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1 | Git User's Manual |
2 | _________________ | |
3 | ||
4 | This manual is designed to be readable by someone with basic unix | |
5 | commandline skills, but no previous knowledge of git. | |
6 | ||
ef89f701 | 7 | Chapter 1 gives a brief overview of git commands, without any |
b181d57f | 8 | explanation; you may prefer to skip to chapter 2 on a first reading. |
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9 | |
10 | Chapters 2 and 3 explain how to fetch and study a project using | |
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11 | git--the tools you'd need to build and test a particular version of a |
12 | software project, to search for regressions, and so on. | |
6bd9b682 | 13 | |
ef89f701 | 14 | Chapter 4 explains how to do development with git, and chapter 5 how |
d5cd5de4 | 15 | to share that development with others. |
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16 | |
17 | Further chapters cover more specialized topics. | |
18 | ||
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19 | Comprehensive reference documentation is available through the man |
20 | pages. For a command such as "git clone", just use | |
21 | ||
22 | ------------------------------------------------ | |
23 | $ man git-clone | |
24 | ------------------------------------------------ | |
25 | ||
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26 | Git Quick Start |
27 | =============== | |
28 | ||
29 | This is a quick summary of the major commands; the following chapters | |
30 | will explain how these work in more detail. | |
31 | ||
32 | Creating a new repository | |
33 | ------------------------- | |
34 | ||
35 | From a tarball: | |
36 | ||
37 | ----------------------------------------------- | |
38 | $ tar xzf project.tar.gz | |
39 | $ cd project | |
40 | $ git init | |
41 | Initialized empty Git repository in .git/ | |
42 | $ git add . | |
43 | $ git commit | |
44 | ----------------------------------------------- | |
45 | ||
46 | From a remote repository: | |
47 | ||
48 | ----------------------------------------------- | |
49 | $ git clone git://example.com/pub/project.git | |
50 | $ cd project | |
51 | ----------------------------------------------- | |
52 | ||
53 | Managing branches | |
54 | ----------------- | |
55 | ||
56 | ----------------------------------------------- | |
57 | $ git branch # list all branches in this repo | |
58 | $ git checkout test # switch working directory to branch "test" | |
59 | $ git branch new # create branch "new" starting at current HEAD | |
60 | $ git branch -d new # delete branch "new" | |
61 | ----------------------------------------------- | |
62 | ||
63 | Instead of basing new branch on current HEAD (the default), use: | |
64 | ||
65 | ----------------------------------------------- | |
66 | $ git branch new test # branch named "test" | |
67 | $ git branch new v2.6.15 # tag named v2.6.15 | |
68 | $ git branch new HEAD^ # commit before the most recent | |
69 | $ git branch new HEAD^^ # commit before that | |
70 | $ git branch new test~10 # ten commits before tip of branch "test" | |
71 | ----------------------------------------------- | |
72 | ||
73 | Create and switch to a new branch at the same time: | |
74 | ||
75 | ----------------------------------------------- | |
76 | $ git checkout -b new v2.6.15 | |
77 | ----------------------------------------------- | |
78 | ||
79 | Update and examine branches from the repository you cloned from: | |
80 | ||
81 | ----------------------------------------------- | |
82 | $ git fetch # update | |
83 | $ git branch -r # list | |
84 | origin/master | |
85 | origin/next | |
86 | ... | |
87 | $ git branch checkout -b masterwork origin/master | |
88 | ----------------------------------------------- | |
89 | ||
90 | Fetch a branch from a different repository, and give it a new | |
91 | name in your repository: | |
92 | ||
93 | ----------------------------------------------- | |
94 | $ git fetch git://example.com/project.git theirbranch:mybranch | |
95 | $ git fetch git://example.com/project.git v2.6.15:mybranch | |
96 | ----------------------------------------------- | |
97 | ||
98 | Keep a list of repositories you work with regularly: | |
99 | ||
100 | ----------------------------------------------- | |
101 | $ git remote add example git://example.com/project.git | |
b181d57f | 102 | $ git remote # list remote repositories |
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103 | example |
104 | origin | |
b181d57f | 105 | $ git remote show example # get details |
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106 | * remote example |
107 | URL: git://example.com/project.git | |
108 | Tracked remote branches | |
109 | master next ... | |
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110 | $ git fetch example # update branches from example |
111 | $ git branch -r # list all remote branches | |
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112 | ----------------------------------------------- |
113 | ||
114 | ||
115 | Exploring history | |
116 | ----------------- | |
117 | ||
118 | ----------------------------------------------- | |
119 | $ gitk # visualize and browse history | |
120 | $ git log # list all commits | |
121 | $ git log src/ # ...modifying src/ | |
122 | $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15 | |
123 | $ git log master..test # ...in branch test, not in branch master | |
124 | $ git log test..master # ...in branch master, but not in test | |
125 | $ git log test...master # ...in one branch, not in both | |
126 | $ git log -S'foo()' # ...where difference contain "foo()" | |
127 | $ git log --since="2 weeks ago" | |
128 | $ git log -p # show patches as well | |
129 | $ git show # most recent commit | |
130 | $ git diff v2.6.15..v2.6.16 # diff between two tagged versions | |
131 | $ git diff v2.6.15..HEAD # diff with current head | |
132 | $ git grep "foo()" # search working directory for "foo()" | |
133 | $ git grep v2.6.15 "foo()" # search old tree for "foo()" | |
134 | $ git show v2.6.15:a.txt # look at old version of a.txt | |
135 | ----------------------------------------------- | |
136 | ||
b181d57f | 137 | Search for regressions: |
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138 | |
139 | ----------------------------------------------- | |
140 | $ git bisect start | |
141 | $ git bisect bad # current version is bad | |
142 | $ git bisect good v2.6.13-rc2 # last known good revision | |
143 | Bisecting: 675 revisions left to test after this | |
144 | # test here, then: | |
145 | $ git bisect good # if this revision is good, or | |
146 | $ git bisect bad # if this revision is bad. | |
147 | # repeat until done. | |
148 | ----------------------------------------------- | |
149 | ||
150 | Making changes | |
151 | -------------- | |
152 | ||
153 | Make sure git knows who to blame: | |
154 | ||
155 | ------------------------------------------------ | |
156 | $ cat >~/.gitconfig <<\EOF | |
157 | [user] | |
158 | name = Your Name Comes Here | |
159 | email = you@yourdomain.example.com | |
160 | EOF | |
161 | ------------------------------------------------ | |
162 | ||
163 | Select file contents to include in the next commit, then make the | |
164 | commit: | |
165 | ||
166 | ----------------------------------------------- | |
167 | $ git add a.txt # updated file | |
168 | $ git add b.txt # new file | |
169 | $ git rm c.txt # old file | |
170 | $ git commit | |
171 | ----------------------------------------------- | |
172 | ||
173 | Or, prepare and create the commit in one step: | |
174 | ||
175 | ----------------------------------------------- | |
b181d57f | 176 | $ git commit d.txt # use latest content only of d.txt |
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177 | $ git commit -a # use latest content of all tracked files |
178 | ----------------------------------------------- | |
179 | ||
180 | Merging | |
181 | ------- | |
182 | ||
183 | ----------------------------------------------- | |
184 | $ git merge test # merge branch "test" into the current branch | |
185 | $ git pull git://example.com/project.git master | |
186 | # fetch and merge in remote branch | |
187 | $ git pull . test # equivalent to git merge test | |
188 | ----------------------------------------------- | |
189 | ||
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190 | Sharing your changes |
191 | -------------------- | |
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192 | |
193 | Importing or exporting patches: | |
194 | ||
195 | ----------------------------------------------- | |
196 | $ git format-patch origin..HEAD # format a patch for each commit | |
197 | # in HEAD but not in origin | |
198 | $ git-am mbox # import patches from the mailbox "mbox" | |
199 | ----------------------------------------------- | |
200 | ||
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201 | Fetch a branch in a different git repository, then merge into the |
202 | current branch: | |
203 | ||
204 | ----------------------------------------------- | |
205 | $ git pull git://example.com/project.git theirbranch | |
206 | ----------------------------------------------- | |
207 | ||
208 | Store the fetched branch into a local branch before merging into the | |
209 | current branch: | |
210 | ||
211 | ----------------------------------------------- | |
212 | $ git pull git://example.com/project.git theirbranch:mybranch | |
213 | ----------------------------------------------- | |
214 | ||
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215 | After creating commits on a local branch, update the remote |
216 | branch with your commits: | |
217 | ||
218 | ----------------------------------------------- | |
219 | $ git push ssh://example.com/project.git mybranch:theirbranch | |
220 | ----------------------------------------------- | |
221 | ||
222 | When remote and local branch are both named "test": | |
223 | ||
224 | ----------------------------------------------- | |
225 | $ git push ssh://example.com/project.git test | |
226 | ----------------------------------------------- | |
227 | ||
228 | Shortcut version for a frequently used remote repository: | |
229 | ||
230 | ----------------------------------------------- | |
231 | $ git remote add example ssh://example.com/project.git | |
232 | $ git push example test | |
233 | ----------------------------------------------- | |
234 | ||
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235 | Repository maintenance |
236 | ---------------------- | |
237 | ||
238 | Check for corruption: | |
239 | ||
240 | ----------------------------------------------- | |
04e50e94 | 241 | $ git fsck |
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242 | ----------------------------------------------- |
243 | ||
244 | Recompress, remove unused cruft: | |
245 | ||
246 | ----------------------------------------------- | |
247 | $ git gc | |
248 | ----------------------------------------------- | |
249 | ||
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250 | Repositories and Branches |
251 | ========================= | |
252 | ||
253 | How to get a git repository | |
254 | --------------------------- | |
255 | ||
256 | It will be useful to have a git repository to experiment with as you | |
257 | read this manual. | |
258 | ||
259 | The best way to get one is by using the gitlink:git-clone[1] command | |
260 | to download a copy of an existing repository for a project that you | |
261 | are interested in. If you don't already have a project in mind, here | |
262 | are some interesting examples: | |
263 | ||
264 | ------------------------------------------------ | |
265 | # git itself (approx. 10MB download): | |
266 | $ git clone git://git.kernel.org/pub/scm/git/git.git | |
267 | # the linux kernel (approx. 150MB download): | |
268 | $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git | |
269 | ------------------------------------------------ | |
270 | ||
271 | The initial clone may be time-consuming for a large project, but you | |
272 | will only need to clone once. | |
273 | ||
274 | The clone command creates a new directory named after the project | |
275 | ("git" or "linux-2.6" in the examples above). After you cd into this | |
276 | directory, you will see that it contains a copy of the project files, | |
277 | together with a special top-level directory named ".git", which | |
278 | contains all the information about the history of the project. | |
279 | ||
d5cd5de4 | 280 | In most of the following, examples will be taken from one of the two |
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281 | repositories above. |
282 | ||
283 | How to check out a different version of a project | |
284 | ------------------------------------------------- | |
285 | ||
286 | Git is best thought of as a tool for storing the history of a | |
287 | collection of files. It stores the history as a compressed | |
288 | collection of interrelated snapshots (versions) of the project's | |
289 | contents. | |
290 | ||
291 | A single git repository may contain multiple branches. Each branch | |
292 | is a bookmark referencing a particular point in the project history. | |
293 | The gitlink:git-branch[1] command shows you the list of branches: | |
294 | ||
295 | ------------------------------------------------ | |
296 | $ git branch | |
297 | * master | |
298 | ------------------------------------------------ | |
299 | ||
300 | A freshly cloned repository contains a single branch, named "master", | |
301 | and the working directory contains the version of the project | |
302 | referred to by the master branch. | |
303 | ||
304 | Most projects also use tags. Tags, like branches, are references | |
305 | into the project's history, and can be listed using the | |
306 | gitlink:git-tag[1] command: | |
307 | ||
308 | ------------------------------------------------ | |
309 | $ git tag -l | |
310 | v2.6.11 | |
311 | v2.6.11-tree | |
312 | v2.6.12 | |
313 | v2.6.12-rc2 | |
314 | v2.6.12-rc3 | |
315 | v2.6.12-rc4 | |
316 | v2.6.12-rc5 | |
317 | v2.6.12-rc6 | |
318 | v2.6.13 | |
319 | ... | |
320 | ------------------------------------------------ | |
321 | ||
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322 | Tags are expected to always point at the same version of a project, |
323 | while branches are expected to advance as development progresses. | |
324 | ||
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325 | Create a new branch pointing to one of these versions and check it |
326 | out using gitlink:git-checkout[1]: | |
327 | ||
328 | ------------------------------------------------ | |
329 | $ git checkout -b new v2.6.13 | |
330 | ------------------------------------------------ | |
331 | ||
332 | The working directory then reflects the contents that the project had | |
333 | when it was tagged v2.6.13, and gitlink:git-branch[1] shows two | |
334 | branches, with an asterisk marking the currently checked-out branch: | |
335 | ||
336 | ------------------------------------------------ | |
337 | $ git branch | |
338 | master | |
339 | * new | |
340 | ------------------------------------------------ | |
341 | ||
342 | If you decide that you'd rather see version 2.6.17, you can modify | |
343 | the current branch to point at v2.6.17 instead, with | |
344 | ||
345 | ------------------------------------------------ | |
346 | $ git reset --hard v2.6.17 | |
347 | ------------------------------------------------ | |
348 | ||
349 | Note that if the current branch was your only reference to a | |
350 | particular point in history, then resetting that branch may leave you | |
351 | with no way to find the history it used to point to; so use this | |
352 | command carefully. | |
353 | ||
354 | Understanding History: Commits | |
355 | ------------------------------ | |
356 | ||
357 | Every change in the history of a project is represented by a commit. | |
358 | The gitlink:git-show[1] command shows the most recent commit on the | |
359 | current branch: | |
360 | ||
361 | ------------------------------------------------ | |
362 | $ git show | |
363 | commit 2b5f6dcce5bf94b9b119e9ed8d537098ec61c3d2 | |
364 | Author: Jamal Hadi Salim <hadi@cyberus.ca> | |
365 | Date: Sat Dec 2 22:22:25 2006 -0800 | |
366 | ||
367 | [XFRM]: Fix aevent structuring to be more complete. | |
368 | ||
369 | aevents can not uniquely identify an SA. We break the ABI with this | |
370 | patch, but consensus is that since it is not yet utilized by any | |
371 | (known) application then it is fine (better do it now than later). | |
372 | ||
373 | Signed-off-by: Jamal Hadi Salim <hadi@cyberus.ca> | |
374 | Signed-off-by: David S. Miller <davem@davemloft.net> | |
375 | ||
376 | diff --git a/Documentation/networking/xfrm_sync.txt b/Documentation/networking/xfrm_sync.txt | |
377 | index 8be626f..d7aac9d 100644 | |
378 | --- a/Documentation/networking/xfrm_sync.txt | |
379 | +++ b/Documentation/networking/xfrm_sync.txt | |
380 | @@ -47,10 +47,13 @@ aevent_id structure looks like: | |
381 | ||
382 | struct xfrm_aevent_id { | |
383 | struct xfrm_usersa_id sa_id; | |
384 | + xfrm_address_t saddr; | |
385 | __u32 flags; | |
386 | + __u32 reqid; | |
387 | }; | |
388 | ... | |
389 | ------------------------------------------------ | |
390 | ||
391 | As you can see, a commit shows who made the latest change, what they | |
392 | did, and why. | |
393 | ||
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394 | Every commit has a 40-hexdigit id, sometimes called the "object name" |
395 | or the "SHA1 id", shown on the first line of the "git show" output. | |
396 | You can usually refer to a commit by a shorter name, such as a tag or a | |
