1 Git User's Manual
2 _________________
4 This manual is designed to be readable by someone with basic unix
5 commandline skills, but no previous knowledge of git.
7 Chapter 1 gives a brief overview of git commands, without any
8 explanation; you may prefer to skip to chapter 2 on a first reading.
10 Chapters 2 and 3 explain how to fetch and study a project using
11 git--the tools you'd need to build and test a particular version of a
12 software project, to search for regressions, and so on.
14 Chapter 4 explains how to do development with git, and chapter 5 how
15 to share that development with others.
17 Further chapters cover more specialized topics.
19 Comprehensive reference documentation is available through the man
20 pages. For a command such as "git clone", just use
22 ------------------------------------------------
23 $ man git-clone
24 ------------------------------------------------
26 Git Quick Start
27 ===============
29 This is a quick summary of the major commands; the following chapters
30 will explain how these work in more detail.
32 Creating a new repository
33 -------------------------
35 From a tarball:
37 -----------------------------------------------
38 $ tar xzf project.tar.gz
39 $ cd project
40 $ git init
41 Initialized empty Git repository in .git/
42 $ git add .
43 $ git commit
44 -----------------------------------------------
46 From a remote repository:
48 -----------------------------------------------
49 $ git clone git://example.com/pub/project.git
50 $ cd project
51 -----------------------------------------------
53 Managing branches
54 -----------------
56 -----------------------------------------------
57 $ git branch # list all branches in this repo
58 $ git checkout test # switch working directory to branch "test"
59 $ git branch new # create branch "new" starting at current HEAD
60 $ git branch -d new # delete branch "new"
61 -----------------------------------------------
63 Instead of basing new branch on current HEAD (the default), use:
65 -----------------------------------------------
66 $ git branch new test # branch named "test"
67 $ git branch new v2.6.15 # tag named v2.6.15
68 $ git branch new HEAD^ # commit before the most recent
69 $ git branch new HEAD^^ # commit before that
70 $ git branch new test~10 # ten commits before tip of branch "test"
71 -----------------------------------------------
73 Create and switch to a new branch at the same time:
75 -----------------------------------------------
76 $ git checkout -b new v2.6.15
77 -----------------------------------------------
79 Update and examine branches from the repository you cloned from:
81 -----------------------------------------------
82 $ git fetch # update
83 $ git branch -r # list
84 origin/master
85 origin/next
86 ...
87 $ git branch checkout -b masterwork origin/master
88 -----------------------------------------------
90 Fetch a branch from a different repository, and give it a new
91 name in your repository:
93 -----------------------------------------------
94 $ git fetch git://example.com/project.git theirbranch:mybranch
95 $ git fetch git://example.com/project.git v2.6.15:mybranch
96 -----------------------------------------------
98 Keep a list of repositories you work with regularly:
100 -----------------------------------------------
101 $ git remote add example git://example.com/project.git
102 $ git remote # list remote repositories
103 example
104 origin
105 $ git remote show example # get details
106 * remote example
107 URL: git://example.com/project.git
108 Tracked remote branches
109 master next ...
110 $ git fetch example # update branches from example
111 $ git branch -r # list all remote branches
112 -----------------------------------------------
115 Exploring history
116 -----------------
118 -----------------------------------------------
119 $ gitk # visualize and browse history
120 $ git log # list all commits
121 $ git log src/ # ...modifying src/
122 $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15
123 $ git log master..test # ...in branch test, not in branch master
124 $ git log test..master # ...in branch master, but not in test
125 $ git log test...master # ...in one branch, not in both
126 $ git log -S'foo()' # ...where difference contain "foo()"
127 $ git log --since="2 weeks ago"
128 $ git log -p # show patches as well
129 $ git show # most recent commit
130 $ git diff v2.6.15..v2.6.16 # diff between two tagged versions
131 $ git diff v2.6.15..HEAD # diff with current head
132 $ git grep "foo()" # search working directory for "foo()"
133 $ git grep v2.6.15 "foo()" # search old tree for "foo()"
134 $ git show v2.6.15:a.txt # look at old version of a.txt
135 -----------------------------------------------
137 Search for regressions:
139 -----------------------------------------------
140 $ git bisect start
141 $ git bisect bad # current version is bad
142 $ git bisect good v2.6.13-rc2 # last known good revision
143 Bisecting: 675 revisions left to test after this
144 # test here, then:
145 $ git bisect good # if this revision is good, or
146 $ git bisect bad # if this revision is bad.
147 # repeat until done.
148 -----------------------------------------------
150 Making changes
151 --------------
153 Make sure git knows who to blame:
155 ------------------------------------------------
156 $ cat >~/.gitconfig <<\EOF
157 [user]
158 name = Your Name Comes Here
159 email = you@yourdomain.example.com
160 EOF
161 ------------------------------------------------
163 Select file contents to include in the next commit, then make the
164 commit:
166 -----------------------------------------------
167 $ git add a.txt # updated file
168 $ git add b.txt # new file
169 $ git rm c.txt # old file
170 $ git commit
171 -----------------------------------------------
173 Or, prepare and create the commit in one step:
175 -----------------------------------------------
176 $ git commit d.txt # use latest content only of d.txt
177 $ git commit -a # use latest content of all tracked files
178 -----------------------------------------------
180 Merging
181 -------
183 -----------------------------------------------
184 $ git merge test # merge branch "test" into the current branch
185 $ git pull git://example.com/project.git master
186 # fetch and merge in remote branch
187 $ git pull . test # equivalent to git merge test
188 -----------------------------------------------
190 Sharing your changes
191 --------------------
193 Importing or exporting patches:
195 -----------------------------------------------
196 $ git format-patch origin..HEAD # format a patch for each commit
197 # in HEAD but not in origin
198 $ git-am mbox # import patches from the mailbox "mbox"
199 -----------------------------------------------
201 Fetch a branch in a different git repository, then merge into the
202 current branch:
204 -----------------------------------------------
205 $ git pull git://example.com/project.git theirbranch
206 -----------------------------------------------
208 Store the fetched branch into a local branch before merging into the
209 current branch:
211 -----------------------------------------------
212 $ git pull git://example.com/project.git theirbranch:mybranch
213 -----------------------------------------------
215 After creating commits on a local branch, update the remote
216 branch with your commits:
218 -----------------------------------------------
219 $ git push ssh://example.com/project.git mybranch:theirbranch
220 -----------------------------------------------
222 When remote and local branch are both named "test":
224 -----------------------------------------------
225 $ git push ssh://example.com/project.git test
226 -----------------------------------------------
228 Shortcut version for a frequently used remote repository:
230 -----------------------------------------------
231 $ git remote add example ssh://example.com/project.git
232 $ git push example test
233 -----------------------------------------------
235 Repository maintenance
236 ----------------------
238 Check for corruption:
240 -----------------------------------------------
241 $ git fsck
242 -----------------------------------------------
244 Recompress, remove unused cruft:
246 -----------------------------------------------
247 $ git gc
248 -----------------------------------------------
250 Repositories and Branches
251 =========================
253 How to get a git repository
254 ---------------------------
256 It will be useful to have a git repository to experiment with as you
257 read this manual.
259 The best way to get one is by using the gitlink:git-clone[1] command
260 to download a copy of an existing repository for a project that you
261 are interested in. If you don't already have a project in mind, here
262 are some interesting examples:
264 ------------------------------------------------
265 # git itself (approx. 10MB download):
266 $ git clone git://git.kernel.org/pub/scm/git/git.git
267 # the linux kernel (approx. 150MB download):
268 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
269 ------------------------------------------------
271 The initial clone may be time-consuming for a large project, but you
272 will only need to clone once.
274 The clone command creates a new directory named after the project
275 ("git" or "linux-2.6" in the examples above). After you cd into this
276 directory, you will see that it contains a copy of the project files,
277 together with a special top-level directory named ".git", which
278 contains all the information about the history of the project.
280 In most of the following, examples will be taken from one of the two
281 repositories above.
283 How to check out a different version of a project
284 -------------------------------------------------
286 Git is best thought of as a tool for storing the history of a
287 collection of files. It stores the history as a compressed
288 collection of interrelated snapshots (versions) of the project's
289 contents.
291 A single git repository may contain multiple branches. Each branch
292 is a bookmark referencing a particular point in the project history.
293 The gitlink:git-branch[1] command shows you the list of branches:
295 ------------------------------------------------
296 $ git branch
297 * master
298 ------------------------------------------------
300 A freshly cloned repository contains a single branch, named "master",
301 and the working directory contains the version of the project
302 referred to by the master branch.
304 Most projects also use tags. Tags, like branches, are references
305 into the project's history, and can be listed using the
306 gitlink:git-tag[1] command:
308 ------------------------------------------------
309 $ git tag -l
310 v2.6.11
311 v2.6.11-tree
312 v2.6.12
313 v2.6.12-rc2
314 v2.6.12-rc3
315 v2.6.12-rc4
316 v2.6.12-rc5
317 v2.6.12-rc6
318 v2.6.13
319 ...
320 ------------------------------------------------
322 Tags are expected to always point at the same version of a project,
323 while branches are expected to advance as development progresses.
325 Create a new branch pointing to one of these versions and check it
326 out using gitlink:git-checkout[1]:
328 ------------------------------------------------
329 $ git checkout -b new v2.6.13
330 ------------------------------------------------
332 The working directory then reflects the contents that the project had
333 when it was tagged v2.6.13, and gitlink:git-branch[1] shows two
334 branches, with an asterisk marking the currently checked-out branch:
336 ------------------------------------------------
337 $ git branch
338 master
339 * new
340 ------------------------------------------------
342 If you decide that you'd rather see version 2.6.17, you can modify
343 the current branch to point at v2.6.17 instead, with
345 ------------------------------------------------
346 $ git reset --hard v2.6.17
347 ------------------------------------------------
349 Note that if the current branch was your only reference to a
350 particular point in history, then resetting that branch may leave you
351 with no way to find the history it used to point to; so use this
352 command carefully.
354 Understanding History: Commits
355 ------------------------------
357 Every change in the history of a project is represented by a commit.
358 The gitlink:git-show[1] command shows the most recent commit on the
359 current branch:
361 ------------------------------------------------
362 $ git show
363 commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2
364 Author: Jamal Hadi Salim <hadi@cyberus.ca>
365 Date: Sat Dec 2 22:22:25 2006 -0800
367 [XFRM]: Fix aevent structuring to be more complete.
369 aevents can not uniquely identify an SA. We break the ABI with this
370 patch, but consensus is that since it is not yet utilized by any
371 (known) application then it is fine (better do it now than later).
373 Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca>
374 Signed-off-by: David S. Miller <davem@davemloft.net>
376 diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt
377 index 8be626f..d7aac9d 100644
378 --- a/Documentation/networking/xfrm_sync.txt
379 +++ b/Documentation/networking/xfrm_sync.txt
380 @@ -47,10 +47,13 @@ aevent_id structure looks like:
382 struct xfrm_aevent_id {
383 struct xfrm_usersa_id sa_id;
384 + xfrm_address_t saddr;
385 __u32 flags;
386 + __u32 reqid;
387 };
388 ...
389 ------------------------------------------------
391 As you can see, a commit shows who made the latest change, what they
392 did, and why.
394 Every commit has a 40-hexdigit id, sometimes called the "object name"
395 or the "SHA1 id", shown on the first line of the "git show" output.
396 You can usually refer to a commit by a shorter name, such as a tag or a
397 branch name, but this longer name can also be useful. Most
398 importantly, it is a globally unique name for this commit: so if you
399 tell somebody else the object name (for example in email), then you are
400 guaranteed that name will refer to the same commit in their repository
401 that you it does in yours (assuming their repository has that commit at
402 all).
