99cb80878b3b710babd00b401dc41d73c34c695b
1 Git User's Manual (for version 1.5.3 or newer)
2 ______________________________________________
5 Git is a fast distributed revision control system.
7 This manual is designed to be readable by someone with basic UNIX
8 command-line skills, but no previous knowledge of git.
10 <<repositories-and-branches>> and <<exploring-git-history>> explain how
11 to fetch and study a project using git--read these chapters to learn how
12 to build and test a particular version of a software project, search for
13 regressions, and so on.
15 People needing to do actual development will also want to read
16 <<Developing-With-git>> and <<sharing-development>>.
18 Further chapters cover more specialized topics.
20 Comprehensive reference documentation is available through the man
21 pages. For a command such as "git clone <repo>", just use
23 ------------------------------------------------
24 $ man git-clone
25 ------------------------------------------------
27 See also <<git-quick-start>> for a brief overview of git commands,
28 without any explanation.
30 Finally, see <<todo>> for ways that you can help make this manual more
31 complete.
34 [[repositories-and-branches]]
35 Repositories and Branches
36 =========================
38 [[how-to-get-a-git-repository]]
39 How to get a git repository
40 ---------------------------
42 It will be useful to have a git repository to experiment with as you
43 read this manual.
45 The best way to get one is by using the linkgit:git-clone[1] command to
46 download a copy of an existing repository. If you don't already have a
47 project in mind, here are some interesting examples:
49 ------------------------------------------------
50 # git itself (approx. 10MB download):
51 $ git clone git://git.kernel.org/pub/scm/git/git.git
52 # the linux kernel (approx. 150MB download):
53 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
54 ------------------------------------------------
56 The initial clone may be time-consuming for a large project, but you
57 will only need to clone once.
59 The clone command creates a new directory named after the project ("git"
60 or "linux-2.6" in the examples above). After you cd into this
61 directory, you will see that it contains a copy of the project files,
62 called the <<def_working_tree,working tree>>, together with a special
63 top-level directory named ".git", which contains all the information
64 about the history of the project.
66 [[how-to-check-out]]
67 How to check out a different version of a project
68 -------------------------------------------------
70 Git is best thought of as a tool for storing the history of a collection
71 of files. It stores the history as a compressed collection of
72 interrelated snapshots of the project's contents. In git each such
73 version is called a <<def_commit,commit>>.
75 Those snapshots aren't necessarily all arranged in a single line from
76 oldest to newest; instead, work may simultaneously proceed along
77 parallel lines of development, called <<def_branch,branches>>, which may
78 merge and diverge.
80 A single git repository can track development on multiple branches. It
81 does this by keeping a list of <<def_head,heads>> which reference the
82 latest commit on each branch; the linkgit:git-branch[1] command shows
83 you the list of branch heads:
85 ------------------------------------------------
86 $ git branch
87 * master
88 ------------------------------------------------
90 A freshly cloned repository contains a single branch head, by default
91 named "master", with the working directory initialized to the state of
92 the project referred to by that branch head.
94 Most projects also use <<def_tag,tags>>. Tags, like heads, are
95 references into the project's history, and can be listed using the
96 linkgit:git-tag[1] command:
98 ------------------------------------------------
99 $ git tag -l
100 v2.6.11
101 v2.6.11-tree
102 v2.6.12
103 v2.6.12-rc2
104 v2.6.12-rc3
105 v2.6.12-rc4
106 v2.6.12-rc5
107 v2.6.12-rc6
108 v2.6.13
109 ...
110 ------------------------------------------------
112 Tags are expected to always point at the same version of a project,
113 while heads are expected to advance as development progresses.
115 Create a new branch head pointing to one of these versions and check it
116 out using linkgit:git-checkout[1]:
118 ------------------------------------------------
119 $ git checkout -b new v2.6.13
120 ------------------------------------------------
122 The working directory then reflects the contents that the project had
123 when it was tagged v2.6.13, and linkgit:git-branch[1] shows two
124 branches, with an asterisk marking the currently checked-out branch:
126 ------------------------------------------------
127 $ git branch
128 master
129 * new
130 ------------------------------------------------
132 If you decide that you'd rather see version 2.6.17, you can modify
133 the current branch to point at v2.6.17 instead, with
135 ------------------------------------------------
136 $ git reset --hard v2.6.17
137 ------------------------------------------------
139 Note that if the current branch head was your only reference to a
140 particular point in history, then resetting that branch may leave you
141 with no way to find the history it used to point to; so use this command
142 carefully.
144 [[understanding-commits]]
145 Understanding History: Commits
146 ------------------------------
148 Every change in the history of a project is represented by a commit.
149 The linkgit:git-show[1] command shows the most recent commit on the
150 current branch:
152 ------------------------------------------------
153 $ git show
154 commit 17cf781661e6d38f737f15f53ab552f1e95960d7
155 Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)>
156 Date: Tue Apr 19 14:11:06 2005 -0700
158 Remove duplicate getenv(DB_ENVIRONMENT) call
160 Noted by Tony Luck.
162 diff --git a/init-db.c b/init-db.c
163 index 65898fa..b002dc6 100644
164 --- a/init-db.c
165 +++ b/init-db.c
166 @@ -7,7 +7,7 @@
168 int main(int argc, char **argv)
169 {
170 - char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
171 + char *sha1_dir, *path;
172 int len, i;
174 if (mkdir(".git", 0755) < 0) {
175 ------------------------------------------------
177 As you can see, a commit shows who made the latest change, what they
178 did, and why.
180 Every commit has a 40-hexdigit id, sometimes called the "object name" or the
181 "SHA1 id", shown on the first line of the "git-show" output. You can usually
182 refer to a commit by a shorter name, such as a tag or a branch name, but this
183 longer name can also be useful. Most importantly, it is a globally unique
184 name for this commit: so if you tell somebody else the object name (for
185 example in email), then you are guaranteed that name will refer to the same
186 commit in their repository that it does in yours (assuming their repository
187 has that commit at all). Since the object name is computed as a hash over the
188 contents of the commit, you are guaranteed that the commit can never change
189 without its name also changing.
191 In fact, in <<git-concepts>> we shall see that everything stored in git
192 history, including file data and directory contents, is stored in an object
193 with a name that is a hash of its contents.
195 [[understanding-reachability]]
196 Understanding history: commits, parents, and reachability
197 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
199 Every commit (except the very first commit in a project) also has a
200 parent commit which shows what happened before this commit.
201 Following the chain of parents will eventually take you back to the
202 beginning of the project.
204 However, the commits do not form a simple list; git allows lines of
205 development to diverge and then reconverge, and the point where two
206 lines of development reconverge is called a "merge". The commit
207 representing a merge can therefore have more than one parent, with
208 each parent representing the most recent commit on one of the lines
209 of development leading to that point.
211 The best way to see how this works is using the linkgit:gitk[1]
212 command; running gitk now on a git repository and looking for merge
213 commits will help understand how the git organizes history.
215 In the following, we say that commit X is "reachable" from commit Y
216 if commit X is an ancestor of commit Y. Equivalently, you could say
217 that Y is a descendant of X, or that there is a chain of parents
218 leading from commit Y to commit X.
220 [[history-diagrams]]
221 Understanding history: History diagrams
222 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
224 We will sometimes represent git history using diagrams like the one
225 below. Commits are shown as "o", and the links between them with
226 lines drawn with - / and \. Time goes left to right:
229 ................................................
230 o--o--o <-- Branch A
231 /
232 o--o--o <-- master
233 \
234 o--o--o <-- Branch B
235 ................................................
237 If we need to talk about a particular commit, the character "o" may
238 be replaced with another letter or number.
240 [[what-is-a-branch]]
241 Understanding history: What is a branch?
242 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
244 When we need to be precise, we will use the word "branch" to mean a line
245 of development, and "branch head" (or just "head") to mean a reference
246 to the most recent commit on a branch. In the example above, the branch
247 head named "A" is a pointer to one particular commit, but we refer to
248 the line of three commits leading up to that point as all being part of
249 "branch A".
251 However, when no confusion will result, we often just use the term
252 "branch" both for branches and for branch heads.
254 [[manipulating-branches]]
255 Manipulating branches
256 ---------------------
258 Creating, deleting, and modifying branches is quick and easy; here's
259 a summary of the commands:
261 git branch::
262 list all branches
263 git branch <branch>::
264 create a new branch named <branch>, referencing the same
265 point in history as the current branch
266 git branch <branch> <start-point>::
267 create a new branch named <branch>, referencing
268 <start-point>, which may be specified any way you like,
269 including using a branch name or a tag name
270 git branch -d <branch>::
271 delete the branch <branch>; if the branch you are deleting
272 points to a commit which is not reachable from the current
273 branch, this command will fail with a warning.
274 git branch -D <branch>::
275 even if the branch points to a commit not reachable
276 from the current branch, you may know that that commit
277 is still reachable from some other branch or tag. In that
278 case it is safe to use this command to force git to delete
279 the branch.
280 git checkout <branch>::
281 make the current branch <branch>, updating the working
282 directory to reflect the version referenced by <branch>
283 git checkout -b <new> <start-point>::
284 create a new branch <new> referencing <start-point>, and
285 check it out.
287 The special symbol "HEAD" can always be used to refer to the current
288 branch. In fact, git uses a file named "HEAD" in the .git directory to
289 remember which branch is current:
291 ------------------------------------------------
292 $ cat .git/HEAD
293 ref: refs/heads/master
294 ------------------------------------------------
296 [[detached-head]]
297 Examining an old version without creating a new branch
298 ------------------------------------------------------
300 The git-checkout command normally expects a branch head, but will also
301 accept an arbitrary commit; for example, you can check out the commit
302 referenced by a tag:
304 ------------------------------------------------
305 $ git checkout v2.6.17
306 Note: moving to "v2.6.17" which isn't a local branch
307 If you want to create a new branch from this checkout, you may do so
308 (now or later) by using -b with the checkout command again. Example:
309 git checkout -b <new_branch_name>
310 HEAD is now at 427abfa... Linux v2.6.17
311 ------------------------------------------------
313 The HEAD then refers to the SHA1 of the commit instead of to a branch,
314 and git branch shows that you are no longer on a branch:
316 ------------------------------------------------
317 $ cat .git/HEAD
318 427abfa28afedffadfca9dd8b067eb6d36bac53f
319 $ git branch
320 * (no branch)
321 master
322 ------------------------------------------------
324 In this case we say that the HEAD is "detached".
326 This is an easy way to check out a particular version without having to
327 make up a name for the new branch. You can still create a new branch
328 (or tag) for this version later if you decide to.
330 [[examining-remote-branches]]
331 Examining branches from a remote repository
332 -------------------------------------------
334 The "master" branch that was created at the time you cloned is a copy
335 of the HEAD in the repository that you cloned from. That repository
336 may also have had other branches, though, and your local repository
337 keeps branches which track each of those remote branches, which you
338 can view using the "-r" option to linkgit:git-branch[1]:
340 ------------------------------------------------
341 $ git branch -r
342 origin/HEAD
343 origin/html
344 origin/maint
345 origin/man
346 origin/master
347 origin/next
348 origin/pu
349 origin/todo
350 ------------------------------------------------
352 You cannot check out these remote-tracking branches, but you can
353 examine them on a branch of your own, just as you would a tag:
355 ------------------------------------------------
356 $ git checkout -b my-todo-copy origin/todo
357 ------------------------------------------------
359 Note that the name "origin" is just the name that git uses by default
360 to refer to the repository that you cloned from.
362 [[how-git-stores-references]]
363 Naming branches, tags, and other references
364 -------------------------------------------
366 Branches, remote-tracking branches, and tags are all references to
367 commits. All references are named with a slash-separated path name
368 starting with "refs"; the names we've been using so far are actually
369 shorthand:
371 - The branch "test" is short for "refs/heads/test".
372 - The tag "v2.6.18" is short for "refs/tags/v2.6.18".
373 - "origin/master" is short for "refs/remotes/origin/master".
375 The full name is occasionally useful if, for example, there ever
376 exists a tag and a branch with the same name.
378 (Newly created refs are actually stored in the .git/refs directory,
379 under the path given by their name. However, for efficiency reasons
380 they may also be packed together in a single file; see
381 linkgit:git-pack-refs[1]).
383 As another useful shortcut, the "HEAD" of a repository can be referred
384 to just using the name of that repository. So, for example, "origin"
385 is usually a shortcut for the HEAD branch in the repository "origin".
387 For the complete list of paths which git checks for references, and
388 the order it uses to decide which to choose when there are multiple
389 references with the same shorthand name, see the "SPECIFYING
390 REVISIONS" section of linkgit:git-rev-parse[1].
392 [[Updating-a-repository-With-git-fetch]]
393 Updating a repository with git-fetch
394 ------------------------------------
396 Eventually the developer cloned from will do additional work in her
397 repository, creating new commits and advancing the branches to point
398 at the new commits.
400 The command "git fetch", with no arguments, will update all of the
401 remote-tracking branches to the latest version found in her
402 repository. It will not touch any of your own branches--not even the
403 "master" branch that was created for you on clone.
405 [[fetching-branches]]
406 Fetching branches from other repositories
407 -----------------------------------------
409 You can also track branches from repositories other than the one you
410 cloned from, using linkgit:git-remote[1]:
412 -------------------------------------------------
413 $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
414 $ git fetch linux-nfs
415 * refs/remotes/linux-nfs/master: storing branch 'master' ...
416 commit: bf81b46
417 -------------------------------------------------
419 New remote-tracking branches will be stored under the shorthand name
420 that you gave "git-remote add", in this case linux-nfs:
422 -------------------------------------------------
423 $ git branch -r
424 linux-nfs/master
425 origin/master
426 -------------------------------------------------
428 If you run "git fetch <remote>" later, the tracking branches for the
429 named <remote> will be updated.
431 If you examine the file .git/config, you will see that git has added
432 a new stanza:
434 -------------------------------------------------
435 $ cat .git/config
436 ...
437 [remote "linux-nfs"]
438 url = git://linux-nfs.org/pub/nfs-2.6.git
439 fetch = +refs/heads/*:refs/remotes/linux-nfs/*
440 ...
441 -------------------------------------------------
443 This is what causes git to track the remote's branches; you may modify
444 or delete these configuration options by editing .git/config with a
445 text editor. (See the "CONFIGURATION FILE" section of
446 linkgit:git-config[1] for details.)
448 [[exploring-git-history]]
449 Exploring git history
450 =====================
452 Git is best thought of as a tool for storing the history of a
453 collection of files. It does this by storing compressed snapshots of
454 the contents of a file hierarchy, together with "commits" which show
455 the relationships between these snapshots.
457 Git provides extremely flexible and fast tools for exploring the
458 history of a project.
460 We start with one specialized tool that is useful for finding the
461 commit that introduced a bug into a project.
463 [[using-bisect]]
464 How to use bisect to find a regression
465 --------------------------------------
467 Suppose version 2.6.18 of your project worked, but the version at
468 "master" crashes. Sometimes the best way to find the cause of such a
469 regression is to perform a brute-force search through the project's
470 history to find the particular commit that caused the problem. The
471 linkgit:git-bisect[1] command can help you do this:
473 -------------------------------------------------
474 $ git bisect start
475 $ git bisect good v2.6.18
476 $ git bisect bad master
477 Bisecting: 3537 revisions left to test after this
478 [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
479 -------------------------------------------------
481 If you run "git branch" at this point, you'll see that git has
482 temporarily moved you in "(no branch)". HEAD is now detached from any
483 branch and points directly to a commit (with commit id 65934...) that
484 is reachable from "master" but not from v2.6.18. Compile and test it,
485 and see whether it crashes. Assume it does crash. Then:
487 -------------------------------------------------
488 $ git bisect bad
489 Bisecting: 1769 revisions left to test after this
490 [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
491 -------------------------------------------------
493 checks out an older version. Continue like this, telling git at each
494 stage whether the version it gives you is good or bad, and notice
495 that the number of revisions left to test is cut approximately in
496 half each time.
498 After about 13 tests (in this case), it will output the commit id of
499 the guilty commit. You can then examine the commit with
500 linkgit:git-show[1], find out who wrote it, and mail them your bug
501 report with the commit id. Finally, run
503 -------------------------------------------------
504 $ git bisect reset
505 -------------------------------------------------
507 to return you to the branch you were on before.
509 Note that the version which git-bisect checks out for you at each
510 point is just a suggestion, and you're free to try a different
511 version if you think it would be a good idea. For example,
512 occasionally you may land on a commit that broke something unrelated;
513 run
515 -------------------------------------------------
516 $ git bisect visualize
517 -------------------------------------------------
519 which will run gitk and label the commit it chose with a marker that
520 says "bisect". Choose a safe-looking commit nearby, note its commit
521 id, and check it out with:
523 -------------------------------------------------
524 $ git reset --hard fb47ddb2db...
525 -------------------------------------------------
527 then test, run "bisect good" or "bisect bad" as appropriate, and
528 continue.
530 Instead of "git bisect visualize" and then "git reset --hard
531 fb47ddb2db...", you might just want to tell git that you want to skip
532 the current commit:
534 -------------------------------------------------
535 $ git bisect skip
536 -------------------------------------------------
538 In this case, though, git may not eventually be able to tell the first
539 bad one between some first skipped commits and a later bad commit.
541 There are also ways to automate the bisecting process if you have a
542 test script that can tell a good from a bad commit. See
543 linkgit:git-bisect[1] for more information about this and other "git
544 bisect" features.
546 [[naming-commits]]
547 Naming commits
548 --------------
550 We have seen several ways of naming commits already:
552 - 40-hexdigit object name
553 - branch name: refers to the commit at the head of the given
554 branch
555 - tag name: refers to the commit pointed to by the given tag
556 (we've seen branches and tags are special cases of
557 <<how-git-stores-references,references>>).
558 - HEAD: refers to the head of the current branch
560 There are many more; see the "SPECIFYING REVISIONS" section of the
561 linkgit:git-rev-parse[1] man page for the complete list of ways to
562 name revisions. Some examples:
564 -------------------------------------------------
565 $ git show fb47ddb2 # the first few characters of the object name
566 # are usually enough to specify it uniquely
567 $ git show HEAD^ # the parent of the HEAD commit
568 $ git show HEAD^^ # the grandparent
569 $ git show HEAD~4 # the great-great-grandparent
570 -------------------------------------------------
572 Recall that merge commits may have more than one parent; by default,
573 ^ and ~ follow the first parent listed in the commit, but you can
574 also choose:
576 -------------------------------------------------
577 $ git show HEAD^1 # show the first parent of HEAD
578 $ git show HEAD^2 # show the second parent of HEAD
579 -------------------------------------------------
581 In addition to HEAD, there are several other special names for
582 commits:
584 Merges (to be discussed later), as well as operations such as
585 git-reset, which change the currently checked-out commit, generally
586 set ORIG_HEAD to the value HEAD had before the current operation.
