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333d7d37 1Git User Manual
145e073b 2===============
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3
4Git is a fast distributed revision control system.
5
02783075 6This manual is designed to be readable by someone with basic UNIX
2de9b711 7command-line skills, but no previous knowledge of Git.
d19fbc3c 8
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9<<repositories-and-branches>> and <<exploring-git-history>> explain how
10to fetch and study a project using git--read these chapters to learn how
11to build and test a particular version of a software project, search for
12regressions, and so on.
ef89f701 13
2624d9a5 14People needing to do actual development will also want to read
aa971cb9 15<<Developing-With-git>> and <<sharing-development>>.
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16
17Further chapters cover more specialized topics.
18
d19fbc3c 19Comprehensive reference documentation is available through the man
b3d98887 20pages, or linkgit:git-help[1] command. For example, for the command
1249d8ad 21`git clone <repo>`, you can either use:
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22
23------------------------------------------------
24$ man git-clone
25------------------------------------------------
26
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27or:
28
29------------------------------------------------
30$ git help clone
31------------------------------------------------
32
33With the latter, you can use the manual viewer of your choice; see
34linkgit:git-help[1] for more information.
35
2de9b711 36See also <<git-quick-start>> for a brief overview of Git commands,
2624d9a5 37without any explanation.
b181d57f 38
99f171bb 39Finally, see <<todo>> for ways that you can help make this manual more
2624d9a5 40complete.
b181d57f 41
b181d57f 42
e34caace 43[[repositories-and-branches]]
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44Repositories and Branches
45=========================
46
e34caace 47[[how-to-get-a-git-repository]]
2de9b711 48How to get a Git repository
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49---------------------------
50
2de9b711 51It will be useful to have a Git repository to experiment with as you
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52read this manual.
53
5162e697 54The best way to get one is by using the linkgit:git-clone[1] command to
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55download a copy of an existing repository. If you don't already have a
56project in mind, here are some interesting examples:
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57
58------------------------------------------------
4b9ced27 59 # Git itself (approx. 40MB download):
d19fbc3c 60$ git clone git://git.kernel.org/pub/scm/git/git.git
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61 # the Linux kernel (approx. 640MB download):
62$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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63------------------------------------------------
64
65The initial clone may be time-consuming for a large project, but you
66will only need to clone once.
67
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68The clone command creates a new directory named after the project
69(`git` or `linux` in the examples above). After you cd into this
d19fbc3c 70directory, you will see that it contains a copy of the project files,
0c4a33b5 71called the <<def_working_tree,working tree>>, together with a special
1249d8ad 72top-level directory named `.git`, which contains all the information
0c4a33b5 73about the history of the project.
d19fbc3c 74
e34caace 75[[how-to-check-out]]
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76How to check out a different version of a project
77-------------------------------------------------
78
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79Git is best thought of as a tool for storing the history of a collection
80of files. It stores the history as a compressed collection of
2de9b711 81interrelated snapshots of the project's contents. In Git each such
a2ef9d63 82version is called a <<def_commit,commit>>.
d19fbc3c 83
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84Those snapshots aren't necessarily all arranged in a single line from
85oldest to newest; instead, work may simultaneously proceed along
57283291 86parallel lines of development, called <<def_branch,branches>>, which may
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87merge and diverge.
88
2de9b711 89A single Git repository can track development on multiple branches. It
0c4a33b5 90does this by keeping a list of <<def_head,heads>> which reference the
5162e697 91latest commit on each branch; the linkgit:git-branch[1] command shows
81b6c950 92you the list of branch heads:
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93
94------------------------------------------------
95$ git branch
96* master
97------------------------------------------------
98
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99A freshly cloned repository contains a single branch head, by default
100named "master", with the working directory initialized to the state of
101the project referred to by that branch head.
d19fbc3c 102
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103Most projects also use <<def_tag,tags>>. Tags, like heads, are
104references into the project's history, and can be listed using the
5162e697 105linkgit:git-tag[1] command:
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106
107------------------------------------------------
108$ git tag -l
109v2.6.11
110v2.6.11-tree
111v2.6.12
112v2.6.12-rc2
113v2.6.12-rc3
114v2.6.12-rc4
115v2.6.12-rc5
116v2.6.12-rc6
117v2.6.13
118...
119------------------------------------------------
120
fe4b3e59 121Tags are expected to always point at the same version of a project,
81b6c950 122while heads are expected to advance as development progresses.
fe4b3e59 123
81b6c950 124Create a new branch head pointing to one of these versions and check it
5162e697 125out using linkgit:git-checkout[1]:
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126
127------------------------------------------------
128$ git checkout -b new v2.6.13
129------------------------------------------------
130
131The working directory then reflects the contents that the project had
5162e697 132when it was tagged v2.6.13, and linkgit:git-branch[1] shows two
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133branches, with an asterisk marking the currently checked-out branch:
134
135------------------------------------------------
136$ git branch
137 master
138* new
139------------------------------------------------
140
141If you decide that you'd rather see version 2.6.17, you can modify
142the current branch to point at v2.6.17 instead, with
143
144------------------------------------------------
145$ git reset --hard v2.6.17
146------------------------------------------------
147
81b6c950 148Note that if the current branch head was your only reference to a
d19fbc3c 149particular point in history, then resetting that branch may leave you
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150with no way to find the history it used to point to; so use this command
151carefully.
d19fbc3c 152
e34caace 153[[understanding-commits]]
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154Understanding History: Commits
155------------------------------
156
157Every change in the history of a project is represented by a commit.
5162e697 158The linkgit:git-show[1] command shows the most recent commit on the
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159current branch:
160
161------------------------------------------------
162$ git show
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163commit 17cf781661e6d38f737f15f53ab552f1e95960d7
164Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)>
165Date: Tue Apr 19 14:11:06 2005 -0700
166
167 Remove duplicate getenv(DB_ENVIRONMENT) call
168
169 Noted by Tony Luck.
170
171diff --git a/init-db.c b/init-db.c
172index 65898fa..b002dc6 100644
173--- a/init-db.c
174+++ b/init-db.c
175@@ -7,7 +7,7 @@
d19fbc3c 176
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177 int main(int argc, char **argv)
178 {
179- char *sha1_dir = getenv(DB_ENVIRONMENT), *path;
180+ char *sha1_dir, *path;
181 int len, i;
182
183 if (mkdir(".git", 0755) < 0) {
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184------------------------------------------------
185
186As you can see, a commit shows who made the latest change, what they
187did, and why.
188
35121930 189Every commit has a 40-hexdigit id, sometimes called the "object name" or the
1249d8ad 190"SHA-1 id", shown on the first line of the `git show` output. You can usually
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191refer to a commit by a shorter name, such as a tag or a branch name, but this
192longer name can also be useful. Most importantly, it is a globally unique
193name for this commit: so if you tell somebody else the object name (for
194example in email), then you are guaranteed that name will refer to the same
195commit in their repository that it does in yours (assuming their repository
196has that commit at all). Since the object name is computed as a hash over the
197contents of the commit, you are guaranteed that the commit can never change
198without its name also changing.
199
2de9b711 200In fact, in <<git-concepts>> we shall see that everything stored in Git
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201history, including file data and directory contents, is stored in an object
202with a name that is a hash of its contents.
d19fbc3c 203
e34caace 204[[understanding-reachability]]
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205Understanding history: commits, parents, and reachability
206~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
207
208Every commit (except the very first commit in a project) also has a
209parent commit which shows what happened before this commit.
210Following the chain of parents will eventually take you back to the
211beginning of the project.
212
2de9b711 213However, the commits do not form a simple list; Git allows lines of
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214development to diverge and then reconverge, and the point where two
215lines of development reconverge is called a "merge". The commit
216representing a merge can therefore have more than one parent, with
217each parent representing the most recent commit on one of the lines
218of development leading to that point.
219
5162e697 220The best way to see how this works is using the linkgit:gitk[1]
2de9b711 221command; running gitk now on a Git repository and looking for merge
ddd4ddef 222commits will help understand how Git organizes history.
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223
224In the following, we say that commit X is "reachable" from commit Y
225if commit X is an ancestor of commit Y. Equivalently, you could say
02783075 226that Y is a descendant of X, or that there is a chain of parents
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227leading from commit Y to commit X.
228
e34caace 229[[history-diagrams]]
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230Understanding history: History diagrams
231~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 232
2de9b711 233We will sometimes represent Git history using diagrams like the one
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234below. Commits are shown as "o", and the links between them with
235lines drawn with - / and \. Time goes left to right:
236
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237
238................................................
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239 o--o--o <-- Branch A
240 /
241 o--o--o <-- master
242 \
243 o--o--o <-- Branch B
1dc71a91 244................................................
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245
246If we need to talk about a particular commit, the character "o" may
247be replaced with another letter or number.
248
e34caace 249[[what-is-a-branch]]
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250Understanding history: What is a branch?
251~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
252
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253When we need to be precise, we will use the word "branch" to mean a line
254of development, and "branch head" (or just "head") to mean a reference
255to the most recent commit on a branch. In the example above, the branch
256head named "A" is a pointer to one particular commit, but we refer to
257the line of three commits leading up to that point as all being part of
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258"branch A".
259
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260However, when no confusion will result, we often just use the term
261"branch" both for branches and for branch heads.
d19fbc3c 262
e34caace 263[[manipulating-branches]]
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264Manipulating branches
265---------------------
266
267Creating, deleting, and modifying branches is quick and easy; here's
268a summary of the commands:
269
1249d8ad 270`git branch`::
df47da75 271 list all branches.
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272`git branch <branch>`::
273 create a new branch named `<branch>`, referencing the same
df47da75 274 point in history as the current branch.
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275`git branch <branch> <start-point>`::
276 create a new branch named `<branch>`, referencing
277 `<start-point>`, which may be specified any way you like,
df47da75 278 including using a branch name or a tag name.
1249d8ad 279`git branch -d <branch>`::
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280 delete the branch `<branch>`; if the branch is not fully
281 merged in its upstream branch or contained in the current branch,
282 this command will fail with a warning.
1249d8ad 283`git branch -D <branch>`::
df47da75 284 delete the branch `<branch>` irrespective of its merged status.
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285`git checkout <branch>`::
286 make the current branch `<branch>`, updating the working
df47da75 287 directory to reflect the version referenced by `<branch>`.
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288`git checkout -b <new> <start-point>`::
289 create a new branch `<new>` referencing `<start-point>`, and
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290 check it out.
291
72a76c95 292The special symbol "HEAD" can always be used to refer to the current
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293branch. In fact, Git uses a file named `HEAD` in the `.git` directory
294to remember which branch is current:
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295
296------------------------------------------------
297$ cat .git/HEAD
298ref: refs/heads/master
299------------------------------------------------
300
25d9f3fa 301[[detached-head]]
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302Examining an old version without creating a new branch
303------------------------------------------------------
304
6127c086 305The `git checkout` command normally expects a branch head, but will also
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306accept an arbitrary commit; for example, you can check out the commit
307referenced by a tag:
308
309------------------------------------------------
310$ git checkout v2.6.17
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311Note: checking out 'v2.6.17'.
312
313You are in 'detached HEAD' state. You can look around, make experimental
314changes and commit them, and you can discard any commits you make in this
315state without impacting any branches by performing another checkout.
316
317If you want to create a new branch to retain commits you create, you may
318do so (now or later) by using -b with the checkout command again. Example:
319
320 git checkout -b new_branch_name
321
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322HEAD is now at 427abfa... Linux v2.6.17
323------------------------------------------------
324
a6e5ef7d 325The HEAD then refers to the SHA-1 of the commit instead of to a branch,
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326and git branch shows that you are no longer on a branch:
327
328------------------------------------------------
329$ cat .git/HEAD
330427abfa28afedffadfca9dd8b067eb6d36bac53f
953f3d6f 331$ git branch
95f9be55 332* (detached from v2.6.17)
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333 master
334------------------------------------------------
335
336In this case we say that the HEAD is "detached".
337
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338This is an easy way to check out a particular version without having to
339make up a name for the new branch. You can still create a new branch
340(or tag) for this version later if you decide to.
d19fbc3c 341
e34caace 342[[examining-remote-branches]]
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343Examining branches from a remote repository
344-------------------------------------------
345
346The "master" branch that was created at the time you cloned is a copy
347of the HEAD in the repository that you cloned from. That repository
348may also have had other branches, though, and your local repository
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349keeps branches which track each of those remote branches, called
350remote-tracking branches, which you
1249d8ad 351can view using the `-r` option to linkgit:git-branch[1]:
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352
353------------------------------------------------
354$ git branch -r
355 origin/HEAD
356 origin/html
357 origin/maint
358 origin/man
359 origin/master
360 origin/next
361 origin/pu
362 origin/todo
363------------------------------------------------
364
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365In this example, "origin" is called a remote repository, or "remote"
366for short. The branches of this repository are called "remote
367branches" from our point of view. The remote-tracking branches listed
368above were created based on the remote branches at clone time and will
1249d8ad 369be updated by `git fetch` (hence `git pull`) and `git push`. See
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370<<Updating-a-repository-With-git-fetch>> for details.
371
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372You might want to build on one of these remote-tracking branches
373on a branch of your own, just as you would for a tag:
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374
375------------------------------------------------
376$ git checkout -b my-todo-copy origin/todo
377------------------------------------------------
378
1249d8ad 379You can also check out `origin/todo` directly to examine it or
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380write a one-off patch. See <<detached-head,detached head>>.
381
2de9b711 382Note that the name "origin" is just the name that Git uses by default
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383to refer to the repository that you cloned from.
384
385[[how-git-stores-references]]
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386Naming branches, tags, and other references
387-------------------------------------------
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388
389Branches, remote-tracking branches, and tags are all references to
f60b9642 390commits. All references are named with a slash-separated path name
1249d8ad 391starting with `refs`; the names we've been using so far are actually
f60b9642 392shorthand:
d19fbc3c 393
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394 - The branch `test` is short for `refs/heads/test`.
395 - The tag `v2.6.18` is short for `refs/tags/v2.6.18`.
396 - `origin/master` is short for `refs/remotes/origin/master`.
d19fbc3c 397
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398The full name is occasionally useful if, for example, there ever
399exists a tag and a branch with the same name.
d19fbc3c 400
1249d8ad 401(Newly created refs are actually stored in the `.git/refs` directory,
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402under the path given by their name. However, for efficiency reasons
403they may also be packed together in a single file; see
5162e697 404linkgit:git-pack-refs[1]).
fc74ecc1 405
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406As another useful shortcut, the "HEAD" of a repository can be referred
407to just using the name of that repository. So, for example, "origin"
408is usually a shortcut for the HEAD branch in the repository "origin".
d19fbc3c 409
2de9b711 410For the complete list of paths which Git checks for references, and
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411the order it uses to decide which to choose when there are multiple
412references with the same shorthand name, see the "SPECIFYING
9d83e382 413REVISIONS" section of linkgit:gitrevisions[7].
d19fbc3c 414
aa971cb9 415[[Updating-a-repository-With-git-fetch]]
6127c086 416Updating a repository with git fetch
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417------------------------------------
418
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419After you clone a repository and commit a few changes of your own, you
420may wish to check the original repository for updates.
d19fbc3c 421
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422The `git-fetch` command, with no arguments, will update all of the
423remote-tracking branches to the latest version found in the original
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424repository. It will not touch any of your own branches--not even the
425"master" branch that was created for you on clone.