404 Understanding history: commits, parents, and reachability
405 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
407 Every commit (except the very first commit in a project) also has a
408 parent commit which shows what happened before this commit.
409 Following the chain of parents will eventually take you back to the
410 beginning of the project.
412 However, the commits do not form a simple list; git allows lines of
413 development to diverge and then reconverge, and the point where two
414 lines of development reconverge is called a "merge". The commit
415 representing a merge can therefore have more than one parent, with
416 each parent representing the most recent commit on one of the lines
417 of development leading to that point.
419 The best way to see how this works is using the gitlink:gitk[1]
420 command; running gitk now on a git repository and looking for merge
421 commits will help understand how the git organizes history.
423 In the following, we say that commit X is "reachable" from commit Y
424 if commit X is an ancestor of commit Y. Equivalently, you could say
425 that Y is a descendent of X, or that there is a chain of parents
426 leading from commit Y to commit X.
428 Undestanding history: History diagrams
429 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
431 We will sometimes represent git history using diagrams like the one
432 below. Commits are shown as "o", and the links between them with
433 lines drawn with - / and \. Time goes left to right:
435 o--o--o <-- Branch A
436 /
437 o--o--o <-- master
438 \
439 o--o--o <-- Branch B
441 If we need to talk about a particular commit, the character "o" may
442 be replaced with another letter or number.
444 Understanding history: What is a branch?
445 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
447 Though we've been using the word "branch" to mean a kind of reference
448 to a particular commit, the word branch is also commonly used to
449 refer to the line of commits leading up to that point. In the
450 example above, git may think of the branch named "A" as just a
451 pointer to one particular commit, but we may refer informally to the
452 line of three commits leading up to that point as all being part of
453 "branch A".
455 If we need to make it clear that we're just talking about the most
456 recent commit on the branch, we may refer to that commit as the
457 "head" of the branch.
459 Manipulating branches
460 ---------------------
462 Creating, deleting, and modifying branches is quick and easy; here's
463 a summary of the commands:
465 git branch::
466 list all branches
467 git branch <branch>::
468 create a new branch named <branch>, referencing the same
469 point in history as the current branch
470 git branch <branch> <start-point>::
471 create a new branch named <branch>, referencing
472 <start-point>, which may be specified any way you like,
473 including using a branch name or a tag name
474 git branch -d <branch>::
475 delete the branch <branch>; if the branch you are deleting
476 points to a commit which is not reachable from this branch,
477 this command will fail with a warning.
478 git branch -D <branch>::
479 even if the branch points to a commit not reachable
480 from the current branch, you may know that that commit
481 is still reachable from some other branch or tag. In that
482 case it is safe to use this command to force git to delete
483 the branch.
484 git checkout <branch>::
485 make the current branch <branch>, updating the working
486 directory to reflect the version referenced by <branch>
487 git checkout -b <new> <start-point>::
488 create a new branch <new> referencing <start-point>, and
489 check it out.
491 It is also useful to know that the special symbol "HEAD" can always
492 be used to refer to the current branch.
494 Examining branches from a remote repository
495 -------------------------------------------
497 The "master" branch that was created at the time you cloned is a copy
498 of the HEAD in the repository that you cloned from. That repository
499 may also have had other branches, though, and your local repository
500 keeps branches which track each of those remote branches, which you
501 can view using the "-r" option to gitlink:git-branch[1]:
503 ------------------------------------------------
504 $ git branch -r
505 origin/HEAD
506 origin/html
507 origin/maint
508 origin/man
509 origin/master
510 origin/next
511 origin/pu
512 origin/todo
513 ------------------------------------------------
515 You cannot check out these remote-tracking branches, but you can
516 examine them on a branch of your own, just as you would a tag:
518 ------------------------------------------------
519 $ git checkout -b my-todo-copy origin/todo
520 ------------------------------------------------
522 Note that the name "origin" is just the name that git uses by default
523 to refer to the repository that you cloned from.
525 [[how-git-stores-references]]
526 Naming branches, tags, and other references
527 -------------------------------------------
529 Branches, remote-tracking branches, and tags are all references to
530 commits. All references are named with a slash-separated path name
531 starting with "refs"; the names we've been using so far are actually
532 shorthand:
534 - The branch "test" is short for "refs/heads/test".
535 - The tag "v2.6.18" is short for "refs/tags/v2.6.18".
536 - "origin/master" is short for "refs/remotes/origin/master".
538 The full name is occasionally useful if, for example, there ever
539 exists a tag and a branch with the same name.
541 As another useful shortcut, if the repository "origin" posesses only
542 a single branch, you can refer to that branch as just "origin".
544 More generally, if you have defined a remote repository named
545 "example", you can refer to the branch in that repository as
546 "example". And for a repository with multiple branches, this will
547 refer to the branch designated as the "HEAD" branch.
549 For the complete list of paths which git checks for references, and
550 the order it uses to decide which to choose when there are multiple
551 references with the same shorthand name, see the "SPECIFYING
552 REVISIONS" section of gitlink:git-rev-parse[1].
554 [[Updating-a-repository-with-git-fetch]]
555 Updating a repository with git fetch
556 ------------------------------------
558 Eventually the developer cloned from will do additional work in her
559 repository, creating new commits and advancing the branches to point
560 at the new commits.
562 The command "git fetch", with no arguments, will update all of the
563 remote-tracking branches to the latest version found in her
564 repository. It will not touch any of your own branches--not even the
565 "master" branch that was created for you on clone.
567 Fetching branches from other repositories
568 -----------------------------------------
570 You can also track branches from repositories other than the one you
571 cloned from, using gitlink:git-remote[1]:
573 -------------------------------------------------
574 $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
575 $ git fetch
576 * refs/remotes/linux-nfs/master: storing branch 'master' ...
577 commit: bf81b46
578 -------------------------------------------------
580 New remote-tracking branches will be stored under the shorthand name
581 that you gave "git remote add", in this case linux-nfs:
583 -------------------------------------------------
584 $ git branch -r
585 linux-nfs/master
586 origin/master
587 -------------------------------------------------
589 If you run "git fetch <remote>" later, the tracking branches for the
590 named <remote> will be updated.
592 If you examine the file .git/config, you will see that git has added
593 a new stanza:
595 -------------------------------------------------
596 $ cat .git/config
597 ...
598 [remote "linux-nfs"]
599 url = git://linux-nfs.org/~bfields/git.git
600 fetch = +refs/heads/*:refs/remotes/linux-nfs-read/*
601 ...
602 -------------------------------------------------
604 This is what causes git to track the remote's branches; you may
605 modify or delete these configuration options by editing .git/config
606 with a text editor.
608 Exploring git history
609 =====================
611 Git is best thought of as a tool for storing the history of a
612 collection of files. It does this by storing compressed snapshots of
613 the contents of a file heirarchy, together with "commits" which show
614 the relationships between these snapshots.
616 Git provides extremely flexible and fast tools for exploring the
617 history of a project.
619 We start with one specialized tool which is useful for finding the
620 commit that introduced a bug into a project.
622 How to use bisect to find a regression
623 --------------------------------------
625 Suppose version 2.6.18 of your project worked, but the version at
626 "master" crashes. Sometimes the best way to find the cause of such a
627 regression is to perform a brute-force search through the project's
628 history to find the particular commit that caused the problem. The
629 gitlink:git-bisect[1] command can help you do this:
631 -------------------------------------------------
632 $ git bisect start
633 $ git bisect good v2.6.18
634 $ git bisect bad master
635 Bisecting: 3537 revisions left to test after this
636 [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
637 -------------------------------------------------
639 If you run "git branch" at this point, you'll see that git has
640 temporarily moved you to a new branch named "bisect". This branch
641 points to a commit (with commit id 65934...) that is reachable from
642 v2.6.19 but not from v2.6.18. Compile and test it, and see whether
643 it crashes. Assume it does crash. Then:
645 -------------------------------------------------
646 $ git bisect bad
647 Bisecting: 1769 revisions left to test after this
648 [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
649 -------------------------------------------------
651 checks out an older version. Continue like this, telling git at each
652 stage whether the version it gives you is good or bad, and notice
653 that the number of revisions left to test is cut approximately in
654 half each time.
656 After about 13 tests (in this case), it will output the commit id of
657 the guilty commit. You can then examine the commit with
658 gitlink:git-show[1], find out who wrote it, and mail them your bug
659 report with the commit id. Finally, run
661 -------------------------------------------------
662 $ git bisect reset
663 -------------------------------------------------
665 to return you to the branch you were on before and delete the
666 temporary "bisect" branch.
668 Note that the version which git-bisect checks out for you at each
669 point is just a suggestion, and you're free to try a different
670 version if you think it would be a good idea. For example,
671 occasionally you may land on a commit that broke something unrelated;
672 run
674 -------------------------------------------------
675 $ git bisect-visualize
676 -------------------------------------------------
678 which will run gitk and label the commit it chose with a marker that
679 says "bisect". Chose a safe-looking commit nearby, note its commit
680 id, and check it out with:
682 -------------------------------------------------
683 $ git reset --hard fb47ddb2db...
684 -------------------------------------------------
686 then test, run "bisect good" or "bisect bad" as appropriate, and
687 continue.
689 Naming commits
690 --------------
692 We have seen several ways of naming commits already:
694 - 40-hexdigit SHA1 id
695 - branch name: refers to the commit at the head of the given
696 branch
697 - tag name: refers to the commit pointed to by the given tag
698 (we've seen branches and tags are special cases of
699 <<how-git-stores-references,references>>).
700 - HEAD: refers to the head of the current branch
702 There are many more; see the "SPECIFYING REVISIONS" section of the
703 gitlink:git-rev-parse[1] man page for the complete list of ways to
704 name revisions. Some examples:
706 -------------------------------------------------
707 $ git show fb47ddb2 # the first few characters of the SHA1 id
708 # are usually enough to specify it uniquely
709 $ git show HEAD^ # the parent of the HEAD commit
710 $ git show HEAD^^ # the grandparent
711 $ git show HEAD~4 # the great-great-grandparent
712 -------------------------------------------------
714 Recall that merge commits may have more than one parent; by default,
715 ^ and ~ follow the first parent listed in the commit, but you can
716 also choose:
718 -------------------------------------------------
719 $ git show HEAD^1 # show the first parent of HEAD
720 $ git show HEAD^2 # show the second parent of HEAD
721 -------------------------------------------------
723 In addition to HEAD, there are several other special names for
724 commits:
726 Merges (to be discussed later), as well as operations such as
727 git-reset, which change the currently checked-out commit, generally
728 set ORIG_HEAD to the value HEAD had before the current operation.
730 The git-fetch operation always stores the head of the last fetched
731 branch in FETCH_HEAD. For example, if you run git fetch without
732 specifying a local branch as the target of the operation
734 -------------------------------------------------
735 $ git fetch git://example.com/proj.git theirbranch
736 -------------------------------------------------
738 the fetched commits will still be available from FETCH_HEAD.
740 When we discuss merges we'll also see the special name MERGE_HEAD,
741 which refers to the other branch that we're merging in to the current
742 branch.
744 The gitlink:git-rev-parse[1] command is a low-level command that is
745 occasionally useful for translating some name for a commit to the SHA1 id for
746 that commit:
748 -------------------------------------------------
749 $ git rev-parse origin
750 e05db0fd4f31dde7005f075a84f96b360d05984b
751 -------------------------------------------------
753 Creating tags
754 -------------
756 We can also create a tag to refer to a particular commit; after
757 running
759 -------------------------------------------------
760 $ git-tag stable-1 1b2e1d63ff
761 -------------------------------------------------
763 You can use stable-1 to refer to the commit 1b2e1d63ff.
765 This creates a "lightweight" tag. If the tag is a tag you wish to
766 share with others, and possibly sign cryptographically, then you
767 should create a tag object instead; see the gitlink:git-tag[1] man
768 page for details.
