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1 | Git User's Manual |
2 | _________________ | |
3 | ||
4 | This manual is designed to be readable by someone with basic unix | |
79c96c57 | 5 | command-line skills, but no previous knowledge of git. |
d19fbc3c | 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" or the |
395 | "SHA1 id", shown on the first line of the "git show" output. You can usually | |
396 | refer to a commit by a shorter name, such as a tag or a branch name, but this | |
397 | longer name can also be useful. Most importantly, it is a globally unique | |
398 | name for this commit: so if you tell somebody else the object name (for | |
399 | example in email), then you are guaranteed that name will refer to the same | |
400 | commit in their repository that it does in yours (assuming their repository | |
401 | has that commit at all). Since the object name is computed as a hash over the | |
402 | contents of the commit, you are guaranteed that the commit can never change | |
403 | without its name also changing. | |
404 | ||
405 | In fact, in <<git-internals>> we shall see that everything stored in git | |
406 | history, including file data and directory contents, is stored in an object | |
407 | with a name that is a hash of its contents. | |
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408 | |
409 | Understanding history: commits, parents, and reachability | |
410 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
411 | ||
412 | Every commit (except the very first commit in a project) also has a | |
413 | parent commit which shows what happened before this commit. | |
414 | Following the chain of parents will eventually take you back to the | |
415 | beginning of the project. | |
416 | ||
417 | However, the commits do not form a simple list; git allows lines of | |
418 | development to diverge and then reconverge, and the point where two | |
419 | lines of development reconverge is called a "merge". The commit | |
420 | representing a merge can therefore have more than one parent, with | |
421 | each parent representing the most recent commit on one of the lines | |
422 | of development leading to that point. | |
423 | ||
424 | The best way to see how this works is using the gitlink:gitk[1] | |
425 | command; running gitk now on a git repository and looking for merge | |
426 | commits will help understand how the git organizes history. | |
427 | ||
428 | In the following, we say that commit X is "reachable" from commit Y | |
429 | if commit X is an ancestor of commit Y. Equivalently, you could say | |
430 | that Y is a descendent of X, or that there is a chain of parents | |
431 | leading from commit Y to commit X. | |
432 | ||
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433 | Understanding history: History diagrams |
434 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
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435 | |
436 | We will sometimes represent git history using diagrams like the one | |
437 | below. Commits are shown as "o", and the links between them with | |
438 | lines drawn with - / and \. Time goes left to right: | |
439 | ||
440 | o--o--o <-- Branch A | |
441 | / | |
442 | o--o--o <-- master | |
443 | \ | |
444 | o--o--o <-- Branch B | |
445 | ||
446 | If we need to talk about a particular commit, the character "o" may | |
447 | be replaced with another letter or number. | |
448 | ||
449 | Understanding history: What is a branch? | |
450 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
451 | ||
452 | Though we've been using the word "branch" to mean a kind of reference | |
453 | to a particular commit, the word branch is also commonly used to | |
454 | refer to the line of commits leading up to that point. In the | |
455 | example above, git may think of the branch named "A" as just a | |
456 | pointer to one particular commit, but we may refer informally to the | |
457 | line of three commits leading up to that point as all being part of | |
458 | "branch A". | |
459 | ||
460 | If we need to make it clear that we're just talking about the most | |
461 | recent commit on the branch, we may refer to that commit as the | |
462 | "head" of the branch. | |
463 | ||
464 | Manipulating branches | |
465 | --------------------- | |
466 | ||
467 | Creating, deleting, and modifying branches is quick and easy; here's | |
468 | a summary of the commands: | |
469 | ||
470 | git branch:: | |
471 | list all branches | |
472 | git branch <branch>:: | |
473 | create a new branch named <branch>, referencing the same | |
474 | point in history as the current branch | |
475 | git branch <branch> <start-point>:: | |
476 | create a new branch named <branch>, referencing | |
477 | <start-point>, which may be specified any way you like, | |
478 | including using a branch name or a tag name | |
479 | git branch -d <branch>:: | |
480 | delete the branch <branch>; if the branch you are deleting | |
481 | points to a commit which is not reachable from this branch, | |
482 | this command will fail with a warning. | |
483 | git branch -D <branch>:: | |
484 | even if the branch points to a commit not reachable | |
485 | from the current branch, you may know that that commit | |
486 | is still reachable from some other branch or tag. In that | |
487 | case it is safe to use this command to force git to delete | |
488 | the branch. | |
489 | git checkout <branch>:: | |
490 | make the current branch <branch>, updating the working | |
491 | directory to reflect the version referenced by <branch> | |
492 | git checkout -b <new> <start-point>:: | |
493 | create a new branch <new> referencing <start-point>, and | |
494 | check it out. | |
495 | ||
496 | It is also useful to know that the special symbol "HEAD" can always | |
497 | be used to refer to the current branch. | |
498 | ||
499 | Examining branches from a remote repository | |
500 | ------------------------------------------- | |
501 | ||
502 | The "master" branch that was created at the time you cloned is a copy | |
503 | of the HEAD in the repository that you cloned from. That repository | |
504 | may also have had other branches, though, and your local repository | |
505 | keeps branches which track each of those remote branches, which you | |
506 | can view using the "-r" option to gitlink:git-branch[1]: | |
507 | ||
508 | ------------------------------------------------ | |
509 | $ git branch -r | |
510 | origin/HEAD | |
511 | origin/html | |
512 | origin/maint | |
513 | origin/man | |
514 | origin/master | |
515 | origin/next | |
516 | origin/pu | |
517 | origin/todo | |
518 | ------------------------------------------------ | |
519 | ||
520 | You cannot check out these remote-tracking branches, but you can | |
521 | examine them on a branch of your own, just as you would a tag: | |
522 | ||
523 | ------------------------------------------------ | |
524 | $ git checkout -b my-todo-copy origin/todo | |
525 | ------------------------------------------------ | |
526 | ||
527 | Note that the name "origin" is just the name that git uses by default | |
528 | to refer to the repository that you cloned from. | |
529 | ||
530 | [[how-git-stores-references]] | |
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531 | Naming branches, tags, and other references |
532 | ------------------------------------------- | |
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533 | |
534 | Branches, remote-tracking branches, and tags are all references to | |
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535 | commits. All references are named with a slash-separated path name |
536 | starting with "refs"; the names we've been using so far are actually | |
537 | shorthand: | |
d19fbc3c | 538 | |
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539 | - The branch "test" is short for "refs/heads/test". |
540 | - The tag "v2.6.18" is short for "refs/tags/v2.6.18". | |
541 | - "origin/master" is short for "refs/remotes/origin/master". | |
d19fbc3c | 542 | |
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543 | The full name is occasionally useful if, for example, there ever |
544 | exists a tag and a branch with the same name. | |
d19fbc3c | 545 | |
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546 | As another useful shortcut, if the repository "origin" posesses only |
547 | a single branch, you can refer to that branch as just "origin". | |
d19fbc3c | 548 | |
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549 | More generally, if you have defined a remote repository named |
550 | "example", you can refer to the branch in that repository as | |
551 | "example". And for a repository with multiple branches, this will | |
552 | refer to the branch designated as the "HEAD" branch. | |
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553 | |
554 | For the complete list of paths which git checks for references, and | |
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555 | the order it uses to decide which to choose when there are multiple |
556 | references with the same shorthand name, see the "SPECIFYING | |
557 | REVISIONS" section of gitlink:git-rev-parse[1]. | |
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558 | |
559 | [[Updating-a-repository-with-git-fetch]] | |
560 | Updating a repository with git fetch | |
561 | ------------------------------------ | |