588 The git-fetch operation always stores the head of the last fetched
589 branch in FETCH_HEAD. For example, if you run git fetch without
590 specifying a local branch as the target of the operation
592 -------------------------------------------------
593 $ git fetch git://example.com/proj.git theirbranch
594 -------------------------------------------------
596 the fetched commits will still be available from FETCH_HEAD.
598 When we discuss merges we'll also see the special name MERGE_HEAD,
599 which refers to the other branch that we're merging in to the current
600 branch.
602 The linkgit:git-rev-parse[1] command is a low-level command that is
603 occasionally useful for translating some name for a commit to the object
604 name for that commit:
606 -------------------------------------------------
607 $ git rev-parse origin
608 e05db0fd4f31dde7005f075a84f96b360d05984b
609 -------------------------------------------------
611 [[creating-tags]]
612 Creating tags
613 -------------
615 We can also create a tag to refer to a particular commit; after
616 running
618 -------------------------------------------------
619 $ git tag stable-1 1b2e1d63ff
620 -------------------------------------------------
622 You can use stable-1 to refer to the commit 1b2e1d63ff.
624 This creates a "lightweight" tag. If you would also like to include a
625 comment with the tag, and possibly sign it cryptographically, then you
626 should create a tag object instead; see the linkgit:git-tag[1] man page
627 for details.
629 [[browsing-revisions]]
630 Browsing revisions
631 ------------------
633 The linkgit:git-log[1] command can show lists of commits. On its
634 own, it shows all commits reachable from the parent commit; but you
635 can also make more specific requests:
637 -------------------------------------------------
638 $ git log v2.5.. # commits since (not reachable from) v2.5
639 $ git log test..master # commits reachable from master but not test
640 $ git log master..test # ...reachable from test but not master
641 $ git log master...test # ...reachable from either test or master,
642 # but not both
643 $ git log --since="2 weeks ago" # commits from the last 2 weeks
644 $ git log Makefile # commits which modify Makefile
645 $ git log fs/ # ... which modify any file under fs/
646 $ git log -S'foo()' # commits which add or remove any file data
647 # matching the string 'foo()'
648 -------------------------------------------------
650 And of course you can combine all of these; the following finds
651 commits since v2.5 which touch the Makefile or any file under fs:
653 -------------------------------------------------
654 $ git log v2.5.. Makefile fs/
655 -------------------------------------------------
657 You can also ask git log to show patches:
659 -------------------------------------------------
660 $ git log -p
661 -------------------------------------------------
663 See the "--pretty" option in the linkgit:git-log[1] man page for more
664 display options.
666 Note that git log starts with the most recent commit and works
667 backwards through the parents; however, since git history can contain
668 multiple independent lines of development, the particular order that
669 commits are listed in may be somewhat arbitrary.
671 [[generating-diffs]]
672 Generating diffs
673 ----------------
675 You can generate diffs between any two versions using
676 linkgit:git-diff[1]:
678 -------------------------------------------------
679 $ git diff master..test
680 -------------------------------------------------
682 That will produce the diff between the tips of the two branches. If
683 you'd prefer to find the diff from their common ancestor to test, you
684 can use three dots instead of two:
686 -------------------------------------------------
687 $ git diff master...test
688 -------------------------------------------------
690 Sometimes what you want instead is a set of patches; for this you can
691 use linkgit:git-format-patch[1]:
693 -------------------------------------------------
694 $ git format-patch master..test
695 -------------------------------------------------
697 will generate a file with a patch for each commit reachable from test
698 but not from master.
700 [[viewing-old-file-versions]]
701 Viewing old file versions
702 -------------------------
704 You can always view an old version of a file by just checking out the
705 correct revision first. But sometimes it is more convenient to be
706 able to view an old version of a single file without checking
707 anything out; this command does that:
709 -------------------------------------------------
710 $ git show v2.5:fs/locks.c
711 -------------------------------------------------
713 Before the colon may be anything that names a commit, and after it
714 may be any path to a file tracked by git.
716 [[history-examples]]
717 Examples
718 --------
720 [[counting-commits-on-a-branch]]
721 Counting the number of commits on a branch
722 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
724 Suppose you want to know how many commits you've made on "mybranch"
725 since it diverged from "origin":
727 -------------------------------------------------
728 $ git log --pretty=oneline origin..mybranch | wc -l
729 -------------------------------------------------
731 Alternatively, you may often see this sort of thing done with the
732 lower-level command linkgit:git-rev-list[1], which just lists the SHA1's
733 of all the given commits:
735 -------------------------------------------------
736 $ git rev-list origin..mybranch | wc -l
737 -------------------------------------------------
739 [[checking-for-equal-branches]]
740 Check whether two branches point at the same history
741 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
743 Suppose you want to check whether two branches point at the same point
744 in history.
746 -------------------------------------------------
747 $ git diff origin..master
748 -------------------------------------------------
750 will tell you whether the contents of the project are the same at the
751 two branches; in theory, however, it's possible that the same project
752 contents could have been arrived at by two different historical
753 routes. You could compare the object names:
755 -------------------------------------------------
756 $ git rev-list origin
757 e05db0fd4f31dde7005f075a84f96b360d05984b
758 $ git rev-list master
759 e05db0fd4f31dde7005f075a84f96b360d05984b
760 -------------------------------------------------
762 Or you could recall that the ... operator selects all commits
763 contained reachable from either one reference or the other but not
764 both: so
766 -------------------------------------------------
767 $ git log origin...master
768 -------------------------------------------------
770 will return no commits when the two branches are equal.
772 [[finding-tagged-descendants]]
773 Find first tagged version including a given fix
774 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
776 Suppose you know that the commit e05db0fd fixed a certain problem.
777 You'd like to find the earliest tagged release that contains that
778 fix.
780 Of course, there may be more than one answer--if the history branched
781 after commit e05db0fd, then there could be multiple "earliest" tagged
782 releases.
784 You could just visually inspect the commits since e05db0fd:
786 -------------------------------------------------
787 $ gitk e05db0fd..
788 -------------------------------------------------
790 Or you can use linkgit:git-name-rev[1], which will give the commit a
791 name based on any tag it finds pointing to one of the commit's
792 descendants:
794 -------------------------------------------------
795 $ git name-rev --tags e05db0fd
796 e05db0fd tags/v1.5.0-rc1^0~23
797 -------------------------------------------------
799 The linkgit:git-describe[1] command does the opposite, naming the
800 revision using a tag on which the given commit is based:
802 -------------------------------------------------
803 $ git describe e05db0fd
804 v1.5.0-rc0-260-ge05db0f
805 -------------------------------------------------
807 but that may sometimes help you guess which tags might come after the
808 given commit.
810 If you just want to verify whether a given tagged version contains a
811 given commit, you could use linkgit:git-merge-base[1]:
813 -------------------------------------------------
814 $ git merge-base e05db0fd v1.5.0-rc1
815 e05db0fd4f31dde7005f075a84f96b360d05984b
816 -------------------------------------------------
818 The merge-base command finds a common ancestor of the given commits,
819 and always returns one or the other in the case where one is a
820 descendant of the other; so the above output shows that e05db0fd
821 actually is an ancestor of v1.5.0-rc1.
823 Alternatively, note that
825 -------------------------------------------------
826 $ git log v1.5.0-rc1..e05db0fd
827 -------------------------------------------------
829 will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
830 because it outputs only commits that are not reachable from v1.5.0-rc1.
832 As yet another alternative, the linkgit:git-show-branch[1] command lists
833 the commits reachable from its arguments with a display on the left-hand
834 side that indicates which arguments that commit is reachable from. So,
835 you can run something like
837 -------------------------------------------------
838 $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
839 ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
840 available
841 ! [v1.5.0-rc0] GIT v1.5.0 preview
842 ! [v1.5.0-rc1] GIT v1.5.0-rc1
843 ! [v1.5.0-rc2] GIT v1.5.0-rc2
844 ...
845 -------------------------------------------------
847 then search for a line that looks like
849 -------------------------------------------------
850 + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
851 available
852 -------------------------------------------------
854 Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
855 from v1.5.0-rc2, but not from v1.5.0-rc0.
857 [[showing-commits-unique-to-a-branch]]
858 Showing commits unique to a given branch
859 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
861 Suppose you would like to see all the commits reachable from the branch
862 head named "master" but not from any other head in your repository.
864 We can list all the heads in this repository with
865 linkgit:git-show-ref[1]:
867 -------------------------------------------------
868 $ git show-ref --heads
869 bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
870 db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
871 a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
872 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
873 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
874 -------------------------------------------------
876 We can get just the branch-head names, and remove "master", with
877 the help of the standard utilities cut and grep:
879 -------------------------------------------------
880 $ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
881 refs/heads/core-tutorial
882 refs/heads/maint
883 refs/heads/tutorial-2
884 refs/heads/tutorial-fixes
885 -------------------------------------------------
887 And then we can ask to see all the commits reachable from master
888 but not from these other heads:
890 -------------------------------------------------
891 $ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
892 grep -v '^refs/heads/master' )
893 -------------------------------------------------
895 Obviously, endless variations are possible; for example, to see all
896 commits reachable from some head but not from any tag in the repository:
898 -------------------------------------------------
899 $ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
900 -------------------------------------------------
902 (See linkgit:git-rev-parse[1] for explanations of commit-selecting
903 syntax such as `--not`.)
905 [[making-a-release]]
906 Creating a changelog and tarball for a software release
907 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
909 The linkgit:git-archive[1] command can create a tar or zip archive from
910 any version of a project; for example:
912 -------------------------------------------------
913 $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
914 -------------------------------------------------
916 will use HEAD to produce a tar archive in which each filename is
917 preceded by "project/".
919 If you're releasing a new version of a software project, you may want
920 to simultaneously make a changelog to include in the release
921 announcement.
923 Linus Torvalds, for example, makes new kernel releases by tagging them,
924 then running:
926 -------------------------------------------------
927 $ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
928 -------------------------------------------------
930 where release-script is a shell script that looks like:
932 -------------------------------------------------
933 #!/bin/sh
934 stable="$1"
935 last="$2"
936 new="$3"
937 echo "# git tag v$new"
938 echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
939 echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
940 echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
941 echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
942 echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
943 -------------------------------------------------
945 and then he just cut-and-pastes the output commands after verifying that
946 they look OK.
948 [[Finding-comments-With-given-Content]]
949 Finding commits referencing a file with given content
950 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
952 Somebody hands you a copy of a file, and asks which commits modified a
953 file such that it contained the given content either before or after the
954 commit. You can find out with this:
956 -------------------------------------------------
957 $ git log --raw --abbrev=40 --pretty=oneline |
958 grep -B 1 `git hash-object filename`
959 -------------------------------------------------
961 Figuring out why this works is left as an exercise to the (advanced)
962 student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and
963 linkgit:git-hash-object[1] man pages may prove helpful.
965 [[Developing-With-git]]
966 Developing with git
967 ===================
969 [[telling-git-your-name]]
970 Telling git your name
971 ---------------------
973 Before creating any commits, you should introduce yourself to git. The
974 easiest way to do so is to make sure the following lines appear in a
975 file named .gitconfig in your home directory:
977 ------------------------------------------------
978 [user]
979 name = Your Name Comes Here
980 email = you@yourdomain.example.com
981 ------------------------------------------------
983 (See the "CONFIGURATION FILE" section of linkgit:git-config[1] for
984 details on the configuration file.)
987 [[creating-a-new-repository]]
988 Creating a new repository
989 -------------------------
991 Creating a new repository from scratch is very easy:
993 -------------------------------------------------
994 $ mkdir project
995 $ cd project
996 $ git init
997 -------------------------------------------------
999 If you have some initial content (say, a tarball):
1001 -------------------------------------------------
1002 $ tar -xzvf project.tar.gz
1003 $ cd project
1004 $ git init
1005 $ git add . # include everything below ./ in the first commit:
1006 $ git commit
1007 -------------------------------------------------
1009 [[how-to-make-a-commit]]
1010 How to make a commit
1011 --------------------
1013 Creating a new commit takes three steps:
1015 1. Making some changes to the working directory using your
1016 favorite editor.
1017 2. Telling git about your changes.
1018 3. Creating the commit using the content you told git about
1019 in step 2.
1021 In practice, you can interleave and repeat steps 1 and 2 as many
1022 times as you want: in order to keep track of what you want committed
1023 at step 3, git maintains a snapshot of the tree's contents in a
1024 special staging area called "the index."
1026 At the beginning, the content of the index will be identical to
1027 that of the HEAD. The command "git diff --cached", which shows
1028 the difference between the HEAD and the index, should therefore
1029 produce no output at that point.
1031 Modifying the index is easy:
1033 To update the index with the new contents of a modified file, use
1035 -------------------------------------------------
1036 $ git add path/to/file
1037 -------------------------------------------------
1039 To add the contents of a new file to the index, use
1041 -------------------------------------------------
1042 $ git add path/to/file
1043 -------------------------------------------------
1045 To remove a file from the index and from the working tree,
1047 -------------------------------------------------
1048 $ git rm path/to/file
1049 -------------------------------------------------
1051 After each step you can verify that
1053 -------------------------------------------------
1054 $ git diff --cached
1055 -------------------------------------------------
1057 always shows the difference between the HEAD and the index file--this
1058 is what you'd commit if you created the commit now--and that
1060 -------------------------------------------------
1061 $ git diff
1062 -------------------------------------------------
1064 shows the difference between the working tree and the index file.
1066 Note that "git-add" always adds just the current contents of a file
1067 to the index; further changes to the same file will be ignored unless
1068 you run git-add on the file again.
1070 When you're ready, just run
1072 -------------------------------------------------
1073 $ git commit
1074 -------------------------------------------------
1076 and git will prompt you for a commit message and then create the new
1077 commit. Check to make sure it looks like what you expected with
1079 -------------------------------------------------
1080 $ git show
1081 -------------------------------------------------
1083 As a special shortcut,
1085 -------------------------------------------------
1086 $ git commit -a
1087 -------------------------------------------------
1089 will update the index with any files that you've modified or removed
1090 and create a commit, all in one step.
1092 A number of commands are useful for keeping track of what you're
1093 about to commit:
1095 -------------------------------------------------
1096 $ git diff --cached # difference between HEAD and the index; what
1097 # would be committed if you ran "commit" now.
1098 $ git diff # difference between the index file and your
1099 # working directory; changes that would not
1100 # be included if you ran "commit" now.
1101 $ git diff HEAD # difference between HEAD and working tree; what
1102 # would be committed if you ran "commit -a" now.
1103 $ git status # a brief per-file summary of the above.
1104 -------------------------------------------------
1106 You can also use linkgit:git-gui[1] to create commits, view changes in
1107 the index and the working tree files, and individually select diff hunks
1108 for inclusion in the index (by right-clicking on the diff hunk and
1109 choosing "Stage Hunk For Commit").
1111 [[creating-good-commit-messages]]
1112 Creating good commit messages
1113 -----------------------------
1115 Though not required, it's a good idea to begin the commit message
1116 with a single short (less than 50 character) line summarizing the
1117 change, followed by a blank line and then a more thorough
1118 description. Tools that turn commits into email, for example, use
1119 the first line on the Subject line and the rest of the commit in the
1120 body.
1122 [[ignoring-files]]
1123 Ignoring files
1124 --------------
1126 A project will often generate files that you do 'not' want to track with git.
1127 This typically includes files generated by a build process or temporary
1128 backup files made by your editor. Of course, 'not' tracking files with git
1129 is just a matter of 'not' calling "`git-add`" on them. But it quickly becomes
1130 annoying to have these untracked files lying around; e.g. they make
1131 "`git add .`" practically useless, and they keep showing up in the output of
1132 "`git status`".
1134 You can tell git to ignore certain files by creating a file called .gitignore
1135 in the top level of your working directory, with contents such as:
1137 -------------------------------------------------
1138 # Lines starting with '#' are considered comments.
1139 # Ignore any file named foo.txt.
1140 foo.txt
1141 # Ignore (generated) html files,
1142 *.html
1143 # except foo.html which is maintained by hand.
1144 !foo.html
1145 # Ignore objects and archives.
1146 *.[oa]
1147 -------------------------------------------------
1149 See linkgit:gitignore[5] for a detailed explanation of the syntax. You can
1150 also place .gitignore files in other directories in your working tree, and they
1151 will apply to those directories and their subdirectories. The `.gitignore`
1152 files can be added to your repository like any other files (just run `git add
1153 .gitignore` and `git commit`, as usual), which is convenient when the exclude
1154 patterns (such as patterns matching build output files) would also make sense
1155 for other users who clone your repository.
1157 If you wish the exclude patterns to affect only certain repositories
1158 (instead of every repository for a given project), you may instead put
1159 them in a file in your repository named .git/info/exclude, or in any file
1160 specified by the `core.excludesfile` configuration variable. Some git
1161 commands can also take exclude patterns directly on the command line.
1162 See linkgit:gitignore[5] for the details.
1164 [[how-to-merge]]
1165 How to merge
1166 ------------
1168 You can rejoin two diverging branches of development using
1169 linkgit:git-merge[1]:
1171 -------------------------------------------------
1172 $ git merge branchname
1173 -------------------------------------------------
1175 merges the development in the branch "branchname" into the current
1176 branch. If there are conflicts--for example, if the same file is
1177 modified in two different ways in the remote branch and the local
1178 branch--then you are warned; the output may look something like this:
1180 -------------------------------------------------
1181 $ git merge next
1182 100% (4/4) done
1183 Auto-merged file.txt
1184 CONFLICT (content): Merge conflict in file.txt
1185 Automatic merge failed; fix conflicts and then commit the result.
1186 -------------------------------------------------
1188 Conflict markers are left in the problematic files, and after
1189 you resolve the conflicts manually, you can update the index
1190 with the contents and run git commit, as you normally would when
1191 creating a new file.
1193 If you examine the resulting commit using gitk, you will see that it
1194 has two parents, one pointing to the top of the current branch, and
1195 one to the top of the other branch.
1197 [[resolving-a-merge]]
1198 Resolving a merge
1199 -----------------
1201 When a merge isn't resolved automatically, git leaves the index and
1202 the working tree in a special state that gives you all the
1203 information you need to help resolve the merge.