397 | branch name, but this longer name can also be useful. Most | |
398 | importantly, it is a globally unique name for this commit: so if you | |
399 | tell somebody else the object name (for example in email), then you are | |
400 | guaranteed that name will refer to the same commit in their repository | |
401 | that you it does in yours (assuming their repository has that commit at | |
402 | all). | |
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403 | |
404 | Understanding history: commits, parents, and reachability | |
405 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
406 | ||
407 | Every commit (except the very first commit in a project) also has a | |
408 | parent commit which shows what happened before this commit. | |
409 | Following the chain of parents will eventually take you back to the | |
410 | beginning of the project. | |
411 | ||
412 | However, the commits do not form a simple list; git allows lines of | |
413 | development to diverge and then reconverge, and the point where two | |
414 | lines of development reconverge is called a "merge". The commit | |
415 | representing a merge can therefore have more than one parent, with | |
416 | each parent representing the most recent commit on one of the lines | |
417 | of development leading to that point. | |
418 | ||
419 | The best way to see how this works is using the gitlink:gitk[1] | |
420 | command; running gitk now on a git repository and looking for merge | |
421 | commits will help understand how the git organizes history. | |
422 | ||
423 | In the following, we say that commit X is "reachable" from commit Y | |
424 | if commit X is an ancestor of commit Y. Equivalently, you could say | |
425 | that Y is a descendent of X, or that there is a chain of parents | |
426 | leading from commit Y to commit X. | |
427 | ||
428 | Undestanding history: History diagrams | |
429 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
430 | ||
431 | We will sometimes represent git history using diagrams like the one | |
432 | below. Commits are shown as "o", and the links between them with | |
433 | lines drawn with - / and \. Time goes left to right: | |
434 | ||
435 | o--o--o <-- Branch A | |
436 | / | |
437 | o--o--o <-- master | |
438 | \ | |
439 | o--o--o <-- Branch B | |
440 | ||
441 | If we need to talk about a particular commit, the character "o" may | |
442 | be replaced with another letter or number. | |
443 | ||
444 | Understanding history: What is a branch? | |
445 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
446 | ||
447 | Though we've been using the word "branch" to mean a kind of reference | |
448 | to a particular commit, the word branch is also commonly used to | |
449 | refer to the line of commits leading up to that point. In the | |
450 | example above, git may think of the branch named "A" as just a | |
451 | pointer to one particular commit, but we may refer informally to the | |
452 | line of three commits leading up to that point as all being part of | |
453 | "branch A". | |
454 | ||
455 | If we need to make it clear that we're just talking about the most | |
456 | recent commit on the branch, we may refer to that commit as the | |
457 | "head" of the branch. | |
458 | ||
459 | Manipulating branches | |
460 | --------------------- | |
461 | ||
462 | Creating, deleting, and modifying branches is quick and easy; here's | |
463 | a summary of the commands: | |
464 | ||
465 | git branch:: | |
466 | list all branches | |
467 | git branch <branch>:: | |
468 | create a new branch named <branch>, referencing the same | |
469 | point in history as the current branch | |
470 | git branch <branch> <start-point>:: | |
471 | create a new branch named <branch>, referencing | |
472 | <start-point>, which may be specified any way you like, | |
473 | including using a branch name or a tag name | |
474 | git branch -d <branch>:: | |
475 | delete the branch <branch>; if the branch you are deleting | |
476 | points to a commit which is not reachable from this branch, | |
477 | this command will fail with a warning. | |
478 | git branch -D <branch>:: | |
479 | even if the branch points to a commit not reachable | |
480 | from the current branch, you may know that that commit | |
481 | is still reachable from some other branch or tag. In that | |
482 | case it is safe to use this command to force git to delete | |
483 | the branch. | |
484 | git checkout <branch>:: | |
485 | make the current branch <branch>, updating the working | |
486 | directory to reflect the version referenced by <branch> | |
487 | git checkout -b <new> <start-point>:: | |
488 | create a new branch <new> referencing <start-point>, and | |
489 | check it out. | |
490 | ||
491 | It is also useful to know that the special symbol "HEAD" can always | |
492 | be used to refer to the current branch. | |
493 | ||
494 | Examining branches from a remote repository | |
495 | ------------------------------------------- | |
496 | ||
497 | The "master" branch that was created at the time you cloned is a copy | |
498 | of the HEAD in the repository that you cloned from. That repository | |
499 | may also have had other branches, though, and your local repository | |
500 | keeps branches which track each of those remote branches, which you | |
501 | can view using the "-r" option to gitlink:git-branch[1]: | |
502 | ||
503 | ------------------------------------------------ | |
504 | $ git branch -r | |
505 | origin/HEAD | |
506 | origin/html | |
507 | origin/maint | |
508 | origin/man | |
509 | origin/master | |
510 | origin/next | |
511 | origin/pu | |
512 | origin/todo | |
513 | ------------------------------------------------ | |
514 | ||
515 | You cannot check out these remote-tracking branches, but you can | |
516 | examine them on a branch of your own, just as you would a tag: | |
517 | ||
518 | ------------------------------------------------ | |
519 | $ git checkout -b my-todo-copy origin/todo | |
520 | ------------------------------------------------ | |
521 | ||
522 | Note that the name "origin" is just the name that git uses by default | |
523 | to refer to the repository that you cloned from. | |
524 | ||
525 | [[how-git-stores-references]] | |
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526 | Naming branches, tags, and other references |
527 | ------------------------------------------- | |
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528 | |
529 | Branches, remote-tracking branches, and tags are all references to | |
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530 | commits. All references are named with a slash-separated path name |
531 | starting with "refs"; the names we've been using so far are actually | |
532 | shorthand: | |
d19fbc3c | 533 | |
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534 | - The branch "test" is short for "refs/heads/test". |
535 | - The tag "v2.6.18" is short for "refs/tags/v2.6.18". | |
536 | - "origin/master" is short for "refs/remotes/origin/master". | |
d19fbc3c | 537 | |
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538 | The full name is occasionally useful if, for example, there ever |
539 | exists a tag and a branch with the same name. | |
d19fbc3c | 540 | |
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541 | As another useful shortcut, if the repository "origin" posesses only |
542 | a single branch, you can refer to that branch as just "origin". | |
d19fbc3c | 543 | |
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544 | More generally, if you have defined a remote repository named |
545 | "example", you can refer to the branch in that repository as | |
546 | "example". And for a repository with multiple branches, this will | |
547 | refer to the branch designated as the "HEAD" branch. | |
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548 | |
549 | For the complete list of paths which git checks for references, and | |
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550 | the order it uses to decide which to choose when there are multiple |
551 | references with the same shorthand name, see the "SPECIFYING | |
552 | REVISIONS" section of gitlink:git-rev-parse[1]. | |
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553 | |
554 | [[Updating-a-repository-with-git-fetch]] | |
555 | Updating a repository with git fetch | |
556 | ------------------------------------ | |
557 | ||
558 | Eventually the developer cloned from will do additional work in her | |
559 | repository, creating new commits and advancing the branches to point | |
560 | at the new commits. | |
561 | ||
562 | The command "git fetch", with no arguments, will update all of the | |
563 | remote-tracking branches to the latest version found in her | |
564 | repository. It will not touch any of your own branches--not even the | |
565 | "master" branch that was created for you on clone. | |
566 | ||
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567 | Fetching branches from other repositories |
568 | ----------------------------------------- | |
569 | ||
570 | You can also track branches from repositories other than the one you | |
571 | cloned from, using gitlink:git-remote[1]: | |
572 | ||
573 | ------------------------------------------------- | |
574 | $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git | |
575 | $ git fetch | |
576 | * refs/remotes/linux-nfs/master: storing branch 'master' ... | |
577 | commit: bf81b46 | |
578 | ------------------------------------------------- | |
579 | ||
580 | New remote-tracking branches will be stored under the shorthand name | |
581 | that you gave "git remote add", in this case linux-nfs: | |
582 | ||
583 | ------------------------------------------------- | |
584 | $ git branch -r | |
585 | linux-nfs/master | |
586 | origin/master | |
587 | ------------------------------------------------- | |
588 | ||
589 | If you run "git fetch <remote>" later, the tracking branches for the | |
590 | named <remote> will be updated. | |
591 | ||
592 | If you examine the file .git/config, you will see that git has added | |
593 | a new stanza: | |
594 | ||
595 | ------------------------------------------------- | |
596 | $ cat .git/config | |
597 | ... | |
598 | [remote "linux-nfs"] | |
599 | url = git://linux-nfs.org/~bfields/git.git | |
600 | fetch = +refs/heads/*:refs/remotes/linux-nfs-read/* | |
601 | ... | |
602 | ------------------------------------------------- | |
603 | ||
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604 | This is what causes git to track the remote's branches; you may modify |
605 | or delete these configuration options by editing .git/config with a | |
606 | text editor. (See the "CONFIGURATION FILE" section of | |
607 | gitlink:git-config[1] for details.) | |
d5cd5de4 | 608 | |
d19fbc3c BF |
609 | Exploring git history |
610 | ===================== | |
611 | ||
612 | Git is best thought of as a tool for storing the history of a | |
613 | collection of files. It does this by storing compressed snapshots of | |
614 | the contents of a file heirarchy, together with "commits" which show | |
615 | the relationships between these snapshots. | |
616 | ||
617 | Git provides extremely flexible and fast tools for exploring the | |
618 | history of a project. | |
619 | ||
620 | We start with one specialized tool which is useful for finding the | |
621 | commit that introduced a bug into a project. | |
622 | ||
623 | How to use bisect to find a regression | |
624 | -------------------------------------- | |
625 | ||
626 | Suppose version 2.6.18 of your project worked, but the version at | |
627 | "master" crashes. Sometimes the best way to find the cause of such a | |
628 | regression is to perform a brute-force search through the project's | |
629 | history to find the particular commit that caused the problem. The | |
630 | gitlink:git-bisect[1] command can help you do this: | |
631 | ||
632 | ------------------------------------------------- | |
633 | $ git bisect start | |
634 | $ git bisect good v2.6.18 | |
635 | $ git bisect bad master | |
636 | Bisecting: 3537 revisions left to test after this | |
637 | [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6] | |
638 | ------------------------------------------------- | |
639 | ||
640 | If you run "git branch" at this point, you'll see that git has | |
641 | temporarily moved you to a new branch named "bisect". This branch | |
642 | points to a commit (with commit id 65934...) that is reachable from | |
643 | v2.6.19 but not from v2.6.18. Compile and test it, and see whether | |
644 | it crashes. Assume it does crash. Then: | |
645 | ||
646 | ------------------------------------------------- | |
647 | $ git bisect bad | |
648 | Bisecting: 1769 revisions left to test after this | |
649 | [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings | |
650 | ------------------------------------------------- | |
651 | ||
652 | checks out an older version. Continue like this, telling git at each | |
653 | stage whether the version it gives you is good or bad, and notice | |
654 | that the number of revisions left to test is cut approximately in | |
655 | half each time. | |
656 | ||
657 | After about 13 tests (in this case), it will output the commit id of | |
658 | the guilty commit. You can then examine the commit with | |
659 | gitlink:git-show[1], find out who wrote it, and mail them your bug | |
660 | report with the commit id. Finally, run | |
661 | ||
662 | ------------------------------------------------- | |
663 | $ git bisect reset | |
664 | ------------------------------------------------- | |
665 | ||
666 | to return you to the branch you were on before and delete the | |
667 | temporary "bisect" branch. | |
668 | ||
669 | Note that the version which git-bisect checks out for you at each | |
670 | point is just a suggestion, and you're free to try a different | |
671 | version if you think it would be a good idea. For example, | |
672 | occasionally you may land on a commit that broke something unrelated; | |
673 | run | |
674 | ||
675 | ------------------------------------------------- | |
676 | $ git bisect-visualize | |
677 | ------------------------------------------------- | |
678 | ||
679 | which will run gitk and label the commit it chose with a marker that | |
680 | says "bisect". Chose a safe-looking commit nearby, note its commit | |
681 | id, and check it out with: | |
682 | ||
683 | ------------------------------------------------- | |
684 | $ git reset --hard fb47ddb2db... | |
685 | ------------------------------------------------- | |
686 | ||
687 | then test, run "bisect good" or "bisect bad" as appropriate, and | |
688 | continue. | |
689 | ||
690 | Naming commits | |
691 | -------------- | |
692 | ||
693 | We have seen several ways of naming commits already: | |
694 | ||
d55ae921 | 695 | - 40-hexdigit object name |
d19fbc3c BF |
696 | - branch name: refers to the commit at the head of the given |
697 | branch | |
698 | - tag name: refers to the commit pointed to by the given tag | |
699 | (we've seen branches and tags are special cases of | |
700 | <<how-git-stores-references,references>>). | |
701 | - HEAD: refers to the head of the current branch | |
702 | ||
eb6ae7f4 | 703 | There are many more; see the "SPECIFYING REVISIONS" section of the |
aec053bb | 704 | gitlink:git-rev-parse[1] man page for the complete list of ways to |
d19fbc3c BF |
705 | name revisions. Some examples: |
706 | ||
707 | ------------------------------------------------- | |
d55ae921 | 708 | $ git show fb47ddb2 # the first few characters of the object name |
d19fbc3c BF |
709 | # are usually enough to specify it uniquely |
710 | $ git show HEAD^ # the parent of the HEAD commit | |
711 | $ git show HEAD^^ # the grandparent | |
712 | $ git show HEAD~4 # the great-great-grandparent | |
713 | ------------------------------------------------- | |
714 | ||
715 | Recall that merge commits may have more than one parent; by default, | |
716 | ^ and ~ follow the first parent listed in the commit, but you can | |
717 | also choose: | |
718 | ||
719 | ------------------------------------------------- | |
720 | $ git show HEAD^1 # show the first parent of HEAD | |
721 | $ git show HEAD^2 # show the second parent of HEAD | |
722 | ------------------------------------------------- | |
723 | ||
724 | In addition to HEAD, there are several other special names for | |
725 | commits: | |
726 | ||
727 | Merges (to be discussed later), as well as operations such as | |
728 | git-reset, which change the currently checked-out commit, generally | |
729 | set ORIG_HEAD to the value HEAD had before the current operation. | |
730 | ||
731 | The git-fetch operation always stores the head of the last fetched | |
732 | branch in FETCH_HEAD. For example, if you run git fetch without | |
733 | specifying a local branch as the target of the operation | |
734 | ||
735 | ------------------------------------------------- | |
736 | $ git fetch git://example.com/proj.git theirbranch | |
737 | ------------------------------------------------- | |
738 | ||
739 | the fetched commits will still be available from FETCH_HEAD. | |
740 | ||
741 | When we discuss merges we'll also see the special name MERGE_HEAD, | |
742 | which refers to the other branch that we're merging in to the current | |
743 | branch. | |
744 | ||
aec053bb | 745 | The gitlink:git-rev-parse[1] command is a low-level command that is |
d55ae921 BF |
746 | occasionally useful for translating some name for a commit to the object |
747 | name for that commit: | |
aec053bb BF |
748 | |
749 | ------------------------------------------------- | |
750 | $ git rev-parse origin | |
751 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