562 | ||
563 | Eventually the developer cloned from will do additional work in her | |
564 | repository, creating new commits and advancing the branches to point | |
565 | at the new commits. | |
566 | ||
567 | The command "git fetch", with no arguments, will update all of the | |
568 | remote-tracking branches to the latest version found in her | |
569 | repository. It will not touch any of your own branches--not even the | |
570 | "master" branch that was created for you on clone. | |
571 | ||
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572 | Fetching branches from other repositories |
573 | ----------------------------------------- | |
574 | ||
575 | You can also track branches from repositories other than the one you | |
576 | cloned from, using gitlink:git-remote[1]: | |
577 | ||
578 | ------------------------------------------------- | |
579 | $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git | |
580 | $ git fetch | |
581 | * refs/remotes/linux-nfs/master: storing branch 'master' ... | |
582 | commit: bf81b46 | |
583 | ------------------------------------------------- | |
584 | ||
585 | New remote-tracking branches will be stored under the shorthand name | |
586 | that you gave "git remote add", in this case linux-nfs: | |
587 | ||
588 | ------------------------------------------------- | |
589 | $ git branch -r | |
590 | linux-nfs/master | |
591 | origin/master | |
592 | ------------------------------------------------- | |
593 | ||
594 | If you run "git fetch <remote>" later, the tracking branches for the | |
595 | named <remote> will be updated. | |
596 | ||
597 | If you examine the file .git/config, you will see that git has added | |
598 | a new stanza: | |
599 | ||
600 | ------------------------------------------------- | |
601 | $ cat .git/config | |
602 | ... | |
603 | [remote "linux-nfs"] | |
923642fe BF |
604 | url = git://linux-nfs.org/pub/nfs-2.6.git |
605 | fetch = +refs/heads/*:refs/remotes/linux-nfs/* | |
d5cd5de4 BF |
606 | ... |
607 | ------------------------------------------------- | |
608 | ||
fc90c536 BF |
609 | This is what causes git to track the remote's branches; you may modify |
610 | or delete these configuration options by editing .git/config with a | |
611 | text editor. (See the "CONFIGURATION FILE" section of | |
612 | gitlink:git-config[1] for details.) | |
d5cd5de4 | 613 | |
d19fbc3c BF |
614 | Exploring git history |
615 | ===================== | |
616 | ||
617 | Git is best thought of as a tool for storing the history of a | |
618 | collection of files. It does this by storing compressed snapshots of | |
619 | the contents of a file heirarchy, together with "commits" which show | |
620 | the relationships between these snapshots. | |
621 | ||
622 | Git provides extremely flexible and fast tools for exploring the | |
623 | history of a project. | |
624 | ||
aacd404e | 625 | We start with one specialized tool that is useful for finding the |
d19fbc3c BF |
626 | commit that introduced a bug into a project. |
627 | ||
628 | How to use bisect to find a regression | |
629 | -------------------------------------- | |
630 | ||
631 | Suppose version 2.6.18 of your project worked, but the version at | |
632 | "master" crashes. Sometimes the best way to find the cause of such a | |
633 | regression is to perform a brute-force search through the project's | |
634 | history to find the particular commit that caused the problem. The | |
635 | gitlink:git-bisect[1] command can help you do this: | |
636 | ||
637 | ------------------------------------------------- | |
638 | $ git bisect start | |
639 | $ git bisect good v2.6.18 | |
640 | $ git bisect bad master | |
641 | Bisecting: 3537 revisions left to test after this | |
642 | [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6] | |
643 | ------------------------------------------------- | |
644 | ||
645 | If you run "git branch" at this point, you'll see that git has | |
646 | temporarily moved you to a new branch named "bisect". This branch | |
647 | points to a commit (with commit id 65934...) that is reachable from | |
648 | v2.6.19 but not from v2.6.18. Compile and test it, and see whether | |
649 | it crashes. Assume it does crash. Then: | |
650 | ||
651 | ------------------------------------------------- | |
652 | $ git bisect bad | |
653 | Bisecting: 1769 revisions left to test after this | |
654 | [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings | |
655 | ------------------------------------------------- | |
656 | ||
657 | checks out an older version. Continue like this, telling git at each | |
658 | stage whether the version it gives you is good or bad, and notice | |
659 | that the number of revisions left to test is cut approximately in | |
660 | half each time. | |
661 | ||
662 | After about 13 tests (in this case), it will output the commit id of | |
663 | the guilty commit. You can then examine the commit with | |
664 | gitlink:git-show[1], find out who wrote it, and mail them your bug | |
665 | report with the commit id. Finally, run | |
666 | ||
667 | ------------------------------------------------- | |
668 | $ git bisect reset | |
669 | ------------------------------------------------- | |
670 | ||
671 | to return you to the branch you were on before and delete the | |
672 | temporary "bisect" branch. | |
673 | ||
674 | Note that the version which git-bisect checks out for you at each | |
675 | point is just a suggestion, and you're free to try a different | |
676 | version if you think it would be a good idea. For example, | |
677 | occasionally you may land on a commit that broke something unrelated; | |
678 | run | |
679 | ||
680 | ------------------------------------------------- | |
681 | $ git bisect-visualize | |
682 | ------------------------------------------------- | |
683 | ||
684 | which will run gitk and label the commit it chose with a marker that | |
685 | says "bisect". Chose a safe-looking commit nearby, note its commit | |
686 | id, and check it out with: | |
687 | ||
688 | ------------------------------------------------- | |
689 | $ git reset --hard fb47ddb2db... | |
690 | ------------------------------------------------- | |
691 | ||
692 | then test, run "bisect good" or "bisect bad" as appropriate, and | |
693 | continue. | |
694 | ||
695 | Naming commits | |
696 | -------------- | |
697 | ||
698 | We have seen several ways of naming commits already: | |
699 | ||
d55ae921 | 700 | - 40-hexdigit object name |
d19fbc3c BF |
701 | - branch name: refers to the commit at the head of the given |
702 | branch | |
703 | - tag name: refers to the commit pointed to by the given tag | |
704 | (we've seen branches and tags are special cases of | |
705 | <<how-git-stores-references,references>>). | |
706 | - HEAD: refers to the head of the current branch | |
707 | ||
eb6ae7f4 | 708 | There are many more; see the "SPECIFYING REVISIONS" section of the |
aec053bb | 709 | gitlink:git-rev-parse[1] man page for the complete list of ways to |
d19fbc3c BF |
710 | name revisions. Some examples: |
711 | ||
712 | ------------------------------------------------- | |
d55ae921 | 713 | $ git show fb47ddb2 # the first few characters of the object name |
d19fbc3c BF |
714 | # are usually enough to specify it uniquely |
715 | $ git show HEAD^ # the parent of the HEAD commit | |
716 | $ git show HEAD^^ # the grandparent | |
717 | $ git show HEAD~4 # the great-great-grandparent | |
718 | ------------------------------------------------- | |
719 | ||
720 | Recall that merge commits may have more than one parent; by default, | |
721 | ^ and ~ follow the first parent listed in the commit, but you can | |
722 | also choose: | |
723 | ||
724 | ------------------------------------------------- | |
725 | $ git show HEAD^1 # show the first parent of HEAD | |
726 | $ git show HEAD^2 # show the second parent of HEAD | |
727 | ------------------------------------------------- | |
728 | ||
729 | In addition to HEAD, there are several other special names for | |
730 | commits: | |
731 | ||
732 | Merges (to be discussed later), as well as operations such as | |
733 | git-reset, which change the currently checked-out commit, generally | |
734 | set ORIG_HEAD to the value HEAD had before the current operation. | |
735 | ||
736 | The git-fetch operation always stores the head of the last fetched | |
737 | branch in FETCH_HEAD. For example, if you run git fetch without | |
738 | specifying a local branch as the target of the operation | |
739 | ||
740 | ------------------------------------------------- | |
741 | $ git fetch git://example.com/proj.git theirbranch | |
742 | ------------------------------------------------- | |
743 | ||
744 | the fetched commits will still be available from FETCH_HEAD. | |
745 | ||
746 | When we discuss merges we'll also see the special name MERGE_HEAD, | |
747 | which refers to the other branch that we're merging in to the current | |
748 | branch. | |
749 | ||
aec053bb | 750 | The gitlink:git-rev-parse[1] command is a low-level command that is |
d55ae921 BF |
751 | occasionally useful for translating some name for a commit to the object |
752 | name for that commit: | |
aec053bb BF |
753 | |
754 | ------------------------------------------------- | |
755 | $ git rev-parse origin | |
756 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