770 Browsing revisions
771 ------------------
773 The gitlink:git-log[1] command can show lists of commits. On its
774 own, it shows all commits reachable from the parent commit; but you
775 can also make more specific requests:
777 -------------------------------------------------
778 $ git log v2.5.. # commits since (not reachable from) v2.5
779 $ git log test..master # commits reachable from master but not test
780 $ git log master..test # ...reachable from test but not master
781 $ git log master...test # ...reachable from either test or master,
782 # but not both
783 $ git log --since="2 weeks ago" # commits from the last 2 weeks
784 $ git log Makefile # commits which modify Makefile
785 $ git log fs/ # ... which modify any file under fs/
786 $ git log -S'foo()' # commits which add or remove any file data
787 # matching the string 'foo()'
788 -------------------------------------------------
790 And of course you can combine all of these; the following finds
791 commits since v2.5 which touch the Makefile or any file under fs:
793 -------------------------------------------------
794 $ git log v2.5.. Makefile fs/
795 -------------------------------------------------
797 You can also ask git log to show patches:
799 -------------------------------------------------
800 $ git log -p
801 -------------------------------------------------
803 See the "--pretty" option in the gitlink:git-log[1] man page for more
804 display options.
806 Note that git log starts with the most recent commit and works
807 backwards through the parents; however, since git history can contain
808 multiple independant lines of development, the particular order that
809 commits are listed in may be somewhat arbitrary.
811 Generating diffs
812 ----------------
814 You can generate diffs between any two versions using
815 gitlink:git-diff[1]:
817 -------------------------------------------------
818 $ git diff master..test
819 -------------------------------------------------
821 Sometimes what you want instead is a set of patches:
823 -------------------------------------------------
824 $ git format-patch master..test
825 -------------------------------------------------
827 will generate a file with a patch for each commit reachable from test
828 but not from master. Note that if master also has commits which are
829 not reachable from test, then the combined result of these patches
830 will not be the same as the diff produced by the git-diff example.
832 Viewing old file versions
833 -------------------------
835 You can always view an old version of a file by just checking out the
836 correct revision first. But sometimes it is more convenient to be
837 able to view an old version of a single file without checking
838 anything out; this command does that:
840 -------------------------------------------------
841 $ git show v2.5:fs/locks.c
842 -------------------------------------------------
844 Before the colon may be anything that names a commit, and after it
845 may be any path to a file tracked by git.
847 Examples
848 --------
850 Check whether two branches point at the same history
851 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
853 Suppose you want to check whether two branches point at the same point
854 in history.
856 -------------------------------------------------
857 $ git diff origin..master
858 -------------------------------------------------
860 will tell you whether the contents of the project are the same at the
861 two branches; in theory, however, it's possible that the same project
862 contents could have been arrived at by two different historical
863 routes. You could compare the SHA1 id's:
865 -------------------------------------------------
866 $ git rev-list origin
867 e05db0fd4f31dde7005f075a84f96b360d05984b
868 $ git rev-list master
869 e05db0fd4f31dde7005f075a84f96b360d05984b
870 -------------------------------------------------
872 Or you could recall that the ... operator selects all commits
873 contained reachable from either one reference or the other but not
874 both: so
876 -------------------------------------------------
877 $ git log origin...master
878 -------------------------------------------------
880 will return no commits when the two branches are equal.
882 Find first tagged version including a given fix
883 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
885 Suppose you know that the commit e05db0fd fixed a certain problem.
886 You'd like to find the earliest tagged release that contains that
887 fix.
889 Of course, there may be more than one answer--if the history branched
890 after commit e05db0fd, then there could be multiple "earliest" tagged
891 releases.
893 You could just visually inspect the commits since e05db0fd:
895 -------------------------------------------------
896 $ gitk e05db0fd..
897 -------------------------------------------------
899 Or you can use gitlink:git-name-rev[1], which will give the commit a
900 name based on any tag it finds pointing to one of the commit's
901 descendants:
903 -------------------------------------------------
904 $ git name-rev e05db0fd
905 e05db0fd tags/v1.5.0-rc1^0~23
906 -------------------------------------------------
908 The gitlink:git-describe[1] command does the opposite, naming the
909 revision using a tag on which the given commit is based:
911 -------------------------------------------------
912 $ git describe e05db0fd
913 v1.5.0-rc0-ge05db0f
914 -------------------------------------------------
916 but that may sometimes help you guess which tags might come after the
917 given commit.
919 If you just want to verify whether a given tagged version contains a
920 given commit, you could use gitlink:git-merge-base[1]:
922 -------------------------------------------------
923 $ git merge-base e05db0fd v1.5.0-rc1
924 e05db0fd4f31dde7005f075a84f96b360d05984b
925 -------------------------------------------------
927 The merge-base command finds a common ancestor of the given commits,
928 and always returns one or the other in the case where one is a
929 descendant of the other; so the above output shows that e05db0fd
930 actually is an ancestor of v1.5.0-rc1.
932 Alternatively, note that
934 -------------------------------------------------
935 $ git log v1.5.0-rc1..305db0fd
936 -------------------------------------------------
938 will produce empty output if and only if v1.5.0-rc1 includes 305db0fd,
939 because it outputs only commits that are not reachable from v1.5.0-rc1.
941 Developing with git
942 ===================
944 Telling git your name
945 ---------------------
947 Before creating any commits, you should introduce yourself to git. The
948 easiest way to do so is:
950 ------------------------------------------------
951 $ cat >~/.gitconfig <<\EOF
952 [user]
953 name = Your Name Comes Here
954 email = you@yourdomain.example.com
955 EOF
956 ------------------------------------------------
959 Creating a new repository
960 -------------------------
962 Creating a new repository from scratch is very easy:
964 -------------------------------------------------
965 $ mkdir project
966 $ cd project
967 $ git init
968 -------------------------------------------------
970 If you have some initial content (say, a tarball):
972 -------------------------------------------------
973 $ tar -xzvf project.tar.gz
974 $ cd project
975 $ git init
976 $ git add . # include everything below ./ in the first commit:
977 $ git commit
978 -------------------------------------------------
980 [[how-to-make-a-commit]]
981 how to make a commit
982 --------------------
984 Creating a new commit takes three steps:
986 1. Making some changes to the working directory using your
987 favorite editor.
988 2. Telling git about your changes.
989 3. Creating the commit using the content you told git about
990 in step 2.
992 In practice, you can interleave and repeat steps 1 and 2 as many
993 times as you want: in order to keep track of what you want committed
994 at step 3, git maintains a snapshot of the tree's contents in a
995 special staging area called "the index."
997 At the beginning, the content of the index will be identical to
998 that of the HEAD. The command "git diff --cached", which shows
999 the difference between the HEAD and the index, should therefore
1000 produce no output at that point.
1002 Modifying the index is easy:
1004 To update the index with the new contents of a modified file, use
1006 -------------------------------------------------
1007 $ git add path/to/file
1008 -------------------------------------------------
1010 To add the contents of a new file to the index, use
1012 -------------------------------------------------
1013 $ git add path/to/file
1014 -------------------------------------------------
1016 To remove a file from the index and from the working tree,
1018 -------------------------------------------------
1019 $ git rm path/to/file
1020 -------------------------------------------------
1022 After each step you can verify that
1024 -------------------------------------------------
1025 $ git diff --cached
1026 -------------------------------------------------
1028 always shows the difference between the HEAD and the index file--this
1029 is what you'd commit if you created the commit now--and that
1031 -------------------------------------------------
1032 $ git diff
1033 -------------------------------------------------
1035 shows the difference between the working tree and the index file.
1037 Note that "git add" always adds just the current contents of a file
1038 to the index; further changes to the same file will be ignored unless
1039 you run git-add on the file again.
1041 When you're ready, just run
1043 -------------------------------------------------
1044 $ git commit
1045 -------------------------------------------------
1047 and git will prompt you for a commit message and then create the new
1048 commmit. Check to make sure it looks like what you expected with
1050 -------------------------------------------------
1051 $ git show
1052 -------------------------------------------------
1054 As a special shortcut,
1056 -------------------------------------------------
1057 $ git commit -a
1058 -------------------------------------------------
1060 will update the index with any files that you've modified or removed
1061 and create a commit, all in one step.
1063 A number of commands are useful for keeping track of what you're
1064 about to commit:
1066 -------------------------------------------------
1067 $ git diff --cached # difference between HEAD and the index; what
1068 # would be commited if you ran "commit" now.
1069 $ git diff # difference between the index file and your
1070 # working directory; changes that would not
1071 # be included if you ran "commit" now.
1072 $ git status # a brief per-file summary of the above.
1073 -------------------------------------------------
1075 creating good commit messages
1076 -----------------------------
1078 Though not required, it's a good idea to begin the commit message
1079 with a single short (less than 50 character) line summarizing the
1080 change, followed by a blank line and then a more thorough
1081 description. Tools that turn commits into email, for example, use
1082 the first line on the Subject line and the rest of the commit in the
1083 body.
1085 how to merge
1086 ------------
1088 You can rejoin two diverging branches of development using
1089 gitlink:git-merge[1]:
1091 -------------------------------------------------
1092 $ git merge branchname
1093 -------------------------------------------------
1095 merges the development in the branch "branchname" into the current
1096 branch. If there are conflicts--for example, if the same file is
1097 modified in two different ways in the remote branch and the local
1098 branch--then you are warned; the output may look something like this:
1100 -------------------------------------------------
1101 $ git pull . next
1102 Trying really trivial in-index merge...
1103 fatal: Merge requires file-level merging
1104 Nope.
1105 Merging HEAD with 77976da35a11db4580b80ae27e8d65caf5208086
1106 Merging:
1107 15e2162 world
1108 77976da goodbye
1109 found 1 common ancestor(s):
1110 d122ed4 initial
1111 Auto-merging file.txt
1112 CONFLICT (content): Merge conflict in file.txt
1113 Automatic merge failed; fix conflicts and then commit the result.
1114 -------------------------------------------------
1116 Conflict markers are left in the problematic files, and after
1117 you resolve the conflicts manually, you can update the index
1118 with the contents and run git commit, as you normally would when
1119 creating a new file.
1121 If you examine the resulting commit using gitk, you will see that it
1122 has two parents, one pointing to the top of the current branch, and
1123 one to the top of the other branch.
1125 In more detail:
1127 [[resolving-a-merge]]
1128 Resolving a merge
1129 -----------------
1131 When a merge isn't resolved automatically, git leaves the index and
1132 the working tree in a special state that gives you all the
1133 information you need to help resolve the merge.
1135 Files with conflicts are marked specially in the index, so until you
1136 resolve the problem and update the index, git commit will fail:
1138 -------------------------------------------------
1139 $ git commit
1140 file.txt: needs merge
1141 -------------------------------------------------
1143 Also, git status will list those files as "unmerged".
1145 All of the changes that git was able to merge automatically are
1146 already added to the index file, so gitlink:git-diff[1] shows only
1147 the conflicts. Also, it uses a somewhat unusual syntax:
1149 -------------------------------------------------
1150 $ git diff
1151 diff --cc file.txt
1152 index 802992c,2b60207..0000000
1153 --- a/file.txt
1154 +++ b/file.txt
1155 @@@ -1,1 -1,1 +1,5 @@@
1156 ++<<<<<<< HEAD:file.txt
1157 +Hello world
1158 ++=======
1159 + Goodbye
1160 ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1161 -------------------------------------------------
1163 Recall that the commit which will be commited after we resolve this
1164 conflict will have two parents instead of the usual one: one parent
1165 will be HEAD, the tip of the current branch; the other will be the
1166 tip of the other branch, which is stored temporarily in MERGE_HEAD.