752 | ------------------------------------------------- | |
753 | ||
d19fbc3c BF |
754 | Creating tags |
755 | ------------- | |
756 | ||
757 | We can also create a tag to refer to a particular commit; after | |
758 | running | |
759 | ||
760 | ------------------------------------------------- | |
761 | $ git-tag stable-1 1b2e1d63ff | |
762 | ------------------------------------------------- | |
763 | ||
764 | You can use stable-1 to refer to the commit 1b2e1d63ff. | |
765 | ||
766 | This creates a "lightweight" tag. If the tag is a tag you wish to | |
767 | share with others, and possibly sign cryptographically, then you | |
768 | should create a tag object instead; see the gitlink:git-tag[1] man | |
769 | page for details. | |
770 | ||
771 | Browsing revisions | |
772 | ------------------ | |
773 | ||
774 | The gitlink:git-log[1] command can show lists of commits. On its | |
775 | own, it shows all commits reachable from the parent commit; but you | |
776 | can also make more specific requests: | |
777 | ||
778 | ------------------------------------------------- | |
779 | $ git log v2.5.. # commits since (not reachable from) v2.5 | |
780 | $ git log test..master # commits reachable from master but not test | |
781 | $ git log master..test # ...reachable from test but not master | |
782 | $ git log master...test # ...reachable from either test or master, | |
783 | # but not both | |
784 | $ git log --since="2 weeks ago" # commits from the last 2 weeks | |
785 | $ git log Makefile # commits which modify Makefile | |
786 | $ git log fs/ # ... which modify any file under fs/ | |
787 | $ git log -S'foo()' # commits which add or remove any file data | |
788 | # matching the string 'foo()' | |
789 | ------------------------------------------------- | |
790 | ||
791 | And of course you can combine all of these; the following finds | |
792 | commits since v2.5 which touch the Makefile or any file under fs: | |
793 | ||
794 | ------------------------------------------------- | |
795 | $ git log v2.5.. Makefile fs/ | |
796 | ------------------------------------------------- | |
797 | ||
798 | You can also ask git log to show patches: | |
799 | ||
800 | ------------------------------------------------- | |
801 | $ git log -p | |
802 | ------------------------------------------------- | |
803 | ||
804 | See the "--pretty" option in the gitlink:git-log[1] man page for more | |
805 | display options. | |
806 | ||
807 | Note that git log starts with the most recent commit and works | |
808 | backwards through the parents; however, since git history can contain | |
809 | multiple independant lines of development, the particular order that | |
810 | commits are listed in may be somewhat arbitrary. | |
811 | ||
812 | Generating diffs | |
813 | ---------------- | |
814 | ||
815 | You can generate diffs between any two versions using | |
816 | gitlink:git-diff[1]: | |
817 | ||
818 | ------------------------------------------------- | |
819 | $ git diff master..test | |
820 | ------------------------------------------------- | |
821 | ||
822 | Sometimes what you want instead is a set of patches: | |
823 | ||
824 | ------------------------------------------------- | |
825 | $ git format-patch master..test | |
826 | ------------------------------------------------- | |
827 | ||
828 | will generate a file with a patch for each commit reachable from test | |
829 | but not from master. Note that if master also has commits which are | |
830 | not reachable from test, then the combined result of these patches | |
831 | will not be the same as the diff produced by the git-diff example. | |
832 | ||
833 | Viewing old file versions | |
834 | ------------------------- | |
835 | ||
836 | You can always view an old version of a file by just checking out the | |
837 | correct revision first. But sometimes it is more convenient to be | |
838 | able to view an old version of a single file without checking | |
839 | anything out; this command does that: | |
840 | ||
841 | ------------------------------------------------- | |
842 | $ git show v2.5:fs/locks.c | |
843 | ------------------------------------------------- | |
844 | ||
845 | Before the colon may be anything that names a commit, and after it | |
846 | may be any path to a file tracked by git. | |
847 | ||
aec053bb BF |
848 | Examples |
849 | -------- | |
850 | ||
851 | Check whether two branches point at the same history | |
2f99710c | 852 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
aec053bb BF |
853 | |
854 | Suppose you want to check whether two branches point at the same point | |
855 | in history. | |
856 | ||
857 | ------------------------------------------------- | |
858 | $ git diff origin..master | |
859 | ------------------------------------------------- | |
860 | ||
69f7ad73 BF |
861 | will tell you whether the contents of the project are the same at the |
862 | two branches; in theory, however, it's possible that the same project | |
863 | contents could have been arrived at by two different historical | |
d55ae921 | 864 | routes. You could compare the object names: |
aec053bb BF |
865 | |
866 | ------------------------------------------------- | |
867 | $ git rev-list origin | |
868 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
869 | $ git rev-list master | |
870 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
871 | ------------------------------------------------- | |
872 | ||
69f7ad73 BF |
873 | Or you could recall that the ... operator selects all commits |
874 | contained reachable from either one reference or the other but not | |
875 | both: so | |
aec053bb BF |
876 | |
877 | ------------------------------------------------- | |
878 | $ git log origin...master | |
879 | ------------------------------------------------- | |
880 | ||
881 | will return no commits when the two branches are equal. | |
882 | ||
b181d57f BF |
883 | Find first tagged version including a given fix |
884 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
aec053bb | 885 | |
69f7ad73 BF |
886 | Suppose you know that the commit e05db0fd fixed a certain problem. |
887 | You'd like to find the earliest tagged release that contains that | |
888 | fix. | |
889 | ||
890 | Of course, there may be more than one answer--if the history branched | |
891 | after commit e05db0fd, then there could be multiple "earliest" tagged | |
892 | releases. | |
893 | ||
894 | You could just visually inspect the commits since e05db0fd: | |
895 | ||
896 | ------------------------------------------------- | |
897 | $ gitk e05db0fd.. | |
898 | ------------------------------------------------- | |
899 | ||
b181d57f BF |
900 | Or you can use gitlink:git-name-rev[1], which will give the commit a |
901 | name based on any tag it finds pointing to one of the commit's | |
902 | descendants: | |
903 | ||
904 | ------------------------------------------------- | |
905 | $ git name-rev e05db0fd | |
906 | e05db0fd tags/v1.5.0-rc1^0~23 | |
907 | ------------------------------------------------- | |
908 | ||
909 | The gitlink:git-describe[1] command does the opposite, naming the | |
910 | revision using a tag on which the given commit is based: | |
911 | ||
912 | ------------------------------------------------- | |
913 | $ git describe e05db0fd | |
914 | v1.5.0-rc0-ge05db0f | |
915 | ------------------------------------------------- | |
916 | ||
917 | but that may sometimes help you guess which tags might come after the | |
918 | given commit. | |
919 | ||
920 | If you just want to verify whether a given tagged version contains a | |
921 | given commit, you could use gitlink:git-merge-base[1]: | |
922 | ||
923 | ------------------------------------------------- | |
924 | $ git merge-base e05db0fd v1.5.0-rc1 | |
925 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
926 | ------------------------------------------------- | |
927 | ||
928 | The merge-base command finds a common ancestor of the given commits, | |
929 | and always returns one or the other in the case where one is a | |
930 | descendant of the other; so the above output shows that e05db0fd | |
931 | actually is an ancestor of v1.5.0-rc1. | |
932 | ||
933 | Alternatively, note that | |
934 | ||
935 | ------------------------------------------------- | |
4a7979ca | 936 | $ git log v1.5.0-rc1..e05db0fd |
b181d57f BF |
937 | ------------------------------------------------- |
938 | ||
4a7979ca | 939 | will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, |
b181d57f | 940 | because it outputs only commits that are not reachable from v1.5.0-rc1. |
aec053bb | 941 | |
4a7979ca BF |
942 | As yet another alternative, the gitlink:git-show-branch[1] command lists |
943 | the commits reachable from its arguments with a display on the left-hand | |
944 | side that indicates which arguments that commit is reachable from. So, | |
945 | you can run something like | |
946 | ||
947 | ------------------------------------------------- | |
948 | $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 | |
949 | ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
950 | available | |
951 | ! [v1.5.0-rc0] GIT v1.5.0 preview | |
952 | ! [v1.5.0-rc1] GIT v1.5.0-rc1 | |
953 | ! [v1.5.0-rc2] GIT v1.5.0-rc2 | |
954 | ... | |
955 | ------------------------------------------------- | |
956 | ||
957 | then search for a line that looks like | |
958 | ||
959 | ------------------------------------------------- | |
960 | + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
961 | available | |
962 | ------------------------------------------------- | |
963 | ||
964 | Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and | |
965 | from v1.5.0-rc2, but not from v1.5.0-rc0. | |
966 | ||
967 | ||
d19fbc3c BF |
968 | Developing with git |
969 | =================== | |
970 | ||
971 | Telling git your name | |
972 | --------------------- | |
973 | ||
974 | Before creating any commits, you should introduce yourself to git. The | |
975 | easiest way to do so is: | |
976 | ||
977 | ------------------------------------------------ | |
978 | $ cat >~/.gitconfig <<\EOF | |
979 | [user] | |
980 | name = Your Name Comes Here | |
981 | email = you@yourdomain.example.com | |
982 | EOF | |
983 | ------------------------------------------------ | |
984 | ||
fc90c536 BF |
985 | (See the "CONFIGURATION FILE" section of gitlink:git-config[1] for |
986 | details on the configuration file.) | |
987 | ||
d19fbc3c BF |
988 | |
989 | Creating a new repository | |
990 | ------------------------- | |
991 | ||
992 | Creating a new repository from scratch is very easy: | |
993 | ||
994 | ------------------------------------------------- | |
995 | $ mkdir project | |
996 | $ cd project | |
f1d2b477 | 997 | $ git init |
d19fbc3c BF |
998 | ------------------------------------------------- |
999 | ||
1000 | If you have some initial content (say, a tarball): | |
1001 | ||
1002 | ------------------------------------------------- | |
1003 | $ tar -xzvf project.tar.gz | |
1004 | $ cd project | |
f1d2b477 | 1005 | $ git init |
d19fbc3c BF |
1006 | $ git add . # include everything below ./ in the first commit: |
1007 | $ git commit | |
1008 | ------------------------------------------------- | |
1009 | ||
1010 | [[how-to-make-a-commit]] | |
1011 | how to make a commit | |
1012 | -------------------- | |
1013 | ||
1014 | Creating a new commit takes three steps: | |
1015 | ||
1016 | 1. Making some changes to the working directory using your | |
1017 | favorite editor. | |
1018 | 2. Telling git about your changes. | |
1019 | 3. Creating the commit using the content you told git about | |
1020 | in step 2. | |
1021 | ||
1022 | In practice, you can interleave and repeat steps 1 and 2 as many | |
1023 | times as you want: in order to keep track of what you want committed | |
1024 | at step 3, git maintains a snapshot of the tree's contents in a | |
1025 | special staging area called "the index." | |
1026 | ||
01997b4a BF |
1027 | At the beginning, the content of the index will be identical to |
1028 | that of the HEAD. The command "git diff --cached", which shows | |
1029 | the difference between the HEAD and the index, should therefore | |
1030 | produce no output at that point. | |
eb6ae7f4 | 1031 | |
d19fbc3c BF |
1032 | Modifying the index is easy: |
1033 | ||
1034 | To update the index with the new contents of a modified file, use | |
1035 | ||
1036 | ------------------------------------------------- | |
1037 | $ git add path/to/file | |
1038 | ------------------------------------------------- | |
1039 | ||
1040 | To add the contents of a new file to the index, use | |
1041 | ||
1042 | ------------------------------------------------- | |
1043 | $ git add path/to/file | |
1044 | ------------------------------------------------- | |
1045 | ||
eb6ae7f4 | 1046 | To remove a file from the index and from the working tree, |
d19fbc3c BF |
1047 | |
1048 | ------------------------------------------------- | |
1049 | $ git rm path/to/file | |
1050 | ------------------------------------------------- | |
1051 | ||
1052 | After each step you can verify that | |
1053 | ||
1054 | ------------------------------------------------- | |
1055 | $ git diff --cached | |
1056 | ------------------------------------------------- | |
1057 | ||
1058 | always shows the difference between the HEAD and the index file--this | |
1059 | is what you'd commit if you created the commit now--and that | |
1060 | ||
1061 | ------------------------------------------------- | |
1062 | $ git diff | |
1063 | ------------------------------------------------- | |
1064 | ||
1065 | shows the difference between the working tree and the index file. | |
1066 | ||
1067 | Note that "git add" always adds just the current contents of a file | |
1068 | to the index; further changes to the same file will be ignored unless | |
1069 | you run git-add on the file again. | |
1070 | ||
1071 | When you're ready, just run | |
1072 | ||
1073 | ------------------------------------------------- | |
1074 | $ git commit | |
1075 | ------------------------------------------------- | |
1076 | ||
1077 | and git will prompt you for a commit message and then create the new | |
1078 | commmit. Check to make sure it looks like what you expected with | |
1079 | ||
1080 | ------------------------------------------------- | |
1081 | $ git show | |
1082 | ------------------------------------------------- | |
1083 | ||
1084 | As a special shortcut, | |
1085 | ||
1086 | ------------------------------------------------- | |
1087 | $ git commit -a | |
1088 | ------------------------------------------------- | |
1089 | ||
1090 | will update the index with any files that you've modified or removed | |
1091 | and create a commit, all in one step. | |
1092 | ||
1093 | A number of commands are useful for keeping track of what you're | |
1094 | about to commit: | |
1095 | ||
1096 | ------------------------------------------------- | |
1097 | $ git diff --cached # difference between HEAD and the index; what | |
1098 | # would be commited if you ran "commit" now. | |
1099 | $ git diff # difference between the index file and your | |
1100 | # working directory; changes that would not | |
1101 | # be included if you ran "commit" now. | |
1102 | $ git status # a brief per-file summary of the above. | |
1103 | ------------------------------------------------- | |
1104 | ||
1105 | creating good commit messages | |
1106 | ----------------------------- | |
1107 | ||
1108 | Though not required, it's a good idea to begin the commit message | |
1109 | with a single short (less than 50 character) line summarizing the | |
1110 | change, followed by a blank line and then a more thorough | |
1111 | description. Tools that turn commits into email, for example, use | |
1112 | the first line on the Subject line and the rest of the commit in the | |
1113 | body. | |
1114 | ||
1115 | how to merge | |
1116 | ------------ | |
1117 | ||
1118 | You can rejoin two diverging branches of development using | |
1119 | gitlink:git-merge[1]: | |
1120 | ||
1121 | ------------------------------------------------- | |
1122 | $ git merge branchname | |
1123 | ------------------------------------------------- | |
1124 | ||
1125 | merges the development in the branch "branchname" into the current | |
1126 | branch. If there are conflicts--for example, if the same file is | |
1127 | modified in two different ways in the remote branch and the local | |
1128 | branch--then you are warned; the output may look something like this: | |
1129 | ||
1130 | ------------------------------------------------- | |
1131 | $ git pull . next | |
1132 | Trying really trivial in-index merge... | |
1133 | fatal: Merge requires file-level merging | |
1134 | Nope. | |
1135 | Merging HEAD with 77976da35a11db4580b80ae27e8d65caf5208086 | |
1136 | Merging: | |
1137 | 15e2162 world | |
1138 | 77976da goodbye | |
1139 | found 1 common ancestor(s): | |
1140 | d122ed4 initial | |
1141 | Auto-merging file.txt | |
1142 | CONFLICT (content): Merge conflict in file.txt | |
1143 | Automatic merge failed; fix conflicts and then commit the result. | |
1144 | ------------------------------------------------- | |
1145 | ||
1146 | Conflict markers are left in the problematic files, and after | |
1147 | you resolve the conflicts manually, you can update the index | |
1148 | with the contents and run git commit, as you normally would when | |
1149 | creating a new file. | |
1150 | ||
1151 | If you examine the resulting commit using gitk, you will see that it | |
1152 | has two parents, one pointing to the top of the current branch, and | |
1153 | one to the top of the other branch. | |
1154 | ||
1155 | In more detail: | |
1156 | ||
1157 | [[resolving-a-merge]] | |
1158 | Resolving a merge | |
