
3590 ^
3591 write-tree | |
3592 tree obj | |
3593 | | read-tree
3594 | | tree obj
3595 V
3596 +-----------+
3597 | Index |
3598 | "cache" |
3599 +-----------+
3600 update-index ^
3601 blob obj | |
3602 | |
3603 checkout-index -u | | checkout-index
3604 stat | | blob obj
3605 V
3606 +-----------+
3607 | Working |
3608 | Directory |
3609 +-----------+
3610
3611 ------------
3612
3613
3614 [[examining-the-data]]
3615 Examining the data
3616 ------------------
3617
3618 You can examine the data represented in the object database and the
3619 index with various helper tools. For every object, you can use
3620 gitlink:git-cat-file[1] to examine details about the
3621 object:
3622
3623 -------------------------------------------------
3624 $ git-cat-file -t <objectname>
3625 -------------------------------------------------
3626
3627 shows the type of the object, and once you have the type (which is
3628 usually implicit in where you find the object), you can use
3629
3630 -------------------------------------------------
3631 $ git-cat-file blob|tree|commit|tag <objectname>
3632 -------------------------------------------------
3633
3634 to show its contents. NOTE! Trees have binary content, and as a result
3635 there is a special helper for showing that content, called
3636 `git-ls-tree`, which turns the binary content into a more easily
3637 readable form.
3638
3639 It's especially instructive to look at "commit" objects, since those
3640 tend to be small and fairly self-explanatory. In particular, if you
3641 follow the convention of having the top commit name in `.git/HEAD`,
3642 you can do
3643
3644 -------------------------------------------------
3645 $ git-cat-file commit HEAD
3646 -------------------------------------------------
3647
3648 to see what the top commit was.
3649
3650 [[merging-multiple-trees]]
3651 Merging multiple trees
3652 ----------------------
3653
3654 Git helps you do a three-way merge, which you can expand to n-way by
3655 repeating the merge procedure arbitrary times until you finally
3656 "commit" the state. The normal situation is that you'd only do one
3657 three-way merge (two parents), and commit it, but if you like to, you
3658 can do multiple parents in one go.
3659
3660 To do a three-way merge, you need the two sets of "commit" objects
3661 that you want to merge, use those to find the closest common parent (a
3662 third "commit" object), and then use those commit objects to find the
3663 state of the directory ("tree" object) at these points.
3664
3665 To get the "base" for the merge, you first look up the common parent
3666 of two commits with
3667
3668 -------------------------------------------------
3669 $ git-merge-base <commit1> <commit2>
3670 -------------------------------------------------
3671
3672 which will return you the commit they are both based on. You should
3673 now look up the "tree" objects of those commits, which you can easily
3674 do with (for example)
3675
3676 -------------------------------------------------
3677 $ git-cat-file commit <commitname> | head -1
3678 -------------------------------------------------
3679
3680 since the tree object information is always the first line in a commit
3681 object.
3682
3683 Once you know the three trees you are going to merge (the one "original"
3684 tree, aka the common tree, and the two "result" trees, aka the branches
3685 you want to merge), you do a "merge" read into the index. This will
3686 complain if it has to throw away your old index contents, so you should
3687 make sure that you've committed those - in fact you would normally
3688 always do a merge against your last commit (which should thus match what
3689 you have in your current index anyway).
3690
3691 To do the merge, do
3692
3693 -------------------------------------------------
3694 $ git-read-tree -m -u <origtree> <yourtree> <targettree>
3695 -------------------------------------------------
3696
3697 which will do all trivial merge operations for you directly in the
3698 index file, and you can just write the result out with
3699 `git-write-tree`.
3700
3701
3702 [[merging-multiple-trees-2]]
3703 Merging multiple trees, continued
3704 ---------------------------------
3705
3706 Sadly, many merges aren't trivial. If there are files that have
3707 been added.moved or removed, or if both branches have modified the
3708 same file, you will be left with an index tree that contains "merge
3709 entries" in it. Such an index tree can 'NOT' be written out to a tree
3710 object, and you will have to resolve any such merge clashes using
3711 other tools before you can write out the result.
3712
3713 You can examine such index state with `git-ls-files --unmerged`
3714 command. An example:
3715
3716 ------------------------------------------------
3717 $ git-read-tree -m $orig HEAD $target
3718 $ git-ls-files --unmerged
3719 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c
3720 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c
3721 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c
3722 ------------------------------------------------
3723
3724 Each line of the `git-ls-files --unmerged` output begins with
3725 the blob mode bits, blob SHA1, 'stage number', and the
3726 filename. The 'stage number' is git's way to say which tree it
3727 came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD`
3728 tree, and stage3 `$target` tree.
