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0eb4f7cd 1Git User's Manual (for version 1.5.3 or newer)
71f4b183 2______________________________________________
d19fbc3c 3
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4
5Git is a fast distributed revision control system.
6
02783075 7This manual is designed to be readable by someone with basic UNIX
79c96c57 8command-line skills, but no previous knowledge of git.
d19fbc3c 9
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10<<repositories-and-branches>> and <<exploring-git-history>> explain how
11to fetch and study a project using git--read these chapters to learn how
12to build and test a particular version of a software project, search for
13regressions, and so on.
ef89f701 14
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15People needing to do actual development will also want to read
16<<Developing-with-git>> and <<sharing-development>>.
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17
18Further chapters cover more specialized topics.
19
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20Comprehensive reference documentation is available through the man
21pages. For a command such as "git clone", just use
22
23------------------------------------------------
24$ man git-clone
25------------------------------------------------
26
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27See also <<git-quick-start>> for a brief overview of git commands,
28without any explanation.
b181d57f 29
99f171bb 30Finally, see <<todo>> for ways that you can help make this manual more
2624d9a5 31complete.
b181d57f 32
b181d57f 33
e34caace 34[[repositories-and-branches]]
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35Repositories and Branches
36=========================
37
e34caace 38[[how-to-get-a-git-repository]]
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39How to get a git repository
40---------------------------
41
42It will be useful to have a git repository to experiment with as you
43read this manual.
44
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45The best way to get one is by using the gitlink:git-clone[1] command to
46download a copy of an existing repository. If you don't already have a
47project in mind, here are some interesting examples:
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48
49------------------------------------------------
50 # git itself (approx. 10MB download):
51$ git clone git://git.kernel.org/pub/scm/git/git.git
52 # the linux kernel (approx. 150MB download):
53$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git
54------------------------------------------------
55
56The initial clone may be time-consuming for a large project, but you
57will only need to clone once.
58
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59The clone command creates a new directory named after the project ("git"
60or "linux-2.6" in the examples above). After you cd into this
d19fbc3c 61directory, you will see that it contains a copy of the project files,
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62called the <<def_working_tree,working tree>>, together with a special
63top-level directory named ".git", which contains all the information
64about the history of the project.
d19fbc3c 65
e34caace 66[[how-to-check-out]]
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67How to check out a different version of a project
68-------------------------------------------------
69
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70Git is best thought of as a tool for storing the history of a collection
71of files. It stores the history as a compressed collection of
72interrelated snapshots of the project's contents. In git each such
73version is called a <<def_commit,commit>>.
d19fbc3c 74
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75Those snapshots aren't necessarily all arranged in a single line from
76oldest to newest; instead, work may simultaneously proceed along
77parallel lines of development, called <def_branch,branches>>, which may
78merge and diverge.
79
80A single git repository can track development on multiple branches. It
81does this by keeping a list of <<def_head,heads>> which reference the
a2ef9d63 82latest commit on each branch; the gitlink:git-branch[1] command shows
81b6c950 83you the list of branch heads:
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84
85------------------------------------------------
86$ git branch
87* master
88------------------------------------------------
89
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90A freshly cloned repository contains a single branch head, by default
91named "master", with the working directory initialized to the state of
92the project referred to by that branch head.
d19fbc3c 93
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94Most projects also use <<def_tag,tags>>. Tags, like heads, are
95references into the project's history, and can be listed using the
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96gitlink:git-tag[1] command:
97
98------------------------------------------------
99$ git tag -l
100v2.6.11
101v2.6.11-tree
102v2.6.12
103v2.6.12-rc2
104v2.6.12-rc3
105v2.6.12-rc4
106v2.6.12-rc5
107v2.6.12-rc6
108v2.6.13
109...
110------------------------------------------------
111
fe4b3e59 112Tags are expected to always point at the same version of a project,
81b6c950 113while heads are expected to advance as development progresses.
fe4b3e59 114
81b6c950 115Create a new branch head pointing to one of these versions and check it
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116out using gitlink:git-checkout[1]:
117
118------------------------------------------------
119$ git checkout -b new v2.6.13
120------------------------------------------------
121
122The working directory then reflects the contents that the project had
123when it was tagged v2.6.13, and gitlink:git-branch[1] shows two
124branches, with an asterisk marking the currently checked-out branch:
125
126------------------------------------------------
127$ git branch
128 master
129* new
130------------------------------------------------
131
132If you decide that you'd rather see version 2.6.17, you can modify
133the current branch to point at v2.6.17 instead, with
134
135------------------------------------------------
136$ git reset --hard v2.6.17
137------------------------------------------------
138
81b6c950 139Note that if the current branch head was your only reference to a
d19fbc3c 140particular point in history, then resetting that branch may leave you
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141with no way to find the history it used to point to; so use this command
142carefully.
d19fbc3c 143
e34caace 144[[understanding-commits]]
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145Understanding History: Commits
146------------------------------
147
148Every change in the history of a project is represented by a commit.
149The gitlink:git-show[1] command shows the most recent commit on the
150current branch:
151
152------------------------------------------------
153$ git show
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154commit 17cf781661e6d38f737f15f53ab552f1e95960d7
155Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)>
156Date: Tue Apr 19 14:11:06 2005 -0700
157
158 Remove duplicate getenv(DB_ENVIRONMENT) call
159
160 Noted by Tony Luck.
161
162diff --git a/init-db.c b/init-db.c
163index 65898fa..b002dc6 100644
164--- a/init-db.c
165+++ b/init-db.c
166@@ -7,7 +7,7 @@
d19fbc3c 167
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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;
173
174 if (mkdir(".git", 0755) < 0) {
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175------------------------------------------------
176
177As you can see, a commit shows who made the latest change, what they
178did, and why.
179
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180Every 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
182refer to a commit by a shorter name, such as a tag or a branch name, but this
183longer name can also be useful. Most importantly, it is a globally unique
184name for this commit: so if you tell somebody else the object name (for
185example in email), then you are guaranteed that name will refer to the same
186commit in their repository that it does in yours (assuming their repository
187has that commit at all). Since the object name is computed as a hash over the
188contents of the commit, you are guaranteed that the commit can never change
189without its name also changing.
190
036f8199 191In fact, in <<git-concepts>> we shall see that everything stored in git
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192history, including file data and directory contents, is stored in an object
193with a name that is a hash of its contents.
d19fbc3c 194
e34caace 195[[understanding-reachability]]
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196Understanding history: commits, parents, and reachability
197~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
198
199Every commit (except the very first commit in a project) also has a
200parent commit which shows what happened before this commit.
201Following the chain of parents will eventually take you back to the
202beginning of the project.
203
204However, the commits do not form a simple list; git allows lines of
205development to diverge and then reconverge, and the point where two
206lines of development reconverge is called a "merge". The commit
207representing a merge can therefore have more than one parent, with
208each parent representing the most recent commit on one of the lines
209of development leading to that point.
210
211The best way to see how this works is using the gitlink:gitk[1]
212command; running gitk now on a git repository and looking for merge
213commits will help understand how the git organizes history.
214
215In the following, we say that commit X is "reachable" from commit Y
216if commit X is an ancestor of commit Y. Equivalently, you could say
02783075 217that Y is a descendant of X, or that there is a chain of parents
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218leading from commit Y to commit X.
219
e34caace 220[[history-diagrams]]
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221Understanding history: History diagrams
222~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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223
224We will sometimes represent git history using diagrams like the one
225below. Commits are shown as "o", and the links between them with
226lines drawn with - / and \. Time goes left to right:
227
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228
229................................................
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230 o--o--o <-- Branch A
231 /
232 o--o--o <-- master
233 \
234 o--o--o <-- Branch B
1dc71a91 235................................................
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236
237If we need to talk about a particular commit, the character "o" may
238be replaced with another letter or number.
239
e34caace 240[[what-is-a-branch]]
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241Understanding history: What is a branch?
242~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
243
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244When we need to be precise, we will use the word "branch" to mean a line
245of development, and "branch head" (or just "head") to mean a reference
246to the most recent commit on a branch. In the example above, the branch
247head named "A" is a pointer to one particular commit, but we refer to
248the line of three commits leading up to that point as all being part of
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249"branch A".
250
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251However, when no confusion will result, we often just use the term
252"branch" both for branches and for branch heads.
d19fbc3c 253
e34caace 254[[manipulating-branches]]
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255Manipulating branches
256---------------------
257
258Creating, deleting, and modifying branches is quick and easy; here's
259a summary of the commands:
260
261git branch::
262 list all branches
263git branch <branch>::
264 create a new branch named <branch>, referencing the same
265 point in history as the current branch
266git 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
270git branch -d <branch>::
271 delete the branch <branch>; if the branch you are deleting
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272 points to a commit which is not reachable from the current
273 branch, this command will fail with a warning.
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274git 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.
280git checkout <branch>::
281 make the current branch <branch>, updating the working
282 directory to reflect the version referenced by <branch>
283git checkout -b <new> <start-point>::
284 create a new branch <new> referencing <start-point>, and
285 check it out.
286
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287The special symbol "HEAD" can always be used to refer to the current
288branch. In fact, git uses a file named "HEAD" in the .git directory to
289remember which branch is current:
290
291------------------------------------------------
292$ cat .git/HEAD
293ref: refs/heads/master
294------------------------------------------------
295
25d9f3fa 296[[detached-head]]
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297Examining an old version without creating a new branch
298------------------------------------------------------
299
300The git-checkout command normally expects a branch head, but will also
301accept an arbitrary commit; for example, you can check out the commit
302referenced by a tag:
303
304------------------------------------------------
305$ git checkout v2.6.17
306Note: moving to "v2.6.17" which isn't a local branch
307If 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>
310HEAD is now at 427abfa... Linux v2.6.17
311------------------------------------------------
312
313The HEAD then refers to the SHA1 of the commit instead of to a branch,
314and git branch shows that you are no longer on a branch:
315
316------------------------------------------------
317$ cat .git/HEAD
318427abfa28afedffadfca9dd8b067eb6d36bac53f
953f3d6f 319$ git branch
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320* (no branch)
321 master
322------------------------------------------------
323
324In this case we say that the HEAD is "detached".
325
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326This is an easy way to check out a particular version without having to
327make 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.
d19fbc3c 329
e34caace 330[[examining-remote-branches]]
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331Examining branches from a remote repository
332-------------------------------------------
333
334The "master" branch that was created at the time you cloned is a copy
335of the HEAD in the repository that you cloned from. That repository
336may also have had other branches, though, and your local repository
337keeps branches which track each of those remote branches, which you
338can view using the "-r" option to gitlink:git-branch[1]:
339
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------------------------------------------------
351
352You cannot check out these remote-tracking branches, but you can
353examine them on a branch of your own, just as you would a tag:
354
355------------------------------------------------
356$ git checkout -b my-todo-copy origin/todo
357------------------------------------------------
358
359Note that the name "origin" is just the name that git uses by default
360to refer to the repository that you cloned from.
361
362[[how-git-stores-references]]
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363Naming branches, tags, and other references
364-------------------------------------------
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365
366Branches, remote-tracking branches, and tags are all references to
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367commits. All references are named with a slash-separated path name
368starting with "refs"; the names we've been using so far are actually
369shorthand:
d19fbc3c 370
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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".
d19fbc3c 374
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375The full name is occasionally useful if, for example, there ever
376exists a tag and a branch with the same name.
d19fbc3c 377
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378(Newly created refs are actually stored in the .git/refs directory,
379under the path given by their name. However, for efficiency reasons
380they may also be packed together in a single file; see
381gitlink:git-pack-refs[1]).
382
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383As another useful shortcut, the "HEAD" of a repository can be referred
384to just using the name of that repository. So, for example, "origin"
385is usually a shortcut for the HEAD branch in the repository "origin".
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386
387For the complete list of paths which git checks for references, and
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388the order it uses to decide which to choose when there are multiple
389references with the same shorthand name, see the "SPECIFYING
390REVISIONS" section of gitlink:git-rev-parse[1].
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391
392[[Updating-a-repository-with-git-fetch]]
393Updating a repository with git fetch
394------------------------------------
395
396Eventually the developer cloned from will do additional work in her
397repository, creating new commits and advancing the branches to point
398at the new commits.
399
400The command "git fetch", with no arguments, will update all of the
401remote-tracking branches to the latest version found in her
402repository. It will not touch any of your own branches--not even the
403"master" branch that was created for you on clone.
404
e34caace 405[[fetching-branches]]
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406Fetching branches from other repositories
407-----------------------------------------
408
409You can also track branches from repositories other than the one you
410cloned from, using gitlink:git-remote[1]:
411
412-------------------------------------------------
413$ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git
04483524 414$ git fetch linux-nfs
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415* refs/remotes/linux-nfs/master: storing branch 'master' ...
416 commit: bf81b46
417-------------------------------------------------
418
419New remote-tracking branches will be stored under the shorthand name
420that you gave "git remote add", in this case linux-nfs:
421
422-------------------------------------------------
423$ git branch -r
424linux-nfs/master
425origin/master
426-------------------------------------------------
427
428If you run "git fetch <remote>" later, the tracking branches for the
429named <remote> will be updated.
430
431If you examine the file .git/config, you will see that git has added
432a new stanza:
433
434-------------------------------------------------
435$ cat .git/config
436...
437[remote "linux-nfs"]
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438 url = git://linux-nfs.org/pub/nfs-2.6.git
439 fetch = +refs/heads/*:refs/remotes/linux-nfs/*
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440...
441-------------------------------------------------
442
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443This is what causes git to track the remote's branches; you may modify
444or delete these configuration options by editing .git/config with a
445text editor. (See the "CONFIGURATION FILE" section of
446gitlink:git-config[1] for details.)
d5cd5de4 447
e34caace 448[[exploring-git-history]]
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449Exploring git history
450=====================
451
452Git is best thought of as a tool for storing the history of a
453collection of files. It does this by storing compressed snapshots of
1130845b 454the contents of a file hierarchy, together with "commits" which show
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455the relationships between these snapshots.
456
457Git provides extremely flexible and fast tools for exploring the
458history of a project.
459
aacd404e 460We start with one specialized tool that is useful for finding the
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461commit that introduced a bug into a project.
462
e34caace 463[[using-bisect]]
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464How to use bisect to find a regression
465--------------------------------------
466
467Suppose 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
469regression is to perform a brute-force search through the project's
470history to find the particular commit that caused the problem. The
471gitlink:git-bisect[1] command can help you do this:
472
473-------------------------------------------------
474$ git bisect start
475$ git bisect good v2.6.18
476$ git bisect bad master
477Bisecting: 3537 revisions left to test after this
478[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
479-------------------------------------------------
480
481If you run "git branch" at this point, you'll see that git has
482temporarily moved you to a new branch named "bisect". This branch
483points to a commit (with commit id 65934...) that is reachable from
484v2.6.19 but not from v2.6.18. Compile and test it, and see whether
485it crashes. Assume it does crash. Then:
486
487-------------------------------------------------
488$ git bisect bad
489Bisecting: 1769 revisions left to test after this
490[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
491-------------------------------------------------
492
493checks out an older version. Continue like this, telling git at each
494stage whether the version it gives you is good or bad, and notice
495that the number of revisions left to test is cut approximately in
496half each time.