757 | ------------------------------------------------- | |
758 | ||
d19fbc3c BF |
759 | Creating tags |
760 | ------------- | |
761 | ||
762 | We can also create a tag to refer to a particular commit; after | |
763 | running | |
764 | ||
765 | ------------------------------------------------- | |
766 | $ git-tag stable-1 1b2e1d63ff | |
767 | ------------------------------------------------- | |
768 | ||
769 | You can use stable-1 to refer to the commit 1b2e1d63ff. | |
770 | ||
771 | This creates a "lightweight" tag. If the tag is a tag you wish to | |
772 | share with others, and possibly sign cryptographically, then you | |
773 | should create a tag object instead; see the gitlink:git-tag[1] man | |
774 | page for details. | |
775 | ||
776 | Browsing revisions | |
777 | ------------------ | |
778 | ||
779 | The gitlink:git-log[1] command can show lists of commits. On its | |
780 | own, it shows all commits reachable from the parent commit; but you | |
781 | can also make more specific requests: | |
782 | ||
783 | ------------------------------------------------- | |
784 | $ git log v2.5.. # commits since (not reachable from) v2.5 | |
785 | $ git log test..master # commits reachable from master but not test | |
786 | $ git log master..test # ...reachable from test but not master | |
787 | $ git log master...test # ...reachable from either test or master, | |
788 | # but not both | |
789 | $ git log --since="2 weeks ago" # commits from the last 2 weeks | |
790 | $ git log Makefile # commits which modify Makefile | |
791 | $ git log fs/ # ... which modify any file under fs/ | |
792 | $ git log -S'foo()' # commits which add or remove any file data | |
793 | # matching the string 'foo()' | |
794 | ------------------------------------------------- | |
795 | ||
796 | And of course you can combine all of these; the following finds | |
797 | commits since v2.5 which touch the Makefile or any file under fs: | |
798 | ||
799 | ------------------------------------------------- | |
800 | $ git log v2.5.. Makefile fs/ | |
801 | ------------------------------------------------- | |
802 | ||
803 | You can also ask git log to show patches: | |
804 | ||
805 | ------------------------------------------------- | |
806 | $ git log -p | |
807 | ------------------------------------------------- | |
808 | ||
809 | See the "--pretty" option in the gitlink:git-log[1] man page for more | |
810 | display options. | |
811 | ||
812 | Note that git log starts with the most recent commit and works | |
813 | backwards through the parents; however, since git history can contain | |
3dff5379 | 814 | multiple independent lines of development, the particular order that |
d19fbc3c BF |
815 | commits are listed in may be somewhat arbitrary. |
816 | ||
817 | Generating diffs | |
818 | ---------------- | |
819 | ||
820 | You can generate diffs between any two versions using | |
821 | gitlink:git-diff[1]: | |
822 | ||
823 | ------------------------------------------------- | |
824 | $ git diff master..test | |
825 | ------------------------------------------------- | |
826 | ||
827 | Sometimes what you want instead is a set of patches: | |
828 | ||
829 | ------------------------------------------------- | |
830 | $ git format-patch master..test | |
831 | ------------------------------------------------- | |
832 | ||
833 | will generate a file with a patch for each commit reachable from test | |
834 | but not from master. Note that if master also has commits which are | |
835 | not reachable from test, then the combined result of these patches | |
836 | will not be the same as the diff produced by the git-diff example. | |
837 | ||
838 | Viewing old file versions | |
839 | ------------------------- | |
840 | ||
841 | You can always view an old version of a file by just checking out the | |
842 | correct revision first. But sometimes it is more convenient to be | |
843 | able to view an old version of a single file without checking | |
844 | anything out; this command does that: | |
845 | ||
846 | ------------------------------------------------- | |
847 | $ git show v2.5:fs/locks.c | |
848 | ------------------------------------------------- | |
849 | ||
850 | Before the colon may be anything that names a commit, and after it | |
851 | may be any path to a file tracked by git. | |
852 | ||
aec053bb BF |
853 | Examples |
854 | -------- | |
855 | ||
856 | Check whether two branches point at the same history | |
2f99710c | 857 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
aec053bb BF |
858 | |
859 | Suppose you want to check whether two branches point at the same point | |
860 | in history. | |
861 | ||
862 | ------------------------------------------------- | |
863 | $ git diff origin..master | |
864 | ------------------------------------------------- | |
865 | ||
69f7ad73 BF |
866 | will tell you whether the contents of the project are the same at the |
867 | two branches; in theory, however, it's possible that the same project | |
868 | contents could have been arrived at by two different historical | |
d55ae921 | 869 | routes. You could compare the object names: |
aec053bb BF |
870 | |
871 | ------------------------------------------------- | |
872 | $ git rev-list origin | |
873 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
874 | $ git rev-list master | |
875 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
876 | ------------------------------------------------- | |
877 | ||
69f7ad73 BF |
878 | Or you could recall that the ... operator selects all commits |
879 | contained reachable from either one reference or the other but not | |
880 | both: so | |
aec053bb BF |
881 | |
882 | ------------------------------------------------- | |
883 | $ git log origin...master | |
884 | ------------------------------------------------- | |
885 | ||
886 | will return no commits when the two branches are equal. | |
887 | ||
b181d57f BF |
888 | Find first tagged version including a given fix |
889 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
aec053bb | 890 | |
69f7ad73 BF |
891 | Suppose you know that the commit e05db0fd fixed a certain problem. |
892 | You'd like to find the earliest tagged release that contains that | |
893 | fix. | |
894 | ||
895 | Of course, there may be more than one answer--if the history branched | |
896 | after commit e05db0fd, then there could be multiple "earliest" tagged | |
897 | releases. | |
898 | ||
899 | You could just visually inspect the commits since e05db0fd: | |
900 | ||
901 | ------------------------------------------------- | |
902 | $ gitk e05db0fd.. | |
903 | ------------------------------------------------- | |
904 | ||
b181d57f BF |
905 | Or you can use gitlink:git-name-rev[1], which will give the commit a |
906 | name based on any tag it finds pointing to one of the commit's | |
907 | descendants: | |
908 | ||
909 | ------------------------------------------------- | |
910 | $ git name-rev e05db0fd | |
911 | e05db0fd tags/v1.5.0-rc1^0~23 | |
912 | ------------------------------------------------- | |
913 | ||
914 | The gitlink:git-describe[1] command does the opposite, naming the | |
915 | revision using a tag on which the given commit is based: | |
916 | ||
917 | ------------------------------------------------- | |
918 | $ git describe e05db0fd | |
919 | v1.5.0-rc0-ge05db0f | |
920 | ------------------------------------------------- | |
921 | ||
922 | but that may sometimes help you guess which tags might come after the | |
923 | given commit. | |
924 | ||
925 | If you just want to verify whether a given tagged version contains a | |
926 | given commit, you could use gitlink:git-merge-base[1]: | |
927 | ||
928 | ------------------------------------------------- | |
929 | $ git merge-base e05db0fd v1.5.0-rc1 | |
930 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
931 | ------------------------------------------------- | |
932 | ||
933 | The merge-base command finds a common ancestor of the given commits, | |
934 | and always returns one or the other in the case where one is a | |
935 | descendant of the other; so the above output shows that e05db0fd | |
936 | actually is an ancestor of v1.5.0-rc1. | |
937 | ||
938 | Alternatively, note that | |
939 | ||
940 | ------------------------------------------------- | |
4a7979ca | 941 | $ git log v1.5.0-rc1..e05db0fd |
b181d57f BF |
942 | ------------------------------------------------- |
943 | ||
4a7979ca | 944 | will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, |
b181d57f | 945 | because it outputs only commits that are not reachable from v1.5.0-rc1. |
aec053bb | 946 | |
4a7979ca BF |
947 | As yet another alternative, the gitlink:git-show-branch[1] command lists |
948 | the commits reachable from its arguments with a display on the left-hand | |
949 | side that indicates which arguments that commit is reachable from. So, | |
950 | you can run something like | |
951 | ||
952 | ------------------------------------------------- | |
953 | $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 | |
954 | ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
955 | available | |
956 | ! [v1.5.0-rc0] GIT v1.5.0 preview | |
957 | ! [v1.5.0-rc1] GIT v1.5.0-rc1 | |
958 | ! [v1.5.0-rc2] GIT v1.5.0-rc2 | |
959 | ... | |
960 | ------------------------------------------------- | |
961 | ||