1168 The diff above shows the differences between the working-tree version
1169 of file.txt and two previous version: one version from HEAD, and one
1170 from MERGE_HEAD. So instead of preceding each line by a single "+"
1171 or "-", it now uses two columns: the first column is used for
1172 differences between the first parent and the working directory copy,
1173 and the second for differences between the second parent and the
1174 working directory copy. Thus after resolving the conflict in the
1175 obvious way, the diff will look like:
1177 -------------------------------------------------
1178 $ git diff
1179 diff --cc file.txt
1180 index 802992c,2b60207..0000000
1181 --- a/file.txt
1182 +++ b/file.txt
1183 @@@ -1,1 -1,1 +1,1 @@@
1184 - Hello world
1185 -Goodbye
1186 ++Goodbye world
1187 -------------------------------------------------
1189 This shows that our resolved version deleted "Hello world" from the
1190 first parent, deleted "Goodbye" from the second parent, and added
1191 "Goodbye world", which was previously absent from both.
1193 The gitlink:git-log[1] command also provides special help for merges:
1195 -------------------------------------------------
1196 $ git log --merge
1197 -------------------------------------------------
1199 This will list all commits which exist only on HEAD or on MERGE_HEAD,
1200 and which touch an unmerged file.
1202 We can now add the resolved version to the index and commit:
1204 -------------------------------------------------
1205 $ git add file.txt
1206 $ git commit
1207 -------------------------------------------------
1209 Note that the commit message will already be filled in for you with
1210 some information about the merge. Normally you can just use this
1211 default message unchanged, but you may add additional commentary of
1212 your own if desired.
1214 [[undoing-a-merge]]
1215 undoing a merge
1216 ---------------
1218 If you get stuck and decide to just give up and throw the whole mess
1219 away, you can always return to the pre-merge state with
1221 -------------------------------------------------
1222 $ git reset --hard HEAD
1223 -------------------------------------------------
1225 Or, if you've already commited the merge that you want to throw away,
1227 -------------------------------------------------
1228 $ git reset --hard HEAD^
1229 -------------------------------------------------
1231 However, this last command can be dangerous in some cases--never
1232 throw away a commit you have already committed if that commit may
1233 itself have been merged into another branch, as doing so may confuse
1234 further merges.
1236 Fast-forward merges
1237 -------------------
1239 There is one special case not mentioned above, which is treated
1240 differently. Normally, a merge results in a merge commit, with two
1241 parents, one pointing at each of the two lines of development that
1242 were merged.
1244 However, if one of the two lines of development is completely
1245 contained within the other--so every commit present in the one is
1246 already contained in the other--then git just performs a
1247 <<fast-forwards,fast forward>>; the head of the current branch is
1248 moved forward to point at the head of the merged-in branch, without
1249 any new commits being created.
1251 Fixing mistakes
1252 ---------------
1254 If you've messed up the working tree, but haven't yet committed your
1255 mistake, you can return the entire working tree to the last committed
1256 state with
1258 -------------------------------------------------
1259 $ git reset --hard HEAD
1260 -------------------------------------------------
1262 If you make a commit that you later wish you hadn't, there are two
1263 fundamentally different ways to fix the problem:
1265 1. You can create a new commit that undoes whatever was done
1266 by the previous commit. This is the correct thing if your
1267 mistake has already been made public.
1269 2. You can go back and modify the old commit. You should
1270 never do this if you have already made the history public;
1271 git does not normally expect the "history" of a project to
1272 change, and cannot correctly perform repeated merges from
1273 a branch that has had its history changed.
1275 Fixing a mistake with a new commit
1276 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1278 Creating a new commit that reverts an earlier change is very easy;
1279 just pass the gitlink:git-revert[1] command a reference to the bad
1280 commit; for example, to revert the most recent commit:
1282 -------------------------------------------------
1283 $ git revert HEAD
1284 -------------------------------------------------
1286 This will create a new commit which undoes the change in HEAD. You
1287 will be given a chance to edit the commit message for the new commit.
1289 You can also revert an earlier change, for example, the next-to-last:
1291 -------------------------------------------------
1292 $ git revert HEAD^
1293 -------------------------------------------------
1295 In this case git will attempt to undo the old change while leaving
1296 intact any changes made since then. If more recent changes overlap
1297 with the changes to be reverted, then you will be asked to fix
1298 conflicts manually, just as in the case of <<resolving-a-merge,
1299 resolving a merge>>.
1301 Fixing a mistake by editing history
1302 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1304 If the problematic commit is the most recent commit, and you have not
1305 yet made that commit public, then you may just
1306 <<undoing-a-merge,destroy it using git-reset>>.
1308 Alternatively, you
1309 can edit the working directory and update the index to fix your
1310 mistake, just as if you were going to <<how-to-make-a-commit,create a
1311 new commit>>, then run
1313 -------------------------------------------------
1314 $ git commit --amend
1315 -------------------------------------------------
1317 which will replace the old commit by a new commit incorporating your
1318 changes, giving you a chance to edit the old commit message first.
1320 Again, you should never do this to a commit that may already have
1321 been merged into another branch; use gitlink:git-revert[1] instead in
1322 that case.
1324 It is also possible to edit commits further back in the history, but
1325 this is an advanced topic to be left for
1326 <<cleaning-up-history,another chapter>>.
1328 Checking out an old version of a file
1329 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1331 In the process of undoing a previous bad change, you may find it
1332 useful to check out an older version of a particular file using
1333 gitlink:git-checkout[1]. We've used git checkout before to switch
1334 branches, but it has quite different behavior if it is given a path
1335 name: the command
1337 -------------------------------------------------
1338 $ git checkout HEAD^ path/to/file
1339 -------------------------------------------------
1341 replaces path/to/file by the contents it had in the commit HEAD^, and
1342 also updates the index to match. It does not change branches.
1344 If you just want to look at an old version of the file, without
1345 modifying the working directory, you can do that with
1346 gitlink:git-show[1]:
1348 -------------------------------------------------
1349 $ git show HEAD^ path/to/file
1350 -------------------------------------------------
1352 which will display the given version of the file.
1354 Ensuring good performance
1355 -------------------------
1357 On large repositories, git depends on compression to keep the history
1358 information from taking up to much space on disk or in memory.
1360 This compression is not performed automatically. Therefore you
1361 should occasionally run gitlink:git-gc[1]:
1363 -------------------------------------------------
1364 $ git gc
1365 -------------------------------------------------
1367 to recompress the archive. This can be very time-consuming, so
1368 you may prefer to run git-gc when you are not doing other work.
1370 Ensuring reliability
1371 --------------------
1373 Checking the repository for corruption
1374 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1376 The gitlink:git-fsck[1] command runs a number of self-consistency
1377 checks on the repository, and reports on any problems. This may take some
1378 time. The most common warning by far is about "dangling" objects:
1380 -------------------------------------------------
1381 $ git fsck
1382 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1383 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1384 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1385 dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1386 dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1387 dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1388 dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1389 dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1390 ...
1391 -------------------------------------------------
1393 Dangling objects are objects that are harmless, but also unnecessary; you can
1394 remove them at any time with gitlink:git-prune[1] or the --prune option to
1395 gitlink:git-gc[1]:
1397 -------------------------------------------------
1398 $ git gc --prune
1399 -------------------------------------------------
1401 This may be time-consuming. Unlike most other git operations (including git-gc
1402 when run without any options), it is not safe to prune while other git
1403 operations are in progress in the same repository.
1405 For more about dangling merges, see <<dangling-merges>>.
1408 Recovering lost changes
1409 ~~~~~~~~~~~~~~~~~~~~~~~
1411 TODO:
1412 reflog
1413 git-fsck
1414 low-level examination of objects
1416 Sharing development with others
1417 ===============================
1419 [[getting-updates-with-git-pull]]
1420 Getting updates with git pull
1421 -----------------------------
1423 After you clone a repository and make a few changes of your own, you
1424 may wish to check the original repository for updates and merge them
1425 into your own work.
1427 We have already seen <<Updating-a-repository-with-git-fetch,how to
1428 keep remote tracking branches up to date>> with gitlink:git-fetch[1],
1429 and how to merge two branches. So you can merge in changes from the
1430 original repository's master branch with:
1432 -------------------------------------------------
1433 $ git fetch
1434 $ git merge origin/master
1435 -------------------------------------------------
1437 However, the gitlink:git-pull[1] command provides a way to do this in
1438 one step:
1440 -------------------------------------------------
1441 $ git pull origin master
1442 -------------------------------------------------
1444 In fact, "origin" is normally the default repository to pull from,
1445 and the default branch is normally the HEAD of the remote repository,
1446 so often you can accomplish the above with just
1448 -------------------------------------------------
1449 $ git pull
1450 -------------------------------------------------
1452 See the descriptions of the branch.<name>.remote and
1453 branch.<name>.merge options in gitlink:git-config[1] to learn
1454 how to control these defaults depending on the current branch.
1456 In addition to saving you keystrokes, "git pull" also helps you by
1457 producing a default commit message documenting the branch and
1458 repository that you pulled from.
1460 (But note that no such commit will be created in the case of a
1461 <<fast-forwards,fast forward>>; instead, your branch will just be
1462 updated to point to the latest commit from the upstream branch).
1464 The git-pull command can also be given "." as the "remote" repository, in
1465 which case it just merges in a branch from the current repository; so
1466 the commands
1468 -------------------------------------------------
1469 $ git pull . branch
1470 $ git merge branch
1471 -------------------------------------------------
1473 are roughly equivalent. The former is actually very commonly used.
1475 Submitting patches to a project
1476 -------------------------------
1478 If you just have a few changes, the simplest way to submit them may
1479 just be to send them as patches in email:
1481 First, use gitlink:git-format-patches[1]; for example:
1483 -------------------------------------------------
1484 $ git format-patch origin
1485 -------------------------------------------------
1487 will produce a numbered series of files in the current directory, one
1488 for each patch in the current branch but not in origin/HEAD.
1490 You can then import these into your mail client and send them by
1491 hand. However, if you have a lot to send at once, you may prefer to
1492 use the gitlink:git-send-email[1] script to automate the process.
1493 Consult the mailing list for your project first to determine how they
1494 prefer such patches be handled.
1496 Importing patches to a project
1497 ------------------------------
1499 Git also provides a tool called gitlink:git-am[1] (am stands for
1500 "apply mailbox"), for importing such an emailed series of patches.
1501 Just save all of the patch-containing messages, in order, into a
1502 single mailbox file, say "patches.mbox", then run
1504 -------------------------------------------------
1505 $ git am -3 patches.mbox
1506 -------------------------------------------------
1508 Git will apply each patch in order; if any conflicts are found, it
1509 will stop, and you can fix the conflicts as described in
1510 "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1511 git to perform a merge; if you would prefer it just to abort and
1512 leave your tree and index untouched, you may omit that option.)
1514 Once the index is updated with the results of the conflict
1515 resolution, instead of creating a new commit, just run
1517 -------------------------------------------------
1518 $ git am --resolved
1519 -------------------------------------------------
1521 and git will create the commit for you and continue applying the
1522 remaining patches from the mailbox.
1524 The final result will be a series of commits, one for each patch in
1525 the original mailbox, with authorship and commit log message each
1526 taken from the message containing each patch.