497
498After about 13 tests (in this case), it will output the commit id of
499the guilty commit. You can then examine the commit with
500gitlink:git-show[1], find out who wrote it, and mail them your bug
501report with the commit id. Finally, run
502
503-------------------------------------------------
504$ git bisect reset
505-------------------------------------------------
506
507to return you to the branch you were on before and delete the
508temporary "bisect" branch.
509
510Note that the version which git-bisect checks out for you at each
511point is just a suggestion, and you're free to try a different
512version if you think it would be a good idea. For example,
513occasionally you may land on a commit that broke something unrelated;
514run
515
516-------------------------------------------------
04483524 517$ git bisect visualize
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518-------------------------------------------------
519
520which will run gitk and label the commit it chose with a marker that
521says "bisect". Chose a safe-looking commit nearby, note its commit
522id, and check it out with:
523
524-------------------------------------------------
525$ git reset --hard fb47ddb2db...
526-------------------------------------------------
527
528then test, run "bisect good" or "bisect bad" as appropriate, and
529continue.
530
e34caace 531[[naming-commits]]
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532Naming commits
533--------------
534
535We have seen several ways of naming commits already:
536
d55ae921 537 - 40-hexdigit object name
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538 - branch name: refers to the commit at the head of the given
539 branch
540 - tag name: refers to the commit pointed to by the given tag
541 (we've seen branches and tags are special cases of
542 <<how-git-stores-references,references>>).
543 - HEAD: refers to the head of the current branch
544
eb6ae7f4 545There are many more; see the "SPECIFYING REVISIONS" section of the
aec053bb 546gitlink:git-rev-parse[1] man page for the complete list of ways to
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547name revisions. Some examples:
548
549-------------------------------------------------
d55ae921 550$ git show fb47ddb2 # the first few characters of the object name
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551 # are usually enough to specify it uniquely
552$ git show HEAD^ # the parent of the HEAD commit
553$ git show HEAD^^ # the grandparent
554$ git show HEAD~4 # the great-great-grandparent
555-------------------------------------------------
556
557Recall that merge commits may have more than one parent; by default,
558^ and ~ follow the first parent listed in the commit, but you can
559also choose:
560
561-------------------------------------------------
562$ git show HEAD^1 # show the first parent of HEAD
563$ git show HEAD^2 # show the second parent of HEAD
564-------------------------------------------------
565
566In addition to HEAD, there are several other special names for
567commits:
568
569Merges (to be discussed later), as well as operations such as
570git-reset, which change the currently checked-out commit, generally
571set ORIG_HEAD to the value HEAD had before the current operation.
572
573The git-fetch operation always stores the head of the last fetched
574branch in FETCH_HEAD. For example, if you run git fetch without
575specifying a local branch as the target of the operation
576
577-------------------------------------------------
578$ git fetch git://example.com/proj.git theirbranch
579-------------------------------------------------
580
581the fetched commits will still be available from FETCH_HEAD.
582
583When we discuss merges we'll also see the special name MERGE_HEAD,
584which refers to the other branch that we're merging in to the current
585branch.
586
aec053bb 587The gitlink:git-rev-parse[1] command is a low-level command that is
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588occasionally useful for translating some name for a commit to the object
589name for that commit:
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590
591-------------------------------------------------
592$ git rev-parse origin
593e05db0fd4f31dde7005f075a84f96b360d05984b
594-------------------------------------------------
595
e34caace 596[[creating-tags]]
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597Creating tags
598-------------
599
600We can also create a tag to refer to a particular commit; after
601running
602
603-------------------------------------------------
04483524 604$ git tag stable-1 1b2e1d63ff
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605-------------------------------------------------
606
607You can use stable-1 to refer to the commit 1b2e1d63ff.
608
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609This creates a "lightweight" tag. If you would also like to include a
610comment with the tag, and possibly sign it cryptographically, then you
611should create a tag object instead; see the gitlink:git-tag[1] man page
612for details.
d19fbc3c 613
e34caace 614[[browsing-revisions]]
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615Browsing revisions
616------------------
617
618The gitlink:git-log[1] command can show lists of commits. On its
619own, it shows all commits reachable from the parent commit; but you
620can also make more specific requests:
621
622-------------------------------------------------
623$ git log v2.5.. # commits since (not reachable from) v2.5
624$ git log test..master # commits reachable from master but not test
625$ git log master..test # ...reachable from test but not master
626$ git log master...test # ...reachable from either test or master,
627 # but not both
628$ git log --since="2 weeks ago" # commits from the last 2 weeks
629$ git log Makefile # commits which modify Makefile
630$ git log fs/ # ... which modify any file under fs/
631$ git log -S'foo()' # commits which add or remove any file data
632 # matching the string 'foo()'
633-------------------------------------------------
634
635And of course you can combine all of these; the following finds
636commits since v2.5 which touch the Makefile or any file under fs:
637
638-------------------------------------------------
639$ git log v2.5.. Makefile fs/
640-------------------------------------------------
641
642You can also ask git log to show patches:
643
644-------------------------------------------------
645$ git log -p
646-------------------------------------------------
647
648See the "--pretty" option in the gitlink:git-log[1] man page for more
649display options.
650
651Note that git log starts with the most recent commit and works
652backwards through the parents; however, since git history can contain
3dff5379 653multiple independent lines of development, the particular order that
d19fbc3c
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654commits are listed in may be somewhat arbitrary.
655
e34caace 656[[generating-diffs]]
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657Generating diffs
658----------------
659
660You can generate diffs between any two versions using
661gitlink:git-diff[1]:
662
663-------------------------------------------------
664$ git diff master..test
665-------------------------------------------------
666
5b98d9bc
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667That will produce the diff between the tips of the two branches. If
668you'd prefer to find the diff from their common ancestor to test, you
669can use three dots instead of two:
670
671-------------------------------------------------
672$ git diff master...test
673-------------------------------------------------
674
675Sometimes what you want instead is a set of patches; for this you can
676use gitlink:git-format-patch[1]:
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677
678-------------------------------------------------
679$ git format-patch master..test
680-------------------------------------------------
681
682will generate a file with a patch for each commit reachable from test
5b98d9bc 683but not from master.
d19fbc3c 684
e34caace 685[[viewing-old-file-versions]]
d19fbc3c
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686Viewing old file versions
687-------------------------
688
689You can always view an old version of a file by just checking out the
690correct revision first. But sometimes it is more convenient to be
691able to view an old version of a single file without checking
692anything out; this command does that:
693
694-------------------------------------------------
695$ git show v2.5:fs/locks.c
696-------------------------------------------------
697
698Before the colon may be anything that names a commit, and after it
699may be any path to a file tracked by git.
700
e34caace 701[[history-examples]]
aec053bb
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702Examples
703--------
704
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705[[counting-commits-on-a-branch]]
706Counting the number of commits on a branch
707~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
708
709Suppose you want to know how many commits you've made on "mybranch"
710since it diverged from "origin":
711
712-------------------------------------------------
713$ git log --pretty=oneline origin..mybranch | wc -l
714-------------------------------------------------
715
716Alternatively, you may often see this sort of thing done with the
717lower-level command gitlink:git-rev-list[1], which just lists the SHA1's
718of all the given commits:
719
720-------------------------------------------------
721$ git rev-list origin..mybranch | wc -l
722-------------------------------------------------
723
e34caace 724[[checking-for-equal-branches]]
aec053bb 725Check whether two branches point at the same history
2f99710c 726~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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727
728Suppose you want to check whether two branches point at the same point
729in history.
730
731-------------------------------------------------
732$ git diff origin..master
733-------------------------------------------------
734
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735will tell you whether the contents of the project are the same at the
736two branches; in theory, however, it's possible that the same project
737contents could have been arrived at by two different historical
d55ae921 738routes. You could compare the object names:
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739
740-------------------------------------------------
741$ git rev-list origin
742e05db0fd4f31dde7005f075a84f96b360d05984b
743$ git rev-list master
744e05db0fd4f31dde7005f075a84f96b360d05984b
745-------------------------------------------------
746
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747Or you could recall that the ... operator selects all commits
748contained reachable from either one reference or the other but not
749both: so
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750
751-------------------------------------------------
752$ git log origin...master
753-------------------------------------------------
754
755will return no commits when the two branches are equal.
756
e34caace 757[[finding-tagged-descendants]]
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758Find first tagged version including a given fix
759~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
aec053bb 760
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761Suppose you know that the commit e05db0fd fixed a certain problem.
762You'd like to find the earliest tagged release that contains that
763fix.
764
765Of course, there may be more than one answer--if the history branched
766after commit e05db0fd, then there could be multiple "earliest" tagged
767releases.
768
769You could just visually inspect the commits since e05db0fd:
770
771-------------------------------------------------
772$ gitk e05db0fd..
773-------------------------------------------------
774
b181d57f
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775Or you can use gitlink:git-name-rev[1], which will give the commit a
776name based on any tag it finds pointing to one of the commit's
777descendants:
778
779-------------------------------------------------
04483524 780$ git name-rev --tags e05db0fd
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781e05db0fd tags/v1.5.0-rc1^0~23
782-------------------------------------------------
783
784The gitlink:git-describe[1] command does the opposite, naming the
785revision using a tag on which the given commit is based:
786
787-------------------------------------------------
788$ git describe e05db0fd
04483524 789v1.5.0-rc0-260-ge05db0f
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790-------------------------------------------------
791
792but that may sometimes help you guess which tags might come after the
793given commit.
794
795If you just want to verify whether a given tagged version contains a
796given commit, you could use gitlink:git-merge-base[1]:
797
798-------------------------------------------------
799$ git merge-base e05db0fd v1.5.0-rc1
800e05db0fd4f31dde7005f075a84f96b360d05984b
801-------------------------------------------------
802
803The merge-base command finds a common ancestor of the given commits,
804and always returns one or the other in the case where one is a
805descendant of the other; so the above output shows that e05db0fd
806actually is an ancestor of v1.5.0-rc1.
807
808Alternatively, note that
809
810-------------------------------------------------
4a7979ca 811$ git log v1.5.0-rc1..e05db0fd
b181d57f
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812-------------------------------------------------
813
4a7979ca 814will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
b181d57f 815because it outputs only commits that are not reachable from v1.5.0-rc1.
aec053bb 816
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817As yet another alternative, the gitlink:git-show-branch[1] command lists
818the commits reachable from its arguments with a display on the left-hand
819side that indicates which arguments that commit is reachable from. So,
820you can run something like
821
822-------------------------------------------------
823$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
824! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
825available
826 ! [v1.5.0-rc0] GIT v1.5.0 preview
827 ! [v1.5.0-rc1] GIT v1.5.0-rc1
828 ! [v1.5.0-rc2] GIT v1.5.0-rc2
829...
830-------------------------------------------------
831
832then search for a line that looks like
833
834-------------------------------------------------
835+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
836available
837-------------------------------------------------
838
839Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
840from v1.5.0-rc2, but not from v1.5.0-rc0.
841
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842[[showing-commits-unique-to-a-branch]]
843Showing commits unique to a given branch
844~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4a7979ca 845
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846Suppose you would like to see all the commits reachable from the branch
847head named "master" but not from any other head in your repository.
d19fbc3c 848
629d9f78
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849We can list all the heads in this repository with
850gitlink:git-show-ref[1]:
d19fbc3c 851
629d9f78
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852-------------------------------------------------
853$ git show-ref --heads
854bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
855db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
856a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
85724dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
8581e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
859-------------------------------------------------
d19fbc3c 860
629d9f78
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861We can get just the branch-head names, and remove "master", with
862the help of the standard utilities cut and grep:
863
864-------------------------------------------------
865$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
866refs/heads/core-tutorial
867refs/heads/maint
868refs/heads/tutorial-2
869refs/heads/tutorial-fixes
870-------------------------------------------------
871
872And then we can ask to see all the commits reachable from master
873but not from these other heads:
874
875-------------------------------------------------
876$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
877 grep -v '^refs/heads/master' )
878-------------------------------------------------
879
880Obviously, endless variations are possible; for example, to see all
881commits reachable from some head but not from any tag in the repository:
882
883-------------------------------------------------
c78974f7 884$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
629d9f78
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885-------------------------------------------------
886
887(See gitlink:git-rev-parse[1] for explanations of commit-selecting
888syntax such as `--not`.)
889
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890[[making-a-release]]
891Creating a changelog and tarball for a software release
892~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
893
894The gitlink:git-archive[1] command can create a tar or zip archive from
895any version of a project; for example:
896
897-------------------------------------------------
898$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
899-------------------------------------------------
900
901will use HEAD to produce a tar archive in which each filename is
ccd71866 902preceded by "project/".
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903
904If you're releasing a new version of a software project, you may want
905to simultaneously make a changelog to include in the release
906announcement.
907
908Linus Torvalds, for example, makes new kernel releases by tagging them,
909then running:
910
911-------------------------------------------------
912$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
913-------------------------------------------------
914
915where release-script is a shell script that looks like:
916
917-------------------------------------------------
918#!/bin/sh
919stable="$1"
920last="$2"
921new="$3"
922echo "# git tag v$new"
923echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
924echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
925echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
926echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
927echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
928-------------------------------------------------
929
930and then he just cut-and-pastes the output commands after verifying that
931they look OK.
4a7979ca 932
8ceca74a 933[[Finding-comments-with-given-content]]
187b0d80 934Finding commits referencing a file with given content
d5821de2 935~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
187b0d80
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936
937Somebody hands you a copy of a file, and asks which commits modified a
938file such that it contained the given content either before or after the
939commit. You can find out with this:
940
941-------------------------------------------------
170c0438 942$ git log --raw --abbrev=40 --pretty=oneline -- filename |
187b0d80
BF
943 grep -B 1 `git hash-object filename`
944-------------------------------------------------
945
946Figuring out why this works is left as an exercise to the (advanced)
947student. The gitlink:git-log[1], gitlink:git-diff-tree[1], and
948gitlink:git-hash-object[1] man pages may prove helpful.
949
e34caace 950[[Developing-with-git]]
d19fbc3c
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951Developing with git
952===================
953
e34caace 954[[telling-git-your-name]]
d19fbc3c
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955Telling git your name
956---------------------
957
958Before creating any commits, you should introduce yourself to git. The
58c19d1f
BF
959easiest way to do so is to make sure the following lines appear in a
960file named .gitconfig in your home directory:
d19fbc3c
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961
962------------------------------------------------
d19fbc3c
BF
963[user]
964 name = Your Name Comes Here
965 email = you@yourdomain.example.com
d19fbc3c
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966------------------------------------------------
967
fc90c536
BF
968(See the "CONFIGURATION FILE" section of gitlink:git-config[1] for
969details on the configuration file.)
970
d19fbc3c 971
e34caace 972[[creating-a-new-repository]]
d19fbc3c
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973Creating a new repository
974-------------------------
975
976Creating a new repository from scratch is very easy:
977
978-------------------------------------------------
979$ mkdir project
980$ cd project
f1d2b477 981$ git init
d19fbc3c
BF
982-------------------------------------------------
983
984If you have some initial content (say, a tarball):
985
986-------------------------------------------------
987$ tar -xzvf project.tar.gz
988$ cd project
f1d2b477 989$ git init
d19fbc3c
BF
990$ git add . # include everything below ./ in the first commit:
991$ git commit
992-------------------------------------------------
993
994[[how-to-make-a-commit]]
ae25c67a 995How to make a commit
d19fbc3c
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996--------------------
997
998Creating a new commit takes three steps:
999
1000 1. Making some changes to the working directory using your
1001 favorite editor.