3729
3730 Earlier we said that trivial merges are done inside
3731 `git-read-tree -m`. For example, if the file did not change
3732 from `$orig` to `HEAD` nor `$target`, or if the file changed
3733 from `$orig` to `HEAD` and `$orig` to `$target` the same way,
3734 obviously the final outcome is what is in `HEAD`. What the
3735 above example shows is that file `hello.c` was changed from
3736 `$orig` to `HEAD` and `$orig` to `$target` in a different way.
3737 You could resolve this by running your favorite 3-way merge
3738 program, e.g. `diff3`, `merge`, or git's own merge-file, on
3739 the blob objects from these three stages yourself, like this:
3740
3741 ------------------------------------------------
3742 $ git-cat-file blob 263414f... >hello.c~1
3743 $ git-cat-file blob 06fa6a2... >hello.c~2
3744 $ git-cat-file blob cc44c73... >hello.c~3
3745 $ git merge-file hello.c~2 hello.c~1 hello.c~3
3746 ------------------------------------------------
3747
3748 This would leave the merge result in `hello.c~2` file, along
3749 with conflict markers if there are conflicts. After verifying
3750 the merge result makes sense, you can tell git what the final
3751 merge result for this file is by:
3752
3753 -------------------------------------------------
3754 $ mv -f hello.c~2 hello.c
3755 $ git-update-index hello.c
3756 -------------------------------------------------
3757
3758 When a path is in unmerged state, running `git-update-index` for
3759 that path tells git to mark the path resolved.
3760
3761 The above is the description of a git merge at the lowest level,
3762 to help you understand what conceptually happens under the hood.
3763 In practice, nobody, not even git itself, uses three `git-cat-file`
3764 for this. There is `git-merge-index` program that extracts the
3765 stages to temporary files and calls a "merge" script on it:
3766
3767 -------------------------------------------------
3768 $ git-merge-index git-merge-one-file hello.c
3769 -------------------------------------------------
3770
3771 and that is what higher level `git merge -s resolve` is implemented with.
3772
3773 [[hacking-git]]
3774 Hacking git
3775 ===========
3776
3777 This chapter covers internal details of the git implementation which
3778 probably only git developers need to understand.
3779
3780 [[object-details]]
3781 Object storage format
3782 ---------------------
3783
3784 All objects have a statically determined "type" which identifies the
3785 format of the object (i.e. how it is used, and how it can refer to other
3786 objects). There are currently four different object types: "blob",
3787 "tree", "commit", and "tag".
3788
3789 Regardless of object type, all objects share the following
3790 characteristics: they are all deflated with zlib, and have a header
3791 that not only specifies their type, but also provides size information
3792 about the data in the object. It's worth noting that the SHA1 hash
3793 that is used to name the object is the hash of the original data
3794 plus this header, so `sha1sum` 'file' does not match the object name
3795 for 'file'.
3796 (Historical note: in the dawn of the age of git the hash
3797 was the sha1 of the 'compressed' object.)
3798
3799 As a result, the general consistency of an object can always be tested
3800 independently of the contents or the type of the object: all objects can
3801 be validated by verifying that (a) their hashes match the content of the
3802 file and (b) the object successfully inflates to a stream of bytes that
3803 forms a sequence of <ascii type without space> {plus} <space> {plus} <ascii decimal
3804 size> {plus} <byte\0> {plus} <binary object data>.
3805
3806 The structured objects can further have their structure and
3807 connectivity to other objects verified. This is generally done with
3808 the `git-fsck` program, which generates a full dependency graph
3809 of all objects, and verifies their internal consistency (in addition
3810 to just verifying their superficial consistency through the hash).
3811
3812 [[birdview-on-the-source-code]]
3813 A birds-eye view of Git's source code
3814 -------------------------------------
3815
3816 It is not always easy for new developers to find their way through Git's
3817 source code. This section gives you a little guidance to show where to
3818 start.
3819
3820 A good place to start is with the contents of the initial commit, with:
3821
3822 ----------------------------------------------------
3823 $ git checkout e83c5163
3824 ----------------------------------------------------
3825
3826 The initial revision lays the foundation for almost everything git has
3827 today, but is small enough to read in one sitting.