426
e34caace 427[[fetching-branches]]
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428Fetching branches from other repositories
429-----------------------------------------
430
431You can also track branches from repositories other than the one you
5162e697 432cloned from, using linkgit:git-remote[1]:
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433
434-------------------------------------------------
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435$ git remote add staging git://git.kernel.org/.../gregkh/staging.git
436$ git fetch staging
437...
438From git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging
439 * [new branch] master -> staging/master
440 * [new branch] staging-linus -> staging/staging-linus
441 * [new branch] staging-next -> staging/staging-next
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442-------------------------------------------------
443
444New remote-tracking branches will be stored under the shorthand name
34a25d4c 445that you gave `git remote add`, in this case `staging`:
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446
447-------------------------------------------------
448$ git branch -r
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449 origin/HEAD -> origin/master
450 origin/master
451 staging/master
452 staging/staging-linus
453 staging/staging-next
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454-------------------------------------------------
455
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456If you run `git fetch <remote>` later, the remote-tracking branches
457for the named `<remote>` will be updated.
d5cd5de4 458
1249d8ad 459If you examine the file `.git/config`, you will see that Git has added
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460a new stanza:
461
462-------------------------------------------------
463$ cat .git/config
464...
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465[remote "staging"]
466 url = git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/staging.git
467 fetch = +refs/heads/*:refs/remotes/staging/*
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468...
469-------------------------------------------------
470
2de9b711 471This is what causes Git to track the remote's branches; you may modify
1249d8ad 472or delete these configuration options by editing `.git/config` with a
fc90c536 473text editor. (See the "CONFIGURATION FILE" section of
5162e697 474linkgit:git-config[1] for details.)
d5cd5de4 475
e34caace 476[[exploring-git-history]]
2de9b711 477Exploring Git history
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478=====================
479
480Git is best thought of as a tool for storing the history of a
481collection of files. It does this by storing compressed snapshots of
1130845b 482the contents of a file hierarchy, together with "commits" which show
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483the relationships between these snapshots.
484
485Git provides extremely flexible and fast tools for exploring the
486history of a project.
487
aacd404e 488We start with one specialized tool that is useful for finding the
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489commit that introduced a bug into a project.
490
e34caace 491[[using-bisect]]
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492How to use bisect to find a regression
493--------------------------------------
494
495Suppose version 2.6.18 of your project worked, but the version at
496"master" crashes. Sometimes the best way to find the cause of such a
497regression is to perform a brute-force search through the project's
498history to find the particular commit that caused the problem. The
5162e697 499linkgit:git-bisect[1] command can help you do this:
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500
501-------------------------------------------------
502$ git bisect start
503$ git bisect good v2.6.18
504$ git bisect bad master
505Bisecting: 3537 revisions left to test after this
506[65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6]
507-------------------------------------------------
508
1249d8ad 509If you run `git branch` at this point, you'll see that Git has
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510temporarily moved you in "(no branch)". HEAD is now detached from any
511branch and points directly to a commit (with commit id 65934...) that
512is reachable from "master" but not from v2.6.18. Compile and test it,
513and see whether it crashes. Assume it does crash. Then:
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514
515-------------------------------------------------
516$ git bisect bad
517Bisecting: 1769 revisions left to test after this
518[7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings
519-------------------------------------------------
520
2de9b711 521checks out an older version. Continue like this, telling Git at each
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522stage whether the version it gives you is good or bad, and notice
523that the number of revisions left to test is cut approximately in
524half each time.
525
526After about 13 tests (in this case), it will output the commit id of
527the guilty commit. You can then examine the commit with
5162e697 528linkgit:git-show[1], find out who wrote it, and mail them your bug
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529report with the commit id. Finally, run
530
531-------------------------------------------------
532$ git bisect reset
533-------------------------------------------------
534
0e25790f 535to return you to the branch you were on before.
d19fbc3c 536
6127c086 537Note that the version which `git bisect` checks out for you at each
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538point is just a suggestion, and you're free to try a different
539version if you think it would be a good idea. For example,
540occasionally you may land on a commit that broke something unrelated;
541run
542
543-------------------------------------------------
04483524 544$ git bisect visualize
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545-------------------------------------------------
546
547which will run gitk and label the commit it chose with a marker that
843c81dc 548says "bisect". Choose a safe-looking commit nearby, note its commit
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549id, and check it out with:
550
551-------------------------------------------------
552$ git reset --hard fb47ddb2db...
553-------------------------------------------------
554
1249d8ad 555then test, run `bisect good` or `bisect bad` as appropriate, and
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556continue.
557
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558Instead of `git bisect visualize` and then `git reset --hard
559fb47ddb2db...`, you might just want to tell Git that you want to skip
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560the current commit:
561
562-------------------------------------------------
563$ git bisect skip
564-------------------------------------------------
565
2de9b711 566In this case, though, Git may not eventually be able to tell the first
a0178ae2 567bad one between some first skipped commits and a later bad commit.
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568
569There are also ways to automate the bisecting process if you have a
570test script that can tell a good from a bad commit. See
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571linkgit:git-bisect[1] for more information about this and other `git
572bisect` features.
0e25790f 573
e34caace 574[[naming-commits]]
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575Naming commits
576--------------
577
578We have seen several ways of naming commits already:
579
d55ae921 580 - 40-hexdigit object name
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581 - branch name: refers to the commit at the head of the given
582 branch
583 - tag name: refers to the commit pointed to by the given tag
584 (we've seen branches and tags are special cases of
585 <<how-git-stores-references,references>>).
586 - HEAD: refers to the head of the current branch
587
eb6ae7f4 588There are many more; see the "SPECIFYING REVISIONS" section of the
9d83e382 589linkgit:gitrevisions[7] man page for the complete list of ways to
d19fbc3c
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590name revisions. Some examples:
591
592-------------------------------------------------
d55ae921 593$ git show fb47ddb2 # the first few characters of the object name
d19fbc3c
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594 # are usually enough to specify it uniquely
595$ git show HEAD^ # the parent of the HEAD commit
596$ git show HEAD^^ # the grandparent
597$ git show HEAD~4 # the great-great-grandparent
598-------------------------------------------------
599
600Recall that merge commits may have more than one parent; by default,
1249d8ad 601`^` and `~` follow the first parent listed in the commit, but you can
d19fbc3c
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602also choose:
603
604-------------------------------------------------
605$ git show HEAD^1 # show the first parent of HEAD
606$ git show HEAD^2 # show the second parent of HEAD
607-------------------------------------------------
608
609In addition to HEAD, there are several other special names for
610commits:
611
612Merges (to be discussed later), as well as operations such as
6127c086 613`git reset`, which change the currently checked-out commit, generally
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614set ORIG_HEAD to the value HEAD had before the current operation.
615
6127c086
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616The `git fetch` operation always stores the head of the last fetched
617branch in FETCH_HEAD. For example, if you run `git fetch` without
d19fbc3c
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618specifying a local branch as the target of the operation
619
620-------------------------------------------------
621$ git fetch git://example.com/proj.git theirbranch
622-------------------------------------------------
623
624the fetched commits will still be available from FETCH_HEAD.
625
626When we discuss merges we'll also see the special name MERGE_HEAD,
627which refers to the other branch that we're merging in to the current
628branch.
629
5162e697 630The linkgit:git-rev-parse[1] command is a low-level command that is
d55ae921
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631occasionally useful for translating some name for a commit to the object
632name for that commit:
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633
634-------------------------------------------------
635$ git rev-parse origin
636e05db0fd4f31dde7005f075a84f96b360d05984b
637-------------------------------------------------
638
e34caace 639[[creating-tags]]
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640Creating tags
641-------------
642
643We can also create a tag to refer to a particular commit; after
644running
645
646-------------------------------------------------
04483524 647$ git tag stable-1 1b2e1d63ff
d19fbc3c
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648-------------------------------------------------
649
1249d8ad 650You can use `stable-1` to refer to the commit 1b2e1d63ff.
d19fbc3c 651
c64415e2
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652This creates a "lightweight" tag. If you would also like to include a
653comment with the tag, and possibly sign it cryptographically, then you
5162e697 654should create a tag object instead; see the linkgit:git-tag[1] man page
c64415e2 655for details.
d19fbc3c 656
e34caace 657[[browsing-revisions]]
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658Browsing revisions
659------------------
660
5162e697 661The linkgit:git-log[1] command can show lists of commits. On its
d19fbc3c
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662own, it shows all commits reachable from the parent commit; but you
663can also make more specific requests:
664
665-------------------------------------------------
666$ git log v2.5.. # commits since (not reachable from) v2.5
667$ git log test..master # commits reachable from master but not test
668$ git log master..test # ...reachable from test but not master
669$ git log master...test # ...reachable from either test or master,
670 # but not both
671$ git log --since="2 weeks ago" # commits from the last 2 weeks
672$ git log Makefile # commits which modify Makefile
673$ git log fs/ # ... which modify any file under fs/
674$ git log -S'foo()' # commits which add or remove any file data
675 # matching the string 'foo()'
676-------------------------------------------------
677
678And of course you can combine all of these; the following finds
1249d8ad 679commits since v2.5 which touch the `Makefile` or any file under `fs`:
d19fbc3c
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680
681-------------------------------------------------
682$ git log v2.5.. Makefile fs/
683-------------------------------------------------
684
685You can also ask git log to show patches:
686
687-------------------------------------------------
688$ git log -p
689-------------------------------------------------
690
1249d8ad 691See the `--pretty` option in the linkgit:git-log[1] man page for more
d19fbc3c
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692display options.
693
694Note that git log starts with the most recent commit and works
2de9b711 695backwards through the parents; however, since Git history can contain
3dff5379 696multiple independent lines of development, the particular order that
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697commits are listed in may be somewhat arbitrary.
698
e34caace 699[[generating-diffs]]
d19fbc3c
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700Generating diffs
701----------------
702
703You can generate diffs between any two versions using
5162e697 704linkgit:git-diff[1]:
d19fbc3c
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705
706-------------------------------------------------
707$ git diff master..test
708-------------------------------------------------
709
5b98d9bc
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710That will produce the diff between the tips of the two branches. If
711you'd prefer to find the diff from their common ancestor to test, you
712can use three dots instead of two:
713
714-------------------------------------------------
715$ git diff master...test
716-------------------------------------------------
717
718Sometimes what you want instead is a set of patches; for this you can
5162e697 719use linkgit:git-format-patch[1]:
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720
721-------------------------------------------------
722$ git format-patch master..test
723-------------------------------------------------
724
725will generate a file with a patch for each commit reachable from test
5b98d9bc 726but not from master.
d19fbc3c 727
e34caace 728[[viewing-old-file-versions]]
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729Viewing old file versions
730-------------------------
731
732You can always view an old version of a file by just checking out the
733correct revision first. But sometimes it is more convenient to be
734able to view an old version of a single file without checking
735anything out; this command does that:
736
737-------------------------------------------------
738$ git show v2.5:fs/locks.c
739-------------------------------------------------
740
741Before the colon may be anything that names a commit, and after it
2de9b711 742may be any path to a file tracked by Git.
d19fbc3c 743
e34caace 744[[history-examples]]
aec053bb
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745Examples
746--------
747
46acd3fa
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748[[counting-commits-on-a-branch]]
749Counting the number of commits on a branch
750~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
751
1249d8ad
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752Suppose you want to know how many commits you've made on `mybranch`
753since it diverged from `origin`:
46acd3fa
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754
755-------------------------------------------------
756$ git log --pretty=oneline origin..mybranch | wc -l
757-------------------------------------------------
758
759Alternatively, you may often see this sort of thing done with the
a6e5ef7d 760lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's
46acd3fa
BF
761of all the given commits:
762
763-------------------------------------------------
764$ git rev-list origin..mybranch | wc -l
765-------------------------------------------------
766
e34caace 767[[checking-for-equal-branches]]
aec053bb 768Check whether two branches point at the same history
2f99710c 769~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
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770
771Suppose you want to check whether two branches point at the same point
772in history.
773
774-------------------------------------------------
775$ git diff origin..master
776-------------------------------------------------
777
69f7ad73
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778will tell you whether the contents of the project are the same at the
779two branches; in theory, however, it's possible that the same project
780contents could have been arrived at by two different historical
d55ae921 781routes. You could compare the object names:
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782
783-------------------------------------------------
784$ git rev-list origin
785e05db0fd4f31dde7005f075a84f96b360d05984b
786$ git rev-list master
787e05db0fd4f31dde7005f075a84f96b360d05984b
788-------------------------------------------------
789
1249d8ad 790Or you could recall that the `...` operator selects all commits
ddd4ddef 791reachable from either one reference or the other but not
ddd2369c 792both; so
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793
794-------------------------------------------------
795$ git log origin...master
796-------------------------------------------------
797
798will return no commits when the two branches are equal.
799
e34caace 800[[finding-tagged-descendants]]
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801Find first tagged version including a given fix
802~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
aec053bb 803
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804Suppose you know that the commit e05db0fd fixed a certain problem.
805You'd like to find the earliest tagged release that contains that
806fix.
807
808Of course, there may be more than one answer--if the history branched
809after commit e05db0fd, then there could be multiple "earliest" tagged
810releases.
811
812You could just visually inspect the commits since e05db0fd:
813
814-------------------------------------------------
815$ gitk e05db0fd..
816-------------------------------------------------
817
ddd4ddef 818or you can use linkgit:git-name-rev[1], which will give the commit a
b181d57f
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819name based on any tag it finds pointing to one of the commit's
820descendants:
821
822-------------------------------------------------
04483524 823$ git name-rev --tags e05db0fd
b181d57f
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824e05db0fd tags/v1.5.0-rc1^0~23
825-------------------------------------------------
826
5162e697 827The linkgit:git-describe[1] command does the opposite, naming the
b181d57f
BF
828revision using a tag on which the given commit is based:
829
830-------------------------------------------------
831$ git describe e05db0fd
04483524 832v1.5.0-rc0-260-ge05db0f
b181d57f
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833-------------------------------------------------
834
835but that may sometimes help you guess which tags might come after the
836given commit.
837
838If you just want to verify whether a given tagged version contains a
5162e697 839given commit, you could use linkgit:git-merge-base[1]:
b181d57f
BF
840
841-------------------------------------------------
842$ git merge-base e05db0fd v1.5.0-rc1
843e05db0fd4f31dde7005f075a84f96b360d05984b
844-------------------------------------------------
845
846The merge-base command finds a common ancestor of the given commits,
847and always returns one or the other in the case where one is a
848descendant of the other; so the above output shows that e05db0fd
849actually is an ancestor of v1.5.0-rc1.
850
851Alternatively, note that
852
853-------------------------------------------------
4a7979ca 854$ git log v1.5.0-rc1..e05db0fd
b181d57f
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855-------------------------------------------------
856
4a7979ca 857will produce empty output if and only if v1.5.0-rc1 includes e05db0fd,
b181d57f 858because it outputs only commits that are not reachable from v1.5.0-rc1.
aec053bb 859
5162e697 860As yet another alternative, the linkgit:git-show-branch[1] command lists
4a7979ca 861the commits reachable from its arguments with a display on the left-hand
ddd4ddef
TA
862side that indicates which arguments that commit is reachable from.