1528 [[setting-up-a-public-repository]]
1529 Setting up a public repository
1530 ------------------------------
1532 Another way to submit changes to a project is to simply tell the
1533 maintainer of that project to pull from your repository, exactly as
1534 you did in the section "<<getting-updates-with-git-pull, Getting
1535 updates with git pull>>".
1537 If you and maintainer both have accounts on the same machine, then
1538 then you can just pull changes from each other's repositories
1539 directly; note that all of the command (gitlink:git-clone[1],
1540 git-fetch[1], git-pull[1], etc.) which accept a URL as an argument
1541 will also accept a local file patch; so, for example, you can
1542 use
1544 -------------------------------------------------
1545 $ git clone /path/to/repository
1546 $ git pull /path/to/other/repository
1547 -------------------------------------------------
1549 If this sort of setup is inconvenient or impossible, another (more
1550 common) option is to set up a public repository on a public server.
1551 This also allows you to cleanly separate private work in progress
1552 from publicly visible work.
1554 You will continue to do your day-to-day work in your personal
1555 repository, but periodically "push" changes from your personal
1556 repository into your public repository, allowing other developers to
1557 pull from that repository. So the flow of changes, in a situation
1558 where there is one other developer with a public repository, looks
1559 like this:
1561 you push
1562 your personal repo ------------------> your public repo
1563 ^ |
1564 | |
1565 | you pull | they pull
1566 | |
1567 | |
1568 | they push V
1569 their public repo <------------------- their repo
1571 Now, assume your personal repository is in the directory ~/proj. We
1572 first create a new clone of the repository:
1574 -------------------------------------------------
1575 $ git clone --bare proj-clone.git
1576 -------------------------------------------------
1578 The resulting directory proj-clone.git will contains a "bare" git
1579 repository--it is just the contents of the ".git" directory, without
1580 a checked-out copy of a working directory.
1582 Next, copy proj-clone.git to the server where you plan to host the
1583 public repository. You can use scp, rsync, or whatever is most
1584 convenient.
1586 If somebody else maintains the public server, they may already have
1587 set up a git service for you, and you may skip to the section
1588 "<<pushing-changes-to-a-public-repository,Pushing changes to a public
1589 repository>>", below.
1591 Otherwise, the following sections explain how to export your newly
1592 created public repository:
1594 [[exporting-via-http]]
1595 Exporting a git repository via http
1596 -----------------------------------
1598 The git protocol gives better performance and reliability, but on a
1599 host with a web server set up, http exports may be simpler to set up.
1601 All you need to do is place the newly created bare git repository in
1602 a directory that is exported by the web server, and make some
1603 adjustments to give web clients some extra information they need:
1605 -------------------------------------------------
1606 $ mv proj.git /home/you/public_html/proj.git
1607 $ cd proj.git
1608 $ git update-server-info
1609 $ chmod a+x hooks/post-update
1610 -------------------------------------------------
1612 (For an explanation of the last two lines, see
1613 gitlink:git-update-server-info[1], and the documentation
1614 link:hooks.txt[Hooks used by git].)
1616 Advertise the url of proj.git. Anybody else should then be able to
1617 clone or pull from that url, for example with a commandline like:
1619 -------------------------------------------------
1620 $ git clone http://yourserver.com/~you/proj.git
1621 -------------------------------------------------
1623 (See also
1624 link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1625 for a slightly more sophisticated setup using WebDAV which also
1626 allows pushing over http.)
1628 [[exporting-via-git]]
1629 Exporting a git repository via the git protocol
1630 -----------------------------------------------
1632 This is the preferred method.
1634 For now, we refer you to the gitlink:git-daemon[1] man page for
1635 instructions. (See especially the examples section.)
1637 [[pushing-changes-to-a-public-repository]]
1638 Pushing changes to a public repository
1639 --------------------------------------
1641 Note that the two techniques outline above (exporting via
1642 <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1643 maintainers to fetch your latest changes, but they do not allow write
1644 access, which you will need to update the public repository with the
1645 latest changes created in your private repository.
1647 The simplest way to do this is using gitlink:git-push[1] and ssh; to
1648 update the remote branch named "master" with the latest state of your
1649 branch named "master", run
1651 -------------------------------------------------
1652 $ git push ssh://yourserver.com/~you/proj.git master:master
1653 -------------------------------------------------
1655 or just
1657 -------------------------------------------------
1658 $ git push ssh://yourserver.com/~you/proj.git master
1659 -------------------------------------------------
1661 As with git-fetch, git-push will complain if this does not result in
1662 a <<fast-forwards,fast forward>>. Normally this is a sign of
1663 something wrong. However, if you are sure you know what you're
1664 doing, you may force git-push to perform the update anyway by
1665 proceeding the branch name by a plus sign:
1667 -------------------------------------------------
1668 $ git push ssh://yourserver.com/~you/proj.git +master
1669 -------------------------------------------------
1671 As with git-fetch, you may also set up configuration options to
1672 save typing; so, for example, after
1674 -------------------------------------------------
1675 $ cat >.git/config <<EOF
1676 [remote "public-repo"]
1677 url = ssh://yourserver.com/~you/proj.git
1678 EOF
1679 -------------------------------------------------
1681 you should be able to perform the above push with just
1683 -------------------------------------------------
1684 $ git push public-repo master
1685 -------------------------------------------------
1687 See the explanations of the remote.<name>.url, branch.<name>.remote,
1688 and remote.<name>.push options in gitlink:git-config[1] for
1689 details.
1691 Setting up a shared repository
1692 ------------------------------
1694 Another way to collaborate is by using a model similar to that
1695 commonly used in CVS, where several developers with special rights
1696 all push to and pull from a single shared repository. See
1697 link:cvs-migration.txt[git for CVS users] for instructions on how to
1698 set this up.
1700 Allow web browsing of a repository
1701 ----------------------------------
1703 TODO: Brief setup-instructions for gitweb
1705 Examples
1706 --------
1708 TODO: topic branches, typical roles as in everyday.txt, ?
1711 Working with other version control systems
1712 ==========================================
1714 TODO: CVS, Subversion, series-of-release-tarballs, etc.
1716 [[cleaning-up-history]]
1717 Rewriting history and maintaining patch series
1718 ==============================================
1720 Normally commits are only added to a project, never taken away or
1721 replaced. Git is designed with this assumption, and violating it will
1722 cause git's merge machinery (for example) to do the wrong thing.
1724 However, there is a situation in which it can be useful to violate this
1725 assumption.
1727 Creating the perfect patch series
1728 ---------------------------------
1730 Suppose you are a contributor to a large project, and you want to add a
1731 complicated feature, and to present it to the other developers in a way
1732 that makes it easy for them to read your changes, verify that they are
1733 correct, and understand why you made each change.
1735 If you present all of your changes as a single patch (or commit), they
1736 may find it is too much to digest all at once.
1738 If you present them with the entire history of your work, complete with
1739 mistakes, corrections, and dead ends, they may be overwhelmed.
1741 So the ideal is usually to produce a series of patches such that:
1743 1. Each patch can be applied in order.
1745 2. Each patch includes a single logical change, together with a
1746 message explaining the change.
1748 3. No patch introduces a regression: after applying any initial
1749 part of the series, the resulting project still compiles and
1750 works, and has no bugs that it didn't have before.
1752 4. The complete series produces the same end result as your own
1753 (probably much messier!) development process did.
1755 We will introduce some tools that can help you do this, explain how to
1756 use them, and then explain some of the problems that can arise because
1757 you are rewriting history.
1759 Keeping a patch series up to date using git-rebase
1760 --------------------------------------------------
1762 Suppose you have a series of commits in a branch "mywork", which
1763 originally branched off from "origin".
1765 Suppose you create a branch "mywork" on a remote-tracking branch
1766 "origin", and created some commits on top of it:
1768 -------------------------------------------------
1769 $ git checkout -b mywork origin
1770 $ vi file.txt
1771 $ git commit
1772 $ vi otherfile.txt
1773 $ git commit
1774 ...
1775 -------------------------------------------------
1777 You have performed no merges into mywork, so it is just a simple linear
1778 sequence of patches on top of "origin":
1781 o--o--o <-- origin
1782 \
1783 o--o--o <-- mywork
1785 Some more interesting work has been done in the upstream project, and
1786 "origin" has advanced:
1788 o--o--O--o--o--o <-- origin
1789 \
1790 a--b--c <-- mywork
1792 At this point, you could use "pull" to merge your changes back in;
1793 the result would create a new merge commit, like this:
1796 o--o--O--o--o--o <-- origin
1797 \ \
1798 a--b--c--m <-- mywork
1800 However, if you prefer to keep the history in mywork a simple series of
1801 commits without any merges, you may instead choose to use
1802 gitlink:git-rebase[1]:
1804 -------------------------------------------------
1805 $ git checkout mywork
1806 $ git rebase origin
1807 -------------------------------------------------
1809 This will remove each of your commits from mywork, temporarily saving
1810 them as patches (in a directory named ".dotest"), update mywork to
1811 point at the latest version of origin, then apply each of the saved
1812 patches to the new mywork. The result will look like:
1815 o--o--O--o--o--o <-- origin
1816 \
1817 a'--b'--c' <-- mywork
1819 In the process, it may discover conflicts. In that case it will stop
1820 and allow you to fix the conflicts; after fixing conflicts, use "git
1821 add" to update the index with those contents, and then, instead of
1822 running git-commit, just run
1824 -------------------------------------------------
1825 $ git rebase --continue
1826 -------------------------------------------------
1828 and git will continue applying the rest of the patches.
1830 At any point you may use the --abort option to abort this process and
1831 return mywork to the state it had before you started the rebase:
1833 -------------------------------------------------
1834 $ git rebase --abort
1835 -------------------------------------------------
1837 Reordering or selecting from a patch series
1838 -------------------------------------------
1840 Given one existing commit, the gitlink:git-cherry-pick[1] command
1841 allows you to apply the change introduced by that commit and create a
1842 new commit that records it. So, for example, if "mywork" points to a
1843 series of patches on top of "origin", you might do something like:
1845 -------------------------------------------------
1846 $ git checkout -b mywork-new origin
1847 $ gitk origin..mywork &
1848 -------------------------------------------------
1850 And browse through the list of patches in the mywork branch using gitk,
1851 applying them (possibly in a different order) to mywork-new using
1852 cherry-pick, and possibly modifying them as you go using commit
1853 --amend.
1855 Another technique is to use git-format-patch to create a series of
1856 patches, then reset the state to before the patches:
1858 -------------------------------------------------
1859 $ git format-patch origin
1860 $ git reset --hard origin
1861 -------------------------------------------------
1863 Then modify, reorder, or eliminate patches as preferred before applying
1864 them again with gitlink:git-am[1].
1866 Other tools
1867 -----------
1869 There are numerous other tools, such as stgit, which exist for the
1870 purpose of maintaining a patch series. These are out of the scope of
1871 this manual.
1873 Problems with rewriting history
1874 -------------------------------
1876 The primary problem with rewriting the history of a branch has to do
1877 with merging. Suppose somebody fetches your branch and merges it into
1878 their branch, with a result something like this:
1880 o--o--O--o--o--o <-- origin
1881 \ \
1882 t--t--t--m <-- their branch:
1884 Then suppose you modify the last three commits:
1886 o--o--o <-- new head of origin
1887 /
1888 o--o--O--o--o--o <-- old head of origin
1890 If we examined all this history together in one repository, it will
1891 look like:
1893 o--o--o <-- new head of origin
1894 /
1895 o--o--O--o--o--o <-- old head of origin
1896 \ \
1897 t--t--t--m <-- their branch:
1899 Git has no way of knowing that the new head is an updated version of
1900 the old head; it treats this situation exactly the same as it would if
1901 two developers had independently done the work on the old and new heads
1902 in parallel. At this point, if someone attempts to merge the new head
1903 in to their branch, git will attempt to merge together the two (old and
1904 new) lines of development, instead of trying to replace the old by the
1905 new. The results are likely to be unexpected.