1205 Files with conflicts are marked specially in the index, so until you
1206 resolve the problem and update the index, linkgit:git-commit[1] will
1207 fail:
1209 -------------------------------------------------
1210 $ git commit
1211 file.txt: needs merge
1212 -------------------------------------------------
1214 Also, linkgit:git-status[1] will list those files as "unmerged", and the
1215 files with conflicts will have conflict markers added, like this:
1217 -------------------------------------------------
1218 <<<<<<< HEAD:file.txt
1219 Hello world
1220 =======
1221 Goodbye
1222 >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1223 -------------------------------------------------
1225 All you need to do is edit the files to resolve the conflicts, and then
1227 -------------------------------------------------
1228 $ git add file.txt
1229 $ git commit
1230 -------------------------------------------------
1232 Note that the commit message will already be filled in for you with
1233 some information about the merge. Normally you can just use this
1234 default message unchanged, but you may add additional commentary of
1235 your own if desired.
1237 The above is all you need to know to resolve a simple merge. But git
1238 also provides more information to help resolve conflicts:
1240 [[conflict-resolution]]
1241 Getting conflict-resolution help during a merge
1242 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1244 All of the changes that git was able to merge automatically are
1245 already added to the index file, so linkgit:git-diff[1] shows only
1246 the conflicts. It uses an unusual syntax:
1248 -------------------------------------------------
1249 $ git diff
1250 diff --cc file.txt
1251 index 802992c,2b60207..0000000
1252 --- a/file.txt
1253 +++ b/file.txt
1254 @@@ -1,1 -1,1 +1,5 @@@
1255 ++<<<<<<< HEAD:file.txt
1256 +Hello world
1257 ++=======
1258 + Goodbye
1259 ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1260 -------------------------------------------------
1262 Recall that the commit which will be committed after we resolve this
1263 conflict will have two parents instead of the usual one: one parent
1264 will be HEAD, the tip of the current branch; the other will be the
1265 tip of the other branch, which is stored temporarily in MERGE_HEAD.
1267 During the merge, the index holds three versions of each file. Each of
1268 these three "file stages" represents a different version of the file:
1270 -------------------------------------------------
1271 $ git show :1:file.txt # the file in a common ancestor of both branches
1272 $ git show :2:file.txt # the version from HEAD.
1273 $ git show :3:file.txt # the version from MERGE_HEAD.
1274 -------------------------------------------------
1276 When you ask linkgit:git-diff[1] to show the conflicts, it runs a
1277 three-way diff between the conflicted merge results in the work tree with
1278 stages 2 and 3 to show only hunks whose contents come from both sides,
1279 mixed (in other words, when a hunk's merge results come only from stage 2,
1280 that part is not conflicting and is not shown. Same for stage 3).
1282 The diff above shows the differences between the working-tree version of
1283 file.txt and the stage 2 and stage 3 versions. So instead of preceding
1284 each line by a single "+" or "-", it now uses two columns: the first
1285 column is used for differences between the first parent and the working
1286 directory copy, and the second for differences between the second parent
1287 and the working directory copy. (See the "COMBINED DIFF FORMAT" section
1288 of linkgit:git-diff-files[1] for a details of the format.)
1290 After resolving the conflict in the obvious way (but before updating the
1291 index), the diff will look like:
1293 -------------------------------------------------
1294 $ git diff
1295 diff --cc file.txt
1296 index 802992c,2b60207..0000000
1297 --- a/file.txt
1298 +++ b/file.txt
1299 @@@ -1,1 -1,1 +1,1 @@@
1300 - Hello world
1301 -Goodbye
1302 ++Goodbye world
1303 -------------------------------------------------
1305 This shows that our resolved version deleted "Hello world" from the
1306 first parent, deleted "Goodbye" from the second parent, and added
1307 "Goodbye world", which was previously absent from both.
1309 Some special diff options allow diffing the working directory against
1310 any of these stages:
1312 -------------------------------------------------
1313 $ git diff -1 file.txt # diff against stage 1
1314 $ git diff --base file.txt # same as the above
1315 $ git diff -2 file.txt # diff against stage 2
1316 $ git diff --ours file.txt # same as the above
1317 $ git diff -3 file.txt # diff against stage 3
1318 $ git diff --theirs file.txt # same as the above.
1319 -------------------------------------------------
1321 The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
1322 for merges:
1324 -------------------------------------------------
1325 $ git log --merge
1326 $ gitk --merge
1327 -------------------------------------------------
1329 These will display all commits which exist only on HEAD or on
1330 MERGE_HEAD, and which touch an unmerged file.
1332 You may also use linkgit:git-mergetool[1], which lets you merge the
1333 unmerged files using external tools such as emacs or kdiff3.
1335 Each time you resolve the conflicts in a file and update the index:
1337 -------------------------------------------------
1338 $ git add file.txt
1339 -------------------------------------------------
1341 the different stages of that file will be "collapsed", after which
1342 git-diff will (by default) no longer show diffs for that file.
1344 [[undoing-a-merge]]
1345 Undoing a merge
1346 ---------------
1348 If you get stuck and decide to just give up and throw the whole mess
1349 away, you can always return to the pre-merge state with
1351 -------------------------------------------------
1352 $ git reset --hard HEAD
1353 -------------------------------------------------
1355 Or, if you've already committed the merge that you want to throw away,
1357 -------------------------------------------------
1358 $ git reset --hard ORIG_HEAD
1359 -------------------------------------------------
1361 However, this last command can be dangerous in some cases--never
1362 throw away a commit you have already committed if that commit may
1363 itself have been merged into another branch, as doing so may confuse
1364 further merges.
1366 [[fast-forwards]]
1367 Fast-forward merges
1368 -------------------
1370 There is one special case not mentioned above, which is treated
1371 differently. Normally, a merge results in a merge commit, with two
1372 parents, one pointing at each of the two lines of development that
1373 were merged.
1375 However, if the current branch is a descendant of the other--so every
1376 commit present in the one is already contained in the other--then git
1377 just performs a "fast forward"; the head of the current branch is moved
1378 forward to point at the head of the merged-in branch, without any new
1379 commits being created.
1381 [[fixing-mistakes]]
1382 Fixing mistakes
1383 ---------------
1385 If you've messed up the working tree, but haven't yet committed your
1386 mistake, you can return the entire working tree to the last committed
1387 state with
1389 -------------------------------------------------
1390 $ git reset --hard HEAD
1391 -------------------------------------------------
1393 If you make a commit that you later wish you hadn't, there are two
1394 fundamentally different ways to fix the problem:
1396 1. You can create a new commit that undoes whatever was done
1397 by the old commit. This is the correct thing if your
1398 mistake has already been made public.
1400 2. You can go back and modify the old commit. You should
1401 never do this if you have already made the history public;
1402 git does not normally expect the "history" of a project to
1403 change, and cannot correctly perform repeated merges from
1404 a branch that has had its history changed.
1406 [[reverting-a-commit]]
1407 Fixing a mistake with a new commit
1408 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1410 Creating a new commit that reverts an earlier change is very easy;
1411 just pass the linkgit:git-revert[1] command a reference to the bad
1412 commit; for example, to revert the most recent commit:
1414 -------------------------------------------------
1415 $ git revert HEAD
1416 -------------------------------------------------
1418 This will create a new commit which undoes the change in HEAD. You
1419 will be given a chance to edit the commit message for the new commit.
1421 You can also revert an earlier change, for example, the next-to-last:
1423 -------------------------------------------------
1424 $ git revert HEAD^
1425 -------------------------------------------------
1427 In this case git will attempt to undo the old change while leaving
1428 intact any changes made since then. If more recent changes overlap
1429 with the changes to be reverted, then you will be asked to fix
1430 conflicts manually, just as in the case of <<resolving-a-merge,
1431 resolving a merge>>.
1433 [[fixing-a-mistake-by-rewriting-history]]
1434 Fixing a mistake by rewriting history
1435 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1437 If the problematic commit is the most recent commit, and you have not
1438 yet made that commit public, then you may just
1439 <<undoing-a-merge,destroy it using git-reset>>.
1441 Alternatively, you
1442 can edit the working directory and update the index to fix your
1443 mistake, just as if you were going to <<how-to-make-a-commit,create a
1444 new commit>>, then run
1446 -------------------------------------------------
1447 $ git commit --amend
1448 -------------------------------------------------
1450 which will replace the old commit by a new commit incorporating your
1451 changes, giving you a chance to edit the old commit message first.
1453 Again, you should never do this to a commit that may already have
1454 been merged into another branch; use linkgit:git-revert[1] instead in
1455 that case.
1457 It is also possible to replace commits further back in the history, but
1458 this is an advanced topic to be left for
1459 <<cleaning-up-history,another chapter>>.
1461 [[checkout-of-path]]
1462 Checking out an old version of a file
1463 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1465 In the process of undoing a previous bad change, you may find it
1466 useful to check out an older version of a particular file using
1467 linkgit:git-checkout[1]. We've used git-checkout before to switch
1468 branches, but it has quite different behavior if it is given a path
1469 name: the command
1471 -------------------------------------------------
1472 $ git checkout HEAD^ path/to/file
1473 -------------------------------------------------
1475 replaces path/to/file by the contents it had in the commit HEAD^, and
1476 also updates the index to match. It does not change branches.
1478 If you just want to look at an old version of the file, without
1479 modifying the working directory, you can do that with
1480 linkgit:git-show[1]:
1482 -------------------------------------------------
1483 $ git show HEAD^:path/to/file
1484 -------------------------------------------------
1486 which will display the given version of the file.
1488 [[interrupted-work]]
1489 Temporarily setting aside work in progress
1490 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1492 While you are in the middle of working on something complicated, you
1493 find an unrelated but obvious and trivial bug. You would like to fix it
1494 before continuing. You can use linkgit:git-stash[1] to save the current
1495 state of your work, and after fixing the bug (or, optionally after doing
1496 so on a different branch and then coming back), unstash the
1497 work-in-progress changes.
1499 ------------------------------------------------
1500 $ git stash "work in progress for foo feature"
1501 ------------------------------------------------
1503 This command will save your changes away to the `stash`, and
1504 reset your working tree and the index to match the tip of your
1505 current branch. Then you can make your fix as usual.
1507 ------------------------------------------------
1508 ... edit and test ...
1509 $ git commit -a -m "blorpl: typofix"
1510 ------------------------------------------------
1512 After that, you can go back to what you were working on with
1513 `git stash apply`:
1515 ------------------------------------------------
1516 $ git stash apply
1517 ------------------------------------------------
1520 [[ensuring-good-performance]]
1521 Ensuring good performance
1522 -------------------------
1524 On large repositories, git depends on compression to keep the history
1525 information from taking up too much space on disk or in memory.
1527 This compression is not performed automatically. Therefore you
1528 should occasionally run linkgit:git-gc[1]:
1530 -------------------------------------------------
1531 $ git gc
1532 -------------------------------------------------
1534 to recompress the archive. This can be very time-consuming, so
1535 you may prefer to run git-gc when you are not doing other work.
1538 [[ensuring-reliability]]
1539 Ensuring reliability
1540 --------------------
1542 [[checking-for-corruption]]
1543 Checking the repository for corruption
1544 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1546 The linkgit:git-fsck[1] command runs a number of self-consistency checks
1547 on the repository, and reports on any problems. This may take some
1548 time. The most common warning by far is about "dangling" objects:
1550 -------------------------------------------------
1551 $ git fsck
1552 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1553 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1554 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1555 dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1556 dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1557 dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1558 dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1559 dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1560 ...
1561 -------------------------------------------------
1563 Dangling objects are not a problem. At worst they may take up a little
1564 extra disk space. They can sometimes provide a last-resort method for
1565 recovering lost work--see <<dangling-objects>> for details.
1567 [[recovering-lost-changes]]
1568 Recovering lost changes
1569 ~~~~~~~~~~~~~~~~~~~~~~~
1571 [[reflogs]]
1572 Reflogs
1573 ^^^^^^^
1575 Say you modify a branch with `linkgit:git-reset[1] --hard`, and then
1576 realize that the branch was the only reference you had to that point in
1577 history.
1579 Fortunately, git also keeps a log, called a "reflog", of all the
1580 previous values of each branch. So in this case you can still find the
1581 old history using, for example,
1583 -------------------------------------------------
1584 $ git log master@{1}
1585 -------------------------------------------------
1587 This lists the commits reachable from the previous version of the
1588 "master" branch head. This syntax can be used with any git command
1589 that accepts a commit, not just with git log. Some other examples:
1591 -------------------------------------------------
1592 $ git show master@{2} # See where the branch pointed 2,
1593 $ git show master@{3} # 3, ... changes ago.
1594 $ gitk master@{yesterday} # See where it pointed yesterday,
1595 $ gitk master@{"1 week ago"} # ... or last week
1596 $ git log --walk-reflogs master # show reflog entries for master
1597 -------------------------------------------------
1599 A separate reflog is kept for the HEAD, so
1601 -------------------------------------------------
1602 $ git show HEAD@{"1 week ago"}
1603 -------------------------------------------------
1605 will show what HEAD pointed to one week ago, not what the current branch
1606 pointed to one week ago. This allows you to see the history of what
1607 you've checked out.
1609 The reflogs are kept by default for 30 days, after which they may be
1610 pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn
1611 how to control this pruning, and see the "SPECIFYING REVISIONS"
1612 section of linkgit:git-rev-parse[1] for details.
1614 Note that the reflog history is very different from normal git history.
1615 While normal history is shared by every repository that works on the
1616 same project, the reflog history is not shared: it tells you only about
1617 how the branches in your local repository have changed over time.
1619 [[dangling-object-recovery]]
1620 Examining dangling objects
1621 ^^^^^^^^^^^^^^^^^^^^^^^^^^
1623 In some situations the reflog may not be able to save you. For example,
1624 suppose you delete a branch, then realize you need the history it
1625 contained. The reflog is also deleted; however, if you have not yet
1626 pruned the repository, then you may still be able to find the lost
1627 commits in the dangling objects that git-fsck reports. See
1628 <<dangling-objects>> for the details.
1630 -------------------------------------------------
1631 $ git fsck
1632 dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1633 dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1634 dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1635 ...
1636 -------------------------------------------------
1638 You can examine
1639 one of those dangling commits with, for example,
1641 ------------------------------------------------
1642 $ gitk 7281251ddd --not --all
1643 ------------------------------------------------
1645 which does what it sounds like: it says that you want to see the commit
1646 history that is described by the dangling commit(s), but not the
1647 history that is described by all your existing branches and tags. Thus
1648 you get exactly the history reachable from that commit that is lost.
1649 (And notice that it might not be just one commit: we only report the
1650 "tip of the line" as being dangling, but there might be a whole deep
1651 and complex commit history that was dropped.)
1653 If you decide you want the history back, you can always create a new
1654 reference pointing to it, for example, a new branch:
1656 ------------------------------------------------
1657 $ git branch recovered-branch 7281251ddd
1658 ------------------------------------------------
1660 Other types of dangling objects (blobs and trees) are also possible, and
1661 dangling objects can arise in other situations.
1664 [[sharing-development]]
1665 Sharing development with others
1666 ===============================
1668 [[getting-updates-With-git-pull]]
1669 Getting updates with git-pull
1670 -----------------------------
1672 After you clone a repository and make a few changes of your own, you
1673 may wish to check the original repository for updates and merge them
1674 into your own work.
1676 We have already seen <<Updating-a-repository-With-git-fetch,how to
1677 keep remote tracking branches up to date>> with linkgit:git-fetch[1],
1678 and how to merge two branches. So you can merge in changes from the
1679 original repository's master branch with:
1681 -------------------------------------------------
1682 $ git fetch
1683 $ git merge origin/master
1684 -------------------------------------------------
1686 However, the linkgit:git-pull[1] command provides a way to do this in
1687 one step:
1689 -------------------------------------------------
1690 $ git pull origin master
1691 -------------------------------------------------
1693 In fact, if you have "master" checked out, then by default "git pull"
1694 merges from the HEAD branch of the origin repository. So often you can
1695 accomplish the above with just a simple
1697 -------------------------------------------------
1698 $ git pull
1699 -------------------------------------------------
1701 More generally, a branch that is created from a remote branch will pull
1702 by default from that branch. See the descriptions of the
1703 branch.<name>.remote and branch.<name>.merge options in
1704 linkgit:git-config[1], and the discussion of the `--track` option in
1705 linkgit:git-checkout[1], to learn how to control these defaults.
1707 In addition to saving you keystrokes, "git pull" also helps you by
1708 producing a default commit message documenting the branch and
1709 repository that you pulled from.
1711 (But note that no such commit will be created in the case of a
1712 <<fast-forwards,fast forward>>; instead, your branch will just be
1713 updated to point to the latest commit from the upstream branch.)
1715 The git-pull command can also be given "." as the "remote" repository,
1716 in which case it just merges in a branch from the current repository; so
1717 the commands
1719 -------------------------------------------------
1720 $ git pull . branch
1721 $ git merge branch
1722 -------------------------------------------------
1724 are roughly equivalent. The former is actually very commonly used.
1726 [[submitting-patches]]
1727 Submitting patches to a project
1728 -------------------------------
1730 If you just have a few changes, the simplest way to submit them may
1731 just be to send them as patches in email:
1733 First, use linkgit:git-format-patch[1]; for example:
1735 -------------------------------------------------
1736 $ git format-patch origin
1737 -------------------------------------------------
1739 will produce a numbered series of files in the current directory, one
1740 for each patch in the current branch but not in origin/HEAD.
1742 You can then import these into your mail client and send them by
1743 hand. However, if you have a lot to send at once, you may prefer to
1744 use the linkgit:git-send-email[1] script to automate the process.
1745 Consult the mailing list for your project first to determine how they
1746 prefer such patches be handled.
1748 [[importing-patches]]
1749 Importing patches to a project
1750 ------------------------------
1752 Git also provides a tool called linkgit:git-am[1] (am stands for
1753 "apply mailbox"), for importing such an emailed series of patches.
1754 Just save all of the patch-containing messages, in order, into a
1755 single mailbox file, say "patches.mbox", then run
1757 -------------------------------------------------
1758 $ git am -3 patches.mbox
1759 -------------------------------------------------
1761 Git will apply each patch in order; if any conflicts are found, it
1762 will stop, and you can fix the conflicts as described in
1763 "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1764 git to perform a merge; if you would prefer it just to abort and
1765 leave your tree and index untouched, you may omit that option.)
1767 Once the index is updated with the results of the conflict
1768 resolution, instead of creating a new commit, just run
1770 -------------------------------------------------
1771 $ git am --resolved
1772 -------------------------------------------------
1774 and git will create the commit for you and continue applying the
1775 remaining patches from the mailbox.