1002 2. Telling git about your changes.
1003 3. Creating the commit using the content you told git about
1004 in step 2.
1005
1006In practice, you can interleave and repeat steps 1 and 2 as many
1007times as you want: in order to keep track of what you want committed
1008at step 3, git maintains a snapshot of the tree's contents in a
1009special staging area called "the index."
1010
01997b4a
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1011At the beginning, the content of the index will be identical to
1012that of the HEAD. The command "git diff --cached", which shows
1013the difference between the HEAD and the index, should therefore
1014produce no output at that point.
eb6ae7f4 1015
d19fbc3c
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1016Modifying the index is easy:
1017
1018To update the index with the new contents of a modified file, use
1019
1020-------------------------------------------------
1021$ git add path/to/file
1022-------------------------------------------------
1023
1024To add the contents of a new file to the index, use
1025
1026-------------------------------------------------
1027$ git add path/to/file
1028-------------------------------------------------
1029
eb6ae7f4 1030To remove a file from the index and from the working tree,
d19fbc3c
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1031
1032-------------------------------------------------
1033$ git rm path/to/file
1034-------------------------------------------------
1035
1036After each step you can verify that
1037
1038-------------------------------------------------
1039$ git diff --cached
1040-------------------------------------------------
1041
1042always shows the difference between the HEAD and the index file--this
1043is what you'd commit if you created the commit now--and that
1044
1045-------------------------------------------------
1046$ git diff
1047-------------------------------------------------
1048
1049shows the difference between the working tree and the index file.
1050
1051Note that "git add" always adds just the current contents of a file
1052to the index; further changes to the same file will be ignored unless
1053you run git-add on the file again.
1054
1055When you're ready, just run
1056
1057-------------------------------------------------
1058$ git commit
1059-------------------------------------------------
1060
1061and git will prompt you for a commit message and then create the new
3dff5379 1062commit. Check to make sure it looks like what you expected with
d19fbc3c
BF
1063
1064-------------------------------------------------
1065$ git show
1066-------------------------------------------------
1067
1068As a special shortcut,
a6080a0a 1069
d19fbc3c
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1070-------------------------------------------------
1071$ git commit -a
1072-------------------------------------------------
1073
1074will update the index with any files that you've modified or removed
1075and create a commit, all in one step.
1076
1077A number of commands are useful for keeping track of what you're
1078about to commit:
1079
1080-------------------------------------------------
1081$ git diff --cached # difference between HEAD and the index; what
1130845b 1082 # would be committed if you ran "commit" now.
d19fbc3c
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1083$ git diff # difference between the index file and your
1084 # working directory; changes that would not
1085 # be included if you ran "commit" now.
c64415e2
BF
1086$ git diff HEAD # difference between HEAD and working tree; what
1087 # would be committed if you ran "commit -a" now.
d19fbc3c
BF
1088$ git status # a brief per-file summary of the above.
1089-------------------------------------------------
1090
407c0c87
BF
1091You can also use gitlink:git-gui[1] to create commits, view changes in
1092the index and the working tree files, and individually select diff hunks
1093for inclusion in the index (by right-clicking on the diff hunk and
1094choosing "Stage Hunk For Commit").
1095
e34caace 1096[[creating-good-commit-messages]]
ae25c67a 1097Creating good commit messages
d19fbc3c
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1098-----------------------------
1099
1100Though not required, it's a good idea to begin the commit message
1101with a single short (less than 50 character) line summarizing the
1102change, followed by a blank line and then a more thorough
1103description. Tools that turn commits into email, for example, use
1104the first line on the Subject line and the rest of the commit in the
1105body.
1106
2dc53617
JH
1107[[ignoring-files]]
1108Ignoring files
1109--------------
1110
1111A project will often generate files that you do 'not' want to track with git.
1112This typically includes files generated by a build process or temporary
1113backup files made by your editor. Of course, 'not' tracking files with git
1114is just a matter of 'not' calling "`git add`" on them. But it quickly becomes
1115annoying to have these untracked files lying around; e.g. they make
1116"`git add .`" and "`git commit -a`" practically useless, and they keep
464a8a7a 1117showing up in the output of "`git status`".
2dc53617 1118
464a8a7a
BF
1119You can tell git to ignore certain files by creating a file called .gitignore
1120in the top level of your working directory, with contents such as:
2dc53617
JH
1121
1122-------------------------------------------------
1123# Lines starting with '#' are considered comments.
464a8a7a 1124# Ignore any file named foo.txt.
2dc53617
JH
1125foo.txt
1126# Ignore (generated) html files,
1127*.html
1128# except foo.html which is maintained by hand.
1129!foo.html
1130# Ignore objects and archives.
1131*.[oa]
1132-------------------------------------------------
1133
464a8a7a
BF
1134See gitlink:gitignore[5] for a detailed explanation of the syntax. You can
1135also place .gitignore files in other directories in your working tree, and they
1136will apply to those directories and their subdirectories. The `.gitignore`
1137files can be added to your repository like any other files (just run `git add
1138.gitignore` and `git commit`, as usual), which is convenient when the exclude
1139patterns (such as patterns matching build output files) would also make sense
1140for other users who clone your repository.
1141
1142If you wish the exclude patterns to affect only certain repositories
1143(instead of every repository for a given project), you may instead put
1144them in a file in your repository named .git/info/exclude, or in any file
1145specified by the `core.excludesfile` configuration variable. Some git
1146commands can also take exclude patterns directly on the command line.
1147See gitlink:gitignore[5] for the details.
2dc53617 1148
e34caace 1149[[how-to-merge]]
ae25c67a 1150How to merge
d19fbc3c
BF
1151------------
1152
1153You can rejoin two diverging branches of development using
1154gitlink:git-merge[1]:
1155
1156-------------------------------------------------
1157$ git merge branchname
1158-------------------------------------------------
1159
1160merges the development in the branch "branchname" into the current
1161branch. If there are conflicts--for example, if the same file is
1162modified in two different ways in the remote branch and the local
1163branch--then you are warned; the output may look something like this:
1164
1165-------------------------------------------------
fabbd8f6
BF
1166$ git merge next
1167 100% (4/4) done
1168Auto-merged file.txt
d19fbc3c
BF
1169CONFLICT (content): Merge conflict in file.txt
1170Automatic merge failed; fix conflicts and then commit the result.
1171-------------------------------------------------
1172
1173Conflict markers are left in the problematic files, and after
1174you resolve the conflicts manually, you can update the index
1175with the contents and run git commit, as you normally would when
1176creating a new file.
1177
1178If you examine the resulting commit using gitk, you will see that it
1179has two parents, one pointing to the top of the current branch, and
1180one to the top of the other branch.
1181
d19fbc3c
BF
1182[[resolving-a-merge]]
1183Resolving a merge
1184-----------------
1185
1186When a merge isn't resolved automatically, git leaves the index and
1187the working tree in a special state that gives you all the
1188information you need to help resolve the merge.
1189
1190Files with conflicts are marked specially in the index, so until you
ef561ac7
BF
1191resolve the problem and update the index, gitlink:git-commit[1] will
1192fail:
d19fbc3c
BF
1193
1194-------------------------------------------------
1195$ git commit
1196file.txt: needs merge
1197-------------------------------------------------
1198
ef561ac7
BF
1199Also, gitlink:git-status[1] will list those files as "unmerged", and the
1200files with conflicts will have conflict markers added, like this:
1201
1202-------------------------------------------------
1203<<<<<<< HEAD:file.txt
1204Hello world
1205=======
1206Goodbye
1207>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1208-------------------------------------------------
1209
1210All you need to do is edit the files to resolve the conflicts, and then
1211
1212-------------------------------------------------
1213$ git add file.txt
1214$ git commit
1215-------------------------------------------------
1216
1217Note that the commit message will already be filled in for you with
1218some information about the merge. Normally you can just use this
1219default message unchanged, but you may add additional commentary of
1220your own if desired.
1221
1222The above is all you need to know to resolve a simple merge. But git
1223also provides more information to help resolve conflicts:
1224
e34caace 1225[[conflict-resolution]]
ef561ac7
BF
1226Getting conflict-resolution help during a merge
1227~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1228
1229All of the changes that git was able to merge automatically are
1230already added to the index file, so gitlink:git-diff[1] shows only
ef561ac7 1231the conflicts. It uses an unusual syntax:
d19fbc3c
BF
1232
1233-------------------------------------------------
1234$ git diff
1235diff --cc file.txt
1236index 802992c,2b60207..0000000
1237--- a/file.txt
1238+++ b/file.txt
1239@@@ -1,1 -1,1 +1,5 @@@
1240++<<<<<<< HEAD:file.txt
1241 +Hello world
1242++=======
1243+ Goodbye
1244++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1245-------------------------------------------------
1246
1130845b 1247Recall that the commit which will be committed after we resolve this
d19fbc3c
BF
1248conflict will have two parents instead of the usual one: one parent
1249will be HEAD, the tip of the current branch; the other will be the
1250tip of the other branch, which is stored temporarily in MERGE_HEAD.
1251
ef561ac7
BF
1252During the merge, the index holds three versions of each file. Each of
1253these three "file stages" represents a different version of the file:
1254
1255-------------------------------------------------
1256$ git show :1:file.txt # the file in a common ancestor of both branches
1257$ git show :2:file.txt # the version from HEAD, but including any
1258 # nonconflicting changes from MERGE_HEAD
1259$ git show :3:file.txt # the version from MERGE_HEAD, but including any
1260 # nonconflicting changes from HEAD.
1261-------------------------------------------------
1262
1263Since the stage 2 and stage 3 versions have already been updated with
1264nonconflicting changes, the only remaining differences between them are
1265the important ones; thus gitlink:git-diff[1] can use the information in
1266the index to show only those conflicts.
1267
1268The diff above shows the differences between the working-tree version of
1269file.txt and the stage 2 and stage 3 versions. So instead of preceding
1270each line by a single "+" or "-", it now uses two columns: the first
1271column is used for differences between the first parent and the working
1272directory copy, and the second for differences between the second parent
1273and the working directory copy. (See the "COMBINED DIFF FORMAT" section
1274of gitlink:git-diff-files[1] for a details of the format.)
1275
1276After resolving the conflict in the obvious way (but before updating the
1277index), the diff will look like:
d19fbc3c
BF
1278
1279-------------------------------------------------
1280$ git diff
1281diff --cc file.txt
1282index 802992c,2b60207..0000000
1283--- a/file.txt
1284+++ b/file.txt
1285@@@ -1,1 -1,1 +1,1 @@@
1286- Hello world
1287 -Goodbye
1288++Goodbye world
1289-------------------------------------------------
1290
1291This shows that our resolved version deleted "Hello world" from the
1292first parent, deleted "Goodbye" from the second parent, and added
1293"Goodbye world", which was previously absent from both.
1294
ef561ac7
BF
1295Some special diff options allow diffing the working directory against
1296any of these stages:
1297
1298-------------------------------------------------
1299$ git diff -1 file.txt # diff against stage 1
1300$ git diff --base file.txt # same as the above
1301$ git diff -2 file.txt # diff against stage 2
1302$ git diff --ours file.txt # same as the above
1303$ git diff -3 file.txt # diff against stage 3
1304$ git diff --theirs file.txt # same as the above.
1305-------------------------------------------------
1306
1307The gitlink:git-log[1] and gitk[1] commands also provide special help
1308for merges:
d19fbc3c
BF
1309
1310-------------------------------------------------
1311$ git log --merge
ef561ac7 1312$ gitk --merge
d19fbc3c
BF
1313-------------------------------------------------
1314
ef561ac7
BF
1315These will display all commits which exist only on HEAD or on
1316MERGE_HEAD, and which touch an unmerged file.
d19fbc3c 1317
61d72564 1318You may also use gitlink:git-mergetool[1], which lets you merge the
c64415e2
BF
1319unmerged files using external tools such as emacs or kdiff3.
1320
ef561ac7 1321Each time you resolve the conflicts in a file and update the index:
d19fbc3c
BF
1322
1323-------------------------------------------------
1324$ git add file.txt
d19fbc3c
BF
1325-------------------------------------------------
1326
ef561ac7
BF
1327the different stages of that file will be "collapsed", after which
1328git-diff will (by default) no longer show diffs for that file.
d19fbc3c
BF
1329
1330[[undoing-a-merge]]
ae25c67a 1331Undoing a merge
d19fbc3c
BF
1332---------------
1333
1334If you get stuck and decide to just give up and throw the whole mess
1335away, you can always return to the pre-merge state with
1336
1337-------------------------------------------------
1338$ git reset --hard HEAD
1339-------------------------------------------------
1340
1130845b 1341Or, if you've already committed the merge that you want to throw away,
d19fbc3c
BF
1342
1343-------------------------------------------------
1c73bb0e 1344$ git reset --hard ORIG_HEAD
d19fbc3c
BF
1345-------------------------------------------------
1346
1347However, this last command can be dangerous in some cases--never
1348throw away a commit you have already committed if that commit may
1349itself have been merged into another branch, as doing so may confuse
1350further merges.
1351
e34caace 1352[[fast-forwards]]
d19fbc3c
BF
1353Fast-forward merges
1354-------------------
1355
1356There is one special case not mentioned above, which is treated
1357differently. Normally, a merge results in a merge commit, with two
1358parents, one pointing at each of the two lines of development that
1359were merged.
1360
59723040
BF
1361However, if the current branch is a descendant of the other--so every
1362commit present in the one is already contained in the other--then git
1363just performs a "fast forward"; the head of the current branch is moved
1364forward to point at the head of the merged-in branch, without any new
1365commits being created.
d19fbc3c 1366
e34caace 1367[[fixing-mistakes]]
b684f830
BF
1368Fixing mistakes
1369---------------
1370
1371If you've messed up the working tree, but haven't yet committed your
1372mistake, you can return the entire working tree to the last committed
1373state with
1374
1375-------------------------------------------------
1376$ git reset --hard HEAD
1377-------------------------------------------------
1378
1379If you make a commit that you later wish you hadn't, there are two
1380fundamentally different ways to fix the problem:
1381
1382 1. You can create a new commit that undoes whatever was done
1383 by the previous commit. This is the correct thing if your
1384 mistake has already been made public.
1385
1386 2. You can go back and modify the old commit. You should
1387 never do this if you have already made the history public;
1388 git does not normally expect the "history" of a project to
1389 change, and cannot correctly perform repeated merges from
1390 a branch that has had its history changed.
1391
e34caace 1392[[reverting-a-commit]]
b684f830
BF
1393Fixing a mistake with a new commit
1394~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1395
1396Creating a new commit that reverts an earlier change is very easy;
1397just pass the gitlink:git-revert[1] command a reference to the bad
1398commit; for example, to revert the most recent commit:
1399
1400-------------------------------------------------
1401$ git revert HEAD
1402-------------------------------------------------
1403
1404This will create a new commit which undoes the change in HEAD. You
1405will be given a chance to edit the commit message for the new commit.
1406
1407You can also revert an earlier change, for example, the next-to-last:
1408
1409-------------------------------------------------
1410$ git revert HEAD^
1411-------------------------------------------------
1412
1413In this case git will attempt to undo the old change while leaving
1414intact any changes made since then. If more recent changes overlap
1415with the changes to be reverted, then you will be asked to fix
1416conflicts manually, just as in the case of <<resolving-a-merge,
1417resolving a merge>>.