863So, if you run something like
4a7979ca
BF
864
865-------------------------------------------------
866$ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2
867! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
868available
869 ! [v1.5.0-rc0] GIT v1.5.0 preview
870 ! [v1.5.0-rc1] GIT v1.5.0-rc1
871 ! [v1.5.0-rc2] GIT v1.5.0-rc2
872...
873-------------------------------------------------
874
ddd4ddef 875then a line like
4a7979ca
BF
876
877-------------------------------------------------
878+ ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if
879available
880-------------------------------------------------
881
ddd4ddef
TA
882shows that e05db0fd is reachable from itself, from v1.5.0-rc1,
883and from v1.5.0-rc2, and not from v1.5.0-rc0.
4a7979ca 884
629d9f78
BF
885[[showing-commits-unique-to-a-branch]]
886Showing commits unique to a given branch
887~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
4a7979ca 888
629d9f78 889Suppose you would like to see all the commits reachable from the branch
1249d8ad 890head named `master` but not from any other head in your repository.
d19fbc3c 891
629d9f78 892We can list all the heads in this repository with
5162e697 893linkgit:git-show-ref[1]:
d19fbc3c 894
629d9f78
BF
895-------------------------------------------------
896$ git show-ref --heads
897bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial
898db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint
899a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master
90024dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2
9011e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes
902-------------------------------------------------
d19fbc3c 903
1249d8ad 904We can get just the branch-head names, and remove `master`, with
629d9f78
BF
905the help of the standard utilities cut and grep:
906
907-------------------------------------------------
908$ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master'
909refs/heads/core-tutorial
910refs/heads/maint
911refs/heads/tutorial-2
912refs/heads/tutorial-fixes
913-------------------------------------------------
914
915And then we can ask to see all the commits reachable from master
916but not from these other heads:
917
918-------------------------------------------------
919$ gitk master --not $( git show-ref --heads | cut -d' ' -f2 |
920 grep -v '^refs/heads/master' )
921-------------------------------------------------
922
923Obviously, endless variations are possible; for example, to see all
924commits reachable from some head but not from any tag in the repository:
925
926-------------------------------------------------
c78974f7 927$ gitk $( git show-ref --heads ) --not $( git show-ref --tags )
629d9f78
BF
928-------------------------------------------------
929
9d83e382 930(See linkgit:gitrevisions[7] for explanations of commit-selecting
629d9f78
BF
931syntax such as `--not`.)
932
82c8bf28
BF
933[[making-a-release]]
934Creating a changelog and tarball for a software release
935~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
936
5162e697 937The linkgit:git-archive[1] command can create a tar or zip archive from
82c8bf28
BF
938any version of a project; for example:
939
940-------------------------------------------------
7ed1690c 941$ git archive -o latest.tar.gz --prefix=project/ HEAD
82c8bf28
BF
942-------------------------------------------------
943
7ed1690c
TK
944will use HEAD to produce a gzipped tar archive in which each filename
945is preceded by `project/`. The output file format is inferred from
946the output file extension if possible, see linkgit:git-archive[1] for
947details.
948
1249d8ad 949Versions of Git older than 1.7.7 don't know about the `tar.gz` format,
7ed1690c
TK
950you'll need to use gzip explicitly:
951
952-------------------------------------------------
953$ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz
954-------------------------------------------------
82c8bf28
BF
955
956If you're releasing a new version of a software project, you may want
957to simultaneously make a changelog to include in the release
958announcement.
959
960Linus Torvalds, for example, makes new kernel releases by tagging them,
961then running:
962
963-------------------------------------------------
964$ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7
965-------------------------------------------------
966
967where release-script is a shell script that looks like:
968
969-------------------------------------------------
970#!/bin/sh
971stable="$1"
972last="$2"
973new="$3"
974echo "# git tag v$new"
975echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz"
976echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz"
977echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new"
978echo "git shortlog --no-merges v$new ^v$last > ../ShortLog"
979echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new"
980-------------------------------------------------
981
982and then he just cut-and-pastes the output commands after verifying that
983they look OK.
4a7979ca 984
e1ba4c32 985[[Finding-commits-With-given-Content]]
187b0d80 986Finding commits referencing a file with given content
d5821de2 987~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
187b0d80
BF
988
989Somebody hands you a copy of a file, and asks which commits modified a
990file such that it contained the given content either before or after the
991commit. You can find out with this:
992
993-------------------------------------------------
477ff5b7 994$ git log --raw --abbrev=40 --pretty=oneline |
187b0d80
BF
995 grep -B 1 `git hash-object filename`
996-------------------------------------------------
997
998Figuring out why this works is left as an exercise to the (advanced)
5162e697
DM
999student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and
1000linkgit:git-hash-object[1] man pages may prove helpful.
187b0d80 1001
aa971cb9 1002[[Developing-With-git]]
2de9b711 1003Developing with Git
d19fbc3c
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1004===================
1005
e34caace 1006[[telling-git-your-name]]
2de9b711 1007Telling Git your name
d19fbc3c
BF
1008---------------------
1009
632cc3e6
TK
1010Before creating any commits, you should introduce yourself to Git.
1011The easiest way to do so is to use linkgit:git-config[1]:
1012
1013------------------------------------------------
1014$ git config --global user.name 'Your Name Comes Here'
1015$ git config --global user.email 'you@yourdomain.example.com'
1016------------------------------------------------
1017
1018Which will add the following to a file named `.gitconfig` in your
1019home directory:
d19fbc3c
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1020
1021------------------------------------------------
d19fbc3c
BF
1022[user]
1023 name = Your Name Comes Here
1024 email = you@yourdomain.example.com
d19fbc3c
BF
1025------------------------------------------------
1026
632cc3e6
TK
1027See the "CONFIGURATION FILE" section of linkgit:git-config[1] for
1028details on the configuration file. The file is plain text, so you can
1029also edit it with your favorite editor.
fc90c536 1030
d19fbc3c 1031
e34caace 1032[[creating-a-new-repository]]
d19fbc3c
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1033Creating a new repository
1034-------------------------
1035
1036Creating a new repository from scratch is very easy:
1037
1038-------------------------------------------------
1039$ mkdir project
1040$ cd project
f1d2b477 1041$ git init
d19fbc3c
BF
1042-------------------------------------------------
1043
1044If you have some initial content (say, a tarball):
1045
1046-------------------------------------------------
0ddd93b2 1047$ tar xzvf project.tar.gz
d19fbc3c 1048$ cd project
f1d2b477 1049$ git init
d19fbc3c
BF
1050$ git add . # include everything below ./ in the first commit:
1051$ git commit
1052-------------------------------------------------
1053
1054[[how-to-make-a-commit]]
ae25c67a 1055How to make a commit
d19fbc3c
BF
1056--------------------
1057
1058Creating a new commit takes three steps:
1059
1060 1. Making some changes to the working directory using your
1061 favorite editor.
2de9b711
TA
1062 2. Telling Git about your changes.
1063 3. Creating the commit using the content you told Git about
d19fbc3c
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1064 in step 2.
1065
1066In practice, you can interleave and repeat steps 1 and 2 as many
1067times as you want: in order to keep track of what you want committed
2de9b711 1068at step 3, Git maintains a snapshot of the tree's contents in a
d19fbc3c
BF
1069special staging area called "the index."
1070
01997b4a 1071At the beginning, the content of the index will be identical to
1249d8ad 1072that of the HEAD. The command `git diff --cached`, which shows
01997b4a
BF
1073the difference between the HEAD and the index, should therefore
1074produce no output at that point.
eb6ae7f4 1075
d19fbc3c
BF
1076Modifying the index is easy:
1077
d39765b1 1078To update the index with the contents of a new or modified file, use
d19fbc3c
BF
1079
1080-------------------------------------------------
1081$ git add path/to/file
1082-------------------------------------------------
1083
d39765b1 1084To remove a file from the index and from the working tree, use
d19fbc3c
BF
1085
1086-------------------------------------------------
1087$ git rm path/to/file
1088-------------------------------------------------
1089
1090After each step you can verify that
1091
1092-------------------------------------------------
1093$ git diff --cached
1094-------------------------------------------------
1095
1096always shows the difference between the HEAD and the index file--this
1097is what you'd commit if you created the commit now--and that
1098
1099-------------------------------------------------
1100$ git diff
1101-------------------------------------------------
1102
1103shows the difference between the working tree and the index file.
1104
1249d8ad 1105Note that `git add` always adds just the current contents of a file
d19fbc3c 1106to the index; further changes to the same file will be ignored unless
6127c086 1107you run `git add` on the file again.
d19fbc3c
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1108
1109When you're ready, just run
1110
1111-------------------------------------------------
1112$ git commit
1113-------------------------------------------------
1114
2de9b711 1115and Git will prompt you for a commit message and then create the new
3dff5379 1116commit. Check to make sure it looks like what you expected with
d19fbc3c
BF
1117
1118-------------------------------------------------
1119$ git show
1120-------------------------------------------------
1121
1122As a special shortcut,
a6080a0a 1123
d19fbc3c
BF
1124-------------------------------------------------
1125$ git commit -a
1126-------------------------------------------------
1127
1128will update the index with any files that you've modified or removed
1129and create a commit, all in one step.
1130
1131A number of commands are useful for keeping track of what you're
1132about to commit:
1133
1134-------------------------------------------------
1135$ git diff --cached # difference between HEAD and the index; what
1130845b 1136 # would be committed if you ran "commit" now.
d19fbc3c
BF
1137$ git diff # difference between the index file and your
1138 # working directory; changes that would not
1139 # be included if you ran "commit" now.
c64415e2
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1140$ git diff HEAD # difference between HEAD and working tree; what
1141 # would be committed if you ran "commit -a" now.
d19fbc3c
BF
1142$ git status # a brief per-file summary of the above.
1143-------------------------------------------------
1144
5162e697 1145You can also use linkgit:git-gui[1] to create commits, view changes in
407c0c87
BF
1146the index and the working tree files, and individually select diff hunks
1147for inclusion in the index (by right-clicking on the diff hunk and
1148choosing "Stage Hunk For Commit").
1149
e34caace 1150[[creating-good-commit-messages]]
ae25c67a 1151Creating good commit messages
d19fbc3c
BF
1152-----------------------------
1153
1154Though not required, it's a good idea to begin the commit message
1155with a single short (less than 50 character) line summarizing the
1156change, followed by a blank line and then a more thorough
52ffe995
JW
1157description. The text up to the first blank line in a commit
1158message is treated as the commit title, and that title is used
2de9b711 1159throughout Git. For example, linkgit:git-format-patch[1] turns a
52ffe995
JW
1160commit into email, and it uses the title on the Subject line and the
1161rest of the commit in the body.
1162
d19fbc3c 1163
2dc53617
JH
1164[[ignoring-files]]
1165Ignoring files
1166--------------
1167
2de9b711 1168A project will often generate files that you do 'not' want to track with Git.
2dc53617 1169This typically includes files generated by a build process or temporary
2de9b711 1170backup files made by your editor. Of course, 'not' tracking files with Git
6127c086 1171is just a matter of 'not' calling `git add` on them. But it quickly becomes
2dc53617 1172annoying to have these untracked files lying around; e.g. they make
dcb11263
CJ
1173`git add .` practically useless, and they keep showing up in the output of
1174`git status`.
2dc53617 1175
1249d8ad
TK
1176You can tell Git to ignore certain files by creating a file called
1177`.gitignore` in the top level of your working directory, with contents
1178such as:
2dc53617
JH
1179
1180-------------------------------------------------
1181# Lines starting with '#' are considered comments.
464a8a7a 1182# Ignore any file named foo.txt.
2dc53617
JH
1183foo.txt
1184# Ignore (generated) html files,
1185*.html
1186# except foo.html which is maintained by hand.
1187!foo.html
1188# Ignore objects and archives.
1189*.[oa]
1190-------------------------------------------------
1191
5162e697 1192See linkgit:gitignore[5] for a detailed explanation of the syntax. You can
464a8a7a
BF
1193also place .gitignore files in other directories in your working tree, and they
1194will apply to those directories and their subdirectories. The `.gitignore`
1195files can be added to your repository like any other files (just run `git add
1196.gitignore` and `git commit`, as usual), which is convenient when the exclude
1197patterns (such as patterns matching build output files) would also make sense
1198for other users who clone your repository.
1199
1200If you wish the exclude patterns to affect only certain repositories
1201(instead of every repository for a given project), you may instead put
1249d8ad 1202them in a file in your repository named `.git/info/exclude`, or in any
da0005b8 1203file specified by the `core.excludesFile` configuration variable.
1249d8ad
TK
1204Some Git commands can also take exclude patterns directly on the
1205command line. See linkgit:gitignore[5] for the details.
2dc53617 1206
e34caace 1207[[how-to-merge]]
ae25c67a 1208How to merge
d19fbc3c
BF
1209------------
1210
1211You can rejoin two diverging branches of development using
5162e697 1212linkgit:git-merge[1]:
d19fbc3c
BF
1213
1214-------------------------------------------------
1215$ git merge branchname
1216-------------------------------------------------
1217
1249d8ad 1218merges the development in the branch `branchname` into the current
e63ec003
MM
1219branch.
1220
1249d8ad 1221A merge is made by combining the changes made in `branchname` and the
e63ec003
MM
1222changes made up to the latest commit in your current branch since
1223their histories forked. The work tree is overwritten by the result of
1224the merge when this combining is done cleanly, or overwritten by a
1225half-merged results when this combining results in conflicts.
1226Therefore, if you have uncommitted changes touching the same files as
1227the ones impacted by the merge, Git will refuse to proceed. Most of
1228the time, you will want to commit your changes before you can merge,
1229and if you don't, then linkgit:git-stash[1] can take these changes
1230away while you're doing the merge, and reapply them afterwards.
1231
6a5d0b0a 1232If the changes are independent enough, Git will automatically complete
e63ec003
MM
1233the merge and commit the result (or reuse an existing commit in case
1234of <<fast-forwards,fast-forward>>, see below). On the other hand,
1235if there are conflicts--for example, if the same file is
d19fbc3c
BF
1236modified in two different ways in the remote branch and the local
1237branch--then you are warned; the output may look something like this:
1238
1239-------------------------------------------------
fabbd8f6
BF
1240$ git merge next
1241 100% (4/4) done
1242Auto-merged file.txt
d19fbc3c
BF
1243CONFLICT (content): Merge conflict in file.txt
1244Automatic merge failed; fix conflicts and then commit the result.
1245-------------------------------------------------
1246
1247Conflict markers are left in the problematic files, and after
1248you resolve the conflicts manually, you can update the index
2de9b711 1249with the contents and run Git commit, as you normally would when
d19fbc3c
BF
1250creating a new file.
1251
1252If you examine the resulting commit using gitk, you will see that it
1253has two parents, one pointing to the top of the current branch, and
1254one to the top of the other branch.
1255
d19fbc3c
BF
1256[[resolving-a-merge]]
1257Resolving a merge
1258-----------------
1259
2de9b711 1260When a merge isn't resolved automatically, Git leaves the index and
d19fbc3c
BF
1261the working tree in a special state that gives you all the
1262information you need to help resolve the merge.