1777 The final result will be a series of commits, one for each patch in
1778 the original mailbox, with authorship and commit log message each
1779 taken from the message containing each patch.
1781 [[public-repositories]]
1782 Public git repositories
1783 -----------------------
1785 Another way to submit changes to a project is to tell the maintainer
1786 of that project to pull the changes from your repository using
1787 linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull,
1788 Getting updates with git-pull>>" we described this as a way to get
1789 updates from the "main" repository, but it works just as well in the
1790 other direction.
1792 If you and the maintainer both have accounts on the same machine, then
1793 you can just pull changes from each other's repositories directly;
1794 commands that accept repository URLs as arguments will also accept a
1795 local directory name:
1797 -------------------------------------------------
1798 $ git clone /path/to/repository
1799 $ git pull /path/to/other/repository
1800 -------------------------------------------------
1802 or an ssh URL:
1804 -------------------------------------------------
1805 $ git clone ssh://yourhost/~you/repository
1806 -------------------------------------------------
1808 For projects with few developers, or for synchronizing a few private
1809 repositories, this may be all you need.
1811 However, the more common way to do this is to maintain a separate public
1812 repository (usually on a different host) for others to pull changes
1813 from. This is usually more convenient, and allows you to cleanly
1814 separate private work in progress from publicly visible work.
1816 You will continue to do your day-to-day work in your personal
1817 repository, but periodically "push" changes from your personal
1818 repository into your public repository, allowing other developers to
1819 pull from that repository. So the flow of changes, in a situation
1820 where there is one other developer with a public repository, looks
1821 like this:
1823 you push
1824 your personal repo ------------------> your public repo
1825 ^ |
1826 | |
1827 | you pull | they pull
1828 | |
1829 | |
1830 | they push V
1831 their public repo <------------------- their repo
1833 We explain how to do this in the following sections.
1835 [[setting-up-a-public-repository]]
1836 Setting up a public repository
1837 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1839 Assume your personal repository is in the directory ~/proj. We
1840 first create a new clone of the repository and tell git-daemon that it
1841 is meant to be public:
1843 -------------------------------------------------
1844 $ git clone --bare ~/proj proj.git
1845 $ touch proj.git/git-daemon-export-ok
1846 -------------------------------------------------
1848 The resulting directory proj.git contains a "bare" git repository--it is
1849 just the contents of the ".git" directory, without any files checked out
1850 around it.
1852 Next, copy proj.git to the server where you plan to host the
1853 public repository. You can use scp, rsync, or whatever is most
1854 convenient.
1856 [[exporting-via-git]]
1857 Exporting a git repository via the git protocol
1858 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1860 This is the preferred method.
1862 If someone else administers the server, they should tell you what
1863 directory to put the repository in, and what git:// URL it will appear
1864 at. You can then skip to the section
1865 "<<pushing-changes-to-a-public-repository,Pushing changes to a public
1866 repository>>", below.
1868 Otherwise, all you need to do is start linkgit:git-daemon[1]; it will
1869 listen on port 9418. By default, it will allow access to any directory
1870 that looks like a git directory and contains the magic file
1871 git-daemon-export-ok. Passing some directory paths as git-daemon
1872 arguments will further restrict the exports to those paths.
1874 You can also run git-daemon as an inetd service; see the
1875 linkgit:git-daemon[1] man page for details. (See especially the
1876 examples section.)
1878 [[exporting-via-http]]
1879 Exporting a git repository via http
1880 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1882 The git protocol gives better performance and reliability, but on a
1883 host with a web server set up, http exports may be simpler to set up.
1885 All you need to do is place the newly created bare git repository in
1886 a directory that is exported by the web server, and make some
1887 adjustments to give web clients some extra information they need:
1889 -------------------------------------------------
1890 $ mv proj.git /home/you/public_html/proj.git
1891 $ cd proj.git
1892 $ git --bare update-server-info
1893 $ mv hooks/post-update.sample hooks/post-update
1894 -------------------------------------------------
1896 (For an explanation of the last two lines, see
1897 linkgit:git-update-server-info[1] and linkgit:githooks[5].)
1899 Advertise the URL of proj.git. Anybody else should then be able to
1900 clone or pull from that URL, for example with a command line like:
1902 -------------------------------------------------
1903 $ git clone http://yourserver.com/~you/proj.git
1904 -------------------------------------------------
1906 (See also
1907 link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1908 for a slightly more sophisticated setup using WebDAV which also
1909 allows pushing over http.)
1911 [[pushing-changes-to-a-public-repository]]
1912 Pushing changes to a public repository
1913 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1915 Note that the two techniques outlined above (exporting via
1916 <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1917 maintainers to fetch your latest changes, but they do not allow write
1918 access, which you will need to update the public repository with the
1919 latest changes created in your private repository.
1921 The simplest way to do this is using linkgit:git-push[1] and ssh; to
1922 update the remote branch named "master" with the latest state of your
1923 branch named "master", run
1925 -------------------------------------------------
1926 $ git push ssh://yourserver.com/~you/proj.git master:master
1927 -------------------------------------------------
1929 or just
1931 -------------------------------------------------
1932 $ git push ssh://yourserver.com/~you/proj.git master
1933 -------------------------------------------------
1935 As with git-fetch, git-push will complain if this does not result in a
1936 <<fast-forwards,fast forward>>; see the following section for details on
1937 handling this case.
1939 Note that the target of a "push" is normally a
1940 <<def_bare_repository,bare>> repository. You can also push to a
1941 repository that has a checked-out working tree, but the working tree
1942 will not be updated by the push. This may lead to unexpected results if
1943 the branch you push to is the currently checked-out branch!
1945 As with git-fetch, you may also set up configuration options to
1946 save typing; so, for example, after
1948 -------------------------------------------------
1949 $ cat >>.git/config <<EOF
1950 [remote "public-repo"]
1951 url = ssh://yourserver.com/~you/proj.git
1952 EOF
1953 -------------------------------------------------
1955 you should be able to perform the above push with just
1957 -------------------------------------------------
1958 $ git push public-repo master
1959 -------------------------------------------------
1961 See the explanations of the remote.<name>.url, branch.<name>.remote,
1962 and remote.<name>.push options in linkgit:git-config[1] for
1963 details.
1965 [[forcing-push]]
1966 What to do when a push fails
1967 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1969 If a push would not result in a <<fast-forwards,fast forward>> of the
1970 remote branch, then it will fail with an error like:
1972 -------------------------------------------------
1973 error: remote 'refs/heads/master' is not an ancestor of
1974 local 'refs/heads/master'.
1975 Maybe you are not up-to-date and need to pull first?
1976 error: failed to push to 'ssh://yourserver.com/~you/proj.git'
1977 -------------------------------------------------
1979 This can happen, for example, if you:
1981 - use `git-reset --hard` to remove already-published commits, or
1982 - use `git-commit --amend` to replace already-published commits
1983 (as in <<fixing-a-mistake-by-rewriting-history>>), or
1984 - use `git-rebase` to rebase any already-published commits (as
1985 in <<using-git-rebase>>).
1987 You may force git-push to perform the update anyway by preceding the
1988 branch name with a plus sign:
1990 -------------------------------------------------
1991 $ git push ssh://yourserver.com/~you/proj.git +master
1992 -------------------------------------------------
1994 Normally whenever a branch head in a public repository is modified, it
1995 is modified to point to a descendant of the commit that it pointed to
1996 before. By forcing a push in this situation, you break that convention.
1997 (See <<problems-With-rewriting-history>>.)
1999 Nevertheless, this is a common practice for people that need a simple
2000 way to publish a work-in-progress patch series, and it is an acceptable
2001 compromise as long as you warn other developers that this is how you
2002 intend to manage the branch.
2004 It's also possible for a push to fail in this way when other people have
2005 the right to push to the same repository. In that case, the correct
2006 solution is to retry the push after first updating your work: either by a
2007 pull, or by a fetch followed by a rebase; see the
2008 <<setting-up-a-shared-repository,next section>> and
2009 linkgit:gitcvs-migration[7] for more.
2011 [[setting-up-a-shared-repository]]
2012 Setting up a shared repository
2013 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2015 Another way to collaborate is by using a model similar to that
2016 commonly used in CVS, where several developers with special rights
2017 all push to and pull from a single shared repository. See
2018 linkgit:gitcvs-migration[7] for instructions on how to
2019 set this up.
2021 However, while there is nothing wrong with git's support for shared
2022 repositories, this mode of operation is not generally recommended,
2023 simply because the mode of collaboration that git supports--by
2024 exchanging patches and pulling from public repositories--has so many
2025 advantages over the central shared repository:
2027 - Git's ability to quickly import and merge patches allows a
2028 single maintainer to process incoming changes even at very
2029 high rates. And when that becomes too much, git-pull provides
2030 an easy way for that maintainer to delegate this job to other
2031 maintainers while still allowing optional review of incoming
2032 changes.
2033 - Since every developer's repository has the same complete copy
2034 of the project history, no repository is special, and it is
2035 trivial for another developer to take over maintenance of a
2036 project, either by mutual agreement, or because a maintainer
2037 becomes unresponsive or difficult to work with.
2038 - The lack of a central group of "committers" means there is
2039 less need for formal decisions about who is "in" and who is
2040 "out".
2042 [[setting-up-gitweb]]
2043 Allowing web browsing of a repository
2044 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2046 The gitweb cgi script provides users an easy way to browse your
2047 project's files and history without having to install git; see the file
2048 gitweb/INSTALL in the git source tree for instructions on setting it up.
2050 [[sharing-development-examples]]
2051 Examples
2052 --------
2054 [[maintaining-topic-branches]]
2055 Maintaining topic branches for a Linux subsystem maintainer
2056 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2058 This describes how Tony Luck uses git in his role as maintainer of the
2059 IA64 architecture for the Linux kernel.
2061 He uses two public branches:
2063 - A "test" tree into which patches are initially placed so that they
2064 can get some exposure when integrated with other ongoing development.
2065 This tree is available to Andrew for pulling into -mm whenever he
2066 wants.
2068 - A "release" tree into which tested patches are moved for final sanity
2069 checking, and as a vehicle to send them upstream to Linus (by sending
2070 him a "please pull" request.)
2072 He also uses a set of temporary branches ("topic branches"), each
2073 containing a logical grouping of patches.
2075 To set this up, first create your work tree by cloning Linus's public
2076 tree:
2078 -------------------------------------------------
2079 $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2080 $ cd work
2081 -------------------------------------------------
2083 Linus's tree will be stored in the remote branch named origin/master,
2084 and can be updated using linkgit:git-fetch[1]; you can track other
2085 public trees using linkgit:git-remote[1] to set up a "remote" and
2086 linkgit:git-fetch[1] to keep them up-to-date; see
2087 <<repositories-and-branches>>.
2089 Now create the branches in which you are going to work; these start out
2090 at the current tip of origin/master branch, and should be set up (using
2091 the --track option to linkgit:git-branch[1]) to merge changes in from
2092 Linus by default.
2094 -------------------------------------------------
2095 $ git branch --track test origin/master
2096 $ git branch --track release origin/master
2097 -------------------------------------------------
2099 These can be easily kept up to date using linkgit:git-pull[1].
2101 -------------------------------------------------
2102 $ git checkout test && git pull
2103 $ git checkout release && git pull
2104 -------------------------------------------------
2106 Important note! If you have any local changes in these branches, then
2107 this merge will create a commit object in the history (with no local
2108 changes git will simply do a "Fast forward" merge). Many people dislike
2109 the "noise" that this creates in the Linux history, so you should avoid
2110 doing this capriciously in the "release" branch, as these noisy commits
2111 will become part of the permanent history when you ask Linus to pull
2112 from the release branch.
2114 A few configuration variables (see linkgit:git-config[1]) can
2115 make it easy to push both branches to your public tree. (See
2116 <<setting-up-a-public-repository>>.)
2118 -------------------------------------------------
2119 $ cat >> .git/config <<EOF
2120 [remote "mytree"]
2121 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2122 push = release
2123 push = test
2124 EOF
2125 -------------------------------------------------
2127 Then you can push both the test and release trees using
2128 linkgit:git-push[1]:
2130 -------------------------------------------------
2131 $ git push mytree
2132 -------------------------------------------------
2134 or push just one of the test and release branches using:
2136 -------------------------------------------------
2137 $ git push mytree test
2138 -------------------------------------------------
2140 or
2142 -------------------------------------------------
2143 $ git push mytree release
2144 -------------------------------------------------
2146 Now to apply some patches from the community. Think of a short
2147 snappy name for a branch to hold this patch (or related group of
2148 patches), and create a new branch from the current tip of Linus's
2149 branch:
2151 -------------------------------------------------
2152 $ git checkout -b speed-up-spinlocks origin
2153 -------------------------------------------------
2155 Now you apply the patch(es), run some tests, and commit the change(s). If
2156 the patch is a multi-part series, then you should apply each as a separate
2157 commit to this branch.
2159 -------------------------------------------------
2160 $ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2161 -------------------------------------------------
2163 When you are happy with the state of this change, you can pull it into the
2164 "test" branch in preparation to make it public:
2166 -------------------------------------------------
2167 $ git checkout test && git pull . speed-up-spinlocks
2168 -------------------------------------------------
2170 It is unlikely that you would have any conflicts here ... but you might if you
2171 spent a while on this step and had also pulled new versions from upstream.
2173 Some time later when enough time has passed and testing done, you can pull the
2174 same branch into the "release" tree ready to go upstream. This is where you
2175 see the value of keeping each patch (or patch series) in its own branch. It
2176 means that the patches can be moved into the "release" tree in any order.
2178 -------------------------------------------------
2179 $ git checkout release && git pull . speed-up-spinlocks
2180 -------------------------------------------------
2182 After a while, you will have a number of branches, and despite the
2183 well chosen names you picked for each of them, you may forget what
2184 they are for, or what status they are in. To get a reminder of what
2185 changes are in a specific branch, use:
2187 -------------------------------------------------
2188 $ git log linux..branchname | git shortlog
2189 -------------------------------------------------
2191 To see whether it has already been merged into the test or release branches,
2192 use:
2194 -------------------------------------------------
2195 $ git log test..branchname
2196 -------------------------------------------------
2198 or
2200 -------------------------------------------------
2201 $ git log release..branchname
2202 -------------------------------------------------
2204 (If this branch has not yet been merged, you will see some log entries.
2205 If it has been merged, then there will be no output.)
2207 Once a patch completes the great cycle (moving from test to release,
2208 then pulled by Linus, and finally coming back into your local
2209 "origin/master" branch), the branch for this change is no longer needed.
2210 You detect this when the output from:
2212 -------------------------------------------------
2213 $ git log origin..branchname
2214 -------------------------------------------------
2216 is empty. At this point the branch can be deleted:
2218 -------------------------------------------------
2219 $ git branch -d branchname
2220 -------------------------------------------------
2222 Some changes are so trivial that it is not necessary to create a separate
2223 branch and then merge into each of the test and release branches. For
2224 these changes, just apply directly to the "release" branch, and then
2225 merge that into the "test" branch.
2227 To create diffstat and shortlog summaries of changes to include in a "please
2228 pull" request to Linus you can use:
2230 -------------------------------------------------
2231 $ git diff --stat origin..release
2232 -------------------------------------------------
2234 and
2236 -------------------------------------------------
2237 $ git log -p origin..release | git shortlog
2238 -------------------------------------------------
2240 Here are some of the scripts that simplify all this even further.
2242 -------------------------------------------------
2243 ==== update script ====
2244 # Update a branch in my GIT tree. If the branch to be updated
2245 # is origin, then pull from kernel.org. Otherwise merge
2246 # origin/master branch into test|release branch
2248 case "$1" in
2249 test|release)
2250 git checkout $1 && git pull . origin
2251 ;;
2252 origin)
2253 before=$(git rev-parse refs/remotes/origin/master)
2254 git fetch origin
2255 after=$(git rev-parse refs/remotes/origin/master)
2256 if [ $before != $after ]
2257 then
2258 git log $before..$after | git shortlog
2259 fi
2260 ;;
2261 *)
2262 echo "Usage: $0 origin|test|release" 1>&2
2263 exit 1
2264 ;;
2265 esac
2266 -------------------------------------------------
2268 -------------------------------------------------
2269 ==== merge script ====
2270 # Merge a branch into either the test or release branch
2272 pname=$0
2274 usage()
2275 {
2276 echo "Usage: $pname branch test|release" 1>&2
2277 exit 1
2278 }
2280 git show-ref -q --verify -- refs/heads/"$1" || {
2281 echo "Can't see branch <$1>" 1>&2
2282 usage
2283 }
2285 case "$2" in
2286 test|release)
2287 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2288 then
2289 echo $1 already merged into $2 1>&2
2290 exit 1
2291 fi
2292 git checkout $2 && git pull . $1
2293 ;;
2294 *)
2295 usage
2296 ;;
2297 esac
2298 -------------------------------------------------
2300 -------------------------------------------------
2301 ==== status script ====
2302 # report on status of my ia64 GIT tree
2304 gb=$(tput setab 2)
2305 rb=$(tput setab 1)
2306 restore=$(tput setab 9)
2308 if [ `git rev-list test..release | wc -c` -gt 0 ]
2309 then
2310 echo $rb Warning: commits in release that are not in test $restore
2311 git log test..release
2312 fi
2314 for branch in `git show-ref --heads | sed 's|^.*/||'`
2315 do
2316 if [ $branch = test -o $branch = release ]
2317 then
2318 continue
2319 fi
2321 echo -n $gb ======= $branch ====== $restore " "
2322 status=
2323 for ref in test release origin/master
2324 do
2325 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2326 then
2327 status=$status${ref:0:1}
2328 fi
2329 done
2330 case $status in
2331 trl)
2332 echo $rb Need to pull into test $restore
2333 ;;
2334 rl)
2335 echo "In test"
2336 ;;
2337 l)
2338 echo "Waiting for linus"
2339 ;;
2340 "")
2341 echo $rb All done $restore
2342 ;;
2343 *)
2344 echo $rb "<$status>" $restore
2345 ;;
2346 esac
2347 git log origin/master..$branch | git shortlog
2348 done
2349 -------------------------------------------------
2352 [[cleaning-up-history]]
2353 Rewriting history and maintaining patch series
2354 ==============================================
2356 Normally commits are only added to a project, never taken away or
2357 replaced. Git is designed with this assumption, and violating it will
2358 cause git's merge machinery (for example) to do the wrong thing.
2360 However, there is a situation in which it can be useful to violate this
2361 assumption.