1907 You may still choose to publish branches whose history is rewritten,
1908 and it may be useful for others to be able to fetch those branches in
1909 order to examine or test them, but they should not attempt to pull such
1910 branches into their own work.
1912 For true distributed development that supports proper merging,
1913 published branches should never be rewritten.
1915 Advanced branch management
1916 ==========================
1918 Fetching individual branches
1919 ----------------------------
1921 Instead of using gitlink:git-remote[1], you can also choose just
1922 to update one branch at a time, and to store it locally under an
1923 arbitrary name:
1925 -------------------------------------------------
1926 $ git fetch origin todo:my-todo-work
1927 -------------------------------------------------
1929 The first argument, "origin", just tells git to fetch from the
1930 repository you originally cloned from. The second argument tells git
1931 to fetch the branch named "todo" from the remote repository, and to
1932 store it locally under the name refs/heads/my-todo-work.
1934 You can also fetch branches from other repositories; so
1936 -------------------------------------------------
1937 $ git fetch git://example.com/proj.git master:example-master
1938 -------------------------------------------------
1940 will create a new branch named "example-master" and store in it the
1941 branch named "master" from the repository at the given URL. If you
1942 already have a branch named example-master, it will attempt to
1943 "fast-forward" to the commit given by example.com's master branch. So
1944 next we explain what a fast-forward is:
1946 [[fast-forwards]]
1947 Understanding git history: fast-forwards
1948 ----------------------------------------
1950 In the previous example, when updating an existing branch, "git
1951 fetch" checks to make sure that the most recent commit on the remote
1952 branch is a descendant of the most recent commit on your copy of the
1953 branch before updating your copy of the branch to point at the new
1954 commit. Git calls this process a "fast forward".
1956 A fast forward looks something like this:
1958 o--o--o--o <-- old head of the branch
1959 \
1960 o--o--o <-- new head of the branch
1963 In some cases it is possible that the new head will *not* actually be
1964 a descendant of the old head. For example, the developer may have
1965 realized she made a serious mistake, and decided to backtrack,
1966 resulting in a situation like:
1968 o--o--o--o--a--b <-- old head of the branch
1969 \
1970 o--o--o <-- new head of the branch
1974 In this case, "git fetch" will fail, and print out a warning.
1976 In that case, you can still force git to update to the new head, as
1977 described in the following section. However, note that in the
1978 situation above this may mean losing the commits labeled "a" and "b",
1979 unless you've already created a reference of your own pointing to
1980 them.
1982 Forcing git fetch to do non-fast-forward updates
1983 ------------------------------------------------
1985 If git fetch fails because the new head of a branch is not a
1986 descendant of the old head, you may force the update with:
1988 -------------------------------------------------
1989 $ git fetch git://example.com/proj.git +master:refs/remotes/example/master
1990 -------------------------------------------------
1992 Note the addition of the "+" sign. Be aware that commits which the
1993 old version of example/master pointed at may be lost, as we saw in
1994 the previous section.
1996 Configuring remote branches
1997 ---------------------------
1999 We saw above that "origin" is just a shortcut to refer to the
2000 repository which you originally cloned from. This information is
2001 stored in git configuration variables, which you can see using
2002 gitlink:git-config[1]:
2004 -------------------------------------------------
2005 $ git config -l
2006 core.repositoryformatversion=0
2007 core.filemode=true
2008 core.logallrefupdates=true
2009 remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2010 remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2011 branch.master.remote=origin
2012 branch.master.merge=refs/heads/master
2013 -------------------------------------------------
2015 If there are other repositories that you also use frequently, you can
2016 create similar configuration options to save typing; for example,
2017 after
2019 -------------------------------------------------
2020 $ git config remote.example.url git://example.com/proj.git
2021 -------------------------------------------------
2023 then the following two commands will do the same thing:
2025 -------------------------------------------------
2026 $ git fetch git://example.com/proj.git master:refs/remotes/example/master
2027 $ git fetch example master:refs/remotes/example/master
2028 -------------------------------------------------
2030 Even better, if you add one more option:
2032 -------------------------------------------------
2033 $ git config remote.example.fetch master:refs/remotes/example/master
2034 -------------------------------------------------
2036 then the following commands will all do the same thing:
2038 -------------------------------------------------
2039 $ git fetch git://example.com/proj.git master:ref/remotes/example/master
2040 $ git fetch example master:ref/remotes/example/master
2041 $ git fetch example example/master
2042 $ git fetch example
2043 -------------------------------------------------
2045 You can also add a "+" to force the update each time:
2047 -------------------------------------------------
2048 $ git config remote.example.fetch +master:ref/remotes/example/master
2049 -------------------------------------------------
2051 Don't do this unless you're sure you won't mind "git fetch" possibly
2052 throwing away commits on mybranch.
2054 Also note that all of the above configuration can be performed by
2055 directly editing the file .git/config instead of using
2056 gitlink:git-config[1].
2058 See gitlink:git-config[1] for more details on the configuration
2059 options mentioned above.
2062 Git internals
2063 =============
2065 There are two object abstractions: the "object database", and the
2066 "current directory cache" aka "index".
2068 The Object Database
2069 -------------------
2071 The object database is literally just a content-addressable collection
2072 of objects. All objects are named by their content, which is
2073 approximated by the SHA1 hash of the object itself. Objects may refer
2074 to other objects (by referencing their SHA1 hash), and so you can
2075 build up a hierarchy of objects.
2077 All objects have a statically determined "type" aka "tag", which is
2078 determined at object creation time, and which identifies the format of
2079 the object (i.e. how it is used, and how it can refer to other
2080 objects). There are currently four different object types: "blob",
2081 "tree", "commit" and "tag".
2083 A "blob" object cannot refer to any other object, and is, like the type
2084 implies, a pure storage object containing some user data. It is used to
2085 actually store the file data, i.e. a blob object is associated with some
2086 particular version of some file.
2088 A "tree" object is an object that ties one or more "blob" objects into a
2089 directory structure. In addition, a tree object can refer to other tree
2090 objects, thus creating a directory hierarchy.
2092 A "commit" object ties such directory hierarchies together into
2093 a DAG of revisions - each "commit" is associated with exactly one tree
2094 (the directory hierarchy at the time of the commit). In addition, a
2095 "commit" refers to one or more "parent" commit objects that describe the
2096 history of how we arrived at that directory hierarchy.
2098 As a special case, a commit object with no parents is called the "root"
2099 object, and is the point of an initial project commit. Each project
2100 must have at least one root, and while you can tie several different
2101 root objects together into one project by creating a commit object which
2102 has two or more separate roots as its ultimate parents, that's probably
2103 just going to confuse people. So aim for the notion of "one root object
2104 per project", even if git itself does not enforce that.
2106 A "tag" object symbolically identifies and can be used to sign other
2107 objects. It contains the identifier and type of another object, a
2108 symbolic name (of course!) and, optionally, a signature.
2110 Regardless of object type, all objects share the following
2111 characteristics: they are all deflated with zlib, and have a header
2112 that not only specifies their type, but also provides size information
2113 about the data in the object. It's worth noting that the SHA1 hash
2114 that is used to name the object is the hash of the original data
2115 plus this header, so `sha1sum` 'file' does not match the object name
2116 for 'file'.
2117 (Historical note: in the dawn of the age of git the hash
2118 was the sha1 of the 'compressed' object.)
2120 As a result, the general consistency of an object can always be tested
2121 independently of the contents or the type of the object: all objects can
2122 be validated by verifying that (a) their hashes match the content of the
2123 file and (b) the object successfully inflates to a stream of bytes that
2124 forms a sequence of <ascii type without space> + <space> + <ascii decimal
2125 size> + <byte\0> + <binary object data>.
2127 The structured objects can further have their structure and
2128 connectivity to other objects verified. This is generally done with
2129 the `git-fsck` program, which generates a full dependency graph
2130 of all objects, and verifies their internal consistency (in addition
2131 to just verifying their superficial consistency through the hash).
2133 The object types in some more detail:
2135 Blob Object
2136 -----------
2138 A "blob" object is nothing but a binary blob of data, and doesn't
2139 refer to anything else. There is no signature or any other
2140 verification of the data, so while the object is consistent (it 'is'
2141 indexed by its sha1 hash, so the data itself is certainly correct), it
2142 has absolutely no other attributes. No name associations, no
2143 permissions. It is purely a blob of data (i.e. normally "file
2144 contents").
2146 In particular, since the blob is entirely defined by its data, if two
2147 files in a directory tree (or in multiple different versions of the
2148 repository) have the same contents, they will share the same blob
2149 object. The object is totally independent of its location in the
2150 directory tree, and renaming a file does not change the object that
2151 file is associated with in any way.
2153 A blob is typically created when gitlink:git-update-index[1]
2154 is run, and its data can be accessed by gitlink:git-cat-file[1].
2156 Tree Object
2157 -----------
2159 The next hierarchical object type is the "tree" object. A tree object
2160 is a list of mode/name/blob data, sorted by name. Alternatively, the
2161 mode data may specify a directory mode, in which case instead of
2162 naming a blob, that name is associated with another TREE object.
2164 Like the "blob" object, a tree object is uniquely determined by the
2165 set contents, and so two separate but identical trees will always
2166 share the exact same object. This is true at all levels, i.e. it's
2167 true for a "leaf" tree (which does not refer to any other trees, only
2168 blobs) as well as for a whole subdirectory.
2170 For that reason a "tree" object is just a pure data abstraction: it
2171 has no history, no signatures, no verification of validity, except
2172 that since the contents are again protected by the hash itself, we can
2173 trust that the tree is immutable and its contents never change.
2175 So you can trust the contents of a tree to be valid, the same way you
2176 can trust the contents of a blob, but you don't know where those
2177 contents 'came' from.
2179 Side note on trees: since a "tree" object is a sorted list of
2180 "filename+content", you can create a diff between two trees without
2181 actually having to unpack two trees. Just ignore all common parts,
2182 and your diff will look right. In other words, you can effectively
2183 (and efficiently) tell the difference between any two random trees by
2184 O(n) where "n" is the size of the difference, rather than the size of
2185 the tree.
2187 Side note 2 on trees: since the name of a "blob" depends entirely and
2188 exclusively on its contents (i.e. there are no names or permissions
2189 involved), you can see trivial renames or permission changes by
2190 noticing that the blob stayed the same. However, renames with data
2191 changes need a smarter "diff" implementation.
2193 A tree is created with gitlink:git-write-tree[1] and
2194 its data can be accessed by gitlink:git-ls-tree[1].
2195 Two trees can be compared with gitlink:git-diff-tree[1].
2197 Commit Object
2198 -------------
2200 The "commit" object is an object that introduces the notion of
2201 history into the picture. In contrast to the other objects, it
2202 doesn't just describe the physical state of a tree, it describes how
2203 we got there, and why.
2205 A "commit" is defined by the tree-object that it results in, the
2206 parent commits (zero, one or more) that led up to that point, and a
2207 comment on what happened. Again, a commit is not trusted per se:
2208 the contents are well-defined and "safe" due to the cryptographically
2209 strong signatures at all levels, but there is no reason to believe
2210 that the tree is "good" or that the merge information makes sense.
2211 The parents do not have to actually have any relationship with the
2212 result, for example.