1159 | ----------------- | |
1160 | ||
1161 | When a merge isn't resolved automatically, git leaves the index and | |
1162 | the working tree in a special state that gives you all the | |
1163 | information you need to help resolve the merge. | |
1164 | ||
1165 | Files with conflicts are marked specially in the index, so until you | |
1166 | resolve the problem and update the index, git commit will fail: | |
1167 | ||
1168 | ------------------------------------------------- | |
1169 | $ git commit | |
1170 | file.txt: needs merge | |
1171 | ------------------------------------------------- | |
1172 | ||
1173 | Also, git status will list those files as "unmerged". | |
1174 | ||
1175 | All of the changes that git was able to merge automatically are | |
1176 | already added to the index file, so gitlink:git-diff[1] shows only | |
1177 | the conflicts. Also, it uses a somewhat unusual syntax: | |
1178 | ||
1179 | ------------------------------------------------- | |
1180 | $ git diff | |
1181 | diff --cc file.txt | |
1182 | index 802992c,2b60207..0000000 | |
1183 | --- a/file.txt | |
1184 | +++ b/file.txt | |
1185 | @@@ -1,1 -1,1 +1,5 @@@ | |
1186 | ++<<<<<<< HEAD:file.txt | |
1187 | +Hello world | |
1188 | ++======= | |
1189 | + Goodbye | |
1190 | ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt | |
1191 | ------------------------------------------------- | |
1192 | ||
1193 | Recall that the commit which will be commited after we resolve this | |
1194 | conflict will have two parents instead of the usual one: one parent | |
1195 | will be HEAD, the tip of the current branch; the other will be the | |
1196 | tip of the other branch, which is stored temporarily in MERGE_HEAD. | |
1197 | ||
1198 | The diff above shows the differences between the working-tree version | |
1199 | of file.txt and two previous version: one version from HEAD, and one | |
1200 | from MERGE_HEAD. So instead of preceding each line by a single "+" | |
1201 | or "-", it now uses two columns: the first column is used for | |
1202 | differences between the first parent and the working directory copy, | |
1203 | and the second for differences between the second parent and the | |
1204 | working directory copy. Thus after resolving the conflict in the | |
1205 | obvious way, the diff will look like: | |
1206 | ||
1207 | ------------------------------------------------- | |
1208 | $ git diff | |
1209 | diff --cc file.txt | |
1210 | index 802992c,2b60207..0000000 | |
1211 | --- a/file.txt | |
1212 | +++ b/file.txt | |
1213 | @@@ -1,1 -1,1 +1,1 @@@ | |
1214 | - Hello world | |
1215 | -Goodbye | |
1216 | ++Goodbye world | |
1217 | ------------------------------------------------- | |
1218 | ||
1219 | This shows that our resolved version deleted "Hello world" from the | |
1220 | first parent, deleted "Goodbye" from the second parent, and added | |
1221 | "Goodbye world", which was previously absent from both. | |
1222 | ||
1223 | The gitlink:git-log[1] command also provides special help for merges: | |
1224 | ||
1225 | ------------------------------------------------- | |
1226 | $ git log --merge | |
1227 | ------------------------------------------------- | |
1228 | ||
1229 | This will list all commits which exist only on HEAD or on MERGE_HEAD, | |
1230 | and which touch an unmerged file. | |
1231 | ||
1232 | We can now add the resolved version to the index and commit: | |
1233 | ||
1234 | ------------------------------------------------- | |
1235 | $ git add file.txt | |
1236 | $ git commit | |
1237 | ------------------------------------------------- | |
1238 | ||
1239 | Note that the commit message will already be filled in for you with | |
1240 | some information about the merge. Normally you can just use this | |
1241 | default message unchanged, but you may add additional commentary of | |
1242 | your own if desired. | |
1243 | ||
1244 | [[undoing-a-merge]] | |
1245 | undoing a merge | |
1246 | --------------- | |
1247 | ||
1248 | If you get stuck and decide to just give up and throw the whole mess | |
1249 | away, you can always return to the pre-merge state with | |
1250 | ||
1251 | ------------------------------------------------- | |
1252 | $ git reset --hard HEAD | |
1253 | ------------------------------------------------- | |
1254 | ||
1255 | Or, if you've already commited the merge that you want to throw away, | |
1256 | ||
1257 | ------------------------------------------------- | |
1258 | $ git reset --hard HEAD^ | |
1259 | ------------------------------------------------- | |
1260 | ||
1261 | However, this last command can be dangerous in some cases--never | |
1262 | throw away a commit you have already committed if that commit may | |
1263 | itself have been merged into another branch, as doing so may confuse | |
1264 | further merges. | |
1265 | ||
1266 | Fast-forward merges | |
1267 | ------------------- | |
1268 | ||
1269 | There is one special case not mentioned above, which is treated | |
1270 | differently. Normally, a merge results in a merge commit, with two | |
1271 | parents, one pointing at each of the two lines of development that | |
1272 | were merged. | |
1273 | ||
1274 | However, if one of the two lines of development is completely | |
1275 | contained within the other--so every commit present in the one is | |
1276 | already contained in the other--then git just performs a | |
1277 | <<fast-forwards,fast forward>>; the head of the current branch is | |
1278 | moved forward to point at the head of the merged-in branch, without | |
1279 | any new commits being created. | |
1280 | ||
b684f830 BF |
1281 | Fixing mistakes |
1282 | --------------- | |
1283 | ||
1284 | If you've messed up the working tree, but haven't yet committed your | |
1285 | mistake, you can return the entire working tree to the last committed | |
1286 | state with | |
1287 | ||
1288 | ------------------------------------------------- | |
1289 | $ git reset --hard HEAD | |
1290 | ------------------------------------------------- | |
1291 | ||
1292 | If you make a commit that you later wish you hadn't, there are two | |
1293 | fundamentally different ways to fix the problem: | |
1294 | ||
1295 | 1. You can create a new commit that undoes whatever was done | |
1296 | by the previous commit. This is the correct thing if your | |
1297 | mistake has already been made public. | |
1298 | ||
1299 | 2. You can go back and modify the old commit. You should | |
1300 | never do this if you have already made the history public; | |
1301 | git does not normally expect the "history" of a project to | |
1302 | change, and cannot correctly perform repeated merges from | |
1303 | a branch that has had its history changed. | |
1304 | ||
1305 | Fixing a mistake with a new commit | |
1306 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1307 | ||
1308 | Creating a new commit that reverts an earlier change is very easy; | |
1309 | just pass the gitlink:git-revert[1] command a reference to the bad | |
1310 | commit; for example, to revert the most recent commit: | |
1311 | ||
1312 | ------------------------------------------------- | |
1313 | $ git revert HEAD | |
1314 | ------------------------------------------------- | |
1315 | ||
1316 | This will create a new commit which undoes the change in HEAD. You | |
1317 | will be given a chance to edit the commit message for the new commit. | |
1318 | ||
1319 | You can also revert an earlier change, for example, the next-to-last: | |
1320 | ||
1321 | ------------------------------------------------- | |
1322 | $ git revert HEAD^ | |
1323 | ------------------------------------------------- | |
1324 | ||
1325 | In this case git will attempt to undo the old change while leaving | |
1326 | intact any changes made since then. If more recent changes overlap | |
1327 | with the changes to be reverted, then you will be asked to fix | |
1328 | conflicts manually, just as in the case of <<resolving-a-merge, | |
1329 | resolving a merge>>. | |
1330 | ||
1331 | Fixing a mistake by editing history | |
1332 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1333 | ||
1334 | If the problematic commit is the most recent commit, and you have not | |
1335 | yet made that commit public, then you may just | |
1336 | <<undoing-a-merge,destroy it using git-reset>>. | |
1337 | ||
1338 | Alternatively, you | |
1339 | can edit the working directory and update the index to fix your | |
1340 | mistake, just as if you were going to <<how-to-make-a-commit,create a | |
1341 | new commit>>, then run | |
1342 | ||
1343 | ------------------------------------------------- | |
1344 | $ git commit --amend | |
1345 | ------------------------------------------------- | |
1346 | ||
1347 | which will replace the old commit by a new commit incorporating your | |
1348 | changes, giving you a chance to edit the old commit message first. | |
1349 | ||
1350 | Again, you should never do this to a commit that may already have | |
1351 | been merged into another branch; use gitlink:git-revert[1] instead in | |
1352 | that case. | |
1353 | ||
1354 | It is also possible to edit commits further back in the history, but | |
1355 | this is an advanced topic to be left for | |
1356 | <<cleaning-up-history,another chapter>>. | |
1357 | ||
1358 | Checking out an old version of a file | |
1359 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1360 | ||
1361 | In the process of undoing a previous bad change, you may find it | |
1362 | useful to check out an older version of a particular file using | |
1363 | gitlink:git-checkout[1]. We've used git checkout before to switch | |
1364 | branches, but it has quite different behavior if it is given a path | |
1365 | name: the command | |
1366 | ||
1367 | ------------------------------------------------- | |
1368 | $ git checkout HEAD^ path/to/file | |
1369 | ------------------------------------------------- | |
1370 | ||
1371 | replaces path/to/file by the contents it had in the commit HEAD^, and | |
1372 | also updates the index to match. It does not change branches. | |
1373 | ||
1374 | If you just want to look at an old version of the file, without | |
1375 | modifying the working directory, you can do that with | |
1376 | gitlink:git-show[1]: | |
1377 | ||
1378 | ------------------------------------------------- | |
1379 | $ git show HEAD^ path/to/file | |
1380 | ------------------------------------------------- | |
1381 | ||
1382 | which will display the given version of the file. | |
1383 | ||
d19fbc3c BF |
1384 | Ensuring good performance |
1385 | ------------------------- | |
1386 | ||
1387 | On large repositories, git depends on compression to keep the history | |
1388 | information from taking up to much space on disk or in memory. | |
1389 | ||
1390 | This compression is not performed automatically. Therefore you | |
17217090 | 1391 | should occasionally run gitlink:git-gc[1]: |
d19fbc3c BF |
1392 | |
1393 | ------------------------------------------------- | |
1394 | $ git gc | |
1395 | ------------------------------------------------- | |
1396 | ||
17217090 BF |
1397 | to recompress the archive. This can be very time-consuming, so |
1398 | you may prefer to run git-gc when you are not doing other work. | |
d19fbc3c | 1399 | |
11e016a3 BF |
1400 | Ensuring reliability |
1401 | -------------------- | |
1402 | ||
1403 | Checking the repository for corruption | |
1404 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1405 | ||
1191ee18 BF |
1406 | The gitlink:git-fsck[1] command runs a number of self-consistency checks |
1407 | on the repository, and reports on any problems. This may take some | |
21dcb3b7 BF |
1408 | time. The most common warning by far is about "dangling" objects: |
1409 | ||
1410 | ------------------------------------------------- | |
04e50e94 | 1411 | $ git fsck |
21dcb3b7 BF |
1412 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
1413 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1414 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1415 | dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb | |
1416 | dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f | |
1417 | dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e | |
1418 | dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 | |
1419 | dangling tree b24c2473f1fd3d91352a624795be026d64c8841f | |
1420 | ... | |
1421 | ------------------------------------------------- | |
1422 | ||
1191ee18 BF |
1423 | Dangling objects are objects that are harmless, but also unnecessary; |
1424 | you can remove them at any time with gitlink:git-prune[1] or the --prune | |
1425 | option to gitlink:git-gc[1]: | |
21dcb3b7 BF |
1426 | |
1427 | ------------------------------------------------- | |
1428 | $ git gc --prune | |
1429 | ------------------------------------------------- | |
1430 | ||
1191ee18 BF |
1431 | This may be time-consuming. Unlike most other git operations (including |
1432 | git-gc when run without any options), it is not safe to prune while | |
1433 | other git operations are in progress in the same repository. | |
21dcb3b7 | 1434 | |
988b27d3 | 1435 | For more about dangling objects, see <<dangling-objects>>. |
21dcb3b7 | 1436 | |
11e016a3 BF |
1437 | |
1438 | Recovering lost changes | |
1439 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
1440 | ||
559e4d7a BF |
1441 | Reflogs |
1442 | ^^^^^^^ | |
1443 | ||
1444 | Say you modify a branch with gitlink:git-reset[1] --hard, and then | |
1445 | realize that the branch was the only reference you had to that point in | |
1446 | history. | |
1447 | ||
1448 | Fortunately, git also keeps a log, called a "reflog", of all the | |
1449 | previous values of each branch. So in this case you can still find the | |
1450 | old history using, for example, | |
1451 | ||
1452 | ------------------------------------------------- | |
1453 | $ git log master@{1} | |
1454 | ------------------------------------------------- | |
1455 | ||
1456 | This lists the commits reachable from the previous version of the head. | |
1457 | This syntax can be used to with any git command that accepts a commit, | |
1458 | not just with git log. Some other examples: | |
1459 | ||
1460 | ------------------------------------------------- | |
1461 | $ git show master@{2} # See where the branch pointed 2, | |
1462 | $ git show master@{3} # 3, ... changes ago. | |
1463 | $ gitk master@{yesterday} # See where it pointed yesterday, | |
1464 | $ gitk master@{"1 week ago"} # ... or last week | |
1465 | ------------------------------------------------- | |
1466 | ||
1467 | The reflogs are kept by default for 30 days, after which they may be | |
1468 | pruned. See gitlink:git-reflink[1] and gitlink:git-gc[1] to learn | |
1469 | how to control this pruning, and see the "SPECIFYING REVISIONS" | |
1470 | section of gitlink:git-rev-parse[1] for details. | |
1471 | ||
1472 | Note that the reflog history is very different from normal git history. | |
1473 | While normal history is shared by every repository that works on the | |
1474 | same project, the reflog history is not shared: it tells you only about | |
1475 | how the branches in your local repository have changed over time. | |
1476 | ||
1477 | Examining dangling objects | |
1478 | ^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
1479 | ||
1480 | In some situations the reflog may not be able to save you. For | |
1481 | example, suppose you delete a branch, then realize you need the history | |
1482 | it pointed you. The reflog is also deleted; however, if you have not | |
1483 | yet pruned the repository, then you may still be able to find | |
1484 | the lost commits; run git-fsck and watch for output that mentions | |
1485 | "dangling commits": | |
1486 | ||
1487 | ------------------------------------------------- | |
1488 | $ git fsck | |
1489 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 | |
1490 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1491 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1492 | ... | |
1493 | ------------------------------------------------- | |
1494 | ||
1495 | and watch for output that mentions "dangling commits". You can examine | |
1496 | one of those dangling commits with, for example, | |
1497 | ||
1498 | ------------------------------------------------ | |
1499 | $ gitk 7281251ddd --not --all | |
1500 | ------------------------------------------------ | |
1501 | ||
1502 | which does what it sounds like: it says that you want to see the commit | |
1503 | history that is described by the dangling commit(s), but not the | |
1504 | history that is described by all your existing branches and tags. Thus | |
1505 | you get exactly the history reachable from that commit that is lost. | |
1506 | (And notice that it might not be just one commit: we only report the | |
1507 | "tip of the line" as being dangling, but there might be a whole deep | |
1508 | and complex commit history that was gotten dropped.) | |
1509 | ||
1510 | If you decide you want the history back, you can always create a new | |
1511 | reference pointing to it, for example, a new branch: | |
1512 | ||
1513 | ------------------------------------------------ | |
1514 | $ git branch recovered-branch 7281251ddd | |
1515 | ------------------------------------------------ | |
1516 | ||
11e016a3 | 1517 | |
d19fbc3c | 1518 | Sharing development with others |
b684f830 | 1519 | =============================== |
d19fbc3c BF |
1520 | |
1521 | [[getting-updates-with-git-pull]] | |
1522 | Getting updates with git pull | |
b684f830 | 1523 | ----------------------------- |
d19fbc3c BF |
1524 | |
1525 | After you clone a repository and make a few changes of your own, you | |
1526 | may wish to check the original repository for updates and merge them | |
1527 | into your own work. | |
