User's Manual: remove duplicated url at the end of Appendix B
[git/git.git] / Documentation / user-manual.txt
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0eb4f7cd 1Git User's Manual (for version 1.5.3 or newer)
71f4b183 2______________________________________________
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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
d19fbc3c 20Comprehensive reference documentation is available through the man
3861cd55 21pages. For a command such as "git clone <repo>", just use
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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
5162e697 45The best way to get one is by using the linkgit:git-clone[1] command to
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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
57283291 77parallel lines of development, called <<def_branch,branches>>, which may
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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
5162e697 82latest commit on each branch; the linkgit: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
5162e697 96linkgit:git-tag[1] command:
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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
5162e697 116out using linkgit:git-checkout[1]:
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117
118------------------------------------------------
119$ git checkout -b new v2.6.13
120------------------------------------------------
121
122The working directory then reflects the contents that the project had
5162e697 123when it was tagged v2.6.13, and linkgit:git-branch[1] shows two
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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.
5162e697 149The linkgit:git-show[1] command shows the most recent commit on the
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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
35121930 180Every commit has a 40-hexdigit id, sometimes called the "object name" or the
b1889c36 181"SHA1 id", shown on the first line of the "git-show" output. You can usually
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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
5162e697 211The best way to see how this works is using the linkgit:gitk[1]
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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
5162e697 338can view using the "-r" option to linkgit:git-branch[1]:
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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
5162e697 381linkgit:git-pack-refs[1]).
fc74ecc1 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
5162e697 390REVISIONS" section of linkgit:git-rev-parse[1].
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391
392[[Updating-a-repository-with-git-fetch]]
b1889c36 393Updating a repository with git-fetch
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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
5162e697 410cloned from, using linkgit:git-remote[1]:
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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
b1889c36 420that you gave "git-remote add", in this case linux-nfs:
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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
5162e697 446linkgit: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
5162e697 471linkgit:git-bisect[1] command can help you do this:
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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
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482temporarily moved you in "(no branch)". HEAD is now detached from any
483branch and points directly to a commit (with commit id 65934...) that
484is reachable from "master" but not from v2.6.18. Compile and test it,
485and see whether it crashes. Assume it does crash. Then:
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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
5162e697 500linkgit:git-show[1], find out who wrote it, and mail them your bug
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501report with the commit id. Finally, run
502
503-------------------------------------------------
504$ git bisect reset
505-------------------------------------------------
506
0e25790f 507to return you to the branch you were on before.
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508
509Note that the version which git-bisect checks out for you at each
510point is just a suggestion, and you're free to try a different
511version if you think it would be a good idea. For example,
512occasionally you may land on a commit that broke something unrelated;
513run
514
515-------------------------------------------------
04483524 516$ git bisect visualize
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517-------------------------------------------------
518
519which will run gitk and label the commit it chose with a marker that
843c81dc 520says "bisect". Choose a safe-looking commit nearby, note its commit
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521id, and check it out with:
522
523-------------------------------------------------
524$ git reset --hard fb47ddb2db...
525-------------------------------------------------
526
527then test, run "bisect good" or "bisect bad" as appropriate, and
528continue.
529
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530Instead of "git bisect visualize" and then "git reset --hard
531fb47ddb2db...", you might just want to tell git that you want to skip
532the current commit:
533
534-------------------------------------------------
535$ git bisect skip
536-------------------------------------------------
537
538In this case, though, git may not eventually be able to tell the first
a0178ae2 539bad one between some first skipped commits and a later bad commit.
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540
541There are also ways to automate the bisecting process if you have a
542test script that can tell a good from a bad commit. See
543linkgit:git-bisect[1] for more information about this and other "git
544bisect" features.
545
e34caace 546[[naming-commits]]
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547Naming commits
548--------------
549
550We have seen several ways of naming commits already:
551
d55ae921 552 - 40-hexdigit object name
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553 - branch name: refers to the commit at the head of the given
554 branch
555 - tag name: refers to the commit pointed to by the given tag
556 (we've seen branches and tags are special cases of
557 <<how-git-stores-references,references>>).
558 - HEAD: refers to the head of the current branch
559
eb6ae7f4 560There are many more; see the "SPECIFYING REVISIONS" section of the
5162e697 561linkgit:git-rev-parse[1] man page for the complete list of ways to
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562name revisions. Some examples:
563
564-------------------------------------------------
d55ae921 565$ git show fb47ddb2 # the first few characters of the object name
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566 # are usually enough to specify it uniquely
567$ git show HEAD^ # the parent of the HEAD commit
568$ git show HEAD^^ # the grandparent
569$ git show HEAD~4 # the great-great-grandparent
570-------------------------------------------------
571
572Recall that merge commits may have more than one parent; by default,
573^ and ~ follow the first parent listed in the commit, but you can
574also choose:
575
576-------------------------------------------------
577$ git show HEAD^1 # show the first parent of HEAD
578$ git show HEAD^2 # show the second parent of HEAD
579-------------------------------------------------
580
581In addition to HEAD, there are several other special names for
582commits:
583
584Merges (to be discussed later), as well as operations such as
585git-reset, which change the currently checked-out commit, generally
586set ORIG_HEAD to the value HEAD had before the current operation.
587
588The git-fetch operation always stores the head of the last fetched
589branch in FETCH_HEAD. For example, if you run git fetch without
590specifying a local branch as the target of the operation
591
592-------------------------------------------------
593$ git fetch git://example.com/proj.git theirbranch
594-------------------------------------------------
595
596the fetched commits will still be available from FETCH_HEAD.
597
598When we discuss merges we'll also see the special name MERGE_HEAD,
599which refers to the other branch that we're merging in to the current
600branch.
601
5162e697 602The linkgit:git-rev-parse[1] command is a low-level command that is
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603occasionally useful for translating some name for a commit to the object
604name for that commit:
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605
606-------------------------------------------------
607$ git rev-parse origin
608e05db0fd4f31dde7005f075a84f96b360d05984b
609-------------------------------------------------
610
e34caace 611[[creating-tags]]
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612Creating tags
613-------------
614
615We can also create a tag to refer to a particular commit; after
616running
617
618-------------------------------------------------
04483524 619$ git tag stable-1 1b2e1d63ff
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620-------------------------------------------------
621
622You can use stable-1 to refer to the commit 1b2e1d63ff.
623
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624This creates a "lightweight" tag. If you would also like to include a
625comment with the tag, and possibly sign it cryptographically, then you
5162e697 626should create a tag object instead; see the linkgit:git-tag[1] man page
c64415e2 627for details.
d19fbc3c 628
e34caace 629[[browsing-revisions]]
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630Browsing revisions
631------------------
632
5162e697 633The linkgit:git-log[1] command can show lists of commits. On its
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634own, it shows all commits reachable from the parent commit; but you
635can also make more specific requests:
636
637-------------------------------------------------
638$ git log v2.5.. # commits since (not reachable from) v2.5
639$ git log test..master # commits reachable from master but not test
640$ git log master..test # ...reachable from test but not master
641$ git log master...test # ...reachable from either test or master,
642 # but not both
643$ git log --since="2 weeks ago" # commits from the last 2 weeks
644$ git log Makefile # commits which modify Makefile
645$ git log fs/ # ... which modify any file under fs/
646$ git log -S'foo()' # commits which add or remove any file data
647 # matching the string 'foo()'
648-------------------------------------------------
649
650And of course you can combine all of these; the following finds
651commits since v2.5 which touch the Makefile or any file under fs:
652
653-------------------------------------------------
654$ git log v2.5.. Makefile fs/
655-------------------------------------------------
656
657You can also ask git log to show patches:
658
659-------------------------------------------------
660$ git log -p
661-------------------------------------------------
662
5162e697 663See the "--pretty" option in the linkgit:git-log[1] man page for more
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664display options.
665
666Note that git log starts with the most recent commit and works
667backwards through the parents; however, since git history can contain
3dff5379 668multiple independent lines of development, the particular order that
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669commits are listed in may be somewhat arbitrary.
670
e34caace 671[[generating-diffs]]
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672Generating diffs
673----------------
674
675You can generate diffs between any two versions using
5162e697 676linkgit:git-diff[1]:
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677
678-------------------------------------------------
679$ git diff master..test
680-------------------------------------------------
681
5b98d9bc
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682That will produce the diff between the tips of the two branches. If
683you'd prefer to find the diff from their common ancestor to test, you
684can use three dots instead of two:
685
686-------------------------------------------------
687$ git diff master...test
688-------------------------------------------------
689
690Sometimes what you want instead is a set of patches; for this you can
5162e697 691use linkgit:git-format-patch[1]:
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692
693-------------------------------------------------
694$ git format-patch master..test
695-------------------------------------------------
696
697will generate a file with a patch for each commit reachable from test
5b98d9bc 698but not from master.
d19fbc3c 699
e34caace 700[[viewing-old-file-versions]]
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701Viewing old file versions
702-------------------------
703
704You can always view an old version of a file by just checking out the
705correct revision first. But sometimes it is more convenient to be
706able to view an old version of a single file without checking
707anything out; this command does that:
708
709-------------------------------------------------
710$ git show v2.5:fs/locks.c
711-------------------------------------------------
712
713Before the colon may be anything that names a commit, and after it
714may be any path to a file tracked by git.
715
e34caace 716[[history-examples]]
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717Examples
718--------
719
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720[[counting-commits-on-a-branch]]
721Counting the number of commits on a branch
722~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
723
724Suppose you want to know how many commits you've made on "mybranch"
725since it diverged from "origin":
726
727-------------------------------------------------
728$ git log --pretty=oneline origin..mybranch | wc -l
729-------------------------------------------------
730
731Alternatively, you may often see this sort of thing done with the
5162e697 732lower-level command linkgit:git-rev-list[1], which just lists the SHA1's
46acd3fa
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733of all the given commits:
734
735-------------------------------------------------
736$ git rev-list origin..mybranch | wc -l
737-------------------------------------------------
738
e34caace 739[[checking-for-equal-branches]]
aec053bb 740Check whether two branches point at the same history
2f99710c 741~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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742
743Suppose you want to check whether two branches point at the same point
744in history.
745
746-------------------------------------------------
747$ git diff origin..master
748-------------------------------------------------
749
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750will tell you whether the contents of the project are the same at the
751two branches; in theory, however, it's possible that the same project
752contents could have been arrived at by two different historical
d55ae921 753routes. You could compare the object names:
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754
755-------------------------------------------------
756$ git rev-list origin
757e05db0fd4f31dde7005f075a84f96b360d05984b
758$ git rev-list master
759e05db0fd4f31dde7005f075a84f96b360d05984b
760-------------------------------------------------
761
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762Or you could recall that the ... operator selects all commits
763contained reachable from either one reference or the other but not
764both: so
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765
766-------------------------------------------------
767$ git log origin...master
768-------------------------------------------------
769
770will return no commits when the two branches are equal.
771
e34caace 772[[finding-tagged-descendants]]
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773Find first tagged version including a given fix
774~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
aec053bb 775
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776Suppose you know that the commit e05db0fd fixed a certain problem.
777You'd like to find the earliest tagged release that contains that
778fix.
779
780Of course, there may be more than one answer--if the history branched
781after commit e05db0fd, then there could be multiple "earliest" tagged
782releases.
783
784You could just visually inspect the commits since e05db0fd:
785
786-------------------------------------------------
787$ gitk e05db0fd..
788-------------------------------------------------
789
5162e697 790Or you can use linkgit:git-name-rev[1], which will give the commit a
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791name based on any tag it finds pointing to one of the commit's
792descendants:
793
794-------------------------------------------------
04483524 795$ git name-rev --tags e05db0fd
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796e05db0fd tags/v1.5.0-rc1^0~23
797-------------------------------------------------
798
5162e697 799The linkgit:git-describe[1] command does the opposite, naming the
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800revision using a tag on which the given commit is based:
801
802-------------------------------------------------
803$ git describe e05db0fd
04483524 804v1.5.0-rc0-260-ge05db0f
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805-------------------------------------------------
806
807but that may sometimes help you guess which tags might come after the
808given commit.
809
810If you just want to verify whether a given tagged version contains a
5162e697 811given commit, you could use linkgit:git-merge-base[1]:
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812
813-------------------------------------------------
814$ git merge-base e05db0fd v1.5.0-rc1
815e05db0fd4f31dde7005f075a84f96b360d05984b
816-------------------------------------------------
817
818The merge-base command finds a common ancestor of the given commits,
819and always returns one or the other in the case where one is a
820descendant of the other; so the above output shows that e05db0fd
821actually is an ancestor of v1.5.0-rc1.
822
823Alternatively, note that
824
825-------------------------------------------------
4a7979ca 826$ git log v1.5.0-rc1..e05db0fd
b181d57f
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827-------------------------------------------------
828
4a7979ca 829will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
b181d57f 830because it outputs only commits that are not reachable from v1.5.0-rc1.
aec053bb 831
5162e697 832As yet another alternative, the linkgit:git-show-branch[1] command lists
4a7979ca
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833the commits reachable from its arguments with a display on the left-hand
834side that indicates which arguments that commit is reachable from. So,
835you can run something like
836
837-------------------------------------------------
838$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
839! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
840available
841 ! [v1.5.0-rc0] GIT v1.5.0 preview
842 ! [v1.5.0-rc1] GIT v1.5.0-rc1
843 ! [v1.5.0-rc2] GIT v1.5.0-rc2
844...