962 | then search for a line that looks like | |
963 | ||
964 | ------------------------------------------------- | |
965 | + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
966 | available | |
967 | ------------------------------------------------- | |
968 | ||
969 | Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and | |
970 | from v1.5.0-rc2, but not from v1.5.0-rc0. | |
971 | ||
972 | ||
d19fbc3c BF |
973 | Developing with git |
974 | =================== | |
975 | ||
976 | Telling git your name | |
977 | --------------------- | |
978 | ||
979 | Before creating any commits, you should introduce yourself to git. The | |
980 | easiest way to do so is: | |
981 | ||
982 | ------------------------------------------------ | |
983 | $ cat >~/.gitconfig <<\EOF | |
984 | [user] | |
985 | name = Your Name Comes Here | |
986 | email = you@yourdomain.example.com | |
987 | EOF | |
988 | ------------------------------------------------ | |
989 | ||
fc90c536 BF |
990 | (See the "CONFIGURATION FILE" section of gitlink:git-config[1] for |
991 | details on the configuration file.) | |
992 | ||
d19fbc3c BF |
993 | |
994 | Creating a new repository | |
995 | ------------------------- | |
996 | ||
997 | Creating a new repository from scratch is very easy: | |
998 | ||
999 | ------------------------------------------------- | |
1000 | $ mkdir project | |
1001 | $ cd project | |
f1d2b477 | 1002 | $ git init |
d19fbc3c BF |
1003 | ------------------------------------------------- |
1004 | ||
1005 | If you have some initial content (say, a tarball): | |
1006 | ||
1007 | ------------------------------------------------- | |
1008 | $ tar -xzvf project.tar.gz | |
1009 | $ cd project | |
f1d2b477 | 1010 | $ git init |
d19fbc3c BF |
1011 | $ git add . # include everything below ./ in the first commit: |
1012 | $ git commit | |
1013 | ------------------------------------------------- | |
1014 | ||
1015 | [[how-to-make-a-commit]] | |
1016 | how to make a commit | |
1017 | -------------------- | |
1018 | ||
1019 | Creating a new commit takes three steps: | |
1020 | ||
1021 | 1. Making some changes to the working directory using your | |
1022 | favorite editor. | |
1023 | 2. Telling git about your changes. | |
1024 | 3. Creating the commit using the content you told git about | |
1025 | in step 2. | |
1026 | ||
1027 | In practice, you can interleave and repeat steps 1 and 2 as many | |
1028 | times as you want: in order to keep track of what you want committed | |
1029 | at step 3, git maintains a snapshot of the tree's contents in a | |
1030 | special staging area called "the index." | |
1031 | ||
01997b4a BF |
1032 | At the beginning, the content of the index will be identical to |
1033 | that of the HEAD. The command "git diff --cached", which shows | |
1034 | the difference between the HEAD and the index, should therefore | |
1035 | produce no output at that point. | |
eb6ae7f4 | 1036 | |
d19fbc3c BF |
1037 | Modifying the index is easy: |
1038 | ||
1039 | To update the index with the new contents of a modified file, use | |
1040 | ||
1041 | ------------------------------------------------- | |
1042 | $ git add path/to/file | |
1043 | ------------------------------------------------- | |
1044 | ||
1045 | To add the contents of a new file to the index, use | |
1046 | ||
1047 | ------------------------------------------------- | |
1048 | $ git add path/to/file | |
1049 | ------------------------------------------------- | |
1050 | ||
eb6ae7f4 | 1051 | To remove a file from the index and from the working tree, |
d19fbc3c BF |
1052 | |
1053 | ------------------------------------------------- | |
1054 | $ git rm path/to/file | |
1055 | ------------------------------------------------- | |
1056 | ||
1057 | After each step you can verify that | |
1058 | ||
1059 | ------------------------------------------------- | |
1060 | $ git diff --cached | |
1061 | ------------------------------------------------- | |
1062 | ||
1063 | always shows the difference between the HEAD and the index file--this | |
1064 | is what you'd commit if you created the commit now--and that | |
1065 | ||
1066 | ------------------------------------------------- | |
1067 | $ git diff | |
1068 | ------------------------------------------------- | |
1069 | ||
1070 | shows the difference between the working tree and the index file. | |
1071 | ||
1072 | Note that "git add" always adds just the current contents of a file | |
1073 | to the index; further changes to the same file will be ignored unless | |
1074 | you run git-add on the file again. | |
1075 | ||
1076 | When you're ready, just run | |
1077 | ||
1078 | ------------------------------------------------- | |
1079 | $ git commit | |
1080 | ------------------------------------------------- | |
1081 | ||
1082 | and git will prompt you for a commit message and then create the new | |
3dff5379 | 1083 | commit. Check to make sure it looks like what you expected with |
d19fbc3c BF |
1084 | |
1085 | ------------------------------------------------- | |
1086 | $ git show | |
1087 | ------------------------------------------------- | |
1088 | ||
1089 | As a special shortcut, | |
1090 | ||
1091 | ------------------------------------------------- | |
1092 | $ git commit -a | |
1093 | ------------------------------------------------- | |
1094 | ||
1095 | will update the index with any files that you've modified or removed | |
1096 | and create a commit, all in one step. | |
1097 | ||
1098 | A number of commands are useful for keeping track of what you're | |
1099 | about to commit: | |
1100 | ||
1101 | ------------------------------------------------- | |
1102 | $ git diff --cached # difference between HEAD and the index; what | |
1103 | # would be commited if you ran "commit" now. | |
1104 | $ git diff # difference between the index file and your | |
1105 | # working directory; changes that would not | |
1106 | # be included if you ran "commit" now. | |
1107 | $ git status # a brief per-file summary of the above. | |
1108 | ------------------------------------------------- | |
1109 | ||
1110 | creating good commit messages | |
1111 | ----------------------------- | |
1112 | ||
1113 | Though not required, it's a good idea to begin the commit message | |
1114 | with a single short (less than 50 character) line summarizing the | |
1115 | change, followed by a blank line and then a more thorough | |
1116 | description. Tools that turn commits into email, for example, use | |
1117 | the first line on the Subject line and the rest of the commit in the | |
1118 | body. | |
1119 | ||
1120 | how to merge | |
1121 | ------------ | |
1122 | ||
1123 | You can rejoin two diverging branches of development using | |
1124 | gitlink:git-merge[1]: | |
1125 | ||
1126 | ------------------------------------------------- | |
1127 | $ git merge branchname | |
1128 | ------------------------------------------------- | |
1129 | ||
1130 | merges the development in the branch "branchname" into the current | |
1131 | branch. If there are conflicts--for example, if the same file is | |
1132 | modified in two different ways in the remote branch and the local | |
1133 | branch--then you are warned; the output may look something like this: | |
1134 | ||
1135 | ------------------------------------------------- | |
fabbd8f6 BF |
1136 | $ git merge next |
1137 | 100% (4/4) done | |
1138 | Auto-merged file.txt | |
d19fbc3c BF |
1139 | CONFLICT (content): Merge conflict in file.txt |
1140 | Automatic merge failed; fix conflicts and then commit the result. | |
1141 | ------------------------------------------------- | |
1142 | ||
1143 | Conflict markers are left in the problematic files, and after | |
1144 | you resolve the conflicts manually, you can update the index | |
1145 | with the contents and run git commit, as you normally would when | |
1146 | creating a new file. | |
1147 | ||
1148 | If you examine the resulting commit using gitk, you will see that it | |
1149 | has two parents, one pointing to the top of the current branch, and | |
1150 | one to the top of the other branch. | |
1151 | ||
1152 | In more detail: | |
1153 | ||
1154 | [[resolving-a-merge]] | |
1155 | Resolving a merge | |
1156 | ----------------- | |
1157 | ||
1158 | When a merge isn't resolved automatically, git leaves the index and | |
1159 | the working tree in a special state that gives you all the | |
1160 | information you need to help resolve the merge. | |
1161 | ||
1162 | Files with conflicts are marked specially in the index, so until you | |
ef561ac7 BF |
1163 | resolve the problem and update the index, gitlink:git-commit[1] will |
1164 | fail: | |
d19fbc3c BF |
1165 | |
1166 | ------------------------------------------------- | |
1167 | $ git commit | |
1168 | file.txt: needs merge | |
1169 | ------------------------------------------------- | |
1170 | ||
ef561ac7 BF |
1171 | Also, gitlink:git-status[1] will list those files as "unmerged", and the |
1172 | files with conflicts will have conflict markers added, like this: | |
1173 | ||
1174 | ------------------------------------------------- | |
1175 | <<<<<<< HEAD:file.txt | |
1176 | Hello world | |
1177 | ======= | |
1178 | Goodbye | |
1179 | >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt | |
1180 | ------------------------------------------------- | |
1181 | ||