1528 | ||
1529 | We have already seen <<Updating-a-repository-with-git-fetch,how to | |
1530 | keep remote tracking branches up to date>> with gitlink:git-fetch[1], | |
1531 | and how to merge two branches. So you can merge in changes from the | |
1532 | original repository's master branch with: | |
1533 | ||
1534 | ------------------------------------------------- | |
1535 | $ git fetch | |
1536 | $ git merge origin/master | |
1537 | ------------------------------------------------- | |
1538 | ||
1539 | However, the gitlink:git-pull[1] command provides a way to do this in | |
1540 | one step: | |
1541 | ||
1542 | ------------------------------------------------- | |
1543 | $ git pull origin master | |
1544 | ------------------------------------------------- | |
1545 | ||
1546 | In fact, "origin" is normally the default repository to pull from, | |
1547 | and the default branch is normally the HEAD of the remote repository, | |
1548 | so often you can accomplish the above with just | |
1549 | ||
1550 | ------------------------------------------------- | |
1551 | $ git pull | |
1552 | ------------------------------------------------- | |
1553 | ||
1554 | See the descriptions of the branch.<name>.remote and | |
9d13bda3 | 1555 | branch.<name>.merge options in gitlink:git-config[1] to learn |
d19fbc3c BF |
1556 | how to control these defaults depending on the current branch. |
1557 | ||
1558 | In addition to saving you keystrokes, "git pull" also helps you by | |
1559 | producing a default commit message documenting the branch and | |
1560 | repository that you pulled from. | |
1561 | ||
1562 | (But note that no such commit will be created in the case of a | |
1563 | <<fast-forwards,fast forward>>; instead, your branch will just be | |
1564 | updated to point to the latest commit from the upstream branch). | |
1565 | ||
1191ee18 BF |
1566 | The git-pull command can also be given "." as the "remote" repository, |
1567 | in which case it just merges in a branch from the current repository; so | |
4c63ff45 BF |
1568 | the commands |
1569 | ||
1570 | ------------------------------------------------- | |
1571 | $ git pull . branch | |
1572 | $ git merge branch | |
1573 | ------------------------------------------------- | |
1574 | ||
1575 | are roughly equivalent. The former is actually very commonly used. | |
1576 | ||
d19fbc3c | 1577 | Submitting patches to a project |
b684f830 | 1578 | ------------------------------- |
d19fbc3c BF |
1579 | |
1580 | If you just have a few changes, the simplest way to submit them may | |
1581 | just be to send them as patches in email: | |
1582 | ||
1583 | First, use gitlink:git-format-patches[1]; for example: | |
1584 | ||
1585 | ------------------------------------------------- | |
eb6ae7f4 | 1586 | $ git format-patch origin |
d19fbc3c BF |
1587 | ------------------------------------------------- |
1588 | ||
1589 | will produce a numbered series of files in the current directory, one | |
1590 | for each patch in the current branch but not in origin/HEAD. | |
1591 | ||
1592 | You can then import these into your mail client and send them by | |
1593 | hand. However, if you have a lot to send at once, you may prefer to | |
1594 | use the gitlink:git-send-email[1] script to automate the process. | |
1595 | Consult the mailing list for your project first to determine how they | |
1596 | prefer such patches be handled. | |
1597 | ||
1598 | Importing patches to a project | |
b684f830 | 1599 | ------------------------------ |
d19fbc3c BF |
1600 | |
1601 | Git also provides a tool called gitlink:git-am[1] (am stands for | |
1602 | "apply mailbox"), for importing such an emailed series of patches. | |
1603 | Just save all of the patch-containing messages, in order, into a | |
1604 | single mailbox file, say "patches.mbox", then run | |
1605 | ||
1606 | ------------------------------------------------- | |
eb6ae7f4 | 1607 | $ git am -3 patches.mbox |
d19fbc3c BF |
1608 | ------------------------------------------------- |
1609 | ||
1610 | Git will apply each patch in order; if any conflicts are found, it | |
1611 | will stop, and you can fix the conflicts as described in | |
01997b4a BF |
1612 | "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells |
1613 | git to perform a merge; if you would prefer it just to abort and | |
1614 | leave your tree and index untouched, you may omit that option.) | |
1615 | ||
1616 | Once the index is updated with the results of the conflict | |
1617 | resolution, instead of creating a new commit, just run | |
d19fbc3c BF |
1618 | |
1619 | ------------------------------------------------- | |
1620 | $ git am --resolved | |
1621 | ------------------------------------------------- | |
1622 | ||
1623 | and git will create the commit for you and continue applying the | |
1624 | remaining patches from the mailbox. | |
1625 | ||
1626 | The final result will be a series of commits, one for each patch in | |
1627 | the original mailbox, with authorship and commit log message each | |
1628 | taken from the message containing each patch. | |
1629 | ||
1630 | [[setting-up-a-public-repository]] | |
1631 | Setting up a public repository | |
b684f830 | 1632 | ------------------------------ |
d19fbc3c BF |
1633 | |
1634 | Another way to submit changes to a project is to simply tell the | |
1635 | maintainer of that project to pull from your repository, exactly as | |
1636 | you did in the section "<<getting-updates-with-git-pull, Getting | |
1637 | updates with git pull>>". | |
1638 | ||
1639 | If you and maintainer both have accounts on the same machine, then | |
1640 | then you can just pull changes from each other's repositories | |
1641 | directly; note that all of the command (gitlink:git-clone[1], | |
1642 | git-fetch[1], git-pull[1], etc.) which accept a URL as an argument | |
1643 | will also accept a local file patch; so, for example, you can | |
1644 | use | |
1645 | ||
1646 | ------------------------------------------------- | |
1647 | $ git clone /path/to/repository | |
1648 | $ git pull /path/to/other/repository | |
1649 | ------------------------------------------------- | |
1650 | ||
1651 | If this sort of setup is inconvenient or impossible, another (more | |
1652 | common) option is to set up a public repository on a public server. | |
1653 | This also allows you to cleanly separate private work in progress | |
1654 | from publicly visible work. | |
1655 | ||
1656 | You will continue to do your day-to-day work in your personal | |
1657 | repository, but periodically "push" changes from your personal | |
1658 | repository into your public repository, allowing other developers to | |
1659 | pull from that repository. So the flow of changes, in a situation | |
1660 | where there is one other developer with a public repository, looks | |
1661 | like this: | |
1662 | ||
1663 | you push | |
1664 | your personal repo ------------------> your public repo | |
1665 | ^ | | |
1666 | | | | |
1667 | | you pull | they pull | |
1668 | | | | |
1669 | | | | |
1670 | | they push V | |
1671 | their public repo <------------------- their repo | |
1672 | ||
1673 | Now, assume your personal repository is in the directory ~/proj. We | |
1674 | first create a new clone of the repository: | |
1675 | ||
1676 | ------------------------------------------------- | |
1677 | $ git clone --bare proj-clone.git | |
1678 | ------------------------------------------------- | |
1679 | ||
1680 | The resulting directory proj-clone.git will contains a "bare" git | |
1681 | repository--it is just the contents of the ".git" directory, without | |
1682 | a checked-out copy of a working directory. | |
1683 | ||
1684 | Next, copy proj-clone.git to the server where you plan to host the | |
1685 | public repository. You can use scp, rsync, or whatever is most | |
1686 | convenient. | |
1687 | ||
1688 | If somebody else maintains the public server, they may already have | |
1689 | set up a git service for you, and you may skip to the section | |
1690 | "<<pushing-changes-to-a-public-repository,Pushing changes to a public | |
1691 | repository>>", below. | |
1692 | ||
1693 | Otherwise, the following sections explain how to export your newly | |
1694 | created public repository: | |
1695 | ||
1696 | [[exporting-via-http]] | |
1697 | Exporting a git repository via http | |
b684f830 | 1698 | ----------------------------------- |
d19fbc3c BF |
1699 | |
1700 | The git protocol gives better performance and reliability, but on a | |
1701 | host with a web server set up, http exports may be simpler to set up. | |
1702 | ||
1703 | All you need to do is place the newly created bare git repository in | |
1704 | a directory that is exported by the web server, and make some | |
1705 | adjustments to give web clients some extra information they need: | |
1706 | ||
1707 | ------------------------------------------------- | |
1708 | $ mv proj.git /home/you/public_html/proj.git | |
1709 | $ cd proj.git | |
1710 | $ git update-server-info | |
1711 | $ chmod a+x hooks/post-update | |
1712 | ------------------------------------------------- | |
1713 | ||
1714 | (For an explanation of the last two lines, see | |
1715 | gitlink:git-update-server-info[1], and the documentation | |
1716 | link:hooks.txt[Hooks used by git].) | |
1717 | ||
1718 | Advertise the url of proj.git. Anybody else should then be able to | |
1719 | clone or pull from that url, for example with a commandline like: | |
1720 | ||
1721 | ------------------------------------------------- | |
1722 | $ git clone http://yourserver.com/~you/proj.git | |
1723 | ------------------------------------------------- | |
1724 | ||
1725 | (See also | |
1726 | link:howto/setup-git-server-over-http.txt[setup-git-server-over-http] | |
1727 | for a slightly more sophisticated setup using WebDAV which also | |
1728 | allows pushing over http.) | |
1729 | ||
1730 | [[exporting-via-git]] | |
1731 | Exporting a git repository via the git protocol | |
b684f830 | 1732 | ----------------------------------------------- |
d19fbc3c BF |
1733 | |
1734 | This is the preferred method. | |
1735 | ||
1736 | For now, we refer you to the gitlink:git-daemon[1] man page for | |
1737 | instructions. (See especially the examples section.) | |
1738 | ||
1739 | [[pushing-changes-to-a-public-repository]] | |
1740 | Pushing changes to a public repository | |
b684f830 | 1741 | -------------------------------------- |
d19fbc3c BF |
1742 | |
1743 | Note that the two techniques outline above (exporting via | |
1744 | <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other | |
1745 | maintainers to fetch your latest changes, but they do not allow write | |
1746 | access, which you will need to update the public repository with the | |
1747 | latest changes created in your private repository. | |
1748 | ||
1749 | The simplest way to do this is using gitlink:git-push[1] and ssh; to | |
1750 | update the remote branch named "master" with the latest state of your | |
1751 | branch named "master", run | |
1752 | ||
1753 | ------------------------------------------------- | |
1754 | $ git push ssh://yourserver.com/~you/proj.git master:master | |
1755 | ------------------------------------------------- | |
1756 | ||
1757 | or just | |
1758 | ||
1759 | ------------------------------------------------- | |
1760 | $ git push ssh://yourserver.com/~you/proj.git master | |
1761 | ------------------------------------------------- | |
1762 | ||
1763 | As with git-fetch, git-push will complain if this does not result in | |
1764 | a <<fast-forwards,fast forward>>. Normally this is a sign of | |
1765 | something wrong. However, if you are sure you know what you're | |
1766 | doing, you may force git-push to perform the update anyway by | |
1767 | proceeding the branch name by a plus sign: | |
1768 | ||
1769 | ------------------------------------------------- | |
1770 | $ git push ssh://yourserver.com/~you/proj.git +master | |
1771 | ------------------------------------------------- | |
1772 | ||
1773 | As with git-fetch, you may also set up configuration options to | |
1774 | save typing; so, for example, after | |
1775 | ||
1776 | ------------------------------------------------- | |
1777 | $ cat >.git/config <<EOF | |
1778 | [remote "public-repo"] | |
1779 | url = ssh://yourserver.com/~you/proj.git | |
1780 | EOF | |
1781 | ------------------------------------------------- | |
1782 | ||
1783 | you should be able to perform the above push with just | |
1784 | ||
1785 | ------------------------------------------------- | |
1786 | $ git push public-repo master | |
1787 | ------------------------------------------------- | |
1788 | ||
1789 | See the explanations of the remote.<name>.url, branch.<name>.remote, | |
9d13bda3 | 1790 | and remote.<name>.push options in gitlink:git-config[1] for |
d19fbc3c BF |
1791 | details. |
1792 | ||
1793 | Setting up a shared repository | |
b684f830 | 1794 | ------------------------------ |
d19fbc3c BF |
1795 | |
1796 | Another way to collaborate is by using a model similar to that | |
1797 | commonly used in CVS, where several developers with special rights | |
1798 | all push to and pull from a single shared repository. See | |
1799 | link:cvs-migration.txt[git for CVS users] for instructions on how to | |
1800 | set this up. | |
1801 | ||
b684f830 BF |
1802 | Allow web browsing of a repository |
1803 | ---------------------------------- | |
d19fbc3c | 1804 | |
b684f830 | 1805 | TODO: Brief setup-instructions for gitweb |
d19fbc3c | 1806 | |
b684f830 BF |
1807 | Examples |
1808 | -------- | |
d19fbc3c | 1809 | |
b684f830 | 1810 | TODO: topic branches, typical roles as in everyday.txt, ? |
d19fbc3c | 1811 | |
d19fbc3c | 1812 | |
d19fbc3c | 1813 | [[cleaning-up-history]] |
4c63ff45 BF |
1814 | Rewriting history and maintaining patch series |
1815 | ============================================== | |
1816 | ||
1817 | Normally commits are only added to a project, never taken away or | |
1818 | replaced. Git is designed with this assumption, and violating it will | |
1819 | cause git's merge machinery (for example) to do the wrong thing. | |
1820 | ||
1821 | However, there is a situation in which it can be useful to violate this | |
1822 | assumption. | |
1823 | ||
1824 | Creating the perfect patch series | |
1825 | --------------------------------- | |
1826 | ||
1827 | Suppose you are a contributor to a large project, and you want to add a | |
1828 | complicated feature, and to present it to the other developers in a way | |
1829 | that makes it easy for them to read your changes, verify that they are | |
1830 | correct, and understand why you made each change. | |
1831 | ||
b181d57f BF |
1832 | If you present all of your changes as a single patch (or commit), they |
1833 | may find it is too much to digest all at once. | |
4c63ff45 BF |
1834 | |
1835 | If you present them with the entire history of your work, complete with | |
1836 | mistakes, corrections, and dead ends, they may be overwhelmed. | |
1837 | ||
1838 | So the ideal is usually to produce a series of patches such that: | |
1839 | ||
1840 | 1. Each patch can be applied in order. | |
1841 | ||
1842 | 2. Each patch includes a single logical change, together with a | |
1843 | message explaining the change. | |
1844 | ||
1845 | 3. No patch introduces a regression: after applying any initial | |
1846 | part of the series, the resulting project still compiles and | |
1847 | works, and has no bugs that it didn't have before. | |
1848 | ||
1849 | 4. The complete series produces the same end result as your own | |
1850 | (probably much messier!) development process did. | |
1851 | ||
b181d57f BF |
1852 | We will introduce some tools that can help you do this, explain how to |
1853 | use them, and then explain some of the problems that can arise because | |
1854 | you are rewriting history. | |
4c63ff45 BF |
1855 | |
1856 | Keeping a patch series up to date using git-rebase | |
1857 | -------------------------------------------------- | |
1858 | ||
1859 | Suppose you have a series of commits in a branch "mywork", which | |
1860 | originally branched off from "origin". | |
1861 | ||
b181d57f BF |
1862 | Suppose you create a branch "mywork" on a remote-tracking branch |
1863 | "origin", and created some commits on top of it: | |
4c63ff45 BF |
1864 | |
1865 | ------------------------------------------------- | |
1866 | $ git checkout -b mywork origin | |
1867 | $ vi file.txt | |
1868 | $ git commit | |
1869 | $ vi otherfile.txt | |
1870 | $ git commit | |
1871 | ... | |
1872 | ------------------------------------------------- | |
1873 | ||
1874 | You have performed no merges into mywork, so it is just a simple linear | |
1875 | sequence of patches on top of "origin": | |
1876 | ||
1877 | ||
1878 | o--o--o <-- origin | |
1879 | \ | |
1880 | o--o--o <-- mywork | |
1881 | ||
1882 | Some more interesting work has been done in the upstream project, and | |
1883 | "origin" has advanced: | |
1884 | ||
1885 | o--o--O--o--o--o <-- origin | |
1886 | \ | |
1887 | a--b--c <-- mywork | |
1888 | ||
1889 | At this point, you could use "pull" to merge your changes back in; | |
1890 | the result would create a new merge commit, like this: | |
1891 | ||
1892 | ||
1893 | o--o--O--o--o--o <-- origin | |
1894 | \ \ | |
1895 | a--b--c--m <-- mywork | |
1896 | ||
1897 | However, if you prefer to keep the history in mywork a simple series of | |
1898 | commits without any merges, you may instead choose to use | |
1899 | gitlink:git-rebase[1]: | |
1900 | ||
1901 | ------------------------------------------------- | |
1902 | $ git checkout mywork | |
1903 | $ git rebase origin | |
1904 | ------------------------------------------------- | |
1905 | ||