2363 [[patch-series]]
2364 Creating the perfect patch series
2365 ---------------------------------
2367 Suppose you are a contributor to a large project, and you want to add a
2368 complicated feature, and to present it to the other developers in a way
2369 that makes it easy for them to read your changes, verify that they are
2370 correct, and understand why you made each change.
2372 If you present all of your changes as a single patch (or commit), they
2373 may find that it is too much to digest all at once.
2375 If you present them with the entire history of your work, complete with
2376 mistakes, corrections, and dead ends, they may be overwhelmed.
2378 So the ideal is usually to produce a series of patches such that:
2380 1. Each patch can be applied in order.
2382 2. Each patch includes a single logical change, together with a
2383 message explaining the change.
2385 3. No patch introduces a regression: after applying any initial
2386 part of the series, the resulting project still compiles and
2387 works, and has no bugs that it didn't have before.
2389 4. The complete series produces the same end result as your own
2390 (probably much messier!) development process did.
2392 We will introduce some tools that can help you do this, explain how to
2393 use them, and then explain some of the problems that can arise because
2394 you are rewriting history.
2396 [[using-git-rebase]]
2397 Keeping a patch series up to date using git-rebase
2398 --------------------------------------------------
2400 Suppose that you create a branch "mywork" on a remote-tracking branch
2401 "origin", and create some commits on top of it:
2403 -------------------------------------------------
2404 $ git checkout -b mywork origin
2405 $ vi file.txt
2406 $ git commit
2407 $ vi otherfile.txt
2408 $ git commit
2409 ...
2410 -------------------------------------------------
2412 You have performed no merges into mywork, so it is just a simple linear
2413 sequence of patches on top of "origin":
2415 ................................................
2416 o--o--o <-- origin
2417 \
2418 o--o--o <-- mywork
2419 ................................................
2421 Some more interesting work has been done in the upstream project, and
2422 "origin" has advanced:
2424 ................................................
2425 o--o--O--o--o--o <-- origin
2426 \
2427 a--b--c <-- mywork
2428 ................................................
2430 At this point, you could use "pull" to merge your changes back in;
2431 the result would create a new merge commit, like this:
2433 ................................................
2434 o--o--O--o--o--o <-- origin
2435 \ \
2436 a--b--c--m <-- mywork
2437 ................................................
2439 However, if you prefer to keep the history in mywork a simple series of
2440 commits without any merges, you may instead choose to use
2441 linkgit:git-rebase[1]:
2443 -------------------------------------------------
2444 $ git checkout mywork
2445 $ git rebase origin
2446 -------------------------------------------------
2448 This will remove each of your commits from mywork, temporarily saving
2449 them as patches (in a directory named ".git/rebase-apply"), update mywork to
2450 point at the latest version of origin, then apply each of the saved
2451 patches to the new mywork. The result will look like:
2454 ................................................
2455 o--o--O--o--o--o <-- origin
2456 \
2457 a'--b'--c' <-- mywork
2458 ................................................
2460 In the process, it may discover conflicts. In that case it will stop
2461 and allow you to fix the conflicts; after fixing conflicts, use "git-add"
2462 to update the index with those contents, and then, instead of
2463 running git-commit, just run
2465 -------------------------------------------------
2466 $ git rebase --continue
2467 -------------------------------------------------
2469 and git will continue applying the rest of the patches.
2471 At any point you may use the `--abort` option to abort this process and
2472 return mywork to the state it had before you started the rebase:
2474 -------------------------------------------------
2475 $ git rebase --abort
2476 -------------------------------------------------
2478 [[rewriting-one-commit]]
2479 Rewriting a single commit
2480 -------------------------
2482 We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
2483 most recent commit using
2485 -------------------------------------------------
2486 $ git commit --amend
2487 -------------------------------------------------
2489 which will replace the old commit by a new commit incorporating your
2490 changes, giving you a chance to edit the old commit message first.
2492 You can also use a combination of this and linkgit:git-rebase[1] to
2493 replace a commit further back in your history and recreate the
2494 intervening changes on top of it. First, tag the problematic commit
2495 with
2497 -------------------------------------------------
2498 $ git tag bad mywork~5
2499 -------------------------------------------------
2501 (Either gitk or git-log may be useful for finding the commit.)
2503 Then check out that commit, edit it, and rebase the rest of the series
2504 on top of it (note that we could check out the commit on a temporary
2505 branch, but instead we're using a <<detached-head,detached head>>):
2507 -------------------------------------------------
2508 $ git checkout bad
2509 $ # make changes here and update the index
2510 $ git commit --amend
2511 $ git rebase --onto HEAD bad mywork
2512 -------------------------------------------------
2514 When you're done, you'll be left with mywork checked out, with the top
2515 patches on mywork reapplied on top of your modified commit. You can
2516 then clean up with
2518 -------------------------------------------------
2519 $ git tag -d bad
2520 -------------------------------------------------
2522 Note that the immutable nature of git history means that you haven't really
2523 "modified" existing commits; instead, you have replaced the old commits with
2524 new commits having new object names.
2526 [[reordering-patch-series]]
2527 Reordering or selecting from a patch series
2528 -------------------------------------------
2530 Given one existing commit, the linkgit:git-cherry-pick[1] command
2531 allows you to apply the change introduced by that commit and create a
2532 new commit that records it. So, for example, if "mywork" points to a
2533 series of patches on top of "origin", you might do something like:
2535 -------------------------------------------------
2536 $ git checkout -b mywork-new origin
2537 $ gitk origin..mywork &
2538 -------------------------------------------------
2540 and browse through the list of patches in the mywork branch using gitk,
2541 applying them (possibly in a different order) to mywork-new using
2542 cherry-pick, and possibly modifying them as you go using `commit --amend`.
2543 The linkgit:git-gui[1] command may also help as it allows you to
2544 individually select diff hunks for inclusion in the index (by
2545 right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
2547 Another technique is to use git-format-patch to create a series of
2548 patches, then reset the state to before the patches:
2550 -------------------------------------------------
2551 $ git format-patch origin
2552 $ git reset --hard origin
2553 -------------------------------------------------
2555 Then modify, reorder, or eliminate patches as preferred before applying
2556 them again with linkgit:git-am[1].
2558 [[patch-series-tools]]
2559 Other tools
2560 -----------
2562 There are numerous other tools, such as StGIT, which exist for the
2563 purpose of maintaining a patch series. These are outside of the scope of
2564 this manual.
2566 [[problems-With-rewriting-history]]
2567 Problems with rewriting history
2568 -------------------------------
2570 The primary problem with rewriting the history of a branch has to do
2571 with merging. Suppose somebody fetches your branch and merges it into
2572 their branch, with a result something like this:
2574 ................................................
2575 o--o--O--o--o--o <-- origin
2576 \ \
2577 t--t--t--m <-- their branch:
2578 ................................................
2580 Then suppose you modify the last three commits:
2582 ................................................
2583 o--o--o <-- new head of origin
2584 /
2585 o--o--O--o--o--o <-- old head of origin
2586 ................................................
2588 If we examined all this history together in one repository, it will
2589 look like:
2591 ................................................
2592 o--o--o <-- new head of origin
2593 /
2594 o--o--O--o--o--o <-- old head of origin
2595 \ \
2596 t--t--t--m <-- their branch:
2597 ................................................
2599 Git has no way of knowing that the new head is an updated version of
2600 the old head; it treats this situation exactly the same as it would if
2601 two developers had independently done the work on the old and new heads
2602 in parallel. At this point, if someone attempts to merge the new head
2603 in to their branch, git will attempt to merge together the two (old and
2604 new) lines of development, instead of trying to replace the old by the
2605 new. The results are likely to be unexpected.
2607 You may still choose to publish branches whose history is rewritten,
2608 and it may be useful for others to be able to fetch those branches in
2609 order to examine or test them, but they should not attempt to pull such
2610 branches into their own work.
2612 For true distributed development that supports proper merging,
2613 published branches should never be rewritten.
2615 [[bisect-merges]]
2616 Why bisecting merge commits can be harder than bisecting linear history
2617 -----------------------------------------------------------------------
2619 The linkgit:git-bisect[1] command correctly handles history that
2620 includes merge commits. However, when the commit that it finds is a
2621 merge commit, the user may need to work harder than usual to figure out
2622 why that commit introduced a problem.
2624 Imagine this history:
2626 ................................................
2627 ---Z---o---X---...---o---A---C---D
2628 \ /
2629 o---o---Y---...---o---B
2630 ................................................
2632 Suppose that on the upper line of development, the meaning of one
2633 of the functions that exists at Z is changed at commit X. The
2634 commits from Z leading to A change both the function's
2635 implementation and all calling sites that exist at Z, as well
2636 as new calling sites they add, to be consistent. There is no
2637 bug at A.
2639 Suppose that in the meantime on the lower line of development somebody
2640 adds a new calling site for that function at commit Y. The
2641 commits from Z leading to B all assume the old semantics of that
2642 function and the callers and the callee are consistent with each
2643 other. There is no bug at B, either.
2645 Suppose further that the two development lines merge cleanly at C,
2646 so no conflict resolution is required.
2648 Nevertheless, the code at C is broken, because the callers added
2649 on the lower line of development have not been converted to the new
2650 semantics introduced on the upper line of development. So if all
2651 you know is that D is bad, that Z is good, and that
2652 linkgit:git-bisect[1] identifies C as the culprit, how will you
2653 figure out that the problem is due to this change in semantics?
2655 When the result of a git-bisect is a non-merge commit, you should
2656 normally be able to discover the problem by examining just that commit.
2657 Developers can make this easy by breaking their changes into small
2658 self-contained commits. That won't help in the case above, however,
2659 because the problem isn't obvious from examination of any single
2660 commit; instead, a global view of the development is required. To
2661 make matters worse, the change in semantics in the problematic
2662 function may be just one small part of the changes in the upper
2663 line of development.
2665 On the other hand, if instead of merging at C you had rebased the
2666 history between Z to B on top of A, you would have gotten this
2667 linear history:
2669 ................................................................
2670 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2671 ................................................................
2673 Bisecting between Z and D* would hit a single culprit commit Y*,
2674 and understanding why Y* was broken would probably be easier.
2676 Partly for this reason, many experienced git users, even when
2677 working on an otherwise merge-heavy project, keep the history
2678 linear by rebasing against the latest upstream version before
2679 publishing.
2681 [[advanced-branch-management]]
2682 Advanced branch management
2683 ==========================
2685 [[fetching-individual-branches]]
2686 Fetching individual branches
2687 ----------------------------
2689 Instead of using linkgit:git-remote[1], you can also choose just
2690 to update one branch at a time, and to store it locally under an
2691 arbitrary name:
2693 -------------------------------------------------
2694 $ git fetch origin todo:my-todo-work
2695 -------------------------------------------------
2697 The first argument, "origin", just tells git to fetch from the
2698 repository you originally cloned from. The second argument tells git
2699 to fetch the branch named "todo" from the remote repository, and to
2700 store it locally under the name refs/heads/my-todo-work.
2702 You can also fetch branches from other repositories; so
2704 -------------------------------------------------
2705 $ git fetch git://example.com/proj.git master:example-master
2706 -------------------------------------------------
2708 will create a new branch named "example-master" and store in it the
2709 branch named "master" from the repository at the given URL. If you
2710 already have a branch named example-master, it will attempt to
2711 <<fast-forwards,fast-forward>> to the commit given by example.com's
2712 master branch. In more detail:
2714 [[fetch-fast-forwards]]
2715 git fetch and fast-forwards
2716 ---------------------------
2718 In the previous example, when updating an existing branch, "git-fetch"
2719 checks to make sure that the most recent commit on the remote
2720 branch is a descendant of the most recent commit on your copy of the
2721 branch before updating your copy of the branch to point at the new
2722 commit. Git calls this process a <<fast-forwards,fast forward>>.
2724 A fast forward looks something like this:
2726 ................................................
2727 o--o--o--o <-- old head of the branch
2728 \
2729 o--o--o <-- new head of the branch
2730 ................................................
2733 In some cases it is possible that the new head will *not* actually be
2734 a descendant of the old head. For example, the developer may have
2735 realized she made a serious mistake, and decided to backtrack,
2736 resulting in a situation like:
2738 ................................................
2739 o--o--o--o--a--b <-- old head of the branch
2740 \
2741 o--o--o <-- new head of the branch
2742 ................................................
2744 In this case, "git-fetch" will fail, and print out a warning.
2746 In that case, you can still force git to update to the new head, as
2747 described in the following section. However, note that in the
2748 situation above this may mean losing the commits labeled "a" and "b",
2749 unless you've already created a reference of your own pointing to
2750 them.
2752 [[forcing-fetch]]
2753 Forcing git-fetch to do non-fast-forward updates
2754 ------------------------------------------------
2756 If git fetch fails because the new head of a branch is not a
2757 descendant of the old head, you may force the update with:
2759 -------------------------------------------------
2760 $ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2761 -------------------------------------------------
2763 Note the addition of the "+" sign. Alternatively, you can use the "-f"
2764 flag to force updates of all the fetched branches, as in:
2766 -------------------------------------------------
2767 $ git fetch -f origin
2768 -------------------------------------------------
2770 Be aware that commits that the old version of example/master pointed at
2771 may be lost, as we saw in the previous section.
2773 [[remote-branch-configuration]]
2774 Configuring remote branches
2775 ---------------------------
2777 We saw above that "origin" is just a shortcut to refer to the
2778 repository that you originally cloned from. This information is
2779 stored in git configuration variables, which you can see using
2780 linkgit:git-config[1]:
2782 -------------------------------------------------
2783 $ git config -l
2784 core.repositoryformatversion=0
2785 core.filemode=true
2786 core.logallrefupdates=true
2787 remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2788 remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2789 branch.master.remote=origin
2790 branch.master.merge=refs/heads/master
2791 -------------------------------------------------
2793 If there are other repositories that you also use frequently, you can
2794 create similar configuration options to save typing; for example,
2795 after
2797 -------------------------------------------------
2798 $ git config remote.example.url git://example.com/proj.git
2799 -------------------------------------------------
2801 then the following two commands will do the same thing:
2803 -------------------------------------------------
2804 $ git fetch git://example.com/proj.git master:refs/remotes/example/master
2805 $ git fetch example master:refs/remotes/example/master
2806 -------------------------------------------------
2808 Even better, if you add one more option:
2810 -------------------------------------------------
2811 $ git config remote.example.fetch master:refs/remotes/example/master
2812 -------------------------------------------------
2814 then the following commands will all do the same thing:
2816 -------------------------------------------------
2817 $ git fetch git://example.com/proj.git master:refs/remotes/example/master
2818 $ git fetch example master:refs/remotes/example/master
2819 $ git fetch example
2820 -------------------------------------------------
2822 You can also add a "+" to force the update each time:
2824 -------------------------------------------------
2825 $ git config remote.example.fetch +master:ref/remotes/example/master
2826 -------------------------------------------------
2828 Don't do this unless you're sure you won't mind "git fetch" possibly
2829 throwing away commits on 'example/master'.
2831 Also note that all of the above configuration can be performed by
2832 directly editing the file .git/config instead of using
2833 linkgit:git-config[1].
2835 See linkgit:git-config[1] for more details on the configuration
2836 options mentioned above.
2839 [[git-concepts]]
2840 Git concepts
2841 ============
2843 Git is built on a small number of simple but powerful ideas. While it
2844 is possible to get things done without understanding them, you will find
2845 git much more intuitive if you do.
2847 We start with the most important, the <<def_object_database,object
2848 database>> and the <<def_index,index>>.
2850 [[the-object-database]]
2851 The Object Database
2852 -------------------
2855 We already saw in <<understanding-commits>> that all commits are stored
2856 under a 40-digit "object name". In fact, all the information needed to
2857 represent the history of a project is stored in objects with such names.
2858 In each case the name is calculated by taking the SHA1 hash of the
2859 contents of the object. The SHA1 hash is a cryptographic hash function.
2860 What that means to us is that it is impossible to find two different
2861 objects with the same name. This has a number of advantages; among
2862 others:
2864 - Git can quickly determine whether two objects are identical or not,
2865 just by comparing names.
2866 - Since object names are computed the same way in every repository, the
2867 same content stored in two repositories will always be stored under
2868 the same name.
2869 - Git can detect errors when it reads an object, by checking that the
2870 object's name is still the SHA1 hash of its contents.
2872 (See <<object-details>> for the details of the object formatting and
2873 SHA1 calculation.)
2875 There are four different types of objects: "blob", "tree", "commit", and
2876 "tag".
2878 - A <<def_blob_object,"blob" object>> is used to store file data.
2879 - A <<def_tree_object,"tree" object>> ties one or more
2880 "blob" objects into a directory structure. In addition, a tree object
2881 can refer to other tree objects, thus creating a directory hierarchy.
2882 - A <<def_commit_object,"commit" object>> ties such directory hierarchies
2883 together into a <<def_DAG,directed acyclic graph>> of revisions--each
2884 commit contains the object name of exactly one tree designating the
2885 directory hierarchy at the time of the commit. In addition, a commit
2886 refers to "parent" commit objects that describe the history of how we
2887 arrived at that directory hierarchy.
2888 - A <<def_tag_object,"tag" object>> symbolically identifies and can be
2889 used to sign other objects. It contains the object name and type of
2890 another object, a symbolic name (of course!) and, optionally, a
2891 signature.
2893 The object types in some more detail:
2895 [[commit-object]]
2896 Commit Object
2897 ~~~~~~~~~~~~~
2899 The "commit" object links a physical state of a tree with a description
2900 of how we got there and why. Use the --pretty=raw option to
2901 linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite
2902 commit:
2904 ------------------------------------------------
2905 $ git show -s --pretty=raw 2be7fcb476
2906 commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2907 tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2908 parent 257a84d9d02e90447b149af58b271c19405edb6a
2909 author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2910 committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2912 Fix misspelling of 'suppress' in docs
2914 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2915 ------------------------------------------------
2917 As you can see, a commit is defined by:
2919 - a tree: The SHA1 name of a tree object (as defined below), representing
2920 the contents of a directory at a certain point in time.
2921 - parent(s): The SHA1 name of some number of commits which represent the
2922 immediately previous step(s) in the history of the project. The
2923 example above has one parent; merge commits may have more than
2924 one. A commit with no parents is called a "root" commit, and
2925 represents the initial revision of a project. Each project must have
2926 at least one root. A project can also have multiple roots, though
2927 that isn't common (or necessarily a good idea).
2928 - an author: The name of the person responsible for this change, together
2929 with its date.