3828
3829 Note that terminology has changed since that revision. For example, the
3830 README in that revision uses the word "changeset" to describe what we
3831 now call a <<def_commit_object,commit>>.
3832
3833 Also, we do not call it "cache" any more, but "index", however, the
3834 file is still called `cache.h`. Remark: Not much reason to change it now,
3835 especially since there is no good single name for it anyway, because it is
3836 basically _the_ header file which is included by _all_ of Git's C sources.
3837
3838 If you grasp the ideas in that initial commit, you should check out a
3839 more recent version and skim `cache.h`, `object.h` and `commit.h`.
3840
3841 In the early days, Git (in the tradition of UNIX) was a bunch of programs
3842 which were extremely simple, and which you used in scripts, piping the
3843 output of one into another. This turned out to be good for initial
3844 development, since it was easier to test new things. However, recently
3845 many of these parts have become builtins, and some of the core has been
3846 "libified", i.e. put into libgit.a for performance, portability reasons,
3847 and to avoid code duplication.
3848
3849 By now, you know what the index is (and find the corresponding data
3850 structures in `cache.h`), and that there are just a couple of object types
3851 (blobs, trees, commits and tags) which inherit their common structure from
3852 `struct object`, which is their first member (and thus, you can cast e.g.
3853 `(struct object *)commit` to achieve the _same_ as `&commit->object`, i.e.
3854 get at the object name and flags).
3855
3856 Now is a good point to take a break to let this information sink in.
3857
3858 Next step: get familiar with the object naming. Read <<naming-commits>>.
3859 There are quite a few ways to name an object (and not only revisions!).
3860 All of these are handled in `sha1_name.c`. Just have a quick look at
3861 the function `get_sha1()`. A lot of the special handling is done by
3862 functions like `get_sha1_basic()` or the likes.
3863
3864 This is just to get you into the groove for the most libified part of Git:
3865 the revision walker.
3866
3867 Basically, the initial version of `git log` was a shell script:
3868
3869 ----------------------------------------------------------------
3870 $ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \
3871 LESS=-S ${PAGER:-less}
3872 ----------------------------------------------------------------
3873
3874 What does this mean?
3875
3876 `git-rev-list` is the original version of the revision walker, which
3877 _always_ printed a list of revisions to stdout. It is still functional,
3878 and needs to, since most new Git programs start out as scripts using
3879 `git-rev-list`.
3880
3881 `git-rev-parse` is not as important any more; it was only used to filter out
3882 options that were relevant for the different plumbing commands that were
3883 called by the script.
3884
3885 Most of what `git-rev-list` did is contained in `revision.c` and
3886 `revision.h`. It wraps the options in a struct named `rev_info`, which
3887 controls how and what revisions are walked, and more.
3888
3889 The original job of `git-rev-parse` is now taken by the function
3890 `setup_revisions()`, which parses the revisions and the common command line
3891 options for the revision walker. This information is stored in the struct
3892 `rev_info` for later consumption. You can do your own command line option
3893 parsing after calling `setup_revisions()`. After that, you have to call
3894 `prepare_revision_walk()` for initialization, and then you can get the
3895 commits one by one with the function `get_revision()`.
3896
3897 If you are interested in more details of the revision walking process,
3898 just have a look at the first implementation of `cmd_log()`; call
3899 `git-show v1.3.0~155^2~4` and scroll down to that function (note that you
3900 no longer need to call `setup_pager()` directly).
3901
3902 Nowadays, `git log` is a builtin, which means that it is _contained_ in the
3903 command `git`. The source side of a builtin is
3904
3905 - a function called `cmd_<bla>`, typically defined in `builtin-<bla>.c`,
3906 and declared in `builtin.h`,
3907
3908 - an entry in the `commands[]` array in `git.c`, and
3909
3910 - an entry in `BUILTIN_OBJECTS` in the `Makefile`.
3911
3912 Sometimes, more than one builtin is contained in one source file. For
3913 example, `cmd_whatchanged()` and `cmd_log()` both reside in `builtin-log.c`,
3914 since they share quite a bit of code. In that case, the commands which are
3915 _not_ named like the `.c` file in which they live have to be listed in
3916 `BUILT_INS` in the `Makefile`.
3917
3918 `git log` looks more complicated in C than it does in the original script,
3919 but that allows for a much greater flexibility and performance.