1182 | All you need to do is edit the files to resolve the conflicts, and then | |
1183 | ||
1184 | ------------------------------------------------- | |
1185 | $ git add file.txt | |
1186 | $ git commit | |
1187 | ------------------------------------------------- | |
1188 | ||
1189 | Note that the commit message will already be filled in for you with | |
1190 | some information about the merge. Normally you can just use this | |
1191 | default message unchanged, but you may add additional commentary of | |
1192 | your own if desired. | |
1193 | ||
1194 | The above is all you need to know to resolve a simple merge. But git | |
1195 | also provides more information to help resolve conflicts: | |
1196 | ||
1197 | Getting conflict-resolution help during a merge | |
1198 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
d19fbc3c BF |
1199 | |
1200 | All of the changes that git was able to merge automatically are | |
1201 | already added to the index file, so gitlink:git-diff[1] shows only | |
ef561ac7 | 1202 | the conflicts. It uses an unusual syntax: |
d19fbc3c BF |
1203 | |
1204 | ------------------------------------------------- | |
1205 | $ git diff | |
1206 | diff --cc file.txt | |
1207 | index 802992c,2b60207..0000000 | |
1208 | --- a/file.txt | |
1209 | +++ b/file.txt | |
1210 | @@@ -1,1 -1,1 +1,5 @@@ | |
1211 | ++<<<<<<< HEAD:file.txt | |
1212 | +Hello world | |
1213 | ++======= | |
1214 | + Goodbye | |
1215 | ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt | |
1216 | ------------------------------------------------- | |
1217 | ||
1218 | Recall that the commit which will be commited after we resolve this | |
1219 | conflict will have two parents instead of the usual one: one parent | |
1220 | will be HEAD, the tip of the current branch; the other will be the | |
1221 | tip of the other branch, which is stored temporarily in MERGE_HEAD. | |
1222 | ||
ef561ac7 BF |
1223 | During the merge, the index holds three versions of each file. Each of |
1224 | these three "file stages" represents a different version of the file: | |
1225 | ||
1226 | ------------------------------------------------- | |
1227 | $ git show :1:file.txt # the file in a common ancestor of both branches | |
1228 | $ git show :2:file.txt # the version from HEAD, but including any | |
1229 | # nonconflicting changes from MERGE_HEAD | |
1230 | $ git show :3:file.txt # the version from MERGE_HEAD, but including any | |
1231 | # nonconflicting changes from HEAD. | |
1232 | ------------------------------------------------- | |
1233 | ||
1234 | Since the stage 2 and stage 3 versions have already been updated with | |
1235 | nonconflicting changes, the only remaining differences between them are | |
1236 | the important ones; thus gitlink:git-diff[1] can use the information in | |
1237 | the index to show only those conflicts. | |
1238 | ||
1239 | The diff above shows the differences between the working-tree version of | |
1240 | file.txt and the stage 2 and stage 3 versions. So instead of preceding | |
1241 | each line by a single "+" or "-", it now uses two columns: the first | |
1242 | column is used for differences between the first parent and the working | |
1243 | directory copy, and the second for differences between the second parent | |
1244 | and the working directory copy. (See the "COMBINED DIFF FORMAT" section | |
1245 | of gitlink:git-diff-files[1] for a details of the format.) | |
1246 | ||
1247 | After resolving the conflict in the obvious way (but before updating the | |
1248 | index), the diff will look like: | |
d19fbc3c BF |
1249 | |
1250 | ------------------------------------------------- | |
1251 | $ git diff | |
1252 | diff --cc file.txt | |
1253 | index 802992c,2b60207..0000000 | |
1254 | --- a/file.txt | |
1255 | +++ b/file.txt | |
1256 | @@@ -1,1 -1,1 +1,1 @@@ | |
1257 | - Hello world | |
1258 | -Goodbye | |
1259 | ++Goodbye world | |
1260 | ------------------------------------------------- | |
1261 | ||
1262 | This shows that our resolved version deleted "Hello world" from the | |
1263 | first parent, deleted "Goodbye" from the second parent, and added | |
1264 | "Goodbye world", which was previously absent from both. | |
1265 | ||
ef561ac7 BF |
1266 | Some special diff options allow diffing the working directory against |
1267 | any of these stages: | |
1268 | ||
1269 | ------------------------------------------------- | |
1270 | $ git diff -1 file.txt # diff against stage 1 | |
1271 | $ git diff --base file.txt # same as the above | |
1272 | $ git diff -2 file.txt # diff against stage 2 | |
1273 | $ git diff --ours file.txt # same as the above | |
1274 | $ git diff -3 file.txt # diff against stage 3 | |
1275 | $ git diff --theirs file.txt # same as the above. | |
1276 | ------------------------------------------------- | |
1277 | ||
1278 | The gitlink:git-log[1] and gitk[1] commands also provide special help | |
1279 | for merges: | |
d19fbc3c BF |
1280 | |
1281 | ------------------------------------------------- | |
1282 | $ git log --merge | |
ef561ac7 | 1283 | $ gitk --merge |
d19fbc3c BF |
1284 | ------------------------------------------------- |
1285 | ||
ef561ac7 BF |
1286 | These will display all commits which exist only on HEAD or on |
1287 | MERGE_HEAD, and which touch an unmerged file. | |
d19fbc3c | 1288 | |
ef561ac7 | 1289 | Each time you resolve the conflicts in a file and update the index: |
d19fbc3c BF |
1290 | |
1291 | ------------------------------------------------- | |
1292 | $ git add file.txt | |
d19fbc3c BF |
1293 | ------------------------------------------------- |
1294 | ||
ef561ac7 BF |
1295 | the different stages of that file will be "collapsed", after which |
1296 | git-diff will (by default) no longer show diffs for that file. | |
d19fbc3c BF |
1297 | |
1298 | [[undoing-a-merge]] | |
1299 | undoing a merge | |
1300 | --------------- | |
1301 | ||
1302 | If you get stuck and decide to just give up and throw the whole mess | |
1303 | away, you can always return to the pre-merge state with | |
1304 | ||
1305 | ------------------------------------------------- | |
1306 | $ git reset --hard HEAD | |
1307 | ------------------------------------------------- | |
1308 | ||
1309 | Or, if you've already commited the merge that you want to throw away, | |
1310 | ||
1311 | ------------------------------------------------- | |
1c73bb0e | 1312 | $ git reset --hard ORIG_HEAD |
d19fbc3c BF |
1313 | ------------------------------------------------- |
1314 | ||
1315 | However, this last command can be dangerous in some cases--never | |
1316 | throw away a commit you have already committed if that commit may | |
1317 | itself have been merged into another branch, as doing so may confuse | |
1318 | further merges. | |
1319 | ||
1320 | Fast-forward merges | |
1321 | ------------------- | |
1322 | ||
1323 | There is one special case not mentioned above, which is treated | |
1324 | differently. Normally, a merge results in a merge commit, with two | |
1325 | parents, one pointing at each of the two lines of development that | |
1326 | were merged. | |
1327 | ||
1328 | However, if one of the two lines of development is completely | |
1329 | contained within the other--so every commit present in the one is | |
1330 | already contained in the other--then git just performs a | |
1331 | <<fast-forwards,fast forward>>; the head of the current branch is | |
1332 | moved forward to point at the head of the merged-in branch, without | |
1333 | any new commits being created. | |
1334 | ||
b684f830 BF |
1335 | Fixing mistakes |
1336 | --------------- | |
1337 | ||
1338 | If you've messed up the working tree, but haven't yet committed your | |
1339 | mistake, you can return the entire working tree to the last committed | |
1340 | state with | |
1341 | ||
1342 | ------------------------------------------------- | |
1343 | $ git reset --hard HEAD | |
1344 | ------------------------------------------------- | |
1345 | ||
1346 | If you make a commit that you later wish you hadn't, there are two | |
1347 | fundamentally different ways to fix the problem: | |
1348 | ||
1349 | 1. You can create a new commit that undoes whatever was done | |
1350 | by the previous commit. This is the correct thing if your | |
1351 | mistake has already been made public. | |
1352 | ||
1353 | 2. You can go back and modify the old commit. You should | |
1354 | never do this if you have already made the history public; | |
1355 | git does not normally expect the "history" of a project to | |
1356 | change, and cannot correctly perform repeated merges from | |
1357 | a branch that has had its history changed. | |
1358 | ||
1359 | Fixing a mistake with a new commit | |
1360 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1361 | ||
1362 | Creating a new commit that reverts an earlier change is very easy; | |
1363 | just pass the gitlink:git-revert[1] command a reference to the bad | |
1364 | commit; for example, to revert the most recent commit: | |
1365 | ||
1366 | ------------------------------------------------- | |
1367 | $ git revert HEAD | |
1368 | ------------------------------------------------- | |
1369 | ||
1370 | This will create a new commit which undoes the change in HEAD. You | |
1371 | will be given a chance to edit the commit message for the new commit. | |
1372 | ||
1373 | You can also revert an earlier change, for example, the next-to-last: | |
