Merge branch 'svn-crlf' of git://bogomips.org/git-svn into ew/svn-crlf
[git/git.git] / Documentation / user-manual.txt
1 Git User Manual
2 ===============
3
4 Git is a fast distributed revision control system.
5
6 This manual is designed to be readable by someone with basic UNIX
7 command-line skills, but no previous knowledge of Git.
8
9 <<repositories-and-branches>> and <<exploring-git-history>> explain how
10 to fetch and study a project using git--read these chapters to learn how
11 to build and test a particular version of a software project, search for
12 regressions, and so on.
13
14 People needing to do actual development will also want to read
15 <<Developing-With-git>> and <<sharing-development>>.
16
17 Further chapters cover more specialized topics.
18
19 Comprehensive reference documentation is available through the man
20 pages, or linkgit:git-help[1] command. For example, for the command
21 `git clone <repo>`, you can either use:
22
23 ------------------------------------------------
24 $ man git-clone
25 ------------------------------------------------
26
27 or:
28
29 ------------------------------------------------
30 $ git help clone
31 ------------------------------------------------
32
33 With the latter, you can use the manual viewer of your choice; see
34 linkgit:git-help[1] for more information.
35
36 See also <<git-quick-start>> for a brief overview of Git commands,
37 without any explanation.
38
39 Finally, see <<todo>> for ways that you can help make this manual more
40 complete.
41
42
43 [[repositories-and-branches]]
44 Repositories and Branches
45 =========================
46
47 [[how-to-get-a-git-repository]]
48 How to get a Git repository
49 ---------------------------
50
51 It will be useful to have a Git repository to experiment with as you
52 read this manual.
53
54 The best way to get one is by using the linkgit:git-clone[1] command to
55 download a copy of an existing repository. If you don't already have a
56 project in mind, here are some interesting examples:
57
58 ------------------------------------------------
59 # Git itself (approx. 40MB download):
60 $ git clone git://git.kernel.org/pub/scm/git/git.git
61 # the Linux kernel (approx. 640MB download):
62 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
63 ------------------------------------------------
64
65 The initial clone may be time-consuming for a large project, but you
66 will only need to clone once.
67
68 The clone command creates a new directory named after the project
69 (`git` or `linux` in the examples above). After you cd into this
70 directory, you will see that it contains a copy of the project files,
71 called the <<def_working_tree,working tree>>, together with a special
72 top-level directory named `.git`, which contains all the information
73 about the history of the project.
74
75 [[how-to-check-out]]
76 How to check out a different version of a project
77 -------------------------------------------------
78
79 Git is best thought of as a tool for storing the history of a collection
80 of files. It stores the history as a compressed collection of
81 interrelated snapshots of the project's contents. In Git each such
82 version is called a <<def_commit,commit>>.
83
84 Those snapshots aren't necessarily all arranged in a single line from
85 oldest to newest; instead, work may simultaneously proceed along
86 parallel lines of development, called <<def_branch,branches>>, which may
87 merge and diverge.
88
89 A single Git repository can track development on multiple branches. It
90 does this by keeping a list of <<def_head,heads>> which reference the
91 latest commit on each branch; the linkgit:git-branch[1] command shows
92 you the list of branch heads:
93
94 ------------------------------------------------
95 $ git branch
96 * master
97 ------------------------------------------------
98
99 A freshly cloned repository contains a single branch head, by default
100 named "master", with the working directory initialized to the state of
101 the project referred to by that branch head.
102
103 Most projects also use <<def_tag,tags>>. Tags, like heads, are
104 references into the project's history, and can be listed using the
105 linkgit:git-tag[1] command:
106
107 ------------------------------------------------
108 $ git tag -l
109 v2.6.11
110 v2.6.11-tree
111 v2.6.12
112 v2.6.12-rc2
113 v2.6.12-rc3
114 v2.6.12-rc4
115 v2.6.12-rc5
116 v2.6.12-rc6
117 v2.6.13
118 ...
119 ------------------------------------------------
120
121 Tags are expected to always point at the same version of a project,
122 while heads are expected to advance as development progresses.
123
124 Create a new branch head pointing to one of these versions and check it
125 out using linkgit:git-checkout[1]:
126
127 ------------------------------------------------
128 $ git checkout -b new v2.6.13
129 ------------------------------------------------
130
131 The working directory then reflects the contents that the project had
132 when it was tagged v2.6.13, and linkgit:git-branch[1] shows two
133 branches, with an asterisk marking the currently checked-out branch:
134
135 ------------------------------------------------
136 $ git branch
137 master
138 * new
139 ------------------------------------------------
140
141 If you decide that you'd rather see version 2.6.17, you can modify
142 the current branch to point at v2.6.17 instead, with
143
144 ------------------------------------------------
145 $ git reset --hard v2.6.17
146 ------------------------------------------------
147
148 Note that if the current branch head was your only reference to a
149 particular point in history, then resetting that branch may leave you
150 with no way to find the history it used to point to; so use this command
151 carefully.
152
153 [[understanding-commits]]
154 Understanding History: Commits
155 ------------------------------
156
157 Every change in the history of a project is represented by a commit.
158 The linkgit:git-show[1] command shows the most recent commit on the
159 current branch:
160
161 ------------------------------------------------
162 $ git show
163 commit 17cf781661e6d38f737f15f53ab552f1e95960d7
164 Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)>
165 Date: Tue Apr 19 14:11:06 2005 -0700
166
167 Remove duplicate getenv(DB_ENVIRONMENT) call
168
169 Noted by Tony Luck.
170
171 diff --git a/init-db.c b/init-db.c
172 index 65898fa..b002dc6 100644
173 --- a/init-db.c
174 +++ b/init-db.c
175 @@ -7,7 +7,7 @@
176
177 int main(int argc, char **argv)
178 {
179 - char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
180 + char *sha1_dir, *path;
181 int len, i;
182
183 if (mkdir(".git", 0755) < 0) {
184 ------------------------------------------------
185
186 As you can see, a commit shows who made the latest change, what they
187 did, and why.
188
189 Every commit has a 40-hexdigit id, sometimes called the "object name" or the
190 "SHA-1 id", shown on the first line of the `git show` output. You can usually
191 refer to a commit by a shorter name, such as a tag or a branch name, but this
192 longer name can also be useful. Most importantly, it is a globally unique
193 name for this commit: so if you tell somebody else the object name (for
194 example in email), then you are guaranteed that name will refer to the same
195 commit in their repository that it does in yours (assuming their repository
196 has that commit at all). Since the object name is computed as a hash over the
197 contents of the commit, you are guaranteed that the commit can never change
198 without its name also changing.
199
200 In fact, in <<git-concepts>> we shall see that everything stored in Git
201 history, including file data and directory contents, is stored in an object
202 with a name that is a hash of its contents.
203
204 [[understanding-reachability]]
205 Understanding history: commits, parents, and reachability
206 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
207
208 Every commit (except the very first commit in a project) also has a
209 parent commit which shows what happened before this commit.
210 Following the chain of parents will eventually take you back to the
211 beginning of the project.
212
213 However, the commits do not form a simple list; Git allows lines of
214 development to diverge and then reconverge, and the point where two
215 lines of development reconverge is called a "merge". The commit
216 representing a merge can therefore have more than one parent, with
217 each parent representing the most recent commit on one of the lines
218 of development leading to that point.
219
220 The best way to see how this works is using the linkgit:gitk[1]
221 command; running gitk now on a Git repository and looking for merge
222 commits will help understand how Git organizes history.
223
224 In the following, we say that commit X is "reachable" from commit Y
225 if commit X is an ancestor of commit Y. Equivalently, you could say
226 that Y is a descendant of X, or that there is a chain of parents
227 leading from commit Y to commit X.
228
229 [[history-diagrams]]
230 Understanding history: History diagrams
231 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
232
233 We will sometimes represent Git history using diagrams like the one
234 below. Commits are shown as "o", and the links between them with
235 lines drawn with - / and \. Time goes left to right:
236
237
238 ................................................
239 o--o--o <-- Branch A
240 /
241 o--o--o <-- master
242 \
243 o--o--o <-- Branch B
244 ................................................
245
246 If we need to talk about a particular commit, the character "o" may
247 be replaced with another letter or number.
248
249 [[what-is-a-branch]]
250 Understanding history: What is a branch?
251 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
252
253 When we need to be precise, we will use the word "branch" to mean a line
254 of development, and "branch head" (or just "head") to mean a reference
255 to the most recent commit on a branch. In the example above, the branch
256 head named "A" is a pointer to one particular commit, but we refer to
257 the line of three commits leading up to that point as all being part of
258 "branch A".
259
260 However, when no confusion will result, we often just use the term
261 "branch" both for branches and for branch heads.
262
263 [[manipulating-branches]]
264 Manipulating branches
265 ---------------------
266
267 Creating, deleting, and modifying branches is quick and easy; here's
268 a summary of the commands:
269
270 `git branch`::
271 list all branches.
272 `git branch <branch>`::
273 create a new branch named `<branch>`, referencing the same
274 point in history as the current branch.
275 `git branch <branch> <start-point>`::
276 create a new branch named `<branch>`, referencing
277 `<start-point>`, which may be specified any way you like,
278 including using a branch name or a tag name.
279 `git branch -d <branch>`::
280 delete the branch `<branch>`; if the branch is not fully
281 merged in its upstream branch or contained in the current branch,
282 this command will fail with a warning.
283 `git branch -D <branch>`::
284 delete the branch `<branch>` irrespective of its merged status.
285 `git checkout <branch>`::
286 make the current branch `<branch>`, updating the working
287 directory to reflect the version referenced by `<branch>`.
288 `git checkout -b <new> <start-point>`::
289 create a new branch `<new>` referencing `<start-point>`, and
290 check it out.
291
292 The special symbol "HEAD" can always be used to refer to the current
293 branch. In fact, Git uses a file named `HEAD` in the `.git` directory
294 to remember which branch is current:
295
296 ------------------------------------------------
297 $ cat .git/HEAD
298 ref: refs/heads/master
299 ------------------------------------------------
300
301 [[detached-head]]
302 Examining an old version without creating a new branch
303 ------------------------------------------------------
304
305 The `git checkout` command normally expects a branch head, but will also
306 accept an arbitrary commit; for example, you can check out the commit
307 referenced by a tag:
308
309 ------------------------------------------------
310 $ git checkout v2.6.17
311 Note: checking out 'v2.6.17'.
312
313 You are in 'detached HEAD' state. You can look around, make experimental
314 changes and commit them, and you can discard any commits you make in this
315 state without impacting any branches by performing another checkout.
316
317 If you want to create a new branch to retain commits you create, you may
318 do so (now or later) by using -b with the checkout command again. Example:
319
320 git checkout -b new_branch_name
321
322 HEAD is now at 427abfa... Linux v2.6.17
323 ------------------------------------------------
324
325 The HEAD then refers to the SHA-1 of the commit instead of to a branch,
326 and git branch shows that you are no longer on a branch:
327
328 ------------------------------------------------
329 $ cat .git/HEAD
330 427abfa28afedffadfca9dd8b067eb6d36bac53f
331 $ git branch
332 * (detached from v2.6.17)
333 master
334 ------------------------------------------------
335
336 In this case we say that the HEAD is "detached".
337
338 This is an easy way to check out a particular version without having to
339 make up a name for the new branch. You can still create a new branch
340 (or tag) for this version later if you decide to.
341
342 [[examining-remote-branches]]
343 Examining branches from a remote repository
344 -------------------------------------------
345
346 The "master" branch that was created at the time you cloned is a copy
347 of the HEAD in the repository that you cloned from. That repository
348 may also have had other branches, though, and your local repository
349 keeps branches which track each of those remote branches, called
350 remote-tracking branches, which you
351 can view using the `-r` option to linkgit:git-branch[1]:
352
353 ------------------------------------------------
354 $ git branch -r
355 origin/HEAD
356 origin/html
357 origin/maint
358 origin/man
359 origin/master
360 origin/next
361 origin/pu
362 origin/todo
363 ------------------------------------------------
364
365 In this example, "origin" is called a remote repository, or "remote"
366 for short. The branches of this repository are called "remote
367 branches" from our point of view. The remote-tracking branches listed
368 above were created based on the remote branches at clone time and will
369 be updated by `git fetch` (hence `git pull`) and `git push`. See
370 <<Updating-a-repository-With-git-fetch>> for details.
371
372 You might want to build on one of these remote-tracking branches
373 on a branch of your own, just as you would for a tag:
374
375 ------------------------------------------------
376 $ git checkout -b my-todo-copy origin/todo
377 ------------------------------------------------
378
379 You can also check out `origin/todo` directly to examine it or
380 write a one-off patch. See <<detached-head,detached head>>.
381
382 Note that the name "origin" is just the name that Git uses by default
383 to refer to the repository that you cloned from.
384
385 [[how-git-stores-references]]
386 Naming branches, tags, and other references
387 -------------------------------------------
388
389 Branches, remote-tracking branches, and tags are all references to
390 commits. All references are named with a slash-separated path name
391 starting with `refs`; the names we've been using so far are actually
392 shorthand:
393
394 - The branch `test` is short for `refs/heads/test`.
395 - The tag `v2.6.18` is short for `refs/tags/v2.6.18`.
396 - `origin/master` is short for `refs/remotes/origin/master`.
397
398 The full name is occasionally useful if, for example, there ever
399 exists a tag and a branch with the same name.
400
401 (Newly created refs are actually stored in the `.git/refs` directory,
402 under the path given by their name. However, for efficiency reasons
403 they may also be packed together in a single file; see
404 linkgit:git-pack-refs[1]).
405
406 As another useful shortcut, the "HEAD" of a repository can be referred
407 to just using the name of that repository. So, for example, "origin"
408 is usually a shortcut for the HEAD branch in the repository "origin".
409
410 For the complete list of paths which Git checks for references, and
411 the order it uses to decide which to choose when there are multiple
412 references with the same shorthand name, see the "SPECIFYING
413 REVISIONS" section of linkgit:gitrevisions[7].
414
415 [[Updating-a-repository-With-git-fetch]]
416 Updating a repository with git fetch
417 ------------------------------------
418
419 After you clone a repository and commit a few changes of your own, you
420 may wish to check the original repository for updates.
421
422 The `git-fetch` command, with no arguments, will update all of the
423 remote-tracking branches to the latest version found in the original
424 repository. It will not touch any of your own branches--not even the
425 "master" branch that was created for you on clone.
426
427 [[fetching-branches]]
428 Fetching branches from other repositories
429 -----------------------------------------
430
431 You can also track branches from repositories other than the one you
432 cloned from, using linkgit:git-remote[1]:
433
434 -------------------------------------------------
435 $ git remote add staging git://git.kernel.org/.../gregkh/staging.git
436 $ git fetch staging
437 ...
438 From git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging
439 * [new branch] master -> staging/master
440 * [new branch] staging-linus -> staging/staging-linus
441 * [new branch] staging-next -> staging/staging-next
442 -------------------------------------------------
443
444 New remote-tracking branches will be stored under the shorthand name
445 that you gave `git remote add`, in this case `staging`:
446
447 -------------------------------------------------
448 $ git branch -r
449 origin/HEAD -> origin/master
450 origin/master
451 staging/master
452 staging/staging-linus
453 staging/staging-next
454 -------------------------------------------------
455
456 If you run `git fetch <remote>` later, the remote-tracking branches
457 for the named `<remote>` will be updated.
458
459 If you examine the file `.git/config`, you will see that Git has added
460 a new stanza:
461
462 -------------------------------------------------
463 $ cat .git/config
464 ...
465 [remote "staging"]
466 url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
467 fetch = +refs/heads/*:refs/remotes/staging/*
468 ...
469 -------------------------------------------------
470
471 This is what causes Git to track the remote's branches; you may modify
472 or delete these configuration options by editing `.git/config` with a
473 text editor. (See the "CONFIGURATION FILE" section of
474 linkgit:git-config[1] for details.)
475
476 [[exploring-git-history]]
477 Exploring Git history
478 =====================
479
480 Git is best thought of as a tool for storing the history of a
481 collection of files. It does this by storing compressed snapshots of
482 the contents of a file hierarchy, together with "commits" which show
483 the relationships between these snapshots.
484
485 Git provides extremely flexible and fast tools for exploring the
486 history of a project.
487
488 We start with one specialized tool that is useful for finding the
489 commit that introduced a bug into a project.
490
491 [[using-bisect]]
492 How to use bisect to find a regression
493 --------------------------------------
494
495 Suppose version 2.6.18 of your project worked, but the version at
496 "master" crashes. Sometimes the best way to find the cause of such a
497 regression is to perform a brute-force search through the project's
498 history to find the particular commit that caused the problem. The
499 linkgit:git-bisect[1] command can help you do this:
500
501 -------------------------------------------------
502 $ git bisect start
503 $ git bisect good v2.6.18
504 $ git bisect bad master
505 Bisecting: 3537 revisions left to test after this
506 [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
507 -------------------------------------------------
508
509 If you run `git branch` at this point, you'll see that Git has
510 temporarily moved you in "(no branch)". HEAD is now detached from any
511 branch and points directly to a commit (with commit id 65934...) that
512 is reachable from "master" but not from v2.6.18. Compile and test it,
513 and see whether it crashes. Assume it does crash. Then:
514
515 -------------------------------------------------
516 $ git bisect bad
517 Bisecting: 1769 revisions left to test after this
518 [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
519 -------------------------------------------------
520
521 checks out an older version. Continue like this, telling Git at each
522 stage whether the version it gives you is good or bad, and notice
523 that the number of revisions left to test is cut approximately in
524 half each time.
525
526 After about 13 tests (in this case), it will output the commit id of
527 the guilty commit. You can then examine the commit with
528 linkgit:git-show[1], find out who wrote it, and mail them your bug
529 report with the commit id. Finally, run
530
531 -------------------------------------------------
532 $ git bisect reset
533 -------------------------------------------------
534
535 to return you to the branch you were on before.
536
537 Note that the version which `git bisect` checks out for you at each
538 point is just a suggestion, and you're free to try a different
539 version if you think it would be a good idea. For example,
540 occasionally you may land on a commit that broke something unrelated;
541 run
542
543 -------------------------------------------------
544 $ git bisect visualize
545 -------------------------------------------------
546
547 which will run gitk and label the commit it chose with a marker that
548 says "bisect". Choose a safe-looking commit nearby, note its commit
549 id, and check it out with:
550
551 -------------------------------------------------
552 $ git reset --hard fb47ddb2db...
553 -------------------------------------------------
554
555 then test, run `bisect good` or `bisect bad` as appropriate, and
556 continue.
557
558 Instead of `git bisect visualize` and then `git reset --hard
559 fb47ddb2db...`, you might just want to tell Git that you want to skip
560 the current commit:
561
562 -------------------------------------------------
563 $ git bisect skip
564 -------------------------------------------------
565
566 In this case, though, Git may not eventually be able to tell the first
567 bad one between some first skipped commits and a later bad commit.
568
569 There are also ways to automate the bisecting process if you have a
570 test script that can tell a good from a bad commit. See
571 linkgit:git-bisect[1] for more information about this and other `git
572 bisect` features.
573
574 [[naming-commits]]
575 Naming commits
576 --------------
577
578 We have seen several ways of naming commits already:
579
580 - 40-hexdigit object name
581 - branch name: refers to the commit at the head of the given
582 branch
583 - tag name: refers to the commit pointed to by the given tag
584 (we've seen branches and tags are special cases of
585 <<how-git-stores-references,references>>).
586 - HEAD: refers to the head of the current branch
587
588 There are many more; see the "SPECIFYING REVISIONS" section of the
589 linkgit:gitrevisions[7] man page for the complete list of ways to
590 name revisions. Some examples:
591
592 -------------------------------------------------
593 $ git show fb47ddb2 # the first few characters of the object name
594 # are usually enough to specify it uniquely
595 $ git show HEAD^ # the parent of the HEAD commit
596 $ git show HEAD^^ # the grandparent
597 $ git show HEAD~4 # the great-great-grandparent
598 -------------------------------------------------
599
600 Recall that merge commits may have more than one parent; by default,
601 `^` and `~` follow the first parent listed in the commit, but you can
602 also choose:
603
604 -------------------------------------------------
605 $ git show HEAD^1 # show the first parent of HEAD
606 $ git show HEAD^2 # show the second parent of HEAD
607 -------------------------------------------------
608
609 In addition to HEAD, there are several other special names for
610 commits:
611
612 Merges (to be discussed later), as well as operations such as
613 `git reset`, which change the currently checked-out commit, generally
614 set ORIG_HEAD to the value HEAD had before the current operation.