2214 Note on commits: unlike real SCM's, commits do not contain
2215 rename information or file mode change information. All of that is
2216 implicit in the trees involved (the result tree, and the result trees
2217 of the parents), and describing that makes no sense in this idiotic
2218 file manager.
2220 A commit is created with gitlink:git-commit-tree[1] and
2221 its data can be accessed by gitlink:git-cat-file[1].
2223 Trust
2224 -----
2226 An aside on the notion of "trust". Trust is really outside the scope
2227 of "git", but it's worth noting a few things. First off, since
2228 everything is hashed with SHA1, you 'can' trust that an object is
2229 intact and has not been messed with by external sources. So the name
2230 of an object uniquely identifies a known state - just not a state that
2231 you may want to trust.
2233 Furthermore, since the SHA1 signature of a commit refers to the
2234 SHA1 signatures of the tree it is associated with and the signatures
2235 of the parent, a single named commit specifies uniquely a whole set
2236 of history, with full contents. You can't later fake any step of the
2237 way once you have the name of a commit.
2239 So to introduce some real trust in the system, the only thing you need
2240 to do is to digitally sign just 'one' special note, which includes the
2241 name of a top-level commit. Your digital signature shows others
2242 that you trust that commit, and the immutability of the history of
2243 commits tells others that they can trust the whole history.
2245 In other words, you can easily validate a whole archive by just
2246 sending out a single email that tells the people the name (SHA1 hash)
2247 of the top commit, and digitally sign that email using something
2248 like GPG/PGP.
2250 To assist in this, git also provides the tag object...
2252 Tag Object
2253 ----------
2255 Git provides the "tag" object to simplify creating, managing and
2256 exchanging symbolic and signed tokens. The "tag" object at its
2257 simplest simply symbolically identifies another object by containing
2258 the sha1, type and symbolic name.
2260 However it can optionally contain additional signature information
2261 (which git doesn't care about as long as there's less than 8k of
2262 it). This can then be verified externally to git.
2264 Note that despite the tag features, "git" itself only handles content
2265 integrity; the trust framework (and signature provision and
2266 verification) has to come from outside.
2268 A tag is created with gitlink:git-mktag[1],
2269 its data can be accessed by gitlink:git-cat-file[1],
2270 and the signature can be verified by
2271 gitlink:git-verify-tag[1].
2274 The "index" aka "Current Directory Cache"
2275 -----------------------------------------
2277 The index is a simple binary file, which contains an efficient
2278 representation of a virtual directory content at some random time. It
2279 does so by a simple array that associates a set of names, dates,
2280 permissions and content (aka "blob") objects together. The cache is
2281 always kept ordered by name, and names are unique (with a few very
2282 specific rules) at any point in time, but the cache has no long-term
2283 meaning, and can be partially updated at any time.
2285 In particular, the index certainly does not need to be consistent with
2286 the current directory contents (in fact, most operations will depend on
2287 different ways to make the index 'not' be consistent with the directory
2288 hierarchy), but it has three very important attributes:
2290 '(a) it can re-generate the full state it caches (not just the
2291 directory structure: it contains pointers to the "blob" objects so
2292 that it can regenerate the data too)'
2294 As a special case, there is a clear and unambiguous one-way mapping
2295 from a current directory cache to a "tree object", which can be
2296 efficiently created from just the current directory cache without
2297 actually looking at any other data. So a directory cache at any one
2298 time uniquely specifies one and only one "tree" object (but has
2299 additional data to make it easy to match up that tree object with what
2300 has happened in the directory)
2302 '(b) it has efficient methods for finding inconsistencies between that
2303 cached state ("tree object waiting to be instantiated") and the
2304 current state.'
2306 '(c) it can additionally efficiently represent information about merge
2307 conflicts between different tree objects, allowing each pathname to be
2308 associated with sufficient information about the trees involved that
2309 you can create a three-way merge between them.'
2311 Those are the three ONLY things that the directory cache does. It's a
2312 cache, and the normal operation is to re-generate it completely from a
2313 known tree object, or update/compare it with a live tree that is being
2314 developed. If you blow the directory cache away entirely, you generally
2315 haven't lost any information as long as you have the name of the tree
2316 that it described.
2318 At the same time, the index is at the same time also the
2319 staging area for creating new trees, and creating a new tree always
2320 involves a controlled modification of the index file. In particular,
2321 the index file can have the representation of an intermediate tree that
2322 has not yet been instantiated. So the index can be thought of as a
2323 write-back cache, which can contain dirty information that has not yet
2324 been written back to the backing store.
2328 The Workflow
2329 ------------
2331 Generally, all "git" operations work on the index file. Some operations
2332 work *purely* on the index file (showing the current state of the
2333 index), but most operations move data to and from the index file. Either
2334 from the database or from the working directory. Thus there are four
2335 main combinations:
2337 working directory -> index
2338 ~~~~~~~~~~~~~~~~~~~~~~~~~~
2340 You update the index with information from the working directory with
2341 the gitlink:git-update-index[1] command. You
2342 generally update the index information by just specifying the filename
2343 you want to update, like so:
2345 -------------------------------------------------
2346 $ git-update-index filename
2347 -------------------------------------------------
2349 but to avoid common mistakes with filename globbing etc, the command
2350 will not normally add totally new entries or remove old entries,
2351 i.e. it will normally just update existing cache entries.
2353 To tell git that yes, you really do realize that certain files no
2354 longer exist, or that new files should be added, you
2355 should use the `--remove` and `--add` flags respectively.
2357 NOTE! A `--remove` flag does 'not' mean that subsequent filenames will
2358 necessarily be removed: if the files still exist in your directory
2359 structure, the index will be updated with their new status, not
2360 removed. The only thing `--remove` means is that update-cache will be
2361 considering a removed file to be a valid thing, and if the file really
2362 does not exist any more, it will update the index accordingly.
2364 As a special case, you can also do `git-update-index --refresh`, which
2365 will refresh the "stat" information of each index to match the current
2366 stat information. It will 'not' update the object status itself, and
2367 it will only update the fields that are used to quickly test whether
2368 an object still matches its old backing store object.
2370 index -> object database
2371 ~~~~~~~~~~~~~~~~~~~~~~~~
2373 You write your current index file to a "tree" object with the program
2375 -------------------------------------------------
2376 $ git-write-tree
2377 -------------------------------------------------
2379 that doesn't come with any options - it will just write out the
2380 current index into the set of tree objects that describe that state,
2381 and it will return the name of the resulting top-level tree. You can
2382 use that tree to re-generate the index at any time by going in the
2383 other direction:
2385 object database -> index
2386 ~~~~~~~~~~~~~~~~~~~~~~~~
2388 You read a "tree" file from the object database, and use that to
2389 populate (and overwrite - don't do this if your index contains any
2390 unsaved state that you might want to restore later!) your current
2391 index. Normal operation is just
2393 -------------------------------------------------
2394 $ git-read-tree <sha1 of tree>
2395 -------------------------------------------------
2397 and your index file will now be equivalent to the tree that you saved
2398 earlier. However, that is only your 'index' file: your working
2399 directory contents have not been modified.
2401 index -> working directory
2402 ~~~~~~~~~~~~~~~~~~~~~~~~~~
2404 You update your working directory from the index by "checking out"
2405 files. This is not a very common operation, since normally you'd just
2406 keep your files updated, and rather than write to your working
2407 directory, you'd tell the index files about the changes in your
2408 working directory (i.e. `git-update-index`).
2410 However, if you decide to jump to a new version, or check out somebody
2411 else's version, or just restore a previous tree, you'd populate your
2412 index file with read-tree, and then you need to check out the result
2413 with
2415 -------------------------------------------------
2416 $ git-checkout-index filename
2417 -------------------------------------------------
2419 or, if you want to check out all of the index, use `-a`.
2421 NOTE! git-checkout-index normally refuses to overwrite old files, so
2422 if you have an old version of the tree already checked out, you will
2423 need to use the "-f" flag ('before' the "-a" flag or the filename) to
2424 'force' the checkout.
2427 Finally, there are a few odds and ends which are not purely moving
2428 from one representation to the other:
2430 Tying it all together
2431 ~~~~~~~~~~~~~~~~~~~~~
2433 To commit a tree you have instantiated with "git-write-tree", you'd
2434 create a "commit" object that refers to that tree and the history
2435 behind it - most notably the "parent" commits that preceded it in
2436 history.
2438 Normally a "commit" has one parent: the previous state of the tree
2439 before a certain change was made. However, sometimes it can have two
2440 or more parent commits, in which case we call it a "merge", due to the
2441 fact that such a commit brings together ("merges") two or more
2442 previous states represented by other commits.
2444 In other words, while a "tree" represents a particular directory state
2445 of a working directory, a "commit" represents that state in "time",
2446 and explains how we got there.
2448 You create a commit object by giving it the tree that describes the
2449 state at the time of the commit, and a list of parents:
2451 -------------------------------------------------
2452 $ git-commit-tree <tree> -p <parent> [-p <parent2> ..]
2453 -------------------------------------------------
2455 and then giving the reason for the commit on stdin (either through
2456 redirection from a pipe or file, or by just typing it at the tty).
2458 git-commit-tree will return the name of the object that represents
2459 that commit, and you should save it away for later use. Normally,
2460 you'd commit a new `HEAD` state, and while git doesn't care where you
2461 save the note about that state, in practice we tend to just write the
2462 result to the file pointed at by `.git/HEAD`, so that we can always see
2463 what the last committed state was.
2465 Here is an ASCII art by Jon Loeliger that illustrates how
2466 various pieces fit together.
2468 ------------
2470 commit-tree
2471 commit obj
2472 +----+
2473 | |
2474 | |
2475 V V
2476 +-----------+
2477 | Object DB |
2478 | Backing |
2479 | Store |
2480 +-----------+
2481 ^
2482 write-tree | |
2483 tree obj | |
2484 | | read-tree
2485 | | tree obj
2486 V
2487 +-----------+
2488 | Index |
2489 | "cache" |
2490 +-----------+
2491 update-index ^
2492 blob obj | |
2493 | |
2494 checkout-index -u | | checkout-index
2495 stat | | blob obj
2496 V
2497 +-----------+
2498 | Working |
2499 | Directory |
2500 +-----------+
2502 ------------
2505 Examining the data
2506 ------------------
2508 You can examine the data represented in the object database and the
2509 index with various helper tools. For every object, you can use
2510 gitlink:git-cat-file[1] to examine details about the
2511 object:
2513 -------------------------------------------------
2514 $ git-cat-file -t <objectname>
2515 -------------------------------------------------
2517 shows the type of the object, and once you have the type (which is
2518 usually implicit in where you find the object), you can use
2520 -------------------------------------------------
2521 $ git-cat-file blob|tree|commit|tag <objectname>
2522 -------------------------------------------------
2524 to show its contents. NOTE! Trees have binary content, and as a result
2525 there is a special helper for showing that content, called
2526 `git-ls-tree`, which turns the binary content into a more easily
2527 readable form.
2529 It's especially instructive to look at "commit" objects, since those
2530 tend to be small and fairly self-explanatory. In particular, if you
2531 follow the convention of having the top commit name in `.git/HEAD`,
2532 you can do
2534 -------------------------------------------------
2535 $ git-cat-file commit HEAD
2536 -------------------------------------------------
2538 to see what the top commit was.
2540 Merging multiple trees
2541 ----------------------
2543 Git helps you do a three-way merge, which you can expand to n-way by
2544 repeating the merge procedure arbitrary times until you finally
2545 "commit" the state. The normal situation is that you'd only do one
2546 three-way merge (two parents), and commit it, but if you like to, you
2547 can do multiple parents in one go.