b181d57f BF |
1906 | This will remove each of your commits from mywork, temporarily saving |
1907 | them as patches (in a directory named ".dotest"), update mywork to | |
1908 | point at the latest version of origin, then apply each of the saved | |
1909 | patches to the new mywork. The result will look like: | |
4c63ff45 BF |
1910 | |
1911 | ||
1912 | o--o--O--o--o--o <-- origin | |
1913 | \ | |
1914 | a'--b'--c' <-- mywork | |
1915 | ||
b181d57f BF |
1916 | In the process, it may discover conflicts. In that case it will stop |
1917 | and allow you to fix the conflicts; after fixing conflicts, use "git | |
1918 | add" to update the index with those contents, and then, instead of | |
1919 | running git-commit, just run | |
4c63ff45 BF |
1920 | |
1921 | ------------------------------------------------- | |
1922 | $ git rebase --continue | |
1923 | ------------------------------------------------- | |
1924 | ||
1925 | and git will continue applying the rest of the patches. | |
1926 | ||
1927 | At any point you may use the --abort option to abort this process and | |
1928 | return mywork to the state it had before you started the rebase: | |
1929 | ||
1930 | ------------------------------------------------- | |
1931 | $ git rebase --abort | |
1932 | ------------------------------------------------- | |
1933 | ||
1934 | Reordering or selecting from a patch series | |
1935 | ------------------------------------------- | |
1936 | ||
b181d57f BF |
1937 | Given one existing commit, the gitlink:git-cherry-pick[1] command |
1938 | allows you to apply the change introduced by that commit and create a | |
1939 | new commit that records it. So, for example, if "mywork" points to a | |
1940 | series of patches on top of "origin", you might do something like: | |
1941 | ||
1942 | ------------------------------------------------- | |
1943 | $ git checkout -b mywork-new origin | |
1944 | $ gitk origin..mywork & | |
1945 | ------------------------------------------------- | |
1946 | ||
1947 | And browse through the list of patches in the mywork branch using gitk, | |
1948 | applying them (possibly in a different order) to mywork-new using | |
1949 | cherry-pick, and possibly modifying them as you go using commit | |
1950 | --amend. | |
1951 | ||
1952 | Another technique is to use git-format-patch to create a series of | |
1953 | patches, then reset the state to before the patches: | |
4c63ff45 | 1954 | |
b181d57f BF |
1955 | ------------------------------------------------- |
1956 | $ git format-patch origin | |
1957 | $ git reset --hard origin | |
1958 | ------------------------------------------------- | |
4c63ff45 | 1959 | |
b181d57f BF |
1960 | Then modify, reorder, or eliminate patches as preferred before applying |
1961 | them again with gitlink:git-am[1]. | |
4c63ff45 BF |
1962 | |
1963 | Other tools | |
1964 | ----------- | |
1965 | ||
b181d57f BF |
1966 | There are numerous other tools, such as stgit, which exist for the |
1967 | purpose of maintaining a patch series. These are out of the scope of | |
1968 | this manual. | |
4c63ff45 BF |
1969 | |
1970 | Problems with rewriting history | |
1971 | ------------------------------- | |
1972 | ||
b181d57f BF |
1973 | The primary problem with rewriting the history of a branch has to do |
1974 | with merging. Suppose somebody fetches your branch and merges it into | |
1975 | their branch, with a result something like this: | |
1976 | ||
1977 | o--o--O--o--o--o <-- origin | |
1978 | \ \ | |
1979 | t--t--t--m <-- their branch: | |
1980 | ||
1981 | Then suppose you modify the last three commits: | |
1982 | ||
1983 | o--o--o <-- new head of origin | |
1984 | / | |
1985 | o--o--O--o--o--o <-- old head of origin | |
1986 | ||
1987 | If we examined all this history together in one repository, it will | |
1988 | look like: | |
1989 | ||
1990 | o--o--o <-- new head of origin | |
1991 | / | |
1992 | o--o--O--o--o--o <-- old head of origin | |
1993 | \ \ | |
1994 | t--t--t--m <-- their branch: | |
1995 | ||
1996 | Git has no way of knowing that the new head is an updated version of | |
1997 | the old head; it treats this situation exactly the same as it would if | |
1998 | two developers had independently done the work on the old and new heads | |
1999 | in parallel. At this point, if someone attempts to merge the new head | |
2000 | in to their branch, git will attempt to merge together the two (old and | |
2001 | new) lines of development, instead of trying to replace the old by the | |
2002 | new. The results are likely to be unexpected. | |
2003 | ||
2004 | You may still choose to publish branches whose history is rewritten, | |
2005 | and it may be useful for others to be able to fetch those branches in | |
2006 | order to examine or test them, but they should not attempt to pull such | |
2007 | branches into their own work. | |
2008 | ||
2009 | For true distributed development that supports proper merging, | |
2010 | published branches should never be rewritten. | |
2011 | ||
2012 | Advanced branch management | |
2013 | ========================== | |
4c63ff45 | 2014 | |
b181d57f BF |
2015 | Fetching individual branches |
2016 | ---------------------------- | |
2017 | ||
2018 | Instead of using gitlink:git-remote[1], you can also choose just | |
2019 | to update one branch at a time, and to store it locally under an | |
2020 | arbitrary name: | |
2021 | ||
2022 | ------------------------------------------------- | |
2023 | $ git fetch origin todo:my-todo-work | |
2024 | ------------------------------------------------- | |
2025 | ||
2026 | The first argument, "origin", just tells git to fetch from the | |
2027 | repository you originally cloned from. The second argument tells git | |
2028 | to fetch the branch named "todo" from the remote repository, and to | |
2029 | store it locally under the name refs/heads/my-todo-work. | |
2030 | ||
2031 | You can also fetch branches from other repositories; so | |
2032 | ||
2033 | ------------------------------------------------- | |
2034 | $ git fetch git://example.com/proj.git master:example-master | |
2035 | ------------------------------------------------- | |
2036 | ||
2037 | will create a new branch named "example-master" and store in it the | |
2038 | branch named "master" from the repository at the given URL. If you | |
2039 | already have a branch named example-master, it will attempt to | |
2040 | "fast-forward" to the commit given by example.com's master branch. So | |
2041 | next we explain what a fast-forward is: | |
2042 | ||
2043 | [[fast-forwards]] | |
2044 | Understanding git history: fast-forwards | |
2045 | ---------------------------------------- | |
2046 | ||
2047 | In the previous example, when updating an existing branch, "git | |
2048 | fetch" checks to make sure that the most recent commit on the remote | |
2049 | branch is a descendant of the most recent commit on your copy of the | |
2050 | branch before updating your copy of the branch to point at the new | |
2051 | commit. Git calls this process a "fast forward". | |
2052 | ||
2053 | A fast forward looks something like this: | |
2054 | ||
2055 | o--o--o--o <-- old head of the branch | |
2056 | \ | |
2057 | o--o--o <-- new head of the branch | |
2058 | ||
2059 | ||
2060 | In some cases it is possible that the new head will *not* actually be | |
2061 | a descendant of the old head. For example, the developer may have | |
2062 | realized she made a serious mistake, and decided to backtrack, | |
2063 | resulting in a situation like: | |
2064 | ||
2065 | o--o--o--o--a--b <-- old head of the branch | |
2066 | \ | |
2067 | o--o--o <-- new head of the branch | |
2068 | ||
2069 | ||
2070 | ||
2071 | In this case, "git fetch" will fail, and print out a warning. | |
2072 | ||
2073 | In that case, you can still force git to update to the new head, as | |
2074 | described in the following section. However, note that in the | |
2075 | situation above this may mean losing the commits labeled "a" and "b", | |
2076 | unless you've already created a reference of your own pointing to | |
2077 | them. | |
2078 | ||
2079 | Forcing git fetch to do non-fast-forward updates | |
2080 | ------------------------------------------------ | |
2081 | ||
2082 | If git fetch fails because the new head of a branch is not a | |
2083 | descendant of the old head, you may force the update with: | |
2084 | ||
2085 | ------------------------------------------------- | |
2086 | $ git fetch git://example.com/proj.git +master:refs/remotes/example/master | |
2087 | ------------------------------------------------- | |
2088 | ||
2089 | Note the addition of the "+" sign. Be aware that commits which the | |
2090 | old version of example/master pointed at may be lost, as we saw in | |
2091 | the previous section. | |
2092 | ||
2093 | Configuring remote branches | |
2094 | --------------------------- | |
2095 | ||
2096 | We saw above that "origin" is just a shortcut to refer to the | |
2097 | repository which you originally cloned from. This information is | |
2098 | stored in git configuration variables, which you can see using | |
9d13bda3 | 2099 | gitlink:git-config[1]: |
b181d57f BF |
2100 | |
2101 | ------------------------------------------------- | |
9d13bda3 | 2102 | $ git config -l |
b181d57f BF |
2103 | core.repositoryformatversion=0 |
2104 | core.filemode=true | |
2105 | core.logallrefupdates=true | |
2106 | remote.origin.url=git://git.kernel.org/pub/scm/git/git.git | |
2107 | remote.origin.fetch=+refs/heads/*:refs/remotes/origin/* | |
2108 | branch.master.remote=origin | |
2109 | branch.master.merge=refs/heads/master | |
2110 | ------------------------------------------------- | |
2111 | ||
2112 | If there are other repositories that you also use frequently, you can | |
2113 | create similar configuration options to save typing; for example, | |
2114 | after | |
2115 | ||
2116 | ------------------------------------------------- | |
9d13bda3 | 2117 | $ git config remote.example.url git://example.com/proj.git |
b181d57f BF |
2118 | ------------------------------------------------- |
2119 | ||
2120 | then the following two commands will do the same thing: | |
2121 | ||
2122 | ------------------------------------------------- | |
2123 | $ git fetch git://example.com/proj.git master:refs/remotes/example/master | |
2124 | $ git fetch example master:refs/remotes/example/master | |
2125 | ------------------------------------------------- | |
2126 | ||
2127 | Even better, if you add one more option: | |
2128 | ||
2129 | ------------------------------------------------- | |
9d13bda3 | 2130 | $ git config remote.example.fetch master:refs/remotes/example/master |
b181d57f BF |
2131 | ------------------------------------------------- |
2132 | ||
2133 | then the following commands will all do the same thing: | |
2134 | ||
2135 | ------------------------------------------------- | |
2136 | $ git fetch git://example.com/proj.git master:ref/remotes/example/master | |
2137 | $ git fetch example master:ref/remotes/example/master | |
2138 | $ git fetch example example/master | |
2139 | $ git fetch example | |
2140 | ------------------------------------------------- | |
2141 | ||
2142 | You can also add a "+" to force the update each time: | |
2143 | ||
2144 | ------------------------------------------------- | |
9d13bda3 | 2145 | $ git config remote.example.fetch +master:ref/remotes/example/master |
b181d57f BF |
2146 | ------------------------------------------------- |
2147 | ||
2148 | Don't do this unless you're sure you won't mind "git fetch" possibly | |
2149 | throwing away commits on mybranch. | |
2150 | ||
2151 | Also note that all of the above configuration can be performed by | |
2152 | directly editing the file .git/config instead of using | |
9d13bda3 | 2153 | gitlink:git-config[1]. |
b181d57f | 2154 | |
9d13bda3 | 2155 | See gitlink:git-config[1] for more details on the configuration |
b181d57f | 2156 | options mentioned above. |
d19fbc3c | 2157 | |
d19fbc3c BF |
2158 | |
2159 | Git internals | |
2160 | ============= | |
2161 | ||
b181d57f BF |
2162 | There are two object abstractions: the "object database", and the |
2163 | "current directory cache" aka "index". | |
2164 | ||
2165 | The Object Database | |
2166 | ------------------- | |
2167 | ||
2168 | The object database is literally just a content-addressable collection | |
2169 | of objects. All objects are named by their content, which is | |
2170 | approximated by the SHA1 hash of the object itself. Objects may refer | |
2171 | to other objects (by referencing their SHA1 hash), and so you can | |
2172 | build up a hierarchy of objects. | |
2173 | ||
2174 | All objects have a statically determined "type" aka "tag", which is | |
2175 | determined at object creation time, and which identifies the format of | |
2176 | the object (i.e. how it is used, and how it can refer to other | |
2177 | objects). There are currently four different object types: "blob", | |
2178 | "tree", "commit" and "tag". | |
2179 | ||
2180 | A "blob" object cannot refer to any other object, and is, like the type | |
2181 | implies, a pure storage object containing some user data. It is used to | |
2182 | actually store the file data, i.e. a blob object is associated with some | |
2183 | particular version of some file. | |
2184 | ||
2185 | A "tree" object is an object that ties one or more "blob" objects into a | |
2186 | directory structure. In addition, a tree object can refer to other tree | |
2187 | objects, thus creating a directory hierarchy. | |
2188 | ||
2189 | A "commit" object ties such directory hierarchies together into | |
2190 | a DAG of revisions - each "commit" is associated with exactly one tree | |
2191 | (the directory hierarchy at the time of the commit). In addition, a | |
2192 | "commit" refers to one or more "parent" commit objects that describe the | |
2193 | history of how we arrived at that directory hierarchy. | |
2194 | ||
2195 | As a special case, a commit object with no parents is called the "root" | |
2196 | object, and is the point of an initial project commit. Each project | |
2197 | must have at least one root, and while you can tie several different | |
2198 | root objects together into one project by creating a commit object which | |
2199 | has two or more separate roots as its ultimate parents, that's probably | |
2200 | just going to confuse people. So aim for the notion of "one root object | |
2201 | per project", even if git itself does not enforce that. | |
2202 | ||
2203 | A "tag" object symbolically identifies and can be used to sign other | |
2204 | objects. It contains the identifier and type of another object, a | |
2205 | symbolic name (of course!) and, optionally, a signature. | |
2206 | ||
2207 | Regardless of object type, all objects share the following | |
2208 | characteristics: they are all deflated with zlib, and have a header | |
2209 | that not only specifies their type, but also provides size information | |
2210 | about the data in the object. It's worth noting that the SHA1 hash | |
2211 | that is used to name the object is the hash of the original data | |
2212 | plus this header, so `sha1sum` 'file' does not match the object name | |
2213 | for 'file'. | |
2214 | (Historical note: in the dawn of the age of git the hash | |
2215 | was the sha1 of the 'compressed' object.) | |
2216 | ||
2217 | As a result, the general consistency of an object can always be tested | |
2218 | independently of the contents or the type of the object: all objects can | |
2219 | be validated by verifying that (a) their hashes match the content of the | |
2220 | file and (b) the object successfully inflates to a stream of bytes that | |
2221 | forms a sequence of <ascii type without space> + <space> + <ascii decimal | |
2222 | size> + <byte\0> + <binary object data>. | |
2223 | ||
2224 | The structured objects can further have their structure and | |
2225 | connectivity to other objects verified. This is generally done with | |
04e50e94 | 2226 | the `git-fsck` program, which generates a full dependency graph |
b181d57f BF |
2227 | of all objects, and verifies their internal consistency (in addition |
2228 | to just verifying their superficial consistency through the hash). | |
2229 | ||
2230 | The object types in some more detail: | |
2231 | ||
2232 | Blob Object | |
2233 | ----------- | |
2234 | ||
2235 | A "blob" object is nothing but a binary blob of data, and doesn't | |
2236 | refer to anything else. There is no signature or any other | |
2237 | verification of the data, so while the object is consistent (it 'is' | |
2238 | indexed by its sha1 hash, so the data itself is certainly correct), it | |
2239 | has absolutely no other attributes. No name associations, no | |
2240 | permissions. It is purely a blob of data (i.e. normally "file | |
2241 | contents"). | |
2242 | ||
2243 | In particular, since the blob is entirely defined by its data, if two | |
2244 | files in a directory tree (or in multiple different versions of the | |
2245 | repository) have the same contents, they will share the same blob | |
2246 | object. The object is totally independent of its location in the | |
2247 | directory tree, and renaming a file does not change the object that | |
2248 | file is associated with in any way. | |
2249 | ||
2250 | A blob is typically created when gitlink:git-update-index[1] | |
2251 | is run, and its data can be accessed by gitlink:git-cat-file[1]. | |
2252 | ||
2253 | Tree Object | |
2254 | ----------- | |
2255 | ||
2256 | The next hierarchical object type is the "tree" object. A tree object | |
2257 | is a list of mode/name/blob data, sorted by name. Alternatively, the | |
2258 | mode data may specify a directory mode, in which case instead of | |