1374 | ||
1375 | ------------------------------------------------- | |
1376 | $ git revert HEAD^ | |
1377 | ------------------------------------------------- | |
1378 | ||
1379 | In this case git will attempt to undo the old change while leaving | |
1380 | intact any changes made since then. If more recent changes overlap | |
1381 | with the changes to be reverted, then you will be asked to fix | |
1382 | conflicts manually, just as in the case of <<resolving-a-merge, | |
1383 | resolving a merge>>. | |
1384 | ||
365aa199 | 1385 | [[fixing-a-mistake-by-editing-history]] |
b684f830 BF |
1386 | Fixing a mistake by editing history |
1387 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1388 | ||
1389 | If the problematic commit is the most recent commit, and you have not | |
1390 | yet made that commit public, then you may just | |
1391 | <<undoing-a-merge,destroy it using git-reset>>. | |
1392 | ||
1393 | Alternatively, you | |
1394 | can edit the working directory and update the index to fix your | |
1395 | mistake, just as if you were going to <<how-to-make-a-commit,create a | |
1396 | new commit>>, then run | |
1397 | ||
1398 | ------------------------------------------------- | |
1399 | $ git commit --amend | |
1400 | ------------------------------------------------- | |
1401 | ||
1402 | which will replace the old commit by a new commit incorporating your | |
1403 | changes, giving you a chance to edit the old commit message first. | |
1404 | ||
1405 | Again, you should never do this to a commit that may already have | |
1406 | been merged into another branch; use gitlink:git-revert[1] instead in | |
1407 | that case. | |
1408 | ||
1409 | It is also possible to edit commits further back in the history, but | |
1410 | this is an advanced topic to be left for | |
1411 | <<cleaning-up-history,another chapter>>. | |
1412 | ||
1413 | Checking out an old version of a file | |
1414 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1415 | ||
1416 | In the process of undoing a previous bad change, you may find it | |
1417 | useful to check out an older version of a particular file using | |
1418 | gitlink:git-checkout[1]. We've used git checkout before to switch | |
1419 | branches, but it has quite different behavior if it is given a path | |
1420 | name: the command | |
1421 | ||
1422 | ------------------------------------------------- | |
1423 | $ git checkout HEAD^ path/to/file | |
1424 | ------------------------------------------------- | |
1425 | ||
1426 | replaces path/to/file by the contents it had in the commit HEAD^, and | |
1427 | also updates the index to match. It does not change branches. | |
1428 | ||
1429 | If you just want to look at an old version of the file, without | |
1430 | modifying the working directory, you can do that with | |
1431 | gitlink:git-show[1]: | |
1432 | ||
1433 | ------------------------------------------------- | |
1434 | $ git show HEAD^ path/to/file | |
1435 | ------------------------------------------------- | |
1436 | ||
1437 | which will display the given version of the file. | |
1438 | ||
d19fbc3c BF |
1439 | Ensuring good performance |
1440 | ------------------------- | |
1441 | ||
1442 | On large repositories, git depends on compression to keep the history | |
1443 | information from taking up to much space on disk or in memory. | |
1444 | ||
1445 | This compression is not performed automatically. Therefore you | |
17217090 | 1446 | should occasionally run gitlink:git-gc[1]: |
d19fbc3c BF |
1447 | |
1448 | ------------------------------------------------- | |
1449 | $ git gc | |
1450 | ------------------------------------------------- | |
1451 | ||
17217090 BF |
1452 | to recompress the archive. This can be very time-consuming, so |
1453 | you may prefer to run git-gc when you are not doing other work. | |
d19fbc3c | 1454 | |
11e016a3 BF |
1455 | Ensuring reliability |
1456 | -------------------- | |
1457 | ||
1458 | Checking the repository for corruption | |
1459 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1460 | ||
1191ee18 BF |
1461 | The gitlink:git-fsck[1] command runs a number of self-consistency checks |
1462 | on the repository, and reports on any problems. This may take some | |
21dcb3b7 BF |
1463 | time. The most common warning by far is about "dangling" objects: |
1464 | ||
1465 | ------------------------------------------------- | |
04e50e94 | 1466 | $ git fsck |
21dcb3b7 BF |
1467 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
1468 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1469 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1470 | dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb | |
1471 | dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f | |
1472 | dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e | |
1473 | dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 | |
1474 | dangling tree b24c2473f1fd3d91352a624795be026d64c8841f | |
1475 | ... | |
1476 | ------------------------------------------------- | |
1477 | ||
1191ee18 BF |
1478 | Dangling objects are objects that are harmless, but also unnecessary; |
1479 | you can remove them at any time with gitlink:git-prune[1] or the --prune | |
1480 | option to gitlink:git-gc[1]: | |
21dcb3b7 BF |
1481 | |
1482 | ------------------------------------------------- | |
1483 | $ git gc --prune | |
1484 | ------------------------------------------------- | |
1485 | ||
1191ee18 BF |
1486 | This may be time-consuming. Unlike most other git operations (including |
1487 | git-gc when run without any options), it is not safe to prune while | |
1488 | other git operations are in progress in the same repository. | |
21dcb3b7 | 1489 | |
988b27d3 | 1490 | For more about dangling objects, see <<dangling-objects>>. |
21dcb3b7 | 1491 | |
11e016a3 BF |
1492 | |
1493 | Recovering lost changes | |
1494 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
1495 | ||
559e4d7a BF |
1496 | Reflogs |
1497 | ^^^^^^^ | |
1498 | ||
1499 | Say you modify a branch with gitlink:git-reset[1] --hard, and then | |
1500 | realize that the branch was the only reference you had to that point in | |
1501 | history. | |
1502 | ||
1503 | Fortunately, git also keeps a log, called a "reflog", of all the | |
1504 | previous values of each branch. So in this case you can still find the | |
1505 | old history using, for example, | |
1506 | ||
1507 | ------------------------------------------------- | |
1508 | $ git log master@{1} | |
1509 | ------------------------------------------------- | |
1510 | ||
1511 | This lists the commits reachable from the previous version of the head. | |
1512 | This syntax can be used to with any git command that accepts a commit, | |
1513 | not just with git log. Some other examples: | |
1514 | ||
1515 | ------------------------------------------------- | |
1516 | $ git show master@{2} # See where the branch pointed 2, | |
1517 | $ git show master@{3} # 3, ... changes ago. | |
1518 | $ gitk master@{yesterday} # See where it pointed yesterday, | |
1519 | $ gitk master@{"1 week ago"} # ... or last week | |
1520 | ------------------------------------------------- | |
1521 | ||
1522 | The reflogs are kept by default for 30 days, after which they may be | |
036be17e | 1523 | pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn |
559e4d7a BF |
1524 | how to control this pruning, and see the "SPECIFYING REVISIONS" |
1525 | section of gitlink:git-rev-parse[1] for details. | |
1526 | ||
1527 | Note that the reflog history is very different from normal git history. | |
1528 | While normal history is shared by every repository that works on the | |
1529 | same project, the reflog history is not shared: it tells you only about | |
1530 | how the branches in your local repository have changed over time. | |
1531 | ||
1532 | Examining dangling objects | |
1533 | ^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
1534 | ||
1535 | In some situations the reflog may not be able to save you. For | |
1536 | example, suppose you delete a branch, then realize you need the history | |
79c96c57 | 1537 | it contained. The reflog is also deleted; however, if you have not |
559e4d7a BF |
1538 | yet pruned the repository, then you may still be able to find |
1539 | the lost commits; run git-fsck and watch for output that mentions | |
1540 | "dangling commits": | |
1541 | ||
1542 | ------------------------------------------------- | |
1543 | $ git fsck | |
1544 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 | |
1545 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1546 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1547 | ... | |
1548 | ------------------------------------------------- | |
1549 | ||
aacd404e | 1550 | You can examine |
559e4d7a BF |
1551 | one of those dangling commits with, for example, |
1552 | ||
1553 | ------------------------------------------------ | |
1554 | $ gitk 7281251ddd --not --all | |
1555 | ------------------------------------------------ | |
1556 | ||
1557 | which does what it sounds like: it says that you want to see the commit | |
1558 | history that is described by the dangling commit(s), but not the | |
1559 | history that is described by all your existing branches and tags. Thus | |
1560 | you get exactly the history reachable from that commit that is lost. | |