615
616 The `git fetch` operation always stores the head of the last fetched
617 branch in FETCH_HEAD. For example, if you run `git fetch` without
618 specifying a local branch as the target of the operation
619
620 -------------------------------------------------
621 $ git fetch git://example.com/proj.git theirbranch
622 -------------------------------------------------
623
624 the fetched commits will still be available from FETCH_HEAD.
625
626 When we discuss merges we'll also see the special name MERGE_HEAD,
627 which refers to the other branch that we're merging in to the current
628 branch.
629
630 The linkgit:git-rev-parse[1] command is a low-level command that is
631 occasionally useful for translating some name for a commit to the object
632 name for that commit:
633
634 -------------------------------------------------
635 $ git rev-parse origin
636 e05db0fd4f31dde7005f075a84f96b360d05984b
637 -------------------------------------------------
638
639 [[creating-tags]]
640 Creating tags
641 -------------
642
643 We can also create a tag to refer to a particular commit; after
644 running
645
646 -------------------------------------------------
647 $ git tag stable-1 1b2e1d63ff
648 -------------------------------------------------
649
650 You can use `stable-1` to refer to the commit 1b2e1d63ff.
651
652 This creates a "lightweight" tag. If you would also like to include a
653 comment with the tag, and possibly sign it cryptographically, then you
654 should create a tag object instead; see the linkgit:git-tag[1] man page
655 for details.
656
657 [[browsing-revisions]]
658 Browsing revisions
659 ------------------
660
661 The linkgit:git-log[1] command can show lists of commits. On its
662 own, it shows all commits reachable from the parent commit; but you
663 can also make more specific requests:
664
665 -------------------------------------------------
666 $ git log v2.5.. # commits since (not reachable from) v2.5
667 $ git log test..master # commits reachable from master but not test
668 $ git log master..test # ...reachable from test but not master
669 $ git log master...test # ...reachable from either test or master,
670 # but not both
671 $ git log --since="2 weeks ago" # commits from the last 2 weeks
672 $ git log Makefile # commits which modify Makefile
673 $ git log fs/ # ... which modify any file under fs/
674 $ git log -S'foo()' # commits which add or remove any file data
675 # matching the string 'foo()'
676 -------------------------------------------------
677
678 And of course you can combine all of these; the following finds
679 commits since v2.5 which touch the `Makefile` or any file under `fs`:
680
681 -------------------------------------------------
682 $ git log v2.5.. Makefile fs/
683 -------------------------------------------------
684
685 You can also ask git log to show patches:
686
687 -------------------------------------------------
688 $ git log -p
689 -------------------------------------------------
690
691 See the `--pretty` option in the linkgit:git-log[1] man page for more
692 display options.
693
694 Note that git log starts with the most recent commit and works
695 backwards through the parents; however, since Git history can contain
696 multiple independent lines of development, the particular order that
697 commits are listed in may be somewhat arbitrary.
698
699 [[generating-diffs]]
700 Generating diffs
701 ----------------
702
703 You can generate diffs between any two versions using
704 linkgit:git-diff[1]:
705
706 -------------------------------------------------
707 $ git diff master..test
708 -------------------------------------------------
709
710 That will produce the diff between the tips of the two branches. If
711 you'd prefer to find the diff from their common ancestor to test, you
712 can use three dots instead of two:
713
714 -------------------------------------------------
715 $ git diff master...test
716 -------------------------------------------------
717
718 Sometimes what you want instead is a set of patches; for this you can
719 use linkgit:git-format-patch[1]:
720
721 -------------------------------------------------
722 $ git format-patch master..test
723 -------------------------------------------------
724
725 will generate a file with a patch for each commit reachable from test
726 but not from master.
727
728 [[viewing-old-file-versions]]
729 Viewing old file versions
730 -------------------------
731
732 You can always view an old version of a file by just checking out the
733 correct revision first. But sometimes it is more convenient to be
734 able to view an old version of a single file without checking
735 anything out; this command does that:
736
737 -------------------------------------------------
738 $ git show v2.5:fs/locks.c
739 -------------------------------------------------
740
741 Before the colon may be anything that names a commit, and after it
742 may be any path to a file tracked by Git.
743
744 [[history-examples]]
745 Examples
746 --------
747
748 [[counting-commits-on-a-branch]]
749 Counting the number of commits on a branch
750 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
751
752 Suppose you want to know how many commits you've made on `mybranch`
753 since it diverged from `origin`:
754
755 -------------------------------------------------
756 $ git log --pretty=oneline origin..mybranch | wc -l
757 -------------------------------------------------
758
759 Alternatively, you may often see this sort of thing done with the
760 lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's
761 of all the given commits:
762
763 -------------------------------------------------
764 $ git rev-list origin..mybranch | wc -l
765 -------------------------------------------------
766
767 [[checking-for-equal-branches]]
768 Check whether two branches point at the same history
769 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
770
771 Suppose you want to check whether two branches point at the same point
772 in history.
773
774 -------------------------------------------------
775 $ git diff origin..master
776 -------------------------------------------------
777
778 will tell you whether the contents of the project are the same at the
779 two branches; in theory, however, it's possible that the same project
780 contents could have been arrived at by two different historical
781 routes. You could compare the object names:
782
783 -------------------------------------------------
784 $ git rev-list origin
785 e05db0fd4f31dde7005f075a84f96b360d05984b
786 $ git rev-list master
787 e05db0fd4f31dde7005f075a84f96b360d05984b
788 -------------------------------------------------
789
790 Or you could recall that the `...` operator selects all commits
791 reachable from either one reference or the other but not
792 both; so
793
794 -------------------------------------------------
795 $ git log origin...master
796 -------------------------------------------------
797
798 will return no commits when the two branches are equal.
799
800 [[finding-tagged-descendants]]
801 Find first tagged version including a given fix
802 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
803
804 Suppose you know that the commit e05db0fd fixed a certain problem.
805 You'd like to find the earliest tagged release that contains that
806 fix.
807
808 Of course, there may be more than one answer--if the history branched
809 after commit e05db0fd, then there could be multiple "earliest" tagged
810 releases.
811
812 You could just visually inspect the commits since e05db0fd:
813
814 -------------------------------------------------
815 $ gitk e05db0fd..
816 -------------------------------------------------
817
818 or you can use linkgit:git-name-rev[1], which will give the commit a
819 name based on any tag it finds pointing to one of the commit's
820 descendants:
821
822 -------------------------------------------------
823 $ git name-rev --tags e05db0fd
824 e05db0fd tags/v1.5.0-rc1^0~23
825 -------------------------------------------------
826
827 The linkgit:git-describe[1] command does the opposite, naming the
828 revision using a tag on which the given commit is based:
829
830 -------------------------------------------------
831 $ git describe e05db0fd
832 v1.5.0-rc0-260-ge05db0f
833 -------------------------------------------------
834
835 but that may sometimes help you guess which tags might come after the
836 given commit.
837
838 If you just want to verify whether a given tagged version contains a
839 given commit, you could use linkgit:git-merge-base[1]:
840
841 -------------------------------------------------
842 $ git merge-base e05db0fd v1.5.0-rc1
843 e05db0fd4f31dde7005f075a84f96b360d05984b
844 -------------------------------------------------
845
846 The merge-base command finds a common ancestor of the given commits,
847 and always returns one or the other in the case where one is a
848 descendant of the other; so the above output shows that e05db0fd
849 actually is an ancestor of v1.5.0-rc1.
850
851 Alternatively, note that
852
853 -------------------------------------------------
854 $ git log v1.5.0-rc1..e05db0fd
855 -------------------------------------------------
856
857 will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
858 because it outputs only commits that are not reachable from v1.5.0-rc1.
859
860 As yet another alternative, the linkgit:git-show-branch[1] command lists
861 the commits reachable from its arguments with a display on the left-hand
862 side that indicates which arguments that commit is reachable from.
863 So, if you run something like
864
865 -------------------------------------------------
866 $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
867 ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
868 available
869 ! [v1.5.0-rc0] GIT v1.5.0 preview
870 ! [v1.5.0-rc1] GIT v1.5.0-rc1
871 ! [v1.5.0-rc2] GIT v1.5.0-rc2
872 ...
873 -------------------------------------------------
874
875 then a line like
876
877 -------------------------------------------------
878 + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
879 available
880 -------------------------------------------------
881
882 shows that e05db0fd is reachable from itself, from v1.5.0-rc1,
883 and from v1.5.0-rc2, and not from v1.5.0-rc0.
884
885 [[showing-commits-unique-to-a-branch]]
886 Showing commits unique to a given branch
887 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
888
889 Suppose you would like to see all the commits reachable from the branch
890 head named `master` but not from any other head in your repository.
891
892 We can list all the heads in this repository with
893 linkgit:git-show-ref[1]:
894
895 -------------------------------------------------
896 $ git show-ref --heads
897 bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
898 db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
899 a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
900 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
901 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
902 -------------------------------------------------
903
904 We can get just the branch-head names, and remove `master`, with
905 the help of the standard utilities cut and grep:
906
907 -------------------------------------------------
908 $ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
909 refs/heads/core-tutorial
910 refs/heads/maint
911 refs/heads/tutorial-2
912 refs/heads/tutorial-fixes
913 -------------------------------------------------
914
915 And then we can ask to see all the commits reachable from master
916 but not from these other heads:
917
918 -------------------------------------------------
919 $ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
920 grep -v '^refs/heads/master' )
921 -------------------------------------------------
922
923 Obviously, endless variations are possible; for example, to see all
924 commits reachable from some head but not from any tag in the repository:
925
926 -------------------------------------------------
927 $ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
928 -------------------------------------------------
929
930 (See linkgit:gitrevisions[7] for explanations of commit-selecting
931 syntax such as `--not`.)
932
933 [[making-a-release]]
934 Creating a changelog and tarball for a software release
935 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
936
937 The linkgit:git-archive[1] command can create a tar or zip archive from
938 any version of a project; for example:
939
940 -------------------------------------------------
941 $ git archive -o latest.tar.gz --prefix=project/ HEAD
942 -------------------------------------------------
943
944 will use HEAD to produce a gzipped tar archive in which each filename
945 is preceded by `project/`. The output file format is inferred from
946 the output file extension if possible, see linkgit:git-archive[1] for
947 details.
948
949 Versions of Git older than 1.7.7 don't know about the `tar.gz` format,
950 you'll need to use gzip explicitly:
951
952 -------------------------------------------------
953 $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
954 -------------------------------------------------
955
956 If you're releasing a new version of a software project, you may want
957 to simultaneously make a changelog to include in the release
958 announcement.
959
960 Linus Torvalds, for example, makes new kernel releases by tagging them,
961 then running:
962
963 -------------------------------------------------
964 $ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
965 -------------------------------------------------
966
967 where release-script is a shell script that looks like:
968
969 -------------------------------------------------
970 #!/bin/sh
971 stable="$1"
972 last="$2"
973 new="$3"
974 echo "# git tag v$new"
975 echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
976 echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
977 echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
978 echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
979 echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
980 -------------------------------------------------
981
982 and then he just cut-and-pastes the output commands after verifying that
983 they look OK.
984
985 [[Finding-commits-With-given-Content]]
986 Finding commits referencing a file with given content
987 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
988
989 Somebody hands you a copy of a file, and asks which commits modified a
990 file such that it contained the given content either before or after the
991 commit. You can find out with this:
992
993 -------------------------------------------------
994 $ git log --raw --abbrev=40 --pretty=oneline |
995 grep -B 1 `git hash-object filename`
996 -------------------------------------------------
997
998 Figuring out why this works is left as an exercise to the (advanced)
999 student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and
1000 linkgit:git-hash-object[1] man pages may prove helpful.
1001
1002 [[Developing-With-git]]
1003 Developing with Git
1004 ===================
1005
1006 [[telling-git-your-name]]
1007 Telling Git your name
1008 ---------------------
1009
1010 Before creating any commits, you should introduce yourself to Git.
1011 The easiest way to do so is to use linkgit:git-config[1]:
1012
1013 ------------------------------------------------
1014 $ git config --global user.name 'Your Name Comes Here'
1015 $ git config --global user.email 'you@yourdomain.example.com'
1016 ------------------------------------------------
1017
1018 Which will add the following to a file named `.gitconfig` in your
1019 home directory:
1020
1021 ------------------------------------------------
1022 [user]
1023 name = Your Name Comes Here
1024 email = you@yourdomain.example.com
1025 ------------------------------------------------
1026
1027 See the "CONFIGURATION FILE" section of linkgit:git-config[1] for
1028 details on the configuration file. The file is plain text, so you can
1029 also edit it with your favorite editor.
1030
1031
1032 [[creating-a-new-repository]]
1033 Creating a new repository
1034 -------------------------
1035
1036 Creating a new repository from scratch is very easy:
1037
1038 -------------------------------------------------
1039 $ mkdir project
1040 $ cd project
1041 $ git init
1042 -------------------------------------------------
1043
1044 If you have some initial content (say, a tarball):
1045
1046 -------------------------------------------------
1047 $ tar xzvf project.tar.gz
1048 $ cd project
1049 $ git init
1050 $ git add . # include everything below ./ in the first commit:
1051 $ git commit
1052 -------------------------------------------------
1053
1054 [[how-to-make-a-commit]]
1055 How to make a commit
1056 --------------------
1057
1058 Creating a new commit takes three steps:
1059
1060 1. Making some changes to the working directory using your
1061 favorite editor.
1062 2. Telling Git about your changes.
1063 3. Creating the commit using the content you told Git about
1064 in step 2.
1065
1066 In practice, you can interleave and repeat steps 1 and 2 as many
1067 times as you want: in order to keep track of what you want committed
1068 at step 3, Git maintains a snapshot of the tree's contents in a
1069 special staging area called "the index."
1070
1071 At the beginning, the content of the index will be identical to
1072 that of the HEAD. The command `git diff --cached`, which shows
1073 the difference between the HEAD and the index, should therefore
1074 produce no output at that point.
1075
1076 Modifying the index is easy:
1077
1078 To update the index with the contents of a new or modified file, use
1079
1080 -------------------------------------------------
1081 $ git add path/to/file
1082 -------------------------------------------------
1083
1084 To remove a file from the index and from the working tree, use
1085
1086 -------------------------------------------------
1087 $ git rm path/to/file
1088 -------------------------------------------------
1089
1090 After each step you can verify that
1091
1092 -------------------------------------------------
1093 $ git diff --cached
1094 -------------------------------------------------
1095
1096 always shows the difference between the HEAD and the index file--this
1097 is what you'd commit if you created the commit now--and that
1098
1099 -------------------------------------------------
1100 $ git diff
1101 -------------------------------------------------
1102
1103 shows the difference between the working tree and the index file.
1104
1105 Note that `git add` always adds just the current contents of a file
1106 to the index; further changes to the same file will be ignored unless
1107 you run `git add` on the file again.
1108
1109 When you're ready, just run
1110
1111 -------------------------------------------------
1112 $ git commit
1113 -------------------------------------------------
1114
1115 and Git will prompt you for a commit message and then create the new
1116 commit. Check to make sure it looks like what you expected with
1117
1118 -------------------------------------------------
1119 $ git show
1120 -------------------------------------------------
1121
1122 As a special shortcut,
1123
1124 -------------------------------------------------
1125 $ git commit -a
1126 -------------------------------------------------
1127
1128 will update the index with any files that you've modified or removed
1129 and create a commit, all in one step.
1130
1131 A number of commands are useful for keeping track of what you're
1132 about to commit:
1133
1134 -------------------------------------------------
1135 $ git diff --cached # difference between HEAD and the index; what
1136 # would be committed if you ran "commit" now.
1137 $ git diff # difference between the index file and your
1138 # working directory; changes that would not
1139 # be included if you ran "commit" now.
1140 $ git diff HEAD # difference between HEAD and working tree; what
1141 # would be committed if you ran "commit -a" now.
1142 $ git status # a brief per-file summary of the above.
1143 -------------------------------------------------
1144
1145 You can also use linkgit:git-gui[1] to create commits, view changes in
1146 the index and the working tree files, and individually select diff hunks
1147 for inclusion in the index (by right-clicking on the diff hunk and
1148 choosing "Stage Hunk For Commit").
1149
1150 [[creating-good-commit-messages]]
1151 Creating good commit messages
1152 -----------------------------
1153
1154 Though not required, it's a good idea to begin the commit message
1155 with a single short (less than 50 character) line summarizing the
1156 change, followed by a blank line and then a more thorough
1157 description. The text up to the first blank line in a commit
1158 message is treated as the commit title, and that title is used
1159 throughout Git. For example, linkgit:git-format-patch[1] turns a
1160 commit into email, and it uses the title on the Subject line and the
1161 rest of the commit in the body.
1162
1163
1164 [[ignoring-files]]
1165 Ignoring files
1166 --------------
1167
1168 A project will often generate files that you do 'not' want to track with Git.
1169 This typically includes files generated by a build process or temporary
1170 backup files made by your editor. Of course, 'not' tracking files with Git
1171 is just a matter of 'not' calling `git add` on them. But it quickly becomes
1172 annoying to have these untracked files lying around; e.g. they make
1173 `git add .` practically useless, and they keep showing up in the output of
1174 `git status`.
1175
1176 You can tell Git to ignore certain files by creating a file called
1177 `.gitignore` in the top level of your working directory, with contents
1178 such as:
1179
1180 -------------------------------------------------
1181 # Lines starting with '#' are considered comments.
1182 # Ignore any file named foo.txt.
1183 foo.txt
1184 # Ignore (generated) html files,
1185 *.html
1186 # except foo.html which is maintained by hand.
1187 !foo.html
1188 # Ignore objects and archives.
1189 *.[oa]
1190 -------------------------------------------------
1191
1192 See linkgit:gitignore[5] for a detailed explanation of the syntax. You can
1193 also place .gitignore files in other directories in your working tree, and they
1194 will apply to those directories and their subdirectories. The `.gitignore`
1195 files can be added to your repository like any other files (just run `git add
1196 .gitignore` and `git commit`, as usual), which is convenient when the exclude
1197 patterns (such as patterns matching build output files) would also make sense
1198 for other users who clone your repository.
1199
1200 If you wish the exclude patterns to affect only certain repositories
1201 (instead of every repository for a given project), you may instead put
1202 them in a file in your repository named `.git/info/exclude`, or in any
1203 file specified by the `core.excludesFile` configuration variable.
1204 Some Git commands can also take exclude patterns directly on the
1205 command line. See linkgit:gitignore[5] for the details.
1206
1207 [[how-to-merge]]
1208 How to merge
1209 ------------
1210
1211 You can rejoin two diverging branches of development using
1212 linkgit:git-merge[1]:
1213
1214 -------------------------------------------------
1215 $ git merge branchname
1216 -------------------------------------------------
1217
1218 merges the development in the branch `branchname` into the current
1219 branch.
1220
1221 A merge is made by combining the changes made in `branchname` and the
1222 changes made up to the latest commit in your current branch since
1223 their histories forked. The work tree is overwritten by the result of
1224 the merge when this combining is done cleanly, or overwritten by a
1225 half-merged results when this combining results in conflicts.
1226 Therefore, if you have uncommitted changes touching the same files as
1227 the ones impacted by the merge, Git will refuse to proceed. Most of
1228 the time, you will want to commit your changes before you can merge,
1229 and if you don't, then linkgit:git-stash[1] can take these changes
1230 away while you're doing the merge, and reapply them afterwards.
1231
1232 If the changes are independent enough, Git will automatically complete
1233 the merge and commit the result (or reuse an existing commit in case
1234 of <<fast-forwards,fast-forward>>, see below). On the other hand,
1235 if there are conflicts--for example, if the same file is
1236 modified in two different ways in the remote branch and the local
1237 branch--then you are warned; the output may look something like this:
1238
1239 -------------------------------------------------
1240 $ git merge next
1241 100% (4/4) done
1242 Auto-merged file.txt
1243 CONFLICT (content): Merge conflict in file.txt
1244 Automatic merge failed; fix conflicts and then commit the result.
1245 -------------------------------------------------
1246
1247 Conflict markers are left in the problematic files, and after
1248 you resolve the conflicts manually, you can update the index
1249 with the contents and run Git commit, as you normally would when
1250 creating a new file.