845-------------------------------------------------
846
847then search for a line that looks like
848
849-------------------------------------------------
850+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
851available
852-------------------------------------------------
853
854Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and
855from v1.5.0-rc2, but not from v1.5.0-rc0.
856
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857[[showing-commits-unique-to-a-branch]]
858Showing commits unique to a given branch
859~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4a7979ca 860
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861Suppose you would like to see all the commits reachable from the branch
862head named "master" but not from any other head in your repository.
d19fbc3c 863
629d9f78 864We can list all the heads in this repository with
5162e697 865linkgit:git-show-ref[1]:
d19fbc3c 866
629d9f78
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867-------------------------------------------------
868$ git show-ref --heads
869bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
870db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
871a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
87224dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
8731e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
874-------------------------------------------------
d19fbc3c 875
629d9f78
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876We can get just the branch-head names, and remove "master", with
877the help of the standard utilities cut and grep:
878
879-------------------------------------------------
880$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
881refs/heads/core-tutorial
882refs/heads/maint
883refs/heads/tutorial-2
884refs/heads/tutorial-fixes
885-------------------------------------------------
886
887And then we can ask to see all the commits reachable from master
888but not from these other heads:
889
890-------------------------------------------------
891$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
892 grep -v '^refs/heads/master' )
893-------------------------------------------------
894
895Obviously, endless variations are possible; for example, to see all
896commits reachable from some head but not from any tag in the repository:
897
898-------------------------------------------------
c78974f7 899$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
629d9f78
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900-------------------------------------------------
901
5162e697 902(See linkgit:git-rev-parse[1] for explanations of commit-selecting
629d9f78
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903syntax such as `--not`.)
904
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905[[making-a-release]]
906Creating a changelog and tarball for a software release
907~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
908
5162e697 909The linkgit:git-archive[1] command can create a tar or zip archive from
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BF
910any version of a project; for example:
911
912-------------------------------------------------
913$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
914-------------------------------------------------
915
916will use HEAD to produce a tar archive in which each filename is
ccd71866 917preceded by "project/".
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918
919If you're releasing a new version of a software project, you may want
920to simultaneously make a changelog to include in the release
921announcement.
922
923Linus Torvalds, for example, makes new kernel releases by tagging them,
924then running:
925
926-------------------------------------------------
927$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
928-------------------------------------------------
929
930where release-script is a shell script that looks like:
931
932-------------------------------------------------
933#!/bin/sh
934stable="$1"
935last="$2"
936new="$3"
937echo "# git tag v$new"
938echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
939echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
940echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
941echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
942echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
943-------------------------------------------------
944
945and then he just cut-and-pastes the output commands after verifying that
946they look OK.
4a7979ca 947
8ceca74a 948[[Finding-comments-with-given-content]]
187b0d80 949Finding commits referencing a file with given content
d5821de2 950~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
187b0d80
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951
952Somebody hands you a copy of a file, and asks which commits modified a
953file such that it contained the given content either before or after the
954commit. You can find out with this:
955
956-------------------------------------------------
477ff5b7 957$ git log --raw --abbrev=40 --pretty=oneline |
187b0d80
BF
958 grep -B 1 `git hash-object filename`
959-------------------------------------------------
960
961Figuring out why this works is left as an exercise to the (advanced)
5162e697
DM
962student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and
963linkgit:git-hash-object[1] man pages may prove helpful.
187b0d80 964
e34caace 965[[Developing-with-git]]
d19fbc3c
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966Developing with git
967===================
968
e34caace 969[[telling-git-your-name]]
d19fbc3c
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970Telling git your name
971---------------------
972
973Before creating any commits, you should introduce yourself to git. The
58c19d1f
BF
974easiest way to do so is to make sure the following lines appear in a
975file named .gitconfig in your home directory:
d19fbc3c
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976
977------------------------------------------------
d19fbc3c
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978[user]
979 name = Your Name Comes Here
980 email = you@yourdomain.example.com
d19fbc3c
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981------------------------------------------------
982
5162e697 983(See the "CONFIGURATION FILE" section of linkgit:git-config[1] for
fc90c536
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984details on the configuration file.)
985
d19fbc3c 986
e34caace 987[[creating-a-new-repository]]
d19fbc3c
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988Creating a new repository
989-------------------------
990
991Creating a new repository from scratch is very easy:
992
993-------------------------------------------------
994$ mkdir project
995$ cd project
f1d2b477 996$ git init
d19fbc3c
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997-------------------------------------------------
998
999If you have some initial content (say, a tarball):
1000
1001-------------------------------------------------
1002$ tar -xzvf project.tar.gz
1003$ cd project
f1d2b477 1004$ git init
d19fbc3c
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1005$ git add . # include everything below ./ in the first commit:
1006$ git commit
1007-------------------------------------------------
1008
1009[[how-to-make-a-commit]]
ae25c67a 1010How to make a commit
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1011--------------------
1012
1013Creating a new commit takes three steps:
1014
1015 1. Making some changes to the working directory using your
1016 favorite editor.
1017 2. Telling git about your changes.
1018 3. Creating the commit using the content you told git about
1019 in step 2.
1020
1021In practice, you can interleave and repeat steps 1 and 2 as many
1022times as you want: in order to keep track of what you want committed
1023at step 3, git maintains a snapshot of the tree's contents in a
1024special staging area called "the index."
1025
01997b4a
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1026At the beginning, the content of the index will be identical to
1027that of the HEAD. The command "git diff --cached", which shows
1028the difference between the HEAD and the index, should therefore
1029produce no output at that point.
eb6ae7f4 1030
d19fbc3c
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1031Modifying the index is easy:
1032
1033To update the index with the new contents of a modified file, use
1034
1035-------------------------------------------------
1036$ git add path/to/file
1037-------------------------------------------------
1038
1039To add the contents of a new file to the index, use
1040
1041-------------------------------------------------
1042$ git add path/to/file
1043-------------------------------------------------
1044
eb6ae7f4 1045To remove a file from the index and from the working tree,
d19fbc3c
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1046
1047-------------------------------------------------
1048$ git rm path/to/file
1049-------------------------------------------------
1050
1051After each step you can verify that
1052
1053-------------------------------------------------
1054$ git diff --cached
1055-------------------------------------------------
1056
1057always shows the difference between the HEAD and the index file--this
1058is what you'd commit if you created the commit now--and that
1059
1060-------------------------------------------------
1061$ git diff
1062-------------------------------------------------
1063
1064shows the difference between the working tree and the index file.
1065
b1889c36 1066Note that "git-add" always adds just the current contents of a file
d19fbc3c
BF
1067to the index; further changes to the same file will be ignored unless
1068you run git-add on the file again.
1069
1070When you're ready, just run
1071
1072-------------------------------------------------
1073$ git commit
1074-------------------------------------------------
1075
1076and git will prompt you for a commit message and then create the new
3dff5379 1077commit. Check to make sure it looks like what you expected with
d19fbc3c
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1078
1079-------------------------------------------------
1080$ git show
1081-------------------------------------------------
1082
1083As a special shortcut,
a6080a0a 1084
d19fbc3c
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1085-------------------------------------------------
1086$ git commit -a
1087-------------------------------------------------
1088
1089will update the index with any files that you've modified or removed
1090and create a commit, all in one step.
1091
1092A number of commands are useful for keeping track of what you're
1093about to commit:
1094
1095-------------------------------------------------
1096$ git diff --cached # difference between HEAD and the index; what
1130845b 1097 # would be committed if you ran "commit" now.
d19fbc3c
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1098$ git diff # difference between the index file and your
1099 # working directory; changes that would not
1100 # be included if you ran "commit" now.
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1101$ git diff HEAD # difference between HEAD and working tree; what
1102 # would be committed if you ran "commit -a" now.
d19fbc3c
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1103$ git status # a brief per-file summary of the above.
1104-------------------------------------------------
1105
5162e697 1106You can also use linkgit:git-gui[1] to create commits, view changes in
407c0c87
BF
1107the index and the working tree files, and individually select diff hunks
1108for inclusion in the index (by right-clicking on the diff hunk and
1109choosing "Stage Hunk For Commit").
1110
e34caace 1111[[creating-good-commit-messages]]
ae25c67a 1112Creating good commit messages
d19fbc3c
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1113-----------------------------
1114
1115Though not required, it's a good idea to begin the commit message
1116with a single short (less than 50 character) line summarizing the
1117change, followed by a blank line and then a more thorough
1118description. Tools that turn commits into email, for example, use
1119the first line on the Subject line and the rest of the commit in the
1120body.
1121
2dc53617
JH
1122[[ignoring-files]]
1123Ignoring files
1124--------------
1125
1126A project will often generate files that you do 'not' want to track with git.
1127This typically includes files generated by a build process or temporary
1128backup files made by your editor. Of course, 'not' tracking files with git
b1889c36 1129is just a matter of 'not' calling "`git-add`" on them. But it quickly becomes
2dc53617 1130annoying to have these untracked files lying around; e.g. they make
7be73ae9
JN
1131"`git add .`" practically useless, and they keep showing up in the output of
1132"`git status`".
2dc53617 1133
464a8a7a
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1134You can tell git to ignore certain files by creating a file called .gitignore
1135in the top level of your working directory, with contents such as:
2dc53617
JH
1136
1137-------------------------------------------------
1138# Lines starting with '#' are considered comments.
464a8a7a 1139# Ignore any file named foo.txt.
2dc53617
JH
1140foo.txt
1141# Ignore (generated) html files,
1142*.html
1143# except foo.html which is maintained by hand.
1144!foo.html
1145# Ignore objects and archives.
1146*.[oa]
1147-------------------------------------------------
1148
5162e697 1149See linkgit:gitignore[5] for a detailed explanation of the syntax. You can
464a8a7a
BF
1150also place .gitignore files in other directories in your working tree, and they
1151will apply to those directories and their subdirectories. The `.gitignore`
1152files can be added to your repository like any other files (just run `git add
1153.gitignore` and `git commit`, as usual), which is convenient when the exclude
1154patterns (such as patterns matching build output files) would also make sense
1155for other users who clone your repository.
1156
1157If you wish the exclude patterns to affect only certain repositories
1158(instead of every repository for a given project), you may instead put
1159them in a file in your repository named .git/info/exclude, or in any file
1160specified by the `core.excludesfile` configuration variable. Some git
1161commands can also take exclude patterns directly on the command line.
5162e697 1162See linkgit:gitignore[5] for the details.
2dc53617 1163
e34caace 1164[[how-to-merge]]
ae25c67a 1165How to merge
d19fbc3c
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1166------------
1167
1168You can rejoin two diverging branches of development using
5162e697 1169linkgit:git-merge[1]:
d19fbc3c
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1170
1171-------------------------------------------------
1172$ git merge branchname
1173-------------------------------------------------
1174
1175merges the development in the branch "branchname" into the current
1176branch. If there are conflicts--for example, if the same file is
1177modified in two different ways in the remote branch and the local
1178branch--then you are warned; the output may look something like this:
1179
1180-------------------------------------------------
fabbd8f6
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1181$ git merge next
1182 100% (4/4) done
1183Auto-merged file.txt
d19fbc3c
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1184CONFLICT (content): Merge conflict in file.txt
1185Automatic merge failed; fix conflicts and then commit the result.
1186-------------------------------------------------
1187
1188Conflict markers are left in the problematic files, and after
1189you resolve the conflicts manually, you can update the index
1190with the contents and run git commit, as you normally would when
1191creating a new file.
1192
1193If you examine the resulting commit using gitk, you will see that it
1194has two parents, one pointing to the top of the current branch, and
1195one to the top of the other branch.
1196
d19fbc3c
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1197[[resolving-a-merge]]
1198Resolving a merge
1199-----------------
1200
1201When a merge isn't resolved automatically, git leaves the index and
1202the working tree in a special state that gives you all the
1203information you need to help resolve the merge.
1204
1205Files with conflicts are marked specially in the index, so until you
5162e697 1206resolve the problem and update the index, linkgit:git-commit[1] will
ef561ac7 1207fail:
d19fbc3c
BF
1208
1209-------------------------------------------------
1210$ git commit
1211file.txt: needs merge
1212-------------------------------------------------
1213
5162e697 1214Also, linkgit:git-status[1] will list those files as "unmerged", and the
ef561ac7
BF
1215files with conflicts will have conflict markers added, like this:
1216
1217-------------------------------------------------
1218<<<<<<< HEAD:file.txt
1219Hello world
1220=======
1221Goodbye
1222>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1223-------------------------------------------------
1224
1225All you need to do is edit the files to resolve the conflicts, and then
1226
1227-------------------------------------------------
1228$ git add file.txt
1229$ git commit
1230-------------------------------------------------
1231
1232Note that the commit message will already be filled in for you with
1233some information about the merge. Normally you can just use this
1234default message unchanged, but you may add additional commentary of
1235your own if desired.