1263
1264Files with conflicts are marked specially in the index, so until you
5162e697 1265resolve the problem and update the index, linkgit:git-commit[1] will
ef561ac7 1266fail:
d19fbc3c
BF
1267
1268-------------------------------------------------
1269$ git commit
1270file.txt: needs merge
1271-------------------------------------------------
1272
5162e697 1273Also, linkgit:git-status[1] will list those files as "unmerged", and the
ef561ac7
BF
1274files with conflicts will have conflict markers added, like this:
1275
1276-------------------------------------------------
1277<<<<<<< HEAD:file.txt
1278Hello world
1279=======
1280Goodbye
1281>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1282-------------------------------------------------
1283
1284All you need to do is edit the files to resolve the conflicts, and then
1285
1286-------------------------------------------------
1287$ git add file.txt
1288$ git commit
1289-------------------------------------------------
1290
1291Note that the commit message will already be filled in for you with
1292some information about the merge. Normally you can just use this
1293default message unchanged, but you may add additional commentary of
1294your own if desired.
1295
2de9b711 1296The above is all you need to know to resolve a simple merge. But Git
ef561ac7
BF
1297also provides more information to help resolve conflicts:
1298
e34caace 1299[[conflict-resolution]]
ef561ac7
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1300Getting conflict-resolution help during a merge
1301~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1302
2de9b711 1303All of the changes that Git was able to merge automatically are
5162e697 1304already added to the index file, so linkgit:git-diff[1] shows only
ef561ac7 1305the conflicts. It uses an unusual syntax:
d19fbc3c
BF
1306
1307-------------------------------------------------
1308$ git diff
1309diff --cc file.txt
1310index 802992c,2b60207..0000000
1311--- a/file.txt
1312+++ b/file.txt
1313@@@ -1,1 -1,1 +1,5 @@@
1314++<<<<<<< HEAD:file.txt
1315 +Hello world
1316++=======
1317+ Goodbye
1318++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt
1319-------------------------------------------------
1320
1130845b 1321Recall that the commit which will be committed after we resolve this
d19fbc3c
BF
1322conflict will have two parents instead of the usual one: one parent
1323will be HEAD, the tip of the current branch; the other will be the
1324tip of the other branch, which is stored temporarily in MERGE_HEAD.
1325
ef561ac7
BF
1326During the merge, the index holds three versions of each file. Each of
1327these three "file stages" represents a different version of the file:
1328
1329-------------------------------------------------
1330$ git show :1:file.txt # the file in a common ancestor of both branches
4209752d
JH
1331$ git show :2:file.txt # the version from HEAD.
1332$ git show :3:file.txt # the version from MERGE_HEAD.
ef561ac7
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1333-------------------------------------------------
1334
4209752d
JH
1335When you ask linkgit:git-diff[1] to show the conflicts, it runs a
1336three-way diff between the conflicted merge results in the work tree with
1337stages 2 and 3 to show only hunks whose contents come from both sides,
1338mixed (in other words, when a hunk's merge results come only from stage 2,
1339that part is not conflicting and is not shown. Same for stage 3).
ef561ac7
BF
1340
1341The diff above shows the differences between the working-tree version of
1342file.txt and the stage 2 and stage 3 versions. So instead of preceding
1249d8ad 1343each line by a single `+` or `-`, it now uses two columns: the first
ef561ac7
BF
1344column is used for differences between the first parent and the working
1345directory copy, and the second for differences between the second parent
1346and the working directory copy. (See the "COMBINED DIFF FORMAT" section
5162e697 1347of linkgit:git-diff-files[1] for a details of the format.)
ef561ac7
BF
1348
1349After resolving the conflict in the obvious way (but before updating the
1350index), the diff will look like:
d19fbc3c
BF
1351
1352-------------------------------------------------
1353$ git diff
1354diff --cc file.txt
1355index 802992c,2b60207..0000000
1356--- a/file.txt
1357+++ b/file.txt
1358@@@ -1,1 -1,1 +1,1 @@@
1359- Hello world
1360 -Goodbye
1361++Goodbye world
1362-------------------------------------------------
1363
1364This shows that our resolved version deleted "Hello world" from the
1365first parent, deleted "Goodbye" from the second parent, and added
1366"Goodbye world", which was previously absent from both.
1367
ef561ac7
BF
1368Some special diff options allow diffing the working directory against
1369any of these stages:
1370
1371-------------------------------------------------
1372$ git diff -1 file.txt # diff against stage 1
1373$ git diff --base file.txt # same as the above
1374$ git diff -2 file.txt # diff against stage 2
1375$ git diff --ours file.txt # same as the above
1376$ git diff -3 file.txt # diff against stage 3
1377$ git diff --theirs file.txt # same as the above.
1378-------------------------------------------------
1379
0cafe944 1380The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help
ef561ac7 1381for merges:
d19fbc3c
BF
1382
1383-------------------------------------------------
1384$ git log --merge
ef561ac7 1385$ gitk --merge
d19fbc3c
BF
1386-------------------------------------------------
1387
ef561ac7
BF
1388These will display all commits which exist only on HEAD or on
1389MERGE_HEAD, and which touch an unmerged file.
d19fbc3c 1390
5162e697 1391You may also use linkgit:git-mergetool[1], which lets you merge the
c7719fbe 1392unmerged files using external tools such as Emacs or kdiff3.
c64415e2 1393
ef561ac7 1394Each time you resolve the conflicts in a file and update the index:
d19fbc3c
BF
1395
1396-------------------------------------------------
1397$ git add file.txt
d19fbc3c
BF
1398-------------------------------------------------
1399
ef561ac7 1400the different stages of that file will be "collapsed", after which
6127c086 1401`git diff` will (by default) no longer show diffs for that file.
d19fbc3c
BF
1402
1403[[undoing-a-merge]]
ae25c67a 1404Undoing a merge
d19fbc3c
BF
1405---------------
1406
1407If you get stuck and decide to just give up and throw the whole mess
1408away, you can always return to the pre-merge state with
1409
1410-------------------------------------------------
1411$ git reset --hard HEAD
1412-------------------------------------------------
1413
1130845b 1414Or, if you've already committed the merge that you want to throw away,
d19fbc3c
BF
1415
1416-------------------------------------------------
1c73bb0e 1417$ git reset --hard ORIG_HEAD
d19fbc3c
BF
1418-------------------------------------------------
1419
1420However, this last command can be dangerous in some cases--never
1421throw away a commit you have already committed if that commit may
1422itself have been merged into another branch, as doing so may confuse
1423further merges.
1424
e34caace 1425[[fast-forwards]]
d19fbc3c
BF
1426Fast-forward merges
1427-------------------
1428
1429There is one special case not mentioned above, which is treated
1430differently. Normally, a merge results in a merge commit, with two
1431parents, one pointing at each of the two lines of development that
1432were merged.
1433
b2af4829
XF
1434However, if the current branch is an ancestor of the other--so every commit
1435present in the current branch is already contained in the other branch--then Git
1436just performs a "fast-forward"; the head of the current branch is moved forward
1437to point at the head of the merged-in branch, without any new commits being
1438created.
d19fbc3c 1439
e34caace 1440[[fixing-mistakes]]
b684f830
BF
1441Fixing mistakes
1442---------------
1443
1444If you've messed up the working tree, but haven't yet committed your
1445mistake, you can return the entire working tree to the last committed
1446state with
1447
1448-------------------------------------------------
1449$ git reset --hard HEAD
1450-------------------------------------------------
1451
1452If you make a commit that you later wish you hadn't, there are two
1453fundamentally different ways to fix the problem:
1454
1455 1. You can create a new commit that undoes whatever was done
93cbbd71 1456 by the old commit. This is the correct thing if your
b684f830
BF
1457 mistake has already been made public.
1458
1459 2. You can go back and modify the old commit. You should
1460 never do this if you have already made the history public;
2de9b711 1461 Git does not normally expect the "history" of a project to
b684f830
BF
1462 change, and cannot correctly perform repeated merges from
1463 a branch that has had its history changed.
1464
e34caace 1465[[reverting-a-commit]]
b684f830
BF
1466Fixing a mistake with a new commit
1467~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1468
1469Creating a new commit that reverts an earlier change is very easy;
5162e697 1470just pass the linkgit:git-revert[1] command a reference to the bad
b684f830
BF
1471commit; for example, to revert the most recent commit:
1472
1473-------------------------------------------------
1474$ git revert HEAD
1475-------------------------------------------------
1476
1477This will create a new commit which undoes the change in HEAD. You
1478will be given a chance to edit the commit message for the new commit.
1479
1480You can also revert an earlier change, for example, the next-to-last:
1481
1482-------------------------------------------------
1483$ git revert HEAD^
1484-------------------------------------------------
1485
2de9b711 1486In this case Git will attempt to undo the old change while leaving
b684f830
BF
1487intact any changes made since then. If more recent changes overlap
1488with the changes to be reverted, then you will be asked to fix
1489conflicts manually, just as in the case of <<resolving-a-merge,
1490resolving a merge>>.
1491
7cb192ea
BF
1492[[fixing-a-mistake-by-rewriting-history]]
1493Fixing a mistake by rewriting history
a3e1fa97 1494~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
b684f830
BF
1495
1496If the problematic commit is the most recent commit, and you have not
1497yet made that commit public, then you may just
6127c086 1498<<undoing-a-merge,destroy it using `git reset`>>.
b684f830
BF
1499
1500Alternatively, you
1501can edit the working directory and update the index to fix your
1502mistake, just as if you were going to <<how-to-make-a-commit,create a
1503new commit>>, then run
1504
1505-------------------------------------------------
1506$ git commit --amend
1507-------------------------------------------------
1508
1509which will replace the old commit by a new commit incorporating your
1510changes, giving you a chance to edit the old commit message first.
1511
1512Again, you should never do this to a commit that may already have
5162e697 1513been merged into another branch; use linkgit:git-revert[1] instead in
b684f830
BF
1514that case.
1515
7cb192ea 1516It is also possible to replace commits further back in the history, but
b684f830
BF
1517this is an advanced topic to be left for
1518<<cleaning-up-history,another chapter>>.
1519
e34caace 1520[[checkout-of-path]]
b684f830
BF
1521Checking out an old version of a file
1522~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1523
1524In the process of undoing a previous bad change, you may find it
1525useful to check out an older version of a particular file using
6127c086 1526linkgit:git-checkout[1]. We've used `git checkout` before to switch
b684f830
BF
1527branches, but it has quite different behavior if it is given a path
1528name: the command
1529
1530-------------------------------------------------
1531$ git checkout HEAD^ path/to/file
1532-------------------------------------------------
1533
1534replaces path/to/file by the contents it had in the commit HEAD^, and
1535also updates the index to match. It does not change branches.
1536
1537If you just want to look at an old version of the file, without
1538modifying the working directory, you can do that with
5162e697 1539linkgit:git-show[1]:
b684f830
BF
1540
1541-------------------------------------------------
ed4eb0d8 1542$ git show HEAD^:path/to/file
b684f830
BF
1543-------------------------------------------------
1544
1545which will display the given version of the file.
1546
7a7cc594
JH
1547[[interrupted-work]]
1548Temporarily setting aside work in progress
1549~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1550
1551While you are in the middle of working on something complicated, you
1552find an unrelated but obvious and trivial bug. You would like to fix it
5162e697 1553before continuing. You can use linkgit:git-stash[1] to save the current
7a7cc594
JH
1554state of your work, and after fixing the bug (or, optionally after doing
1555so on a different branch and then coming back), unstash the
1556work-in-progress changes.
1557
1558------------------------------------------------
7a85f6ae 1559$ git stash save "work in progress for foo feature"
7a7cc594
JH
1560------------------------------------------------
1561
1562This command will save your changes away to the `stash`, and
1563reset your working tree and the index to match the tip of your
1564current branch. Then you can make your fix as usual.
1565
1566------------------------------------------------
1567... edit and test ...
1568$ git commit -a -m "blorpl: typofix"
1569------------------------------------------------
1570
1571After that, you can go back to what you were working on with
7b8988e1 1572`git stash pop`:
7a7cc594
JH
1573
1574------------------------------------------------
7b8988e1 1575$ git stash pop
7a7cc594
JH
1576------------------------------------------------
1577
1578
e34caace 1579[[ensuring-good-performance]]
d19fbc3c
BF
1580Ensuring good performance
1581-------------------------
1582
2de9b711 1583On large repositories, Git depends on compression to keep the history
901fd180 1584information from taking up too much space on disk or in memory. Some
e1ebf212 1585Git commands may automatically run linkgit:git-gc[1], so you don't
901fd180
TK
1586have to worry about running it manually. However, compressing a large
1587repository may take a while, so you may want to call `gc` explicitly
1588to avoid automatic compression kicking in when it is not convenient.
d19fbc3c 1589
e34caace
BF
1590
1591[[ensuring-reliability]]
11e016a3
BF
1592Ensuring reliability
1593--------------------
1594
e34caace 1595[[checking-for-corruption]]
11e016a3
BF
1596Checking the repository for corruption
1597~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1598
5162e697 1599The linkgit:git-fsck[1] command runs a number of self-consistency checks
1191ee18 1600on the repository, and reports on any problems. This may take some
c6a13b2c 1601time.
21dcb3b7
BF
1602
1603-------------------------------------------------
04e50e94 1604$ git fsck
21dcb3b7
BF
1605dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1606dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1607dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1608dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb
1609dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f
1610dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e
1611dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085
1612dangling tree b24c2473f1fd3d91352a624795be026d64c8841f
1613...
1614-------------------------------------------------
1615
c6a13b2c
JH
1616You will see informational messages on dangling objects. They are objects
1617that still exist in the repository but are no longer referenced by any of
1249d8ad 1618your branches, and can (and will) be removed after a while with `gc`.
b4ab1980 1619You can run `git fsck --no-dangling` to suppress these messages, and still
c6a13b2c 1620view real errors.
1cdade2c 1621
e34caace 1622[[recovering-lost-changes]]
11e016a3
BF
1623Recovering lost changes
1624~~~~~~~~~~~~~~~~~~~~~~~
1625
e34caace 1626[[reflogs]]
559e4d7a
BF
1627Reflogs
1628^^^^^^^
1629
1249d8ad
TK
1630Say you modify a branch with <<fixing-mistakes,`git reset --hard`>>,
1631and then realize that the branch was the only reference you had to
1632that point in history.
559e4d7a 1633
2de9b711 1634Fortunately, Git also keeps a log, called a "reflog", of all the
559e4d7a 1635previous values of each branch. So in this case you can still find the
a6080a0a 1636old history using, for example,
559e4d7a
BF
1637
1638-------------------------------------------------
1639$ git log master@{1}
1640-------------------------------------------------
1641
e502c2c3 1642This lists the commits reachable from the previous version of the
1249d8ad
TK
1643`master` branch head. This syntax can be used with any Git command
1644that accepts a commit, not just with `git log`. Some other examples:
559e4d7a
BF
1645
1646-------------------------------------------------
1647$ git show master@{2} # See where the branch pointed 2,
1648$ git show master@{3} # 3, ... changes ago.
1649$ gitk master@{yesterday} # See where it pointed yesterday,
1650$ gitk master@{"1 week ago"} # ... or last week
953f3d6f
BF
1651$ git log --walk-reflogs master # show reflog entries for master
1652-------------------------------------------------
1653
1654A separate reflog is kept for the HEAD, so
1655
1656-------------------------------------------------
1657$ git show HEAD@{"1 week ago"}
559e4d7a
BF
1658-------------------------------------------------
1659
953f3d6f
BF
1660will show what HEAD pointed to one week ago, not what the current branch
1661pointed to one week ago. This allows you to see the history of what
1662you've checked out.