2930 - a committer: The name of the person who actually created the commit,
2931 with the date it was done. This may be different from the author, for
2932 example, if the author was someone who wrote a patch and emailed it
2933 to the person who used it to create the commit.
2934 - a comment describing this commit.
2936 Note that a commit does not itself contain any information about what
2937 actually changed; all changes are calculated by comparing the contents
2938 of the tree referred to by this commit with the trees associated with
2939 its parents. In particular, git does not attempt to record file renames
2940 explicitly, though it can identify cases where the existence of the same
2941 file data at changing paths suggests a rename. (See, for example, the
2942 -M option to linkgit:git-diff[1]).
2944 A commit is usually created by linkgit:git-commit[1], which creates a
2945 commit whose parent is normally the current HEAD, and whose tree is
2946 taken from the content currently stored in the index.
2948 [[tree-object]]
2949 Tree Object
2950 ~~~~~~~~~~~
2952 The ever-versatile linkgit:git-show[1] command can also be used to
2953 examine tree objects, but linkgit:git-ls-tree[1] will give you more
2954 details:
2956 ------------------------------------------------
2957 $ git ls-tree fb3a8bdd0ce
2958 100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
2959 100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
2960 100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
2961 040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
2962 100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
2963 100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
2964 100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
2965 100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
2966 ...
2967 ------------------------------------------------
2969 As you can see, a tree object contains a list of entries, each with a
2970 mode, object type, SHA1 name, and name, sorted by name. It represents
2971 the contents of a single directory tree.
2973 The object type may be a blob, representing the contents of a file, or
2974 another tree, representing the contents of a subdirectory. Since trees
2975 and blobs, like all other objects, are named by the SHA1 hash of their
2976 contents, two trees have the same SHA1 name if and only if their
2977 contents (including, recursively, the contents of all subdirectories)
2978 are identical. This allows git to quickly determine the differences
2979 between two related tree objects, since it can ignore any entries with
2980 identical object names.
2982 (Note: in the presence of submodules, trees may also have commits as
2983 entries. See <<submodules>> for documentation.)
2985 Note that the files all have mode 644 or 755: git actually only pays
2986 attention to the executable bit.
2988 [[blob-object]]
2989 Blob Object
2990 ~~~~~~~~~~~
2992 You can use linkgit:git-show[1] to examine the contents of a blob; take,
2993 for example, the blob in the entry for "COPYING" from the tree above:
2995 ------------------------------------------------
2996 $ git show 6ff87c4664
2998 Note that the only valid version of the GPL as far as this project
2999 is concerned is _this_ particular version of the license (ie v2, not
3000 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
3001 ...
3002 ------------------------------------------------
3004 A "blob" object is nothing but a binary blob of data. It doesn't refer
3005 to anything else or have attributes of any kind.
3007 Since the blob is entirely defined by its data, if two files in a
3008 directory tree (or in multiple different versions of the repository)
3009 have the same contents, they will share the same blob object. The object
3010 is totally independent of its location in the directory tree, and
3011 renaming a file does not change the object that file is associated with.
3013 Note that any tree or blob object can be examined using
3014 linkgit:git-show[1] with the <revision>:<path> syntax. This can
3015 sometimes be useful for browsing the contents of a tree that is not
3016 currently checked out.
3018 [[trust]]
3019 Trust
3020 ~~~~~
3022 If you receive the SHA1 name of a blob from one source, and its contents
3023 from another (possibly untrusted) source, you can still trust that those
3024 contents are correct as long as the SHA1 name agrees. This is because
3025 the SHA1 is designed so that it is infeasible to find different contents
3026 that produce the same hash.
3028 Similarly, you need only trust the SHA1 name of a top-level tree object
3029 to trust the contents of the entire directory that it refers to, and if
3030 you receive the SHA1 name of a commit from a trusted source, then you
3031 can easily verify the entire history of commits reachable through
3032 parents of that commit, and all of those contents of the trees referred
3033 to by those commits.
3035 So to introduce some real trust in the system, the only thing you need
3036 to do is to digitally sign just 'one' special note, which includes the
3037 name of a top-level commit. Your digital signature shows others
3038 that you trust that commit, and the immutability of the history of
3039 commits tells others that they can trust the whole history.
3041 In other words, you can easily validate a whole archive by just
3042 sending out a single email that tells the people the name (SHA1 hash)
3043 of the top commit, and digitally sign that email using something
3044 like GPG/PGP.
3046 To assist in this, git also provides the tag object...
3048 [[tag-object]]
3049 Tag Object
3050 ~~~~~~~~~~
3052 A tag object contains an object, object type, tag name, the name of the
3053 person ("tagger") who created the tag, and a message, which may contain
3054 a signature, as can be seen using linkgit:git-cat-file[1]:
3056 ------------------------------------------------
3057 $ git cat-file tag v1.5.0
3058 object 437b1b20df4b356c9342dac8d38849f24ef44f27
3059 type commit
3060 tag v1.5.0
3061 tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
3063 GIT 1.5.0
3064 -----BEGIN PGP SIGNATURE-----
3065 Version: GnuPG v1.4.6 (GNU/Linux)
3067 iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
3068 nLE/L9aUXdWeTFPron96DLA=
3069 =2E+0
3070 -----END PGP SIGNATURE-----
3071 ------------------------------------------------
3073 See the linkgit:git-tag[1] command to learn how to create and verify tag
3074 objects. (Note that linkgit:git-tag[1] can also be used to create
3075 "lightweight tags", which are not tag objects at all, but just simple
3076 references whose names begin with "refs/tags/").
3078 [[pack-files]]
3079 How git stores objects efficiently: pack files
3080 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3082 Newly created objects are initially created in a file named after the
3083 object's SHA1 hash (stored in .git/objects).
3085 Unfortunately this system becomes inefficient once a project has a
3086 lot of objects. Try this on an old project:
3088 ------------------------------------------------
3089 $ git count-objects
3090 6930 objects, 47620 kilobytes
3091 ------------------------------------------------
3093 The first number is the number of objects which are kept in
3094 individual files. The second is the amount of space taken up by
3095 those "loose" objects.
3097 You can save space and make git faster by moving these loose objects in
3098 to a "pack file", which stores a group of objects in an efficient
3099 compressed format; the details of how pack files are formatted can be
3100 found in link:technical/pack-format.txt[technical/pack-format.txt].
3102 To put the loose objects into a pack, just run git repack:
3104 ------------------------------------------------
3105 $ git repack
3106 Generating pack...
3107 Done counting 6020 objects.
3108 Deltifying 6020 objects.
3109 100% (6020/6020) done
3110 Writing 6020 objects.
3111 100% (6020/6020) done
3112 Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
3113 Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
3114 ------------------------------------------------
3116 You can then run
3118 ------------------------------------------------
3119 $ git prune
3120 ------------------------------------------------
3122 to remove any of the "loose" objects that are now contained in the
3123 pack. This will also remove any unreferenced objects (which may be
3124 created when, for example, you use "git-reset" to remove a commit).
3125 You can verify that the loose objects are gone by looking at the
3126 .git/objects directory or by running
3128 ------------------------------------------------
3129 $ git count-objects
3130 0 objects, 0 kilobytes
3131 ------------------------------------------------
3133 Although the object files are gone, any commands that refer to those
3134 objects will work exactly as they did before.
3136 The linkgit:git-gc[1] command performs packing, pruning, and more for
3137 you, so is normally the only high-level command you need.
3139 [[dangling-objects]]
3140 Dangling objects
3141 ~~~~~~~~~~~~~~~~
3143 The linkgit:git-fsck[1] command will sometimes complain about dangling
3144 objects. They are not a problem.
3146 The most common cause of dangling objects is that you've rebased a
3147 branch, or you have pulled from somebody else who rebased a branch--see
3148 <<cleaning-up-history>>. In that case, the old head of the original
3149 branch still exists, as does everything it pointed to. The branch
3150 pointer itself just doesn't, since you replaced it with another one.
3152 There are also other situations that cause dangling objects. For
3153 example, a "dangling blob" may arise because you did a "git-add" of a
3154 file, but then, before you actually committed it and made it part of the
3155 bigger picture, you changed something else in that file and committed
3156 that *updated* thing--the old state that you added originally ends up
3157 not being pointed to by any commit or tree, so it's now a dangling blob
3158 object.
3160 Similarly, when the "recursive" merge strategy runs, and finds that
3161 there are criss-cross merges and thus more than one merge base (which is
3162 fairly unusual, but it does happen), it will generate one temporary
3163 midway tree (or possibly even more, if you had lots of criss-crossing
3164 merges and more than two merge bases) as a temporary internal merge
3165 base, and again, those are real objects, but the end result will not end
3166 up pointing to them, so they end up "dangling" in your repository.
3168 Generally, dangling objects aren't anything to worry about. They can
3169 even be very useful: if you screw something up, the dangling objects can
3170 be how you recover your old tree (say, you did a rebase, and realized
3171 that you really didn't want to--you can look at what dangling objects
3172 you have, and decide to reset your head to some old dangling state).
3174 For commits, you can just use:
3176 ------------------------------------------------
3177 $ gitk <dangling-commit-sha-goes-here> --not --all
3178 ------------------------------------------------
3180 This asks for all the history reachable from the given commit but not
3181 from any branch, tag, or other reference. If you decide it's something
3182 you want, you can always create a new reference to it, e.g.,
3184 ------------------------------------------------
3185 $ git branch recovered-branch <dangling-commit-sha-goes-here>
3186 ------------------------------------------------
3188 For blobs and trees, you can't do the same, but you can still examine
3189 them. You can just do
3191 ------------------------------------------------
3192 $ git show <dangling-blob/tree-sha-goes-here>
3193 ------------------------------------------------
3195 to show what the contents of the blob were (or, for a tree, basically
3196 what the "ls" for that directory was), and that may give you some idea
3197 of what the operation was that left that dangling object.
3199 Usually, dangling blobs and trees aren't very interesting. They're
3200 almost always the result of either being a half-way mergebase (the blob
3201 will often even have the conflict markers from a merge in it, if you
3202 have had conflicting merges that you fixed up by hand), or simply
3203 because you interrupted a "git-fetch" with ^C or something like that,
3204 leaving _some_ of the new objects in the object database, but just
3205 dangling and useless.
3207 Anyway, once you are sure that you're not interested in any dangling
3208 state, you can just prune all unreachable objects:
3210 ------------------------------------------------
3211 $ git prune
3212 ------------------------------------------------
3214 and they'll be gone. But you should only run "git prune" on a quiescent
3215 repository--it's kind of like doing a filesystem fsck recovery: you
3216 don't want to do that while the filesystem is mounted.
3218 (The same is true of "git-fsck" itself, btw, but since
3219 git-fsck never actually *changes* the repository, it just reports
3220 on what it found, git-fsck itself is never "dangerous" to run.
3221 Running it while somebody is actually changing the repository can cause
3222 confusing and scary messages, but it won't actually do anything bad. In
3223 contrast, running "git prune" while somebody is actively changing the
3224 repository is a *BAD* idea).
3226 [[recovering-from-repository-corruption]]
3227 Recovering from repository corruption
3228 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3230 By design, git treats data trusted to it with caution. However, even in
3231 the absence of bugs in git itself, it is still possible that hardware or
3232 operating system errors could corrupt data.
3234 The first defense against such problems is backups. You can back up a
3235 git directory using clone, or just using cp, tar, or any other backup
3236 mechanism.
3238 As a last resort, you can search for the corrupted objects and attempt
3239 to replace them by hand. Back up your repository before attempting this
3240 in case you corrupt things even more in the process.
3242 We'll assume that the problem is a single missing or corrupted blob,
3243 which is sometimes a solvable problem. (Recovering missing trees and
3244 especially commits is *much* harder).
3246 Before starting, verify that there is corruption, and figure out where
3247 it is with linkgit:git-fsck[1]; this may be time-consuming.
3249 Assume the output looks like this:
3251 ------------------------------------------------
3252 $ git fsck --full
3253 broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
3254 to blob 4b9458b3786228369c63936db65827de3cc06200
3255 missing blob 4b9458b3786228369c63936db65827de3cc06200
3256 ------------------------------------------------
3258 (Typically there will be some "dangling object" messages too, but they
3259 aren't interesting.)
3261 Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6
3262 points to it. If you could find just one copy of that missing blob
3263 object, possibly in some other repository, you could move it into
3264 .git/objects/4b/9458b3... and be done. Suppose you can't. You can
3265 still examine the tree that pointed to it with linkgit:git-ls-tree[1],
3266 which might output something like:
3268 ------------------------------------------------
3269 $ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
3270 100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore
3271 100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap
3272 100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING
3273 ...
3274 100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile
3275 ...
3276 ------------------------------------------------
3278 So now you know that the missing blob was the data for a file named
3279 "myfile". And chances are you can also identify the directory--let's
3280 say it's in "somedirectory". If you're lucky the missing copy might be
3281 the same as the copy you have checked out in your working tree at
3282 "somedirectory/myfile"; you can test whether that's right with
3283 linkgit:git-hash-object[1]:
3285 ------------------------------------------------
3286 $ git hash-object -w somedirectory/myfile
3287 ------------------------------------------------
3289 which will create and store a blob object with the contents of
3290 somedirectory/myfile, and output the sha1 of that object. if you're
3291 extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in
3292 which case you've guessed right, and the corruption is fixed!
3294 Otherwise, you need more information. How do you tell which version of
3295 the file has been lost?
3297 The easiest way to do this is with:
3299 ------------------------------------------------
3300 $ git log --raw --all --full-history -- somedirectory/myfile
3301 ------------------------------------------------
3303 Because you're asking for raw output, you'll now get something like
3305 ------------------------------------------------
3306 commit abc
3307 Author:
3308 Date:
3309 ...
3310 :100644 100644 4b9458b... newsha... M somedirectory/myfile
3313 commit xyz
3314 Author:
3315 Date:
3317 ...
3318 :100644 100644 oldsha... 4b9458b... M somedirectory/myfile
3319 ------------------------------------------------
3321 This tells you that the immediately preceding version of the file was
3322 "newsha", and that the immediately following version was "oldsha".
3323 You also know the commit messages that went with the change from oldsha
3324 to 4b9458b and with the change from 4b9458b to newsha.
3326 If you've been committing small enough changes, you may now have a good
3327 shot at reconstructing the contents of the in-between state 4b9458b.
3329 If you can do that, you can now recreate the missing object with
3331 ------------------------------------------------
3332 $ git hash-object -w <recreated-file>
3333 ------------------------------------------------
3335 and your repository is good again!
3337 (Btw, you could have ignored the fsck, and started with doing a
3339 ------------------------------------------------
3340 $ git log --raw --all
3341 ------------------------------------------------
3343 and just looked for the sha of the missing object (4b9458b..) in that
3344 whole thing. It's up to you - git does *have* a lot of information, it is
3345 just missing one particular blob version.
3347 [[the-index]]
3348 The index
3349 -----------
3351 The index is a binary file (generally kept in .git/index) containing a
3352 sorted list of path names, each with permissions and the SHA1 of a blob
3353 object; linkgit:git-ls-files[1] can show you the contents of the index:
3355 -------------------------------------------------
3356 $ git ls-files --stage
3357 100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore
3358 100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap
3359 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING
3360 100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore
3361 100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile
3362 ...
3363 100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h
3364 100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c
3365 100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h
3366 -------------------------------------------------
3368 Note that in older documentation you may see the index called the
3369 "current directory cache" or just the "cache". It has three important
3370 properties:
3372 1. The index contains all the information necessary to generate a single
3373 (uniquely determined) tree object.
3374 +
3375 For example, running linkgit:git-commit[1] generates this tree object
3376 from the index, stores it in the object database, and uses it as the
3377 tree object associated with the new commit.
3379 2. The index enables fast comparisons between the tree object it defines
3380 and the working tree.
3381 +
3382 It does this by storing some additional data for each entry (such as
3383 the last modified time). This data is not displayed above, and is not
3384 stored in the created tree object, but it can be used to determine
3385 quickly which files in the working directory differ from what was
3386 stored in the index, and thus save git from having to read all of the
3387 data from such files to look for changes.
3389 3. It can efficiently represent information about merge conflicts
3390 between different tree objects, allowing each pathname to be
3391 associated with sufficient information about the trees involved that
3392 you can create a three-way merge between them.
3393 +
3394 We saw in <<conflict-resolution>> that during a merge the index can
3395 store multiple versions of a single file (called "stages"). The third
3396 column in the linkgit:git-ls-files[1] output above is the stage
3397 number, and will take on values other than 0 for files with merge
3398 conflicts.
3400 The index is thus a sort of temporary staging area, which is filled with
3401 a tree which you are in the process of working on.
3403 If you blow the index away entirely, you generally haven't lost any
3404 information as long as you have the name of the tree that it described.
3406 [[submodules]]
3407 Submodules
3408 ==========
3410 Large projects are often composed of smaller, self-contained modules. For
3411 example, an embedded Linux distribution's source tree would include every
3412 piece of software in the distribution with some local modifications; a movie
3413 player might need to build against a specific, known-working version of a
3414 decompression library; several independent programs might all share the same
3415 build scripts.
3417 With centralized revision control systems this is often accomplished by
3418 including every module in one single repository. Developers can check out
3419 all modules or only the modules they need to work with. They can even modify
3420 files across several modules in a single commit while moving things around
3421 or updating APIs and translations.
3423 Git does not allow partial checkouts, so duplicating this approach in Git
3424 would force developers to keep a local copy of modules they are not
3425 interested in touching. Commits in an enormous checkout would be slower
3426 than you'd expect as Git would have to scan every directory for changes.
3427 If modules have a lot of local history, clones would take forever.
3429 On the plus side, distributed revision control systems can much better
3430 integrate with external sources. In a centralized model, a single arbitrary
3431 snapshot of the external project is exported from its own revision control
3432 and then imported into the local revision control on a vendor branch. All
3433 the history is hidden. With distributed revision control you can clone the
3434 entire external history and much more easily follow development and re-merge
3435 local changes.
3437 Git's submodule support allows a repository to contain, as a subdirectory, a
3438 checkout of an external project. Submodules maintain their own identity;
3439 the submodule support just stores the submodule repository location and
3440 commit ID, so other developers who clone the containing project
3441 ("superproject") can easily clone all the submodules at the same revision.
3442 Partial checkouts of the superproject are possible: you can tell Git to
3443 clone none, some or all of the submodules.
3445 The linkgit:git-submodule[1] command is available since Git 1.5.3. Users
3446 with Git 1.5.2 can look up the submodule commits in the repository and
3447 manually check them out; earlier versions won't recognize the submodules at
3448 all.