1236
1237The above is all you need to know to resolve a simple merge. But git
1238also provides more information to help resolve conflicts:
1239
e34caace 1240[[conflict-resolution]]
ef561ac7
BF
1241Getting conflict-resolution help during a merge
1242~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1243
1244All of the changes that git was able to merge automatically are
5162e697 1245already added to the index file, so linkgit:git-diff[1] shows only
ef561ac7 1246the conflicts. It uses an unusual syntax:
d19fbc3c
BF
1247
1248-------------------------------------------------
1249$ git diff
1250diff --cc file.txt
1251index 802992c,2b60207..0000000
1252--- a/file.txt
1253+++ b/file.txt
1254@@@ -1,1 -1,1 +1,5 @@@
1255++<<<<<<< HEAD:file.txt
1256 +Hello world
1257++=======
1258+ Goodbye
1259++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1260-------------------------------------------------
1261
1130845b 1262Recall that the commit which will be committed after we resolve this
d19fbc3c
BF
1263conflict will have two parents instead of the usual one: one parent
1264will be HEAD, the tip of the current branch; the other will be the
1265tip of the other branch, which is stored temporarily in MERGE_HEAD.
1266
ef561ac7
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1267During the merge, the index holds three versions of each file. Each of
1268these three "file stages" represents a different version of the file:
1269
1270-------------------------------------------------
1271$ git show :1:file.txt # the file in a common ancestor of both branches
4209752d
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1272$ git show :2:file.txt # the version from HEAD.
1273$ git show :3:file.txt # the version from MERGE_HEAD.
ef561ac7
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1274-------------------------------------------------
1275
4209752d
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1276When you ask linkgit:git-diff[1] to show the conflicts, it runs a
1277three-way diff between the conflicted merge results in the work tree with
1278stages 2 and 3 to show only hunks whose contents come from both sides,
1279mixed (in other words, when a hunk's merge results come only from stage 2,
1280that part is not conflicting and is not shown. Same for stage 3).
ef561ac7
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1281
1282The diff above shows the differences between the working-tree version of
1283file.txt and the stage 2 and stage 3 versions. So instead of preceding
1284each line by a single "+" or "-", it now uses two columns: the first
1285column is used for differences between the first parent and the working
1286directory copy, and the second for differences between the second parent
1287and the working directory copy. (See the "COMBINED DIFF FORMAT" section
5162e697 1288of linkgit:git-diff-files[1] for a details of the format.)
ef561ac7
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1289
1290After resolving the conflict in the obvious way (but before updating the
1291index), the diff will look like:
d19fbc3c
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1292
1293-------------------------------------------------
1294$ git diff
1295diff --cc file.txt
1296index 802992c,2b60207..0000000
1297--- a/file.txt
1298+++ b/file.txt
1299@@@ -1,1 -1,1 +1,1 @@@
1300- Hello world
1301 -Goodbye
1302++Goodbye world
1303-------------------------------------------------
1304
1305This shows that our resolved version deleted "Hello world" from the
1306first parent, deleted "Goodbye" from the second parent, and added
1307"Goodbye world", which was previously absent from both.
1308
ef561ac7
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1309Some special diff options allow diffing the working directory against
1310any of these stages:
1311
1312-------------------------------------------------
1313$ git diff -1 file.txt # diff against stage 1
1314$ git diff --base file.txt # same as the above
1315$ git diff -2 file.txt # diff against stage 2
1316$ git diff --ours file.txt # same as the above
1317$ git diff -3 file.txt # diff against stage 3
1318$ git diff --theirs file.txt # same as the above.
1319-------------------------------------------------
1320
0cafe944 1321The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
ef561ac7 1322for merges:
d19fbc3c
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1323
1324-------------------------------------------------
1325$ git log --merge
ef561ac7 1326$ gitk --merge
d19fbc3c
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1327-------------------------------------------------
1328
ef561ac7
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1329These will display all commits which exist only on HEAD or on
1330MERGE_HEAD, and which touch an unmerged file.
d19fbc3c 1331
5162e697 1332You may also use linkgit:git-mergetool[1], which lets you merge the
c64415e2
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1333unmerged files using external tools such as emacs or kdiff3.
1334
ef561ac7 1335Each time you resolve the conflicts in a file and update the index:
d19fbc3c
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1336
1337-------------------------------------------------
1338$ git add file.txt
d19fbc3c
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1339-------------------------------------------------
1340
ef561ac7
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1341the different stages of that file will be "collapsed", after which
1342git-diff will (by default) no longer show diffs for that file.
d19fbc3c
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1343
1344[[undoing-a-merge]]
ae25c67a 1345Undoing a merge
d19fbc3c
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1346---------------
1347
1348If you get stuck and decide to just give up and throw the whole mess
1349away, you can always return to the pre-merge state with
1350
1351-------------------------------------------------
1352$ git reset --hard HEAD
1353-------------------------------------------------
1354
1130845b 1355Or, if you've already committed the merge that you want to throw away,
d19fbc3c
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1356
1357-------------------------------------------------
1c73bb0e 1358$ git reset --hard ORIG_HEAD
d19fbc3c
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1359-------------------------------------------------
1360
1361However, this last command can be dangerous in some cases--never
1362throw away a commit you have already committed if that commit may
1363itself have been merged into another branch, as doing so may confuse
1364further merges.
1365
e34caace 1366[[fast-forwards]]
d19fbc3c
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1367Fast-forward merges
1368-------------------
1369
1370There is one special case not mentioned above, which is treated
1371differently. Normally, a merge results in a merge commit, with two
1372parents, one pointing at each of the two lines of development that
1373were merged.
1374
59723040
BF
1375However, if the current branch is a descendant of the other--so every
1376commit present in the one is already contained in the other--then git
1377just performs a "fast forward"; the head of the current branch is moved
1378forward to point at the head of the merged-in branch, without any new
1379commits being created.
d19fbc3c 1380
e34caace 1381[[fixing-mistakes]]
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1382Fixing mistakes
1383---------------
1384
1385If you've messed up the working tree, but haven't yet committed your
1386mistake, you can return the entire working tree to the last committed
1387state with
1388
1389-------------------------------------------------
1390$ git reset --hard HEAD
1391-------------------------------------------------
1392
1393If you make a commit that you later wish you hadn't, there are two
1394fundamentally different ways to fix the problem:
1395
1396 1. You can create a new commit that undoes whatever was done
93cbbd71 1397 by the old commit. This is the correct thing if your
b684f830
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1398 mistake has already been made public.
1399
1400 2. You can go back and modify the old commit. You should
1401 never do this if you have already made the history public;
1402 git does not normally expect the "history" of a project to
1403 change, and cannot correctly perform repeated merges from
1404 a branch that has had its history changed.
1405
e34caace 1406[[reverting-a-commit]]
b684f830
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1407Fixing a mistake with a new commit
1408~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1409
1410Creating a new commit that reverts an earlier change is very easy;
5162e697 1411just pass the linkgit:git-revert[1] command a reference to the bad
b684f830
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1412commit; for example, to revert the most recent commit:
1413
1414-------------------------------------------------
1415$ git revert HEAD
1416-------------------------------------------------
1417
1418This will create a new commit which undoes the change in HEAD. You
1419will be given a chance to edit the commit message for the new commit.
1420
1421You can also revert an earlier change, for example, the next-to-last:
1422
1423-------------------------------------------------
1424$ git revert HEAD^
1425-------------------------------------------------
1426
1427In this case git will attempt to undo the old change while leaving
1428intact any changes made since then. If more recent changes overlap
1429with the changes to be reverted, then you will be asked to fix
1430conflicts manually, just as in the case of <<resolving-a-merge,
1431resolving a merge>>.
1432
7cb192ea
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1433[[fixing-a-mistake-by-rewriting-history]]
1434Fixing a mistake by rewriting history
b684f830
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1435~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1436
1437If the problematic commit is the most recent commit, and you have not
1438yet made that commit public, then you may just
1439<<undoing-a-merge,destroy it using git-reset>>.
1440
1441Alternatively, you
1442can edit the working directory and update the index to fix your
1443mistake, just as if you were going to <<how-to-make-a-commit,create a
1444new commit>>, then run
1445
1446-------------------------------------------------
1447$ git commit --amend
1448-------------------------------------------------
1449
1450which will replace the old commit by a new commit incorporating your
1451changes, giving you a chance to edit the old commit message first.
1452
1453Again, you should never do this to a commit that may already have
5162e697 1454been merged into another branch; use linkgit:git-revert[1] instead in
b684f830
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1455that case.
1456
7cb192ea 1457It is also possible to replace commits further back in the history, but
b684f830
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1458this is an advanced topic to be left for
1459<<cleaning-up-history,another chapter>>.
1460
e34caace 1461[[checkout-of-path]]
b684f830
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1462Checking out an old version of a file
1463~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1464
1465In the process of undoing a previous bad change, you may find it
1466useful to check out an older version of a particular file using
b1889c36 1467linkgit:git-checkout[1]. We've used git-checkout before to switch
b684f830
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1468branches, but it has quite different behavior if it is given a path
1469name: the command
1470
1471-------------------------------------------------
1472$ git checkout HEAD^ path/to/file
1473-------------------------------------------------
1474
1475replaces path/to/file by the contents it had in the commit HEAD^, and
1476also updates the index to match. It does not change branches.
1477
1478If you just want to look at an old version of the file, without
1479modifying the working directory, you can do that with
5162e697 1480linkgit:git-show[1]:
b684f830
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1481
1482-------------------------------------------------
ed4eb0d8 1483$ git show HEAD^:path/to/file
b684f830
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1484-------------------------------------------------
1485
1486which will display the given version of the file.
1487
7a7cc594
JH
1488[[interrupted-work]]
1489Temporarily setting aside work in progress
1490~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1491
1492While you are in the middle of working on something complicated, you
1493find an unrelated but obvious and trivial bug. You would like to fix it
5162e697 1494before continuing. You can use linkgit:git-stash[1] to save the current
7a7cc594
JH
1495state of your work, and after fixing the bug (or, optionally after doing
1496so on a different branch and then coming back), unstash the
1497work-in-progress changes.
1498
1499------------------------------------------------
1500$ git stash "work in progress for foo feature"
1501------------------------------------------------
1502
1503This command will save your changes away to the `stash`, and
1504reset your working tree and the index to match the tip of your
1505current branch. Then you can make your fix as usual.
1506
1507------------------------------------------------
1508... edit and test ...
1509$ git commit -a -m "blorpl: typofix"
1510------------------------------------------------
1511
1512After that, you can go back to what you were working on with
1513`git stash apply`:
1514
1515------------------------------------------------
1516$ git stash apply
1517------------------------------------------------
1518
1519
e34caace 1520[[ensuring-good-performance]]
d19fbc3c
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1521Ensuring good performance
1522-------------------------
1523
1524On large repositories, git depends on compression to keep the history
06ada152 1525information from taking up too much space on disk or in memory.
d19fbc3c
BF
1526
1527This compression is not performed automatically. Therefore you
5162e697 1528should occasionally run linkgit:git-gc[1]:
d19fbc3c
BF
1529
1530-------------------------------------------------
1531$ git gc
1532-------------------------------------------------
1533
17217090
BF
1534to recompress the archive. This can be very time-consuming, so
1535you may prefer to run git-gc when you are not doing other work.
d19fbc3c 1536
e34caace
BF
1537
1538[[ensuring-reliability]]
11e016a3
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1539Ensuring reliability
1540--------------------
1541
e34caace 1542[[checking-for-corruption]]
11e016a3
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1543Checking the repository for corruption
1544~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1545
5162e697 1546The linkgit:git-fsck[1] command runs a number of self-consistency checks
1191ee18 1547on the repository, and reports on any problems. This may take some
21dcb3b7
BF
1548time. The most common warning by far is about "dangling" objects:
1549
1550-------------------------------------------------
04e50e94 1551$ git fsck
21dcb3b7
BF
1552dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1553dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1554dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1555dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1556dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1557dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1558dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1559dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1560...
1561-------------------------------------------------
1562
59723040 1563Dangling objects are not a problem. At worst they may take up a little
54782859 1564extra disk space. They can sometimes provide a last-resort method for
208641cf 1565recovering lost work--see <<dangling-objects>> for details.
1cdade2c 1566
e34caace 1567[[recovering-lost-changes]]
11e016a3
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1568Recovering lost changes
1569~~~~~~~~~~~~~~~~~~~~~~~
1570
e34caace 1571[[reflogs]]
559e4d7a
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1572Reflogs
1573^^^^^^^
1574
5162e697 1575Say you modify a branch with `linkgit:git-reset[1] --hard`, and then
559e4d7a
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1576realize that the branch was the only reference you had to that point in
1577history.
1578
1579Fortunately, git also keeps a log, called a "reflog", of all the
1580previous values of each branch. So in this case you can still find the
a6080a0a 1581old history using, for example,
559e4d7a
BF
1582
1583-------------------------------------------------
1584$ git log master@{1}
1585-------------------------------------------------
1586
e502c2c3
SO
1587This lists the commits reachable from the previous version of the
1588"master" branch head. This syntax can be used with any git command
1589that accepts a commit, not just with git log. Some other examples:
559e4d7a
BF
1590
1591-------------------------------------------------
1592$ git show master@{2} # See where the branch pointed 2,
1593$ git show master@{3} # 3, ... changes ago.
1594$ gitk master@{yesterday} # See where it pointed yesterday,
1595$ gitk master@{"1 week ago"} # ... or last week
953f3d6f
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1596$ git log --walk-reflogs master # show reflog entries for master
1597-------------------------------------------------
1598
1599A separate reflog is kept for the HEAD, so
1600
1601-------------------------------------------------
1602$ git show HEAD@{"1 week ago"}
559e4d7a
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1603-------------------------------------------------
1604
953f3d6f
BF
1605will show what HEAD pointed to one week ago, not what the current branch
1606pointed to one week ago. This allows you to see the history of what
1607you've checked out.