3920
3921 Here again it is a good point to take a pause.
3922
3923 Lesson three is: study the code. Really, it is the best way to learn about
3924 the organization of Git (after you know the basic concepts).
3925
3926 So, think about something which you are interested in, say, "how can I
3927 access a blob just knowing the object name of it?". The first step is to
3928 find a Git command with which you can do it. In this example, it is either
3929 `git show` or `git cat-file`.
3930
3931 For the sake of clarity, let's stay with `git cat-file`, because it
3932
3933 - is plumbing, and
3934
3935 - was around even in the initial commit (it literally went only through
3936 some 20 revisions as `cat-file.c`, was renamed to `builtin-cat-file.c`
3937 when made a builtin, and then saw less than 10 versions).
3938
3939 So, look into `builtin-cat-file.c`, search for `cmd_cat_file()` and look what
3940 it does.
3941
3942 ------------------------------------------------------------------
3943 git_config(git_default_config);
3944 if (argc != 3)
3945 usage("git-cat-file [-t|-s|-e|-p|<type>] <sha1>");
3946 if (get_sha1(argv[2], sha1))
3947 die("Not a valid object name %s", argv[2]);
3948 ------------------------------------------------------------------
3949
3950 Let's skip over the obvious details; the only really interesting part
3951 here is the call to `get_sha1()`. It tries to interpret `argv[2]` as an
3952 object name, and if it refers to an object which is present in the current
3953 repository, it writes the resulting SHA-1 into the variable `sha1`.
3954
3955 Two things are interesting here:
3956
3957 - `get_sha1()` returns 0 on _success_. This might surprise some new
3958 Git hackers, but there is a long tradition in UNIX to return different
3959 negative numbers in case of different errors -- and 0 on success.
3960
3961 - the variable `sha1` in the function signature of `get_sha1()` is `unsigned
3962 char \*`, but is actually expected to be a pointer to `unsigned
3963 char[20]`. This variable will contain the 160-bit SHA-1 of the given
3964 commit. Note that whenever a SHA-1 is passed as `unsigned char \*`, it
3965 is the binary representation, as opposed to the ASCII representation in
3966 hex characters, which is passed as `char *`.
3967
3968 You will see both of these things throughout the code.
3969
3970 Now, for the meat:
3971
3972 -----------------------------------------------------------------------------
3973 case 0:
3974 buf = read_object_with_reference(sha1, argv[1], &size, NULL);
3975 -----------------------------------------------------------------------------
3976
3977 This is how you read a blob (actually, not only a blob, but any type of
3978 object). To know how the function `read_object_with_reference()` actually
3979 works, find the source code for it (something like `git grep
3980 read_object_with | grep ":[a-z]"` in the git repository), and read
3981 the source.
3982
3983 To find out how the result can be used, just read on in `cmd_cat_file()`:
3984
3985 -----------------------------------
3986 write_or_die(1, buf, size);
3987 -----------------------------------
3988
3989 Sometimes, you do not know where to look for a feature. In many such cases,
3990 it helps to search through the output of `git log`, and then `git show` the
3991 corresponding commit.
3992
3993 Example: If you know that there was some test case for `git bundle`, but
3994 do not remember where it was (yes, you _could_ `git grep bundle t/`, but that
3995 does not illustrate the point!):
3996
3997 ------------------------
3998 $ git log --no-merges t/
3999 ------------------------
4000
4001 In the pager (`less`), just search for "bundle", go a few lines back,
4002 and see that it is in commit 18449ab0... Now just copy this object name,
4003 and paste it into the command line
4004
4005 -------------------
4006 $ git show 18449ab0
4007 -------------------
4008
4009 Voila.
4010
4011 Another example: Find out what to do in order to make some script a
4012 builtin:
4013
4014 -------------------------------------------------
4015 $ git log --no-merges --diff-filter=A builtin-*.c
4016 -------------------------------------------------
4017
4018 You see, Git is actually the best tool to find out about the source of Git
4019 itself!
4020
4021 [[glossary]]
4022 include::glossary.txt[]
4023
4024 [[git-quick-start]]
4025 Appendix A: Git Quick Reference
4026 ===============================
4027
4028 This is a quick summary of the major commands; the previous chapters
4029 explain how these work in more detail.
4030
4031 [[quick-creating-a-new-repository]]
4032 Creating a new repository
4033 -------------------------
4034
4035 From a tarball:
4036
4037 -----------------------------------------------
4038 $ tar xzf project.tar.gz
4039 $ cd project
4040 $ git init
4041 Initialized empty Git repository in .git/
4042 $ git add .