1251
1252 If you examine the resulting commit using gitk, you will see that it
1253 has two parents, one pointing to the top of the current branch, and
1254 one to the top of the other branch.
1255
1256 [[resolving-a-merge]]
1257 Resolving a merge
1258 -----------------
1259
1260 When a merge isn't resolved automatically, Git leaves the index and
1261 the working tree in a special state that gives you all the
1262 information you need to help resolve the merge.
1263
1264 Files with conflicts are marked specially in the index, so until you
1265 resolve the problem and update the index, linkgit:git-commit[1] will
1266 fail:
1267
1268 -------------------------------------------------
1269 $ git commit
1270 file.txt: needs merge
1271 -------------------------------------------------
1272
1273 Also, linkgit:git-status[1] will list those files as "unmerged", and the
1274 files with conflicts will have conflict markers added, like this:
1275
1276 -------------------------------------------------
1277 <<<<<<< HEAD:file.txt
1278 Hello world
1279 =======
1280 Goodbye
1281 >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1282 -------------------------------------------------
1283
1284 All you need to do is edit the files to resolve the conflicts, and then
1285
1286 -------------------------------------------------
1287 $ git add file.txt
1288 $ git commit
1289 -------------------------------------------------
1290
1291 Note that the commit message will already be filled in for you with
1292 some information about the merge. Normally you can just use this
1293 default message unchanged, but you may add additional commentary of
1294 your own if desired.
1295
1296 The above is all you need to know to resolve a simple merge. But Git
1297 also provides more information to help resolve conflicts:
1298
1299 [[conflict-resolution]]
1300 Getting conflict-resolution help during a merge
1301 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1302
1303 All of the changes that Git was able to merge automatically are
1304 already added to the index file, so linkgit:git-diff[1] shows only
1305 the conflicts. It uses an unusual syntax:
1306
1307 -------------------------------------------------
1308 $ git diff
1309 diff --cc file.txt
1310 index 802992c,2b60207..0000000
1311 --- a/file.txt
1312 +++ b/file.txt
1313 @@@ -1,1 -1,1 +1,5 @@@
1314 ++<<<<<<< HEAD:file.txt
1315 +Hello world
1316 ++=======
1317 + Goodbye
1318 ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1319 -------------------------------------------------
1320
1321 Recall that the commit which will be committed after we resolve this
1322 conflict will have two parents instead of the usual one: one parent
1323 will be HEAD, the tip of the current branch; the other will be the
1324 tip of the other branch, which is stored temporarily in MERGE_HEAD.
1325
1326 During the merge, the index holds three versions of each file. Each of
1327 these three "file stages" represents a different version of the file:
1328
1329 -------------------------------------------------
1330 $ git show :1:file.txt # the file in a common ancestor of both branches
1331 $ git show :2:file.txt # the version from HEAD.
1332 $ git show :3:file.txt # the version from MERGE_HEAD.
1333 -------------------------------------------------
1334
1335 When you ask linkgit:git-diff[1] to show the conflicts, it runs a
1336 three-way diff between the conflicted merge results in the work tree with
1337 stages 2 and 3 to show only hunks whose contents come from both sides,
1338 mixed (in other words, when a hunk's merge results come only from stage 2,
1339 that part is not conflicting and is not shown. Same for stage 3).
1340
1341 The diff above shows the differences between the working-tree version of
1342 file.txt and the stage 2 and stage 3 versions. So instead of preceding
1343 each line by a single `+` or `-`, it now uses two columns: the first
1344 column is used for differences between the first parent and the working
1345 directory copy, and the second for differences between the second parent
1346 and the working directory copy. (See the "COMBINED DIFF FORMAT" section
1347 of linkgit:git-diff-files[1] for a details of the format.)
1348
1349 After resolving the conflict in the obvious way (but before updating the
1350 index), the diff will look like:
1351
1352 -------------------------------------------------
1353 $ git diff
1354 diff --cc file.txt
1355 index 802992c,2b60207..0000000
1356 --- a/file.txt
1357 +++ b/file.txt
1358 @@@ -1,1 -1,1 +1,1 @@@
1359 - Hello world
1360 -Goodbye
1361 ++Goodbye world
1362 -------------------------------------------------
1363
1364 This shows that our resolved version deleted "Hello world" from the
1365 first parent, deleted "Goodbye" from the second parent, and added
1366 "Goodbye world", which was previously absent from both.
1367
1368 Some special diff options allow diffing the working directory against
1369 any of these stages:
1370
1371 -------------------------------------------------
1372 $ git diff -1 file.txt # diff against stage 1
1373 $ git diff --base file.txt # same as the above
1374 $ git diff -2 file.txt # diff against stage 2
1375 $ git diff --ours file.txt # same as the above
1376 $ git diff -3 file.txt # diff against stage 3
1377 $ git diff --theirs file.txt # same as the above.
1378 -------------------------------------------------
1379
1380 The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
1381 for merges:
1382
1383 -------------------------------------------------
1384 $ git log --merge
1385 $ gitk --merge
1386 -------------------------------------------------
1387
1388 These will display all commits which exist only on HEAD or on
1389 MERGE_HEAD, and which touch an unmerged file.
1390
1391 You may also use linkgit:git-mergetool[1], which lets you merge the
1392 unmerged files using external tools such as Emacs or kdiff3.
1393
1394 Each time you resolve the conflicts in a file and update the index:
1395
1396 -------------------------------------------------
1397 $ git add file.txt
1398 -------------------------------------------------
1399
1400 the different stages of that file will be "collapsed", after which
1401 `git diff` will (by default) no longer show diffs for that file.
1402
1403 [[undoing-a-merge]]
1404 Undoing a merge
1405 ---------------
1406
1407 If you get stuck and decide to just give up and throw the whole mess
1408 away, you can always return to the pre-merge state with
1409
1410 -------------------------------------------------
1411 $ git reset --hard HEAD
1412 -------------------------------------------------
1413
1414 Or, if you've already committed the merge that you want to throw away,
1415
1416 -------------------------------------------------
1417 $ git reset --hard ORIG_HEAD
1418 -------------------------------------------------
1419
1420 However, this last command can be dangerous in some cases--never
1421 throw away a commit you have already committed if that commit may
1422 itself have been merged into another branch, as doing so may confuse
1423 further merges.
1424
1425 [[fast-forwards]]
1426 Fast-forward merges
1427 -------------------
1428
1429 There is one special case not mentioned above, which is treated
1430 differently. Normally, a merge results in a merge commit, with two
1431 parents, one pointing at each of the two lines of development that
1432 were merged.
1433
1434 However, if the current branch is an ancestor of the other--so every commit
1435 present in the current branch is already contained in the other branch--then Git
1436 just performs a "fast-forward"; the head of the current branch is moved forward
1437 to point at the head of the merged-in branch, without any new commits being
1438 created.
1439
1440 [[fixing-mistakes]]
1441 Fixing mistakes
1442 ---------------
1443
1444 If you've messed up the working tree, but haven't yet committed your
1445 mistake, you can return the entire working tree to the last committed
1446 state with
1447
1448 -------------------------------------------------
1449 $ git reset --hard HEAD
1450 -------------------------------------------------
1451
1452 If you make a commit that you later wish you hadn't, there are two
1453 fundamentally different ways to fix the problem:
1454
1455 1. You can create a new commit that undoes whatever was done
1456 by the old commit. This is the correct thing if your
1457 mistake has already been made public.
1458
1459 2. You can go back and modify the old commit. You should
1460 never do this if you have already made the history public;
1461 Git does not normally expect the "history" of a project to
1462 change, and cannot correctly perform repeated merges from
1463 a branch that has had its history changed.
1464
1465 [[reverting-a-commit]]
1466 Fixing a mistake with a new commit
1467 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1468
1469 Creating a new commit that reverts an earlier change is very easy;
1470 just pass the linkgit:git-revert[1] command a reference to the bad
1471 commit; for example, to revert the most recent commit:
1472
1473 -------------------------------------------------
1474 $ git revert HEAD
1475 -------------------------------------------------
1476
1477 This will create a new commit which undoes the change in HEAD. You
1478 will be given a chance to edit the commit message for the new commit.
1479
1480 You can also revert an earlier change, for example, the next-to-last:
1481
1482 -------------------------------------------------
1483 $ git revert HEAD^
1484 -------------------------------------------------
1485
1486 In this case Git will attempt to undo the old change while leaving
1487 intact any changes made since then. If more recent changes overlap
1488 with the changes to be reverted, then you will be asked to fix
1489 conflicts manually, just as in the case of <<resolving-a-merge,
1490 resolving a merge>>.
1491
1492 [[fixing-a-mistake-by-rewriting-history]]
1493 Fixing a mistake by rewriting history
1494 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1495
1496 If the problematic commit is the most recent commit, and you have not
1497 yet made that commit public, then you may just
1498 <<undoing-a-merge,destroy it using `git reset`>>.
1499
1500 Alternatively, you
1501 can edit the working directory and update the index to fix your
1502 mistake, just as if you were going to <<how-to-make-a-commit,create a
1503 new commit>>, then run
1504
1505 -------------------------------------------------
1506 $ git commit --amend
1507 -------------------------------------------------
1508
1509 which will replace the old commit by a new commit incorporating your
1510 changes, giving you a chance to edit the old commit message first.
1511
1512 Again, you should never do this to a commit that may already have
1513 been merged into another branch; use linkgit:git-revert[1] instead in
1514 that case.
1515
1516 It is also possible to replace commits further back in the history, but
1517 this is an advanced topic to be left for
1518 <<cleaning-up-history,another chapter>>.
1519
1520 [[checkout-of-path]]
1521 Checking out an old version of a file
1522 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1523
1524 In the process of undoing a previous bad change, you may find it
1525 useful to check out an older version of a particular file using
1526 linkgit:git-checkout[1]. We've used `git checkout` before to switch
1527 branches, but it has quite different behavior if it is given a path
1528 name: the command
1529
1530 -------------------------------------------------
1531 $ git checkout HEAD^ path/to/file
1532 -------------------------------------------------
1533
1534 replaces path/to/file by the contents it had in the commit HEAD^, and
1535 also updates the index to match. It does not change branches.
1536
1537 If you just want to look at an old version of the file, without
1538 modifying the working directory, you can do that with
1539 linkgit:git-show[1]:
1540
1541 -------------------------------------------------
1542 $ git show HEAD^:path/to/file
1543 -------------------------------------------------
1544
1545 which will display the given version of the file.
1546
1547 [[interrupted-work]]
1548 Temporarily setting aside work in progress
1549 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1550
1551 While you are in the middle of working on something complicated, you
1552 find an unrelated but obvious and trivial bug. You would like to fix it
1553 before continuing. You can use linkgit:git-stash[1] to save the current
1554 state of your work, and after fixing the bug (or, optionally after doing
1555 so on a different branch and then coming back), unstash the
1556 work-in-progress changes.
1557
1558 ------------------------------------------------
1559 $ git stash push -m "work in progress for foo feature"
1560 ------------------------------------------------
1561
1562 This command will save your changes away to the `stash`, and
1563 reset your working tree and the index to match the tip of your
1564 current branch. Then you can make your fix as usual.
1565
1566 ------------------------------------------------
1567 ... edit and test ...
1568 $ git commit -a -m "blorpl: typofix"
1569 ------------------------------------------------
1570
1571 After that, you can go back to what you were working on with
1572 `git stash pop`:
1573
1574 ------------------------------------------------
1575 $ git stash pop
1576 ------------------------------------------------
1577
1578
1579 [[ensuring-good-performance]]
1580 Ensuring good performance
1581 -------------------------
1582
1583 On large repositories, Git depends on compression to keep the history
1584 information from taking up too much space on disk or in memory. Some
1585 Git commands may automatically run linkgit:git-gc[1], so you don't
1586 have to worry about running it manually. However, compressing a large
1587 repository may take a while, so you may want to call `gc` explicitly
1588 to avoid automatic compression kicking in when it is not convenient.
1589
1590
1591 [[ensuring-reliability]]
1592 Ensuring reliability
1593 --------------------
1594
1595 [[checking-for-corruption]]
1596 Checking the repository for corruption
1597 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1598
1599 The linkgit:git-fsck[1] command runs a number of self-consistency checks
1600 on the repository, and reports on any problems. This may take some
1601 time.
1602
1603 -------------------------------------------------
1604 $ git fsck
1605 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1606 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1607 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1608 dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1609 dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1610 dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1611 dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1612 dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1613 ...
1614 -------------------------------------------------
1615
1616 You will see informational messages on dangling objects. They are objects
1617 that still exist in the repository but are no longer referenced by any of
1618 your branches, and can (and will) be removed after a while with `gc`.
1619 You can run `git fsck --no-dangling` to suppress these messages, and still
1620 view real errors.
1621
1622 [[recovering-lost-changes]]
1623 Recovering lost changes
1624 ~~~~~~~~~~~~~~~~~~~~~~~
1625
1626 [[reflogs]]
1627 Reflogs
1628 ^^^^^^^
1629
1630 Say you modify a branch with <<fixing-mistakes,`git reset --hard`>>,
1631 and then realize that the branch was the only reference you had to
1632 that point in history.
1633
1634 Fortunately, Git also keeps a log, called a "reflog", of all the
1635 previous values of each branch. So in this case you can still find the
1636 old history using, for example,
1637
1638 -------------------------------------------------
1639 $ git log master@{1}
1640 -------------------------------------------------
1641
1642 This lists the commits reachable from the previous version of the
1643 `master` branch head. This syntax can be used with any Git command
1644 that accepts a commit, not just with `git log`. Some other examples:
1645
1646 -------------------------------------------------
1647 $ git show master@{2} # See where the branch pointed 2,
1648 $ git show master@{3} # 3, ... changes ago.
1649 $ gitk master@{yesterday} # See where it pointed yesterday,
1650 $ gitk master@{"1 week ago"} # ... or last week
1651 $ git log --walk-reflogs master # show reflog entries for master
1652 -------------------------------------------------
1653
1654 A separate reflog is kept for the HEAD, so
1655
1656 -------------------------------------------------
1657 $ git show HEAD@{"1 week ago"}
1658 -------------------------------------------------
1659
1660 will show what HEAD pointed to one week ago, not what the current branch
1661 pointed to one week ago. This allows you to see the history of what
1662 you've checked out.
1663
1664 The reflogs are kept by default for 30 days, after which they may be
1665 pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn
1666 how to control this pruning, and see the "SPECIFYING REVISIONS"
1667 section of linkgit:gitrevisions[7] for details.
1668
1669 Note that the reflog history is very different from normal Git history.
1670 While normal history is shared by every repository that works on the
1671 same project, the reflog history is not shared: it tells you only about
1672 how the branches in your local repository have changed over time.
1673
1674 [[dangling-object-recovery]]
1675 Examining dangling objects
1676 ^^^^^^^^^^^^^^^^^^^^^^^^^^
1677
1678 In some situations the reflog may not be able to save you. For example,
1679 suppose you delete a branch, then realize you need the history it
1680 contained. The reflog is also deleted; however, if you have not yet
1681 pruned the repository, then you may still be able to find the lost
1682 commits in the dangling objects that `git fsck` reports. See
1683 <<dangling-objects>> for the details.
1684
1685 -------------------------------------------------
1686 $ git fsck
1687 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1688 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1689 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1690 ...
1691 -------------------------------------------------
1692
1693 You can examine
1694 one of those dangling commits with, for example,
1695
1696 ------------------------------------------------
1697 $ gitk 7281251ddd --not --all
1698 ------------------------------------------------
1699
1700 which does what it sounds like: it says that you want to see the commit
1701 history that is described by the dangling commit(s), but not the
1702 history that is described by all your existing branches and tags. Thus
1703 you get exactly the history reachable from that commit that is lost.
1704 (And notice that it might not be just one commit: we only report the
1705 "tip of the line" as being dangling, but there might be a whole deep
1706 and complex commit history that was dropped.)
1707
1708 If you decide you want the history back, you can always create a new
1709 reference pointing to it, for example, a new branch:
1710
1711 ------------------------------------------------
1712 $ git branch recovered-branch 7281251ddd
1713 ------------------------------------------------
1714
1715 Other types of dangling objects (blobs and trees) are also possible, and
1716 dangling objects can arise in other situations.
1717
1718
1719 [[sharing-development]]
1720 Sharing development with others
1721 ===============================
1722
1723 [[getting-updates-With-git-pull]]
1724 Getting updates with git pull
1725 -----------------------------
1726
1727 After you clone a repository and commit a few changes of your own, you
1728 may wish to check the original repository for updates and merge them
1729 into your own work.
1730
1731 We have already seen <<Updating-a-repository-With-git-fetch,how to
1732 keep remote-tracking branches up to date>> with linkgit:git-fetch[1],
1733 and how to merge two branches. So you can merge in changes from the
1734 original repository's master branch with:
1735
1736 -------------------------------------------------
1737 $ git fetch
1738 $ git merge origin/master
1739 -------------------------------------------------
1740
1741 However, the linkgit:git-pull[1] command provides a way to do this in
1742 one step:
1743
1744 -------------------------------------------------
1745 $ git pull origin master
1746 -------------------------------------------------
1747
1748 In fact, if you have `master` checked out, then this branch has been
1749 configured by `git clone` to get changes from the HEAD branch of the
1750 origin repository. So often you can
1751 accomplish the above with just a simple
1752
1753 -------------------------------------------------
1754 $ git pull
1755 -------------------------------------------------
1756
1757 This command will fetch changes from the remote branches to your
1758 remote-tracking branches `origin/*`, and merge the default branch into
1759 the current branch.
1760
1761 More generally, a branch that is created from a remote-tracking branch
1762 will pull
1763 by default from that branch. See the descriptions of the
1764 `branch.<name>.remote` and `branch.<name>.merge` options in
1765 linkgit:git-config[1], and the discussion of the `--track` option in
1766 linkgit:git-checkout[1], to learn how to control these defaults.
1767
1768 In addition to saving you keystrokes, `git pull` also helps you by
1769 producing a default commit message documenting the branch and
1770 repository that you pulled from.
1771
1772 (But note that no such commit will be created in the case of a
1773 <<fast-forwards,fast-forward>>; instead, your branch will just be
1774 updated to point to the latest commit from the upstream branch.)
1775
1776 The `git pull` command can also be given `.` as the "remote" repository,
1777 in which case it just merges in a branch from the current repository; so
1778 the commands
1779
1780 -------------------------------------------------
1781 $ git pull . branch
1782 $ git merge branch
1783 -------------------------------------------------
1784
1785 are roughly equivalent.
1786
1787 [[submitting-patches]]
1788 Submitting patches to a project
1789 -------------------------------
1790
1791 If you just have a few changes, the simplest way to submit them may
1792 just be to send them as patches in email:
1793
1794 First, use linkgit:git-format-patch[1]; for example:
1795
1796 -------------------------------------------------
1797 $ git format-patch origin
1798 -------------------------------------------------
1799
1800 will produce a numbered series of files in the current directory, one
1801 for each patch in the current branch but not in `origin/HEAD`.
1802
1803 `git format-patch` can include an initial "cover letter". You can insert
1804 commentary on individual patches after the three dash line which
1805 `format-patch` places after the commit message but before the patch
1806 itself. If you use `git notes` to track your cover letter material,
1807 `git format-patch --notes` will include the commit's notes in a similar
1808 manner.
1809
1810 You can then import these into your mail client and send them by
1811 hand. However, if you have a lot to send at once, you may prefer to
1812 use the linkgit:git-send-email[1] script to automate the process.
1813 Consult the mailing list for your project first to determine
1814 their requirements for submitting patches.
1815
1816 [[importing-patches]]
1817 Importing patches to a project
1818 ------------------------------
1819
1820 Git also provides a tool called linkgit:git-am[1] (am stands for
1821 "apply mailbox"), for importing such an emailed series of patches.
1822 Just save all of the patch-containing messages, in order, into a
1823 single mailbox file, say `patches.mbox`, then run
1824
1825 -------------------------------------------------
1826 $ git am -3 patches.mbox
1827 -------------------------------------------------
1828
1829 Git will apply each patch in order; if any conflicts are found, it
1830 will stop, and you can fix the conflicts as described in
1831 "<<resolving-a-merge,Resolving a merge>>". (The `-3` option tells
1832 Git to perform a merge; if you would prefer it just to abort and
1833 leave your tree and index untouched, you may omit that option.)