1608
559e4d7a 1609The reflogs are kept by default for 30 days, after which they may be
5162e697 1610pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn
559e4d7a 1611how to control this pruning, and see the "SPECIFYING REVISIONS"
5162e697 1612section of linkgit:git-rev-parse[1] for details.
559e4d7a
BF
1613
1614Note that the reflog history is very different from normal git history.
1615While normal history is shared by every repository that works on the
1616same project, the reflog history is not shared: it tells you only about
1617how the branches in your local repository have changed over time.
1618
59723040 1619[[dangling-object-recovery]]
559e4d7a
BF
1620Examining dangling objects
1621^^^^^^^^^^^^^^^^^^^^^^^^^^
1622
59723040
BF
1623In some situations the reflog may not be able to save you. For example,
1624suppose you delete a branch, then realize you need the history it
1625contained. The reflog is also deleted; however, if you have not yet
1626pruned the repository, then you may still be able to find the lost
1627commits in the dangling objects that git-fsck reports. See
1628<<dangling-objects>> for the details.
559e4d7a
BF
1629
1630-------------------------------------------------
1631$ git fsck
1632dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1633dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1634dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1635...
1636-------------------------------------------------
1637
aacd404e 1638You can examine
559e4d7a
BF
1639one of those dangling commits with, for example,
1640
1641------------------------------------------------
1642$ gitk 7281251ddd --not --all
1643------------------------------------------------
1644
1645which does what it sounds like: it says that you want to see the commit
1646history that is described by the dangling commit(s), but not the
1647history that is described by all your existing branches and tags. Thus
1648you get exactly the history reachable from that commit that is lost.
1649(And notice that it might not be just one commit: we only report the
1650"tip of the line" as being dangling, but there might be a whole deep
79c96c57 1651and complex commit history that was dropped.)
559e4d7a
BF
1652
1653If you decide you want the history back, you can always create a new
1654reference pointing to it, for example, a new branch:
1655
1656------------------------------------------------
a6080a0a 1657$ git branch recovered-branch 7281251ddd
559e4d7a
BF
1658------------------------------------------------
1659
59723040
BF
1660Other types of dangling objects (blobs and trees) are also possible, and
1661dangling objects can arise in other situations.
1662
11e016a3 1663
e34caace 1664[[sharing-development]]
d19fbc3c 1665Sharing development with others
b684f830 1666===============================
d19fbc3c
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1667
1668[[getting-updates-with-git-pull]]
b1889c36 1669Getting updates with git-pull
b684f830 1670-----------------------------
d19fbc3c
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1671
1672After you clone a repository and make a few changes of your own, you
1673may wish to check the original repository for updates and merge them
1674into your own work.
1675
1676We have already seen <<Updating-a-repository-with-git-fetch,how to
5162e697 1677keep remote tracking branches up to date>> with linkgit:git-fetch[1],
d19fbc3c
BF
1678and how to merge two branches. So you can merge in changes from the
1679original repository's master branch with:
1680
1681-------------------------------------------------
1682$ git fetch
1683$ git merge origin/master
1684-------------------------------------------------
1685
5162e697 1686However, the linkgit:git-pull[1] command provides a way to do this in
d19fbc3c
BF
1687one step:
1688
1689-------------------------------------------------
1690$ git pull origin master
1691-------------------------------------------------
1692
0eb4f7cd
BF
1693In fact, if you have "master" checked out, then by default "git pull"
1694merges from the HEAD branch of the origin repository. So often you can
1695accomplish the above with just a simple
d19fbc3c
BF
1696
1697-------------------------------------------------
1698$ git pull
1699-------------------------------------------------
1700
0eb4f7cd
BF
1701More generally, a branch that is created from a remote branch will pull
1702by default from that branch. See the descriptions of the
1703branch.<name>.remote and branch.<name>.merge options in
5162e697
DM
1704linkgit:git-config[1], and the discussion of the `--track` option in
1705linkgit:git-checkout[1], to learn how to control these defaults.
d19fbc3c
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1706
1707In addition to saving you keystrokes, "git pull" also helps you by
1708producing a default commit message documenting the branch and
1709repository that you pulled from.
1710
1711(But note that no such commit will be created in the case of a
1712<<fast-forwards,fast forward>>; instead, your branch will just be
79c96c57 1713updated to point to the latest commit from the upstream branch.)
d19fbc3c 1714
1191ee18
BF
1715The git-pull command can also be given "." as the "remote" repository,
1716in which case it just merges in a branch from the current repository; so
4c63ff45
BF
1717the commands
1718
1719-------------------------------------------------
1720$ git pull . branch
1721$ git merge branch
1722-------------------------------------------------
1723
1724are roughly equivalent. The former is actually very commonly used.
1725
e34caace 1726[[submitting-patches]]
d19fbc3c 1727Submitting patches to a project
b684f830 1728-------------------------------
d19fbc3c
BF
1729
1730If you just have a few changes, the simplest way to submit them may
1731just be to send them as patches in email:
1732
5162e697 1733First, use linkgit:git-format-patch[1]; for example:
d19fbc3c
BF
1734
1735-------------------------------------------------
eb6ae7f4 1736$ git format-patch origin
d19fbc3c
BF
1737-------------------------------------------------
1738
1739will produce a numbered series of files in the current directory, one
1740for each patch in the current branch but not in origin/HEAD.
1741
1742You can then import these into your mail client and send them by
1743hand. However, if you have a lot to send at once, you may prefer to
5162e697 1744use the linkgit:git-send-email[1] script to automate the process.
d19fbc3c
BF
1745Consult the mailing list for your project first to determine how they
1746prefer such patches be handled.
1747
e34caace 1748[[importing-patches]]
d19fbc3c 1749Importing patches to a project
b684f830 1750------------------------------
d19fbc3c 1751
5162e697 1752Git also provides a tool called linkgit:git-am[1] (am stands for
d19fbc3c
BF
1753"apply mailbox"), for importing such an emailed series of patches.
1754Just save all of the patch-containing messages, in order, into a
1755single mailbox file, say "patches.mbox", then run
1756
1757-------------------------------------------------
eb6ae7f4 1758$ git am -3 patches.mbox
d19fbc3c
BF
1759-------------------------------------------------
1760
1761Git will apply each patch in order; if any conflicts are found, it
1762will stop, and you can fix the conflicts as described in
01997b4a
BF
1763"<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells
1764git to perform a merge; if you would prefer it just to abort and
1765leave your tree and index untouched, you may omit that option.)
1766
1767Once the index is updated with the results of the conflict
1768resolution, instead of creating a new commit, just run
d19fbc3c
BF
1769
1770-------------------------------------------------
1771$ git am --resolved
1772-------------------------------------------------
1773
1774and git will create the commit for you and continue applying the
1775remaining patches from the mailbox.
1776
1777The final result will be a series of commits, one for each patch in
1778the original mailbox, with authorship and commit log message each
1779taken from the message containing each patch.
1780
eda69449
BF
1781[[public-repositories]]
1782Public git repositories
1783-----------------------
d19fbc3c 1784
6e30fb0c
DK
1785Another way to submit changes to a project is to tell the maintainer
1786of that project to pull the changes from your repository using
5162e697 1787linkgit:git-pull[1]. In the section "<<getting-updates-with-git-pull,
b1889c36 1788Getting updates with git-pull>>" we described this as a way to get
6e30fb0c
DK
1789updates from the "main" repository, but it works just as well in the
1790other direction.
d19fbc3c 1791
eda69449
BF
1792If you and the maintainer both have accounts on the same machine, then
1793you can just pull changes from each other's repositories directly;
11d51533 1794commands that accept repository URLs as arguments will also accept a
eda69449 1795local directory name:
d19fbc3c
BF
1796
1797-------------------------------------------------
1798$ git clone /path/to/repository
1799$ git pull /path/to/other/repository
1800-------------------------------------------------
1801
c9016158 1802or an ssh URL:
11d51533
BF
1803
1804-------------------------------------------------
1805$ git clone ssh://yourhost/~you/repository
1806-------------------------------------------------
1807
1808For projects with few developers, or for synchronizing a few private
1809repositories, this may be all you need.
1810
eda69449
BF
1811However, the more common way to do this is to maintain a separate public
1812repository (usually on a different host) for others to pull changes
1813from. This is usually more convenient, and allows you to cleanly
1814separate private work in progress from publicly visible work.
d19fbc3c
BF
1815
1816You will continue to do your day-to-day work in your personal
1817repository, but periodically "push" changes from your personal
1818repository into your public repository, allowing other developers to
1819pull from that repository. So the flow of changes, in a situation
1820where there is one other developer with a public repository, looks
1821like this:
1822
1823 you push
1824 your personal repo ------------------> your public repo
a6080a0a 1825 ^ |
d19fbc3c
BF
1826 | |
1827 | you pull | they pull
1828 | |
1829 | |
1830 | they push V
1831 their public repo <------------------- their repo
1832
11d51533
BF
1833We explain how to do this in the following sections.
1834
eda69449
BF
1835[[setting-up-a-public-repository]]
1836Setting up a public repository
1837~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1838
1839Assume your personal repository is in the directory ~/proj. We
1840first create a new clone of the repository and tell git-daemon that it
1841is meant to be public:
d19fbc3c
BF
1842
1843-------------------------------------------------
52c80037 1844$ git clone --bare ~/proj proj.git
eda69449 1845$ touch proj.git/git-daemon-export-ok
d19fbc3c
BF
1846-------------------------------------------------
1847
52c80037 1848The resulting directory proj.git contains a "bare" git repository--it is
eda69449
BF
1849just the contents of the ".git" directory, without any files checked out
1850around it.
d19fbc3c 1851
c64415e2 1852Next, copy proj.git to the server where you plan to host the
d19fbc3c
BF
1853public repository. You can use scp, rsync, or whatever is most
1854convenient.
1855
eda69449
BF
1856[[exporting-via-git]]
1857Exporting a git repository via the git protocol
1858~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1859
1860This is the preferred method.
1861
1862If someone else administers the server, they should tell you what
c9016158 1863directory to put the repository in, and what git:// URL it will appear
eda69449 1864at. You can then skip to the section
d19fbc3c
BF
1865"<<pushing-changes-to-a-public-repository,Pushing changes to a public
1866repository>>", below.
1867
5162e697 1868Otherwise, all you need to do is start linkgit:git-daemon[1]; it will
eda69449
BF
1869listen on port 9418. By default, it will allow access to any directory
1870that looks like a git directory and contains the magic file
1871git-daemon-export-ok. Passing some directory paths as git-daemon
1872arguments will further restrict the exports to those paths.
1873
1874You can also run git-daemon as an inetd service; see the
5162e697 1875linkgit:git-daemon[1] man page for details. (See especially the
eda69449 1876examples section.)
d19fbc3c
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1877
1878[[exporting-via-http]]
1879Exporting a git repository via http
eda69449 1880~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
1881
1882The git protocol gives better performance and reliability, but on a
1883host with a web server set up, http exports may be simpler to set up.
1884
1885All you need to do is place the newly created bare git repository in
1886a directory that is exported by the web server, and make some
1887adjustments to give web clients some extra information they need:
1888
1889-------------------------------------------------
1890$ mv proj.git /home/you/public_html/proj.git
1891$ cd proj.git
c64415e2 1892$ git --bare update-server-info
7dce9918 1893$ mv hooks/post-update.sample hooks/post-update
d19fbc3c
BF
1894-------------------------------------------------
1895
1896(For an explanation of the last two lines, see
6998e4db 1897linkgit:git-update-server-info[1] and linkgit:githooks[5].)
d19fbc3c 1898
c9016158
RW
1899Advertise the URL of proj.git. Anybody else should then be able to
1900clone or pull from that URL, for example with a command line like:
d19fbc3c
BF
1901
1902-------------------------------------------------
1903$ git clone http://yourserver.com/~you/proj.git
1904-------------------------------------------------
1905
1906(See also
1907link:howto/setup-git-server-over-http.txt[setup-git-server-over-http]
1908for a slightly more sophisticated setup using WebDAV which also
1909allows pushing over http.)
1910
d19fbc3c
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1911[[pushing-changes-to-a-public-repository]]
1912Pushing changes to a public repository
eda69449 1913~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1914
eda69449 1915Note that the two techniques outlined above (exporting via
d19fbc3c
BF
1916<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1917maintainers to fetch your latest changes, but they do not allow write
1918access, which you will need to update the public repository with the
1919latest changes created in your private repository.
1920
5162e697 1921The simplest way to do this is using linkgit:git-push[1] and ssh; to
d19fbc3c
BF
1922update the remote branch named "master" with the latest state of your
1923branch named "master", run
1924
1925-------------------------------------------------
1926$ git push ssh://yourserver.com/~you/proj.git master:master
1927-------------------------------------------------
1928
1929or just
1930
1931-------------------------------------------------
1932$ git push ssh://yourserver.com/~you/proj.git master
1933-------------------------------------------------
1934
81eb417a
BF
1935As with git-fetch, git-push will complain if this does not result in a
1936<<fast-forwards,fast forward>>; see the following section for details on
1937handling this case.
d19fbc3c 1938
11d51533
BF
1939Note that the target of a "push" is normally a
1940<<def_bare_repository,bare>> repository. You can also push to a
1941repository that has a checked-out working tree, but the working tree
1942will not be updated by the push. This may lead to unexpected results if
1943the branch you push to is the currently checked-out branch!