1561 | (And notice that it might not be just one commit: we only report the | |
1562 | "tip of the line" as being dangling, but there might be a whole deep | |
79c96c57 | 1563 | and complex commit history that was dropped.) |
559e4d7a BF |
1564 | |
1565 | If you decide you want the history back, you can always create a new | |
1566 | reference pointing to it, for example, a new branch: | |
1567 | ||
1568 | ------------------------------------------------ | |
1569 | $ git branch recovered-branch 7281251ddd | |
1570 | ------------------------------------------------ | |
1571 | ||
11e016a3 | 1572 | |
d19fbc3c | 1573 | Sharing development with others |
b684f830 | 1574 | =============================== |
d19fbc3c BF |
1575 | |
1576 | [[getting-updates-with-git-pull]] | |
1577 | Getting updates with git pull | |
b684f830 | 1578 | ----------------------------- |
d19fbc3c BF |
1579 | |
1580 | After you clone a repository and make a few changes of your own, you | |
1581 | may wish to check the original repository for updates and merge them | |
1582 | into your own work. | |
1583 | ||
1584 | We have already seen <<Updating-a-repository-with-git-fetch,how to | |
1585 | keep remote tracking branches up to date>> with gitlink:git-fetch[1], | |
1586 | and how to merge two branches. So you can merge in changes from the | |
1587 | original repository's master branch with: | |
1588 | ||
1589 | ------------------------------------------------- | |
1590 | $ git fetch | |
1591 | $ git merge origin/master | |
1592 | ------------------------------------------------- | |
1593 | ||
1594 | However, the gitlink:git-pull[1] command provides a way to do this in | |
1595 | one step: | |
1596 | ||
1597 | ------------------------------------------------- | |
1598 | $ git pull origin master | |
1599 | ------------------------------------------------- | |
1600 | ||
1601 | In fact, "origin" is normally the default repository to pull from, | |
1602 | and the default branch is normally the HEAD of the remote repository, | |
1603 | so often you can accomplish the above with just | |
1604 | ||
1605 | ------------------------------------------------- | |
1606 | $ git pull | |
1607 | ------------------------------------------------- | |
1608 | ||
1609 | See the descriptions of the branch.<name>.remote and | |
9d13bda3 | 1610 | branch.<name>.merge options in gitlink:git-config[1] to learn |
d19fbc3c BF |
1611 | how to control these defaults depending on the current branch. |
1612 | ||
1613 | In addition to saving you keystrokes, "git pull" also helps you by | |
1614 | producing a default commit message documenting the branch and | |
1615 | repository that you pulled from. | |
1616 | ||
1617 | (But note that no such commit will be created in the case of a | |
1618 | <<fast-forwards,fast forward>>; instead, your branch will just be | |
79c96c57 | 1619 | updated to point to the latest commit from the upstream branch.) |
d19fbc3c | 1620 | |
1191ee18 BF |
1621 | The git-pull command can also be given "." as the "remote" repository, |
1622 | in which case it just merges in a branch from the current repository; so | |
4c63ff45 BF |
1623 | the commands |
1624 | ||
1625 | ------------------------------------------------- | |
1626 | $ git pull . branch | |
1627 | $ git merge branch | |
1628 | ------------------------------------------------- | |
1629 | ||
1630 | are roughly equivalent. The former is actually very commonly used. | |
1631 | ||
d19fbc3c | 1632 | Submitting patches to a project |
b684f830 | 1633 | ------------------------------- |
d19fbc3c BF |
1634 | |
1635 | If you just have a few changes, the simplest way to submit them may | |
1636 | just be to send them as patches in email: | |
1637 | ||
036be17e | 1638 | First, use gitlink:git-format-patch[1]; for example: |
d19fbc3c BF |
1639 | |
1640 | ------------------------------------------------- | |
eb6ae7f4 | 1641 | $ git format-patch origin |
d19fbc3c BF |
1642 | ------------------------------------------------- |
1643 | ||
1644 | will produce a numbered series of files in the current directory, one | |
1645 | for each patch in the current branch but not in origin/HEAD. | |
1646 | ||
1647 | You can then import these into your mail client and send them by | |
1648 | hand. However, if you have a lot to send at once, you may prefer to | |
1649 | use the gitlink:git-send-email[1] script to automate the process. | |
1650 | Consult the mailing list for your project first to determine how they | |
1651 | prefer such patches be handled. | |
1652 | ||
1653 | Importing patches to a project | |
b684f830 | 1654 | ------------------------------ |
d19fbc3c BF |
1655 | |
1656 | Git also provides a tool called gitlink:git-am[1] (am stands for | |
1657 | "apply mailbox"), for importing such an emailed series of patches. | |
1658 | Just save all of the patch-containing messages, in order, into a | |
1659 | single mailbox file, say "patches.mbox", then run | |
1660 | ||
1661 | ------------------------------------------------- | |
eb6ae7f4 | 1662 | $ git am -3 patches.mbox |
d19fbc3c BF |
1663 | ------------------------------------------------- |
1664 | ||
1665 | Git will apply each patch in order; if any conflicts are found, it | |
1666 | will stop, and you can fix the conflicts as described in | |
01997b4a BF |
1667 | "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells |
1668 | git to perform a merge; if you would prefer it just to abort and | |
1669 | leave your tree and index untouched, you may omit that option.) | |
1670 | ||
1671 | Once the index is updated with the results of the conflict | |
1672 | resolution, instead of creating a new commit, just run | |
d19fbc3c BF |
1673 | |
1674 | ------------------------------------------------- | |
1675 | $ git am --resolved | |
1676 | ------------------------------------------------- | |
1677 | ||
1678 | and git will create the commit for you and continue applying the | |
1679 | remaining patches from the mailbox. | |
1680 | ||
1681 | The final result will be a series of commits, one for each patch in | |
1682 | the original mailbox, with authorship and commit log message each | |
1683 | taken from the message containing each patch. | |
1684 | ||
1685 | [[setting-up-a-public-repository]] | |
1686 | Setting up a public repository | |
b684f830 | 1687 | ------------------------------ |
d19fbc3c BF |
1688 | |
1689 | Another way to submit changes to a project is to simply tell the | |
1690 | maintainer of that project to pull from your repository, exactly as | |
1691 | you did in the section "<<getting-updates-with-git-pull, Getting | |
1692 | updates with git pull>>". | |
1693 | ||
1694 | If you and maintainer both have accounts on the same machine, then | |
1695 | then you can just pull changes from each other's repositories | |
79c96c57 MC |
1696 | directly; note that all of the commands (gitlink:git-clone[1], |
1697 | git-fetch[1], git-pull[1], etc.) that accept a URL as an argument | |
d19fbc3c BF |
1698 | will also accept a local file patch; so, for example, you can |
1699 | use | |
1700 | ||
1701 | ------------------------------------------------- | |
1702 | $ git clone /path/to/repository | |
1703 | $ git pull /path/to/other/repository | |
1704 | ------------------------------------------------- | |
1705 | ||
1706 | If this sort of setup is inconvenient or impossible, another (more | |
1707 | common) option is to set up a public repository on a public server. | |
1708 | This also allows you to cleanly separate private work in progress | |
1709 | from publicly visible work. | |
1710 | ||
1711 | You will continue to do your day-to-day work in your personal | |
1712 | repository, but periodically "push" changes from your personal | |
1713 | repository into your public repository, allowing other developers to | |
1714 | pull from that repository. So the flow of changes, in a situation | |
1715 | where there is one other developer with a public repository, looks | |
1716 | like this: | |
1717 | ||
1718 | you push | |
1719 | your personal repo ------------------> your public repo | |
1720 | ^ | | |
1721 | | | | |
1722 | | you pull | they pull | |
1723 | | | | |
1724 | | | | |
1725 | | they push V | |
1726 | their public repo <------------------- their repo | |
1727 | ||
1728 | Now, assume your personal repository is in the directory ~/proj. We | |
1729 | first create a new clone of the repository: | |
1730 | ||
1731 | ------------------------------------------------- | |
1732 | $ git clone --bare proj-clone.git | |
1733 | ------------------------------------------------- | |
1734 | ||
1735 | The resulting directory proj-clone.git will contains a "bare" git | |
1736 | repository--it is just the contents of the ".git" directory, without | |
1737 | a checked-out copy of a working directory. | |
1738 | ||
1739 | Next, copy proj-clone.git to the server where you plan to host the | |
1740 | public repository. You can use scp, rsync, or whatever is most | |
1741 | convenient. | |
1742 | ||
1743 | If somebody else maintains the public server, they may already have | |
1744 | set up a git service for you, and you may skip to the section | |
1745 | "<<pushing-changes-to-a-public-repository,Pushing changes to a public | |
1746 | repository>>", below. | |
1747 | ||
1748 | Otherwise, the following sections explain how to export your newly | |
1749 | created public repository: | |