4043 $ git commit
4044 -----------------------------------------------
4045
4046 From a remote repository:
4047
4048 -----------------------------------------------
4049 $ git clone git://example.com/pub/project.git
4050 $ cd project
4051 -----------------------------------------------
4052
4053 [[managing-branches]]
4054 Managing branches
4055 -----------------
4056
4057 -----------------------------------------------
4058 $ git branch # list all local branches in this repo
4059 $ git checkout test # switch working directory to branch "test"
4060 $ git branch new # create branch "new" starting at current HEAD
4061 $ git branch -d new # delete branch "new"
4062 -----------------------------------------------
4063
4064 Instead of basing new branch on current HEAD (the default), use:
4065
4066 -----------------------------------------------
4067 $ git branch new test # branch named "test"
4068 $ git branch new v2.6.15 # tag named v2.6.15
4069 $ git branch new HEAD^ # commit before the most recent
4070 $ git branch new HEAD^^ # commit before that
4071 $ git branch new test~10 # ten commits before tip of branch "test"
4072 -----------------------------------------------
4073
4074 Create and switch to a new branch at the same time:
4075
4076 -----------------------------------------------
4077 $ git checkout -b new v2.6.15
4078 -----------------------------------------------
4079
4080 Update and examine branches from the repository you cloned from:
4081
4082 -----------------------------------------------
4083 $ git fetch # update
4084 $ git branch -r # list
4085 origin/master
4086 origin/next
4087 ...
4088 $ git checkout -b masterwork origin/master
4089 -----------------------------------------------
4090
4091 Fetch a branch from a different repository, and give it a new
4092 name in your repository:
4093
4094 -----------------------------------------------
4095 $ git fetch git://example.com/project.git theirbranch:mybranch
4096 $ git fetch git://example.com/project.git v2.6.15:mybranch
4097 -----------------------------------------------
4098
4099 Keep a list of repositories you work with regularly:
4100
4101 -----------------------------------------------
4102 $ git remote add example git://example.com/project.git
4103 $ git remote # list remote repositories
4104 example
4105 origin
4106 $ git remote show example # get details
4107 * remote example
4108 URL: git://example.com/project.git
4109 Tracked remote branches
4110 master next ...
4111 $ git fetch example # update branches from example
4112 $ git branch -r # list all remote branches
4113 -----------------------------------------------
4114
4115
4116 [[exploring-history]]
4117 Exploring history
4118 -----------------
4119
4120 -----------------------------------------------
4121 $ gitk # visualize and browse history
4122 $ git log # list all commits
4123 $ git log src/ # ...modifying src/
4124 $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15
4125 $ git log master..test # ...in branch test, not in branch master
4126 $ git log test..master # ...in branch master, but not in test
4127 $ git log test...master # ...in one branch, not in both
4128 $ git log -S'foo()' # ...where difference contain "foo()"
4129 $ git log --since="2 weeks ago"
4130 $ git log -p # show patches as well
4131 $ git show # most recent commit
4132 $ git diff v2.6.15..v2.6.16 # diff between two tagged versions
4133 $ git diff v2.6.15..HEAD # diff with current head
4134 $ git grep "foo()" # search working directory for "foo()"
4135 $ git grep v2.6.15 "foo()" # search old tree for "foo()"
4136 $ git show v2.6.15:a.txt # look at old version of a.txt
4137 -----------------------------------------------
4138
4139 Search for regressions:
4140
4141 -----------------------------------------------
4142 $ git bisect start
4143 $ git bisect bad # current version is bad
4144 $ git bisect good v2.6.13-rc2 # last known good revision
4145 Bisecting: 675 revisions left to test after this
4146 # test here, then:
4147 $ git bisect good # if this revision is good, or
4148 $ git bisect bad # if this revision is bad.
4149 # repeat until done.