3450 To see how submodule support works, create (for example) four example
3451 repositories that can be used later as a submodule:
3453 -------------------------------------------------
3454 $ mkdir ~/git
3455 $ cd ~/git
3456 $ for i in a b c d
3457 do
3458 mkdir $i
3459 cd $i
3460 git init
3461 echo "module $i" > $i.txt
3462 git add $i.txt
3463 git commit -m "Initial commit, submodule $i"
3464 cd ..
3465 done
3466 -------------------------------------------------
3468 Now create the superproject and add all the submodules:
3470 -------------------------------------------------
3471 $ mkdir super
3472 $ cd super
3473 $ git init
3474 $ for i in a b c d
3475 do
3476 git submodule add ~/git/$i $i
3477 done
3478 -------------------------------------------------
3480 NOTE: Do not use local URLs here if you plan to publish your superproject!
3482 See what files `git-submodule` created:
3484 -------------------------------------------------
3485 $ ls -a
3486 . .. .git .gitmodules a b c d
3487 -------------------------------------------------
3489 The `git-submodule add <repo> <path>` command does a couple of things:
3491 - It clones the submodule from <repo> to the given <path> under the
3492 current directory and by default checks out the master branch.
3493 - It adds the submodule's clone path to the linkgit:gitmodules[5] file and
3494 adds this file to the index, ready to be committed.
3495 - It adds the submodule's current commit ID to the index, ready to be
3496 committed.
3498 Commit the superproject:
3500 -------------------------------------------------
3501 $ git commit -m "Add submodules a, b, c and d."
3502 -------------------------------------------------
3504 Now clone the superproject:
3506 -------------------------------------------------
3507 $ cd ..
3508 $ git clone super cloned
3509 $ cd cloned
3510 -------------------------------------------------
3512 The submodule directories are there, but they're empty:
3514 -------------------------------------------------
3515 $ ls -a a
3516 . ..
3517 $ git submodule status
3518 -d266b9873ad50488163457f025db7cdd9683d88b a
3519 -e81d457da15309b4fef4249aba9b50187999670d b
3520 -c1536a972b9affea0f16e0680ba87332dc059146 c
3521 -d96249ff5d57de5de093e6baff9e0aafa5276a74 d
3522 -------------------------------------------------
3524 NOTE: The commit object names shown above would be different for you, but they
3525 should match the HEAD commit object names of your repositories. You can check
3526 it by running `git ls-remote ../a`.
3528 Pulling down the submodules is a two-step process. First run `git submodule
3529 init` to add the submodule repository URLs to `.git/config`:
3531 -------------------------------------------------
3532 $ git submodule init
3533 -------------------------------------------------
3535 Now use `git-submodule update` to clone the repositories and check out the
3536 commits specified in the superproject:
3538 -------------------------------------------------
3539 $ git submodule update
3540 $ cd a
3541 $ ls -a
3542 . .. .git a.txt
3543 -------------------------------------------------
3545 One major difference between `git-submodule update` and `git-submodule add` is
3546 that `git-submodule update` checks out a specific commit, rather than the tip
3547 of a branch. It's like checking out a tag: the head is detached, so you're not
3548 working on a branch.
3550 -------------------------------------------------
3551 $ git branch
3552 * (no branch)
3553 master
3554 -------------------------------------------------
3556 If you want to make a change within a submodule and you have a detached head,
3557 then you should create or checkout a branch, make your changes, publish the
3558 change within the submodule, and then update the superproject to reference the
3559 new commit:
3561 -------------------------------------------------
3562 $ git checkout master
3563 -------------------------------------------------
3565 or
3567 -------------------------------------------------
3568 $ git checkout -b fix-up
3569 -------------------------------------------------
3571 then
3573 -------------------------------------------------
3574 $ echo "adding a line again" >> a.txt
3575 $ git commit -a -m "Updated the submodule from within the superproject."
3576 $ git push
3577 $ cd ..
3578 $ git diff
3579 diff --git a/a b/a
3580 index d266b98..261dfac 160000
3581 --- a/a
3582 +++ b/a
3583 @@ -1 +1 @@
3584 -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b
3585 +Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24
3586 $ git add a
3587 $ git commit -m "Updated submodule a."
3588 $ git push
3589 -------------------------------------------------
3591 You have to run `git submodule update` after `git pull` if you want to update
3592 submodules, too.
3594 Pitfalls with submodules
3595 ------------------------
3597 Always publish the submodule change before publishing the change to the
3598 superproject that references it. If you forget to publish the submodule change,
3599 others won't be able to clone the repository:
3601 -------------------------------------------------
3602 $ cd ~/git/super/a
3603 $ echo i added another line to this file >> a.txt
3604 $ git commit -a -m "doing it wrong this time"
3605 $ cd ..
3606 $ git add a
3607 $ git commit -m "Updated submodule a again."
3608 $ git push
3609 $ cd ~/git/cloned
3610 $ git pull
3611 $ git submodule update
3612 error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.
3613 Did you forget to 'git add'?
3614 Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'
3615 -------------------------------------------------
3617 You also should not rewind branches in a submodule beyond commits that were
3618 ever recorded in any superproject.
3620 It's not safe to run `git submodule update` if you've made and committed
3621 changes within a submodule without checking out a branch first. They will be
3622 silently overwritten:
3624 -------------------------------------------------
3625 $ cat a.txt
3626 module a
3627 $ echo line added from private2 >> a.txt
3628 $ git commit -a -m "line added inside private2"
3629 $ cd ..
3630 $ git submodule update
3631 Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'
3632 $ cd a
3633 $ cat a.txt
3634 module a
3635 -------------------------------------------------
3637 NOTE: The changes are still visible in the submodule's reflog.
3639 This is not the case if you did not commit your changes.
3641 [[low-level-operations]]
3642 Low-level git operations
3643 ========================
3645 Many of the higher-level commands were originally implemented as shell
3646 scripts using a smaller core of low-level git commands. These can still
3647 be useful when doing unusual things with git, or just as a way to
3648 understand its inner workings.
3650 [[object-manipulation]]
3651 Object access and manipulation
3652 ------------------------------
3654 The linkgit:git-cat-file[1] command can show the contents of any object,
3655 though the higher-level linkgit:git-show[1] is usually more useful.
3657 The linkgit:git-commit-tree[1] command allows constructing commits with
3658 arbitrary parents and trees.
3660 A tree can be created with linkgit:git-write-tree[1] and its data can be
3661 accessed by linkgit:git-ls-tree[1]. Two trees can be compared with
3662 linkgit:git-diff-tree[1].
3664 A tag is created with linkgit:git-mktag[1], and the signature can be
3665 verified by linkgit:git-verify-tag[1], though it is normally simpler to
3666 use linkgit:git-tag[1] for both.
3668 [[the-workflow]]
3669 The Workflow
3670 ------------
3672 High-level operations such as linkgit:git-commit[1],
3673 linkgit:git-checkout[1] and linkgit:git-reset[1] work by moving data
3674 between the working tree, the index, and the object database. Git
3675 provides low-level operations which perform each of these steps
3676 individually.
3678 Generally, all "git" operations work on the index file. Some operations
3679 work *purely* on the index file (showing the current state of the
3680 index), but most operations move data between the index file and either
3681 the database or the working directory. Thus there are four main
3682 combinations:
3684 [[working-directory-to-index]]
3685 working directory -> index
3686 ~~~~~~~~~~~~~~~~~~~~~~~~~~
3688 The linkgit:git-update-index[1] command updates the index with
3689 information from the working directory. You generally update the
3690 index information by just specifying the filename you want to update,
3691 like so:
3693 -------------------------------------------------
3694 $ git update-index filename
3695 -------------------------------------------------
3697 but to avoid common mistakes with filename globbing etc, the command
3698 will not normally add totally new entries or remove old entries,
3699 i.e. it will normally just update existing cache entries.
3701 To tell git that yes, you really do realize that certain files no
3702 longer exist, or that new files should be added, you
3703 should use the `--remove` and `--add` flags respectively.
3705 NOTE! A `--remove` flag does 'not' mean that subsequent filenames will
3706 necessarily be removed: if the files still exist in your directory
3707 structure, the index will be updated with their new status, not
3708 removed. The only thing `--remove` means is that update-index will be
3709 considering a removed file to be a valid thing, and if the file really
3710 does not exist any more, it will update the index accordingly.
3712 As a special case, you can also do `git update-index --refresh`, which
3713 will refresh the "stat" information of each index to match the current
3714 stat information. It will 'not' update the object status itself, and
3715 it will only update the fields that are used to quickly test whether
3716 an object still matches its old backing store object.
3718 The previously introduced linkgit:git-add[1] is just a wrapper for
3719 linkgit:git-update-index[1].
3721 [[index-to-object-database]]
3722 index -> object database
3723 ~~~~~~~~~~~~~~~~~~~~~~~~
3725 You write your current index file to a "tree" object with the program
3727 -------------------------------------------------
3728 $ git write-tree
3729 -------------------------------------------------
3731 that doesn't come with any options--it will just write out the
3732 current index into the set of tree objects that describe that state,
3733 and it will return the name of the resulting top-level tree. You can
3734 use that tree to re-generate the index at any time by going in the
3735 other direction:
3737 [[object-database-to-index]]
3738 object database -> index
3739 ~~~~~~~~~~~~~~~~~~~~~~~~
3741 You read a "tree" file from the object database, and use that to
3742 populate (and overwrite--don't do this if your index contains any
3743 unsaved state that you might want to restore later!) your current
3744 index. Normal operation is just
3746 -------------------------------------------------
3747 $ git read-tree <sha1 of tree>
3748 -------------------------------------------------
3750 and your index file will now be equivalent to the tree that you saved
3751 earlier. However, that is only your 'index' file: your working
3752 directory contents have not been modified.
3754 [[index-to-working-directory]]
3755 index -> working directory
3756 ~~~~~~~~~~~~~~~~~~~~~~~~~~
3758 You update your working directory from the index by "checking out"
3759 files. This is not a very common operation, since normally you'd just
3760 keep your files updated, and rather than write to your working
3761 directory, you'd tell the index files about the changes in your
3762 working directory (i.e. `git-update-index`).
3764 However, if you decide to jump to a new version, or check out somebody
3765 else's version, or just restore a previous tree, you'd populate your
3766 index file with read-tree, and then you need to check out the result
3767 with
3769 -------------------------------------------------
3770 $ git checkout-index filename
3771 -------------------------------------------------
3773 or, if you want to check out all of the index, use `-a`.
3775 NOTE! git-checkout-index normally refuses to overwrite old files, so
3776 if you have an old version of the tree already checked out, you will
3777 need to use the "-f" flag ('before' the "-a" flag or the filename) to
3778 'force' the checkout.
3781 Finally, there are a few odds and ends which are not purely moving
3782 from one representation to the other:
3784 [[tying-it-all-together]]
3785 Tying it all together
3786 ~~~~~~~~~~~~~~~~~~~~~
3788 To commit a tree you have instantiated with "git write-tree", you'd
3789 create a "commit" object that refers to that tree and the history
3790 behind it--most notably the "parent" commits that preceded it in
3791 history.
3793 Normally a "commit" has one parent: the previous state of the tree
3794 before a certain change was made. However, sometimes it can have two
3795 or more parent commits, in which case we call it a "merge", due to the
3796 fact that such a commit brings together ("merges") two or more
3797 previous states represented by other commits.
3799 In other words, while a "tree" represents a particular directory state
3800 of a working directory, a "commit" represents that state in "time",
3801 and explains how we got there.
3803 You create a commit object by giving it the tree that describes the
3804 state at the time of the commit, and a list of parents:
3806 -------------------------------------------------
3807 $ git commit-tree <tree> -p <parent> [-p <parent2> ..]
3808 -------------------------------------------------
3810 and then giving the reason for the commit on stdin (either through
3811 redirection from a pipe or file, or by just typing it at the tty).
3813 git-commit-tree will return the name of the object that represents
3814 that commit, and you should save it away for later use. Normally,
3815 you'd commit a new `HEAD` state, and while git doesn't care where you
3816 save the note about that state, in practice we tend to just write the
3817 result to the file pointed at by `.git/HEAD`, so that we can always see
3818 what the last committed state was.
3820 Here is an ASCII art by Jon Loeliger that illustrates how
3821 various pieces fit together.
3823 ------------
3825 commit-tree
3826 commit obj
3827 +----+
3828 | |
3829 | |
3830 V V
3831 +-----------+
3832 | Object DB |
3833 | Backing |
3834 | Store |
3835 +-----------+
3836 ^
3837 write-tree | |
3838 tree obj | |
3839 | | read-tree
3840 | | tree obj
3841 V
3842 +-----------+
3843 | Index |
3844 | "cache" |
3845 +-----------+
3846 update-index ^
3847 blob obj | |
3848 | |
3849 checkout-index -u | | checkout-index
3850 stat | | blob obj
3851 V
3852 +-----------+
3853 | Working |
3854 | Directory |
3855 +-----------+
3857 ------------
3860 [[examining-the-data]]
3861 Examining the data
3862 ------------------
3864 You can examine the data represented in the object database and the
3865 index with various helper tools. For every object, you can use
3866 linkgit:git-cat-file[1] to examine details about the
3867 object:
3869 -------------------------------------------------
3870 $ git cat-file -t <objectname>
3871 -------------------------------------------------
3873 shows the type of the object, and once you have the type (which is
3874 usually implicit in where you find the object), you can use
3876 -------------------------------------------------
3877 $ git cat-file blob|tree|commit|tag <objectname>
3878 -------------------------------------------------
3880 to show its contents. NOTE! Trees have binary content, and as a result
3881 there is a special helper for showing that content, called
3882 `git-ls-tree`, which turns the binary content into a more easily
3883 readable form.
3885 It's especially instructive to look at "commit" objects, since those
3886 tend to be small and fairly self-explanatory. In particular, if you
3887 follow the convention of having the top commit name in `.git/HEAD`,
3888 you can do
3890 -------------------------------------------------
3891 $ git cat-file commit HEAD
3892 -------------------------------------------------
3894 to see what the top commit was.
3896 [[merging-multiple-trees]]
3897 Merging multiple trees
3898 ----------------------
3900 Git helps you do a three-way merge, which you can expand to n-way by
3901 repeating the merge procedure arbitrary times until you finally
3902 "commit" the state. The normal situation is that you'd only do one
3903 three-way merge (two parents), and commit it, but if you like to, you
3904 can do multiple parents in one go.
3906 To do a three-way merge, you need the two sets of "commit" objects
3907 that you want to merge, use those to find the closest common parent (a
3908 third "commit" object), and then use those commit objects to find the
3909 state of the directory ("tree" object) at these points.
3911 To get the "base" for the merge, you first look up the common parent
3912 of two commits with
3914 -------------------------------------------------
3915 $ git merge-base <commit1> <commit2>
3916 -------------------------------------------------
3918 which will return you the commit they are both based on. You should
3919 now look up the "tree" objects of those commits, which you can easily
3920 do with (for example)
3922 -------------------------------------------------
3923 $ git cat-file commit <commitname> | head -1
3924 -------------------------------------------------
3926 since the tree object information is always the first line in a commit
3927 object.
3929 Once you know the three trees you are going to merge (the one "original"
3930 tree, aka the common tree, and the two "result" trees, aka the branches
3931 you want to merge), you do a "merge" read into the index. This will
3932 complain if it has to throw away your old index contents, so you should
3933 make sure that you've committed those--in fact you would normally
3934 always do a merge against your last commit (which should thus match what
3935 you have in your current index anyway).
3937 To do the merge, do
3939 -------------------------------------------------
3940 $ git read-tree -m -u <origtree> <yourtree> <targettree>
3941 -------------------------------------------------
3943 which will do all trivial merge operations for you directly in the
3944 index file, and you can just write the result out with
3945 `git write-tree`.
3948 [[merging-multiple-trees-2]]
3949 Merging multiple trees, continued
3950 ---------------------------------
3952 Sadly, many merges aren't trivial. If there are files that have
3953 been added, moved or removed, or if both branches have modified the
3954 same file, you will be left with an index tree that contains "merge
3955 entries" in it. Such an index tree can 'NOT' be written out to a tree
3956 object, and you will have to resolve any such merge clashes using
3957 other tools before you can write out the result.
3959 You can examine such index state with `git ls-files --unmerged`
3960 command. An example:
3962 ------------------------------------------------
3963 $ git read-tree -m $orig HEAD $target
3964 $ git ls-files --unmerged
3965 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c
3966 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c
3967 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c
3968 ------------------------------------------------
3970 Each line of the `git ls-files --unmerged` output begins with
3971 the blob mode bits, blob SHA1, 'stage number', and the
3972 filename. The 'stage number' is git's way to say which tree it
3973 came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD`
3974 tree, and stage3 `$target` tree.
3976 Earlier we said that trivial merges are done inside
3977 `git-read-tree -m`. For example, if the file did not change
3978 from `$orig` to `HEAD` nor `$target`, or if the file changed
3979 from `$orig` to `HEAD` and `$orig` to `$target` the same way,
3980 obviously the final outcome is what is in `HEAD`. What the
3981 above example shows is that file `hello.c` was changed from
3982 `$orig` to `HEAD` and `$orig` to `$target` in a different way.
3983 You could resolve this by running your favorite 3-way merge
3984 program, e.g. `diff3`, `merge`, or git's own merge-file, on
3985 the blob objects from these three stages yourself, like this:
3987 ------------------------------------------------
3988 $ git cat-file blob 263414f... >hello.c~1
3989 $ git cat-file blob 06fa6a2... >hello.c~2
3990 $ git cat-file blob cc44c73... >hello.c~3
3991 $ git merge-file hello.c~2 hello.c~1 hello.c~3
3992 ------------------------------------------------
3994 This would leave the merge result in `hello.c~2` file, along
3995 with conflict markers if there are conflicts. After verifying
3996 the merge result makes sense, you can tell git what the final
3997 merge result for this file is by:
3999 -------------------------------------------------
4000 $ mv -f hello.c~2 hello.c
4001 $ git update-index hello.c
4002 -------------------------------------------------
4004 When a path is in the "unmerged" state, running `git-update-index` for
4005 that path tells git to mark the path resolved.
4007 The above is the description of a git merge at the lowest level,
4008 to help you understand what conceptually happens under the hood.
4009 In practice, nobody, not even git itself, runs `git-cat-file` three times
4010 for this. There is a `git-merge-index` program that extracts the
4011 stages to temporary files and calls a "merge" script on it:
4013 -------------------------------------------------
4014 $ git merge-index git-merge-one-file hello.c
4015 -------------------------------------------------
4017 and that is what higher level `git-merge -s resolve` is implemented with.