1418
365aa199 1419[[fixing-a-mistake-by-editing-history]]
b684f830
BF
1420Fixing a mistake by editing history
1421~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1422
1423If the problematic commit is the most recent commit, and you have not
1424yet made that commit public, then you may just
1425<<undoing-a-merge,destroy it using git-reset>>.
1426
1427Alternatively, you
1428can edit the working directory and update the index to fix your
1429mistake, just as if you were going to <<how-to-make-a-commit,create a
1430new commit>>, then run
1431
1432-------------------------------------------------
1433$ git commit --amend
1434-------------------------------------------------
1435
1436which will replace the old commit by a new commit incorporating your
1437changes, giving you a chance to edit the old commit message first.
1438
1439Again, you should never do this to a commit that may already have
1440been merged into another branch; use gitlink:git-revert[1] instead in
1441that case.
1442
1443It is also possible to edit commits further back in the history, but
1444this is an advanced topic to be left for
1445<<cleaning-up-history,another chapter>>.
1446
e34caace 1447[[checkout-of-path]]
b684f830
BF
1448Checking out an old version of a file
1449~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1450
1451In the process of undoing a previous bad change, you may find it
1452useful to check out an older version of a particular file using
1453gitlink:git-checkout[1]. We've used git checkout before to switch
1454branches, but it has quite different behavior if it is given a path
1455name: the command
1456
1457-------------------------------------------------
1458$ git checkout HEAD^ path/to/file
1459-------------------------------------------------
1460
1461replaces path/to/file by the contents it had in the commit HEAD^, and
1462also updates the index to match. It does not change branches.
1463
1464If you just want to look at an old version of the file, without
1465modifying the working directory, you can do that with
1466gitlink:git-show[1]:
1467
1468-------------------------------------------------
ed4eb0d8 1469$ git show HEAD^:path/to/file
b684f830
BF
1470-------------------------------------------------
1471
1472which will display the given version of the file.
1473
7a7cc594
JH
1474[[interrupted-work]]
1475Temporarily setting aside work in progress
1476~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1477
1478While you are in the middle of working on something complicated, you
1479find an unrelated but obvious and trivial bug. You would like to fix it
1480before continuing. You can use gitlink:git-stash[1] to save the current
1481state of your work, and after fixing the bug (or, optionally after doing
1482so on a different branch and then coming back), unstash the
1483work-in-progress changes.
1484
1485------------------------------------------------
1486$ git stash "work in progress for foo feature"
1487------------------------------------------------
1488
1489This command will save your changes away to the `stash`, and
1490reset your working tree and the index to match the tip of your
1491current branch. Then you can make your fix as usual.
1492
1493------------------------------------------------
1494... edit and test ...
1495$ git commit -a -m "blorpl: typofix"
1496------------------------------------------------
1497
1498After that, you can go back to what you were working on with
1499`git stash apply`:
1500
1501------------------------------------------------
1502$ git stash apply
1503------------------------------------------------
1504
1505
e34caace 1506[[ensuring-good-performance]]
d19fbc3c
BF
1507Ensuring good performance
1508-------------------------
1509
1510On large repositories, git depends on compression to keep the history
1511information from taking up to much space on disk or in memory.
1512
1513This compression is not performed automatically. Therefore you
17217090 1514should occasionally run gitlink:git-gc[1]:
d19fbc3c
BF
1515
1516-------------------------------------------------
1517$ git gc
1518-------------------------------------------------
1519
17217090
BF
1520to recompress the archive. This can be very time-consuming, so
1521you may prefer to run git-gc when you are not doing other work.
d19fbc3c 1522
e34caace
BF
1523
1524[[ensuring-reliability]]
11e016a3
BF
1525Ensuring reliability
1526--------------------
1527
e34caace 1528[[checking-for-corruption]]
11e016a3
BF
1529Checking the repository for corruption
1530~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1531
1191ee18
BF
1532The gitlink:git-fsck[1] command runs a number of self-consistency checks
1533on the repository, and reports on any problems. This may take some
21dcb3b7
BF
1534time. The most common warning by far is about "dangling" objects:
1535
1536-------------------------------------------------
04e50e94 1537$ git fsck
21dcb3b7
BF
1538dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1539dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1540dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1541dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1542dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1543dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1544dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1545dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1546...
1547-------------------------------------------------
1548
59723040 1549Dangling objects are not a problem. At worst they may take up a little
54782859
AP
1550extra disk space. They can sometimes provide a last-resort method for
1551recovering lost work--see <<dangling-objects>> for details. However, if
1552you wish, you can remove them with gitlink:git-prune[1] or the --prune
1191ee18 1553option to gitlink:git-gc[1]:
21dcb3b7
BF
1554
1555-------------------------------------------------
1556$ git gc --prune
1557-------------------------------------------------
1558
1191ee18
BF
1559This may be time-consuming. Unlike most other git operations (including
1560git-gc when run without any options), it is not safe to prune while
1561other git operations are in progress in the same repository.
21dcb3b7 1562
e34caace 1563[[recovering-lost-changes]]
11e016a3
BF
1564Recovering lost changes
1565~~~~~~~~~~~~~~~~~~~~~~~
1566
e34caace 1567[[reflogs]]
559e4d7a
BF
1568Reflogs
1569^^^^^^^
1570
1571Say you modify a branch with gitlink:git-reset[1] --hard, and then
1572realize that the branch was the only reference you had to that point in
1573history.
1574
1575Fortunately, git also keeps a log, called a "reflog", of all the
1576previous values of each branch. So in this case you can still find the
a6080a0a 1577old history using, for example,
559e4d7a
BF
1578
1579-------------------------------------------------
1580$ git log master@{1}
1581-------------------------------------------------
1582
1583This lists the commits reachable from the previous version of the head.
1584This syntax can be used to with any git command that accepts a commit,
1585not just with git log. Some other examples:
1586
1587-------------------------------------------------
1588$ git show master@{2} # See where the branch pointed 2,
1589$ git show master@{3} # 3, ... changes ago.
1590$ gitk master@{yesterday} # See where it pointed yesterday,
1591$ gitk master@{"1 week ago"} # ... or last week
953f3d6f
BF
1592$ git log --walk-reflogs master # show reflog entries for master
1593-------------------------------------------------
1594
1595A separate reflog is kept for the HEAD, so
1596
1597-------------------------------------------------
1598$ git show HEAD@{"1 week ago"}
559e4d7a
BF
1599-------------------------------------------------
1600
953f3d6f
BF
1601will show what HEAD pointed to one week ago, not what the current branch
1602pointed to one week ago. This allows you to see the history of what
1603you've checked out.
1604
559e4d7a 1605The reflogs are kept by default for 30 days, after which they may be
036be17e 1606pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn
559e4d7a
BF
1607how to control this pruning, and see the "SPECIFYING REVISIONS"
1608section of gitlink:git-rev-parse[1] for details.
1609
1610Note that the reflog history is very different from normal git history.
1611While normal history is shared by every repository that works on the
1612same project, the reflog history is not shared: it tells you only about
1613how the branches in your local repository have changed over time.
1614
59723040 1615[[dangling-object-recovery]]
559e4d7a
BF
1616Examining dangling objects
1617^^^^^^^^^^^^^^^^^^^^^^^^^^
1618
59723040
BF
1619In some situations the reflog may not be able to save you. For example,
1620suppose you delete a branch, then realize you need the history it
1621contained. The reflog is also deleted; however, if you have not yet
1622pruned the repository, then you may still be able to find the lost
1623commits in the dangling objects that git-fsck reports. See
1624<<dangling-objects>> for the details.
559e4d7a
BF
1625
1626-------------------------------------------------
1627$ git fsck
1628dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1629dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1630dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1631...
1632-------------------------------------------------
1633
aacd404e 1634You can examine
559e4d7a
BF
1635one of those dangling commits with, for example,
1636
1637------------------------------------------------
1638$ gitk 7281251ddd --not --all
1639------------------------------------------------
1640
1641which does what it sounds like: it says that you want to see the commit
1642history that is described by the dangling commit(s), but not the
1643history that is described by all your existing branches and tags. Thus
1644you get exactly the history reachable from that commit that is lost.
1645(And notice that it might not be just one commit: we only report the
1646"tip of the line" as being dangling, but there might be a whole deep
79c96c57 1647and complex commit history that was dropped.)
559e4d7a
BF
1648
1649If you decide you want the history back, you can always create a new
1650reference pointing to it, for example, a new branch:
1651
1652------------------------------------------------
a6080a0a 1653$ git branch recovered-branch 7281251ddd
559e4d7a
BF
1654------------------------------------------------
1655
59723040
BF
1656Other types of dangling objects (blobs and trees) are also possible, and
1657dangling objects can arise in other situations.
1658
11e016a3 1659
e34caace 1660[[sharing-development]]
d19fbc3c 1661Sharing development with others
b684f830 1662===============================
d19fbc3c
BF
1663
1664[[getting-updates-with-git-pull]]
1665Getting updates with git pull
b684f830 1666-----------------------------
d19fbc3c
BF
1667
1668After you clone a repository and make a few changes of your own, you
1669may wish to check the original repository for updates and merge them
1670into your own work.
1671
1672We have already seen <<Updating-a-repository-with-git-fetch,how to
1673keep remote tracking branches up to date>> with gitlink:git-fetch[1],
1674and how to merge two branches. So you can merge in changes from the
1675original repository's master branch with:
1676
1677-------------------------------------------------
1678$ git fetch
1679$ git merge origin/master
1680-------------------------------------------------
1681
1682However, the gitlink:git-pull[1] command provides a way to do this in
1683one step:
1684
1685-------------------------------------------------
1686$ git pull origin master
1687-------------------------------------------------
1688
0eb4f7cd
BF
1689In fact, if you have "master" checked out, then by default "git pull"
1690merges from the HEAD branch of the origin repository. So often you can
1691accomplish the above with just a simple
d19fbc3c
BF
1692
1693-------------------------------------------------
1694$ git pull
1695-------------------------------------------------
1696
0eb4f7cd
BF
1697More generally, a branch that is created from a remote branch will pull
1698by default from that branch. See the descriptions of the
1699branch.<name>.remote and branch.<name>.merge options in
1700gitlink:git-config[1], and the discussion of the --track option in
1701gitlink:git-checkout[1], to learn how to control these defaults.
d19fbc3c
BF
1702
1703In addition to saving you keystrokes, "git pull" also helps you by
1704producing a default commit message documenting the branch and
1705repository that you pulled from.
1706
1707(But note that no such commit will be created in the case of a
1708<<fast-forwards,fast forward>>; instead, your branch will just be
79c96c57 1709updated to point to the latest commit from the upstream branch.)
d19fbc3c 1710
1191ee18
BF
1711The git-pull command can also be given "." as the "remote" repository,
1712in which case it just merges in a branch from the current repository; so
4c63ff45
BF
1713the commands
1714
1715-------------------------------------------------
1716$ git pull . branch
1717$ git merge branch
1718-------------------------------------------------
1719
1720are roughly equivalent. The former is actually very commonly used.
1721
e34caace 1722[[submitting-patches]]
d19fbc3c 1723Submitting patches to a project
b684f830 1724-------------------------------
d19fbc3c
BF
1725
1726If you just have a few changes, the simplest way to submit them may
1727just be to send them as patches in email:
1728
036be17e 1729First, use gitlink:git-format-patch[1]; for example:
d19fbc3c
BF
1730
1731-------------------------------------------------
eb6ae7f4 1732$ git format-patch origin
d19fbc3c
BF
1733-------------------------------------------------
1734
1735will produce a numbered series of files in the current directory, one
1736for each patch in the current branch but not in origin/HEAD.
1737
1738You can then import these into your mail client and send them by
1739hand. However, if you have a lot to send at once, you may prefer to
1740use the gitlink:git-send-email[1] script to automate the process.
1741Consult the mailing list for your project first to determine how they
1742prefer such patches be handled.
1743
e34caace 1744[[importing-patches]]
d19fbc3c 1745Importing patches to a project
b684f830 1746------------------------------
d19fbc3c
BF
1747
1748Git also provides a tool called gitlink:git-am[1] (am stands for
1749"apply mailbox"), for importing such an emailed series of patches.
1750Just save all of the patch-containing messages, in order, into a
1751single mailbox file, say "patches.mbox", then run
1752
1753-------------------------------------------------
eb6ae7f4 1754$ git am -3 patches.mbox
d19fbc3c
BF
1755-------------------------------------------------
1756
1757Git will apply each patch in order; if any conflicts are found, it
1758will stop, and you can fix the conflicts as described in
01997b4a
BF
1759"<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1760git to perform a merge; if you would prefer it just to abort and
1761leave your tree and index untouched, you may omit that option.)
1762
1763Once the index is updated with the results of the conflict
1764resolution, instead of creating a new commit, just run
d19fbc3c
BF
1765
1766-------------------------------------------------
1767$ git am --resolved
1768-------------------------------------------------
1769
1770and git will create the commit for you and continue applying the
1771remaining patches from the mailbox.
1772
1773The final result will be a series of commits, one for each patch in
1774the original mailbox, with authorship and commit log message each
1775taken from the message containing each patch.
1776
eda69449
BF
1777[[public-repositories]]
1778Public git repositories
1779-----------------------
d19fbc3c 1780
6e30fb0c
DK
1781Another way to submit changes to a project is to tell the maintainer
1782of that project to pull the changes from your repository using
1783gitlink:git-pull[1]. In the section "<<getting-updates-with-git-pull,
1784Getting updates with git pull>>" we described this as a way to get
1785updates from the "main" repository, but it works just as well in the
1786other direction.
d19fbc3c 1787
eda69449
BF
1788If you and the maintainer both have accounts on the same machine, then
1789you can just pull changes from each other's repositories directly;
11d51533 1790commands that accept repository URLs as arguments will also accept a
eda69449 1791local directory name:
d19fbc3c
BF
1792
1793-------------------------------------------------
1794$ git clone /path/to/repository
1795$ git pull /path/to/other/repository
1796-------------------------------------------------
1797
11d51533
BF
1798or an ssh url:
1799
1800-------------------------------------------------
1801$ git clone ssh://yourhost/~you/repository
1802-------------------------------------------------
1803
1804For projects with few developers, or for synchronizing a few private
1805repositories, this may be all you need.
1806
eda69449
BF
1807However, the more common way to do this is to maintain a separate public
1808repository (usually on a different host) for others to pull changes
1809from. This is usually more convenient, and allows you to cleanly
1810separate private work in progress from publicly visible work.
d19fbc3c
BF
1811
1812You will continue to do your day-to-day work in your personal
1813repository, but periodically "push" changes from your personal
1814repository into your public repository, allowing other developers to
1815pull from that repository. So the flow of changes, in a situation
1816where there is one other developer with a public repository, looks
1817like this:
1818
1819 you push
1820 your personal repo ------------------> your public repo
a6080a0a 1821 ^ |
d19fbc3c
BF
1822 | |
1823 | you pull | they pull
1824 | |
1825 | |
1826 | they push V
1827 their public repo <------------------- their repo
1828
11d51533
BF
1829We explain how to do this in the following sections.