1834
1835 Once the index is updated with the results of the conflict
1836 resolution, instead of creating a new commit, just run
1837
1838 -------------------------------------------------
1839 $ git am --continue
1840 -------------------------------------------------
1841
1842 and Git will create the commit for you and continue applying the
1843 remaining patches from the mailbox.
1844
1845 The final result will be a series of commits, one for each patch in
1846 the original mailbox, with authorship and commit log message each
1847 taken from the message containing each patch.
1848
1849 [[public-repositories]]
1850 Public Git repositories
1851 -----------------------
1852
1853 Another way to submit changes to a project is to tell the maintainer
1854 of that project to pull the changes from your repository using
1855 linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull,
1856 Getting updates with `git pull`>>" we described this as a way to get
1857 updates from the "main" repository, but it works just as well in the
1858 other direction.
1859
1860 If you and the maintainer both have accounts on the same machine, then
1861 you can just pull changes from each other's repositories directly;
1862 commands that accept repository URLs as arguments will also accept a
1863 local directory name:
1864
1865 -------------------------------------------------
1866 $ git clone /path/to/repository
1867 $ git pull /path/to/other/repository
1868 -------------------------------------------------
1869
1870 or an ssh URL:
1871
1872 -------------------------------------------------
1873 $ git clone ssh://yourhost/~you/repository
1874 -------------------------------------------------
1875
1876 For projects with few developers, or for synchronizing a few private
1877 repositories, this may be all you need.
1878
1879 However, the more common way to do this is to maintain a separate public
1880 repository (usually on a different host) for others to pull changes
1881 from. This is usually more convenient, and allows you to cleanly
1882 separate private work in progress from publicly visible work.
1883
1884 You will continue to do your day-to-day work in your personal
1885 repository, but periodically "push" changes from your personal
1886 repository into your public repository, allowing other developers to
1887 pull from that repository. So the flow of changes, in a situation
1888 where there is one other developer with a public repository, looks
1889 like this:
1890
1891 you push
1892 your personal repo ------------------> your public repo
1893 ^ |
1894 | |
1895 | you pull | they pull
1896 | |
1897 | |
1898 | they push V
1899 their public repo <------------------- their repo
1900
1901 We explain how to do this in the following sections.
1902
1903 [[setting-up-a-public-repository]]
1904 Setting up a public repository
1905 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1906
1907 Assume your personal repository is in the directory `~/proj`. We
1908 first create a new clone of the repository and tell `git daemon` that it
1909 is meant to be public:
1910
1911 -------------------------------------------------
1912 $ git clone --bare ~/proj proj.git
1913 $ touch proj.git/git-daemon-export-ok
1914 -------------------------------------------------
1915
1916 The resulting directory proj.git contains a "bare" git repository--it is
1917 just the contents of the `.git` directory, without any files checked out
1918 around it.
1919
1920 Next, copy `proj.git` to the server where you plan to host the
1921 public repository. You can use scp, rsync, or whatever is most
1922 convenient.
1923
1924 [[exporting-via-git]]
1925 Exporting a Git repository via the Git protocol
1926 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1927
1928 This is the preferred method.
1929
1930 If someone else administers the server, they should tell you what
1931 directory to put the repository in, and what `git://` URL it will
1932 appear at. You can then skip to the section
1933 "<<pushing-changes-to-a-public-repository,Pushing changes to a public
1934 repository>>", below.
1935
1936 Otherwise, all you need to do is start linkgit:git-daemon[1]; it will
1937 listen on port 9418. By default, it will allow access to any directory
1938 that looks like a Git directory and contains the magic file
1939 git-daemon-export-ok. Passing some directory paths as `git daemon`
1940 arguments will further restrict the exports to those paths.
1941
1942 You can also run `git daemon` as an inetd service; see the
1943 linkgit:git-daemon[1] man page for details. (See especially the
1944 examples section.)
1945
1946 [[exporting-via-http]]
1947 Exporting a git repository via HTTP
1948 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1949
1950 The Git protocol gives better performance and reliability, but on a
1951 host with a web server set up, HTTP exports may be simpler to set up.
1952
1953 All you need to do is place the newly created bare Git repository in
1954 a directory that is exported by the web server, and make some
1955 adjustments to give web clients some extra information they need:
1956
1957 -------------------------------------------------
1958 $ mv proj.git /home/you/public_html/proj.git
1959 $ cd proj.git
1960 $ git --bare update-server-info
1961 $ mv hooks/post-update.sample hooks/post-update
1962 -------------------------------------------------
1963
1964 (For an explanation of the last two lines, see
1965 linkgit:git-update-server-info[1] and linkgit:githooks[5].)
1966
1967 Advertise the URL of `proj.git`. Anybody else should then be able to
1968 clone or pull from that URL, for example with a command line like:
1969
1970 -------------------------------------------------
1971 $ git clone http://yourserver.com/~you/proj.git
1972 -------------------------------------------------
1973
1974 (See also
1975 link:howto/setup-git-server-over-http.html[setup-git-server-over-http]
1976 for a slightly more sophisticated setup using WebDAV which also
1977 allows pushing over HTTP.)
1978
1979 [[pushing-changes-to-a-public-repository]]
1980 Pushing changes to a public repository
1981 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1982
1983 Note that the two techniques outlined above (exporting via
1984 <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1985 maintainers to fetch your latest changes, but they do not allow write
1986 access, which you will need to update the public repository with the
1987 latest changes created in your private repository.
1988
1989 The simplest way to do this is using linkgit:git-push[1] and ssh; to
1990 update the remote branch named `master` with the latest state of your
1991 branch named `master`, run
1992
1993 -------------------------------------------------
1994 $ git push ssh://yourserver.com/~you/proj.git master:master
1995 -------------------------------------------------
1996
1997 or just
1998
1999 -------------------------------------------------
2000 $ git push ssh://yourserver.com/~you/proj.git master
2001 -------------------------------------------------
2002
2003 As with `git fetch`, `git push` will complain if this does not result in a
2004 <<fast-forwards,fast-forward>>; see the following section for details on
2005 handling this case.
2006
2007 Note that the target of a `push` is normally a
2008 <<def_bare_repository,bare>> repository. You can also push to a
2009 repository that has a checked-out working tree, but a push to update the
2010 currently checked-out branch is denied by default to prevent confusion.
2011 See the description of the receive.denyCurrentBranch option
2012 in linkgit:git-config[1] for details.
2013
2014 As with `git fetch`, you may also set up configuration options to
2015 save typing; so, for example:
2016
2017 -------------------------------------------------
2018 $ git remote add public-repo ssh://yourserver.com/~you/proj.git
2019 -------------------------------------------------
2020
2021 adds the following to `.git/config`:
2022
2023 -------------------------------------------------
2024 [remote "public-repo"]
2025 url = yourserver.com:proj.git
2026 fetch = +refs/heads/*:refs/remotes/example/*
2027 -------------------------------------------------
2028
2029 which lets you do the same push with just
2030
2031 -------------------------------------------------
2032 $ git push public-repo master
2033 -------------------------------------------------
2034
2035 See the explanations of the `remote.<name>.url`,
2036 `branch.<name>.remote`, and `remote.<name>.push` options in
2037 linkgit:git-config[1] for details.
2038
2039 [[forcing-push]]
2040 What to do when a push fails
2041 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2042
2043 If a push would not result in a <<fast-forwards,fast-forward>> of the
2044 remote branch, then it will fail with an error like:
2045
2046 -------------------------------------------------
2047 ! [rejected] master -> master (non-fast-forward)
2048 error: failed to push some refs to '...'
2049 hint: Updates were rejected because the tip of your current branch is behind
2050 hint: its remote counterpart. Integrate the remote changes (e.g.
2051 hint: 'git pull ...') before pushing again.
2052 hint: See the 'Note about fast-forwards' in 'git push --help' for details.
2053 -------------------------------------------------
2054
2055 This can happen, for example, if you:
2056
2057 - use `git reset --hard` to remove already-published commits, or
2058 - use `git commit --amend` to replace already-published commits
2059 (as in <<fixing-a-mistake-by-rewriting-history>>), or
2060 - use `git rebase` to rebase any already-published commits (as
2061 in <<using-git-rebase>>).
2062
2063 You may force `git push` to perform the update anyway by preceding the
2064 branch name with a plus sign:
2065
2066 -------------------------------------------------
2067 $ git push ssh://yourserver.com/~you/proj.git +master
2068 -------------------------------------------------
2069
2070 Note the addition of the `+` sign. Alternatively, you can use the
2071 `-f` flag to force the remote update, as in:
2072
2073 -------------------------------------------------
2074 $ git push -f ssh://yourserver.com/~you/proj.git master
2075 -------------------------------------------------
2076
2077 Normally whenever a branch head in a public repository is modified, it
2078 is modified to point to a descendant of the commit that it pointed to
2079 before. By forcing a push in this situation, you break that convention.
2080 (See <<problems-With-rewriting-history>>.)
2081
2082 Nevertheless, this is a common practice for people that need a simple
2083 way to publish a work-in-progress patch series, and it is an acceptable
2084 compromise as long as you warn other developers that this is how you
2085 intend to manage the branch.
2086
2087 It's also possible for a push to fail in this way when other people have
2088 the right to push to the same repository. In that case, the correct
2089 solution is to retry the push after first updating your work: either by a
2090 pull, or by a fetch followed by a rebase; see the
2091 <<setting-up-a-shared-repository,next section>> and
2092 linkgit:gitcvs-migration[7] for more.
2093
2094 [[setting-up-a-shared-repository]]
2095 Setting up a shared repository
2096 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2097
2098 Another way to collaborate is by using a model similar to that
2099 commonly used in CVS, where several developers with special rights
2100 all push to and pull from a single shared repository. See
2101 linkgit:gitcvs-migration[7] for instructions on how to
2102 set this up.
2103
2104 However, while there is nothing wrong with Git's support for shared
2105 repositories, this mode of operation is not generally recommended,
2106 simply because the mode of collaboration that Git supports--by
2107 exchanging patches and pulling from public repositories--has so many
2108 advantages over the central shared repository:
2109
2110 - Git's ability to quickly import and merge patches allows a
2111 single maintainer to process incoming changes even at very
2112 high rates. And when that becomes too much, `git pull` provides
2113 an easy way for that maintainer to delegate this job to other
2114 maintainers while still allowing optional review of incoming
2115 changes.
2116 - Since every developer's repository has the same complete copy
2117 of the project history, no repository is special, and it is
2118 trivial for another developer to take over maintenance of a
2119 project, either by mutual agreement, or because a maintainer
2120 becomes unresponsive or difficult to work with.
2121 - The lack of a central group of "committers" means there is
2122 less need for formal decisions about who is "in" and who is
2123 "out".
2124
2125 [[setting-up-gitweb]]
2126 Allowing web browsing of a repository
2127 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2128
2129 The gitweb cgi script provides users an easy way to browse your
2130 project's revisions, file contents and logs without having to install
2131 Git. Features like RSS/Atom feeds and blame/annotation details may
2132 optionally be enabled.
2133
2134 The linkgit:git-instaweb[1] command provides a simple way to start
2135 browsing the repository using gitweb. The default server when using
2136 instaweb is lighttpd.
2137
2138 See the file gitweb/INSTALL in the Git source tree and
2139 linkgit:gitweb[1] for instructions on details setting up a permanent
2140 installation with a CGI or Perl capable server.
2141
2142 [[how-to-get-a-git-repository-with-minimal-history]]
2143 How to get a Git repository with minimal history
2144 ------------------------------------------------
2145
2146 A <<def_shallow_clone,shallow clone>>, with its truncated
2147 history, is useful when one is interested only in recent history
2148 of a project and getting full history from the upstream is
2149 expensive.
2150
2151 A <<def_shallow_clone,shallow clone>> is created by specifying
2152 the linkgit:git-clone[1] `--depth` switch. The depth can later be
2153 changed with the linkgit:git-fetch[1] `--depth` switch, or full
2154 history restored with `--unshallow`.
2155
2156 Merging inside a <<def_shallow_clone,shallow clone>> will work as long
2157 as a merge base is in the recent history.
2158 Otherwise, it will be like merging unrelated histories and may
2159 have to result in huge conflicts. This limitation may make such
2160 a repository unsuitable to be used in merge based workflows.
2161
2162 [[sharing-development-examples]]
2163 Examples
2164 --------
2165
2166 [[maintaining-topic-branches]]
2167 Maintaining topic branches for a Linux subsystem maintainer
2168 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2169
2170 This describes how Tony Luck uses Git in his role as maintainer of the
2171 IA64 architecture for the Linux kernel.
2172
2173 He uses two public branches:
2174
2175 - A "test" tree into which patches are initially placed so that they
2176 can get some exposure when integrated with other ongoing development.
2177 This tree is available to Andrew for pulling into -mm whenever he
2178 wants.
2179
2180 - A "release" tree into which tested patches are moved for final sanity
2181 checking, and as a vehicle to send them upstream to Linus (by sending
2182 him a "please pull" request.)
2183
2184 He also uses a set of temporary branches ("topic branches"), each
2185 containing a logical grouping of patches.
2186
2187 To set this up, first create your work tree by cloning Linus's public
2188 tree:
2189
2190 -------------------------------------------------
2191 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git work
2192 $ cd work
2193 -------------------------------------------------
2194
2195 Linus's tree will be stored in the remote-tracking branch named origin/master,
2196 and can be updated using linkgit:git-fetch[1]; you can track other
2197 public trees using linkgit:git-remote[1] to set up a "remote" and
2198 linkgit:git-fetch[1] to keep them up to date; see
2199 <<repositories-and-branches>>.
2200
2201 Now create the branches in which you are going to work; these start out
2202 at the current tip of origin/master branch, and should be set up (using
2203 the `--track` option to linkgit:git-branch[1]) to merge changes in from
2204 Linus by default.
2205
2206 -------------------------------------------------
2207 $ git branch --track test origin/master
2208 $ git branch --track release origin/master
2209 -------------------------------------------------
2210
2211 These can be easily kept up to date using linkgit:git-pull[1].
2212
2213 -------------------------------------------------
2214 $ git checkout test && git pull
2215 $ git checkout release && git pull
2216 -------------------------------------------------
2217
2218 Important note! If you have any local changes in these branches, then
2219 this merge will create a commit object in the history (with no local
2220 changes Git will simply do a "fast-forward" merge). Many people dislike
2221 the "noise" that this creates in the Linux history, so you should avoid
2222 doing this capriciously in the `release` branch, as these noisy commits
2223 will become part of the permanent history when you ask Linus to pull
2224 from the release branch.
2225
2226 A few configuration variables (see linkgit:git-config[1]) can
2227 make it easy to push both branches to your public tree. (See
2228 <<setting-up-a-public-repository>>.)
2229
2230 -------------------------------------------------
2231 $ cat >> .git/config <<EOF
2232 [remote "mytree"]
2233 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux.git
2234 push = release
2235 push = test
2236 EOF
2237 -------------------------------------------------
2238
2239 Then you can push both the test and release trees using
2240 linkgit:git-push[1]:
2241
2242 -------------------------------------------------
2243 $ git push mytree
2244 -------------------------------------------------
2245
2246 or push just one of the test and release branches using:
2247
2248 -------------------------------------------------
2249 $ git push mytree test
2250 -------------------------------------------------
2251
2252 or
2253
2254 -------------------------------------------------
2255 $ git push mytree release
2256 -------------------------------------------------
2257
2258 Now to apply some patches from the community. Think of a short
2259 snappy name for a branch to hold this patch (or related group of
2260 patches), and create a new branch from a recent stable tag of
2261 Linus's branch. Picking a stable base for your branch will:
2262 1) help you: by avoiding inclusion of unrelated and perhaps lightly
2263 tested changes
2264 2) help future bug hunters that use `git bisect` to find problems
2265
2266 -------------------------------------------------
2267 $ git checkout -b speed-up-spinlocks v2.6.35
2268 -------------------------------------------------
2269
2270 Now you apply the patch(es), run some tests, and commit the change(s). If
2271 the patch is a multi-part series, then you should apply each as a separate
2272 commit to this branch.
2273
2274 -------------------------------------------------
2275 $ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2276 -------------------------------------------------
2277
2278 When you are happy with the state of this change, you can merge it into the
2279 "test" branch in preparation to make it public:
2280
2281 -------------------------------------------------
2282 $ git checkout test && git merge speed-up-spinlocks
2283 -------------------------------------------------
2284
2285 It is unlikely that you would have any conflicts here ... but you might if you
2286 spent a while on this step and had also pulled new versions from upstream.
2287
2288 Sometime later when enough time has passed and testing done, you can pull the
2289 same branch into the `release` tree ready to go upstream. This is where you
2290 see the value of keeping each patch (or patch series) in its own branch. It
2291 means that the patches can be moved into the `release` tree in any order.
2292
2293 -------------------------------------------------
2294 $ git checkout release && git merge speed-up-spinlocks
2295 -------------------------------------------------
2296
2297 After a while, you will have a number of branches, and despite the
2298 well chosen names you picked for each of them, you may forget what
2299 they are for, or what status they are in. To get a reminder of what
2300 changes are in a specific branch, use:
2301
2302 -------------------------------------------------
2303 $ git log linux..branchname | git shortlog
2304 -------------------------------------------------
2305
2306 To see whether it has already been merged into the test or release branches,
2307 use:
2308
2309 -------------------------------------------------
2310 $ git log test..branchname
2311 -------------------------------------------------
2312
2313 or
2314
2315 -------------------------------------------------
2316 $ git log release..branchname
2317 -------------------------------------------------
2318
2319 (If this branch has not yet been merged, you will see some log entries.
2320 If it has been merged, then there will be no output.)
2321
2322 Once a patch completes the great cycle (moving from test to release,
2323 then pulled by Linus, and finally coming back into your local
2324 `origin/master` branch), the branch for this change is no longer needed.
2325 You detect this when the output from:
2326
2327 -------------------------------------------------
2328 $ git log origin..branchname
2329 -------------------------------------------------
2330
2331 is empty. At this point the branch can be deleted:
2332
2333 -------------------------------------------------
2334 $ git branch -d branchname
2335 -------------------------------------------------
2336
2337 Some changes are so trivial that it is not necessary to create a separate
2338 branch and then merge into each of the test and release branches. For
2339 these changes, just apply directly to the `release` branch, and then
2340 merge that into the `test` branch.