4019 [[hacking-git]]
4020 Hacking git
4021 ===========
4023 This chapter covers internal details of the git implementation which
4024 probably only git developers need to understand.
4026 [[object-details]]
4027 Object storage format
4028 ---------------------
4030 All objects have a statically determined "type" which identifies the
4031 format of the object (i.e. how it is used, and how it can refer to other
4032 objects). There are currently four different object types: "blob",
4033 "tree", "commit", and "tag".
4035 Regardless of object type, all objects share the following
4036 characteristics: they are all deflated with zlib, and have a header
4037 that not only specifies their type, but also provides size information
4038 about the data in the object. It's worth noting that the SHA1 hash
4039 that is used to name the object is the hash of the original data
4040 plus this header, so `sha1sum` 'file' does not match the object name
4041 for 'file'.
4042 (Historical note: in the dawn of the age of git the hash
4043 was the sha1 of the 'compressed' object.)
4045 As a result, the general consistency of an object can always be tested
4046 independently of the contents or the type of the object: all objects can
4047 be validated by verifying that (a) their hashes match the content of the
4048 file and (b) the object successfully inflates to a stream of bytes that
4049 forms a sequence of <ascii type without space> {plus} <space> {plus} <ascii decimal
4050 size> {plus} <byte\0> {plus} <binary object data>.
4052 The structured objects can further have their structure and
4053 connectivity to other objects verified. This is generally done with
4054 the `git-fsck` program, which generates a full dependency graph
4055 of all objects, and verifies their internal consistency (in addition
4056 to just verifying their superficial consistency through the hash).
4058 [[birdview-on-the-source-code]]
4059 A birds-eye view of Git's source code
4060 -------------------------------------
4062 It is not always easy for new developers to find their way through Git's
4063 source code. This section gives you a little guidance to show where to
4064 start.
4066 A good place to start is with the contents of the initial commit, with:
4068 ----------------------------------------------------
4069 $ git checkout e83c5163
4070 ----------------------------------------------------
4072 The initial revision lays the foundation for almost everything git has
4073 today, but is small enough to read in one sitting.
4075 Note that terminology has changed since that revision. For example, the
4076 README in that revision uses the word "changeset" to describe what we
4077 now call a <<def_commit_object,commit>>.
4079 Also, we do not call it "cache" any more, but rather "index"; however, the
4080 file is still called `cache.h`. Remark: Not much reason to change it now,
4081 especially since there is no good single name for it anyway, because it is
4082 basically _the_ header file which is included by _all_ of Git's C sources.
4084 If you grasp the ideas in that initial commit, you should check out a
4085 more recent version and skim `cache.h`, `object.h` and `commit.h`.
4087 In the early days, Git (in the tradition of UNIX) was a bunch of programs
4088 which were extremely simple, and which you used in scripts, piping the
4089 output of one into another. This turned out to be good for initial
4090 development, since it was easier to test new things. However, recently
4091 many of these parts have become builtins, and some of the core has been
4092 "libified", i.e. put into libgit.a for performance, portability reasons,
4093 and to avoid code duplication.
4095 By now, you know what the index is (and find the corresponding data
4096 structures in `cache.h`), and that there are just a couple of object types
4097 (blobs, trees, commits and tags) which inherit their common structure from
4098 `struct object`, which is their first member (and thus, you can cast e.g.
4099 `(struct object *)commit` to achieve the _same_ as `&commit->object`, i.e.
4100 get at the object name and flags).
4102 Now is a good point to take a break to let this information sink in.
4104 Next step: get familiar with the object naming. Read <<naming-commits>>.
4105 There are quite a few ways to name an object (and not only revisions!).
4106 All of these are handled in `sha1_name.c`. Just have a quick look at
4107 the function `get_sha1()`. A lot of the special handling is done by
4108 functions like `get_sha1_basic()` or the likes.
4110 This is just to get you into the groove for the most libified part of Git:
4111 the revision walker.
4113 Basically, the initial version of `git-log` was a shell script:
4115 ----------------------------------------------------------------
4116 $ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \
4117 LESS=-S ${PAGER:-less}
4118 ----------------------------------------------------------------
4120 What does this mean?
4122 `git-rev-list` is the original version of the revision walker, which
4123 _always_ printed a list of revisions to stdout. It is still functional,
4124 and needs to, since most new Git programs start out as scripts using
4125 `git-rev-list`.
4127 `git-rev-parse` is not as important any more; it was only used to filter out
4128 options that were relevant for the different plumbing commands that were
4129 called by the script.
4131 Most of what `git-rev-list` did is contained in `revision.c` and
4132 `revision.h`. It wraps the options in a struct named `rev_info`, which
4133 controls how and what revisions are walked, and more.
4135 The original job of `git-rev-parse` is now taken by the function
4136 `setup_revisions()`, which parses the revisions and the common command line
4137 options for the revision walker. This information is stored in the struct
4138 `rev_info` for later consumption. You can do your own command line option
4139 parsing after calling `setup_revisions()`. After that, you have to call
4140 `prepare_revision_walk()` for initialization, and then you can get the
4141 commits one by one with the function `get_revision()`.
4143 If you are interested in more details of the revision walking process,
4144 just have a look at the first implementation of `cmd_log()`; call
4145 `git show v1.3.0{tilde}155^2{tilde}4` and scroll down to that function (note that you
4146 no longer need to call `setup_pager()` directly).
4148 Nowadays, `git-log` is a builtin, which means that it is _contained_ in the
4149 command `git`. The source side of a builtin is
4151 - a function called `cmd_<bla>`, typically defined in `builtin-<bla>.c`,
4152 and declared in `builtin.h`,
4154 - an entry in the `commands[]` array in `git.c`, and
4156 - an entry in `BUILTIN_OBJECTS` in the `Makefile`.
4158 Sometimes, more than one builtin is contained in one source file. For
4159 example, `cmd_whatchanged()` and `cmd_log()` both reside in `builtin-log.c`,
4160 since they share quite a bit of code. In that case, the commands which are
4161 _not_ named like the `.c` file in which they live have to be listed in
4162 `BUILT_INS` in the `Makefile`.
4164 `git-log` looks more complicated in C than it does in the original script,
4165 but that allows for a much greater flexibility and performance.
4167 Here again it is a good point to take a pause.
4169 Lesson three is: study the code. Really, it is the best way to learn about
4170 the organization of Git (after you know the basic concepts).
4172 So, think about something which you are interested in, say, "how can I
4173 access a blob just knowing the object name of it?". The first step is to
4174 find a Git command with which you can do it. In this example, it is either
4175 `git-show` or `git-cat-file`.
4177 For the sake of clarity, let's stay with `git-cat-file`, because it
4179 - is plumbing, and
4181 - was around even in the initial commit (it literally went only through
4182 some 20 revisions as `cat-file.c`, was renamed to `builtin-cat-file.c`
4183 when made a builtin, and then saw less than 10 versions).
4185 So, look into `builtin-cat-file.c`, search for `cmd_cat_file()` and look what
4186 it does.
4188 ------------------------------------------------------------------
4189 git_config(git_default_config);
4190 if (argc != 3)
4191 usage("git-cat-file [-t|-s|-e|-p|<type>] <sha1>");
4192 if (get_sha1(argv[2], sha1))
4193 die("Not a valid object name %s", argv[2]);
4194 ------------------------------------------------------------------
4196 Let's skip over the obvious details; the only really interesting part
4197 here is the call to `get_sha1()`. It tries to interpret `argv[2]` as an
4198 object name, and if it refers to an object which is present in the current
4199 repository, it writes the resulting SHA-1 into the variable `sha1`.
4201 Two things are interesting here:
4203 - `get_sha1()` returns 0 on _success_. This might surprise some new
4204 Git hackers, but there is a long tradition in UNIX to return different
4205 negative numbers in case of different errors--and 0 on success.
4207 - the variable `sha1` in the function signature of `get_sha1()` is `unsigned
4208 char \*`, but is actually expected to be a pointer to `unsigned
4209 char[20]`. This variable will contain the 160-bit SHA-1 of the given
4210 commit. Note that whenever a SHA-1 is passed as `unsigned char \*`, it
4211 is the binary representation, as opposed to the ASCII representation in
4212 hex characters, which is passed as `char *`.
4214 You will see both of these things throughout the code.
4216 Now, for the meat:
4218 -----------------------------------------------------------------------------
4219 case 0:
4220 buf = read_object_with_reference(sha1, argv[1], &size, NULL);
4221 -----------------------------------------------------------------------------
4223 This is how you read a blob (actually, not only a blob, but any type of
4224 object). To know how the function `read_object_with_reference()` actually
4225 works, find the source code for it (something like `git grep
4226 read_object_with | grep ":[a-z]"` in the git repository), and read
4227 the source.
4229 To find out how the result can be used, just read on in `cmd_cat_file()`:
4231 -----------------------------------
4232 write_or_die(1, buf, size);
4233 -----------------------------------
4235 Sometimes, you do not know where to look for a feature. In many such cases,
4236 it helps to search through the output of `git log`, and then `git-show` the
4237 corresponding commit.
4239 Example: If you know that there was some test case for `git-bundle`, but
4240 do not remember where it was (yes, you _could_ `git grep bundle t/`, but that
4241 does not illustrate the point!):
4243 ------------------------
4244 $ git log --no-merges t/
4245 ------------------------
4247 In the pager (`less`), just search for "bundle", go a few lines back,
4248 and see that it is in commit 18449ab0... Now just copy this object name,
4249 and paste it into the command line
4251 -------------------
4252 $ git show 18449ab0
4253 -------------------
4255 Voila.
4257 Another example: Find out what to do in order to make some script a
4258 builtin:
4260 -------------------------------------------------
4261 $ git log --no-merges --diff-filter=A builtin-*.c
4262 -------------------------------------------------
4264 You see, Git is actually the best tool to find out about the source of Git
4265 itself!
4267 [[glossary]]
4268 GIT Glossary
4269 ============
4271 include::glossary-content.txt[]
4273 [[git-quick-start]]
4274 Appendix A: Git Quick Reference
4275 ===============================
4277 This is a quick summary of the major commands; the previous chapters
4278 explain how these work in more detail.
4280 [[quick-creating-a-new-repository]]
4281 Creating a new repository
4282 -------------------------
4284 From a tarball:
4286 -----------------------------------------------
4287 $ tar xzf project.tar.gz
4288 $ cd project
4289 $ git init
4290 Initialized empty Git repository in .git/
4291 $ git add .
4292 $ git commit
4293 -----------------------------------------------
4295 From a remote repository:
4297 -----------------------------------------------
4298 $ git clone git://example.com/pub/project.git
4299 $ cd project
4300 -----------------------------------------------
4302 [[managing-branches]]
4303 Managing branches
4304 -----------------
4306 -----------------------------------------------
4307 $ git branch # list all local branches in this repo
4308 $ git checkout test # switch working directory to branch "test"
4309 $ git branch new # create branch "new" starting at current HEAD
4310 $ git branch -d new # delete branch "new"
4311 -----------------------------------------------
4313 Instead of basing a new branch on current HEAD (the default), use:
4315 -----------------------------------------------
4316 $ git branch new test # branch named "test"
4317 $ git branch new v2.6.15 # tag named v2.6.15
4318 $ git branch new HEAD^ # commit before the most recent
4319 $ git branch new HEAD^^ # commit before that
4320 $ git branch new test~10 # ten commits before tip of branch "test"
4321 -----------------------------------------------
4323 Create and switch to a new branch at the same time:
4325 -----------------------------------------------
4326 $ git checkout -b new v2.6.15
4327 -----------------------------------------------
4329 Update and examine branches from the repository you cloned from:
4331 -----------------------------------------------
4332 $ git fetch # update
4333 $ git branch -r # list
4334 origin/master
4335 origin/next
4336 ...
4337 $ git checkout -b masterwork origin/master
4338 -----------------------------------------------
4340 Fetch a branch from a different repository, and give it a new
4341 name in your repository:
4343 -----------------------------------------------
4344 $ git fetch git://example.com/project.git theirbranch:mybranch
4345 $ git fetch git://example.com/project.git v2.6.15:mybranch
4346 -----------------------------------------------
4348 Keep a list of repositories you work with regularly:
4350 -----------------------------------------------
4351 $ git remote add example git://example.com/project.git
4352 $ git remote # list remote repositories
4353 example
4354 origin
4355 $ git remote show example # get details
4356 * remote example
4357 URL: git://example.com/project.git
4358 Tracked remote branches
4359 master next ...
4360 $ git fetch example # update branches from example
4361 $ git branch -r # list all remote branches
4362 -----------------------------------------------
4365 [[exploring-history]]
4366 Exploring history
4367 -----------------
4369 -----------------------------------------------
4370 $ gitk # visualize and browse history
4371 $ git log # list all commits
4372 $ git log src/ # ...modifying src/
4373 $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15
4374 $ git log master..test # ...in branch test, not in branch master
4375 $ git log test..master # ...in branch master, but not in test
4376 $ git log test...master # ...in one branch, not in both
4377 $ git log -S'foo()' # ...where difference contain "foo()"
4378 $ git log --since="2 weeks ago"
4379 $ git log -p # show patches as well
4380 $ git show # most recent commit
4381 $ git diff v2.6.15..v2.6.16 # diff between two tagged versions
4382 $ git diff v2.6.15..HEAD # diff with current head
4383 $ git grep "foo()" # search working directory for "foo()"
4384 $ git grep v2.6.15 "foo()" # search old tree for "foo()"
4385 $ git show v2.6.15:a.txt # look at old version of a.txt
4386 -----------------------------------------------
4388 Search for regressions:
4390 -----------------------------------------------
4391 $ git bisect start
4392 $ git bisect bad # current version is bad
4393 $ git bisect good v2.6.13-rc2 # last known good revision
4394 Bisecting: 675 revisions left to test after this
4395 # test here, then:
4396 $ git bisect good # if this revision is good, or
4397 $ git bisect bad # if this revision is bad.
4398 # repeat until done.
4399 -----------------------------------------------
4401 [[making-changes]]
4402 Making changes
4403 --------------
4405 Make sure git knows who to blame:
4407 ------------------------------------------------
4408 $ cat >>~/.gitconfig <<\EOF
4409 [user]
4410 name = Your Name Comes Here
4411 email = you@yourdomain.example.com
4412 EOF
4413 ------------------------------------------------
4415 Select file contents to include in the next commit, then make the
4416 commit:
4418 -----------------------------------------------
4419 $ git add a.txt # updated file
4420 $ git add b.txt # new file
4421 $ git rm c.txt # old file
4422 $ git commit
4423 -----------------------------------------------
4425 Or, prepare and create the commit in one step:
4427 -----------------------------------------------
4428 $ git commit d.txt # use latest content only of d.txt
4429 $ git commit -a # use latest content of all tracked files
4430 -----------------------------------------------
4432 [[merging]]
4433 Merging
4434 -------
4436 -----------------------------------------------
4437 $ git merge test # merge branch "test" into the current branch
4438 $ git pull git://example.com/project.git master
4439 # fetch and merge in remote branch
4440 $ git pull . test # equivalent to git merge test
4441 -----------------------------------------------
4443 [[sharing-your-changes]]
4444 Sharing your changes
4445 --------------------
4447 Importing or exporting patches:
4449 -----------------------------------------------
4450 $ git format-patch origin..HEAD # format a patch for each commit
4451 # in HEAD but not in origin
4452 $ git am mbox # import patches from the mailbox "mbox"
4453 -----------------------------------------------
4455 Fetch a branch in a different git repository, then merge into the
4456 current branch:
4458 -----------------------------------------------
4459 $ git pull git://example.com/project.git theirbranch
4460 -----------------------------------------------
4462 Store the fetched branch into a local branch before merging into the
4463 current branch:
4465 -----------------------------------------------
4466 $ git pull git://example.com/project.git theirbranch:mybranch
4467 -----------------------------------------------
4469 After creating commits on a local branch, update the remote
4470 branch with your commits:
4472 -----------------------------------------------
4473 $ git push ssh://example.com/project.git mybranch:theirbranch
4474 -----------------------------------------------
4476 When remote and local branch are both named "test":
4478 -----------------------------------------------
4479 $ git push ssh://example.com/project.git test
4480 -----------------------------------------------
4482 Shortcut version for a frequently used remote repository:
4484 -----------------------------------------------
4485 $ git remote add example ssh://example.com/project.git
4486 $ git push example test
4487 -----------------------------------------------
4489 [[repository-maintenance]]
4490 Repository maintenance
4491 ----------------------
4493 Check for corruption:
4495 -----------------------------------------------
4496 $ git fsck
4497 -----------------------------------------------
4499 Recompress, remove unused cruft:
4501 -----------------------------------------------
4502 $ git gc
4503 -----------------------------------------------
4506 [[todo]]
4507 Appendix B: Notes and todo list for this manual
4508 ===============================================
4510 This is a work in progress.
4512 The basic requirements:
4514 - It must be readable in order, from beginning to end, by someone
4515 intelligent with a basic grasp of the UNIX command line, but without
4516 any special knowledge of git. If necessary, any other prerequisites
4517 should be specifically mentioned as they arise.
4518 - Whenever possible, section headings should clearly describe the task
4519 they explain how to do, in language that requires no more knowledge
4520 than necessary: for example, "importing patches into a project" rather
4521 than "the git-am command"
4523 Think about how to create a clear chapter dependency graph that will
4524 allow people to get to important topics without necessarily reading
4525 everything in between.
4527 Scan Documentation/ for other stuff left out; in particular:
4529 - howto's
4530 - some of technical/?
4531 - hooks
4532 - list of commands in linkgit:git[1]
4534 Scan email archives for other stuff left out
4536 Scan man pages to see if any assume more background than this manual
4537 provides.
4539 Simplify beginning by suggesting disconnected head instead of
4540 temporary branch creation?
4542 Add more good examples. Entire sections of just cookbook examples
4543 might be a good idea; maybe make an "advanced examples" section a
4544 standard end-of-chapter section?
4546 Include cross-references to the glossary, where appropriate.
4548 Document shallow clones? See draft 1.5.0 release notes for some
4549 documentation.
4551 Add a section on working with other version control systems, including
4552 CVS, Subversion, and just imports of series of release tarballs.
4554 More details on gitweb?
4556 Write a chapter on using plumbing and writing scripts.
4558 Alternates, clone -reference, etc.
4560 More on recovery from repository corruption. See:
4561 http://marc.theaimsgroup.com/?l=git&m=117263864820799&w=2
4562 http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2