1830
eda69449
BF
1831[[setting-up-a-public-repository]]
1832Setting up a public repository
1833~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1834
1835Assume your personal repository is in the directory ~/proj. We
1836first create a new clone of the repository and tell git-daemon that it
1837is meant to be public:
d19fbc3c
BF
1838
1839-------------------------------------------------
52c80037 1840$ git clone --bare ~/proj proj.git
eda69449 1841$ touch proj.git/git-daemon-export-ok
d19fbc3c
BF
1842-------------------------------------------------
1843
52c80037 1844The resulting directory proj.git contains a "bare" git repository--it is
eda69449
BF
1845just the contents of the ".git" directory, without any files checked out
1846around it.
d19fbc3c 1847
c64415e2 1848Next, copy proj.git to the server where you plan to host the
d19fbc3c
BF
1849public repository. You can use scp, rsync, or whatever is most
1850convenient.
1851
eda69449
BF
1852[[exporting-via-git]]
1853Exporting a git repository via the git protocol
1854~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1855
1856This is the preferred method.
1857
1858If someone else administers the server, they should tell you what
1859directory to put the repository in, and what git:// url it will appear
1860at. You can then skip to the section
d19fbc3c
BF
1861"<<pushing-changes-to-a-public-repository,Pushing changes to a public
1862repository>>", below.
1863
eda69449
BF
1864Otherwise, all you need to do is start gitlink:git-daemon[1]; it will
1865listen on port 9418. By default, it will allow access to any directory
1866that looks like a git directory and contains the magic file
1867git-daemon-export-ok. Passing some directory paths as git-daemon
1868arguments will further restrict the exports to those paths.
1869
1870You can also run git-daemon as an inetd service; see the
1871gitlink:git-daemon[1] man page for details. (See especially the
1872examples section.)
d19fbc3c
BF
1873
1874[[exporting-via-http]]
1875Exporting a git repository via http
eda69449 1876~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1877
1878The git protocol gives better performance and reliability, but on a
1879host with a web server set up, http exports may be simpler to set up.
1880
1881All you need to do is place the newly created bare git repository in
1882a directory that is exported by the web server, and make some
1883adjustments to give web clients some extra information they need:
1884
1885-------------------------------------------------
1886$ mv proj.git /home/you/public_html/proj.git
1887$ cd proj.git
c64415e2 1888$ git --bare update-server-info
d19fbc3c
BF
1889$ chmod a+x hooks/post-update
1890-------------------------------------------------
1891
1892(For an explanation of the last two lines, see
1893gitlink:git-update-server-info[1], and the documentation
a2983cb7 1894link:hooks.html[Hooks used by git].)
d19fbc3c
BF
1895
1896Advertise the url of proj.git. Anybody else should then be able to
02783075 1897clone or pull from that url, for example with a command line like:
d19fbc3c
BF
1898
1899-------------------------------------------------
1900$ git clone http://yourserver.com/~you/proj.git
1901-------------------------------------------------
1902
1903(See also
1904link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1905for a slightly more sophisticated setup using WebDAV which also
1906allows pushing over http.)
1907
d19fbc3c
BF
1908[[pushing-changes-to-a-public-repository]]
1909Pushing changes to a public repository
eda69449 1910~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1911
eda69449 1912Note that the two techniques outlined above (exporting via
d19fbc3c
BF
1913<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1914maintainers to fetch your latest changes, but they do not allow write
1915access, which you will need to update the public repository with the
1916latest changes created in your private repository.
1917
1918The simplest way to do this is using gitlink:git-push[1] and ssh; to
1919update the remote branch named "master" with the latest state of your
1920branch named "master", run
1921
1922-------------------------------------------------
1923$ git push ssh://yourserver.com/~you/proj.git master:master
1924-------------------------------------------------
1925
1926or just
1927
1928-------------------------------------------------
1929$ git push ssh://yourserver.com/~you/proj.git master
1930-------------------------------------------------
1931
81eb417a
BF
1932As with git-fetch, git-push will complain if this does not result in a
1933<<fast-forwards,fast forward>>; see the following section for details on
1934handling this case.
d19fbc3c 1935
11d51533
BF
1936Note that the target of a "push" is normally a
1937<<def_bare_repository,bare>> repository. You can also push to a
1938repository that has a checked-out working tree, but the working tree
1939will not be updated by the push. This may lead to unexpected results if
1940the branch you push to is the currently checked-out branch!
1941
d19fbc3c
BF
1942As with git-fetch, you may also set up configuration options to
1943save typing; so, for example, after
1944
1945-------------------------------------------------
c64415e2 1946$ cat >>.git/config <<EOF
d19fbc3c
BF
1947[remote "public-repo"]
1948 url = ssh://yourserver.com/~you/proj.git
1949EOF
1950-------------------------------------------------
1951
1952you should be able to perform the above push with just
1953
1954-------------------------------------------------
1955$ git push public-repo master
1956-------------------------------------------------
1957
1958See the explanations of the remote.<name>.url, branch.<name>.remote,
9d13bda3 1959and remote.<name>.push options in gitlink:git-config[1] for
d19fbc3c
BF
1960details.
1961
81eb417a
BF
1962[[forcing-push]]
1963What to do when a push fails
1964~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1965
1966If a push would not result in a <<fast-forwards,fast forward>> of the
1967remote branch, then it will fail with an error like:
1968
1969-------------------------------------------------
1970error: remote 'refs/heads/master' is not an ancestor of
1971 local 'refs/heads/master'.
1972 Maybe you are not up-to-date and need to pull first?
1973error: failed to push to 'ssh://yourserver.com/~you/proj.git'
1974-------------------------------------------------
1975
1976This can happen, for example, if you:
1977
1978 - use `git reset --hard` to remove already-published commits, or
1979 - use `git commit --amend` to replace already-published commits
1980 (as in <<fixing-a-mistake-by-editing-history>>), or
1981 - use `git rebase` to rebase any already-published commits (as
1982 in <<using-git-rebase>>).
1983
1984You may force git-push to perform the update anyway by preceding the
1985branch name with a plus sign:
1986
1987-------------------------------------------------
1988$ git push ssh://yourserver.com/~you/proj.git +master
1989-------------------------------------------------
1990
1991Normally whenever a branch head in a public repository is modified, it
1992is modified to point to a descendent of the commit that it pointed to
1993before. By forcing a push in this situation, you break that convention.
1994(See <<problems-with-rewriting-history>>.)
1995
1996Nevertheless, this is a common practice for people that need a simple
1997way to publish a work-in-progress patch series, and it is an acceptable
1998compromise as long as you warn other developers that this is how you
1999intend to manage the branch.
2000
2001It's also possible for a push to fail in this way when other people have
2002the right to push to the same repository. In that case, the correct
2003solution is to retry the push after first updating your work by either a
2004pull or a fetch followed by a rebase; see the
2005<<setting-up-a-shared-repository,next section>> and
2006link:cvs-migration.html[git for CVS users] for more.
2007
e34caace 2008[[setting-up-a-shared-repository]]
d19fbc3c 2009Setting up a shared repository
eda69449 2010~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
2011
2012Another way to collaborate is by using a model similar to that
2013commonly used in CVS, where several developers with special rights
2014all push to and pull from a single shared repository. See
a2983cb7 2015link:cvs-migration.html[git for CVS users] for instructions on how to
d19fbc3c
BF
2016set this up.
2017
8fae2225
BF
2018However, while there is nothing wrong with git's support for shared
2019repositories, this mode of operation is not generally recommended,
2020simply because the mode of collaboration that git supports--by
2021exchanging patches and pulling from public repositories--has so many
2022advantages over the central shared repository:
2023
2024 - Git's ability to quickly import and merge patches allows a
2025 single maintainer to process incoming changes even at very
2026 high rates. And when that becomes too much, git-pull provides
2027 an easy way for that maintainer to delegate this job to other
2028 maintainers while still allowing optional review of incoming
2029 changes.
2030 - Since every developer's repository has the same complete copy
2031 of the project history, no repository is special, and it is
2032 trivial for another developer to take over maintenance of a
2033 project, either by mutual agreement, or because a maintainer
2034 becomes unresponsive or difficult to work with.
2035 - The lack of a central group of "committers" means there is
2036 less need for formal decisions about who is "in" and who is
2037 "out".
2038
e34caace 2039[[setting-up-gitweb]]
eda69449
BF
2040Allowing web browsing of a repository
2041~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 2042
a8cd1402
BF
2043The gitweb cgi script provides users an easy way to browse your
2044project's files and history without having to install git; see the file
04483524 2045gitweb/INSTALL in the git source tree for instructions on setting it up.
d19fbc3c 2046
e34caace 2047[[sharing-development-examples]]
b684f830
BF
2048Examples
2049--------
d19fbc3c 2050
9e2163ea
BF
2051[[maintaining-topic-branches]]
2052Maintaining topic branches for a Linux subsystem maintainer
2053~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2054
2055This describes how Tony Luck uses git in his role as maintainer of the
2056IA64 architecture for the Linux kernel.
2057
2058He uses two public branches:
2059
2060 - A "test" tree into which patches are initially placed so that they
2061 can get some exposure when integrated with other ongoing development.
2062 This tree is available to Andrew for pulling into -mm whenever he
2063 wants.
2064
2065 - A "release" tree into which tested patches are moved for final sanity
2066 checking, and as a vehicle to send them upstream to Linus (by sending
2067 him a "please pull" request.)
2068
2069He also uses a set of temporary branches ("topic branches"), each
2070containing a logical grouping of patches.
2071
2072To set this up, first create your work tree by cloning Linus's public
2073tree:
2074
2075-------------------------------------------------
2076$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2077$ cd work
2078-------------------------------------------------
2079
2080Linus's tree will be stored in the remote branch named origin/master,
2081and can be updated using gitlink:git-fetch[1]; you can track other
2082public trees using gitlink:git-remote[1] to set up a "remote" and
6e30fb0c
DK
2083gitlink:git-fetch[1] to keep them up-to-date; see
2084<<repositories-and-branches>>.
9e2163ea
BF
2085
2086Now create the branches in which you are going to work; these start out
2087at the current tip of origin/master branch, and should be set up (using
2088the --track option to gitlink:git-branch[1]) to merge changes in from
2089Linus by default.
2090
2091-------------------------------------------------
2092$ git branch --track test origin/master
2093$ git branch --track release origin/master
2094-------------------------------------------------
2095
2096These can be easily kept up to date using gitlink:git-pull[1]
2097
2098-------------------------------------------------
2099$ git checkout test && git pull
2100$ git checkout release && git pull
2101-------------------------------------------------
2102
2103Important note! If you have any local changes in these branches, then
2104this merge will create a commit object in the history (with no local
2105changes git will simply do a "Fast forward" merge). Many people dislike
2106the "noise" that this creates in the Linux history, so you should avoid
2107doing this capriciously in the "release" branch, as these noisy commits
2108will become part of the permanent history when you ask Linus to pull
2109from the release branch.
2110
2111A few configuration variables (see gitlink:git-config[1]) can
2112make it easy to push both branches to your public tree. (See
2113<<setting-up-a-public-repository>>.)
2114
2115-------------------------------------------------
2116$ cat >> .git/config <<EOF
2117[remote "mytree"]
2118 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2119 push = release
2120 push = test
2121EOF
2122-------------------------------------------------
2123
2124Then you can push both the test and release trees using
2125gitlink:git-push[1]:
2126
2127-------------------------------------------------
2128$ git push mytree
2129-------------------------------------------------
2130
2131or push just one of the test and release branches using:
2132
2133-------------------------------------------------
2134$ git push mytree test
2135-------------------------------------------------
2136
2137or
2138
2139-------------------------------------------------
2140$ git push mytree release
2141-------------------------------------------------
2142
2143Now to apply some patches from the community. Think of a short
2144snappy name for a branch to hold this patch (or related group of
2145patches), and create a new branch from the current tip of Linus's
2146branch:
2147
2148-------------------------------------------------
2149$ git checkout -b speed-up-spinlocks origin
2150-------------------------------------------------
2151
2152Now you apply the patch(es), run some tests, and commit the change(s). If
2153the patch is a multi-part series, then you should apply each as a separate
2154commit to this branch.
2155
2156-------------------------------------------------
2157$ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2158-------------------------------------------------
2159
2160When you are happy with the state of this change, you can pull it into the
2161"test" branch in preparation to make it public:
2162
2163-------------------------------------------------
2164$ git checkout test && git pull . speed-up-spinlocks
2165-------------------------------------------------
2166
2167It is unlikely that you would have any conflicts here ... but you might if you
2168spent a while on this step and had also pulled new versions from upstream.
2169
2170Some time later when enough time has passed and testing done, you can pull the
2171same branch into the "release" tree ready to go upstream. This is where you
2172see the value of keeping each patch (or patch series) in its own branch. It
2173means that the patches can be moved into the "release" tree in any order.
2174
2175-------------------------------------------------
2176$ git checkout release && git pull . speed-up-spinlocks
2177-------------------------------------------------
2178
2179After a while, you will have a number of branches, and despite the
2180well chosen names you picked for each of them, you may forget what
2181they are for, or what status they are in. To get a reminder of what
2182changes are in a specific branch, use:
2183
2184-------------------------------------------------
2185$ git log linux..branchname | git-shortlog
2186-------------------------------------------------
2187
2188To see whether it has already been merged into the test or release branches
2189use:
2190
2191-------------------------------------------------
2192$ git log test..branchname
2193-------------------------------------------------
2194
2195or
2196
2197-------------------------------------------------
2198$ git log release..branchname
2199-------------------------------------------------
2200
2201(If this branch has not yet been merged you will see some log entries.
2202If it has been merged, then there will be no output.)
2203
2204Once a patch completes the great cycle (moving from test to release,
2205then pulled by Linus, and finally coming back into your local
2206"origin/master" branch) the branch for this change is no longer needed.
2207You detect this when the output from:
2208
2209-------------------------------------------------
2210$ git log origin..branchname
2211-------------------------------------------------
2212
2213is empty. At this point the branch can be deleted:
2214
2215-------------------------------------------------
2216$ git branch -d branchname
2217-------------------------------------------------
2218
2219Some changes are so trivial that it is not necessary to create a separate
2220branch and then merge into each of the test and release branches. For
2221these changes, just apply directly to the "release" branch, and then
2222merge that into the "test" branch.
2223
2224To create diffstat and shortlog summaries of changes to include in a "please
2225pull" request to Linus you can use:
2226
2227-------------------------------------------------
2228$ git diff --stat origin..release
2229-------------------------------------------------
2230
2231and
2232
2233-------------------------------------------------
2234$ git log -p origin..release | git shortlog
2235-------------------------------------------------
2236
2237Here are some of the scripts that simplify all this even further.