2341
2342 After pushing your work to `mytree`, you can use
2343 linkgit:git-request-pull[1] to prepare a "please pull" request message
2344 to send to Linus:
2345
2346 -------------------------------------------------
2347 $ git push mytree
2348 $ git request-pull origin mytree release
2349 -------------------------------------------------
2350
2351 Here are some of the scripts that simplify all this even further.
2352
2353 -------------------------------------------------
2354 ==== update script ====
2355 # Update a branch in my Git tree. If the branch to be updated
2356 # is origin, then pull from kernel.org. Otherwise merge
2357 # origin/master branch into test|release branch
2358
2359 case "$1" in
2360 test|release)
2361 git checkout $1 && git pull . origin
2362 ;;
2363 origin)
2364 before=$(git rev-parse refs/remotes/origin/master)
2365 git fetch origin
2366 after=$(git rev-parse refs/remotes/origin/master)
2367 if [ $before != $after ]
2368 then
2369 git log $before..$after | git shortlog
2370 fi
2371 ;;
2372 *)
2373 echo "usage: $0 origin|test|release" 1>&2
2374 exit 1
2375 ;;
2376 esac
2377 -------------------------------------------------
2378
2379 -------------------------------------------------
2380 ==== merge script ====
2381 # Merge a branch into either the test or release branch
2382
2383 pname=$0
2384
2385 usage()
2386 {
2387 echo "usage: $pname branch test|release" 1>&2
2388 exit 1
2389 }
2390
2391 git show-ref -q --verify -- refs/heads/"$1" || {
2392 echo "Can't see branch <$1>" 1>&2
2393 usage
2394 }
2395
2396 case "$2" in
2397 test|release)
2398 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2399 then
2400 echo $1 already merged into $2 1>&2
2401 exit 1
2402 fi
2403 git checkout $2 && git pull . $1
2404 ;;
2405 *)
2406 usage
2407 ;;
2408 esac
2409 -------------------------------------------------
2410
2411 -------------------------------------------------
2412 ==== status script ====
2413 # report on status of my ia64 Git tree
2414
2415 gb=$(tput setab 2)
2416 rb=$(tput setab 1)
2417 restore=$(tput setab 9)
2418
2419 if [ `git rev-list test..release | wc -c` -gt 0 ]
2420 then
2421 echo $rb Warning: commits in release that are not in test $restore
2422 git log test..release
2423 fi
2424
2425 for branch in `git show-ref --heads | sed 's|^.*/||'`
2426 do
2427 if [ $branch = test -o $branch = release ]
2428 then
2429 continue
2430 fi
2431
2432 echo -n $gb ======= $branch ====== $restore " "
2433 status=
2434 for ref in test release origin/master
2435 do
2436 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2437 then
2438 status=$status${ref:0:1}
2439 fi
2440 done
2441 case $status in
2442 trl)
2443 echo $rb Need to pull into test $restore
2444 ;;
2445 rl)
2446 echo "In test"
2447 ;;
2448 l)
2449 echo "Waiting for linus"
2450 ;;
2451 "")
2452 echo $rb All done $restore
2453 ;;
2454 *)
2455 echo $rb "<$status>" $restore
2456 ;;
2457 esac
2458 git log origin/master..$branch | git shortlog
2459 done
2460 -------------------------------------------------
2461
2462
2463 [[cleaning-up-history]]
2464 Rewriting history and maintaining patch series
2465 ==============================================
2466
2467 Normally commits are only added to a project, never taken away or
2468 replaced. Git is designed with this assumption, and violating it will
2469 cause Git's merge machinery (for example) to do the wrong thing.
2470
2471 However, there is a situation in which it can be useful to violate this
2472 assumption.
2473
2474 [[patch-series]]
2475 Creating the perfect patch series
2476 ---------------------------------
2477
2478 Suppose you are a contributor to a large project, and you want to add a
2479 complicated feature, and to present it to the other developers in a way
2480 that makes it easy for them to read your changes, verify that they are
2481 correct, and understand why you made each change.
2482
2483 If you present all of your changes as a single patch (or commit), they
2484 may find that it is too much to digest all at once.
2485
2486 If you present them with the entire history of your work, complete with
2487 mistakes, corrections, and dead ends, they may be overwhelmed.
2488
2489 So the ideal is usually to produce a series of patches such that:
2490
2491 1. Each patch can be applied in order.
2492
2493 2. Each patch includes a single logical change, together with a
2494 message explaining the change.
2495
2496 3. No patch introduces a regression: after applying any initial
2497 part of the series, the resulting project still compiles and
2498 works, and has no bugs that it didn't have before.
2499
2500 4. The complete series produces the same end result as your own
2501 (probably much messier!) development process did.
2502
2503 We will introduce some tools that can help you do this, explain how to
2504 use them, and then explain some of the problems that can arise because
2505 you are rewriting history.
2506
2507 [[using-git-rebase]]
2508 Keeping a patch series up to date using git rebase
2509 --------------------------------------------------
2510
2511 Suppose that you create a branch `mywork` on a remote-tracking branch
2512 `origin`, and create some commits on top of it:
2513
2514 -------------------------------------------------
2515 $ git checkout -b mywork origin
2516 $ vi file.txt
2517 $ git commit
2518 $ vi otherfile.txt
2519 $ git commit
2520 ...
2521 -------------------------------------------------
2522
2523 You have performed no merges into mywork, so it is just a simple linear
2524 sequence of patches on top of `origin`:
2525
2526 ................................................
2527 o--o--O <-- origin
2528 \
2529 a--b--c <-- mywork
2530 ................................................
2531
2532 Some more interesting work has been done in the upstream project, and
2533 `origin` has advanced:
2534
2535 ................................................
2536 o--o--O--o--o--o <-- origin
2537 \
2538 a--b--c <-- mywork
2539 ................................................
2540
2541 At this point, you could use `pull` to merge your changes back in;
2542 the result would create a new merge commit, like this:
2543
2544 ................................................
2545 o--o--O--o--o--o <-- origin
2546 \ \
2547 a--b--c--m <-- mywork
2548 ................................................
2549
2550 However, if you prefer to keep the history in mywork a simple series of
2551 commits without any merges, you may instead choose to use
2552 linkgit:git-rebase[1]:
2553
2554 -------------------------------------------------
2555 $ git checkout mywork
2556 $ git rebase origin
2557 -------------------------------------------------
2558
2559 This will remove each of your commits from mywork, temporarily saving
2560 them as patches (in a directory named `.git/rebase-apply`), update mywork to
2561 point at the latest version of origin, then apply each of the saved
2562 patches to the new mywork. The result will look like:
2563
2564
2565 ................................................
2566 o--o--O--o--o--o <-- origin
2567 \
2568 a'--b'--c' <-- mywork
2569 ................................................
2570
2571 In the process, it may discover conflicts. In that case it will stop
2572 and allow you to fix the conflicts; after fixing conflicts, use `git add`
2573 to update the index with those contents, and then, instead of
2574 running `git commit`, just run
2575
2576 -------------------------------------------------
2577 $ git rebase --continue
2578 -------------------------------------------------
2579
2580 and Git will continue applying the rest of the patches.
2581
2582 At any point you may use the `--abort` option to abort this process and
2583 return mywork to the state it had before you started the rebase:
2584
2585 -------------------------------------------------
2586 $ git rebase --abort
2587 -------------------------------------------------
2588
2589 If you need to reorder or edit a number of commits in a branch, it may
2590 be easier to use `git rebase -i`, which allows you to reorder and
2591 squash commits, as well as marking them for individual editing during
2592 the rebase. See <<interactive-rebase>> for details, and
2593 <<reordering-patch-series>> for alternatives.
2594
2595 [[rewriting-one-commit]]
2596 Rewriting a single commit
2597 -------------------------
2598
2599 We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
2600 most recent commit using
2601
2602 -------------------------------------------------
2603 $ git commit --amend
2604 -------------------------------------------------
2605
2606 which will replace the old commit by a new commit incorporating your
2607 changes, giving you a chance to edit the old commit message first.
2608 This is useful for fixing typos in your last commit, or for adjusting
2609 the patch contents of a poorly staged commit.
2610
2611 If you need to amend commits from deeper in your history, you can
2612 use <<interactive-rebase,interactive rebase's `edit` instruction>>.
2613
2614 [[reordering-patch-series]]
2615 Reordering or selecting from a patch series
2616 -------------------------------------------
2617
2618 Sometimes you want to edit a commit deeper in your history. One
2619 approach is to use `git format-patch` to create a series of patches
2620 and then reset the state to before the patches:
2621
2622 -------------------------------------------------
2623 $ git format-patch origin
2624 $ git reset --hard origin
2625 -------------------------------------------------
2626
2627 Then modify, reorder, or eliminate patches as needed before applying
2628 them again with linkgit:git-am[1]:
2629
2630 -------------------------------------------------
2631 $ git am *.patch
2632 -------------------------------------------------
2633
2634 [[interactive-rebase]]
2635 Using interactive rebases
2636 -------------------------
2637
2638 You can also edit a patch series with an interactive rebase. This is
2639 the same as <<reordering-patch-series,reordering a patch series using
2640 `format-patch`>>, so use whichever interface you like best.
2641
2642 Rebase your current HEAD on the last commit you want to retain as-is.
2643 For example, if you want to reorder the last 5 commits, use:
2644
2645 -------------------------------------------------
2646 $ git rebase -i HEAD~5
2647 -------------------------------------------------
2648
2649 This will open your editor with a list of steps to be taken to perform
2650 your rebase.
2651
2652 -------------------------------------------------
2653 pick deadbee The oneline of this commit
2654 pick fa1afe1 The oneline of the next commit
2655 ...
2656
2657 # Rebase c0ffeee..deadbee onto c0ffeee
2658 #
2659 # Commands:
2660 # p, pick = use commit
2661 # r, reword = use commit, but edit the commit message
2662 # e, edit = use commit, but stop for amending
2663 # s, squash = use commit, but meld into previous commit
2664 # f, fixup = like "squash", but discard this commit's log message
2665 # x, exec = run command (the rest of the line) using shell
2666 #
2667 # These lines can be re-ordered; they are executed from top to bottom.
2668 #
2669 # If you remove a line here THAT COMMIT WILL BE LOST.
2670 #
2671 # However, if you remove everything, the rebase will be aborted.
2672 #
2673 # Note that empty commits are commented out
2674 -------------------------------------------------
2675
2676 As explained in the comments, you can reorder commits, squash them
2677 together, edit commit messages, etc. by editing the list. Once you
2678 are satisfied, save the list and close your editor, and the rebase
2679 will begin.
2680
2681 The rebase will stop where `pick` has been replaced with `edit` or
2682 when a step in the list fails to mechanically resolve conflicts and
2683 needs your help. When you are done editing and/or resolving conflicts
2684 you can continue with `git rebase --continue`. If you decide that
2685 things are getting too hairy, you can always bail out with `git rebase
2686 --abort`. Even after the rebase is complete, you can still recover
2687 the original branch by using the <<reflogs,reflog>>.
2688
2689 For a more detailed discussion of the procedure and additional tips,
2690 see the "INTERACTIVE MODE" section of linkgit:git-rebase[1].
2691
2692 [[patch-series-tools]]
2693 Other tools
2694 -----------
2695
2696 There are numerous other tools, such as StGit, which exist for the
2697 purpose of maintaining a patch series. These are outside of the scope of
2698 this manual.
2699
2700 [[problems-With-rewriting-history]]
2701 Problems with rewriting history
2702 -------------------------------
2703
2704 The primary problem with rewriting the history of a branch has to do
2705 with merging. Suppose somebody fetches your branch and merges it into
2706 their branch, with a result something like this:
2707
2708 ................................................
2709 o--o--O--o--o--o <-- origin
2710 \ \
2711 t--t--t--m <-- their branch:
2712 ................................................
2713
2714 Then suppose you modify the last three commits:
2715
2716 ................................................
2717 o--o--o <-- new head of origin
2718 /
2719 o--o--O--o--o--o <-- old head of origin
2720 ................................................
2721
2722 If we examined all this history together in one repository, it will
2723 look like:
2724
2725 ................................................
2726 o--o--o <-- new head of origin
2727 /
2728 o--o--O--o--o--o <-- old head of origin
2729 \ \
2730 t--t--t--m <-- their branch:
2731 ................................................
2732
2733 Git has no way of knowing that the new head is an updated version of
2734 the old head; it treats this situation exactly the same as it would if
2735 two developers had independently done the work on the old and new heads
2736 in parallel. At this point, if someone attempts to merge the new head
2737 in to their branch, Git will attempt to merge together the two (old and
2738 new) lines of development, instead of trying to replace the old by the
2739 new. The results are likely to be unexpected.
2740
2741 You may still choose to publish branches whose history is rewritten,
2742 and it may be useful for others to be able to fetch those branches in
2743 order to examine or test them, but they should not attempt to pull such
2744 branches into their own work.
2745
2746 For true distributed development that supports proper merging,
2747 published branches should never be rewritten.
2748
2749 [[bisect-merges]]
2750 Why bisecting merge commits can be harder than bisecting linear history
2751 -----------------------------------------------------------------------
2752
2753 The linkgit:git-bisect[1] command correctly handles history that
2754 includes merge commits. However, when the commit that it finds is a
2755 merge commit, the user may need to work harder than usual to figure out
2756 why that commit introduced a problem.
2757
2758 Imagine this history:
2759
2760 ................................................
2761 ---Z---o---X---...---o---A---C---D
2762 \ /
2763 o---o---Y---...---o---B
2764 ................................................
2765
2766 Suppose that on the upper line of development, the meaning of one
2767 of the functions that exists at Z is changed at commit X. The
2768 commits from Z leading to A change both the function's
2769 implementation and all calling sites that exist at Z, as well
2770 as new calling sites they add, to be consistent. There is no
2771 bug at A.
2772
2773 Suppose that in the meantime on the lower line of development somebody
2774 adds a new calling site for that function at commit Y. The
2775 commits from Z leading to B all assume the old semantics of that
2776 function and the callers and the callee are consistent with each
2777 other. There is no bug at B, either.
2778
2779 Suppose further that the two development lines merge cleanly at C,
2780 so no conflict resolution is required.
2781
2782 Nevertheless, the code at C is broken, because the callers added
2783 on the lower line of development have not been converted to the new
2784 semantics introduced on the upper line of development. So if all
2785 you know is that D is bad, that Z is good, and that
2786 linkgit:git-bisect[1] identifies C as the culprit, how will you
2787 figure out that the problem is due to this change in semantics?
2788
2789 When the result of a `git bisect` is a non-merge commit, you should
2790 normally be able to discover the problem by examining just that commit.
2791 Developers can make this easy by breaking their changes into small
2792 self-contained commits. That won't help in the case above, however,
2793 because the problem isn't obvious from examination of any single
2794 commit; instead, a global view of the development is required. To
2795 make matters worse, the change in semantics in the problematic
2796 function may be just one small part of the changes in the upper
2797 line of development.
2798
2799 On the other hand, if instead of merging at C you had rebased the
2800 history between Z to B on top of A, you would have gotten this
2801 linear history:
2802
2803 ................................................................
2804 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2805 ................................................................
2806
2807 Bisecting between Z and D* would hit a single culprit commit Y*,
2808 and understanding why Y* was broken would probably be easier.
2809
2810 Partly for this reason, many experienced Git users, even when
2811 working on an otherwise merge-heavy project, keep the history
2812 linear by rebasing against the latest upstream version before
2813 publishing.
2814
2815 [[advanced-branch-management]]
2816 Advanced branch management
2817 ==========================
2818
2819 [[fetching-individual-branches]]
2820 Fetching individual branches
2821 ----------------------------
2822
2823 Instead of using linkgit:git-remote[1], you can also choose just
2824 to update one branch at a time, and to store it locally under an
2825 arbitrary name:
2826
2827 -------------------------------------------------
2828 $ git fetch origin todo:my-todo-work
2829 -------------------------------------------------
2830
2831 The first argument, `origin`, just tells Git to fetch from the
2832 repository you originally cloned from. The second argument tells Git
2833 to fetch the branch named `todo` from the remote repository, and to
2834 store it locally under the name `refs/heads/my-todo-work`.
2835
2836 You can also fetch branches from other repositories; so
2837
2838 -------------------------------------------------
2839 $ git fetch git://example.com/proj.git master:example-master
2840 -------------------------------------------------
2841
2842 will create a new branch named `example-master` and store in it the
2843 branch named `master` from the repository at the given URL. If you
2844 already have a branch named example-master, it will attempt to
2845 <<fast-forwards,fast-forward>> to the commit given by example.com's
2846 master branch. In more detail:
2847
2848 [[fetch-fast-forwards]]
2849 git fetch and fast-forwards
2850 ---------------------------
2851
2852 In the previous example, when updating an existing branch, `git fetch`
2853 checks to make sure that the most recent commit on the remote
2854 branch is a descendant of the most recent commit on your copy of the
2855 branch before updating your copy of the branch to point at the new
2856 commit. Git calls this process a <<fast-forwards,fast-forward>>.
2857
2858 A fast-forward looks something like this:
2859
2860 ................................................
2861 o--o--o--o <-- old head of the branch
2862 \
2863 o--o--o <-- new head of the branch
2864 ................................................
2865
2866
2867 In some cases it is possible that the new head will *not* actually be
2868 a descendant of the old head. For example, the developer may have
2869 realized she made a serious mistake, and decided to backtrack,
2870 resulting in a situation like:
2871
2872 ................................................
2873 o--o--o--o--a--b <-- old head of the branch
2874 \
2875 o--o--o <-- new head of the branch
2876 ................................................
2877
2878 In this case, `git fetch` will fail, and print out a warning.
2879
2880 In that case, you can still force Git to update to the new head, as
2881 described in the following section. However, note that in the
2882 situation above this may mean losing the commits labeled `a` and `b`,
2883 unless you've already created a reference of your own pointing to
2884 them.
2885
2886 [[forcing-fetch]]
2887 Forcing git fetch to do non-fast-forward updates
2888 ------------------------------------------------
2889
2890 If git fetch fails because the new head of a branch is not a
2891 descendant of the old head, you may force the update with:
2892
2893 -------------------------------------------------
2894 $ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2895 -------------------------------------------------
2896
2897 Note the addition of the `+` sign. Alternatively, you can use the `-f`
2898 flag to force updates of all the fetched branches, as in:
2899
2900 -------------------------------------------------
2901 $ git fetch -f origin
2902 -------------------------------------------------
2903
2904 Be aware that commits that the old version of example/master pointed at
2905 may be lost, as we saw in the previous section.
2906
2907 [[remote-branch-configuration]]
2908 Configuring remote-tracking branches
2909 ------------------------------------
2910
2911 We saw above that `origin` is just a shortcut to refer to the
2912 repository that you originally cloned from. This information is
2913 stored in Git configuration variables, which you can see using
2914 linkgit:git-config[1]:
2915
2916 -------------------------------------------------
2917 $ git config -l
2918 core.repositoryformatversion=0
2919 core.filemode=true
2920 core.logallrefupdates=true
2921 remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2922 remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2923 branch.master.remote=origin
2924 branch.master.merge=refs/heads/master
2925 -------------------------------------------------
2926
2927 If there are other repositories that you also use frequently, you can
2928 create similar configuration options to save typing; for example,
2929
2930 -------------------------------------------------
2931 $ git remote add example git://example.com/proj.git
2932 -------------------------------------------------
2933
2934 adds the following to `.git/config`:
2935
2936 -------------------------------------------------
2937 [remote "example"]
2938 url = git://example.com/proj.git
2939 fetch = +refs/heads/*:refs/remotes/example/*
2940 -------------------------------------------------
2941
2942 Also note that the above configuration can be performed by directly
2943 editing the file `.git/config` instead of using linkgit:git-remote[1].
2944
2945 After configuring the remote, the following three commands will do the
2946 same thing:
2947
2948 -------------------------------------------------
2949 $ git fetch git://example.com/proj.git +refs/heads/*:refs/remotes/example/*
2950 $ git fetch example +refs/heads/*:refs/remotes/example/*
2951 $ git fetch example
2952 -------------------------------------------------
2953
2954 See linkgit:git-config[1] for more details on the configuration
2955 options mentioned above and linkgit:git-fetch[1] for more details on
2956 the refspec syntax.
2957
2958
2959 [[git-concepts]]
2960 Git concepts
2961 ============
2962
2963 Git is built on a small number of simple but powerful ideas. While it
2964 is possible to get things done without understanding them, you will find
2965 Git much more intuitive if you do.
2966
2967 We start with the most important, the <<def_object_database,object
2968 database>> and the <<def_index,index>>.
2969
2970 [[the-object-database]]
2971 The Object Database
2972 -------------------
2973
2974
2975 We already saw in <<understanding-commits>> that all commits are stored
2976 under a 40-digit "object name". In fact, all the information needed to
2977 represent the history of a project is stored in objects with such names.
2978 In each case the name is calculated by taking the SHA-1 hash of the
2979 contents of the object. The SHA-1 hash is a cryptographic hash function.
2980 What that means to us is that it is impossible to find two different
2981 objects with the same name. This has a number of advantages; among
2982 others:
2983
2984 - Git can quickly determine whether two objects are identical or not,
2985 just by comparing names.
2986 - Since object names are computed the same way in every repository, the
2987 same content stored in two repositories will always be stored under
2988 the same name.
2989 - Git can detect errors when it reads an object, by checking that the
2990 object's name is still the SHA-1 hash of its contents.
2991
2992 (See <<object-details>> for the details of the object formatting and
2993 SHA-1 calculation.)
2994
2995 There are four different types of objects: "blob", "tree", "commit", and
2996 "tag".
2997
2998 - A <<def_blob_object,"blob" object>> is used to store file data.
2999 - A <<def_tree_object,"tree" object>> ties one or more
3000 "blob" objects into a directory structure. In addition, a tree object
3001 can refer to other tree objects, thus creating a directory hierarchy.