2549 To do a three-way merge, you need the two sets of "commit" objects
2550 that you want to merge, use those to find the closest common parent (a
2551 third "commit" object), and then use those commit objects to find the
2552 state of the directory ("tree" object) at these points.
2554 To get the "base" for the merge, you first look up the common parent
2555 of two commits with
2557 -------------------------------------------------
2558 $ git-merge-base <commit1> <commit2>
2559 -------------------------------------------------
2561 which will return you the commit they are both based on. You should
2562 now look up the "tree" objects of those commits, which you can easily
2563 do with (for example)
2565 -------------------------------------------------
2566 $ git-cat-file commit <commitname> | head -1
2567 -------------------------------------------------
2569 since the tree object information is always the first line in a commit
2570 object.
2572 Once you know the three trees you are going to merge (the one
2573 "original" tree, aka the common case, and the two "result" trees, aka
2574 the branches you want to merge), you do a "merge" read into the
2575 index. This will complain if it has to throw away your old index contents, so you should
2576 make sure that you've committed those - in fact you would normally
2577 always do a merge against your last commit (which should thus match
2578 what you have in your current index anyway).
2580 To do the merge, do
2582 -------------------------------------------------
2583 $ git-read-tree -m -u <origtree> <yourtree> <targettree>
2584 -------------------------------------------------
2586 which will do all trivial merge operations for you directly in the
2587 index file, and you can just write the result out with
2588 `git-write-tree`.
2591 Merging multiple trees, continued
2592 ---------------------------------
2594 Sadly, many merges aren't trivial. If there are files that have
2595 been added.moved or removed, or if both branches have modified the
2596 same file, you will be left with an index tree that contains "merge
2597 entries" in it. Such an index tree can 'NOT' be written out to a tree
2598 object, and you will have to resolve any such merge clashes using
2599 other tools before you can write out the result.
2601 You can examine such index state with `git-ls-files --unmerged`
2602 command. An example:
2604 ------------------------------------------------
2605 $ git-read-tree -m $orig HEAD $target
2606 $ git-ls-files --unmerged
2607 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c
2608 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c
2609 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c
2610 ------------------------------------------------
2612 Each line of the `git-ls-files --unmerged` output begins with
2613 the blob mode bits, blob SHA1, 'stage number', and the
2614 filename. The 'stage number' is git's way to say which tree it
2615 came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD`
2616 tree, and stage3 `$target` tree.
2618 Earlier we said that trivial merges are done inside
2619 `git-read-tree -m`. For example, if the file did not change
2620 from `$orig` to `HEAD` nor `$target`, or if the file changed
2621 from `$orig` to `HEAD` and `$orig` to `$target` the same way,
2622 obviously the final outcome is what is in `HEAD`. What the
2623 above example shows is that file `hello.c` was changed from
2624 `$orig` to `HEAD` and `$orig` to `$target` in a different way.
2625 You could resolve this by running your favorite 3-way merge
2626 program, e.g. `diff3` or `merge`, on the blob objects from
2627 these three stages yourself, like this:
2629 ------------------------------------------------
2630 $ git-cat-file blob 263414f... >hello.c~1
2631 $ git-cat-file blob 06fa6a2... >hello.c~2
2632 $ git-cat-file blob cc44c73... >hello.c~3
2633 $ merge hello.c~2 hello.c~1 hello.c~3
2634 ------------------------------------------------
2636 This would leave the merge result in `hello.c~2` file, along
2637 with conflict markers if there are conflicts. After verifying
2638 the merge result makes sense, you can tell git what the final
2639 merge result for this file is by:
2641 -------------------------------------------------
2642 $ mv -f hello.c~2 hello.c
2643 $ git-update-index hello.c
2644 -------------------------------------------------
2646 When a path is in unmerged state, running `git-update-index` for
2647 that path tells git to mark the path resolved.
2649 The above is the description of a git merge at the lowest level,
2650 to help you understand what conceptually happens under the hood.
2651 In practice, nobody, not even git itself, uses three `git-cat-file`
2652 for this. There is `git-merge-index` program that extracts the
2653 stages to temporary files and calls a "merge" script on it:
2655 -------------------------------------------------
2656 $ git-merge-index git-merge-one-file hello.c
2657 -------------------------------------------------
2659 and that is what higher level `git resolve` is implemented with.
2661 How git stores objects efficiently: pack files
2662 ----------------------------------------------
2664 We've seen how git stores each object in a file named after the
2665 object's SHA1 hash.
2667 Unfortunately this system becomes inefficient once a project has a
2668 lot of objects. Try this on an old project:
2670 ------------------------------------------------
2671 $ git count-objects
2672 6930 objects, 47620 kilobytes
2673 ------------------------------------------------
2675 The first number is the number of objects which are kept in
2676 individual files. The second is the amount of space taken up by
2677 those "loose" objects.
2679 You can save space and make git faster by moving these loose objects in
2680 to a "pack file", which stores a group of objects in an efficient
2681 compressed format; the details of how pack files are formatted can be
2682 found in link:technical/pack-format.txt[technical/pack-format.txt].
2684 To put the loose objects into a pack, just run git repack:
2686 ------------------------------------------------
2687 $ git repack
2688 Generating pack...
2689 Done counting 6020 objects.
2690 Deltifying 6020 objects.
2691 100% (6020/6020) done
2692 Writing 6020 objects.
2693 100% (6020/6020) done
2694 Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
2695 Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
2696 ------------------------------------------------
2698 You can then run
2700 ------------------------------------------------
2701 $ git prune
2702 ------------------------------------------------
2704 to remove any of the "loose" objects that are now contained in the
2705 pack. This will also remove any unreferenced objects (which may be
2706 created when, for example, you use "git reset" to remove a commit).
2707 You can verify that the loose objects are gone by looking at the
2708 .git/objects directory or by running
2710 ------------------------------------------------
2711 $ git count-objects
2712 0 objects, 0 kilobytes
2713 ------------------------------------------------
2715 Although the object files are gone, any commands that refer to those
2716 objects will work exactly as they did before.
2718 The gitlink:git-gc[1] command performs packing, pruning, and more for
2719 you, so is normally the only high-level command you need.
2721 [[dangling-objects]]
2722 Dangling objects
2723 ^^^^^^^^^^^^^^^^
2725 The gitlink:git-fsck[1] command will sometimes complain about dangling
2726 objects. They are not a problem.
2728 The most common cause of dangling objects is that you've rebased a branch, or
2729 you have pulled from somebody else who rebased a branch--see
2730 <<cleaning-up-history>>. In that case, the old head of the original branch
2731 still exists, as does obviously everything it pointed to. The branch pointer
2732 itself just doesn't, since you replaced it with another one.
2734 There are also other situations too that cause dangling objects. For example, a
2735 "dangling blob" may arise because you did a "git add" of a file, but then,
2736 before you actually committed it and made it part of the bigger picture, you
2737 changed something else in that file and committed that *updated* thing - the
2738 old state that you added originally ends up not being pointed to by any
2739 commit or tree, so it's now a dangling blob object.
2741 Similarly, when the "recursive" merge strategy runs, and finds that there
2742 are criss-cross merges and thus more than one merge base (which is fairly
2743 unusual, but it does happen), it will generate one temporary midway tree
2744 (or possibly even more, if you had lots of criss-crossing merges and
2745 more than two merge bases) as a temporary internal merge base, and again,
2746 those are real objects, but the end result will not end up pointing to
2747 them, so they end up "dangling" in your repository.
2749 Generally, dangling objects aren't anything to worry about. They can even
2750 be very useful: if you screw something up, the dangling objects can be how
2751 you recover your old tree (say, you did a rebase, and realized that you
2752 really didn't want to - you can look at what dangling objects you have,
2753 and decide to reset your head to some old dangling state).
2755 For commits, the most useful thing to do with dangling objects tends to be
2756 to do a simple
2758 ------------------------------------------------
2759 $ gitk <dangling-commit-sha-goes-here> --not --all
2760 ------------------------------------------------
2762 which means exactly what it sounds like: it says that you want to see the
2763 commit history that is described by the dangling commit(s), but you do NOT
2764 want to see the history that is described by all your branches and tags
2765 (which are the things you normally reach). That basically shows you in a
2766 nice way what the dangling commit was (and notice that it might not be
2767 just one commit: we only report the "tip of the line" as being dangling,
2768 but there might be a whole deep and complex commit history that has gotten
2769 dropped - rebasing will do that).
2771 For blobs and trees, you can't do the same, but you can examine them. You
2772 can just do
2774 ------------------------------------------------
2775 $ git show <dangling-blob/tree-sha-goes-here>
2776 ------------------------------------------------
2778 to show what the contents of the blob were (or, for a tree, basically what
2779 the "ls" for that directory was), and that may give you some idea of what
2780 the operation was that left that dangling object.
2782 Usually, dangling blobs and trees aren't very interesting. They're almost
2783 always the result of either being a half-way mergebase (the blob will
2784 often even have the conflict markers from a merge in it, if you have had
2785 conflicting merges that you fixed up by hand), or simply because you
2786 interrupted a "git fetch" with ^C or something like that, leaving _some_
2787 of the new objects in the object database, but just dangling and useless.
2789 Anyway, once you are sure that you're not interested in any dangling
2790 state, you can just prune all unreachable objects:
2792 ------------------------------------------------
2793 $ git prune
2794 ------------------------------------------------
2796 and they'll be gone. But you should only run "git prune" on a quiescent
2797 repository - it's kind of like doing a filesystem fsck recovery: you don't
2798 want to do that while the filesystem is mounted.
2800 (The same is true of "git-fsck" itself, btw - but since
2801 git-fsck never actually *changes* the repository, it just reports
2802 on what it found, git-fsck itself is never "dangerous" to run.
2803 Running it while somebody is actually changing the repository can cause
2804 confusing and scary messages, but it won't actually do anything bad. In
2805 contrast, running "git prune" while somebody is actively changing the
2806 repository is a *BAD* idea).
2808 Glossary of git terms
2809 =====================
2811 include::glossary.txt[]
2813 Notes and todo list for this manual
2814 ===================================
2816 This is a work in progress.
2818 The basic requirements:
2819 - It must be readable in order, from beginning to end, by
2820 someone intelligent with a basic grasp of the unix
2821 commandline, but without any special knowledge of git. If
2822 necessary, any other prerequisites should be specifically
2823 mentioned as they arise.
2824 - Whenever possible, section headings should clearly describe
2825 the task they explain how to do, in language that requires
2826 no more knowledge than necessary: for example, "importing
2827 patches into a project" rather than "the git-am command"
2829 Think about how to create a clear chapter dependency graph that will
2830 allow people to get to important topics without necessarily reading
2831 everything in between.
2833 Scan Documentation/ for other stuff left out; in particular:
2834 howto's
2835 README
2836 some of technical/?
2837 hooks
2838 etc.
2840 Scan email archives for other stuff left out
2842 Scan man pages to see if any assume more background than this manual
2843 provides.
2845 Simplify beginning by suggesting disconnected head instead of
2846 temporary branch creation?
2848 Explain how to refer to file stages in the "how to resolve a merge"
2849 section: diff -1, -2, -3, --ours, --theirs :1:/path notation. The
2850 "git ls-files --unmerged --stage" thing is sorta useful too,
2851 actually. And note gitk --merge.
2853 Add more good examples. Entire sections of just cookbook examples
2854 might be a good idea; maybe make an "advanced examples" section a
2855 standard end-of-chapter section?
2857 Include cross-references to the glossary, where appropriate.
2859 To document:
2860 reflogs, git reflog expire
2861 shallow clones?? See draft 1.5.0 release notes for some documentation.