2238
2239-------------------------------------------------
2240==== update script ====
2241# Update a branch in my GIT tree. If the branch to be updated
2242# is origin, then pull from kernel.org. Otherwise merge
2243# origin/master branch into test|release branch
2244
2245case "$1" in
2246test|release)
2247 git checkout $1 && git pull . origin
2248 ;;
2249origin)
fc74ecc1 2250 before=$(git rev-parse refs/remotes/origin/master)
9e2163ea 2251 git fetch origin
fc74ecc1 2252 after=$(git rev-parse refs/remotes/origin/master)
9e2163ea
BF
2253 if [ $before != $after ]
2254 then
2255 git log $before..$after | git shortlog
2256 fi
2257 ;;
2258*)
2259 echo "Usage: $0 origin|test|release" 1>&2
2260 exit 1
2261 ;;
2262esac
2263-------------------------------------------------
2264
2265-------------------------------------------------
2266==== merge script ====
2267# Merge a branch into either the test or release branch
2268
2269pname=$0
2270
2271usage()
2272{
2273 echo "Usage: $pname branch test|release" 1>&2
2274 exit 1
2275}
2276
fc74ecc1 2277git show-ref -q --verify -- refs/heads/"$1" || {
9e2163ea
BF
2278 echo "Can't see branch <$1>" 1>&2
2279 usage
fc74ecc1 2280}
9e2163ea
BF
2281
2282case "$2" in
2283test|release)
2284 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2285 then
2286 echo $1 already merged into $2 1>&2
2287 exit 1
2288 fi
2289 git checkout $2 && git pull . $1
2290 ;;
2291*)
2292 usage
2293 ;;
2294esac
2295-------------------------------------------------
2296
2297-------------------------------------------------
2298==== status script ====
2299# report on status of my ia64 GIT tree
2300
2301gb=$(tput setab 2)
2302rb=$(tput setab 1)
2303restore=$(tput setab 9)
2304
2305if [ `git rev-list test..release | wc -c` -gt 0 ]
2306then
2307 echo $rb Warning: commits in release that are not in test $restore
2308 git log test..release
2309fi
2310
fc74ecc1 2311for branch in `git show-ref --heads | sed 's|^.*/||'`
9e2163ea
BF
2312do
2313 if [ $branch = test -o $branch = release ]
2314 then
2315 continue
2316 fi
2317
2318 echo -n $gb ======= $branch ====== $restore " "
2319 status=
2320 for ref in test release origin/master
2321 do
2322 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2323 then
2324 status=$status${ref:0:1}
2325 fi
2326 done
2327 case $status in
2328 trl)
2329 echo $rb Need to pull into test $restore
2330 ;;
2331 rl)
2332 echo "In test"
2333 ;;
2334 l)
2335 echo "Waiting for linus"
2336 ;;
2337 "")
2338 echo $rb All done $restore
2339 ;;
2340 *)
2341 echo $rb "<$status>" $restore
2342 ;;
2343 esac
2344 git log origin/master..$branch | git shortlog
2345done
2346-------------------------------------------------
d19fbc3c 2347
d19fbc3c 2348
d19fbc3c 2349[[cleaning-up-history]]
4c63ff45
BF
2350Rewriting history and maintaining patch series
2351==============================================
2352
2353Normally commits are only added to a project, never taken away or
2354replaced. Git is designed with this assumption, and violating it will
2355cause git's merge machinery (for example) to do the wrong thing.
2356
2357However, there is a situation in which it can be useful to violate this
2358assumption.
2359
e34caace 2360[[patch-series]]
4c63ff45
BF
2361Creating the perfect patch series
2362---------------------------------
2363
2364Suppose you are a contributor to a large project, and you want to add a
2365complicated feature, and to present it to the other developers in a way
2366that makes it easy for them to read your changes, verify that they are
2367correct, and understand why you made each change.
2368
b181d57f 2369If you present all of your changes as a single patch (or commit), they
79c96c57 2370may find that it is too much to digest all at once.
4c63ff45
BF
2371
2372If you present them with the entire history of your work, complete with
2373mistakes, corrections, and dead ends, they may be overwhelmed.
2374
2375So the ideal is usually to produce a series of patches such that:
2376
2377 1. Each patch can be applied in order.
2378
2379 2. Each patch includes a single logical change, together with a
2380 message explaining the change.
2381
2382 3. No patch introduces a regression: after applying any initial
2383 part of the series, the resulting project still compiles and
2384 works, and has no bugs that it didn't have before.
2385
2386 4. The complete series produces the same end result as your own
2387 (probably much messier!) development process did.
2388
b181d57f
BF
2389We will introduce some tools that can help you do this, explain how to
2390use them, and then explain some of the problems that can arise because
2391you are rewriting history.
4c63ff45 2392
e34caace 2393[[using-git-rebase]]
4c63ff45
BF
2394Keeping a patch series up to date using git-rebase
2395--------------------------------------------------
2396
79c96c57
MC
2397Suppose that you create a branch "mywork" on a remote-tracking branch
2398"origin", and create some commits on top of it:
4c63ff45
BF
2399
2400-------------------------------------------------
2401$ git checkout -b mywork origin
2402$ vi file.txt
2403$ git commit
2404$ vi otherfile.txt
2405$ git commit
2406...
2407-------------------------------------------------
2408
2409You have performed no merges into mywork, so it is just a simple linear
2410sequence of patches on top of "origin":
2411
1dc71a91 2412................................................
4c63ff45
BF
2413 o--o--o <-- origin
2414 \
2415 o--o--o <-- mywork
1dc71a91 2416................................................
4c63ff45
BF
2417
2418Some more interesting work has been done in the upstream project, and
2419"origin" has advanced:
2420
1dc71a91 2421................................................
4c63ff45
BF
2422 o--o--O--o--o--o <-- origin
2423 \
2424 a--b--c <-- mywork
1dc71a91 2425................................................
4c63ff45
BF
2426
2427At this point, you could use "pull" to merge your changes back in;
2428the result would create a new merge commit, like this:
2429
1dc71a91 2430................................................
4c63ff45
BF
2431 o--o--O--o--o--o <-- origin
2432 \ \
2433 a--b--c--m <-- mywork
1dc71a91 2434................................................
a6080a0a 2435
4c63ff45
BF
2436However, if you prefer to keep the history in mywork a simple series of
2437commits without any merges, you may instead choose to use
2438gitlink:git-rebase[1]:
2439
2440-------------------------------------------------
2441$ git checkout mywork
2442$ git rebase origin
2443-------------------------------------------------
2444
b181d57f
BF
2445This will remove each of your commits from mywork, temporarily saving
2446them as patches (in a directory named ".dotest"), update mywork to
2447point at the latest version of origin, then apply each of the saved
2448patches to the new mywork. The result will look like:
4c63ff45
BF
2449
2450
1dc71a91 2451................................................
4c63ff45
BF
2452 o--o--O--o--o--o <-- origin
2453 \
2454 a'--b'--c' <-- mywork
1dc71a91 2455................................................
4c63ff45 2456
b181d57f
BF
2457In the process, it may discover conflicts. In that case it will stop
2458and allow you to fix the conflicts; after fixing conflicts, use "git
2459add" to update the index with those contents, and then, instead of
2460running git-commit, just run
4c63ff45
BF
2461
2462-------------------------------------------------
2463$ git rebase --continue
2464-------------------------------------------------
2465
2466and git will continue applying the rest of the patches.
2467
2468At any point you may use the --abort option to abort this process and
2469return mywork to the state it had before you started the rebase:
2470
2471-------------------------------------------------
2472$ git rebase --abort
2473-------------------------------------------------
2474
e34caace 2475[[modifying-one-commit]]
365aa199
BF
2476Modifying a single commit
2477-------------------------
2478
2479We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the
2480most recent commit using
2481
2482-------------------------------------------------
2483$ git commit --amend
2484-------------------------------------------------
2485
2486which will replace the old commit by a new commit incorporating your
2487changes, giving you a chance to edit the old commit message first.
2488
2489You can also use a combination of this and gitlink:git-rebase[1] to edit
2490commits further back in your history. First, tag the problematic commit with
2491
2492-------------------------------------------------
2493$ git tag bad mywork~5
2494-------------------------------------------------
2495
2496(Either gitk or git-log may be useful for finding the commit.)
2497
25d9f3fa
BF
2498Then check out that commit, edit it, and rebase the rest of the series
2499on top of it (note that we could check out the commit on a temporary
2500branch, but instead we're using a <<detached-head,detached head>>):
365aa199
BF
2501
2502-------------------------------------------------
25d9f3fa 2503$ git checkout bad
365aa199
BF
2504$ # make changes here and update the index
2505$ git commit --amend
25d9f3fa 2506$ git rebase --onto HEAD bad mywork
365aa199
BF
2507-------------------------------------------------
2508
25d9f3fa
BF
2509When you're done, you'll be left with mywork checked out, with the top
2510patches on mywork reapplied on top of your modified commit. You can
365aa199
BF
2511then clean up with
2512
2513-------------------------------------------------
365aa199
BF
2514$ git tag -d bad
2515-------------------------------------------------
2516
2517Note that the immutable nature of git history means that you haven't really
2518"modified" existing commits; instead, you have replaced the old commits with
2519new commits having new object names.
2520
e34caace 2521[[reordering-patch-series]]
4c63ff45
BF
2522Reordering or selecting from a patch series
2523-------------------------------------------
2524
b181d57f
BF
2525Given one existing commit, the gitlink:git-cherry-pick[1] command
2526allows you to apply the change introduced by that commit and create a
2527new commit that records it. So, for example, if "mywork" points to a
2528series of patches on top of "origin", you might do something like:
2529
2530-------------------------------------------------
2531$ git checkout -b mywork-new origin
2532$ gitk origin..mywork &
2533-------------------------------------------------
2534
2535And browse through the list of patches in the mywork branch using gitk,
2536applying them (possibly in a different order) to mywork-new using
407c0c87 2537cherry-pick, and possibly modifying them as you go using commit --amend.
6e30fb0c
DK
2538The gitlink:git-gui[1] command may also help as it allows you to
2539individually select diff hunks for inclusion in the index (by
2540right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
b181d57f
BF
2541
2542Another technique is to use git-format-patch to create a series of
2543patches, then reset the state to before the patches:
4c63ff45 2544
b181d57f
BF
2545-------------------------------------------------
2546$ git format-patch origin
2547$ git reset --hard origin
2548-------------------------------------------------
4c63ff45 2549
b181d57f
BF
2550Then modify, reorder, or eliminate patches as preferred before applying
2551them again with gitlink:git-am[1].
4c63ff45 2552
e34caace 2553[[patch-series-tools]]
4c63ff45
BF
2554Other tools
2555-----------
2556
02783075 2557There are numerous other tools, such as StGIT, which exist for the
79c96c57 2558purpose of maintaining a patch series. These are outside of the scope of
b181d57f 2559this manual.
4c63ff45 2560
e34caace 2561[[problems-with-rewriting-history]]
4c63ff45
BF
2562Problems with rewriting history
2563-------------------------------
2564
b181d57f
BF
2565The primary problem with rewriting the history of a branch has to do
2566with merging. Suppose somebody fetches your branch and merges it into
2567their branch, with a result something like this:
2568
1dc71a91 2569................................................
b181d57f
BF
2570 o--o--O--o--o--o <-- origin
2571 \ \
2572 t--t--t--m <-- their branch:
1dc71a91 2573................................................
b181d57f
BF
2574
2575Then suppose you modify the last three commits:
2576
1dc71a91 2577................................................
b181d57f
BF
2578 o--o--o <-- new head of origin
2579 /
2580 o--o--O--o--o--o <-- old head of origin
1dc71a91 2581................................................
b181d57f
BF
2582
2583If we examined all this history together in one repository, it will
2584look like:
2585
1dc71a91 2586................................................
b181d57f
BF
2587 o--o--o <-- new head of origin
2588 /
2589 o--o--O--o--o--o <-- old head of origin
2590 \ \
2591 t--t--t--m <-- their branch:
1dc71a91 2592................................................
b181d57f
BF
2593
2594Git has no way of knowing that the new head is an updated version of
2595the old head; it treats this situation exactly the same as it would if
2596two developers had independently done the work on the old and new heads
2597in parallel. At this point, if someone attempts to merge the new head
2598in to their branch, git will attempt to merge together the two (old and
2599new) lines of development, instead of trying to replace the old by the
2600new. The results are likely to be unexpected.
2601
2602You may still choose to publish branches whose history is rewritten,
2603and it may be useful for others to be able to fetch those branches in
2604order to examine or test them, but they should not attempt to pull such
2605branches into their own work.
2606
2607For true distributed development that supports proper merging,
2608published branches should never be rewritten.
2609
3fb00282
SP
2610[[bisect-merges]]
2611Why bisecting merge commits can be harder than bisecting linear history
2612-----------------------------------------------------------------------
2613
2614The gitlink:git-bisect[1] command correctly handles history that
2615includes merge commits. However, when the commit that it finds is a
2616merge commit, the user may need to work harder than usual to figure out
2617why that commit introduced a problem.
2618
2619Imagine this history:
2620
2621................................................
2622 ---Z---o---X---...---o---A---C---D
2623 \ /
2624 o---o---Y---...---o---B
2625................................................
2626
2627Suppose that on the upper line of development, the meaning of one
2628of the functions that exists at Z is changed at commit X. The
2629commits from Z leading to A change both the function's
2630implementation and all calling sites that exist at Z, as well
2631as new calling sites they add, to be consistent. There is no
2632bug at A.
2633
2634Suppose that in the meantime on the lower line of development somebody
2635adds a new calling site for that function at commit Y. The
2636commits from Z leading to B all assume the old semantics of that
2637function and the callers and the callee are consistent with each
2638other. There is no bug at B, either.
2639
2640Suppose further that the two development lines merge cleanly at C,
2641so no conflict resolution is required.
2642
2643Nevertheless, the code at C is broken, because the callers added
2644on the lower line of development have not been converted to the new
2645semantics introduced on the upper line of development. So if all
2646you know is that D is bad, that Z is good, and that
2647gitlink:git-bisect[1] identifies C as the culprit, how will you
2648figure out that the problem is due to this change in semantics?
2649
2650When the result of a git-bisect is a non-merge commit, you should
2651normally be able to discover the problem by examining just that commit.
2652Developers can make this easy by breaking their changes into small
2653self-contained commits. That won't help in the case above, however,
2654because the problem isn't obvious from examination of any single
2655commit; instead, a global view of the development is required. To
2656make matters worse, the change in semantics in the problematic
2657function may be just one small part of the changes in the upper
2658line of development.
2659
2660On the other hand, if instead of merging at C you had rebased the
2661history between Z to B on top of A, you would have gotten this
2662linear history:
2663
2664................................................................
2665 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2666................................................................
2667
2668Bisecting between Z and D* would hit a single culprit commit Y*,
2669and understanding why Y* was broken would probably be easier.
2670
2671Partly for this reason, many experienced git users, even when
2672working on an otherwise merge-heavy project, keep the history
2673linear by rebasing against the latest upstream version before
2674publishing.
2675
e34caace 2676[[advanced-branch-management]]
b181d57f
BF
2677Advanced branch management
2678==========================
4c63ff45 2679
e34caace 2680[[fetching-individual-branches]]
b181d57f
BF
2681Fetching individual branches
2682----------------------------
2683
2684Instead of using gitlink:git-remote[1], you can also choose just
2685to update one branch at a time, and to store it locally under an
2686arbitrary name:
2687
2688-------------------------------------------------
2689$ git fetch origin todo:my-todo-work
2690-------------------------------------------------
2691
2692The first argument, "origin", just tells git to fetch from the
2693repository you originally cloned from. The second argument tells git
2694to fetch the branch named "todo" from the remote repository, and to
2695store it locally under the name refs/heads/my-todo-work.