3002 - A <<def_commit_object,"commit" object>> ties such directory hierarchies
3003 together into a <<def_DAG,directed acyclic graph>> of revisions--each
3004 commit contains the object name of exactly one tree designating the
3005 directory hierarchy at the time of the commit. In addition, a commit
3006 refers to "parent" commit objects that describe the history of how we
3007 arrived at that directory hierarchy.
3008 - A <<def_tag_object,"tag" object>> symbolically identifies and can be
3009 used to sign other objects. It contains the object name and type of
3010 another object, a symbolic name (of course!) and, optionally, a
3011 signature.
3012
3013 The object types in some more detail:
3014
3015 [[commit-object]]
3016 Commit Object
3017 ~~~~~~~~~~~~~
3018
3019 The "commit" object links a physical state of a tree with a description
3020 of how we got there and why. Use the `--pretty=raw` option to
3021 linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite
3022 commit:
3023
3024 ------------------------------------------------
3025 $ git show -s --pretty=raw 2be7fcb476
3026 commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
3027 tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
3028 parent 257a84d9d02e90447b149af58b271c19405edb6a
3029 author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
3030 committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
3031
3032 Fix misspelling of 'suppress' in docs
3033
3034 Signed-off-by: Junio C Hamano <gitster@pobox.com>
3035 ------------------------------------------------
3036
3037 As you can see, a commit is defined by:
3038
3039 - a tree: The SHA-1 name of a tree object (as defined below), representing
3040 the contents of a directory at a certain point in time.
3041 - parent(s): The SHA-1 name(s) of some number of commits which represent the
3042 immediately previous step(s) in the history of the project. The
3043 example above has one parent; merge commits may have more than
3044 one. A commit with no parents is called a "root" commit, and
3045 represents the initial revision of a project. Each project must have
3046 at least one root. A project can also have multiple roots, though
3047 that isn't common (or necessarily a good idea).
3048 - an author: The name of the person responsible for this change, together
3049 with its date.
3050 - a committer: The name of the person who actually created the commit,
3051 with the date it was done. This may be different from the author, for
3052 example, if the author was someone who wrote a patch and emailed it
3053 to the person who used it to create the commit.
3054 - a comment describing this commit.
3055
3056 Note that a commit does not itself contain any information about what
3057 actually changed; all changes are calculated by comparing the contents
3058 of the tree referred to by this commit with the trees associated with
3059 its parents. In particular, Git does not attempt to record file renames
3060 explicitly, though it can identify cases where the existence of the same
3061 file data at changing paths suggests a rename. (See, for example, the
3062 `-M` option to linkgit:git-diff[1]).
3063
3064 A commit is usually created by linkgit:git-commit[1], which creates a
3065 commit whose parent is normally the current HEAD, and whose tree is
3066 taken from the content currently stored in the index.
3067
3068 [[tree-object]]
3069 Tree Object
3070 ~~~~~~~~~~~
3071
3072 The ever-versatile linkgit:git-show[1] command can also be used to
3073 examine tree objects, but linkgit:git-ls-tree[1] will give you more
3074 details:
3075
3076 ------------------------------------------------
3077 $ git ls-tree fb3a8bdd0ce
3078 100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
3079 100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
3080 100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
3081 040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
3082 100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
3083 100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
3084 100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
3085 100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
3086 ...
3087 ------------------------------------------------
3088
3089 As you can see, a tree object contains a list of entries, each with a
3090 mode, object type, SHA-1 name, and name, sorted by name. It represents
3091 the contents of a single directory tree.
3092
3093 The object type may be a blob, representing the contents of a file, or
3094 another tree, representing the contents of a subdirectory. Since trees
3095 and blobs, like all other objects, are named by the SHA-1 hash of their
3096 contents, two trees have the same SHA-1 name if and only if their
3097 contents (including, recursively, the contents of all subdirectories)
3098 are identical. This allows Git to quickly determine the differences
3099 between two related tree objects, since it can ignore any entries with
3100 identical object names.
3101
3102 (Note: in the presence of submodules, trees may also have commits as
3103 entries. See <<submodules>> for documentation.)
3104
3105 Note that the files all have mode 644 or 755: Git actually only pays
3106 attention to the executable bit.
3107
3108 [[blob-object]]
3109 Blob Object
3110 ~~~~~~~~~~~
3111
3112 You can use linkgit:git-show[1] to examine the contents of a blob; take,
3113 for example, the blob in the entry for `COPYING` from the tree above:
3114
3115 ------------------------------------------------
3116 $ git show 6ff87c4664
3117
3118 Note that the only valid version of the GPL as far as this project
3119 is concerned is _this_ particular version of the license (ie v2, not
3120 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
3121 ...
3122 ------------------------------------------------
3123
3124 A "blob" object is nothing but a binary blob of data. It doesn't refer
3125 to anything else or have attributes of any kind.
3126
3127 Since the blob is entirely defined by its data, if two files in a
3128 directory tree (or in multiple different versions of the repository)
3129 have the same contents, they will share the same blob object. The object
3130 is totally independent of its location in the directory tree, and
3131 renaming a file does not change the object that file is associated with.
3132
3133 Note that any tree or blob object can be examined using
3134 linkgit:git-show[1] with the <revision>:<path> syntax. This can
3135 sometimes be useful for browsing the contents of a tree that is not
3136 currently checked out.
3137
3138 [[trust]]
3139 Trust
3140 ~~~~~
3141
3142 If you receive the SHA-1 name of a blob from one source, and its contents
3143 from another (possibly untrusted) source, you can still trust that those
3144 contents are correct as long as the SHA-1 name agrees. This is because
3145 the SHA-1 is designed so that it is infeasible to find different contents
3146 that produce the same hash.
3147
3148 Similarly, you need only trust the SHA-1 name of a top-level tree object
3149 to trust the contents of the entire directory that it refers to, and if
3150 you receive the SHA-1 name of a commit from a trusted source, then you
3151 can easily verify the entire history of commits reachable through
3152 parents of that commit, and all of those contents of the trees referred
3153 to by those commits.
3154
3155 So to introduce some real trust in the system, the only thing you need
3156 to do is to digitally sign just 'one' special note, which includes the
3157 name of a top-level commit. Your digital signature shows others
3158 that you trust that commit, and the immutability of the history of
3159 commits tells others that they can trust the whole history.
3160
3161 In other words, you can easily validate a whole archive by just
3162 sending out a single email that tells the people the name (SHA-1 hash)
3163 of the top commit, and digitally sign that email using something
3164 like GPG/PGP.
3165
3166 To assist in this, Git also provides the tag object...
3167
3168 [[tag-object]]
3169 Tag Object
3170 ~~~~~~~~~~
3171
3172 A tag object contains an object, object type, tag name, the name of the
3173 person ("tagger") who created the tag, and a message, which may contain
3174 a signature, as can be seen using linkgit:git-cat-file[1]:
3175
3176 ------------------------------------------------
3177 $ git cat-file tag v1.5.0
3178 object 437b1b20df4b356c9342dac8d38849f24ef44f27
3179 type commit
3180 tag v1.5.0
3181 tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
3182
3183 GIT 1.5.0
3184 -----BEGIN PGP SIGNATURE-----
3185 Version: GnuPG v1.4.6 (GNU/Linux)
3186
3187 iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
3188 nLE/L9aUXdWeTFPron96DLA=
3189 =2E+0
3190 -----END PGP SIGNATURE-----
3191 ------------------------------------------------
3192
3193 See the linkgit:git-tag[1] command to learn how to create and verify tag
3194 objects. (Note that linkgit:git-tag[1] can also be used to create
3195 "lightweight tags", which are not tag objects at all, but just simple
3196 references whose names begin with `refs/tags/`).
3197
3198 [[pack-files]]
3199 How Git stores objects efficiently: pack files
3200 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3201
3202 Newly created objects are initially created in a file named after the
3203 object's SHA-1 hash (stored in `.git/objects`).
3204
3205 Unfortunately this system becomes inefficient once a project has a
3206 lot of objects. Try this on an old project:
3207
3208 ------------------------------------------------
3209 $ git count-objects
3210 6930 objects, 47620 kilobytes
3211 ------------------------------------------------
3212
3213 The first number is the number of objects which are kept in
3214 individual files. The second is the amount of space taken up by
3215 those "loose" objects.
3216
3217 You can save space and make Git faster by moving these loose objects in
3218 to a "pack file", which stores a group of objects in an efficient
3219 compressed format; the details of how pack files are formatted can be
3220 found in link:technical/pack-format.html[pack format].
3221
3222 To put the loose objects into a pack, just run git repack:
3223
3224 ------------------------------------------------
3225 $ git repack
3226 Counting objects: 6020, done.
3227 Delta compression using up to 4 threads.
3228 Compressing objects: 100% (6020/6020), done.
3229 Writing objects: 100% (6020/6020), done.
3230 Total 6020 (delta 4070), reused 0 (delta 0)
3231 ------------------------------------------------
3232
3233 This creates a single "pack file" in .git/objects/pack/
3234 containing all currently unpacked objects. You can then run
3235
3236 ------------------------------------------------
3237 $ git prune
3238 ------------------------------------------------
3239
3240 to remove any of the "loose" objects that are now contained in the
3241 pack. This will also remove any unreferenced objects (which may be
3242 created when, for example, you use `git reset` to remove a commit).
3243 You can verify that the loose objects are gone by looking at the
3244 `.git/objects` directory or by running
3245
3246 ------------------------------------------------
3247 $ git count-objects
3248 0 objects, 0 kilobytes
3249 ------------------------------------------------
3250
3251 Although the object files are gone, any commands that refer to those
3252 objects will work exactly as they did before.
3253
3254 The linkgit:git-gc[1] command performs packing, pruning, and more for
3255 you, so is normally the only high-level command you need.
3256
3257 [[dangling-objects]]
3258 Dangling objects
3259 ~~~~~~~~~~~~~~~~
3260
3261 The linkgit:git-fsck[1] command will sometimes complain about dangling
3262 objects. They are not a problem.
3263
3264 The most common cause of dangling objects is that you've rebased a
3265 branch, or you have pulled from somebody else who rebased a branch--see
3266 <<cleaning-up-history>>. In that case, the old head of the original
3267 branch still exists, as does everything it pointed to. The branch
3268 pointer itself just doesn't, since you replaced it with another one.
3269
3270 There are also other situations that cause dangling objects. For
3271 example, a "dangling blob" may arise because you did a `git add` of a
3272 file, but then, before you actually committed it and made it part of the
3273 bigger picture, you changed something else in that file and committed
3274 that *updated* thing--the old state that you added originally ends up
3275 not being pointed to by any commit or tree, so it's now a dangling blob
3276 object.
3277
3278 Similarly, when the "recursive" merge strategy runs, and finds that
3279 there are criss-cross merges and thus more than one merge base (which is
3280 fairly unusual, but it does happen), it will generate one temporary
3281 midway tree (or possibly even more, if you had lots of criss-crossing
3282 merges and more than two merge bases) as a temporary internal merge
3283 base, and again, those are real objects, but the end result will not end
3284 up pointing to them, so they end up "dangling" in your repository.
3285
3286 Generally, dangling objects aren't anything to worry about. They can
3287 even be very useful: if you screw something up, the dangling objects can
3288 be how you recover your old tree (say, you did a rebase, and realized
3289 that you really didn't want to--you can look at what dangling objects
3290 you have, and decide to reset your head to some old dangling state).
3291
3292 For commits, you can just use:
3293
3294 ------------------------------------------------
3295 $ gitk <dangling-commit-sha-goes-here> --not --all
3296 ------------------------------------------------
3297
3298 This asks for all the history reachable from the given commit but not
3299 from any branch, tag, or other reference. If you decide it's something
3300 you want, you can always create a new reference to it, e.g.,
3301
3302 ------------------------------------------------
3303 $ git branch recovered-branch <dangling-commit-sha-goes-here>
3304 ------------------------------------------------
3305
3306 For blobs and trees, you can't do the same, but you can still examine
3307 them. You can just do
3308
3309 ------------------------------------------------
3310 $ git show <dangling-blob/tree-sha-goes-here>
3311 ------------------------------------------------
3312
3313 to show what the contents of the blob were (or, for a tree, basically
3314 what the `ls` for that directory was), and that may give you some idea
3315 of what the operation was that left that dangling object.
3316
3317 Usually, dangling blobs and trees aren't very interesting. They're
3318 almost always the result of either being a half-way mergebase (the blob
3319 will often even have the conflict markers from a merge in it, if you
3320 have had conflicting merges that you fixed up by hand), or simply
3321 because you interrupted a `git fetch` with ^C or something like that,
3322 leaving _some_ of the new objects in the object database, but just
3323 dangling and useless.
3324
3325 Anyway, once you are sure that you're not interested in any dangling
3326 state, you can just prune all unreachable objects:
3327
3328 ------------------------------------------------
3329 $ git prune
3330 ------------------------------------------------
3331
3332 and they'll be gone. (You should only run `git prune` on a quiescent
3333 repository--it's kind of like doing a filesystem fsck recovery: you
3334 don't want to do that while the filesystem is mounted.
3335 `git prune` is designed not to cause any harm in such cases of concurrent
3336 accesses to a repository but you might receive confusing or scary messages.)
3337
3338 [[recovering-from-repository-corruption]]
3339 Recovering from repository corruption
3340 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3341
3342 By design, Git treats data trusted to it with caution. However, even in
3343 the absence of bugs in Git itself, it is still possible that hardware or
3344 operating system errors could corrupt data.
3345
3346 The first defense against such problems is backups. You can back up a
3347 Git directory using clone, or just using cp, tar, or any other backup
3348 mechanism.
3349
3350 As a last resort, you can search for the corrupted objects and attempt
3351 to replace them by hand. Back up your repository before attempting this
3352 in case you corrupt things even more in the process.
3353
3354 We'll assume that the problem is a single missing or corrupted blob,
3355 which is sometimes a solvable problem. (Recovering missing trees and
3356 especially commits is *much* harder).
3357
3358 Before starting, verify that there is corruption, and figure out where
3359 it is with linkgit:git-fsck[1]; this may be time-consuming.
3360
3361 Assume the output looks like this:
3362
3363 ------------------------------------------------
3364 $ git fsck --full --no-dangling
3365 broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
3366 to blob 4b9458b3786228369c63936db65827de3cc06200
3367 missing blob 4b9458b3786228369c63936db65827de3cc06200
3368 ------------------------------------------------
3369
3370 Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6
3371 points to it. If you could find just one copy of that missing blob
3372 object, possibly in some other repository, you could move it into
3373 `.git/objects/4b/9458b3...` and be done. Suppose you can't. You can
3374 still examine the tree that pointed to it with linkgit:git-ls-tree[1],
3375 which might output something like:
3376
3377 ------------------------------------------------
3378 $ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
3379 100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore
3380 100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap
3381 100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING
3382 ...
3383 100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile
3384 ...
3385 ------------------------------------------------
3386
3387 So now you know that the missing blob was the data for a file named
3388 `myfile`. And chances are you can also identify the directory--let's
3389 say it's in `somedirectory`. If you're lucky the missing copy might be
3390 the same as the copy you have checked out in your working tree at
3391 `somedirectory/myfile`; you can test whether that's right with
3392 linkgit:git-hash-object[1]:
3393
3394 ------------------------------------------------
3395 $ git hash-object -w somedirectory/myfile
3396 ------------------------------------------------
3397
3398 which will create and store a blob object with the contents of
3399 somedirectory/myfile, and output the SHA-1 of that object. if you're
3400 extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in
3401 which case you've guessed right, and the corruption is fixed!
3402
3403 Otherwise, you need more information. How do you tell which version of
3404 the file has been lost?
3405
3406 The easiest way to do this is with:
3407
3408 ------------------------------------------------
3409 $ git log --raw --all --full-history -- somedirectory/myfile
3410 ------------------------------------------------
3411
3412 Because you're asking for raw output, you'll now get something like
3413
3414 ------------------------------------------------
3415 commit abc
3416 Author:
3417 Date:
3418 ...
3419 :100644 100644 4b9458b... newsha... M somedirectory/myfile
3420
3421
3422 commit xyz
3423 Author:
3424 Date:
3425
3426 ...
3427 :100644 100644 oldsha... 4b9458b... M somedirectory/myfile
3428 ------------------------------------------------
3429
3430 This tells you that the immediately following version of the file was
3431 "newsha", and that the immediately preceding version was "oldsha".
3432 You also know the commit messages that went with the change from oldsha
3433 to 4b9458b and with the change from 4b9458b to newsha.
3434
3435 If you've been committing small enough changes, you may now have a good
3436 shot at reconstructing the contents of the in-between state 4b9458b.
3437
3438 If you can do that, you can now recreate the missing object with
3439
3440 ------------------------------------------------
3441 $ git hash-object -w <recreated-file>
3442 ------------------------------------------------
3443
3444 and your repository is good again!
3445
3446 (Btw, you could have ignored the `fsck`, and started with doing a
3447
3448 ------------------------------------------------
3449 $ git log --raw --all
3450 ------------------------------------------------
3451
3452 and just looked for the sha of the missing object (4b9458b..) in that
3453 whole thing. It's up to you--Git does *have* a lot of information, it is
3454 just missing one particular blob version.
3455
3456 [[the-index]]
3457 The index
3458 ---------
3459
3460 The index is a binary file (generally kept in `.git/index`) containing a
3461 sorted list of path names, each with permissions and the SHA-1 of a blob
3462 object; linkgit:git-ls-files[1] can show you the contents of the index:
3463
3464 -------------------------------------------------
3465 $ git ls-files --stage
3466 100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore
3467 100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap
3468 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING
3469 100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore
3470 100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile
3471 ...
3472 100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h
3473 100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c
3474 100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h
3475 -------------------------------------------------
3476
3477 Note that in older documentation you may see the index called the
3478 "current directory cache" or just the "cache". It has three important
3479 properties:
3480
3481 1. The index contains all the information necessary to generate a single
3482 (uniquely determined) tree object.
3483 +
3484 For example, running linkgit:git-commit[1] generates this tree object
3485 from the index, stores it in the object database, and uses it as the
3486 tree object associated with the new commit.
3487
3488 2. The index enables fast comparisons between the tree object it defines
3489 and the working tree.
3490 +
3491 It does this by storing some additional data for each entry (such as
3492 the last modified time). This data is not displayed above, and is not
3493 stored in the created tree object, but it can be used to determine
3494 quickly which files in the working directory differ from what was
3495 stored in the index, and thus save Git from having to read all of the
3496 data from such files to look for changes.
3497
3498 3. It can efficiently represent information about merge conflicts
3499 between different tree objects, allowing each pathname to be
3500 associated with sufficient information about the trees involved that
3501 you can create a three-way merge between them.
3502 +
3503 We saw in <<conflict-resolution>> that during a merge the index can
3504 store multiple versions of a single file (called "stages"). The third
3505 column in the linkgit:git-ls-files[1] output above is the stage
3506 number, and will take on values other than 0 for files with merge
3507 conflicts.
3508
3509 The index is thus a sort of temporary staging area, which is filled with
3510 a tree which you are in the process of working on.
3511
3512 If you blow the index away entirely, you generally haven't lost any
3513 information as long as you have the name of the tree that it described.
3514
3515 [[submodules]]
3516 Submodules
3517 ==========
3518
3519 Large projects are often composed of smaller, self-contained modules. For
3520 example, an embedded Linux distribution's source tree would include every
3521 piece of software in the distribution with some local modifications; a movie
3522 player might need to build against a specific, known-working version of a
3523 decompression library; several independent programs might all share the same
3524 build scripts.
3525
3526 With centralized revision control systems this is often accomplished by
3527 including every module in one single repository. Developers can check out
3528 all modules or only the modules they need to work with. They can even modify
3529 files across several modules in a single commit while moving things around
3530 or updating APIs and translations.
3531
3532 Git does not allow partial checkouts, so duplicating this approach in Git
3533 would force developers to keep a local copy of modules they are not
3534 interested in touching. Commits in an enormous checkout would be slower
3535 than you'd expect as Git would have to scan every directory for changes.
3536 If modules have a lot of local history, clones would take forever.
3537
3538 On the plus side, distributed revision control systems can much better
3539 integrate with external sources. In a centralized model, a single arbitrary
3540 snapshot of the external project is exported from its own revision control
3541 and then imported into the local revision control on a vendor branch. All
3542 the history is hidden. With distributed revision control you can clone the
3543 entire external history and much more easily follow development and re-merge
3544 local changes.