1944
d19fbc3c
BF
1945As with git-fetch, you may also set up configuration options to
1946save typing; so, for example, after
1947
1948-------------------------------------------------
c64415e2 1949$ cat >>.git/config <<EOF
d19fbc3c
BF
1950[remote "public-repo"]
1951 url = ssh://yourserver.com/~you/proj.git
1952EOF
1953-------------------------------------------------
1954
1955you should be able to perform the above push with just
1956
1957-------------------------------------------------
1958$ git push public-repo master
1959-------------------------------------------------
1960
1961See the explanations of the remote.<name>.url, branch.<name>.remote,
5162e697 1962and remote.<name>.push options in linkgit:git-config[1] for
d19fbc3c
BF
1963details.
1964
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1965[[forcing-push]]
1966What to do when a push fails
1967~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1968
1969If a push would not result in a <<fast-forwards,fast forward>> of the
1970remote branch, then it will fail with an error like:
1971
1972-------------------------------------------------
1973error: remote 'refs/heads/master' is not an ancestor of
1974 local 'refs/heads/master'.
1975 Maybe you are not up-to-date and need to pull first?
1976error: failed to push to 'ssh://yourserver.com/~you/proj.git'
1977-------------------------------------------------
1978
1979This can happen, for example, if you:
1980
467c0197
JN
1981 - use `git-reset --hard` to remove already-published commits, or
1982 - use `git-commit --amend` to replace already-published commits
7cb192ea 1983 (as in <<fixing-a-mistake-by-rewriting-history>>), or
467c0197 1984 - use `git-rebase` to rebase any already-published commits (as
81eb417a
BF
1985 in <<using-git-rebase>>).
1986
1987You may force git-push to perform the update anyway by preceding the
1988branch name with a plus sign:
1989
1990-------------------------------------------------
1991$ git push ssh://yourserver.com/~you/proj.git +master
1992-------------------------------------------------
1993
1994Normally whenever a branch head in a public repository is modified, it
9e5d87d4 1995is modified to point to a descendant of the commit that it pointed to
81eb417a
BF
1996before. By forcing a push in this situation, you break that convention.
1997(See <<problems-with-rewriting-history>>.)
1998
1999Nevertheless, this is a common practice for people that need a simple
2000way to publish a work-in-progress patch series, and it is an acceptable
2001compromise as long as you warn other developers that this is how you
2002intend to manage the branch.
2003
2004It's also possible for a push to fail in this way when other people have
2005the right to push to the same repository. In that case, the correct
843c81dc
EH
2006solution is to retry the push after first updating your work: either by a
2007pull, or by a fetch followed by a rebase; see the
81eb417a 2008<<setting-up-a-shared-repository,next section>> and
6998e4db 2009linkgit:gitcvs-migration[7] for more.
81eb417a 2010
e34caace 2011[[setting-up-a-shared-repository]]
d19fbc3c 2012Setting up a shared repository
eda69449 2013~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
2014
2015Another way to collaborate is by using a model similar to that
2016commonly used in CVS, where several developers with special rights
2017all push to and pull from a single shared repository. See
6998e4db 2018linkgit:gitcvs-migration[7] for instructions on how to
d19fbc3c
BF
2019set this up.
2020
8fae2225
BF
2021However, while there is nothing wrong with git's support for shared
2022repositories, this mode of operation is not generally recommended,
2023simply because the mode of collaboration that git supports--by
2024exchanging patches and pulling from public repositories--has so many
2025advantages over the central shared repository:
2026
2027 - Git's ability to quickly import and merge patches allows a
2028 single maintainer to process incoming changes even at very
2029 high rates. And when that becomes too much, git-pull provides
2030 an easy way for that maintainer to delegate this job to other
2031 maintainers while still allowing optional review of incoming
2032 changes.
2033 - Since every developer's repository has the same complete copy
2034 of the project history, no repository is special, and it is
2035 trivial for another developer to take over maintenance of a
2036 project, either by mutual agreement, or because a maintainer
2037 becomes unresponsive or difficult to work with.
2038 - The lack of a central group of "committers" means there is
2039 less need for formal decisions about who is "in" and who is
2040 "out".
2041
e34caace 2042[[setting-up-gitweb]]
eda69449
BF
2043Allowing web browsing of a repository
2044~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 2045
a8cd1402
BF
2046The gitweb cgi script provides users an easy way to browse your
2047project's files and history without having to install git; see the file
04483524 2048gitweb/INSTALL in the git source tree for instructions on setting it up.
d19fbc3c 2049
e34caace 2050[[sharing-development-examples]]
b684f830
BF
2051Examples
2052--------
d19fbc3c 2053
9e2163ea
BF
2054[[maintaining-topic-branches]]
2055Maintaining topic branches for a Linux subsystem maintainer
2056~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2057
2058This describes how Tony Luck uses git in his role as maintainer of the
2059IA64 architecture for the Linux kernel.
2060
2061He uses two public branches:
2062
2063 - A "test" tree into which patches are initially placed so that they
2064 can get some exposure when integrated with other ongoing development.
2065 This tree is available to Andrew for pulling into -mm whenever he
2066 wants.
2067
2068 - A "release" tree into which tested patches are moved for final sanity
2069 checking, and as a vehicle to send them upstream to Linus (by sending
2070 him a "please pull" request.)
2071
2072He also uses a set of temporary branches ("topic branches"), each
2073containing a logical grouping of patches.
2074
2075To set this up, first create your work tree by cloning Linus's public
2076tree:
2077
2078-------------------------------------------------
2079$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work
2080$ cd work
2081-------------------------------------------------
2082
2083Linus's tree will be stored in the remote branch named origin/master,
5162e697
DM
2084and can be updated using linkgit:git-fetch[1]; you can track other
2085public trees using linkgit:git-remote[1] to set up a "remote" and
2086linkgit:git-fetch[1] to keep them up-to-date; see
6e30fb0c 2087<<repositories-and-branches>>.
9e2163ea
BF
2088
2089Now create the branches in which you are going to work; these start out
2090at the current tip of origin/master branch, and should be set up (using
5162e697 2091the --track option to linkgit:git-branch[1]) to merge changes in from
9e2163ea
BF
2092Linus by default.
2093
2094-------------------------------------------------
2095$ git branch --track test origin/master
2096$ git branch --track release origin/master
2097-------------------------------------------------
2098
5162e697 2099These can be easily kept up to date using linkgit:git-pull[1].
9e2163ea
BF
2100
2101-------------------------------------------------
2102$ git checkout test && git pull
2103$ git checkout release && git pull
2104-------------------------------------------------
2105
2106Important note! If you have any local changes in these branches, then
2107this merge will create a commit object in the history (with no local
2108changes git will simply do a "Fast forward" merge). Many people dislike
2109the "noise" that this creates in the Linux history, so you should avoid
2110doing this capriciously in the "release" branch, as these noisy commits
2111will become part of the permanent history when you ask Linus to pull
2112from the release branch.
2113
5162e697 2114A few configuration variables (see linkgit:git-config[1]) can
9e2163ea
BF
2115make it easy to push both branches to your public tree. (See
2116<<setting-up-a-public-repository>>.)
2117
2118-------------------------------------------------
2119$ cat >> .git/config <<EOF
2120[remote "mytree"]
2121 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git
2122 push = release
2123 push = test
2124EOF
2125-------------------------------------------------
2126
2127Then you can push both the test and release trees using
5162e697 2128linkgit:git-push[1]:
9e2163ea
BF
2129
2130-------------------------------------------------
2131$ git push mytree
2132-------------------------------------------------
2133
2134or push just one of the test and release branches using:
2135
2136-------------------------------------------------
2137$ git push mytree test
2138-------------------------------------------------
2139
2140or
2141
2142-------------------------------------------------
2143$ git push mytree release
2144-------------------------------------------------
2145
2146Now to apply some patches from the community. Think of a short
2147snappy name for a branch to hold this patch (or related group of
2148patches), and create a new branch from the current tip of Linus's
2149branch:
2150
2151-------------------------------------------------
2152$ git checkout -b speed-up-spinlocks origin
2153-------------------------------------------------
2154
2155Now you apply the patch(es), run some tests, and commit the change(s). If
2156the patch is a multi-part series, then you should apply each as a separate
2157commit to this branch.
2158
2159-------------------------------------------------
2160$ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2161-------------------------------------------------
2162
2163When you are happy with the state of this change, you can pull it into the
2164"test" branch in preparation to make it public:
2165
2166-------------------------------------------------
2167$ git checkout test && git pull . speed-up-spinlocks
2168-------------------------------------------------
2169
2170It is unlikely that you would have any conflicts here ... but you might if you
2171spent a while on this step and had also pulled new versions from upstream.
2172
2173Some time later when enough time has passed and testing done, you can pull the
2174same branch into the "release" tree ready to go upstream. This is where you
2175see the value of keeping each patch (or patch series) in its own branch. It
2176means that the patches can be moved into the "release" tree in any order.
2177
2178-------------------------------------------------
2179$ git checkout release && git pull . speed-up-spinlocks
2180-------------------------------------------------
2181
2182After a while, you will have a number of branches, and despite the
2183well chosen names you picked for each of them, you may forget what
2184they are for, or what status they are in. To get a reminder of what
2185changes are in a specific branch, use:
2186
2187-------------------------------------------------
467c0197 2188$ git log linux..branchname | git shortlog
9e2163ea
BF
2189-------------------------------------------------
2190
06ada152 2191To see whether it has already been merged into the test or release branches,
9e2163ea
BF
2192use:
2193
2194-------------------------------------------------
2195$ git log test..branchname
2196-------------------------------------------------
2197
2198or
2199
2200-------------------------------------------------
2201$ git log release..branchname
2202-------------------------------------------------
2203
06ada152 2204(If this branch has not yet been merged, you will see some log entries.
9e2163ea
BF
2205If it has been merged, then there will be no output.)
2206
2207Once a patch completes the great cycle (moving from test to release,
2208then pulled by Linus, and finally coming back into your local
06ada152 2209"origin/master" branch), the branch for this change is no longer needed.
9e2163ea
BF
2210You detect this when the output from:
2211
2212-------------------------------------------------
2213$ git log origin..branchname
2214-------------------------------------------------
2215
2216is empty. At this point the branch can be deleted:
2217
2218-------------------------------------------------
2219$ git branch -d branchname
2220-------------------------------------------------
2221
2222Some changes are so trivial that it is not necessary to create a separate
2223branch and then merge into each of the test and release branches. For
2224these changes, just apply directly to the "release" branch, and then
2225merge that into the "test" branch.
2226
2227To create diffstat and shortlog summaries of changes to include in a "please
2228pull" request to Linus you can use:
2229
2230-------------------------------------------------
2231$ git diff --stat origin..release
2232-------------------------------------------------
2233
2234and
2235
2236-------------------------------------------------
2237$ git log -p origin..release | git shortlog
2238-------------------------------------------------
2239
2240Here are some of the scripts that simplify all this even further.
2241
2242-------------------------------------------------
2243==== update script ====
2244# Update a branch in my GIT tree. If the branch to be updated
2245# is origin, then pull from kernel.org. Otherwise merge
2246# origin/master branch into test|release branch
2247
2248case "$1" in
2249test|release)
2250 git checkout $1 && git pull . origin
2251 ;;
2252origin)
fc74ecc1 2253 before=$(git rev-parse refs/remotes/origin/master)
9e2163ea 2254 git fetch origin
fc74ecc1 2255 after=$(git rev-parse refs/remotes/origin/master)
9e2163ea
BF
2256 if [ $before != $after ]
2257 then
2258 git log $before..$after | git shortlog
2259 fi
2260 ;;
2261*)
2262 echo "Usage: $0 origin|test|release" 1>&2
2263 exit 1
2264 ;;
2265esac
2266-------------------------------------------------
2267
2268-------------------------------------------------
2269==== merge script ====
2270# Merge a branch into either the test or release branch
2271
2272pname=$0
2273
2274usage()
2275{
2276 echo "Usage: $pname branch test|release" 1>&2
2277 exit 1
2278}
2279
fc74ecc1 2280git show-ref -q --verify -- refs/heads/"$1" || {
9e2163ea
BF
2281 echo "Can't see branch <$1>" 1>&2
2282 usage
fc74ecc1 2283}
9e2163ea
BF
2284
2285case "$2" in
2286test|release)
2287 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2288 then
2289 echo $1 already merged into $2 1>&2
2290 exit 1
2291 fi
2292 git checkout $2 && git pull . $1
2293 ;;
2294*)
2295 usage
2296 ;;
2297esac
2298-------------------------------------------------
2299
2300-------------------------------------------------
2301==== status script ====
2302# report on status of my ia64 GIT tree
2303
2304gb=$(tput setab 2)
2305rb=$(tput setab 1)
2306restore=$(tput setab 9)
2307
2308if [ `git rev-list test..release | wc -c` -gt 0 ]
2309then
2310 echo $rb Warning: commits in release that are not in test $restore
2311 git log test..release
2312fi
2313
fc74ecc1 2314for branch in `git show-ref --heads | sed 's|^.*/||'`
9e2163ea
BF
2315do
2316 if [ $branch = test -o $branch = release ]
2317 then
2318 continue
2319 fi
2320
2321 echo -n $gb ======= $branch ====== $restore " "
2322 status=
2323 for ref in test release origin/master
2324 do
2325 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2326 then
2327 status=$status${ref:0:1}
2328 fi
2329 done
2330 case $status in
2331 trl)
2332 echo $rb Need to pull into test $restore
2333 ;;
2334 rl)
2335 echo "In test"
2336 ;;
2337 l)
2338 echo "Waiting for linus"
2339 ;;
2340 "")
2341 echo $rb All done $restore
2342 ;;
2343 *)
2344 echo $rb "<$status>" $restore
2345 ;;
2346 esac
2347 git log origin/master..$branch | git shortlog
2348done
2349-------------------------------------------------
d19fbc3c 2350
d19fbc3c 2351
d19fbc3c 2352[[cleaning-up-history]]
4c63ff45
BF
2353Rewriting history and maintaining patch series
2354==============================================
2355
2356Normally commits are only added to a project, never taken away or
2357replaced. Git is designed with this assumption, and violating it will
2358cause git's merge machinery (for example) to do the wrong thing.