1663
559e4d7a 1664The reflogs are kept by default for 30 days, after which they may be
5162e697 1665pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn
559e4d7a 1666how to control this pruning, and see the "SPECIFYING REVISIONS"
9d83e382 1667section of linkgit:gitrevisions[7] for details.
559e4d7a 1668
2de9b711 1669Note that the reflog history is very different from normal Git history.
559e4d7a
BF
1670While normal history is shared by every repository that works on the
1671same project, the reflog history is not shared: it tells you only about
1672how the branches in your local repository have changed over time.
1673
59723040 1674[[dangling-object-recovery]]
559e4d7a
BF
1675Examining dangling objects
1676^^^^^^^^^^^^^^^^^^^^^^^^^^
1677
59723040
BF
1678In some situations the reflog may not be able to save you. For example,
1679suppose you delete a branch, then realize you need the history it
1680contained. The reflog is also deleted; however, if you have not yet
1681pruned the repository, then you may still be able to find the lost
6127c086 1682commits in the dangling objects that `git fsck` reports. See
59723040 1683<<dangling-objects>> for the details.
559e4d7a
BF
1684
1685-------------------------------------------------
1686$ git fsck
1687dangling commit 7281251ddd2a61e38657c827739c57015671a6b3
1688dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63
1689dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5
1690...
1691-------------------------------------------------
1692
aacd404e 1693You can examine
559e4d7a
BF
1694one of those dangling commits with, for example,
1695
1696------------------------------------------------
1697$ gitk 7281251ddd --not --all
1698------------------------------------------------
1699
1700which does what it sounds like: it says that you want to see the commit
1701history that is described by the dangling commit(s), but not the
1702history that is described by all your existing branches and tags. Thus
1703you get exactly the history reachable from that commit that is lost.
1704(And notice that it might not be just one commit: we only report the
1705"tip of the line" as being dangling, but there might be a whole deep
79c96c57 1706and complex commit history that was dropped.)
559e4d7a
BF
1707
1708If you decide you want the history back, you can always create a new
1709reference pointing to it, for example, a new branch:
1710
1711------------------------------------------------
a6080a0a 1712$ git branch recovered-branch 7281251ddd
559e4d7a
BF
1713------------------------------------------------
1714
59723040
BF
1715Other types of dangling objects (blobs and trees) are also possible, and
1716dangling objects can arise in other situations.
1717
11e016a3 1718
e34caace 1719[[sharing-development]]
d19fbc3c 1720Sharing development with others
b684f830 1721===============================
d19fbc3c 1722
aa971cb9 1723[[getting-updates-With-git-pull]]
6127c086 1724Getting updates with git pull
b684f830 1725-----------------------------
d19fbc3c 1726
e63ec003 1727After you clone a repository and commit a few changes of your own, you
d19fbc3c
BF
1728may wish to check the original repository for updates and merge them
1729into your own work.
1730
aa971cb9 1731We have already seen <<Updating-a-repository-With-git-fetch,how to
0e615b25 1732keep remote-tracking branches up to date>> with linkgit:git-fetch[1],
d19fbc3c
BF
1733and how to merge two branches. So you can merge in changes from the
1734original repository's master branch with:
1735
1736-------------------------------------------------
1737$ git fetch
1738$ git merge origin/master
1739-------------------------------------------------
1740
5162e697 1741However, the linkgit:git-pull[1] command provides a way to do this in
d19fbc3c
BF
1742one step:
1743
1744-------------------------------------------------
1745$ git pull origin master
1746-------------------------------------------------
1747
1249d8ad
TK
1748In fact, if you have `master` checked out, then this branch has been
1749configured by `git clone` to get changes from the HEAD branch of the
66a062a1 1750origin repository. So often you can
0eb4f7cd 1751accomplish the above with just a simple
d19fbc3c
BF
1752
1753-------------------------------------------------
1754$ git pull
1755-------------------------------------------------
1756
66a062a1
MM
1757This command will fetch changes from the remote branches to your
1758remote-tracking branches `origin/*`, and merge the default branch into
1759the current branch.
1760
29b9a66f
MM
1761More generally, a branch that is created from a remote-tracking branch
1762will pull
0eb4f7cd 1763by default from that branch. See the descriptions of the
1249d8ad 1764`branch.<name>.remote` and `branch.<name>.merge` options in
5162e697
DM
1765linkgit:git-config[1], and the discussion of the `--track` option in
1766linkgit:git-checkout[1], to learn how to control these defaults.
d19fbc3c 1767
1249d8ad 1768In addition to saving you keystrokes, `git pull` also helps you by
d19fbc3c
BF
1769producing a default commit message documenting the branch and
1770repository that you pulled from.
1771
1772(But note that no such commit will be created in the case of a
a75d7b54 1773<<fast-forwards,fast-forward>>; instead, your branch will just be
79c96c57 1774updated to point to the latest commit from the upstream branch.)
d19fbc3c 1775
1249d8ad 1776The `git pull` command can also be given `.` as the "remote" repository,
1191ee18 1777in which case it just merges in a branch from the current repository; so
4c63ff45
BF
1778the commands
1779
1780-------------------------------------------------
1781$ git pull . branch
1782$ git merge branch
1783-------------------------------------------------
1784
a7bdee11 1785are roughly equivalent.
4c63ff45 1786
e34caace 1787[[submitting-patches]]
d19fbc3c 1788Submitting patches to a project
b684f830 1789-------------------------------
d19fbc3c
BF
1790
1791If you just have a few changes, the simplest way to submit them may
1792just be to send them as patches in email:
1793
5162e697 1794First, use linkgit:git-format-patch[1]; for example:
d19fbc3c
BF
1795
1796-------------------------------------------------
eb6ae7f4 1797$ git format-patch origin
d19fbc3c
BF
1798-------------------------------------------------
1799
1800will produce a numbered series of files in the current directory, one
1249d8ad 1801for each patch in the current branch but not in `origin/HEAD`.
d19fbc3c 1802
d84cef18
PO
1803`git format-patch` can include an initial "cover letter". You can insert
1804commentary on individual patches after the three dash line which
1805`format-patch` places after the commit message but before the patch
1806itself. If you use `git notes` to track your cover letter material,
1807`git format-patch --notes` will include the commit's notes in a similar
1808manner.
1809
d19fbc3c
BF
1810You can then import these into your mail client and send them by
1811hand. However, if you have a lot to send at once, you may prefer to
5162e697 1812use the linkgit:git-send-email[1] script to automate the process.
3c735e07
JM
1813Consult the mailing list for your project first to determine
1814their requirements for submitting patches.
d19fbc3c 1815
e34caace 1816[[importing-patches]]
d19fbc3c 1817Importing patches to a project
b684f830 1818------------------------------
d19fbc3c 1819
5162e697 1820Git also provides a tool called linkgit:git-am[1] (am stands for
d19fbc3c
BF
1821"apply mailbox"), for importing such an emailed series of patches.
1822Just save all of the patch-containing messages, in order, into a
1249d8ad 1823single mailbox file, say `patches.mbox`, then run
d19fbc3c
BF
1824
1825-------------------------------------------------
eb6ae7f4 1826$ git am -3 patches.mbox
d19fbc3c
BF
1827-------------------------------------------------
1828
1829Git will apply each patch in order; if any conflicts are found, it
1830will stop, and you can fix the conflicts as described in
1249d8ad 1831"<<resolving-a-merge,Resolving a merge>>". (The `-3` option tells
2de9b711 1832Git to perform a merge; if you would prefer it just to abort and
01997b4a
BF
1833leave your tree and index untouched, you may omit that option.)
1834
1835Once the index is updated with the results of the conflict
1836resolution, instead of creating a new commit, just run
d19fbc3c
BF
1837
1838-------------------------------------------------
8ceb6fbd 1839$ git am --continue
d19fbc3c
BF
1840-------------------------------------------------
1841
2de9b711 1842and Git will create the commit for you and continue applying the
d19fbc3c
BF
1843remaining patches from the mailbox.
1844
1845The final result will be a series of commits, one for each patch in
1846the original mailbox, with authorship and commit log message each
1847taken from the message containing each patch.
1848
eda69449 1849[[public-repositories]]
2de9b711 1850Public Git repositories
eda69449 1851-----------------------
d19fbc3c 1852
6e30fb0c
DK
1853Another way to submit changes to a project is to tell the maintainer
1854of that project to pull the changes from your repository using
aa971cb9 1855linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull,
6127c086 1856Getting updates with `git pull`>>" we described this as a way to get
6e30fb0c
DK
1857updates from the "main" repository, but it works just as well in the
1858other direction.
d19fbc3c 1859
eda69449
BF
1860If you and the maintainer both have accounts on the same machine, then
1861you can just pull changes from each other's repositories directly;
11d51533 1862commands that accept repository URLs as arguments will also accept a
eda69449 1863local directory name:
d19fbc3c
BF
1864
1865-------------------------------------------------
1866$ git clone /path/to/repository
1867$ git pull /path/to/other/repository
1868-------------------------------------------------
1869
c9016158 1870or an ssh URL:
11d51533
BF
1871
1872-------------------------------------------------
1873$ git clone ssh://yourhost/~you/repository
1874-------------------------------------------------
1875
1876For projects with few developers, or for synchronizing a few private
1877repositories, this may be all you need.
1878
eda69449
BF
1879However, the more common way to do this is to maintain a separate public
1880repository (usually on a different host) for others to pull changes
1881from. This is usually more convenient, and allows you to cleanly
1882separate private work in progress from publicly visible work.
d19fbc3c
BF
1883
1884You will continue to do your day-to-day work in your personal
1885repository, but periodically "push" changes from your personal
1886repository into your public repository, allowing other developers to
1887pull from that repository. So the flow of changes, in a situation
1888where there is one other developer with a public repository, looks
1889like this:
1890
1891 you push
1892 your personal repo ------------------> your public repo
a6080a0a 1893 ^ |
d19fbc3c
BF
1894 | |
1895 | you pull | they pull
1896 | |
1897 | |
1898 | they push V
1899 their public repo <------------------- their repo
1900
11d51533
BF
1901We explain how to do this in the following sections.
1902
eda69449
BF
1903[[setting-up-a-public-repository]]
1904Setting up a public repository
1905~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1906
1249d8ad 1907Assume your personal repository is in the directory `~/proj`. We
6127c086 1908first create a new clone of the repository and tell `git daemon` that it
eda69449 1909is meant to be public:
d19fbc3c
BF
1910
1911-------------------------------------------------
52c80037 1912$ git clone --bare ~/proj proj.git
eda69449 1913$ touch proj.git/git-daemon-export-ok
d19fbc3c
BF
1914-------------------------------------------------
1915
52c80037 1916The resulting directory proj.git contains a "bare" git repository--it is
1249d8ad 1917just the contents of the `.git` directory, without any files checked out
eda69449 1918around it.
d19fbc3c 1919
1249d8ad 1920Next, copy `proj.git` to the server where you plan to host the
d19fbc3c
BF
1921public repository. You can use scp, rsync, or whatever is most
1922convenient.
1923
eda69449 1924[[exporting-via-git]]
2de9b711 1925Exporting a Git repository via the Git protocol
eda69449
BF
1926~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
1927
1928This is the preferred method.
1929
1930If someone else administers the server, they should tell you what
1249d8ad
TK
1931directory to put the repository in, and what `git://` URL it will
1932appear at. You can then skip to the section
d19fbc3c
BF
1933"<<pushing-changes-to-a-public-repository,Pushing changes to a public
1934repository>>", below.
1935
5162e697 1936Otherwise, all you need to do is start linkgit:git-daemon[1]; it will
eda69449 1937listen on port 9418. By default, it will allow access to any directory
2de9b711 1938that looks like a Git directory and contains the magic file
6127c086 1939git-daemon-export-ok. Passing some directory paths as `git daemon`
eda69449
BF
1940arguments will further restrict the exports to those paths.
1941
6127c086 1942You can also run `git daemon` as an inetd service; see the
5162e697 1943linkgit:git-daemon[1] man page for details. (See especially the
eda69449 1944examples section.)
d19fbc3c
BF
1945
1946[[exporting-via-http]]
de3f2c7b 1947Exporting a git repository via HTTP
eda69449 1948~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1949
2de9b711 1950The Git protocol gives better performance and reliability, but on a
de3f2c7b 1951host with a web server set up, HTTP exports may be simpler to set up.
d19fbc3c 1952
2de9b711 1953All you need to do is place the newly created bare Git repository in
d19fbc3c
BF
1954a directory that is exported by the web server, and make some
1955adjustments to give web clients some extra information they need:
1956
1957-------------------------------------------------
1958$ mv proj.git /home/you/public_html/proj.git
1959$ cd proj.git
c64415e2 1960$ git --bare update-server-info
7dce9918 1961$ mv hooks/post-update.sample hooks/post-update
d19fbc3c
BF
1962-------------------------------------------------
1963
1964(For an explanation of the last two lines, see
6998e4db 1965linkgit:git-update-server-info[1] and linkgit:githooks[5].)
d19fbc3c 1966
1249d8ad 1967Advertise the URL of `proj.git`. Anybody else should then be able to
c9016158 1968clone or pull from that URL, for example with a command line like:
d19fbc3c
BF
1969
1970-------------------------------------------------
1971$ git clone http://yourserver.com/~you/proj.git
1972-------------------------------------------------
1973
1974(See also
d5ff3b4b 1975link:howto/setup-git-server-over-http.html[setup-git-server-over-http]
d19fbc3c 1976for a slightly more sophisticated setup using WebDAV which also
de3f2c7b 1977allows pushing over HTTP.)
d19fbc3c 1978
d19fbc3c
BF
1979[[pushing-changes-to-a-public-repository]]
1980Pushing changes to a public repository
eda69449 1981~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 1982
eda69449 1983Note that the two techniques outlined above (exporting via
d19fbc3c
BF
1984<<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other
1985maintainers to fetch your latest changes, but they do not allow write
1986access, which you will need to update the public repository with the
1987latest changes created in your private repository.
1988
5162e697 1989The simplest way to do this is using linkgit:git-push[1] and ssh; to
1249d8ad
TK
1990update the remote branch named `master` with the latest state of your
1991branch named `master`, run
d19fbc3c
BF
1992
1993-------------------------------------------------
1994$ git push ssh://yourserver.com/~you/proj.git master:master
1995-------------------------------------------------
1996
1997or just
1998
1999-------------------------------------------------
2000$ git push ssh://yourserver.com/~you/proj.git master
2001-------------------------------------------------
2002
6127c086 2003As with `git fetch`, `git push` will complain if this does not result in a
a75d7b54 2004<<fast-forwards,fast-forward>>; see the following section for details on
81eb417a 2005handling this case.
d19fbc3c 2006
1249d8ad 2007Note that the target of a `push` is normally a
11d51533 2008<<def_bare_repository,bare>> repository. You can also push to a
d9be2485
TK
2009repository that has a checked-out working tree, but a push to update the
2010currently checked-out branch is denied by default to prevent confusion.