4150 -----------------------------------------------
4151
4152 [[making-changes]]
4153 Making changes
4154 --------------
4155
4156 Make sure git knows who to blame:
4157
4158 ------------------------------------------------
4159 $ cat >>~/.gitconfig <<\EOF
4160 [user]
4161 name = Your Name Comes Here
4162 email = you@yourdomain.example.com
4163 EOF
4164 ------------------------------------------------
4165
4166 Select file contents to include in the next commit, then make the
4167 commit:
4168
4169 -----------------------------------------------
4170 $ git add a.txt # updated file
4171 $ git add b.txt # new file
4172 $ git rm c.txt # old file
4173 $ git commit
4174 -----------------------------------------------
4175
4176 Or, prepare and create the commit in one step:
4177
4178 -----------------------------------------------
4179 $ git commit d.txt # use latest content only of d.txt
4180 $ git commit -a # use latest content of all tracked files
4181 -----------------------------------------------
4182
4183 [[merging]]
4184 Merging
4185 -------
4186
4187 -----------------------------------------------
4188 $ git merge test # merge branch "test" into the current branch
4189 $ git pull git://example.com/project.git master
4190 # fetch and merge in remote branch
4191 $ git pull . test # equivalent to git merge test
4192 -----------------------------------------------
4193
4194 [[sharing-your-changes]]
4195 Sharing your changes
4196 --------------------
4197
4198 Importing or exporting patches:
4199
4200 -----------------------------------------------
4201 $ git format-patch origin..HEAD # format a patch for each commit
4202 # in HEAD but not in origin
4203 $ git am mbox # import patches from the mailbox "mbox"
4204 -----------------------------------------------
4205
4206 Fetch a branch in a different git repository, then merge into the
4207 current branch:
4208
4209 -----------------------------------------------
4210 $ git pull git://example.com/project.git theirbranch
4211 -----------------------------------------------
4212
4213 Store the fetched branch into a local branch before merging into the
4214 current branch:
4215
4216 -----------------------------------------------
4217 $ git pull git://example.com/project.git theirbranch:mybranch
4218 -----------------------------------------------
4219
4220 After creating commits on a local branch, update the remote
4221 branch with your commits:
4222
4223 -----------------------------------------------
4224 $ git push ssh://example.com/project.git mybranch:theirbranch
4225 -----------------------------------------------
4226
4227 When remote and local branch are both named "test":
4228
4229 -----------------------------------------------
4230 $ git push ssh://example.com/project.git test
4231 -----------------------------------------------
4232
4233 Shortcut version for a frequently used remote repository:
4234
4235 -----------------------------------------------
4236 $ git remote add example ssh://example.com/project.git
4237 $ git push example test
4238 -----------------------------------------------
4239
4240 [[repository-maintenance]]
4241 Repository maintenance
4242 ----------------------
4243
4244 Check for corruption:
4245
4246 -----------------------------------------------
4247 $ git fsck
4248 -----------------------------------------------
4249
4250 Recompress, remove unused cruft:
4251
4252 -----------------------------------------------
4253 $ git gc
4254 -----------------------------------------------
4255
4256
4257 [[todo]]
4258 Appendix B: Notes and todo list for this manual
4259 ===============================================
4260
4261 This is a work in progress.
4262
4263 The basic requirements:
4264
4265 - It must be readable in order, from beginning to end, by someone
4266 intelligent with a basic grasp of the UNIX command line, but without
4267 any special knowledge of git. If necessary, any other prerequisites
4268 should be specifically mentioned as they arise.
4269 - Whenever possible, section headings should clearly describe the task
4270 they explain how to do, in language that requires no more knowledge
4271 than necessary: for example, "importing patches into a project" rather
4272 than "the git-am command"
4273
4274 Think about how to create a clear chapter dependency graph that will
4275 allow people to get to important topics without necessarily reading
4276 everything in between.
4277
4278 Scan Documentation/ for other stuff left out; in particular:
4279
4280 - howto's
4281 - some of technical/?
4282 - hooks
4283 - list of commands in gitlink:git[1]
4284
4285 Scan email archives for other stuff left out
4286
4287 Scan man pages to see if any assume more background than this manual
4288 provides.
4289
4290 Simplify beginning by suggesting disconnected head instead of
4291 temporary branch creation?
4292
4293 Add more good examples. Entire sections of just cookbook examples
4294 might be a good idea; maybe make an "advanced examples" section a
4295 standard end-of-chapter section?
4296
4297 Include cross-references to the glossary, where appropriate.
4298
4299 Document shallow clones? See draft 1.5.0 release notes for some
4300 documentation.
4301
4302 Add a section on working with other version control systems, including
4303 CVS, Subversion, and just imports of series of release tarballs.
4304
4305 More details on gitweb?
4306
4307 Write a chapter on using plumbing and writing scripts.
4308
4309 Alternates, clone -reference, etc.
4310
4311 git unpack-objects -r for recovery