3545
3546 Git's submodule support allows a repository to contain, as a subdirectory, a
3547 checkout of an external project. Submodules maintain their own identity;
3548 the submodule support just stores the submodule repository location and
3549 commit ID, so other developers who clone the containing project
3550 ("superproject") can easily clone all the submodules at the same revision.
3551 Partial checkouts of the superproject are possible: you can tell Git to
3552 clone none, some or all of the submodules.
3553
3554 The linkgit:git-submodule[1] command is available since Git 1.5.3. Users
3555 with Git 1.5.2 can look up the submodule commits in the repository and
3556 manually check them out; earlier versions won't recognize the submodules at
3557 all.
3558
3559 To see how submodule support works, create four example
3560 repositories that can be used later as a submodule:
3561
3562 -------------------------------------------------
3563 $ mkdir ~/git
3564 $ cd ~/git
3565 $ for i in a b c d
3566 do
3567 mkdir $i
3568 cd $i
3569 git init
3570 echo "module $i" > $i.txt
3571 git add $i.txt
3572 git commit -m "Initial commit, submodule $i"
3573 cd ..
3574 done
3575 -------------------------------------------------
3576
3577 Now create the superproject and add all the submodules:
3578
3579 -------------------------------------------------
3580 $ mkdir super
3581 $ cd super
3582 $ git init
3583 $ for i in a b c d
3584 do
3585 git submodule add ~/git/$i $i
3586 done
3587 -------------------------------------------------
3588
3589 NOTE: Do not use local URLs here if you plan to publish your superproject!
3590
3591 See what files `git submodule` created:
3592
3593 -------------------------------------------------
3594 $ ls -a
3595 . .. .git .gitmodules a b c d
3596 -------------------------------------------------
3597
3598 The `git submodule add <repo> <path>` command does a couple of things:
3599
3600 - It clones the submodule from `<repo>` to the given `<path>` under the
3601 current directory and by default checks out the master branch.
3602 - It adds the submodule's clone path to the linkgit:gitmodules[5] file and
3603 adds this file to the index, ready to be committed.
3604 - It adds the submodule's current commit ID to the index, ready to be
3605 committed.
3606
3607 Commit the superproject:
3608
3609 -------------------------------------------------
3610 $ git commit -m "Add submodules a, b, c and d."
3611 -------------------------------------------------
3612
3613 Now clone the superproject:
3614
3615 -------------------------------------------------
3616 $ cd ..
3617 $ git clone super cloned
3618 $ cd cloned
3619 -------------------------------------------------
3620
3621 The submodule directories are there, but they're empty:
3622
3623 -------------------------------------------------
3624 $ ls -a a
3625 . ..
3626 $ git submodule status
3627 -d266b9873ad50488163457f025db7cdd9683d88b a
3628 -e81d457da15309b4fef4249aba9b50187999670d b
3629 -c1536a972b9affea0f16e0680ba87332dc059146 c
3630 -d96249ff5d57de5de093e6baff9e0aafa5276a74 d
3631 -------------------------------------------------
3632
3633 NOTE: The commit object names shown above would be different for you, but they
3634 should match the HEAD commit object names of your repositories. You can check
3635 it by running `git ls-remote ../a`.
3636
3637 Pulling down the submodules is a two-step process. First run `git submodule
3638 init` to add the submodule repository URLs to `.git/config`:
3639
3640 -------------------------------------------------
3641 $ git submodule init
3642 -------------------------------------------------
3643
3644 Now use `git submodule update` to clone the repositories and check out the
3645 commits specified in the superproject:
3646
3647 -------------------------------------------------
3648 $ git submodule update
3649 $ cd a
3650 $ ls -a
3651 . .. .git a.txt
3652 -------------------------------------------------
3653
3654 One major difference between `git submodule update` and `git submodule add` is
3655 that `git submodule update` checks out a specific commit, rather than the tip
3656 of a branch. It's like checking out a tag: the head is detached, so you're not
3657 working on a branch.
3658
3659 -------------------------------------------------
3660 $ git branch
3661 * (detached from d266b98)
3662 master
3663 -------------------------------------------------
3664
3665 If you want to make a change within a submodule and you have a detached head,
3666 then you should create or checkout a branch, make your changes, publish the
3667 change within the submodule, and then update the superproject to reference the
3668 new commit:
3669
3670 -------------------------------------------------
3671 $ git checkout master
3672 -------------------------------------------------
3673
3674 or
3675
3676 -------------------------------------------------
3677 $ git checkout -b fix-up
3678 -------------------------------------------------
3679
3680 then
3681
3682 -------------------------------------------------
3683 $ echo "adding a line again" >> a.txt
3684 $ git commit -a -m "Updated the submodule from within the superproject."
3685 $ git push
3686 $ cd ..
3687 $ git diff
3688 diff --git a/a b/a
3689 index d266b98..261dfac 160000
3690 --- a/a
3691 +++ b/a
3692 @@ -1 +1 @@
3693 -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b
3694 +Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24
3695 $ git add a
3696 $ git commit -m "Updated submodule a."
3697 $ git push
3698 -------------------------------------------------
3699
3700 You have to run `git submodule update` after `git pull` if you want to update
3701 submodules, too.
3702
3703 Pitfalls with submodules
3704 ------------------------
3705
3706 Always publish the submodule change before publishing the change to the
3707 superproject that references it. If you forget to publish the submodule change,
3708 others won't be able to clone the repository:
3709
3710 -------------------------------------------------
3711 $ cd ~/git/super/a
3712 $ echo i added another line to this file >> a.txt
3713 $ git commit -a -m "doing it wrong this time"
3714 $ cd ..
3715 $ git add a
3716 $ git commit -m "Updated submodule a again."
3717 $ git push
3718 $ cd ~/git/cloned
3719 $ git pull
3720 $ git submodule update
3721 error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.
3722 Did you forget to 'git add'?
3723 Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'
3724 -------------------------------------------------
3725
3726 In older Git versions it could be easily forgotten to commit new or modified
3727 files in a submodule, which silently leads to similar problems as not pushing
3728 the submodule changes. Starting with Git 1.7.0 both `git status` and `git diff`
3729 in the superproject show submodules as modified when they contain new or
3730 modified files to protect against accidentally committing such a state. `git
3731 diff` will also add a `-dirty` to the work tree side when generating patch
3732 output or used with the `--submodule` option:
3733
3734 -------------------------------------------------
3735 $ git diff
3736 diff --git a/sub b/sub
3737 --- a/sub
3738 +++ b/sub
3739 @@ -1 +1 @@
3740 -Subproject commit 3f356705649b5d566d97ff843cf193359229a453
3741 +Subproject commit 3f356705649b5d566d97ff843cf193359229a453-dirty
3742 $ git diff --submodule
3743 Submodule sub 3f35670..3f35670-dirty:
3744 -------------------------------------------------
3745
3746 You also should not rewind branches in a submodule beyond commits that were
3747 ever recorded in any superproject.
3748
3749 It's not safe to run `git submodule update` if you've made and committed
3750 changes within a submodule without checking out a branch first. They will be
3751 silently overwritten:
3752
3753 -------------------------------------------------
3754 $ cat a.txt
3755 module a
3756 $ echo line added from private2 >> a.txt
3757 $ git commit -a -m "line added inside private2"
3758 $ cd ..
3759 $ git submodule update
3760 Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'
3761 $ cd a
3762 $ cat a.txt
3763 module a
3764 -------------------------------------------------
3765
3766 NOTE: The changes are still visible in the submodule's reflog.
3767
3768 If you have uncommitted changes in your submodule working tree, `git
3769 submodule update` will not overwrite them. Instead, you get the usual
3770 warning about not being able switch from a dirty branch.
3771
3772 [[low-level-operations]]
3773 Low-level Git operations
3774 ========================
3775
3776 Many of the higher-level commands were originally implemented as shell
3777 scripts using a smaller core of low-level Git commands. These can still
3778 be useful when doing unusual things with Git, or just as a way to
3779 understand its inner workings.
3780
3781 [[object-manipulation]]
3782 Object access and manipulation
3783 ------------------------------
3784
3785 The linkgit:git-cat-file[1] command can show the contents of any object,
3786 though the higher-level linkgit:git-show[1] is usually more useful.
3787
3788 The linkgit:git-commit-tree[1] command allows constructing commits with
3789 arbitrary parents and trees.
3790
3791 A tree can be created with linkgit:git-write-tree[1] and its data can be
3792 accessed by linkgit:git-ls-tree[1]. Two trees can be compared with
3793 linkgit:git-diff-tree[1].
3794
3795 A tag is created with linkgit:git-mktag[1], and the signature can be
3796 verified by linkgit:git-verify-tag[1], though it is normally simpler to
3797 use linkgit:git-tag[1] for both.
3798
3799 [[the-workflow]]
3800 The Workflow
3801 ------------
3802
3803 High-level operations such as linkgit:git-commit[1],
3804 linkgit:git-checkout[1] and linkgit:git-reset[1] work by moving data
3805 between the working tree, the index, and the object database. Git
3806 provides low-level operations which perform each of these steps
3807 individually.
3808
3809 Generally, all Git operations work on the index file. Some operations
3810 work *purely* on the index file (showing the current state of the
3811 index), but most operations move data between the index file and either
3812 the database or the working directory. Thus there are four main
3813 combinations:
3814
3815 [[working-directory-to-index]]
3816 working directory -> index
3817 ~~~~~~~~~~~~~~~~~~~~~~~~~~
3818
3819 The linkgit:git-update-index[1] command updates the index with
3820 information from the working directory. You generally update the
3821 index information by just specifying the filename you want to update,
3822 like so:
3823
3824 -------------------------------------------------
3825 $ git update-index filename
3826 -------------------------------------------------
3827
3828 but to avoid common mistakes with filename globbing etc., the command
3829 will not normally add totally new entries or remove old entries,
3830 i.e. it will normally just update existing cache entries.
3831
3832 To tell Git that yes, you really do realize that certain files no
3833 longer exist, or that new files should be added, you
3834 should use the `--remove` and `--add` flags respectively.
3835
3836 NOTE! A `--remove` flag does 'not' mean that subsequent filenames will
3837 necessarily be removed: if the files still exist in your directory
3838 structure, the index will be updated with their new status, not
3839 removed. The only thing `--remove` means is that update-index will be
3840 considering a removed file to be a valid thing, and if the file really
3841 does not exist any more, it will update the index accordingly.
3842
3843 As a special case, you can also do `git update-index --refresh`, which
3844 will refresh the "stat" information of each index to match the current
3845 stat information. It will 'not' update the object status itself, and
3846 it will only update the fields that are used to quickly test whether
3847 an object still matches its old backing store object.
3848
3849 The previously introduced linkgit:git-add[1] is just a wrapper for
3850 linkgit:git-update-index[1].
3851
3852 [[index-to-object-database]]
3853 index -> object database
3854 ~~~~~~~~~~~~~~~~~~~~~~~~
3855
3856 You write your current index file to a "tree" object with the program
3857
3858 -------------------------------------------------
3859 $ git write-tree
3860 -------------------------------------------------
3861
3862 that doesn't come with any options--it will just write out the
3863 current index into the set of tree objects that describe that state,
3864 and it will return the name of the resulting top-level tree. You can
3865 use that tree to re-generate the index at any time by going in the
3866 other direction:
3867
3868 [[object-database-to-index]]
3869 object database -> index
3870 ~~~~~~~~~~~~~~~~~~~~~~~~
3871
3872 You read a "tree" file from the object database, and use that to
3873 populate (and overwrite--don't do this if your index contains any
3874 unsaved state that you might want to restore later!) your current
3875 index. Normal operation is just
3876
3877 -------------------------------------------------
3878 $ git read-tree <SHA-1 of tree>
3879 -------------------------------------------------
3880
3881 and your index file will now be equivalent to the tree that you saved
3882 earlier. However, that is only your 'index' file: your working
3883 directory contents have not been modified.
3884
3885 [[index-to-working-directory]]
3886 index -> working directory
3887 ~~~~~~~~~~~~~~~~~~~~~~~~~~
3888
3889 You update your working directory from the index by "checking out"
3890 files. This is not a very common operation, since normally you'd just
3891 keep your files updated, and rather than write to your working
3892 directory, you'd tell the index files about the changes in your
3893 working directory (i.e. `git update-index`).
3894
3895 However, if you decide to jump to a new version, or check out somebody
3896 else's version, or just restore a previous tree, you'd populate your
3897 index file with read-tree, and then you need to check out the result
3898 with
3899
3900 -------------------------------------------------
3901 $ git checkout-index filename
3902 -------------------------------------------------
3903
3904 or, if you want to check out all of the index, use `-a`.
3905
3906 NOTE! `git checkout-index` normally refuses to overwrite old files, so
3907 if you have an old version of the tree already checked out, you will
3908 need to use the `-f` flag ('before' the `-a` flag or the filename) to
3909 'force' the checkout.
3910
3911
3912 Finally, there are a few odds and ends which are not purely moving
3913 from one representation to the other:
3914
3915 [[tying-it-all-together]]
3916 Tying it all together
3917 ~~~~~~~~~~~~~~~~~~~~~
3918
3919 To commit a tree you have instantiated with `git write-tree`, you'd
3920 create a "commit" object that refers to that tree and the history
3921 behind it--most notably the "parent" commits that preceded it in
3922 history.
3923
3924 Normally a "commit" has one parent: the previous state of the tree
3925 before a certain change was made. However, sometimes it can have two
3926 or more parent commits, in which case we call it a "merge", due to the
3927 fact that such a commit brings together ("merges") two or more
3928 previous states represented by other commits.
3929
3930 In other words, while a "tree" represents a particular directory state
3931 of a working directory, a "commit" represents that state in time,
3932 and explains how we got there.
3933
3934 You create a commit object by giving it the tree that describes the
3935 state at the time of the commit, and a list of parents:
3936
3937 -------------------------------------------------
3938 $ git commit-tree <tree> -p <parent> [(-p <parent2>)...]
3939 -------------------------------------------------
3940
3941 and then giving the reason for the commit on stdin (either through
3942 redirection from a pipe or file, or by just typing it at the tty).
3943
3944 `git commit-tree` will return the name of the object that represents
3945 that commit, and you should save it away for later use. Normally,
3946 you'd commit a new `HEAD` state, and while Git doesn't care where you
3947 save the note about that state, in practice we tend to just write the
3948 result to the file pointed at by `.git/HEAD`, so that we can always see
3949 what the last committed state was.
3950
3951 Here is a picture that illustrates how various pieces fit together:
3952
3953 ------------
3954
3955 commit-tree
3956 commit obj
3957 +----+
3958 | |
3959 | |
3960 V V
3961 +-----------+
3962 | Object DB |
3963 | Backing |
3964 | Store |
3965 +-----------+
3966 ^
3967 write-tree | |
3968 tree obj | |
3969 | | read-tree
3970 | | tree obj
3971 V
3972 +-----------+
3973 | Index |
3974 | "cache" |
3975 +-----------+
3976 update-index ^
3977 blob obj | |
3978 | |
3979 checkout-index -u | | checkout-index
3980 stat | | blob obj
3981 V
3982 +-----------+
3983 | Working |
3984 | Directory |
3985 +-----------+
3986
3987 ------------
3988
3989
3990 [[examining-the-data]]
3991 Examining the data
3992 ------------------
3993
3994 You can examine the data represented in the object database and the
3995 index with various helper tools. For every object, you can use
3996 linkgit:git-cat-file[1] to examine details about the
3997 object:
3998
3999 -------------------------------------------------
4000 $ git cat-file -t <objectname>
4001 -------------------------------------------------
4002
4003 shows the type of the object, and once you have the type (which is
4004 usually implicit in where you find the object), you can use
4005
4006 -------------------------------------------------
4007 $ git cat-file blob|tree|commit|tag <objectname>
4008 -------------------------------------------------
4009
4010 to show its contents. NOTE! Trees have binary content, and as a result
4011 there is a special helper for showing that content, called
4012 `git ls-tree`, which turns the binary content into a more easily
4013 readable form.
4014
4015 It's especially instructive to look at "commit" objects, since those
4016 tend to be small and fairly self-explanatory. In particular, if you
4017 follow the convention of having the top commit name in `.git/HEAD`,
4018 you can do
4019
4020 -------------------------------------------------
4021 $ git cat-file commit HEAD
4022 -------------------------------------------------
4023
4024 to see what the top commit was.
4025
4026 [[merging-multiple-trees]]
4027 Merging multiple trees
4028 ----------------------
4029
4030 Git can help you perform a three-way merge, which can in turn be
4031 used for a many-way merge by repeating the merge procedure several
4032 times. The usual situation is that you only do one three-way merge
4033 (reconciling two lines of history) and commit the result, but if
4034 you like to, you can merge several branches in one go.
4035
4036 To perform a three-way merge, you start with the two commits you
4037 want to merge, find their closest common parent (a third commit),
4038 and compare the trees corresponding to these three commits.
4039
4040 To get the "base" for the merge, look up the common parent of two
4041 commits:
4042
4043 -------------------------------------------------
4044 $ git merge-base <commit1> <commit2>
4045 -------------------------------------------------
4046
4047 This prints the name of a commit they are both based on. You should
4048 now look up the tree objects of those commits, which you can easily
4049 do with
4050
4051 -------------------------------------------------
4052 $ git cat-file commit <commitname> | head -1
4053 -------------------------------------------------
4054
4055 since the tree object information is always the first line in a commit
4056 object.
4057
4058 Once you know the three trees you are going to merge (the one "original"
4059 tree, aka the common tree, and the two "result" trees, aka the branches
4060 you want to merge), you do a "merge" read into the index. This will
4061 complain if it has to throw away your old index contents, so you should
4062 make sure that you've committed those--in fact you would normally
4063 always do a merge against your last commit (which should thus match what
4064 you have in your current index anyway).
4065
4066 To do the merge, do
4067
4068 -------------------------------------------------
4069 $ git read-tree -m -u <origtree> <yourtree> <targettree>
4070 -------------------------------------------------
4071
4072 which will do all trivial merge operations for you directly in the
4073 index file, and you can just write the result out with
4074 `git write-tree`.
4075
4076
4077 [[merging-multiple-trees-2]]
4078 Merging multiple trees, continued
4079 ---------------------------------
4080
4081 Sadly, many merges aren't trivial. If there are files that have
4082 been added, moved or removed, or if both branches have modified the
4083 same file, you will be left with an index tree that contains "merge
4084 entries" in it. Such an index tree can 'NOT' be written out to a tree
4085 object, and you will have to resolve any such merge clashes using
4086 other tools before you can write out the result.
4087
4088 You can examine such index state with `git ls-files --unmerged`
4089 command. An example:
4090
4091 ------------------------------------------------
4092 $ git read-tree -m $orig HEAD $target
4093 $ git ls-files --unmerged
4094 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c
4095 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c
4096 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c
4097 ------------------------------------------------
4098
4099 Each line of the `git ls-files --unmerged` output begins with
4100 the blob mode bits, blob SHA-1, 'stage number', and the
4101 filename. The 'stage number' is Git's way to say which tree it
4102 came from: stage 1 corresponds to the `$orig` tree, stage 2 to
4103 the `HEAD` tree, and stage 3 to the `$target` tree.
4104
4105 Earlier we said that trivial merges are done inside
4106 `git read-tree -m`. For example, if the file did not change
4107 from `$orig` to `HEAD` or `$target`, or if the file changed
4108 from `$orig` to `HEAD` and `$orig` to `$target` the same way,
4109 obviously the final outcome is what is in `HEAD`. What the
4110 above example shows is that file `hello.c` was changed from
4111 `$orig` to `HEAD` and `$orig` to `$target` in a different way.
4112 You could resolve this by running your favorite 3-way merge
4113 program, e.g. `diff3`, `merge`, or Git's own merge-file, on
4114 the blob objects from these three stages yourself, like this:
4115
4116 ------------------------------------------------
4117 $ git cat-file blob 263414f... >hello.c~1
4118 $ git cat-file blob 06fa6a2... >hello.c~2
4119 $ git cat-file blob cc44c73... >hello.c~3
4120 $ git merge-file hello.c~2 hello.c~1 hello.c~3
4121 ------------------------------------------------
4122
4123 This would leave the merge result in `hello.c~2` file, along
4124 with conflict markers if there are conflicts. After verifying
4125 the merge result makes sense, you can tell Git what the final
4126 merge result for this file is by:
4127
4128 -------------------------------------------------
4129 $ mv -f hello.c~2 hello.c
4130 $ git update-index hello.c
4131 -------------------------------------------------
4132
4133 When a path is in the "unmerged" state, running `git update-index` for
4134 that path tells Git to mark the path resolved.