50995edd 2011See the description of the receive.denyCurrentBranch option
d9be2485 2012in linkgit:git-config[1] for details.
11d51533 2013
6127c086 2014As with `git fetch`, you may also set up configuration options to
e9b49083
TK
2015save typing; so, for example:
2016
2017-------------------------------------------------
2018$ git remote add public-repo ssh://yourserver.com/~you/proj.git
2019-------------------------------------------------
2020
2021adds the following to `.git/config`:
d19fbc3c
BF
2022
2023-------------------------------------------------
d19fbc3c 2024[remote "public-repo"]
e9b49083
TK
2025 url = yourserver.com:proj.git
2026 fetch = +refs/heads/*:refs/remotes/example/*
d19fbc3c
BF
2027-------------------------------------------------
2028
e9b49083 2029which lets you do the same push with just
d19fbc3c
BF
2030
2031-------------------------------------------------
2032$ git push public-repo master
2033-------------------------------------------------
2034
1249d8ad
TK
2035See the explanations of the `remote.<name>.url`,
2036`branch.<name>.remote`, and `remote.<name>.push` options in
2037linkgit:git-config[1] for details.
d19fbc3c 2038
81eb417a
BF
2039[[forcing-push]]
2040What to do when a push fails
2041~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2042
a75d7b54 2043If a push would not result in a <<fast-forwards,fast-forward>> of the
81eb417a
BF
2044remote branch, then it will fail with an error like:
2045
2046-------------------------------------------------
2047error: remote 'refs/heads/master' is not an ancestor of
2048 local 'refs/heads/master'.
2049 Maybe you are not up-to-date and need to pull first?
2050error: failed to push to 'ssh://yourserver.com/~you/proj.git'
2051-------------------------------------------------
2052
2053This can happen, for example, if you:
2054
6127c086
FC
2055 - use `git reset --hard` to remove already-published commits, or
2056 - use `git commit --amend` to replace already-published commits
7cb192ea 2057 (as in <<fixing-a-mistake-by-rewriting-history>>), or
6127c086 2058 - use `git rebase` to rebase any already-published commits (as
81eb417a
BF
2059 in <<using-git-rebase>>).
2060
6127c086 2061You may force `git push` to perform the update anyway by preceding the
81eb417a
BF
2062branch name with a plus sign:
2063
2064-------------------------------------------------
2065$ git push ssh://yourserver.com/~you/proj.git +master
2066-------------------------------------------------
2067
d1471e06
TK
2068Note the addition of the `+` sign. Alternatively, you can use the
2069`-f` flag to force the remote update, as in:
2070
2071-------------------------------------------------
2072$ git push -f ssh://yourserver.com/~you/proj.git master
2073-------------------------------------------------
2074
81eb417a 2075Normally whenever a branch head in a public repository is modified, it
9e5d87d4 2076is modified to point to a descendant of the commit that it pointed to
81eb417a 2077before. By forcing a push in this situation, you break that convention.
aa971cb9 2078(See <<problems-With-rewriting-history>>.)
81eb417a
BF
2079
2080Nevertheless, this is a common practice for people that need a simple
2081way to publish a work-in-progress patch series, and it is an acceptable
2082compromise as long as you warn other developers that this is how you
2083intend to manage the branch.
2084
2085It's also possible for a push to fail in this way when other people have
2086the right to push to the same repository. In that case, the correct
843c81dc
EH
2087solution is to retry the push after first updating your work: either by a
2088pull, or by a fetch followed by a rebase; see the
81eb417a 2089<<setting-up-a-shared-repository,next section>> and
6998e4db 2090linkgit:gitcvs-migration[7] for more.
81eb417a 2091
e34caace 2092[[setting-up-a-shared-repository]]
d19fbc3c 2093Setting up a shared repository
eda69449 2094~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c
BF
2095
2096Another way to collaborate is by using a model similar to that
2097commonly used in CVS, where several developers with special rights
2098all push to and pull from a single shared repository. See
6998e4db 2099linkgit:gitcvs-migration[7] for instructions on how to
d19fbc3c
BF
2100set this up.
2101
2de9b711 2102However, while there is nothing wrong with Git's support for shared
8fae2225 2103repositories, this mode of operation is not generally recommended,
2de9b711 2104simply because the mode of collaboration that Git supports--by
8fae2225
BF
2105exchanging patches and pulling from public repositories--has so many
2106advantages over the central shared repository:
2107
2108 - Git's ability to quickly import and merge patches allows a
2109 single maintainer to process incoming changes even at very
6127c086 2110 high rates. And when that becomes too much, `git pull` provides
8fae2225
BF
2111 an easy way for that maintainer to delegate this job to other
2112 maintainers while still allowing optional review of incoming
2113 changes.
2114 - Since every developer's repository has the same complete copy
2115 of the project history, no repository is special, and it is
2116 trivial for another developer to take over maintenance of a
2117 project, either by mutual agreement, or because a maintainer
2118 becomes unresponsive or difficult to work with.
2119 - The lack of a central group of "committers" means there is
2120 less need for formal decisions about who is "in" and who is
2121 "out".
2122
e34caace 2123[[setting-up-gitweb]]
eda69449
BF
2124Allowing web browsing of a repository
2125~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
d19fbc3c 2126
a8cd1402 2127The gitweb cgi script provides users an easy way to browse your
2de9b711
TA
2128project's files and history without having to install Git; see the file
2129gitweb/INSTALL in the Git source tree for instructions on setting it up.
d19fbc3c 2130
e34caace 2131[[sharing-development-examples]]
b684f830
BF
2132Examples
2133--------
d19fbc3c 2134
9e2163ea
BF
2135[[maintaining-topic-branches]]
2136Maintaining topic branches for a Linux subsystem maintainer
2137~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
2138
2de9b711 2139This describes how Tony Luck uses Git in his role as maintainer of the
9e2163ea
BF
2140IA64 architecture for the Linux kernel.
2141
2142He uses two public branches:
2143
2144 - A "test" tree into which patches are initially placed so that they
2145 can get some exposure when integrated with other ongoing development.
2146 This tree is available to Andrew for pulling into -mm whenever he
2147 wants.
2148
2149 - A "release" tree into which tested patches are moved for final sanity
2150 checking, and as a vehicle to send them upstream to Linus (by sending
2151 him a "please pull" request.)
2152
2153He also uses a set of temporary branches ("topic branches"), each
2154containing a logical grouping of patches.
2155
2156To set this up, first create your work tree by cloning Linus's public
2157tree:
2158
2159-------------------------------------------------
283efb01 2160$ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git work
9e2163ea
BF
2161$ cd work
2162-------------------------------------------------
2163
29b9a66f 2164Linus's tree will be stored in the remote-tracking branch named origin/master,
5162e697
DM
2165and can be updated using linkgit:git-fetch[1]; you can track other
2166public trees using linkgit:git-remote[1] to set up a "remote" and
2167linkgit:git-fetch[1] to keep them up-to-date; see
6e30fb0c 2168<<repositories-and-branches>>.
9e2163ea
BF
2169
2170Now create the branches in which you are going to work; these start out
2171at the current tip of origin/master branch, and should be set up (using
1249d8ad 2172the `--track` option to linkgit:git-branch[1]) to merge changes in from
9e2163ea
BF
2173Linus by default.
2174
2175-------------------------------------------------
2176$ git branch --track test origin/master
2177$ git branch --track release origin/master
2178-------------------------------------------------
2179
5162e697 2180These can be easily kept up to date using linkgit:git-pull[1].
9e2163ea
BF
2181
2182-------------------------------------------------
2183$ git checkout test && git pull
2184$ git checkout release && git pull
2185-------------------------------------------------
2186
2187Important note! If you have any local changes in these branches, then
2188this merge will create a commit object in the history (with no local
2de9b711 2189changes Git will simply do a "fast-forward" merge). Many people dislike
9e2163ea 2190the "noise" that this creates in the Linux history, so you should avoid
1249d8ad 2191doing this capriciously in the `release` branch, as these noisy commits
9e2163ea
BF
2192will become part of the permanent history when you ask Linus to pull
2193from the release branch.
2194
5162e697 2195A few configuration variables (see linkgit:git-config[1]) can
9e2163ea
BF
2196make it easy to push both branches to your public tree. (See
2197<<setting-up-a-public-repository>>.)
2198
2199-------------------------------------------------
2200$ cat >> .git/config <<EOF
2201[remote "mytree"]
283efb01 2202 url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux.git
9e2163ea
BF
2203 push = release
2204 push = test
2205EOF
2206-------------------------------------------------
2207
2208Then you can push both the test and release trees using
5162e697 2209linkgit:git-push[1]:
9e2163ea
BF
2210
2211-------------------------------------------------
2212$ git push mytree
2213-------------------------------------------------
2214
2215or push just one of the test and release branches using:
2216
2217-------------------------------------------------
2218$ git push mytree test
2219-------------------------------------------------
2220
2221or
2222
2223-------------------------------------------------
2224$ git push mytree release
2225-------------------------------------------------
2226
2227Now to apply some patches from the community. Think of a short
2228snappy name for a branch to hold this patch (or related group of
352953a5
TL
2229patches), and create a new branch from a recent stable tag of
2230Linus's branch. Picking a stable base for your branch will:
22311) help you: by avoiding inclusion of unrelated and perhaps lightly
2232tested changes
1249d8ad 22332) help future bug hunters that use `git bisect` to find problems
9e2163ea
BF
2234
2235-------------------------------------------------
352953a5 2236$ git checkout -b speed-up-spinlocks v2.6.35
9e2163ea
BF
2237-------------------------------------------------
2238
2239Now you apply the patch(es), run some tests, and commit the change(s). If
2240the patch is a multi-part series, then you should apply each as a separate
2241commit to this branch.
2242
2243-------------------------------------------------
2244$ ... patch ... test ... commit [ ... patch ... test ... commit ]*
2245-------------------------------------------------
2246
a7bdee11 2247When you are happy with the state of this change, you can merge it into the
9e2163ea
BF
2248"test" branch in preparation to make it public:
2249
2250-------------------------------------------------
a7bdee11 2251$ git checkout test && git merge speed-up-spinlocks
9e2163ea
BF
2252-------------------------------------------------
2253
2254It is unlikely that you would have any conflicts here ... but you might if you
2255spent a while on this step and had also pulled new versions from upstream.
2256
3c735e07 2257Sometime later when enough time has passed and testing done, you can pull the
1249d8ad 2258same branch into the `release` tree ready to go upstream. This is where you
9e2163ea 2259see the value of keeping each patch (or patch series) in its own branch. It
1249d8ad 2260means that the patches can be moved into the `release` tree in any order.
9e2163ea
BF
2261
2262-------------------------------------------------
a7bdee11 2263$ git checkout release && git merge speed-up-spinlocks
9e2163ea
BF
2264-------------------------------------------------
2265
2266After a while, you will have a number of branches, and despite the
2267well chosen names you picked for each of them, you may forget what
2268they are for, or what status they are in. To get a reminder of what
2269changes are in a specific branch, use:
2270
2271-------------------------------------------------
467c0197 2272$ git log linux..branchname | git shortlog
9e2163ea
BF
2273-------------------------------------------------
2274
06ada152 2275To see whether it has already been merged into the test or release branches,
9e2163ea
BF
2276use:
2277
2278-------------------------------------------------
2279$ git log test..branchname
2280-------------------------------------------------
2281
2282or
2283
2284-------------------------------------------------
2285$ git log release..branchname
2286-------------------------------------------------
2287
06ada152 2288(If this branch has not yet been merged, you will see some log entries.
9e2163ea
BF
2289If it has been merged, then there will be no output.)
2290
2291Once a patch completes the great cycle (moving from test to release,
2292then pulled by Linus, and finally coming back into your local
1249d8ad 2293`origin/master` branch), the branch for this change is no longer needed.
9e2163ea
BF
2294You detect this when the output from:
2295
2296-------------------------------------------------
2297$ git log origin..branchname
2298-------------------------------------------------
2299
2300is empty. At this point the branch can be deleted:
2301
2302-------------------------------------------------
2303$ git branch -d branchname
2304-------------------------------------------------
2305
2306Some changes are so trivial that it is not necessary to create a separate
2307branch and then merge into each of the test and release branches. For
1249d8ad
TK
2308these changes, just apply directly to the `release` branch, and then
2309merge that into the `test` branch.
9e2163ea 2310
ae6ef554
TK
2311After pushing your work to `mytree`, you can use
2312linkgit:git-request-pull[1] to prepare a "please pull" request message
2313to send to Linus:
9e2163ea
BF
2314
2315-------------------------------------------------
ae6ef554
TK
2316$ git push mytree
2317$ git request-pull origin mytree release
9e2163ea
BF
2318-------------------------------------------------
2319
2320Here are some of the scripts that simplify all this even further.
2321
2322-------------------------------------------------
2323==== update script ====
48a8c26c 2324# Update a branch in my Git tree. If the branch to be updated
9e2163ea
BF
2325# is origin, then pull from kernel.org. Otherwise merge
2326# origin/master branch into test|release branch
2327
2328case "$1" in
2329test|release)
2330 git checkout $1 && git pull . origin
2331 ;;
2332origin)
fc74ecc1 2333 before=$(git rev-parse refs/remotes/origin/master)
9e2163ea 2334 git fetch origin
fc74ecc1 2335 after=$(git rev-parse refs/remotes/origin/master)
9e2163ea
BF
2336 if [ $before != $after ]
2337 then
2338 git log $before..$after | git shortlog
2339 fi
2340 ;;
2341*)
1a2ba8b9 2342 echo "usage: $0 origin|test|release" 1>&2
9e2163ea
BF
2343 exit 1
2344 ;;
2345esac
2346-------------------------------------------------
2347
2348-------------------------------------------------
2349==== merge script ====
2350# Merge a branch into either the test or release branch
2351
2352pname=$0
2353
2354usage()
2355{
1a2ba8b9 2356 echo "usage: $pname branch test|release" 1>&2
9e2163ea
BF
2357 exit 1
2358}
2359
fc74ecc1 2360git show-ref -q --verify -- refs/heads/"$1" || {
9e2163ea
BF
2361 echo "Can't see branch <$1>" 1>&2
2362 usage
fc74ecc1 2363}
9e2163ea
BF
2364
2365case "$2" in
2366test|release)
2367 if [ $(git log $2..$1 | wc -c) -eq 0 ]
2368 then
2369 echo $1 already merged into $2 1>&2
2370 exit 1
2371 fi
2372 git checkout $2 && git pull . $1
2373 ;;
2374*)
2375 usage
2376 ;;
2377esac
2378-------------------------------------------------
2379
2380-------------------------------------------------
2381==== status script ====
48a8c26c 2382# report on status of my ia64 Git tree
9e2163ea
BF
2383
2384gb=$(tput setab 2)
2385rb=$(tput setab 1)
2386restore=$(tput setab 9)
2387
2388if [ `git rev-list test..release | wc -c` -gt 0 ]
2389then
2390 echo $rb Warning: commits in release that are not in test $restore
2391 git log test..release
2392fi
2393
fc74ecc1 2394for branch in `git show-ref --heads | sed 's|^.*/||'`
9e2163ea
BF
2395do
2396 if [ $branch = test -o $branch = release ]
2397 then
2398 continue
2399 fi
2400
2401 echo -n $gb ======= $branch ====== $restore " "
2402 status=
2403 for ref in test release origin/master
2404 do
2405 if [ `git rev-list $ref..$branch | wc -c` -gt 0 ]
2406 then
2407 status=$status${ref:0:1}
2408 fi
2409 done
2410 case $status in
2411 trl)
2412 echo $rb Need to pull into test $restore
2413 ;;
2414 rl)
2415 echo "In test"
2416 ;;
2417 l)
2418 echo "Waiting for linus"
2419 ;;
2420 "")
2421 echo $rb All done $restore
2422 ;;
2423 *)
2424 echo $rb "<$status>" $restore
2425 ;;
2426 esac
2427 git log origin/master..$branch | git shortlog
2428done
2429-------------------------------------------------
d19fbc3c 2430
d19fbc3c 2431
d19fbc3c 2432[[cleaning-up-history]]
4c63ff45
BF
2433Rewriting history and maintaining patch series
2434==============================================
2435
2436Normally commits are only added to a project, never taken away or
2437replaced. Git is designed with this assumption, and violating it will
2de9b711 2438cause Git's merge machinery (for example) to do the wrong thing.