2259 | naming a blob, that name is associated with another TREE object. | |
2260 | ||
2261 | Like the "blob" object, a tree object is uniquely determined by the | |
2262 | set contents, and so two separate but identical trees will always | |
2263 | share the exact same object. This is true at all levels, i.e. it's | |
2264 | true for a "leaf" tree (which does not refer to any other trees, only | |
2265 | blobs) as well as for a whole subdirectory. | |
2266 | ||
2267 | For that reason a "tree" object is just a pure data abstraction: it | |
2268 | has no history, no signatures, no verification of validity, except | |
2269 | that since the contents are again protected by the hash itself, we can | |
2270 | trust that the tree is immutable and its contents never change. | |
2271 | ||
2272 | So you can trust the contents of a tree to be valid, the same way you | |
2273 | can trust the contents of a blob, but you don't know where those | |
2274 | contents 'came' from. | |
2275 | ||
2276 | Side note on trees: since a "tree" object is a sorted list of | |
2277 | "filename+content", you can create a diff between two trees without | |
2278 | actually having to unpack two trees. Just ignore all common parts, | |
2279 | and your diff will look right. In other words, you can effectively | |
2280 | (and efficiently) tell the difference between any two random trees by | |
2281 | O(n) where "n" is the size of the difference, rather than the size of | |
2282 | the tree. | |
2283 | ||
2284 | Side note 2 on trees: since the name of a "blob" depends entirely and | |
2285 | exclusively on its contents (i.e. there are no names or permissions | |
2286 | involved), you can see trivial renames or permission changes by | |
2287 | noticing that the blob stayed the same. However, renames with data | |
2288 | changes need a smarter "diff" implementation. | |
2289 | ||
2290 | A tree is created with gitlink:git-write-tree[1] and | |
2291 | its data can be accessed by gitlink:git-ls-tree[1]. | |
2292 | Two trees can be compared with gitlink:git-diff-tree[1]. | |
2293 | ||
2294 | Commit Object | |
2295 | ------------- | |
2296 | ||
2297 | The "commit" object is an object that introduces the notion of | |
2298 | history into the picture. In contrast to the other objects, it | |
2299 | doesn't just describe the physical state of a tree, it describes how | |
2300 | we got there, and why. | |
2301 | ||
2302 | A "commit" is defined by the tree-object that it results in, the | |
2303 | parent commits (zero, one or more) that led up to that point, and a | |
2304 | comment on what happened. Again, a commit is not trusted per se: | |
2305 | the contents are well-defined and "safe" due to the cryptographically | |
2306 | strong signatures at all levels, but there is no reason to believe | |
2307 | that the tree is "good" or that the merge information makes sense. | |
2308 | The parents do not have to actually have any relationship with the | |
2309 | result, for example. | |
2310 | ||
2311 | Note on commits: unlike real SCM's, commits do not contain | |
2312 | rename information or file mode change information. All of that is | |
2313 | implicit in the trees involved (the result tree, and the result trees | |
2314 | of the parents), and describing that makes no sense in this idiotic | |
2315 | file manager. | |
2316 | ||
2317 | A commit is created with gitlink:git-commit-tree[1] and | |
2318 | its data can be accessed by gitlink:git-cat-file[1]. | |
2319 | ||
2320 | Trust | |
2321 | ----- | |
2322 | ||
2323 | An aside on the notion of "trust". Trust is really outside the scope | |
2324 | of "git", but it's worth noting a few things. First off, since | |
2325 | everything is hashed with SHA1, you 'can' trust that an object is | |
2326 | intact and has not been messed with by external sources. So the name | |
2327 | of an object uniquely identifies a known state - just not a state that | |
2328 | you may want to trust. | |
2329 | ||
2330 | Furthermore, since the SHA1 signature of a commit refers to the | |
2331 | SHA1 signatures of the tree it is associated with and the signatures | |
2332 | of the parent, a single named commit specifies uniquely a whole set | |
2333 | of history, with full contents. You can't later fake any step of the | |
2334 | way once you have the name of a commit. | |
2335 | ||
2336 | So to introduce some real trust in the system, the only thing you need | |
2337 | to do is to digitally sign just 'one' special note, which includes the | |
2338 | name of a top-level commit. Your digital signature shows others | |
2339 | that you trust that commit, and the immutability of the history of | |
2340 | commits tells others that they can trust the whole history. | |
2341 | ||
2342 | In other words, you can easily validate a whole archive by just | |
2343 | sending out a single email that tells the people the name (SHA1 hash) | |
2344 | of the top commit, and digitally sign that email using something | |
2345 | like GPG/PGP. | |
2346 | ||
2347 | To assist in this, git also provides the tag object... | |
2348 | ||
2349 | Tag Object | |
2350 | ---------- | |
2351 | ||
2352 | Git provides the "tag" object to simplify creating, managing and | |
2353 | exchanging symbolic and signed tokens. The "tag" object at its | |
2354 | simplest simply symbolically identifies another object by containing | |
2355 | the sha1, type and symbolic name. | |
2356 | ||
2357 | However it can optionally contain additional signature information | |
2358 | (which git doesn't care about as long as there's less than 8k of | |
2359 | it). This can then be verified externally to git. | |
2360 | ||
2361 | Note that despite the tag features, "git" itself only handles content | |
2362 | integrity; the trust framework (and signature provision and | |
2363 | verification) has to come from outside. | |
2364 | ||
2365 | A tag is created with gitlink:git-mktag[1], | |
2366 | its data can be accessed by gitlink:git-cat-file[1], | |
2367 | and the signature can be verified by | |
2368 | gitlink:git-verify-tag[1]. | |
2369 | ||
2370 | ||
2371 | The "index" aka "Current Directory Cache" | |
2372 | ----------------------------------------- | |
2373 | ||
2374 | The index is a simple binary file, which contains an efficient | |
2375 | representation of a virtual directory content at some random time. It | |
2376 | does so by a simple array that associates a set of names, dates, | |
2377 | permissions and content (aka "blob") objects together. The cache is | |
2378 | always kept ordered by name, and names are unique (with a few very | |
2379 | specific rules) at any point in time, but the cache has no long-term | |
2380 | meaning, and can be partially updated at any time. | |
2381 | ||
2382 | In particular, the index certainly does not need to be consistent with | |
2383 | the current directory contents (in fact, most operations will depend on | |
2384 | different ways to make the index 'not' be consistent with the directory | |
2385 | hierarchy), but it has three very important attributes: | |
2386 | ||
2387 | '(a) it can re-generate the full state it caches (not just the | |
2388 | directory structure: it contains pointers to the "blob" objects so | |
2389 | that it can regenerate the data too)' | |
2390 | ||
2391 | As a special case, there is a clear and unambiguous one-way mapping | |
2392 | from a current directory cache to a "tree object", which can be | |
2393 | efficiently created from just the current directory cache without | |
2394 | actually looking at any other data. So a directory cache at any one | |
2395 | time uniquely specifies one and only one "tree" object (but has | |
2396 | additional data to make it easy to match up that tree object with what | |
2397 | has happened in the directory) | |
2398 | ||
2399 | '(b) it has efficient methods for finding inconsistencies between that | |
2400 | cached state ("tree object waiting to be instantiated") and the | |
2401 | current state.' | |
2402 | ||
2403 | '(c) it can additionally efficiently represent information about merge | |
2404 | conflicts between different tree objects, allowing each pathname to be | |
2405 | associated with sufficient information about the trees involved that | |
2406 | you can create a three-way merge between them.' | |
2407 | ||
2408 | Those are the three ONLY things that the directory cache does. It's a | |
2409 | cache, and the normal operation is to re-generate it completely from a | |
2410 | known tree object, or update/compare it with a live tree that is being | |
2411 | developed. If you blow the directory cache away entirely, you generally | |
2412 | haven't lost any information as long as you have the name of the tree | |
2413 | that it described. | |
2414 | ||
2415 | At the same time, the index is at the same time also the | |
2416 | staging area for creating new trees, and creating a new tree always | |
2417 | involves a controlled modification of the index file. In particular, | |
2418 | the index file can have the representation of an intermediate tree that | |
2419 | has not yet been instantiated. So the index can be thought of as a | |
2420 | write-back cache, which can contain dirty information that has not yet | |
2421 | been written back to the backing store. | |
2422 | ||
2423 | ||
2424 | ||
2425 | The Workflow | |
2426 | ------------ | |
2427 | ||
2428 | Generally, all "git" operations work on the index file. Some operations | |
2429 | work *purely* on the index file (showing the current state of the | |
2430 | index), but most operations move data to and from the index file. Either | |
2431 | from the database or from the working directory. Thus there are four | |
2432 | main combinations: | |
2433 | ||
2434 | working directory -> index | |
2435 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2436 | ||
2437 | You update the index with information from the working directory with | |
2438 | the gitlink:git-update-index[1] command. You | |
2439 | generally update the index information by just specifying the filename | |
2440 | you want to update, like so: | |
2441 | ||
2442 | ------------------------------------------------- | |
2443 | $ git-update-index filename | |
2444 | ------------------------------------------------- | |
2445 | ||
2446 | but to avoid common mistakes with filename globbing etc, the command | |
2447 | will not normally add totally new entries or remove old entries, | |
2448 | i.e. it will normally just update existing cache entries. | |
2449 | ||
2450 | To tell git that yes, you really do realize that certain files no | |
2451 | longer exist, or that new files should be added, you | |
2452 | should use the `--remove` and `--add` flags respectively. | |
2453 | ||
2454 | NOTE! A `--remove` flag does 'not' mean that subsequent filenames will | |
2455 | necessarily be removed: if the files still exist in your directory | |
2456 | structure, the index will be updated with their new status, not | |
2457 | removed. The only thing `--remove` means is that update-cache will be | |
2458 | considering a removed file to be a valid thing, and if the file really | |
2459 | does not exist any more, it will update the index accordingly. | |
2460 | ||
2461 | As a special case, you can also do `git-update-index --refresh`, which | |
2462 | will refresh the "stat" information of each index to match the current | |
2463 | stat information. It will 'not' update the object status itself, and | |
2464 | it will only update the fields that are used to quickly test whether | |
2465 | an object still matches its old backing store object. | |
2466 | ||
2467 | index -> object database | |
2468 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
2469 | ||
2470 | You write your current index file to a "tree" object with the program | |
2471 | ||
2472 | ------------------------------------------------- | |
2473 | $ git-write-tree | |
2474 | ------------------------------------------------- | |
2475 | ||
2476 | that doesn't come with any options - it will just write out the | |
2477 | current index into the set of tree objects that describe that state, | |
2478 | and it will return the name of the resulting top-level tree. You can | |
2479 | use that tree to re-generate the index at any time by going in the | |
2480 | other direction: | |
2481 | ||
2482 | object database -> index | |
2483 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
2484 | ||
2485 | You read a "tree" file from the object database, and use that to | |
2486 | populate (and overwrite - don't do this if your index contains any | |
2487 | unsaved state that you might want to restore later!) your current | |
2488 | index. Normal operation is just | |
2489 | ||
2490 | ------------------------------------------------- | |
2491 | $ git-read-tree <sha1 of tree> | |
2492 | ------------------------------------------------- | |
2493 | ||
2494 | and your index file will now be equivalent to the tree that you saved | |
2495 | earlier. However, that is only your 'index' file: your working | |
2496 | directory contents have not been modified. | |
2497 | ||
2498 | index -> working directory | |
2499 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2500 | ||
2501 | You update your working directory from the index by "checking out" | |
2502 | files. This is not a very common operation, since normally you'd just | |
2503 | keep your files updated, and rather than write to your working | |
2504 | directory, you'd tell the index files about the changes in your | |
2505 | working directory (i.e. `git-update-index`). | |
2506 | ||
2507 | However, if you decide to jump to a new version, or check out somebody | |
2508 | else's version, or just restore a previous tree, you'd populate your | |
2509 | index file with read-tree, and then you need to check out the result | |
2510 | with | |
2511 | ||
2512 | ------------------------------------------------- | |
2513 | $ git-checkout-index filename | |
2514 | ------------------------------------------------- | |
2515 | ||
2516 | or, if you want to check out all of the index, use `-a`. | |
2517 | ||
2518 | NOTE! git-checkout-index normally refuses to overwrite old files, so | |
2519 | if you have an old version of the tree already checked out, you will | |
2520 | need to use the "-f" flag ('before' the "-a" flag or the filename) to | |
2521 | 'force' the checkout. | |
2522 | ||
2523 | ||
2524 | Finally, there are a few odds and ends which are not purely moving | |
2525 | from one representation to the other: | |
2526 | ||
2527 | Tying it all together | |
2528 | ~~~~~~~~~~~~~~~~~~~~~ | |
2529 | ||
2530 | To commit a tree you have instantiated with "git-write-tree", you'd | |
2531 | create a "commit" object that refers to that tree and the history | |
2532 | behind it - most notably the "parent" commits that preceded it in | |
2533 | history. | |
2534 | ||
2535 | Normally a "commit" has one parent: the previous state of the tree | |
2536 | before a certain change was made. However, sometimes it can have two | |
2537 | or more parent commits, in which case we call it a "merge", due to the | |
2538 | fact that such a commit brings together ("merges") two or more | |
2539 | previous states represented by other commits. | |
2540 | ||
2541 | In other words, while a "tree" represents a particular directory state | |
2542 | of a working directory, a "commit" represents that state in "time", | |
2543 | and explains how we got there. | |
2544 | ||
2545 | You create a commit object by giving it the tree that describes the | |
2546 | state at the time of the commit, and a list of parents: | |
2547 | ||
2548 | ------------------------------------------------- | |
2549 | $ git-commit-tree <tree> -p <parent> [-p <parent2> ..] | |
2550 | ------------------------------------------------- | |
2551 | ||
2552 | and then giving the reason for the commit on stdin (either through | |
2553 | redirection from a pipe or file, or by just typing it at the tty). | |
2554 | ||
2555 | git-commit-tree will return the name of the object that represents | |
2556 | that commit, and you should save it away for later use. Normally, | |
2557 | you'd commit a new `HEAD` state, and while git doesn't care where you | |
2558 | save the note about that state, in practice we tend to just write the | |
2559 | result to the file pointed at by `.git/HEAD`, so that we can always see | |
2560 | what the last committed state was. | |
2561 | ||
2562 | Here is an ASCII art by Jon Loeliger that illustrates how | |
2563 | various pieces fit together. | |
2564 | ||
2565 | ------------ | |
2566 | ||
2567 | commit-tree | |
2568 | commit obj | |
2569 | +----+ | |
2570 | | | | |
2571 | | | | |
2572 | V V | |
2573 | +-----------+ | |
2574 | | Object DB | | |
2575 | | Backing | | |
2576 | | Store | | |
2577 | +-----------+ | |
2578 | ^ | |
2579 | write-tree | | | |
2580 | tree obj | | | |
2581 | | | read-tree | |
2582 | | | tree obj | |
2583 | V | |
2584 | +-----------+ | |
2585 | | Index | | |
2586 | | "cache" | | |
2587 | +-----------+ | |
2588 | update-index ^ | |
2589 | blob obj | | | |
2590 | | | | |
2591 | checkout-index -u | | checkout-index | |
2592 | stat | | blob obj | |
2593 | V | |
2594 | +-----------+ | |
2595 | | Working | | |
2596 | | Directory | | |
2597 | +-----------+ | |
2598 | ||
2599 | ------------ | |
2600 | ||
2601 | ||
2602 | Examining the data | |
2603 | ------------------ | |
2604 | ||
2605 | You can examine the data represented in the object database and the | |
2606 | index with various helper tools. For every object, you can use | |
2607 | gitlink:git-cat-file[1] to examine details about the | |
2608 | object: | |
2609 | ||
2610 | ------------------------------------------------- | |
2611 | $ git-cat-file -t <objectname> | |