2359
2360However, there is a situation in which it can be useful to violate this
2361assumption.
2362
e34caace 2363[[patch-series]]
4c63ff45
BF
2364Creating the perfect patch series
2365---------------------------------
2366
2367Suppose you are a contributor to a large project, and you want to add a
2368complicated feature, and to present it to the other developers in a way
2369that makes it easy for them to read your changes, verify that they are
2370correct, and understand why you made each change.
2371
b181d57f 2372If you present all of your changes as a single patch (or commit), they
79c96c57 2373may find that it is too much to digest all at once.
4c63ff45
BF
2374
2375If you present them with the entire history of your work, complete with
2376mistakes, corrections, and dead ends, they may be overwhelmed.
2377
2378So the ideal is usually to produce a series of patches such that:
2379
2380 1. Each patch can be applied in order.
2381
2382 2. Each patch includes a single logical change, together with a
2383 message explaining the change.
2384
2385 3. No patch introduces a regression: after applying any initial
2386 part of the series, the resulting project still compiles and
2387 works, and has no bugs that it didn't have before.
2388
2389 4. The complete series produces the same end result as your own
2390 (probably much messier!) development process did.
2391
b181d57f
BF
2392We will introduce some tools that can help you do this, explain how to
2393use them, and then explain some of the problems that can arise because
2394you are rewriting history.
4c63ff45 2395
e34caace 2396[[using-git-rebase]]
4c63ff45
BF
2397Keeping a patch series up to date using git-rebase
2398--------------------------------------------------
2399
79c96c57
MC
2400Suppose that you create a branch "mywork" on a remote-tracking branch
2401"origin", and create some commits on top of it:
4c63ff45
BF
2402
2403-------------------------------------------------
2404$ git checkout -b mywork origin
2405$ vi file.txt
2406$ git commit
2407$ vi otherfile.txt
2408$ git commit
2409...
2410-------------------------------------------------
2411
2412You have performed no merges into mywork, so it is just a simple linear
2413sequence of patches on top of "origin":
2414
1dc71a91 2415................................................
4c63ff45
BF
2416 o--o--o <-- origin
2417 \
2418 o--o--o <-- mywork
1dc71a91 2419................................................
4c63ff45
BF
2420
2421Some more interesting work has been done in the upstream project, and
2422"origin" has advanced:
2423
1dc71a91 2424................................................
4c63ff45
BF
2425 o--o--O--o--o--o <-- origin
2426 \
2427 a--b--c <-- mywork
1dc71a91 2428................................................
4c63ff45
BF
2429
2430At this point, you could use "pull" to merge your changes back in;
2431the result would create a new merge commit, like this:
2432
1dc71a91 2433................................................
4c63ff45
BF
2434 o--o--O--o--o--o <-- origin
2435 \ \
2436 a--b--c--m <-- mywork
1dc71a91 2437................................................
a6080a0a 2438
4c63ff45
BF
2439However, if you prefer to keep the history in mywork a simple series of
2440commits without any merges, you may instead choose to use
5162e697 2441linkgit:git-rebase[1]:
4c63ff45
BF
2442
2443-------------------------------------------------
2444$ git checkout mywork
2445$ git rebase origin
2446-------------------------------------------------
2447
b181d57f 2448This will remove each of your commits from mywork, temporarily saving
51ef1daa 2449them as patches (in a directory named ".git/rebase-apply"), update mywork to
b181d57f
BF
2450point at the latest version of origin, then apply each of the saved
2451patches to the new mywork. The result will look like:
4c63ff45
BF
2452
2453
1dc71a91 2454................................................
4c63ff45
BF
2455 o--o--O--o--o--o <-- origin
2456 \
2457 a'--b'--c' <-- mywork
1dc71a91 2458................................................
4c63ff45 2459
b181d57f 2460In the process, it may discover conflicts. In that case it will stop
467c0197 2461and allow you to fix the conflicts; after fixing conflicts, use "git-add"
7a7d4ef6 2462to update the index with those contents, and then, instead of
b181d57f 2463running git-commit, just run
4c63ff45
BF
2464
2465-------------------------------------------------
2466$ git rebase --continue
2467-------------------------------------------------
2468
2469and git will continue applying the rest of the patches.
2470
b6cbca38 2471At any point you may use the `--abort` option to abort this process and
4c63ff45
BF
2472return mywork to the state it had before you started the rebase:
2473
2474-------------------------------------------------
2475$ git rebase --abort
2476-------------------------------------------------
2477
7cb192ea
BF
2478[[rewriting-one-commit]]
2479Rewriting a single commit
365aa199
BF
2480-------------------------
2481
7cb192ea 2482We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
365aa199
BF
2483most recent commit using
2484
2485-------------------------------------------------
2486$ git commit --amend
2487-------------------------------------------------
2488
2489which will replace the old commit by a new commit incorporating your
2490changes, giving you a chance to edit the old commit message first.
2491
5162e697 2492You can also use a combination of this and linkgit:git-rebase[1] to
7cb192ea
BF
2493replace a commit further back in your history and recreate the
2494intervening changes on top of it. First, tag the problematic commit
2495with
365aa199
BF
2496
2497-------------------------------------------------
2498$ git tag bad mywork~5
2499-------------------------------------------------
2500
2501(Either gitk or git-log may be useful for finding the commit.)
2502
25d9f3fa
BF
2503Then check out that commit, edit it, and rebase the rest of the series
2504on top of it (note that we could check out the commit on a temporary
2505branch, but instead we're using a <<detached-head,detached head>>):
365aa199
BF
2506
2507-------------------------------------------------
25d9f3fa 2508$ git checkout bad
365aa199
BF
2509$ # make changes here and update the index
2510$ git commit --amend
25d9f3fa 2511$ git rebase --onto HEAD bad mywork
365aa199
BF
2512-------------------------------------------------
2513
25d9f3fa
BF
2514When you're done, you'll be left with mywork checked out, with the top
2515patches on mywork reapplied on top of your modified commit. You can
365aa199
BF
2516then clean up with
2517
2518-------------------------------------------------
365aa199
BF
2519$ git tag -d bad
2520-------------------------------------------------
2521
2522Note that the immutable nature of git history means that you haven't really
2523"modified" existing commits; instead, you have replaced the old commits with
2524new commits having new object names.
2525
e34caace 2526[[reordering-patch-series]]
4c63ff45
BF
2527Reordering or selecting from a patch series
2528-------------------------------------------
2529
5162e697 2530Given one existing commit, the linkgit:git-cherry-pick[1] command
b181d57f
BF
2531allows you to apply the change introduced by that commit and create a
2532new commit that records it. So, for example, if "mywork" points to a
2533series of patches on top of "origin", you might do something like:
2534
2535-------------------------------------------------
2536$ git checkout -b mywork-new origin
2537$ gitk origin..mywork &
2538-------------------------------------------------
2539
06ada152 2540and browse through the list of patches in the mywork branch using gitk,
b181d57f 2541applying them (possibly in a different order) to mywork-new using
b6cbca38 2542cherry-pick, and possibly modifying them as you go using `commit --amend`.
5162e697 2543The linkgit:git-gui[1] command may also help as it allows you to
6e30fb0c
DK
2544individually select diff hunks for inclusion in the index (by
2545right-clicking on the diff hunk and choosing "Stage Hunk for Commit").
b181d57f
BF
2546
2547Another technique is to use git-format-patch to create a series of
2548patches, then reset the state to before the patches:
4c63ff45 2549
b181d57f
BF
2550-------------------------------------------------
2551$ git format-patch origin
2552$ git reset --hard origin
2553-------------------------------------------------
4c63ff45 2554
b181d57f 2555Then modify, reorder, or eliminate patches as preferred before applying
5162e697 2556them again with linkgit:git-am[1].
4c63ff45 2557
e34caace 2558[[patch-series-tools]]
4c63ff45
BF
2559Other tools
2560-----------
2561
02783075 2562There are numerous other tools, such as StGIT, which exist for the
79c96c57 2563purpose of maintaining a patch series. These are outside of the scope of
b181d57f 2564this manual.
4c63ff45 2565
e34caace 2566[[problems-with-rewriting-history]]
4c63ff45
BF
2567Problems with rewriting history
2568-------------------------------
2569
b181d57f
BF
2570The primary problem with rewriting the history of a branch has to do
2571with merging. Suppose somebody fetches your branch and merges it into
2572their branch, with a result something like this:
2573
1dc71a91 2574................................................
b181d57f
BF
2575 o--o--O--o--o--o <-- origin
2576 \ \
2577 t--t--t--m <-- their branch:
1dc71a91 2578................................................
b181d57f
BF
2579
2580Then suppose you modify the last three commits:
2581
1dc71a91 2582................................................
b181d57f
BF
2583 o--o--o <-- new head of origin
2584 /
2585 o--o--O--o--o--o <-- old head of origin
1dc71a91 2586................................................
b181d57f
BF
2587
2588If we examined all this history together in one repository, it will
2589look like:
2590
1dc71a91 2591................................................
b181d57f
BF
2592 o--o--o <-- new head of origin
2593 /
2594 o--o--O--o--o--o <-- old head of origin
2595 \ \
2596 t--t--t--m <-- their branch:
1dc71a91 2597................................................
b181d57f
BF
2598
2599Git has no way of knowing that the new head is an updated version of
2600the old head; it treats this situation exactly the same as it would if
2601two developers had independently done the work on the old and new heads
2602in parallel. At this point, if someone attempts to merge the new head
2603in to their branch, git will attempt to merge together the two (old and
2604new) lines of development, instead of trying to replace the old by the
2605new. The results are likely to be unexpected.
2606
2607You may still choose to publish branches whose history is rewritten,
2608and it may be useful for others to be able to fetch those branches in
2609order to examine or test them, but they should not attempt to pull such
2610branches into their own work.
2611
2612For true distributed development that supports proper merging,
2613published branches should never be rewritten.
2614
3fb00282
SP
2615[[bisect-merges]]
2616Why bisecting merge commits can be harder than bisecting linear history
2617-----------------------------------------------------------------------
2618
5162e697 2619The linkgit:git-bisect[1] command correctly handles history that
3fb00282
SP
2620includes merge commits. However, when the commit that it finds is a
2621merge commit, the user may need to work harder than usual to figure out
2622why that commit introduced a problem.
2623
2624Imagine this history:
2625
2626................................................
2627 ---Z---o---X---...---o---A---C---D
2628 \ /
2629 o---o---Y---...---o---B
2630................................................
2631
2632Suppose that on the upper line of development, the meaning of one
2633of the functions that exists at Z is changed at commit X. The
2634commits from Z leading to A change both the function's
2635implementation and all calling sites that exist at Z, as well
2636as new calling sites they add, to be consistent. There is no
2637bug at A.
2638
2639Suppose that in the meantime on the lower line of development somebody
2640adds a new calling site for that function at commit Y. The
2641commits from Z leading to B all assume the old semantics of that
2642function and the callers and the callee are consistent with each
2643other. There is no bug at B, either.
2644
2645Suppose further that the two development lines merge cleanly at C,
2646so no conflict resolution is required.
2647
2648Nevertheless, the code at C is broken, because the callers added
2649on the lower line of development have not been converted to the new
2650semantics introduced on the upper line of development. So if all
2651you know is that D is bad, that Z is good, and that
5162e697 2652linkgit:git-bisect[1] identifies C as the culprit, how will you
3fb00282
SP
2653figure out that the problem is due to this change in semantics?
2654
2655When the result of a git-bisect is a non-merge commit, you should
2656normally be able to discover the problem by examining just that commit.
2657Developers can make this easy by breaking their changes into small
2658self-contained commits. That won't help in the case above, however,
2659because the problem isn't obvious from examination of any single
2660commit; instead, a global view of the development is required. To
2661make matters worse, the change in semantics in the problematic
2662function may be just one small part of the changes in the upper
2663line of development.
2664
2665On the other hand, if instead of merging at C you had rebased the
2666history between Z to B on top of A, you would have gotten this
2667linear history:
2668
2669................................................................
2670 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2671................................................................
2672
2673Bisecting between Z and D* would hit a single culprit commit Y*,
2674and understanding why Y* was broken would probably be easier.
2675
2676Partly for this reason, many experienced git users, even when
2677working on an otherwise merge-heavy project, keep the history
2678linear by rebasing against the latest upstream version before
2679publishing.