4c63ff45
BF
2439
2440However, there is a situation in which it can be useful to violate this
2441assumption.
2442
e34caace 2443[[patch-series]]
4c63ff45
BF
2444Creating the perfect patch series
2445---------------------------------
2446
2447Suppose you are a contributor to a large project, and you want to add a
2448complicated feature, and to present it to the other developers in a way
2449that makes it easy for them to read your changes, verify that they are
2450correct, and understand why you made each change.
2451
b181d57f 2452If you present all of your changes as a single patch (or commit), they
79c96c57 2453may find that it is too much to digest all at once.
4c63ff45
BF
2454
2455If you present them with the entire history of your work, complete with
2456mistakes, corrections, and dead ends, they may be overwhelmed.
2457
2458So the ideal is usually to produce a series of patches such that:
2459
2460 1. Each patch can be applied in order.
2461
2462 2. Each patch includes a single logical change, together with a
2463 message explaining the change.
2464
2465 3. No patch introduces a regression: after applying any initial
2466 part of the series, the resulting project still compiles and
2467 works, and has no bugs that it didn't have before.
2468
2469 4. The complete series produces the same end result as your own
2470 (probably much messier!) development process did.
2471
b181d57f
BF
2472We will introduce some tools that can help you do this, explain how to
2473use them, and then explain some of the problems that can arise because
2474you are rewriting history.
4c63ff45 2475
e34caace 2476[[using-git-rebase]]
6127c086 2477Keeping a patch series up to date using git rebase
4c63ff45
BF
2478--------------------------------------------------
2479
1249d8ad
TK
2480Suppose that you create a branch `mywork` on a remote-tracking branch
2481`origin`, and create some commits on top of it:
4c63ff45
BF
2482
2483-------------------------------------------------
2484$ git checkout -b mywork origin
2485$ vi file.txt
2486$ git commit
2487$ vi otherfile.txt
2488$ git commit
2489...
2490-------------------------------------------------
2491
2492You have performed no merges into mywork, so it is just a simple linear
1249d8ad 2493sequence of patches on top of `origin`:
4c63ff45 2494
1dc71a91 2495................................................
fa8347b8 2496 o--o--O <-- origin
4c63ff45 2497 \
fa8347b8 2498 a--b--c <-- mywork
1dc71a91 2499................................................
4c63ff45
BF
2500
2501Some more interesting work has been done in the upstream project, and
1249d8ad 2502`origin` has advanced:
4c63ff45 2503
1dc71a91 2504................................................
4c63ff45
BF
2505 o--o--O--o--o--o <-- origin
2506 \
2507 a--b--c <-- mywork
1dc71a91 2508................................................
4c63ff45 2509
1249d8ad 2510At this point, you could use `pull` to merge your changes back in;
4c63ff45
BF
2511the result would create a new merge commit, like this:
2512
1dc71a91 2513................................................
4c63ff45
BF
2514 o--o--O--o--o--o <-- origin
2515 \ \
2516 a--b--c--m <-- mywork
1dc71a91 2517................................................
a6080a0a 2518
4c63ff45
BF
2519However, if you prefer to keep the history in mywork a simple series of
2520commits without any merges, you may instead choose to use
5162e697 2521linkgit:git-rebase[1]:
4c63ff45
BF
2522
2523-------------------------------------------------
2524$ git checkout mywork
2525$ git rebase origin
2526-------------------------------------------------
2527
b181d57f 2528This will remove each of your commits from mywork, temporarily saving
1249d8ad 2529them as patches (in a directory named `.git/rebase-apply`), update mywork to
b181d57f
BF
2530point at the latest version of origin, then apply each of the saved
2531patches to the new mywork. The result will look like:
4c63ff45
BF
2532
2533
1dc71a91 2534................................................
4c63ff45
BF
2535 o--o--O--o--o--o <-- origin
2536 \
2537 a'--b'--c' <-- mywork
1dc71a91 2538................................................
4c63ff45 2539
b181d57f 2540In the process, it may discover conflicts. In that case it will stop
6127c086 2541and allow you to fix the conflicts; after fixing conflicts, use `git add`
7a7d4ef6 2542to update the index with those contents, and then, instead of
6127c086 2543running `git commit`, just run
4c63ff45
BF
2544
2545-------------------------------------------------
2546$ git rebase --continue
2547-------------------------------------------------
2548
2de9b711 2549and Git will continue applying the rest of the patches.
4c63ff45 2550
b6cbca38 2551At any point you may use the `--abort` option to abort this process and
4c63ff45
BF
2552return mywork to the state it had before you started the rebase:
2553
2554-------------------------------------------------
2555$ git rebase --abort
2556-------------------------------------------------
2557
6c26bf4d
TK
2558If you need to reorder or edit a number of commits in a branch, it may
2559be easier to use `git rebase -i`, which allows you to reorder and
2560squash commits, as well as marking them for individual editing during
2561the rebase. See <<interactive-rebase>> for details, and
2562<<reordering-patch-series>> for alternatives.
2563
7cb192ea
BF
2564[[rewriting-one-commit]]
2565Rewriting a single commit
365aa199
BF
2566-------------------------
2567
7cb192ea 2568We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the
365aa199
BF
2569most recent commit using
2570
2571-------------------------------------------------
2572$ git commit --amend
2573-------------------------------------------------
2574
2575which will replace the old commit by a new commit incorporating your
2576changes, giving you a chance to edit the old commit message first.
6c26bf4d
TK
2577This is useful for fixing typos in your last commit, or for adjusting
2578the patch contents of a poorly staged commit.
365aa199 2579
6c26bf4d
TK
2580If you need to amend commits from deeper in your history, you can
2581use <<interactive-rebase,interactive rebase's `edit` instruction>>.
365aa199 2582
6c26bf4d
TK
2583[[reordering-patch-series]]
2584Reordering or selecting from a patch series
2585-------------------------------------------
365aa199 2586
6c26bf4d
TK
2587Sometimes you want to edit a commit deeper in your history. One
2588approach is to use `git format-patch` to create a series of patches
2589and then reset the state to before the patches:
365aa199
BF
2590
2591-------------------------------------------------
6c26bf4d
TK
2592$ git format-patch origin
2593$ git reset --hard origin
365aa199
BF
2594-------------------------------------------------
2595
6c26bf4d
TK
2596Then modify, reorder, or eliminate patches as needed before applying
2597them again with linkgit:git-am[1]:
365aa199
BF
2598
2599-------------------------------------------------
6c26bf4d 2600$ git am *.patch
365aa199
BF
2601-------------------------------------------------
2602
6c26bf4d
TK
2603[[interactive-rebase]]
2604Using interactive rebases
2605-------------------------
365aa199 2606
6c26bf4d
TK
2607You can also edit a patch series with an interactive rebase. This is
2608the same as <<reordering-patch-series,reordering a patch series using
2609`format-patch`>>, so use whichever interface you like best.
4c63ff45 2610
6c26bf4d
TK
2611Rebase your current HEAD on the last commit you want to retain as-is.
2612For example, if you want to reorder the last 5 commits, use:
b181d57f
BF
2613
2614-------------------------------------------------
6c26bf4d 2615$ git rebase -i HEAD~5
b181d57f
BF
2616-------------------------------------------------
2617
6c26bf4d
TK
2618This will open your editor with a list of steps to be taken to perform
2619your rebase.
4c63ff45 2620
b181d57f 2621-------------------------------------------------
6c26bf4d
TK
2622pick deadbee The oneline of this commit
2623pick fa1afe1 The oneline of the next commit
2624...
4c63ff45 2625
6c26bf4d
TK
2626# Rebase c0ffeee..deadbee onto c0ffeee
2627#
2628# Commands:
2629# p, pick = use commit
2630# r, reword = use commit, but edit the commit message
2631# e, edit = use commit, but stop for amending
2632# s, squash = use commit, but meld into previous commit
2633# f, fixup = like "squash", but discard this commit's log message
2634# x, exec = run command (the rest of the line) using shell
2635#
2636# These lines can be re-ordered; they are executed from top to bottom.
2637#
2638# If you remove a line here THAT COMMIT WILL BE LOST.
2639#
2640# However, if you remove everything, the rebase will be aborted.
2641#
2642# Note that empty commits are commented out
2643-------------------------------------------------
2644
2645As explained in the comments, you can reorder commits, squash them
2646together, edit commit messages, etc. by editing the list. Once you
2647are satisfied, save the list and close your editor, and the rebase
2648will begin.
2649
2650The rebase will stop where `pick` has been replaced with `edit` or
2651when a step in the list fails to mechanically resolve conflicts and
2652needs your help. When you are done editing and/or resolving conflicts
2653you can continue with `git rebase --continue`. If you decide that
2654things are getting too hairy, you can always bail out with `git rebase
2655--abort`. Even after the rebase is complete, you can still recover
2656the original branch by using the <<reflogs,reflog>>.
2657
2658For a more detailed discussion of the procedure and additional tips,
2659see the "INTERACTIVE MODE" section of linkgit:git-rebase[1].
4c63ff45 2660
e34caace 2661[[patch-series-tools]]
4c63ff45
BF
2662Other tools
2663-----------
2664
73a1d050 2665There are numerous other tools, such as StGit, which exist for the
79c96c57 2666purpose of maintaining a patch series. These are outside of the scope of
b181d57f 2667this manual.
4c63ff45 2668
aa971cb9 2669[[problems-With-rewriting-history]]
4c63ff45
BF
2670Problems with rewriting history
2671-------------------------------
2672
b181d57f
BF
2673The primary problem with rewriting the history of a branch has to do
2674with merging. Suppose somebody fetches your branch and merges it into
2675their branch, with a result something like this:
2676
1dc71a91 2677................................................
b181d57f
BF
2678 o--o--O--o--o--o <-- origin
2679 \ \
2680 t--t--t--m <-- their branch:
1dc71a91 2681................................................
b181d57f
BF
2682
2683Then suppose you modify the last three commits:
2684
1dc71a91 2685................................................
b181d57f
BF
2686 o--o--o <-- new head of origin
2687 /
2688 o--o--O--o--o--o <-- old head of origin
1dc71a91 2689................................................
b181d57f
BF
2690
2691If we examined all this history together in one repository, it will
2692look like:
2693
1dc71a91 2694................................................
b181d57f
BF
2695 o--o--o <-- new head of origin
2696 /
2697 o--o--O--o--o--o <-- old head of origin
2698 \ \
2699 t--t--t--m <-- their branch:
1dc71a91 2700................................................
b181d57f
BF
2701
2702Git has no way of knowing that the new head is an updated version of
2703the old head; it treats this situation exactly the same as it would if
2704two developers had independently done the work on the old and new heads
2705in parallel. At this point, if someone attempts to merge the new head
2de9b711 2706in to their branch, Git will attempt to merge together the two (old and
b181d57f
BF
2707new) lines of development, instead of trying to replace the old by the
2708new. The results are likely to be unexpected.
2709
2710You may still choose to publish branches whose history is rewritten,
2711and it may be useful for others to be able to fetch those branches in
2712order to examine or test them, but they should not attempt to pull such
2713branches into their own work.
2714
2715For true distributed development that supports proper merging,
2716published branches should never be rewritten.
2717
3fb00282
SP
2718[[bisect-merges]]
2719Why bisecting merge commits can be harder than bisecting linear history
2720-----------------------------------------------------------------------
2721
5162e697 2722The linkgit:git-bisect[1] command correctly handles history that
3fb00282
SP
2723includes merge commits. However, when the commit that it finds is a
2724merge commit, the user may need to work harder than usual to figure out
2725why that commit introduced a problem.
2726
2727Imagine this history:
2728
2729................................................
2730 ---Z---o---X---...---o---A---C---D
2731 \ /
2732 o---o---Y---...---o---B
2733................................................
2734
2735Suppose that on the upper line of development, the meaning of one
2736of the functions that exists at Z is changed at commit X. The
2737commits from Z leading to A change both the function's
2738implementation and all calling sites that exist at Z, as well
2739as new calling sites they add, to be consistent. There is no
2740bug at A.
2741
2742Suppose that in the meantime on the lower line of development somebody
2743adds a new calling site for that function at commit Y. The
2744commits from Z leading to B all assume the old semantics of that
2745function and the callers and the callee are consistent with each
2746other. There is no bug at B, either.
2747
2748Suppose further that the two development lines merge cleanly at C,
2749so no conflict resolution is required.
2750
2751Nevertheless, the code at C is broken, because the callers added
2752on the lower line of development have not been converted to the new
2753semantics introduced on the upper line of development. So if all
2754you know is that D is bad, that Z is good, and that
5162e697 2755linkgit:git-bisect[1] identifies C as the culprit, how will you
3fb00282
SP
2756figure out that the problem is due to this change in semantics?
2757
6127c086 2758When the result of a `git bisect` is a non-merge commit, you should
3fb00282
SP
2759normally be able to discover the problem by examining just that commit.
2760Developers can make this easy by breaking their changes into small
2761self-contained commits. That won't help in the case above, however,
2762because the problem isn't obvious from examination of any single
2763commit; instead, a global view of the development is required. To
2764make matters worse, the change in semantics in the problematic
2765function may be just one small part of the changes in the upper
2766line of development.
2767
2768On the other hand, if instead of merging at C you had rebased the
2769history between Z to B on top of A, you would have gotten this
2770linear history:
2771
2772................................................................
2773 ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D*
2774................................................................
2775
2776Bisecting between Z and D* would hit a single culprit commit Y*,
2777and understanding why Y* was broken would probably be easier.
2778
2de9b711 2779Partly for this reason, many experienced Git users, even when
3fb00282
SP
2780working on an otherwise merge-heavy project, keep the history
2781linear by rebasing against the latest upstream version before
2782publishing.