2696
2697You can also fetch branches from other repositories; so
2698
2699-------------------------------------------------
2700$ git fetch git://example.com/proj.git master:example-master
2701-------------------------------------------------
2702
2703will create a new branch named "example-master" and store in it the
2704branch named "master" from the repository at the given URL. If you
2705already have a branch named example-master, it will attempt to
59723040
BF
2706<<fast-forwards,fast-forward>> to the commit given by example.com's
2707master branch. In more detail:
b181d57f 2708
59723040
BF
2709[[fetch-fast-forwards]]
2710git fetch and fast-forwards
2711---------------------------
b181d57f
BF
2712
2713In the previous example, when updating an existing branch, "git
2714fetch" checks to make sure that the most recent commit on the remote
2715branch is a descendant of the most recent commit on your copy of the
2716branch before updating your copy of the branch to point at the new
59723040 2717commit. Git calls this process a <<fast-forwards,fast forward>>.
b181d57f
BF
2718
2719A fast forward looks something like this:
2720
1dc71a91 2721................................................
b181d57f
BF
2722 o--o--o--o <-- old head of the branch
2723 \
2724 o--o--o <-- new head of the branch
1dc71a91 2725................................................
b181d57f
BF
2726
2727
2728In some cases it is possible that the new head will *not* actually be
2729a descendant of the old head. For example, the developer may have
2730realized she made a serious mistake, and decided to backtrack,
2731resulting in a situation like:
2732
1dc71a91 2733................................................
b181d57f
BF
2734 o--o--o--o--a--b <-- old head of the branch
2735 \
2736 o--o--o <-- new head of the branch
1dc71a91 2737................................................
b181d57f
BF
2738
2739In this case, "git fetch" will fail, and print out a warning.
2740
2741In that case, you can still force git to update to the new head, as
2742described in the following section. However, note that in the
2743situation above this may mean losing the commits labeled "a" and "b",
2744unless you've already created a reference of your own pointing to
2745them.
2746
e34caace 2747[[forcing-fetch]]
b181d57f
BF
2748Forcing git fetch to do non-fast-forward updates
2749------------------------------------------------
2750
2751If git fetch fails because the new head of a branch is not a
2752descendant of the old head, you may force the update with:
2753
2754-------------------------------------------------
2755$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2756-------------------------------------------------
2757
c64415e2
BF
2758Note the addition of the "+" sign. Alternatively, you can use the "-f"
2759flag to force updates of all the fetched branches, as in:
2760
2761-------------------------------------------------
2762$ git fetch -f origin
2763-------------------------------------------------
2764
2765Be aware that commits that the old version of example/master pointed at
2766may be lost, as we saw in the previous section.
b181d57f 2767
e34caace 2768[[remote-branch-configuration]]
b181d57f
BF
2769Configuring remote branches
2770---------------------------
2771
2772We saw above that "origin" is just a shortcut to refer to the
79c96c57 2773repository that you originally cloned from. This information is
b181d57f 2774stored in git configuration variables, which you can see using
9d13bda3 2775gitlink:git-config[1]:
b181d57f
BF
2776
2777-------------------------------------------------
9d13bda3 2778$ git config -l
b181d57f
BF
2779core.repositoryformatversion=0
2780core.filemode=true
2781core.logallrefupdates=true
2782remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2783remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2784branch.master.remote=origin
2785branch.master.merge=refs/heads/master
2786-------------------------------------------------
2787
2788If there are other repositories that you also use frequently, you can
2789create similar configuration options to save typing; for example,
2790after
2791
2792-------------------------------------------------
9d13bda3 2793$ git config remote.example.url git://example.com/proj.git
b181d57f
BF
2794-------------------------------------------------
2795
2796then the following two commands will do the same thing:
2797
2798-------------------------------------------------
2799$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2800$ git fetch example master:refs/remotes/example/master
2801-------------------------------------------------
2802
2803Even better, if you add one more option:
2804
2805-------------------------------------------------
9d13bda3 2806$ git config remote.example.fetch master:refs/remotes/example/master
b181d57f
BF
2807-------------------------------------------------
2808
2809then the following commands will all do the same thing:
2810
2811-------------------------------------------------
52c80037
BF
2812$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2813$ git fetch example master:refs/remotes/example/master
b181d57f
BF
2814$ git fetch example
2815-------------------------------------------------
2816
2817You can also add a "+" to force the update each time:
2818
2819-------------------------------------------------
9d13bda3 2820$ git config remote.example.fetch +master:ref/remotes/example/master
b181d57f
BF
2821-------------------------------------------------
2822
2823Don't do this unless you're sure you won't mind "git fetch" possibly
2824throwing away commits on mybranch.
2825
2826Also note that all of the above configuration can be performed by
2827directly editing the file .git/config instead of using
9d13bda3 2828gitlink:git-config[1].
b181d57f 2829
9d13bda3 2830See gitlink:git-config[1] for more details on the configuration
b181d57f 2831options mentioned above.
d19fbc3c 2832
d19fbc3c 2833
036f8199
BF
2834[[git-concepts]]
2835Git concepts
2836============
d19fbc3c 2837
036f8199
BF
2838Git is built on a small number of simple but powerful ideas. While it
2839is possible to get things done without understanding them, you will find
2840git much more intuitive if you do.
2841
2842We start with the most important, the <<def_object_database,object
2843database>> and the <<def_index,index>>.
b181d57f 2844
e34caace 2845[[the-object-database]]
b181d57f
BF
2846The Object Database
2847-------------------
2848
1bbf1c79
BF
2849
2850We already saw in <<understanding-commits>> that all commits are stored
2851under a 40-digit "object name". In fact, all the information needed to
2852represent the history of a project is stored in objects with such names.
2853In each case the name is calculated by taking the SHA1 hash of the
2854contents of the object. The SHA1 hash is a cryptographic hash function.
2855What that means to us is that it is impossible to find two different
2856objects with the same name. This has a number of advantages; among
2857others:
2858
2859- Git can quickly determine whether two objects are identical or not,
2860 just by comparing names.
2861- Since object names are computed the same way in ever repository, the
2862 same content stored in two repositories will always be stored under
2863 the same name.
2864- Git can detect errors when it reads an object, by checking that the
2865 object's name is still the SHA1 hash of its contents.
2866
2867(See <<object-details>> for the details of the object formatting and
2868SHA1 calculation.)
2869
2870There are four different types of objects: "blob", "tree", "commit", and
2871"tag".
2872
2873- A <<def_blob_object,"blob" object>> is used to store file data.
2874- A <<def_tree_object,"tree" object>> is an object that ties one or more
2875 "blob" objects into a directory structure. In addition, a tree object
2876 can refer to other tree objects, thus creating a directory hierarchy.
2877- A <<def_commit_object,"commit" object>> ties such directory hierarchies
2878 together into a <<def_DAG,directed acyclic graph>> of revisions - each
2879 commit contains the object name of exactly one tree designating the
2880 directory hierarchy at the time of the commit. In addition, a commit
2881 refers to "parent" commit objects that describe the history of how we
2882 arrived at that directory hierarchy.
2883- A <<def_tag_object,"tag" object>> symbolically identifies and can be
2884 used to sign other objects. It contains the object name and type of
2885 another object, a symbolic name (of course!) and, optionally, a
2886 signature.
b181d57f 2887
b181d57f
BF
2888The object types in some more detail:
2889
513d419c
BF
2890[[commit-object]]
2891Commit Object
2892~~~~~~~~~~~~~
b181d57f 2893
1bbf1c79
BF
2894The "commit" object links a physical state of a tree with a description
2895of how we got there and why. Use the --pretty=raw option to
2896gitlink:git-show[1] or gitlink:git-log[1] to examine your favorite
2897commit:
2898
2899------------------------------------------------
2900$ git show -s --pretty=raw 2be7fcb476
2901commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2902tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2903parent 257a84d9d02e90447b149af58b271c19405edb6a
2904author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2905committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2906
2907 Fix misspelling of 'suppress' in docs
2908
2909 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2910------------------------------------------------
2911
2912As you can see, a commit is defined by:
2913
2914- a tree: The SHA1 name of a tree object (as defined below), representing
2915 the contents of a directory at a certain point in time.
2916- parent(s): The SHA1 name of some number of commits which represent the
2917 immediately prevoius step(s) in the history of the project. The
2918 example above has one parent; merge commits may have more than
2919 one. A commit with no parents is called a "root" commit, and
2920 represents the initial revision of a project. Each project must have
2921 at least one root. A project can also have multiple roots, though
2922 that isn't common (or necessarily a good idea).
2923- an author: The name of the person responsible for this change, together
2924 with its date.
2925- a committer: The name of the person who actually created the commit,
2926 with the date it was done. This may be different from the author, for
2927 example, if the author was someone who wrote a patch and emailed it
2928 to the person who used it to create the commit.
2929- a comment describing this commit.
2930
2931Note that a commit does not itself contain any information about what
2932actually changed; all changes are calculated by comparing the contents
2933of the tree referred to by this commit with the trees associated with
2934its parents. In particular, git does not attempt to record file renames
2935explicitly, though it can identify cases where the existence of the same
2936file data at changing paths suggests a rename. (See, for example, the
2937-M option to gitlink:git-diff[1]).
2938
2939A commit is usually created by gitlink:git-commit[1], which creates a
2940commit whose parent is normally the current HEAD, and whose tree is
2941taken from the content currently stored in the index.
b181d57f 2942
e34caace 2943[[tree-object]]
b181d57f 2944Tree Object
971aa71f 2945~~~~~~~~~~~
b181d57f 2946
1bbf1c79
BF
2947The ever-versatile gitlink:git-show[1] command can also be used to
2948examine tree objects, but gitlink:git-ls-tree[1] will give you more
2949details:
2950
2951------------------------------------------------
2952$ git ls-tree fb3a8bdd0ce
2953100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
2954100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
2955100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
2956040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
2957100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
2958100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
2959100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
2960100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
2961...
2962------------------------------------------------
2963
2964As you can see, a tree object contains a list of entries, each with a
2965mode, object type, SHA1 name, and name, sorted by name. It represents
2966the contents of a single directory tree.
2967
2968The object type may be a blob, representing the contents of a file, or
2969another tree, representing the contents of a subdirectory. Since trees
2970and blobs, like all other objects, are named by the SHA1 hash of their
2971contents, two trees have the same SHA1 name if and only if their
2972contents (including, recursively, the contents of all subdirectories)
2973are identical. This allows git to quickly determine the differences
2974between two related tree objects, since it can ignore any entries with
2975identical object names.
2976
2977(Note: in the presence of submodules, trees may also have commits as
6dd14366 2978entries. See <<submodules>> for documentation.)
1bbf1c79
BF
2979
2980Note that the files all have mode 644 or 755: git actually only pays
2981attention to the executable bit.
b181d57f 2982
513d419c
BF
2983[[blob-object]]
2984Blob Object
2985~~~~~~~~~~~
b181d57f 2986
1bbf1c79
BF
2987You can use gitlink:git-show[1] to examine the contents of a blob; take,
2988for example, the blob in the entry for "COPYING" from the tree above:
b181d57f 2989
1bbf1c79
BF
2990------------------------------------------------
2991$ git show 6ff87c4664
2992
2993 Note that the only valid version of the GPL as far as this project
2994 is concerned is _this_ particular version of the license (ie v2, not
2995 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
2996...
2997------------------------------------------------
b181d57f 2998
1bbf1c79
BF
2999A "blob" object is nothing but a binary blob of data. It doesn't refer
3000to anything else or have attributes of any kind.
3001
3002Since the blob is entirely defined by its data, if two files in a
3003directory tree (or in multiple different versions of the repository)
3004have the same contents, they will share the same blob object. The object
3005is totally independent of its location in the directory tree, and
3006renaming a file does not change the object that file is associated with.
3007
3008Note that any tree or blob object can be examined using
3009gitlink:git-show[1] with the <revision>:<path> syntax. This can
3010sometimes be useful for browsing the contents of a tree that is not
3011currently checked out.
b181d57f 3012
e34caace 3013[[trust]]
b181d57f 3014Trust
971aa71f 3015~~~~~
b181d57f 3016
1bbf1c79
BF
3017If you receive the SHA1 name of a blob from one source, and its contents
3018from another (possibly untrusted) source, you can still trust that those
3019contents are correct as long as the SHA1 name agrees. This is because
3020the SHA1 is designed so that it is infeasible to find different contents
3021that produce the same hash.
b181d57f 3022
1bbf1c79
BF
3023Similarly, you need only trust the SHA1 name of a top-level tree object
3024to trust the contents of the entire directory that it refers to, and if
3025you receive the SHA1 name of a commit from a trusted source, then you
3026can easily verify the entire history of commits reachable through
3027parents of that commit, and all of those contents of the trees referred
3028to by those commits.
b181d57f
BF
3029
3030So to introduce some real trust in the system, the only thing you need
3031to do is to digitally sign just 'one' special note, which includes the
3032name of a top-level commit. Your digital signature shows others
3033that you trust that commit, and the immutability of the history of
3034commits tells others that they can trust the whole history.
3035
3036In other words, you can easily validate a whole archive by just
3037sending out a single email that tells the people the name (SHA1 hash)
3038of the top commit, and digitally sign that email using something
3039like GPG/PGP.
3040
3041To assist in this, git also provides the tag object...
3042
e34caace 3043[[tag-object]]
b181d57f 3044Tag Object
971aa71f 3045~~~~~~~~~~
b181d57f 3046
1bbf1c79
BF
3047A tag object contains an object, object type, tag name, the name of the
3048person ("tagger") who created the tag, and a message, which may contain
3049a signature, as can be seen using the gitlink:git-cat-file[1]:
b181d57f 3050
1bbf1c79
BF
3051------------------------------------------------
3052$ git cat-file tag v1.5.0
3053object 437b1b20df4b356c9342dac8d38849f24ef44f27
3054type commit
3055tag v1.5.0
3056tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
3057
3058GIT 1.5.0
3059-----BEGIN PGP SIGNATURE-----
3060Version: GnuPG v1.4.6 (GNU/Linux)
3061
3062iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
3063nLE/L9aUXdWeTFPron96DLA=
3064=2E+0
3065-----END PGP SIGNATURE-----
3066------------------------------------------------
b181d57f 3067
1bbf1c79
BF
3068See the gitlink:git-tag[1] command to learn how to create and verify tag
3069objects. (Note that gitlink:git-tag[1] can also be used to create
3070"lightweight tags", which are not tag objects at all, but just simple
fc74ecc1 3071references whose names begin with "refs/tags/").
b181d57f 3072
09eff7b0
BF
3073[[pack-files]]
3074How git stores objects efficiently: pack files
3075~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3076
9644ffdd
BF
3077Newly created objects are initially created in a file named after the
3078object's SHA1 hash (stored in .git/objects).
09eff7b0
BF
3079
3080Unfortunately this system becomes inefficient once a project has a
3081lot of objects. Try this on an old project:
3082
3083------------------------------------------------
3084$ git count-objects
30856930 objects, 47620 kilobytes
3086------------------------------------------------
3087
3088The first number is the number of objects which are kept in
3089individual files. The second is the amount of space taken up by
3090those "loose" objects.
3091
3092You can save space and make git faster by moving these loose objects in
3093to a "pack file", which stores a group of objects in an efficient
3094compressed format; the details of how pack files are formatted can be
3095found in link:technical/pack-format.txt[technical/pack-format.txt].
3096
3097To put the loose objects into a pack, just run git repack:
3098
3099------------------------------------------------
3100$ git repack
3101Generating pack...
3102Done counting 6020 objects.
3103Deltifying 6020 objects.
3104 100% (6020/6020) done
3105Writing 6020 objects.