2680
e34caace 2681[[advanced-branch-management]]
b181d57f
BF
2682Advanced branch management
2683==========================
4c63ff45 2684
e34caace 2685[[fetching-individual-branches]]
b181d57f
BF
2686Fetching individual branches
2687----------------------------
2688
5162e697 2689Instead of using linkgit:git-remote[1], you can also choose just
b181d57f
BF
2690to update one branch at a time, and to store it locally under an
2691arbitrary name:
2692
2693-------------------------------------------------
2694$ git fetch origin todo:my-todo-work
2695-------------------------------------------------
2696
2697The first argument, "origin", just tells git to fetch from the
2698repository you originally cloned from. The second argument tells git
2699to fetch the branch named "todo" from the remote repository, and to
2700store it locally under the name refs/heads/my-todo-work.
2701
2702You can also fetch branches from other repositories; so
2703
2704-------------------------------------------------
2705$ git fetch git://example.com/proj.git master:example-master
2706-------------------------------------------------
2707
2708will create a new branch named "example-master" and store in it the
2709branch named "master" from the repository at the given URL. If you
2710already have a branch named example-master, it will attempt to
59723040
BF
2711<<fast-forwards,fast-forward>> to the commit given by example.com's
2712master branch. In more detail:
b181d57f 2713
59723040
BF
2714[[fetch-fast-forwards]]
2715git fetch and fast-forwards
2716---------------------------
b181d57f 2717
467c0197 2718In the previous example, when updating an existing branch, "git-fetch"
7a7d4ef6 2719checks to make sure that the most recent commit on the remote
b181d57f
BF
2720branch is a descendant of the most recent commit on your copy of the
2721branch before updating your copy of the branch to point at the new
59723040 2722commit. Git calls this process a <<fast-forwards,fast forward>>.
b181d57f
BF
2723
2724A fast forward looks something like this:
2725
1dc71a91 2726................................................
b181d57f
BF
2727 o--o--o--o <-- old head of the branch
2728 \
2729 o--o--o <-- new head of the branch
1dc71a91 2730................................................
b181d57f
BF
2731
2732
2733In some cases it is possible that the new head will *not* actually be
2734a descendant of the old head. For example, the developer may have
2735realized she made a serious mistake, and decided to backtrack,
2736resulting in a situation like:
2737
1dc71a91 2738................................................
b181d57f
BF
2739 o--o--o--o--a--b <-- old head of the branch
2740 \
2741 o--o--o <-- new head of the branch
1dc71a91 2742................................................
b181d57f 2743
467c0197 2744In this case, "git-fetch" will fail, and print out a warning.
b181d57f
BF
2745
2746In that case, you can still force git to update to the new head, as
2747described in the following section. However, note that in the
2748situation above this may mean losing the commits labeled "a" and "b",
2749unless you've already created a reference of your own pointing to
2750them.
2751
e34caace 2752[[forcing-fetch]]
b1889c36 2753Forcing git-fetch to do non-fast-forward updates
b181d57f
BF
2754------------------------------------------------
2755
2756If git fetch fails because the new head of a branch is not a
2757descendant of the old head, you may force the update with:
2758
2759-------------------------------------------------
2760$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2761-------------------------------------------------
2762
c64415e2
BF
2763Note the addition of the "+" sign. Alternatively, you can use the "-f"
2764flag to force updates of all the fetched branches, as in:
2765
2766-------------------------------------------------
2767$ git fetch -f origin
2768-------------------------------------------------
2769
2770Be aware that commits that the old version of example/master pointed at
2771may be lost, as we saw in the previous section.
b181d57f 2772
e34caace 2773[[remote-branch-configuration]]
b181d57f
BF
2774Configuring remote branches
2775---------------------------
2776
2777We saw above that "origin" is just a shortcut to refer to the
79c96c57 2778repository that you originally cloned from. This information is
b181d57f 2779stored in git configuration variables, which you can see using
5162e697 2780linkgit:git-config[1]:
b181d57f
BF
2781
2782-------------------------------------------------
9d13bda3 2783$ git config -l
b181d57f
BF
2784core.repositoryformatversion=0
2785core.filemode=true
2786core.logallrefupdates=true
2787remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2788remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2789branch.master.remote=origin
2790branch.master.merge=refs/heads/master
2791-------------------------------------------------
2792
2793If there are other repositories that you also use frequently, you can
2794create similar configuration options to save typing; for example,
2795after
2796
2797-------------------------------------------------
9d13bda3 2798$ git config remote.example.url git://example.com/proj.git
b181d57f
BF
2799-------------------------------------------------
2800
2801then the following two commands will do the same thing:
2802
2803-------------------------------------------------
2804$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2805$ git fetch example master:refs/remotes/example/master
2806-------------------------------------------------
2807
2808Even better, if you add one more option:
2809
2810-------------------------------------------------
9d13bda3 2811$ git config remote.example.fetch master:refs/remotes/example/master
b181d57f
BF
2812-------------------------------------------------
2813
2814then the following commands will all do the same thing:
2815
2816-------------------------------------------------
52c80037
BF
2817$ git fetch git://example.com/proj.git master:refs/remotes/example/master
2818$ git fetch example master:refs/remotes/example/master
b181d57f
BF
2819$ git fetch example
2820-------------------------------------------------
2821
2822You can also add a "+" to force the update each time:
2823
2824-------------------------------------------------
9d13bda3 2825$ git config remote.example.fetch +master:ref/remotes/example/master
b181d57f
BF
2826-------------------------------------------------
2827
2828Don't do this unless you're sure you won't mind "git fetch" possibly
4f80b27d 2829throwing away commits on 'example/master'.
b181d57f
BF
2830
2831Also note that all of the above configuration can be performed by
2832directly editing the file .git/config instead of using
5162e697 2833linkgit:git-config[1].
b181d57f 2834
5162e697 2835See linkgit:git-config[1] for more details on the configuration
b181d57f 2836options mentioned above.
d19fbc3c 2837
d19fbc3c 2838
036f8199
BF
2839[[git-concepts]]
2840Git concepts
2841============
d19fbc3c 2842
036f8199
BF
2843Git is built on a small number of simple but powerful ideas. While it
2844is possible to get things done without understanding them, you will find
2845git much more intuitive if you do.
2846
2847We start with the most important, the <<def_object_database,object
2848database>> and the <<def_index,index>>.
b181d57f 2849
e34caace 2850[[the-object-database]]
b181d57f
BF
2851The Object Database
2852-------------------
2853
1bbf1c79
BF
2854
2855We already saw in <<understanding-commits>> that all commits are stored
2856under a 40-digit "object name". In fact, all the information needed to
2857represent the history of a project is stored in objects with such names.
2858In each case the name is calculated by taking the SHA1 hash of the
2859contents of the object. The SHA1 hash is a cryptographic hash function.
2860What that means to us is that it is impossible to find two different
2861objects with the same name. This has a number of advantages; among
2862others:
2863
2864- Git can quickly determine whether two objects are identical or not,
2865 just by comparing names.
06ada152 2866- Since object names are computed the same way in every repository, the
1bbf1c79
BF
2867 same content stored in two repositories will always be stored under
2868 the same name.
2869- Git can detect errors when it reads an object, by checking that the
2870 object's name is still the SHA1 hash of its contents.
2871
2872(See <<object-details>> for the details of the object formatting and
2873SHA1 calculation.)
2874
2875There are four different types of objects: "blob", "tree", "commit", and
2876"tag".
2877
2878- A <<def_blob_object,"blob" object>> is used to store file data.
843c81dc 2879- A <<def_tree_object,"tree" object>> ties one or more
1bbf1c79
BF
2880 "blob" objects into a directory structure. In addition, a tree object
2881 can refer to other tree objects, thus creating a directory hierarchy.
2882- A <<def_commit_object,"commit" object>> ties such directory hierarchies
2ef8ac1b 2883 together into a <<def_DAG,directed acyclic graph>> of revisions--each
1bbf1c79
BF
2884 commit contains the object name of exactly one tree designating the
2885 directory hierarchy at the time of the commit. In addition, a commit
2886 refers to "parent" commit objects that describe the history of how we
2887 arrived at that directory hierarchy.
2888- A <<def_tag_object,"tag" object>> symbolically identifies and can be
2889 used to sign other objects. It contains the object name and type of
2890 another object, a symbolic name (of course!) and, optionally, a
2891 signature.
b181d57f 2892
b181d57f
BF
2893The object types in some more detail:
2894
513d419c
BF
2895[[commit-object]]
2896Commit Object
2897~~~~~~~~~~~~~
b181d57f 2898
1bbf1c79
BF
2899The "commit" object links a physical state of a tree with a description
2900of how we got there and why. Use the --pretty=raw option to
5162e697 2901linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite
1bbf1c79
BF
2902commit:
2903
2904------------------------------------------------
2905$ git show -s --pretty=raw 2be7fcb476
2906commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2907tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2908parent 257a84d9d02e90447b149af58b271c19405edb6a
2909author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2910committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
2911
2912 Fix misspelling of 'suppress' in docs
2913
2914 Signed-off-by: Junio C Hamano <gitster@pobox.com>
2915------------------------------------------------
2916
2917As you can see, a commit is defined by:
2918
2919- a tree: The SHA1 name of a tree object (as defined below), representing
2920 the contents of a directory at a certain point in time.
2921- parent(s): The SHA1 name of some number of commits which represent the
9e5d87d4 2922 immediately previous step(s) in the history of the project. The
1bbf1c79
BF
2923 example above has one parent; merge commits may have more than
2924 one. A commit with no parents is called a "root" commit, and
2925 represents the initial revision of a project. Each project must have
2926 at least one root. A project can also have multiple roots, though
2927 that isn't common (or necessarily a good idea).
2928- an author: The name of the person responsible for this change, together
2929 with its date.
2930- a committer: The name of the person who actually created the commit,
2931 with the date it was done. This may be different from the author, for
2932 example, if the author was someone who wrote a patch and emailed it
2933 to the person who used it to create the commit.
2934- a comment describing this commit.
2935
2936Note that a commit does not itself contain any information about what
2937actually changed; all changes are calculated by comparing the contents
2938of the tree referred to by this commit with the trees associated with
2939its parents. In particular, git does not attempt to record file renames
2940explicitly, though it can identify cases where the existence of the same
2941file data at changing paths suggests a rename. (See, for example, the
5162e697 2942-M option to linkgit:git-diff[1]).
1bbf1c79 2943
5162e697 2944A commit is usually created by linkgit:git-commit[1], which creates a
1bbf1c79
BF
2945commit whose parent is normally the current HEAD, and whose tree is
2946taken from the content currently stored in the index.
b181d57f 2947
e34caace 2948[[tree-object]]
b181d57f 2949Tree Object
971aa71f 2950~~~~~~~~~~~
b181d57f 2951
5162e697
DM
2952The ever-versatile linkgit:git-show[1] command can also be used to
2953examine tree objects, but linkgit:git-ls-tree[1] will give you more
1bbf1c79
BF
2954details:
2955
2956------------------------------------------------
2957$ git ls-tree fb3a8bdd0ce
2958100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
2959100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
2960100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
2961040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
2962100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
2963100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
2964100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
2965100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
2966...
2967------------------------------------------------
2968
2969As you can see, a tree object contains a list of entries, each with a
2970mode, object type, SHA1 name, and name, sorted by name. It represents
2971the contents of a single directory tree.
2972
2973The object type may be a blob, representing the contents of a file, or
2974another tree, representing the contents of a subdirectory. Since trees
2975and blobs, like all other objects, are named by the SHA1 hash of their
2976contents, two trees have the same SHA1 name if and only if their
2977contents (including, recursively, the contents of all subdirectories)
2978are identical. This allows git to quickly determine the differences
2979between two related tree objects, since it can ignore any entries with
2980identical object names.
2981
2982(Note: in the presence of submodules, trees may also have commits as
6dd14366 2983entries. See <<submodules>> for documentation.)
1bbf1c79
BF
2984
2985Note that the files all have mode 644 or 755: git actually only pays
2986attention to the executable bit.
b181d57f 2987
513d419c
BF
2988[[blob-object]]
2989Blob Object
2990~~~~~~~~~~~
b181d57f 2991
5162e697 2992You can use linkgit:git-show[1] to examine the contents of a blob; take,
1bbf1c79 2993for example, the blob in the entry for "COPYING" from the tree above:
b181d57f 2994
1bbf1c79
BF
2995------------------------------------------------
2996$ git show 6ff87c4664
2997
2998 Note that the only valid version of the GPL as far as this project
2999 is concerned is _this_ particular version of the license (ie v2, not
3000 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
3001...
3002------------------------------------------------
b181d57f 3003
1bbf1c79
BF
3004A "blob" object is nothing but a binary blob of data. It doesn't refer
3005to anything else or have attributes of any kind.
3006
3007Since the blob is entirely defined by its data, if two files in a
3008directory tree (or in multiple different versions of the repository)
3009have the same contents, they will share the same blob object. The object
3010is totally independent of its location in the directory tree, and
3011renaming a file does not change the object that file is associated with.