2783
e34caace 2784[[advanced-branch-management]]
b181d57f
BF
2785Advanced branch management
2786==========================
4c63ff45 2787
e34caace 2788[[fetching-individual-branches]]
b181d57f
BF
2789Fetching individual branches
2790----------------------------
2791
5162e697 2792Instead of using linkgit:git-remote[1], you can also choose just
b181d57f
BF
2793to update one branch at a time, and to store it locally under an
2794arbitrary name:
2795
2796-------------------------------------------------
2797$ git fetch origin todo:my-todo-work
2798-------------------------------------------------
2799
1249d8ad 2800The first argument, `origin`, just tells Git to fetch from the
2de9b711 2801repository you originally cloned from. The second argument tells Git
1249d8ad
TK
2802to fetch the branch named `todo` from the remote repository, and to
2803store it locally under the name `refs/heads/my-todo-work`.
b181d57f
BF
2804
2805You can also fetch branches from other repositories; so
2806
2807-------------------------------------------------
2808$ git fetch git://example.com/proj.git master:example-master
2809-------------------------------------------------
2810
1249d8ad
TK
2811will create a new branch named `example-master` and store in it the
2812branch named `master` from the repository at the given URL. If you
b181d57f 2813already have a branch named example-master, it will attempt to
59723040
BF
2814<<fast-forwards,fast-forward>> to the commit given by example.com's
2815master branch. In more detail:
b181d57f 2816
59723040
BF
2817[[fetch-fast-forwards]]
2818git fetch and fast-forwards
2819---------------------------
b181d57f 2820
1249d8ad 2821In the previous example, when updating an existing branch, `git fetch`
7a7d4ef6 2822checks to make sure that the most recent commit on the remote
b181d57f
BF
2823branch is a descendant of the most recent commit on your copy of the
2824branch before updating your copy of the branch to point at the new
a75d7b54 2825commit. Git calls this process a <<fast-forwards,fast-forward>>.
b181d57f 2826
a75d7b54 2827A fast-forward looks something like this:
b181d57f 2828
1dc71a91 2829................................................
b181d57f
BF
2830 o--o--o--o <-- old head of the branch
2831 \
2832 o--o--o <-- new head of the branch
1dc71a91 2833................................................
b181d57f
BF
2834
2835
2836In some cases it is possible that the new head will *not* actually be
2837a descendant of the old head. For example, the developer may have
2838realized she made a serious mistake, and decided to backtrack,
2839resulting in a situation like:
2840
1dc71a91 2841................................................
b181d57f
BF
2842 o--o--o--o--a--b <-- old head of the branch
2843 \
2844 o--o--o <-- new head of the branch
1dc71a91 2845................................................
b181d57f 2846
1249d8ad 2847In this case, `git fetch` will fail, and print out a warning.
b181d57f 2848
2de9b711 2849In that case, you can still force Git to update to the new head, as
b181d57f 2850described in the following section. However, note that in the
1249d8ad 2851situation above this may mean losing the commits labeled `a` and `b`,
b181d57f
BF
2852unless you've already created a reference of your own pointing to
2853them.
2854
e34caace 2855[[forcing-fetch]]
6127c086 2856Forcing git fetch to do non-fast-forward updates
b181d57f
BF
2857------------------------------------------------
2858
2859If git fetch fails because the new head of a branch is not a
2860descendant of the old head, you may force the update with:
2861
2862-------------------------------------------------
2863$ git fetch git://example.com/proj.git +master:refs/remotes/example/master
2864-------------------------------------------------
2865
1249d8ad 2866Note the addition of the `+` sign. Alternatively, you can use the `-f`
c64415e2
BF
2867flag to force updates of all the fetched branches, as in:
2868
2869-------------------------------------------------
2870$ git fetch -f origin
2871-------------------------------------------------
2872
2873Be aware that commits that the old version of example/master pointed at
2874may be lost, as we saw in the previous section.
b181d57f 2875
e34caace 2876[[remote-branch-configuration]]
29b9a66f
MM
2877Configuring remote-tracking branches
2878------------------------------------
b181d57f 2879
1249d8ad 2880We saw above that `origin` is just a shortcut to refer to the
79c96c57 2881repository that you originally cloned from. This information is
2de9b711 2882stored in Git configuration variables, which you can see using
5162e697 2883linkgit:git-config[1]:
b181d57f
BF
2884
2885-------------------------------------------------
9d13bda3 2886$ git config -l
b181d57f
BF
2887core.repositoryformatversion=0
2888core.filemode=true
2889core.logallrefupdates=true
2890remote.origin.url=git://git.kernel.org/pub/scm/git/git.git
2891remote.origin.fetch=+refs/heads/*:refs/remotes/origin/*
2892branch.master.remote=origin
2893branch.master.merge=refs/heads/master
2894-------------------------------------------------
2895
2896If there are other repositories that you also use frequently, you can
2897create similar configuration options to save typing; for example,
b181d57f
BF
2898
2899-------------------------------------------------
47adb8ac 2900$ git remote add example git://example.com/proj.git
b181d57f
BF
2901-------------------------------------------------
2902
47adb8ac 2903adds the following to `.git/config`:
b181d57f
BF
2904
2905-------------------------------------------------
47adb8ac
TK
2906[remote "example"]
2907 url = git://example.com/proj.git
2908 fetch = +refs/heads/*:refs/remotes/example/*
b181d57f
BF
2909-------------------------------------------------
2910
47adb8ac
TK
2911Also note that the above configuration can be performed by directly
2912editing the file `.git/config` instead of using linkgit:git-remote[1].
b181d57f 2913
47adb8ac
TK
2914After configuring the remote, the following three commands will do the
2915same thing:
b181d57f
BF
2916
2917-------------------------------------------------
47adb8ac
TK
2918$ git fetch git://example.com/proj.git +refs/heads/*:refs/remotes/example/*
2919$ git fetch example +refs/heads/*:refs/remotes/example/*
b181d57f
BF
2920$ git fetch example
2921-------------------------------------------------
2922
5162e697 2923See linkgit:git-config[1] for more details on the configuration
47adb8ac
TK
2924options mentioned above and linkgit:git-fetch[1] for more details on
2925the refspec syntax.
d19fbc3c 2926
d19fbc3c 2927
036f8199
BF
2928[[git-concepts]]
2929Git concepts
2930============
d19fbc3c 2931
036f8199
BF
2932Git is built on a small number of simple but powerful ideas. While it
2933is possible to get things done without understanding them, you will find
2de9b711 2934Git much more intuitive if you do.
036f8199
BF
2935
2936We start with the most important, the <<def_object_database,object
2937database>> and the <<def_index,index>>.
b181d57f 2938
e34caace 2939[[the-object-database]]
b181d57f
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2940The Object Database
2941-------------------
2942
1bbf1c79
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2943
2944We already saw in <<understanding-commits>> that all commits are stored
2945under a 40-digit "object name". In fact, all the information needed to
2946represent the history of a project is stored in objects with such names.
a6e5ef7d
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2947In each case the name is calculated by taking the SHA-1 hash of the
2948contents of the object. The SHA-1 hash is a cryptographic hash function.
1bbf1c79
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2949What that means to us is that it is impossible to find two different
2950objects with the same name. This has a number of advantages; among
2951others:
2952
2953- Git can quickly determine whether two objects are identical or not,
2954 just by comparing names.
06ada152 2955- Since object names are computed the same way in every repository, the
1bbf1c79
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2956 same content stored in two repositories will always be stored under
2957 the same name.
2958- Git can detect errors when it reads an object, by checking that the
a6e5ef7d 2959 object's name is still the SHA-1 hash of its contents.
1bbf1c79
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2960
2961(See <<object-details>> for the details of the object formatting and
a6e5ef7d 2962SHA-1 calculation.)
1bbf1c79
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2963
2964There are four different types of objects: "blob", "tree", "commit", and
2965"tag".
2966
2967- A <<def_blob_object,"blob" object>> is used to store file data.
843c81dc 2968- A <<def_tree_object,"tree" object>> ties one or more
1bbf1c79
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2969 "blob" objects into a directory structure. In addition, a tree object
2970 can refer to other tree objects, thus creating a directory hierarchy.
2971- A <<def_commit_object,"commit" object>> ties such directory hierarchies
2ef8ac1b 2972 together into a <<def_DAG,directed acyclic graph>> of revisions--each
1bbf1c79
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2973 commit contains the object name of exactly one tree designating the
2974 directory hierarchy at the time of the commit. In addition, a commit
2975 refers to "parent" commit objects that describe the history of how we
2976 arrived at that directory hierarchy.
2977- A <<def_tag_object,"tag" object>> symbolically identifies and can be
2978 used to sign other objects. It contains the object name and type of
2979 another object, a symbolic name (of course!) and, optionally, a
2980 signature.
b181d57f 2981
b181d57f
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2982The object types in some more detail:
2983
513d419c
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2984[[commit-object]]
2985Commit Object
2986~~~~~~~~~~~~~
b181d57f 2987
1bbf1c79 2988The "commit" object links a physical state of a tree with a description
1249d8ad 2989of how we got there and why. Use the `--pretty=raw` option to
5162e697 2990linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite
1bbf1c79
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2991commit:
2992
2993------------------------------------------------
2994$ git show -s --pretty=raw 2be7fcb476
2995commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4
2996tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf
2997parent 257a84d9d02e90447b149af58b271c19405edb6a
2998author Dave Watson <dwatson@mimvista.com> 1187576872 -0400
2999committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700
3000
3001 Fix misspelling of 'suppress' in docs
3002
3003 Signed-off-by: Junio C Hamano <gitster@pobox.com>
3004------------------------------------------------
3005
3006As you can see, a commit is defined by:
3007
a6e5ef7d 3008- a tree: The SHA-1 name of a tree object (as defined below), representing
1bbf1c79 3009 the contents of a directory at a certain point in time.
edfbbf7e 3010- parent(s): The SHA-1 name(s) of some number of commits which represent the
9e5d87d4 3011 immediately previous step(s) in the history of the project. The
1bbf1c79
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3012 example above has one parent; merge commits may have more than
3013 one. A commit with no parents is called a "root" commit, and
3014 represents the initial revision of a project. Each project must have
3015 at least one root. A project can also have multiple roots, though
3016 that isn't common (or necessarily a good idea).
3017- an author: The name of the person responsible for this change, together
3018 with its date.
3019- a committer: The name of the person who actually created the commit,
3020 with the date it was done. This may be different from the author, for
3021 example, if the author was someone who wrote a patch and emailed it
3022 to the person who used it to create the commit.
3023- a comment describing this commit.
3024
3025Note that a commit does not itself contain any information about what
3026actually changed; all changes are calculated by comparing the contents
3027of the tree referred to by this commit with the trees associated with
2de9b711 3028its parents. In particular, Git does not attempt to record file renames
1bbf1c79
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3029explicitly, though it can identify cases where the existence of the same
3030file data at changing paths suggests a rename. (See, for example, the
1249d8ad 3031`-M` option to linkgit:git-diff[1]).
1bbf1c79 3032
5162e697 3033A commit is usually created by linkgit:git-commit[1], which creates a
1bbf1c79
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3034commit whose parent is normally the current HEAD, and whose tree is
3035taken from the content currently stored in the index.
b181d57f 3036
e34caace 3037[[tree-object]]
b181d57f 3038Tree Object
971aa71f 3039~~~~~~~~~~~
b181d57f 3040
5162e697
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3041The ever-versatile linkgit:git-show[1] command can also be used to
3042examine tree objects, but linkgit:git-ls-tree[1] will give you more
1bbf1c79
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3043details:
3044
3045------------------------------------------------
3046$ git ls-tree fb3a8bdd0ce
3047100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore
3048100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap
3049100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING
3050040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation
3051100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN
3052100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL
3053100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile
3054100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README
3055...
3056------------------------------------------------
3057
3058As you can see, a tree object contains a list of entries, each with a
a6e5ef7d 3059mode, object type, SHA-1 name, and name, sorted by name. It represents
1bbf1c79
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3060the contents of a single directory tree.
3061
3062The object type may be a blob, representing the contents of a file, or
3063another tree, representing the contents of a subdirectory. Since trees
a6e5ef7d
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3064and blobs, like all other objects, are named by the SHA-1 hash of their
3065contents, two trees have the same SHA-1 name if and only if their
1bbf1c79 3066contents (including, recursively, the contents of all subdirectories)
2de9b711 3067are identical. This allows Git to quickly determine the differences
1bbf1c79
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3068between two related tree objects, since it can ignore any entries with
3069identical object names.
3070
3071(Note: in the presence of submodules, trees may also have commits as
6dd14366 3072entries. See <<submodules>> for documentation.)
1bbf1c79 3073
2de9b711 3074Note that the files all have mode 644 or 755: Git actually only pays
1bbf1c79 3075attention to the executable bit.
b181d57f 3076
513d419c
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3077[[blob-object]]
3078Blob Object
3079~~~~~~~~~~~
b181d57f 3080
5162e697 3081You can use linkgit:git-show[1] to examine the contents of a blob; take,
1249d8ad 3082for example, the blob in the entry for `COPYING` from the tree above:
b181d57f 3083
1bbf1c79
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3084------------------------------------------------
3085$ git show 6ff87c4664
3086
3087 Note that the only valid version of the GPL as far as this project
3088 is concerned is _this_ particular version of the license (ie v2, not
3089 v2.2 or v3.x or whatever), unless explicitly otherwise stated.
3090...
3091------------------------------------------------
b181d57f 3092
1bbf1c79
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3093A "blob" object is nothing but a binary blob of data. It doesn't refer
3094to anything else or have attributes of any kind.
3095
3096Since the blob is entirely defined by its data, if two files in a
3097directory tree (or in multiple different versions of the repository)
3098have the same contents, they will share the same blob object. The object
3099is totally independent of its location in the directory tree, and
3100renaming a file does not change the object that file is associated with.
3101
3102Note that any tree or blob object can be examined using
5162e697 3103linkgit:git-show[1] with the <revision>:<path> syntax. This can
1bbf1c79
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3104sometimes be useful for browsing the contents of a tree that is not
3105currently checked out.
b181d57f 3106
e34caace 3107[[trust]]
b181d57f 3108Trust
971aa71f 3109~~~~~
b181d57f 3110
a6e5ef7d 3111If you receive the SHA-1 name of a blob from one source, and its contents
1bbf1c79 3112from another (possibly untrusted) source, you can still trust that those
a6e5ef7d
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3113contents are correct as long as the SHA-1 name agrees. This is because
3114the SHA-1 is designed so that it is infeasible to find different contents
1bbf1c79 3115that produce the same hash.
b181d57f 3116
a6e5ef7d 3117Similarly, you need only trust the SHA-1 name of a top-level tree object
1bbf1c79 3118to trust the contents of the entire directory that it refers to, and if
a6e5ef7d 3119you receive the SHA-1 name of a commit from a trusted source, then you
1bbf1c79
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3120can easily verify the entire history of commits reachable through
3121parents of that commit, and all of those contents of the trees referred
3122to by those commits.
b181d57f
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3123
3124So to introduce some real trust in the system, the only thing you need
3125to do is to digitally sign just 'one' special note, which includes the
3126name of a top-level commit. Your digital signature shows others
3127that you trust that commit, and the immutability of the history of
3128commits tells others that they can trust the whole history.
3129
3130In other words, you can easily validate a whole archive by just
a6e5ef7d 3131sending out a single email that tells the people the name (SHA-1 hash)
b181d57f
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3132of the top commit, and digitally sign that email using something
3133like GPG/PGP.
3134
2de9b711 3135To assist in this, Git also provides the tag object...
b181d57f 3136
e34caace 3137[[tag-object]]
b181d57f 3138Tag Object
971aa71f