3106 100% (6020/6020) done
3107Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
3108Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
3109------------------------------------------------
3110
3111You can then run
3112
3113------------------------------------------------
3114$ git prune
3115------------------------------------------------
3116
3117to remove any of the "loose" objects that are now contained in the
3118pack. This will also remove any unreferenced objects (which may be
3119created when, for example, you use "git reset" to remove a commit).
3120You can verify that the loose objects are gone by looking at the
3121.git/objects directory or by running
3122
3123------------------------------------------------
3124$ git count-objects
31250 objects, 0 kilobytes
3126------------------------------------------------
3127
3128Although the object files are gone, any commands that refer to those
3129objects will work exactly as they did before.
3130
3131The gitlink:git-gc[1] command performs packing, pruning, and more for
3132you, so is normally the only high-level command you need.
3133
3134[[dangling-objects]]
3135Dangling objects
3136~~~~~~~~~~~~~~~~
3137
3138The gitlink:git-fsck[1] command will sometimes complain about dangling
3139objects. They are not a problem.
3140
3141The most common cause of dangling objects is that you've rebased a
3142branch, or you have pulled from somebody else who rebased a branch--see
3143<<cleaning-up-history>>. In that case, the old head of the original
3144branch still exists, as does everything it pointed to. The branch
3145pointer itself just doesn't, since you replaced it with another one.
3146
3147There are also other situations that cause dangling objects. For
3148example, a "dangling blob" may arise because you did a "git add" of a
3149file, but then, before you actually committed it and made it part of the
3150bigger picture, you changed something else in that file and committed
3151that *updated* thing - the old state that you added originally ends up
3152not being pointed to by any commit or tree, so it's now a dangling blob
3153object.
3154
3155Similarly, when the "recursive" merge strategy runs, and finds that
3156there are criss-cross merges and thus more than one merge base (which is
3157fairly unusual, but it does happen), it will generate one temporary
3158midway tree (or possibly even more, if you had lots of criss-crossing
3159merges and more than two merge bases) as a temporary internal merge
3160base, and again, those are real objects, but the end result will not end
3161up pointing to them, so they end up "dangling" in your repository.
3162
3163Generally, dangling objects aren't anything to worry about. They can
3164even be very useful: if you screw something up, the dangling objects can
3165be how you recover your old tree (say, you did a rebase, and realized
3166that you really didn't want to - you can look at what dangling objects
3167you have, and decide to reset your head to some old dangling state).
3168
3169For commits, you can just use:
3170
3171------------------------------------------------
3172$ gitk <dangling-commit-sha-goes-here> --not --all
3173------------------------------------------------
3174
3175This asks for all the history reachable from the given commit but not
3176from any branch, tag, or other reference. If you decide it's something
3177you want, you can always create a new reference to it, e.g.,
3178
3179------------------------------------------------
3180$ git branch recovered-branch <dangling-commit-sha-goes-here>
3181------------------------------------------------
3182
3183For blobs and trees, you can't do the same, but you can still examine
3184them. You can just do
3185
3186------------------------------------------------
3187$ git show <dangling-blob/tree-sha-goes-here>
3188------------------------------------------------
3189
3190to show what the contents of the blob were (or, for a tree, basically
3191what the "ls" for that directory was), and that may give you some idea
3192of what the operation was that left that dangling object.
3193
3194Usually, dangling blobs and trees aren't very interesting. They're
3195almost always the result of either being a half-way mergebase (the blob
3196will often even have the conflict markers from a merge in it, if you
3197have had conflicting merges that you fixed up by hand), or simply
3198because you interrupted a "git fetch" with ^C or something like that,
3199leaving _some_ of the new objects in the object database, but just
3200dangling and useless.
3201
3202Anyway, once you are sure that you're not interested in any dangling
3203state, you can just prune all unreachable objects:
3204
3205------------------------------------------------
3206$ git prune
3207------------------------------------------------
3208
3209and they'll be gone. But you should only run "git prune" on a quiescent
3210repository - it's kind of like doing a filesystem fsck recovery: you
3211don't want to do that while the filesystem is mounted.
3212
3213(The same is true of "git-fsck" itself, btw - but since
3214git-fsck never actually *changes* the repository, it just reports
3215on what it found, git-fsck itself is never "dangerous" to run.
3216Running it while somebody is actually changing the repository can cause
3217confusing and scary messages, but it won't actually do anything bad. In
3218contrast, running "git prune" while somebody is actively changing the
3219repository is a *BAD* idea).
b181d57f 3220
e34caace 3221[[the-index]]
1c097891
BF
3222The index
3223-----------
3224
3225The index is a binary file (generally kept in .git/index) containing a
3226sorted list of path names, each with permissions and the SHA1 of a blob
3227object; gitlink:git-ls-files[1] can show you the contents of the index:
b181d57f 3228
1c097891
BF
3229-------------------------------------------------
3230$ git ls-files --stage
3231100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore
3232100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap
3233100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING
3234100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore
3235100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile
3236...
3237100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h
3238100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c
3239100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h
3240-------------------------------------------------
3241
3242Note that in older documentation you may see the index called the
3243"current directory cache" or just the "cache". It has three important
3244properties:
3245
32461. The index contains all the information necessary to generate a single
3247(uniquely determined) tree object.
3248+
3249For example, running gitlink:git-commit[1] generates this tree object
3250from the index, stores it in the object database, and uses it as the
3251tree object associated with the new commit.
3252
32532. The index enables fast comparisons between the tree object it defines
3254and the working tree.
3255+
3256It does this by storing some additional data for each entry (such as
3257the last modified time). This data is not displayed above, and is not
3258stored in the created tree object, but it can be used to determine
3259quickly which files in the working directory differ from what was
3260stored in the index, and thus save git from having to read all of the
3261data from such files to look for changes.
3262
32633. It can efficiently represent information about merge conflicts
3264between different tree objects, allowing each pathname to be
b181d57f 3265associated with sufficient information about the trees involved that
1c097891
BF
3266you can create a three-way merge between them.
3267+
3268We saw in <<conflict-resolution>> that during a merge the index can
3269store multiple versions of a single file (called "stages"). The third
3270column in the gitlink:git-ls-files[1] output above is the stage
3271number, and will take on values other than 0 for files with merge
3272conflicts.
3273
3274The index is thus a sort of temporary staging area, which is filled with
3275a tree which you are in the process of working on.
3276
3277If you blow the index away entirely, you generally haven't lost any
3278information as long as you have the name of the tree that it described.
b181d57f 3279
38a457ba
MV
3280[[submodules]]
3281Submodules
3282==========
3283
6dd14366
MS
3284Large projects are often composed of smaller, self-contained modules. For
3285example, an embedded Linux distribution's source tree would include every
3286piece of software in the distribution with some local modifications; a movie
3287player might need to build against a specific, known-working version of a
3288decompression library; several independent programs might all share the same
3289build scripts.
3290
3291With centralized revision control systems this is often accomplished by
3292including every module in one single repository. Developers can check out
3293all modules or only the modules they need to work with. They can even modify
3294files across several modules in a single commit while moving things around
3295or updating APIs and translations.
3296
3297Git does not allow partial checkouts, so duplicating this approach in Git
3298would force developers to keep a local copy of modules they are not
3299interested in touching. Commits in an enormous checkout would be slower
3300than you'd expect as Git would have to scan every directory for changes.
3301If modules have a lot of local history, clones would take forever.
3302
3303On the plus side, distributed revision control systems can much better
3304integrate with external sources. In a centralized model, a single arbitrary
3305snapshot of the external project is exported from its own revision control
3306and then imported into the local revision control on a vendor branch. All
3307the history is hidden. With distributed revision control you can clone the
3308entire external history and much more easily follow development and re-merge
3309local changes.
3310
3311Git's submodule support allows a repository to contain, as a subdirectory, a
3312checkout of an external project. Submodules maintain their own identity;
3313the submodule support just stores the submodule repository location and
3314commit ID, so other developers who clone the containing project
3315("superproject") can easily clone all the submodules at the same revision.
3316Partial checkouts of the superproject are possible: you can tell Git to
3317clone none, some or all of the submodules.
3318
3319The gitlink:git-submodule[1] command is available since Git 1.5.3. Users
3320with Git 1.5.2 can look up the submodule commits in the repository and
3321manually check them out; earlier versions won't recognize the submodules at
3322all.
38a457ba
MV
3323
3324To see how submodule support works, create (for example) four example
3325repositories that can be used later as a submodule:
3326
3327-------------------------------------------------
3328$ mkdir ~/git
3329$ cd ~/git
3330$ for i in a b c d
3331do
3332 mkdir $i
3333 cd $i
3334 git init
3335 echo "module $i" > $i.txt
3336 git add $i.txt
3337 git commit -m "Initial commit, submodule $i"
3338 cd ..
3339done
3340-------------------------------------------------
3341
3342Now create the superproject and add all the submodules:
3343
3344-------------------------------------------------
3345$ mkdir super
3346$ cd super
3347$ git init
3348$ for i in a b c d
3349do
3350 git submodule add ~/git/$i
3351done
3352-------------------------------------------------
3353
3354NOTE: Do not use local URLs here if you plan to publish your superproject!
3355
3356See what files `git submodule` created:
3357
3358-------------------------------------------------
3359$ ls -a
3360. .. .git .gitmodules a b c d
3361-------------------------------------------------
3362
3363The `git submodule add` command does a couple of things:
3364
3365- It clones the submodule under the current directory and by default checks out
3366 the master branch.
6dd14366
MS
3367- It adds the submodule's clone path to the gitlink:gitmodules[5] file and
3368 adds this file to the index, ready to be committed.
38a457ba
MV
3369- It adds the submodule's current commit ID to the index, ready to be
3370 committed.
3371
3372Commit the superproject:
3373
3374-------------------------------------------------
3375$ git commit -m "Add submodules a, b, c and d."
3376-------------------------------------------------
3377
3378Now clone the superproject:
3379
3380-------------------------------------------------
3381$ cd ..
3382$ git clone super cloned
3383$ cd cloned
3384-------------------------------------------------
3385
3386The submodule directories are there, but they're empty:
3387
3388-------------------------------------------------
3389$ ls -a a
3390. ..
3391$ git submodule status
3392-d266b9873ad50488163457f025db7cdd9683d88b a
3393-e81d457da15309b4fef4249aba9b50187999670d b
3394-c1536a972b9affea0f16e0680ba87332dc059146 c
3395-d96249ff5d57de5de093e6baff9e0aafa5276a74 d
3396-------------------------------------------------
3397
3398NOTE: The commit object names shown above would be different for you, but they
3399should match the HEAD commit object names of your repositories. You can check
3400it by running `git ls-remote ../a`.
3401
3402Pulling down the submodules is a two-step process. First run `git submodule
3403init` to add the submodule repository URLs to `.git/config`:
3404
3405-------------------------------------------------
3406$ git submodule init
3407-------------------------------------------------
3408
3409Now use `git submodule update` to clone the repositories and check out the
3410commits specified in the superproject:
3411
3412-------------------------------------------------
3413$ git submodule update
3414$ cd a
3415$ ls -a
3416. .. .git a.txt
3417-------------------------------------------------
3418
3419One major difference between `git submodule update` and `git submodule add` is
3420that `git submodule update` checks out a specific commit, rather than the tip
3421of a branch. It's like checking out a tag: the head is detached, so you're not
3422working on a branch.
3423
3424-------------------------------------------------
3425$ git branch
3426* (no branch)
3427 master
3428-------------------------------------------------
3429
3430If you want to make a change within a submodule and you have a detached head,
3431then you should create or checkout a branch, make your changes, publish the
3432change within the submodule, and then update the superproject to reference the
3433new commit:
3434
3435-------------------------------------------------
3436$ git checkout master
3437-------------------------------------------------
3438
3439or
3440
3441-------------------------------------------------
3442$ git checkout -b fix-up
3443-------------------------------------------------
3444
3445then
3446
3447-------------------------------------------------
3448$ echo "adding a line again" >> a.txt
3449$ git commit -a -m "Updated the submodule from within the superproject."
3450$ git push
3451$ cd ..
3452$ git diff
3453diff --git a/a b/a
3454index d266b98..261dfac 160000
3455--- a/a
3456+++ b/a
3457@@ -1 +1 @@
3458-Subproject commit d266b9873ad50488163457f025db7cdd9683d88b
3459+Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24
3460$ git add a
3461$ git commit -m "Updated submodule a."
3462$ git push
3463-------------------------------------------------
3464
3465You have to run `git submodule update` after `git pull` if you want to update
3466submodules, too.
3467
3468Pitfalls with submodules
3469------------------------
3470
3471Always publish the submodule change before publishing the change to the
3472superproject that references it. If you forget to publish the submodule change,
3473others won't be able to clone the repository:
3474
3475-------------------------------------------------
3476$ cd ~/git/super/a
3477$ echo i added another line to this file >> a.txt
3478$ git commit -a -m "doing it wrong this time"
3479$ cd ..
3480$ git add a
3481$ git commit -m "Updated submodule a again."
3482$ git push
3483$ cd ~/git/cloned
3484$ git pull
3485$ git submodule update
3486error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git.
3487Did you forget to 'git add'?
3488Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a'
3489-------------------------------------------------
3490
3491You also should not rewind branches in a submodule beyond commits that were
3492ever recorded in any superproject.
3493
3494It's not safe to run `git submodule update` if you've made and committed
3495changes within a submodule without checking out a branch first. They will be
3496silently overwritten:
3497
3498-------------------------------------------------
3499$ cat a.txt
3500module a
3501$ echo line added from private2 >> a.txt
3502$ git commit -a -m "line added inside private2"
3503$ cd ..
3504$ git submodule update
3505Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b'
3506$ cd a
3507$ cat a.txt
3508module a
3509-------------------------------------------------
3510
3511NOTE: The changes are still visible in the submodule's reflog.
3512
3513This is not the case if you did not commit your changes.
3514
1c6045ff
BF
3515[[low-level-operations]]
3516Low-level git operations
3517========================
b181d57f 3518
1c6045ff
BF
3519Many of the higher-level commands were originally implemented as shell
3520scripts using a smaller core of low-level git commands. These can still
3521be useful when doing unusual things with git, or just as a way to
3522understand its inner workings.
b181d57f 3523
1bbf1c79
BF
3524[[object-manipulation]]
3525Object access and manipulation
3526------------------------------
3527
3528The gitlink:git-cat-file[1] command can show the contents of any object,
3529though the higher-level gitlink:git-show[1] is usually more useful.
3530
3531The gitlink:git-commit-tree[1] command allows constructing commits with
3532arbitrary parents and trees.
3533
3534A tree can be created with gitlink:git-write-tree[1] and its data can be
3535accessed by gitlink:git-ls-tree[1]. Two trees can be compared with
3536gitlink:git-diff-tree[1].
3537
3538A tag is created with gitlink:git-mktag[1], and the signature can be
3539verified by gitlink:git-verify-tag[1], though it is normally simpler to
3540use gitlink:git-tag[1] for both.
3541
e34caace 3542[[the-workflow]]
b181d57f
BF
3543The Workflow
3544------------
3545
1c6045ff
BF
3546High-level operations such as gitlink:git-commit[1],
3547gitlink:git-checkout[1] and git-reset[1] work by moving data between the
3548working tree, the index, and the object database. Git provides
3549low-level operations which perform each of these steps individually.