3012
3013Note that any tree or blob object can be examined using
5162e697 3014linkgit:git-show[1] with the <revision>:<path> syntax. This can
1bbf1c79
BF
3015sometimes be useful for browsing the contents of a tree that is not
3016currently checked out.
b181d57f 3017
e34caace 3018[[trust]]
b181d57f 3019Trust
971aa71f 3020~~~~~
b181d57f 3021
1bbf1c79
BF
3022If you receive the SHA1 name of a blob from one source, and its contents
3023from another (possibly untrusted) source, you can still trust that those
3024contents are correct as long as the SHA1 name agrees. This is because
3025the SHA1 is designed so that it is infeasible to find different contents
3026that produce the same hash.
b181d57f 3027
1bbf1c79
BF
3028Similarly, you need only trust the SHA1 name of a top-level tree object
3029to trust the contents of the entire directory that it refers to, and if
3030you receive the SHA1 name of a commit from a trusted source, then you
3031can easily verify the entire history of commits reachable through
3032parents of that commit, and all of those contents of the trees referred
3033to by those commits.
b181d57f
BF
3034
3035So to introduce some real trust in the system, the only thing you need
3036to do is to digitally sign just 'one' special note, which includes the
3037name of a top-level commit. Your digital signature shows others
3038that you trust that commit, and the immutability of the history of
3039commits tells others that they can trust the whole history.
3040
3041In other words, you can easily validate a whole archive by just
3042sending out a single email that tells the people the name (SHA1 hash)
3043of the top commit, and digitally sign that email using something
3044like GPG/PGP.
3045
3046To assist in this, git also provides the tag object...
3047
e34caace 3048[[tag-object]]
b181d57f 3049Tag Object
971aa71f 3050~~~~~~~~~~
b181d57f 3051
1bbf1c79
BF
3052A tag object contains an object, object type, tag name, the name of the
3053person ("tagger") who created the tag, and a message, which may contain
843c81dc 3054a signature, as can be seen using linkgit:git-cat-file[1]:
b181d57f 3055
1bbf1c79
BF
3056------------------------------------------------
3057$ git cat-file tag v1.5.0
3058object 437b1b20df4b356c9342dac8d38849f24ef44f27
3059type commit
3060tag v1.5.0
3061tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000
3062
3063GIT 1.5.0
3064-----BEGIN PGP SIGNATURE-----
3065Version: GnuPG v1.4.6 (GNU/Linux)
3066
3067iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui
3068nLE/L9aUXdWeTFPron96DLA=
3069=2E+0
3070-----END PGP SIGNATURE-----
3071------------------------------------------------
b181d57f 3072
5162e697
DM
3073See the linkgit:git-tag[1] command to learn how to create and verify tag
3074objects. (Note that linkgit:git-tag[1] can also be used to create
1bbf1c79 3075"lightweight tags", which are not tag objects at all, but just simple
fc74ecc1 3076references whose names begin with "refs/tags/").
b181d57f 3077
09eff7b0
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3078[[pack-files]]
3079How git stores objects efficiently: pack files
3080~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3081
9644ffdd
BF
3082Newly created objects are initially created in a file named after the
3083object's SHA1 hash (stored in .git/objects).
09eff7b0
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3084
3085Unfortunately this system becomes inefficient once a project has a
3086lot of objects. Try this on an old project:
3087
3088------------------------------------------------
3089$ git count-objects
30906930 objects, 47620 kilobytes
3091------------------------------------------------
3092
3093The first number is the number of objects which are kept in
3094individual files. The second is the amount of space taken up by
3095those "loose" objects.
3096
3097You can save space and make git faster by moving these loose objects in
3098to a "pack file", which stores a group of objects in an efficient
3099compressed format; the details of how pack files are formatted can be
3100found in link:technical/pack-format.txt[technical/pack-format.txt].
3101
3102To put the loose objects into a pack, just run git repack:
3103
3104------------------------------------------------
3105$ git repack
3106Generating pack...
3107Done counting 6020 objects.
3108Deltifying 6020 objects.
3109 100% (6020/6020) done
3110Writing 6020 objects.
3111 100% (6020/6020) done
3112Total 6020, written 6020 (delta 4070), reused 0 (delta 0)
3113Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created.
3114------------------------------------------------
3115
3116You can then run
3117
3118------------------------------------------------
3119$ git prune
3120------------------------------------------------
3121
3122to remove any of the "loose" objects that are now contained in the
3123pack. This will also remove any unreferenced objects (which may be
467c0197 3124created when, for example, you use "git-reset" to remove a commit).
09eff7b0
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3125You can verify that the loose objects are gone by looking at the
3126.git/objects directory or by running
3127
3128------------------------------------------------
3129$ git count-objects
31300 objects, 0 kilobytes
3131------------------------------------------------
3132
3133Although the object files are gone, any commands that refer to those
3134objects will work exactly as they did before.
3135
5162e697 3136The linkgit:git-gc[1] command performs packing, pruning, and more for
09eff7b0
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3137you, so is normally the only high-level command you need.
3138
3139[[dangling-objects]]
3140Dangling objects
3141~~~~~~~~~~~~~~~~
3142
5162e697 3143The linkgit:git-fsck[1] command will sometimes complain about dangling
09eff7b0
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3144objects. They are not a problem.
3145
3146The most common cause of dangling objects is that you've rebased a
3147branch, or you have pulled from somebody else who rebased a branch--see
3148<<cleaning-up-history>>. In that case, the old head of the original
3149branch still exists, as does everything it pointed to. The branch
3150pointer itself just doesn't, since you replaced it with another one.
3151
3152There are also other situations that cause dangling objects. For
467c0197 3153example, a "dangling blob" may arise because you did a "git-add" of a
09eff7b0
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3154file, but then, before you actually committed it and made it part of the
3155bigger picture, you changed something else in that file and committed
2ef8ac1b 3156that *updated* thing--the old state that you added originally ends up
09eff7b0
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3157not being pointed to by any commit or tree, so it's now a dangling blob
3158object.
3159
3160Similarly, when the "recursive" merge strategy runs, and finds that
3161there are criss-cross merges and thus more than one merge base (which is
3162fairly unusual, but it does happen), it will generate one temporary
3163midway tree (or possibly even more, if you had lots of criss-crossing
3164merges and more than two merge bases) as a temporary internal merge
3165base, and again, those are real objects, but the end result will not end
3166up pointing to them, so they end up "dangling" in your repository.
3167
3168Generally, dangling objects aren't anything to worry about. They can
3169even be very useful: if you screw something up, the dangling objects can
3170be how you recover your old tree (say, you did a rebase, and realized
2ef8ac1b 3171that you really didn't want to--you can look at what dangling objects
09eff7b0
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3172you have, and decide to reset your head to some old dangling state).
3173
3174For commits, you can just use:
3175
3176------------------------------------------------
3177$ gitk <dangling-commit-sha-goes-here> --not --all
3178------------------------------------------------
3179
3180This asks for all the history reachable from the given commit but not
3181from any branch, tag, or other reference. If you decide it's something
3182you want, you can always create a new reference to it, e.g.,
3183
3184------------------------------------------------
3185$ git branch recovered-branch <dangling-commit-sha-goes-here>
3186------------------------------------------------
3187
3188For blobs and trees, you can't do the same, but you can still examine
3189them. You can just do
3190
3191------------------------------------------------
3192$ git show <dangling-blob/tree-sha-goes-here>
3193------------------------------------------------
3194
3195to show what the contents of the blob were (or, for a tree, basically
3196what the "ls" for that directory was), and that may give you some idea
3197of what the operation was that left that dangling object.
3198
3199Usually, dangling blobs and trees aren't very interesting. They're
3200almost always the result of either being a half-way mergebase (the blob
3201will often even have the conflict markers from a merge in it, if you
3202have had conflicting merges that you fixed up by hand), or simply
467c0197 3203because you interrupted a "git-fetch" with ^C or something like that,
09eff7b0
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3204leaving _some_ of the new objects in the object database, but just
3205dangling and useless.
3206
3207Anyway, once you are sure that you're not interested in any dangling
3208state, you can just prune all unreachable objects:
3209
3210------------------------------------------------
3211$ git prune
3212------------------------------------------------
3213
3214and they'll be gone. But you should only run "git prune" on a quiescent
2ef8ac1b 3215repository--it's kind of like doing a filesystem fsck recovery: you
09eff7b0
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3216don't want to do that while the filesystem is mounted.
3217
2ef8ac1b 3218(The same is true of "git-fsck" itself, btw, but since
09eff7b0
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3219git-fsck never actually *changes* the repository, it just reports
3220on what it found, git-fsck itself is never "dangerous" to run.
3221Running it while somebody is actually changing the repository can cause
3222confusing and scary messages, but it won't actually do anything bad. In
3223contrast, running "git prune" while somebody is actively changing the
3224repository is a *BAD* idea).
b181d57f 3225
1cdade2c
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3226[[recovering-from-repository-corruption]]
3227Recovering from repository corruption
3228~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
3229
3230By design, git treats data trusted to it with caution. However, even in
3231the absence of bugs in git itself, it is still possible that hardware or
3232operating system errors could corrupt data.
3233
3234The first defense against such problems is backups. You can back up a
3235git directory using clone, or just using cp, tar, or any other backup
3236mechanism.
3237
3238As a last resort, you can search for the corrupted objects and attempt
3239to replace them by hand. Back up your repository before attempting this
3240in case you corrupt things even more in the process.
3241
3242We'll assume that the problem is a single missing or corrupted blob,
9e5d87d4 3243which is sometimes a solvable problem. (Recovering missing trees and
1cdade2c
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3244especially commits is *much* harder).
3245
3246Before starting, verify that there is corruption, and figure out where
5162e697 3247it is with linkgit:git-fsck[1]; this may be time-consuming.
1cdade2c
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3248
3249Assume the output looks like this:
3250
3251------------------------------------------------
b1889c36 3252$ git fsck --full
1cdade2c
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3253broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
3254 to blob 4b9458b3786228369c63936db65827de3cc06200
3255missing blob 4b9458b3786228369c63936db65827de3cc06200
3256------------------------------------------------
3257
3258(Typically there will be some "dangling object" messages too, but they
3259aren't interesting.)
3260
3261Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6
3262points to it. If you could find just one copy of that missing blob
3263object, possibly in some other repository, you could move it into
3264.git/objects/4b/9458b3... and be done. Suppose you can't. You can
5162e697 3265still examine the tree that pointed to it with linkgit:git-ls-tree[1],
1cdade2c
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3266which might output something like:
3267
3268------------------------------------------------
3269$ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8
3270100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore
3271100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap
3272100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING
3273...
3274100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile
3275...
3276------------------------------------------------
3277
3278So now you know that the missing blob was the data for a file named
3279"myfile". And chances are you can also identify the directory--let's
3280say it's in "somedirectory". If you're lucky the missing copy might be
3281the same as the copy you have checked out in your working tree at
3282"somedirectory/myfile"; you can test whether that's right with
5162e697 3283linkgit:git-hash-object[1]:
1cdade2c
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3284
3285------------------------------------------------
3286$ git hash-object -w somedirectory/myfile
3287------------------------------------------------
3288
3289which will create and store a blob object with the contents of
3290somedirectory/myfile, and output the sha1 of that object. if you're
3291extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in
3292which case you've guessed right, and the corruption is fixed!
3293
3294Otherwise, you need more information. How do you tell which version of
3295the file has been lost?
3296
3297The easiest way to do this is with:
3298
3299------------------------------------------------
3300$ git log --raw --all --full-history -- somedirectory/myfile
3301------------------------------------------------
3302
3303Because you're asking for raw output, you'll now get something like
3304
3305------------------------------------------------
3306commit abc
3307Author:
3308Date:
3309...
3310:100644 100644 4b9458b... newsha... M somedirectory/myfile
3311
3312
3313commit xyz
3314Author:
3315Date:
3316
3317...
3318:100644 100644 oldsha... 4b9458b... M somedirectory/myfile
3319------------------------------------------------
3320
3321This tells you that the immediately preceding version of the file was
3322"newsha", and that the immediately following version was "oldsha".
3323You also know the commit messages that went with the change from oldsha
3324to 4b9458b and with the change from 4b9458b to newsha.
3325
3326If you've been committing small enough changes, you may now have a good
3327shot at reconstructing the contents of the in-between state 4b9458b.
3328
3329If you can do that, you can now recreate the missing object with
3330
3331------------------------------------------------
3332$ git hash-object -w <recreated-file>
3333------------------------------------------------
3334
3335and your repository is good again!
3336
1ab58e8d 3337(Btw, you could have ignored the fsck, and started with doing a
1cdade2c
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3338
3339------------------------------------------------
3340$ git log --raw --all
3341------------------------------------------------
3342
1ab58e8d
JH
3343and just looked for the sha of the missing object (4b9458b..) in that
3344whole thing. It's up to you - git does *have* a lot of information, it is
1cdade2c
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3345just missing one particular blob version.
3346
e34caace 3347[[the-index]]
1c097891
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3348The index
3349-----------
3350
3351The index is a binary file (generally kept in .git/index) containing a
3352sorted list of path names, each with permissions and the SHA1 of a blob
5162e697 3353object; linkgit:git-ls-files[1] can show you the contents of the index:
b181d57f 3354
1c097891
BF
3355-------------------------------------------------
3356$ git ls-files --stage
3357100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore
3358100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap
3359100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING
3360100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore
3361100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile
3362...
3363100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h
3364100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c
3365100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h
3366-------------------------------------------------
3367
3368Note that in older documentation you may see the index called the
3369"current directory cache" or just the "cache". It has three important
3370properties:
3371