2612 | ------------------------------------------------- | |
2613 | ||
2614 | shows the type of the object, and once you have the type (which is | |
2615 | usually implicit in where you find the object), you can use | |
2616 | ||
2617 | ------------------------------------------------- | |
2618 | $ git-cat-file blob|tree|commit|tag <objectname> | |
2619 | ------------------------------------------------- | |
2620 | ||
2621 | to show its contents. NOTE! Trees have binary content, and as a result | |
2622 | there is a special helper for showing that content, called | |
2623 | `git-ls-tree`, which turns the binary content into a more easily | |
2624 | readable form. | |
2625 | ||
2626 | It's especially instructive to look at "commit" objects, since those | |
2627 | tend to be small and fairly self-explanatory. In particular, if you | |
2628 | follow the convention of having the top commit name in `.git/HEAD`, | |
2629 | you can do | |
2630 | ||
2631 | ------------------------------------------------- | |
2632 | $ git-cat-file commit HEAD | |
2633 | ------------------------------------------------- | |
2634 | ||
2635 | to see what the top commit was. | |
2636 | ||
2637 | Merging multiple trees | |
d19fbc3c BF |
2638 | ---------------------- |
2639 | ||
b181d57f BF |
2640 | Git helps you do a three-way merge, which you can expand to n-way by |
2641 | repeating the merge procedure arbitrary times until you finally | |
2642 | "commit" the state. The normal situation is that you'd only do one | |
2643 | three-way merge (two parents), and commit it, but if you like to, you | |
2644 | can do multiple parents in one go. | |
2645 | ||
2646 | To do a three-way merge, you need the two sets of "commit" objects | |
2647 | that you want to merge, use those to find the closest common parent (a | |
2648 | third "commit" object), and then use those commit objects to find the | |
2649 | state of the directory ("tree" object) at these points. | |
2650 | ||
2651 | To get the "base" for the merge, you first look up the common parent | |
2652 | of two commits with | |
2653 | ||
2654 | ------------------------------------------------- | |
2655 | $ git-merge-base <commit1> <commit2> | |
2656 | ------------------------------------------------- | |
2657 | ||
2658 | which will return you the commit they are both based on. You should | |
2659 | now look up the "tree" objects of those commits, which you can easily | |
2660 | do with (for example) | |
2661 | ||
2662 | ------------------------------------------------- | |
2663 | $ git-cat-file commit <commitname> | head -1 | |
2664 | ------------------------------------------------- | |
2665 | ||
2666 | since the tree object information is always the first line in a commit | |
2667 | object. | |
2668 | ||
1191ee18 BF |
2669 | Once you know the three trees you are going to merge (the one "original" |
2670 | tree, aka the common case, and the two "result" trees, aka the branches | |
2671 | you want to merge), you do a "merge" read into the index. This will | |
2672 | complain if it has to throw away your old index contents, so you should | |
b181d57f | 2673 | make sure that you've committed those - in fact you would normally |
1191ee18 BF |
2674 | always do a merge against your last commit (which should thus match what |
2675 | you have in your current index anyway). | |
b181d57f BF |
2676 | |
2677 | To do the merge, do | |
2678 | ||
2679 | ------------------------------------------------- | |
2680 | $ git-read-tree -m -u <origtree> <yourtree> <targettree> | |
2681 | ------------------------------------------------- | |
2682 | ||
2683 | which will do all trivial merge operations for you directly in the | |
2684 | index file, and you can just write the result out with | |
2685 | `git-write-tree`. | |
2686 | ||
2687 | ||
2688 | Merging multiple trees, continued | |
2689 | --------------------------------- | |
2690 | ||
2691 | Sadly, many merges aren't trivial. If there are files that have | |
2692 | been added.moved or removed, or if both branches have modified the | |
2693 | same file, you will be left with an index tree that contains "merge | |
2694 | entries" in it. Such an index tree can 'NOT' be written out to a tree | |
2695 | object, and you will have to resolve any such merge clashes using | |
2696 | other tools before you can write out the result. | |
2697 | ||
2698 | You can examine such index state with `git-ls-files --unmerged` | |
2699 | command. An example: | |
2700 | ||
2701 | ------------------------------------------------ | |
2702 | $ git-read-tree -m $orig HEAD $target | |
2703 | $ git-ls-files --unmerged | |
2704 | 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c | |
2705 | 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c | |
2706 | 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c | |
2707 | ------------------------------------------------ | |
2708 | ||
2709 | Each line of the `git-ls-files --unmerged` output begins with | |
2710 | the blob mode bits, blob SHA1, 'stage number', and the | |
2711 | filename. The 'stage number' is git's way to say which tree it | |
2712 | came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD` | |
2713 | tree, and stage3 `$target` tree. | |
2714 | ||
2715 | Earlier we said that trivial merges are done inside | |
2716 | `git-read-tree -m`. For example, if the file did not change | |
2717 | from `$orig` to `HEAD` nor `$target`, or if the file changed | |
2718 | from `$orig` to `HEAD` and `$orig` to `$target` the same way, | |
2719 | obviously the final outcome is what is in `HEAD`. What the | |
2720 | above example shows is that file `hello.c` was changed from | |
2721 | `$orig` to `HEAD` and `$orig` to `$target` in a different way. | |
2722 | You could resolve this by running your favorite 3-way merge | |
2723 | program, e.g. `diff3` or `merge`, on the blob objects from | |
2724 | these three stages yourself, like this: | |
2725 | ||
2726 | ------------------------------------------------ | |
2727 | $ git-cat-file blob 263414f... >hello.c~1 | |
2728 | $ git-cat-file blob 06fa6a2... >hello.c~2 | |
2729 | $ git-cat-file blob cc44c73... >hello.c~3 | |
2730 | $ merge hello.c~2 hello.c~1 hello.c~3 | |
2731 | ------------------------------------------------ | |
2732 | ||
2733 | This would leave the merge result in `hello.c~2` file, along | |
2734 | with conflict markers if there are conflicts. After verifying | |
2735 | the merge result makes sense, you can tell git what the final | |
2736 | merge result for this file is by: | |
2737 | ||
2738 | ------------------------------------------------- | |
2739 | $ mv -f hello.c~2 hello.c | |
2740 | $ git-update-index hello.c | |
2741 | ------------------------------------------------- | |
2742 | ||
2743 | When a path is in unmerged state, running `git-update-index` for | |
2744 | that path tells git to mark the path resolved. | |
2745 | ||
2746 | The above is the description of a git merge at the lowest level, | |
2747 | to help you understand what conceptually happens under the hood. | |
2748 | In practice, nobody, not even git itself, uses three `git-cat-file` | |
2749 | for this. There is `git-merge-index` program that extracts the | |
2750 | stages to temporary files and calls a "merge" script on it: | |
2751 | ||
2752 | ------------------------------------------------- | |
2753 | $ git-merge-index git-merge-one-file hello.c | |
2754 | ------------------------------------------------- | |
2755 | ||
2756 | and that is what higher level `git resolve` is implemented with. | |
2757 | ||
2758 | How git stores objects efficiently: pack files | |
2759 | ---------------------------------------------- | |
2760 | ||
2761 | We've seen how git stores each object in a file named after the | |
2762 | object's SHA1 hash. | |
2763 | ||
2764 | Unfortunately this system becomes inefficient once a project has a | |
2765 | lot of objects. Try this on an old project: | |
2766 | ||
2767 | ------------------------------------------------ | |
2768 | $ git count-objects | |
2769 | 6930 objects, 47620 kilobytes | |
2770 | ------------------------------------------------ | |
2771 | ||
2772 | The first number is the number of objects which are kept in | |
2773 | individual files. The second is the amount of space taken up by | |
2774 | those "loose" objects. | |
2775 | ||
2776 | You can save space and make git faster by moving these loose objects in | |
2777 | to a "pack file", which stores a group of objects in an efficient | |
2778 | compressed format; the details of how pack files are formatted can be | |
2779 | found in link:technical/pack-format.txt[technical/pack-format.txt]. | |
2780 | ||
2781 | To put the loose objects into a pack, just run git repack: | |
2782 | ||
2783 | ------------------------------------------------ | |
2784 | $ git repack | |
2785 | Generating pack... | |
2786 | Done counting 6020 objects. | |
2787 | Deltifying 6020 objects. | |
2788 | 100% (6020/6020) done | |
2789 | Writing 6020 objects. | |
2790 | 100% (6020/6020) done | |
2791 | Total 6020, written 6020 (delta 4070), reused 0 (delta 0) | |
2792 | Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created. | |
2793 | ------------------------------------------------ | |
2794 | ||
2795 | You can then run | |
2796 | ||
2797 | ------------------------------------------------ | |
2798 | $ git prune | |
2799 | ------------------------------------------------ | |
2800 | ||
2801 | to remove any of the "loose" objects that are now contained in the | |
2802 | pack. This will also remove any unreferenced objects (which may be | |
2803 | created when, for example, you use "git reset" to remove a commit). | |
2804 | You can verify that the loose objects are gone by looking at the | |
2805 | .git/objects directory or by running | |
2806 | ||
2807 | ------------------------------------------------ | |
2808 | $ git count-objects | |
2809 | 0 objects, 0 kilobytes | |
2810 | ------------------------------------------------ | |
2811 | ||
2812 | Although the object files are gone, any commands that refer to those | |
2813 | objects will work exactly as they did before. | |
2814 | ||
2815 | The gitlink:git-gc[1] command performs packing, pruning, and more for | |
2816 | you, so is normally the only high-level command you need. | |
d19fbc3c | 2817 | |
21dcb3b7 BF |
2818 | [[dangling-objects]] |
2819 | Dangling objects | |
61b41790 | 2820 | ---------------- |
21dcb3b7 | 2821 | |
04e50e94 | 2822 | The gitlink:git-fsck[1] command will sometimes complain about dangling |
21dcb3b7 BF |
2823 | objects. They are not a problem. |
2824 | ||
1191ee18 BF |
2825 | The most common cause of dangling objects is that you've rebased a |
2826 | branch, or you have pulled from somebody else who rebased a branch--see | |
2827 | <<cleaning-up-history>>. In that case, the old head of the original | |
2828 | branch still exists, as does obviously everything it pointed to. The | |
2829 | branch pointer itself just doesn't, since you replaced it with another | |
2830 | one. | |
2831 | ||
2832 | There are also other situations too that cause dangling objects. For | |
2833 | example, a "dangling blob" may arise because you did a "git add" of a | |
2834 | file, but then, before you actually committed it and made it part of the | |
2835 | bigger picture, you changed something else in that file and committed | |
2836 | that *updated* thing - the old state that you added originally ends up | |
2837 | not being pointed to by any commit or tree, so it's now a dangling blob | |
2838 | object. | |
2839 | ||
2840 | Similarly, when the "recursive" merge strategy runs, and finds that | |
2841 | there are criss-cross merges and thus more than one merge base (which is | |
2842 | fairly unusual, but it does happen), it will generate one temporary | |
2843 | midway tree (or possibly even more, if you had lots of criss-crossing | |
2844 | merges and more than two merge bases) as a temporary internal merge | |
2845 | base, and again, those are real objects, but the end result will not end | |
2846 | up pointing to them, so they end up "dangling" in your repository. | |
2847 | ||
2848 | Generally, dangling objects aren't anything to worry about. They can | |
2849 | even be very useful: if you screw something up, the dangling objects can | |
2850 | be how you recover your old tree (say, you did a rebase, and realized | |
2851 | that you really didn't want to - you can look at what dangling objects | |
2852 | you have, and decide to reset your head to some old dangling state). | |
21dcb3b7 | 2853 | |
559e4d7a BF |
2854 | For commits, the most useful thing to do with dangling objects tends to |
2855 | be to do a simple | |
21dcb3b7 BF |
2856 | |
2857 | ------------------------------------------------ | |
2858 | $ gitk <dangling-commit-sha-goes-here> --not --all | |
2859 | ------------------------------------------------ | |
2860 | ||
1191ee18 BF |
2861 | For blobs and trees, you can't do the same, but you can examine them. |
2862 | You can just do | |
21dcb3b7 BF |
2863 | |
2864 | ------------------------------------------------ | |
2865 | $ git show <dangling-blob/tree-sha-goes-here> | |
2866 | ------------------------------------------------ | |
2867 | ||
1191ee18 BF |
2868 | to show what the contents of the blob were (or, for a tree, basically |
2869 | what the "ls" for that directory was), and that may give you some idea | |
2870 | of what the operation was that left that dangling object. | |
21dcb3b7 | 2871 | |
1191ee18 BF |
2872 | Usually, dangling blobs and trees aren't very interesting. They're |
2873 | almost always the result of either being a half-way mergebase (the blob | |
2874 | will often even have the conflict markers from a merge in it, if you | |
2875 | have had conflicting merges that you fixed up by hand), or simply | |
2876 | because you interrupted a "git fetch" with ^C or something like that, | |
2877 | leaving _some_ of the new objects in the object database, but just | |
2878 | dangling and useless. | |
21dcb3b7 BF |
2879 | |
2880 | Anyway, once you are sure that you're not interested in any dangling | |
2881 | state, you can just prune all unreachable objects: | |
2882 | ||
2883 | ------------------------------------------------ | |
2884 | $ git prune | |
2885 | ------------------------------------------------ | |
2886 | ||
1191ee18 BF |
2887 | and they'll be gone. But you should only run "git prune" on a quiescent |
2888 | repository - it's kind of like doing a filesystem fsck recovery: you | |
2889 | don't want to do that while the filesystem is mounted. | |
21dcb3b7 | 2890 | |
04e50e94 BF |
2891 | (The same is true of "git-fsck" itself, btw - but since |
2892 | git-fsck never actually *changes* the repository, it just reports | |
2893 | on what it found, git-fsck itself is never "dangerous" to run. | |
21dcb3b7 BF |
2894 | Running it while somebody is actually changing the repository can cause |
2895 | confusing and scary messages, but it won't actually do anything bad. In | |
2896 | contrast, running "git prune" while somebody is actively changing the | |
2897 | repository is a *BAD* idea). | |
2898 | ||
d19fbc3c BF |
2899 | Glossary of git terms |
2900 | ===================== | |
2901 | ||
2902 | include::glossary.txt[] | |
2903 | ||
6bd9b682 BF |
2904 | Notes and todo list for this manual |
2905 | =================================== | |
2906 | ||
2907 | This is a work in progress. | |
2908 | ||
2909 | The basic requirements: | |
2f99710c BF |
2910 | - It must be readable in order, from beginning to end, by |
2911 | someone intelligent with a basic grasp of the unix | |
2912 | commandline, but without any special knowledge of git. If | |
2913 | necessary, any other prerequisites should be specifically | |
2914 | mentioned as they arise. | |
2915 | - Whenever possible, section headings should clearly describe | |
2916 | the task they explain how to do, in language that requires | |
2917 | no more knowledge than necessary: for example, "importing | |
2918 | patches into a project" rather than "the git-am command" | |
6bd9b682 | 2919 | |
d5cd5de4 BF |
2920 | Think about how to create a clear chapter dependency graph that will |
2921 | allow people to get to important topics without necessarily reading | |
2922 | everything in between. | |
d19fbc3c BF |
2923 | |
2924 | Scan Documentation/ for other stuff left out; in particular: | |
2925 | howto's | |
d19fbc3c BF |
2926 | some of technical/? |
2927 | hooks | |
2928 | etc. | |
2929 | ||
2930 | Scan email archives for other stuff left out | |
2931 | ||
2932 | Scan man pages to see if any assume more background than this manual | |
2933 | provides. | |
2934 | ||
2f99710c | 2935 | Simplify beginning by suggesting disconnected head instead of |
b181d57f | 2936 | temporary branch creation? |
d19fbc3c BF |
2937 | |
2938 | Explain how to refer to file stages in the "how to resolve a merge" | |
e9c0390a | 2939 | section: diff -1, -2, -3, --ours, --theirs :1:/path notation. The |
2f99710c | 2940 | "git ls-files --unmerged --stage" thing is sorta useful too, |
b181d57f | 2941 | actually. And note gitk --merge. |
e9c0390a | 2942 | |
2f99710c BF |
2943 | Add more good examples. Entire sections of just cookbook examples |
2944 | might be a good idea; maybe make an "advanced examples" section a | |
2945 | standard end-of-chapter section? | |
d19fbc3c BF |
2946 | |
2947 | Include cross-references to the glossary, where appropriate. | |
2948 | ||
9a241220 BF |
2949 | Document shallow clones? See draft 1.5.0 release notes for some |
2950 | documentation. | |
2951 | ||
2952 | Add a sectin on working with other version control systems, including | |
2953 | CVS, Subversion, and just imports of series of release tarballs. | |
2954 |