4135
4136 The above is the description of a Git merge at the lowest level,
4137 to help you understand what conceptually happens under the hood.
4138 In practice, nobody, not even Git itself, runs `git cat-file` three times
4139 for this. There is a `git merge-index` program that extracts the
4140 stages to temporary files and calls a "merge" script on it:
4141
4142 -------------------------------------------------
4143 $ git merge-index git-merge-one-file hello.c
4144 -------------------------------------------------
4145
4146 and that is what higher level `git merge -s resolve` is implemented with.
4147
4148 [[hacking-git]]
4149 Hacking Git
4150 ===========
4151
4152 This chapter covers internal details of the Git implementation which
4153 probably only Git developers need to understand.
4154
4155 [[object-details]]
4156 Object storage format
4157 ---------------------
4158
4159 All objects have a statically determined "type" which identifies the
4160 format of the object (i.e. how it is used, and how it can refer to other
4161 objects). There are currently four different object types: "blob",
4162 "tree", "commit", and "tag".
4163
4164 Regardless of object type, all objects share the following
4165 characteristics: they are all deflated with zlib, and have a header
4166 that not only specifies their type, but also provides size information
4167 about the data in the object. It's worth noting that the SHA-1 hash
4168 that is used to name the object is the hash of the original data
4169 plus this header, so `sha1sum` 'file' does not match the object name
4170 for 'file'.
4171
4172 As a result, the general consistency of an object can always be tested
4173 independently of the contents or the type of the object: all objects can
4174 be validated by verifying that (a) their hashes match the content of the
4175 file and (b) the object successfully inflates to a stream of bytes that
4176 forms a sequence of
4177 `<ascii type without space> + <space> + <ascii decimal size> +
4178 <byte\0> + <binary object data>`.
4179
4180 The structured objects can further have their structure and
4181 connectivity to other objects verified. This is generally done with
4182 the `git fsck` program, which generates a full dependency graph
4183 of all objects, and verifies their internal consistency (in addition
4184 to just verifying their superficial consistency through the hash).
4185
4186 [[birdview-on-the-source-code]]
4187 A birds-eye view of Git's source code
4188 -------------------------------------
4189
4190 It is not always easy for new developers to find their way through Git's
4191 source code. This section gives you a little guidance to show where to
4192 start.
4193
4194 A good place to start is with the contents of the initial commit, with:
4195
4196 ----------------------------------------------------
4197 $ git checkout e83c5163
4198 ----------------------------------------------------
4199
4200 The initial revision lays the foundation for almost everything Git has
4201 today, but is small enough to read in one sitting.
4202
4203 Note that terminology has changed since that revision. For example, the
4204 README in that revision uses the word "changeset" to describe what we
4205 now call a <<def_commit_object,commit>>.
4206
4207 Also, we do not call it "cache" any more, but rather "index"; however, the
4208 file is still called `cache.h`. Remark: Not much reason to change it now,
4209 especially since there is no good single name for it anyway, because it is
4210 basically _the_ header file which is included by _all_ of Git's C sources.
4211
4212 If you grasp the ideas in that initial commit, you should check out a
4213 more recent version and skim `cache.h`, `object.h` and `commit.h`.
4214
4215 In the early days, Git (in the tradition of UNIX) was a bunch of programs
4216 which were extremely simple, and which you used in scripts, piping the
4217 output of one into another. This turned out to be good for initial
4218 development, since it was easier to test new things. However, recently
4219 many of these parts have become builtins, and some of the core has been
4220 "libified", i.e. put into libgit.a for performance, portability reasons,
4221 and to avoid code duplication.
4222
4223 By now, you know what the index is (and find the corresponding data
4224 structures in `cache.h`), and that there are just a couple of object types
4225 (blobs, trees, commits and tags) which inherit their common structure from
4226 `struct object`, which is their first member (and thus, you can cast e.g.
4227 `(struct object *)commit` to achieve the _same_ as `&commit->object`, i.e.
4228 get at the object name and flags).
4229
4230 Now is a good point to take a break to let this information sink in.
4231
4232 Next step: get familiar with the object naming. Read <<naming-commits>>.
4233 There are quite a few ways to name an object (and not only revisions!).
4234 All of these are handled in `sha1_name.c`. Just have a quick look at
4235 the function `get_sha1()`. A lot of the special handling is done by
4236 functions like `get_sha1_basic()` or the likes.
4237
4238 This is just to get you into the groove for the most libified part of Git:
4239 the revision walker.
4240
4241 Basically, the initial version of `git log` was a shell script:
4242
4243 ----------------------------------------------------------------
4244 $ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \
4245 LESS=-S ${PAGER:-less}
4246 ----------------------------------------------------------------
4247
4248 What does this mean?
4249
4250 `git rev-list` is the original version of the revision walker, which
4251 _always_ printed a list of revisions to stdout. It is still functional,
4252 and needs to, since most new Git commands start out as scripts using
4253 `git rev-list`.
4254
4255 `git rev-parse` is not as important any more; it was only used to filter out
4256 options that were relevant for the different plumbing commands that were
4257 called by the script.
4258
4259 Most of what `git rev-list` did is contained in `revision.c` and
4260 `revision.h`. It wraps the options in a struct named `rev_info`, which
4261 controls how and what revisions are walked, and more.
4262
4263 The original job of `git rev-parse` is now taken by the function
4264 `setup_revisions()`, which parses the revisions and the common command-line
4265 options for the revision walker. This information is stored in the struct
4266 `rev_info` for later consumption. You can do your own command-line option
4267 parsing after calling `setup_revisions()`. After that, you have to call
4268 `prepare_revision_walk()` for initialization, and then you can get the
4269 commits one by one with the function `get_revision()`.
4270
4271 If you are interested in more details of the revision walking process,
4272 just have a look at the first implementation of `cmd_log()`; call
4273 `git show v1.3.0~155^2~4` and scroll down to that function (note that you
4274 no longer need to call `setup_pager()` directly).
4275
4276 Nowadays, `git log` is a builtin, which means that it is _contained_ in the
4277 command `git`. The source side of a builtin is
4278
4279 - a function called `cmd_<bla>`, typically defined in `builtin/<bla.c>`
4280 (note that older versions of Git used to have it in `builtin-<bla>.c`
4281 instead), and declared in `builtin.h`.
4282
4283 - an entry in the `commands[]` array in `git.c`, and
4284
4285 - an entry in `BUILTIN_OBJECTS` in the `Makefile`.
4286
4287 Sometimes, more than one builtin is contained in one source file. For
4288 example, `cmd_whatchanged()` and `cmd_log()` both reside in `builtin/log.c`,
4289 since they share quite a bit of code. In that case, the commands which are
4290 _not_ named like the `.c` file in which they live have to be listed in
4291 `BUILT_INS` in the `Makefile`.
4292
4293 `git log` looks more complicated in C than it does in the original script,
4294 but that allows for a much greater flexibility and performance.
4295
4296 Here again it is a good point to take a pause.
4297
4298 Lesson three is: study the code. Really, it is the best way to learn about
4299 the organization of Git (after you know the basic concepts).
4300
4301 So, think about something which you are interested in, say, "how can I
4302 access a blob just knowing the object name of it?". The first step is to
4303 find a Git command with which you can do it. In this example, it is either
4304 `git show` or `git cat-file`.
4305
4306 For the sake of clarity, let's stay with `git cat-file`, because it
4307
4308 - is plumbing, and
4309
4310 - was around even in the initial commit (it literally went only through
4311 some 20 revisions as `cat-file.c`, was renamed to `builtin/cat-file.c`
4312 when made a builtin, and then saw less than 10 versions).
4313
4314 So, look into `builtin/cat-file.c`, search for `cmd_cat_file()` and look what
4315 it does.
4316
4317 ------------------------------------------------------------------
4318 git_config(git_default_config);
4319 if (argc != 3)
4320 usage("git cat-file [-t|-s|-e|-p|<type>] <sha1>");
4321 if (get_sha1(argv[2], sha1))
4322 die("Not a valid object name %s", argv[2]);
4323 ------------------------------------------------------------------
4324
4325 Let's skip over the obvious details; the only really interesting part
4326 here is the call to `get_sha1()`. It tries to interpret `argv[2]` as an
4327 object name, and if it refers to an object which is present in the current
4328 repository, it writes the resulting SHA-1 into the variable `sha1`.
4329
4330 Two things are interesting here:
4331
4332 - `get_sha1()` returns 0 on _success_. This might surprise some new
4333 Git hackers, but there is a long tradition in UNIX to return different
4334 negative numbers in case of different errors--and 0 on success.
4335
4336 - the variable `sha1` in the function signature of `get_sha1()` is `unsigned
4337 char *`, but is actually expected to be a pointer to `unsigned
4338 char[20]`. This variable will contain the 160-bit SHA-1 of the given
4339 commit. Note that whenever a SHA-1 is passed as `unsigned char *`, it
4340 is the binary representation, as opposed to the ASCII representation in
4341 hex characters, which is passed as `char *`.
4342
4343 You will see both of these things throughout the code.
4344
4345 Now, for the meat:
4346
4347 -----------------------------------------------------------------------------
4348 case 0:
4349 buf = read_object_with_reference(sha1, argv[1], &size, NULL);
4350 -----------------------------------------------------------------------------
4351
4352 This is how you read a blob (actually, not only a blob, but any type of
4353 object). To know how the function `read_object_with_reference()` actually
4354 works, find the source code for it (something like `git grep
4355 read_object_with | grep ":[a-z]"` in the Git repository), and read
4356 the source.
4357
4358 To find out how the result can be used, just read on in `cmd_cat_file()`:
4359
4360 -----------------------------------
4361 write_or_die(1, buf, size);
4362 -----------------------------------
4363
4364 Sometimes, you do not know where to look for a feature. In many such cases,
4365 it helps to search through the output of `git log`, and then `git show` the
4366 corresponding commit.
4367
4368 Example: If you know that there was some test case for `git bundle`, but
4369 do not remember where it was (yes, you _could_ `git grep bundle t/`, but that
4370 does not illustrate the point!):
4371
4372 ------------------------
4373 $ git log --no-merges t/
4374 ------------------------
4375
4376 In the pager (`less`), just search for "bundle", go a few lines back,
4377 and see that it is in commit 18449ab0... Now just copy this object name,
4378 and paste it into the command line
4379
4380 -------------------
4381 $ git show 18449ab0
4382 -------------------
4383
4384 Voila.
4385
4386 Another example: Find out what to do in order to make some script a
4387 builtin:
4388
4389 -------------------------------------------------
4390 $ git log --no-merges --diff-filter=A builtin/*.c
4391 -------------------------------------------------
4392
4393 You see, Git is actually the best tool to find out about the source of Git
4394 itself!
4395
4396 [[glossary]]
4397 Git Glossary
4398 ============
4399
4400 [[git-explained]]
4401 Git explained
4402 -------------
4403
4404 include::glossary-content.txt[]
4405
4406 [[git-quick-start]]
4407 Appendix A: Git Quick Reference
4408 ===============================
4409
4410 This is a quick summary of the major commands; the previous chapters
4411 explain how these work in more detail.
4412
4413 [[quick-creating-a-new-repository]]
4414 Creating a new repository
4415 -------------------------
4416
4417 From a tarball:
4418
4419 -----------------------------------------------
4420 $ tar xzf project.tar.gz
4421 $ cd project
4422 $ git init
4423 Initialized empty Git repository in .git/
4424 $ git add .
4425 $ git commit
4426 -----------------------------------------------
4427
4428 From a remote repository:
4429
4430 -----------------------------------------------
4431 $ git clone git://example.com/pub/project.git
4432 $ cd project
4433 -----------------------------------------------
4434
4435 [[managing-branches]]
4436 Managing branches
4437 -----------------
4438
4439 -----------------------------------------------
4440 $ git branch # list all local branches in this repo
4441 $ git checkout test # switch working directory to branch "test"
4442 $ git branch new # create branch "new" starting at current HEAD
4443 $ git branch -d new # delete branch "new"
4444 -----------------------------------------------
4445
4446 Instead of basing a new branch on current HEAD (the default), use:
4447
4448 -----------------------------------------------
4449 $ git branch new test # branch named "test"
4450 $ git branch new v2.6.15 # tag named v2.6.15
4451 $ git branch new HEAD^ # commit before the most recent
4452 $ git branch new HEAD^^ # commit before that
4453 $ git branch new test~10 # ten commits before tip of branch "test"
4454 -----------------------------------------------
4455
4456 Create and switch to a new branch at the same time:
4457
4458 -----------------------------------------------
4459 $ git checkout -b new v2.6.15
4460 -----------------------------------------------
4461
4462 Update and examine branches from the repository you cloned from:
4463
4464 -----------------------------------------------
4465 $ git fetch # update
4466 $ git branch -r # list
4467 origin/master
4468 origin/next
4469 ...
4470 $ git checkout -b masterwork origin/master
4471 -----------------------------------------------
4472
4473 Fetch a branch from a different repository, and give it a new
4474 name in your repository:
4475
4476 -----------------------------------------------
4477 $ git fetch git://example.com/project.git theirbranch:mybranch
4478 $ git fetch git://example.com/project.git v2.6.15:mybranch
4479 -----------------------------------------------
4480
4481 Keep a list of repositories you work with regularly:
4482
4483 -----------------------------------------------
4484 $ git remote add example git://example.com/project.git
4485 $ git remote # list remote repositories
4486 example
4487 origin
4488 $ git remote show example # get details
4489 * remote example
4490 URL: git://example.com/project.git
4491 Tracked remote branches
4492 master
4493 next
4494 ...
4495 $ git fetch example # update branches from example
4496 $ git branch -r # list all remote branches
4497 -----------------------------------------------
4498
4499
4500 [[exploring-history]]
4501 Exploring history
4502 -----------------
4503
4504 -----------------------------------------------
4505 $ gitk # visualize and browse history
4506 $ git log # list all commits
4507 $ git log src/ # ...modifying src/
4508 $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15
4509 $ git log master..test # ...in branch test, not in branch master
4510 $ git log test..master # ...in branch master, but not in test
4511 $ git log test...master # ...in one branch, not in both
4512 $ git log -S'foo()' # ...where difference contain "foo()"
4513 $ git log --since="2 weeks ago"
4514 $ git log -p # show patches as well
4515 $ git show # most recent commit
4516 $ git diff v2.6.15..v2.6.16 # diff between two tagged versions
4517 $ git diff v2.6.15..HEAD # diff with current head
4518 $ git grep "foo()" # search working directory for "foo()"
4519 $ git grep v2.6.15 "foo()" # search old tree for "foo()"
4520 $ git show v2.6.15:a.txt # look at old version of a.txt
4521 -----------------------------------------------
4522
4523 Search for regressions:
4524
4525 -----------------------------------------------
4526 $ git bisect start
4527 $ git bisect bad # current version is bad
4528 $ git bisect good v2.6.13-rc2 # last known good revision
4529 Bisecting: 675 revisions left to test after this
4530 # test here, then:
4531 $ git bisect good # if this revision is good, or
4532 $ git bisect bad # if this revision is bad.
4533 # repeat until done.
4534 -----------------------------------------------
4535
4536 [[making-changes]]
4537 Making changes
4538 --------------
4539
4540 Make sure Git knows who to blame:
4541
4542 ------------------------------------------------
4543 $ cat >>~/.gitconfig <<\EOF
4544 [user]
4545 name = Your Name Comes Here
4546 email = you@yourdomain.example.com
4547 EOF
4548 ------------------------------------------------
4549
4550 Select file contents to include in the next commit, then make the
4551 commit:
4552
4553 -----------------------------------------------
4554 $ git add a.txt # updated file
4555 $ git add b.txt # new file
4556 $ git rm c.txt # old file
4557 $ git commit
4558 -----------------------------------------------
4559
4560 Or, prepare and create the commit in one step:
4561
4562 -----------------------------------------------
4563 $ git commit d.txt # use latest content only of d.txt
4564 $ git commit -a # use latest content of all tracked files
4565 -----------------------------------------------
4566
4567 [[merging]]
4568 Merging
4569 -------
4570
4571 -----------------------------------------------
4572 $ git merge test # merge branch "test" into the current branch
4573 $ git pull git://example.com/project.git master
4574 # fetch and merge in remote branch
4575 $ git pull . test # equivalent to git merge test
4576 -----------------------------------------------
4577
4578 [[sharing-your-changes]]
4579 Sharing your changes
4580 --------------------
4581
4582 Importing or exporting patches:
4583
4584 -----------------------------------------------
4585 $ git format-patch origin..HEAD # format a patch for each commit
4586 # in HEAD but not in origin
4587 $ git am mbox # import patches from the mailbox "mbox"
4588 -----------------------------------------------
4589
4590 Fetch a branch in a different Git repository, then merge into the
4591 current branch:
4592
4593 -----------------------------------------------
4594 $ git pull git://example.com/project.git theirbranch
4595 -----------------------------------------------
4596
4597 Store the fetched branch into a local branch before merging into the
4598 current branch:
4599
4600 -----------------------------------------------
4601 $ git pull git://example.com/project.git theirbranch:mybranch
4602 -----------------------------------------------
4603
4604 After creating commits on a local branch, update the remote
4605 branch with your commits:
4606
4607 -----------------------------------------------
4608 $ git push ssh://example.com/project.git mybranch:theirbranch
4609 -----------------------------------------------
4610
4611 When remote and local branch are both named "test":
4612
4613 -----------------------------------------------
4614 $ git push ssh://example.com/project.git test
4615 -----------------------------------------------
4616
4617 Shortcut version for a frequently used remote repository:
4618
4619 -----------------------------------------------
4620 $ git remote add example ssh://example.com/project.git
4621 $ git push example test
4622 -----------------------------------------------
4623
4624 [[repository-maintenance]]
4625 Repository maintenance
4626 ----------------------
4627
4628 Check for corruption:
4629
4630 -----------------------------------------------
4631 $ git fsck
4632 -----------------------------------------------
4633
4634 Recompress, remove unused cruft:
4635
4636 -----------------------------------------------
4637 $ git gc
4638 -----------------------------------------------
4639
4640
4641 [[todo]]
4642 Appendix B: Notes and todo list for this manual
4643 ===============================================
4644
4645 [[todo-list]]
4646 Todo list
4647 ---------
4648
4649 This is a work in progress.
4650
4651 The basic requirements:
4652
4653 - It must be readable in order, from beginning to end, by someone
4654 intelligent with a basic grasp of the UNIX command line, but without
4655 any special knowledge of Git. If necessary, any other prerequisites
4656 should be specifically mentioned as they arise.
4657 - Whenever possible, section headings should clearly describe the task
4658 they explain how to do, in language that requires no more knowledge
4659 than necessary: for example, "importing patches into a project" rather
4660 than "the `git am` command"
4661
4662 Think about how to create a clear chapter dependency graph that will
4663 allow people to get to important topics without necessarily reading
4664 everything in between.
4665
4666 Scan `Documentation/` for other stuff left out; in particular:
4667
4668 - howto's
4669 - some of `technical/`?
4670 - hooks
4671 - list of commands in linkgit:git[1]
4672
4673 Scan email archives for other stuff left out
4674
4675 Scan man pages to see if any assume more background than this manual
4676 provides.
4677
4678 Add more good examples. Entire sections of just cookbook examples
4679 might be a good idea; maybe make an "advanced examples" section a
4680 standard end-of-chapter section?
4681
4682 Include cross-references to the glossary, where appropriate.
4683
4684 Add a section on working with other version control systems, including
4685 CVS, Subversion, and just imports of series of release tarballs.
4686
4687 Write a chapter on using plumbing and writing scripts.
4688
4689 Alternates, clone -reference, etc.
4690
4691 More on recovery from repository corruption. See:
4692 http://marc.info/?l=git&m=117263864820799&w=2
4693 http://marc.info/?l=git&m=117147855503798&w=2