1750 | ||
1751 | [[exporting-via-http]] | |
1752 | Exporting a git repository via http | |
b684f830 | 1753 | ----------------------------------- |
d19fbc3c BF |
1754 | |
1755 | The git protocol gives better performance and reliability, but on a | |
1756 | host with a web server set up, http exports may be simpler to set up. | |
1757 | ||
1758 | All you need to do is place the newly created bare git repository in | |
1759 | a directory that is exported by the web server, and make some | |
1760 | adjustments to give web clients some extra information they need: | |
1761 | ||
1762 | ------------------------------------------------- | |
1763 | $ mv proj.git /home/you/public_html/proj.git | |
1764 | $ cd proj.git | |
1765 | $ git update-server-info | |
1766 | $ chmod a+x hooks/post-update | |
1767 | ------------------------------------------------- | |
1768 | ||
1769 | (For an explanation of the last two lines, see | |
1770 | gitlink:git-update-server-info[1], and the documentation | |
1771 | link:hooks.txt[Hooks used by git].) | |
1772 | ||
1773 | Advertise the url of proj.git. Anybody else should then be able to | |
1774 | clone or pull from that url, for example with a commandline like: | |
1775 | ||
1776 | ------------------------------------------------- | |
1777 | $ git clone http://yourserver.com/~you/proj.git | |
1778 | ------------------------------------------------- | |
1779 | ||
1780 | (See also | |
1781 | link:howto/setup-git-server-over-http.txt[setup-git-server-over-http] | |
1782 | for a slightly more sophisticated setup using WebDAV which also | |
1783 | allows pushing over http.) | |
1784 | ||
1785 | [[exporting-via-git]] | |
1786 | Exporting a git repository via the git protocol | |
b684f830 | 1787 | ----------------------------------------------- |
d19fbc3c BF |
1788 | |
1789 | This is the preferred method. | |
1790 | ||
1791 | For now, we refer you to the gitlink:git-daemon[1] man page for | |
1792 | instructions. (See especially the examples section.) | |
1793 | ||
1794 | [[pushing-changes-to-a-public-repository]] | |
1795 | Pushing changes to a public repository | |
b684f830 | 1796 | -------------------------------------- |
d19fbc3c BF |
1797 | |
1798 | Note that the two techniques outline above (exporting via | |
1799 | <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other | |
1800 | maintainers to fetch your latest changes, but they do not allow write | |
1801 | access, which you will need to update the public repository with the | |
1802 | latest changes created in your private repository. | |
1803 | ||
1804 | The simplest way to do this is using gitlink:git-push[1] and ssh; to | |
1805 | update the remote branch named "master" with the latest state of your | |
1806 | branch named "master", run | |
1807 | ||
1808 | ------------------------------------------------- | |
1809 | $ git push ssh://yourserver.com/~you/proj.git master:master | |
1810 | ------------------------------------------------- | |
1811 | ||
1812 | or just | |
1813 | ||
1814 | ------------------------------------------------- | |
1815 | $ git push ssh://yourserver.com/~you/proj.git master | |
1816 | ------------------------------------------------- | |
1817 | ||
1818 | As with git-fetch, git-push will complain if this does not result in | |
1819 | a <<fast-forwards,fast forward>>. Normally this is a sign of | |
1820 | something wrong. However, if you are sure you know what you're | |
1821 | doing, you may force git-push to perform the update anyway by | |
1822 | proceeding the branch name by a plus sign: | |
1823 | ||
1824 | ------------------------------------------------- | |
1825 | $ git push ssh://yourserver.com/~you/proj.git +master | |
1826 | ------------------------------------------------- | |
1827 | ||
1828 | As with git-fetch, you may also set up configuration options to | |
1829 | save typing; so, for example, after | |
1830 | ||
1831 | ------------------------------------------------- | |
1832 | $ cat >.git/config <<EOF | |
1833 | [remote "public-repo"] | |
1834 | url = ssh://yourserver.com/~you/proj.git | |
1835 | EOF | |
1836 | ------------------------------------------------- | |
1837 | ||
1838 | you should be able to perform the above push with just | |
1839 | ||
1840 | ------------------------------------------------- | |
1841 | $ git push public-repo master | |
1842 | ------------------------------------------------- | |
1843 | ||
1844 | See the explanations of the remote.<name>.url, branch.<name>.remote, | |
9d13bda3 | 1845 | and remote.<name>.push options in gitlink:git-config[1] for |
d19fbc3c BF |
1846 | details. |
1847 | ||
1848 | Setting up a shared repository | |
b684f830 | 1849 | ------------------------------ |
d19fbc3c BF |
1850 | |
1851 | Another way to collaborate is by using a model similar to that | |
1852 | commonly used in CVS, where several developers with special rights | |
1853 | all push to and pull from a single shared repository. See | |
1854 | link:cvs-migration.txt[git for CVS users] for instructions on how to | |
1855 | set this up. | |
1856 | ||
b684f830 BF |
1857 | Allow web browsing of a repository |
1858 | ---------------------------------- | |
d19fbc3c | 1859 | |
a8cd1402 BF |
1860 | The gitweb cgi script provides users an easy way to browse your |
1861 | project's files and history without having to install git; see the file | |
1862 | gitweb/README in the git source tree for instructions on setting it up. | |
d19fbc3c | 1863 | |
b684f830 BF |
1864 | Examples |
1865 | -------- | |
d19fbc3c | 1866 | |
b684f830 | 1867 | TODO: topic branches, typical roles as in everyday.txt, ? |
d19fbc3c | 1868 | |
d19fbc3c | 1869 | |
d19fbc3c | 1870 | [[cleaning-up-history]] |
4c63ff45 BF |
1871 | Rewriting history and maintaining patch series |
1872 | ============================================== | |
1873 | ||
1874 | Normally commits are only added to a project, never taken away or | |
1875 | replaced. Git is designed with this assumption, and violating it will | |
1876 | cause git's merge machinery (for example) to do the wrong thing. | |
1877 | ||
1878 | However, there is a situation in which it can be useful to violate this | |
1879 | assumption. | |
1880 | ||
1881 | Creating the perfect patch series | |
1882 | --------------------------------- | |
1883 | ||
1884 | Suppose you are a contributor to a large project, and you want to add a | |
1885 | complicated feature, and to present it to the other developers in a way | |
1886 | that makes it easy for them to read your changes, verify that they are | |
1887 | correct, and understand why you made each change. | |
1888 | ||
b181d57f | 1889 | If you present all of your changes as a single patch (or commit), they |
79c96c57 | 1890 | may find that it is too much to digest all at once. |
4c63ff45 BF |
1891 | |
1892 | If you present them with the entire history of your work, complete with | |
1893 | mistakes, corrections, and dead ends, they may be overwhelmed. | |
1894 | ||
1895 | So the ideal is usually to produce a series of patches such that: | |
1896 | ||
1897 | 1. Each patch can be applied in order. | |
1898 | ||
1899 | 2. Each patch includes a single logical change, together with a | |
1900 | message explaining the change. | |
1901 | ||
1902 | 3. No patch introduces a regression: after applying any initial | |
1903 | part of the series, the resulting project still compiles and | |
1904 | works, and has no bugs that it didn't have before. | |
1905 | ||
1906 | 4. The complete series produces the same end result as your own | |
1907 | (probably much messier!) development process did. | |
1908 | ||
b181d57f BF |
1909 | We will introduce some tools that can help you do this, explain how to |
1910 | use them, and then explain some of the problems that can arise because | |
1911 | you are rewriting history. | |
4c63ff45 BF |
1912 | |
1913 | Keeping a patch series up to date using git-rebase | |
1914 | -------------------------------------------------- | |
1915 | ||
79c96c57 MC |
1916 | Suppose that you create a branch "mywork" on a remote-tracking branch |
1917 | "origin", and create some commits on top of it: | |
4c63ff45 BF |
1918 | |
1919 | ------------------------------------------------- | |
1920 | $ git checkout -b mywork origin | |
1921 | $ vi file.txt | |
1922 | $ git commit | |
1923 | $ vi otherfile.txt | |
1924 | $ git commit | |
1925 | ... | |
1926 | ------------------------------------------------- | |
1927 | ||
1928 | You have performed no merges into mywork, so it is just a simple linear | |
1929 | sequence of patches on top of "origin": | |
1930 | ||
1931 | ||
1932 | o--o--o <-- origin | |
1933 | \ | |
1934 | o--o--o <-- mywork | |
1935 | ||
1936 | Some more interesting work has been done in the upstream project, and | |
1937 | "origin" has advanced: | |
1938 | ||
1939 | o--o--O--o--o--o <-- origin | |
1940 | \ | |
1941 | a--b--c <-- mywork | |
1942 | ||
1943 | At this point, you could use "pull" to merge your changes back in; | |
1944 | the result would create a new merge commit, like this: | |
1945 | ||
1946 | ||
1947 | o--o--O--o--o--o <-- origin | |
1948 | \ \ | |
1949 | a--b--c--m <-- mywork | |
1950 | ||
1951 | However, if you prefer to keep the history in mywork a simple series of | |
1952 | commits without any merges, you may instead choose to use | |
1953 | gitlink:git-rebase[1]: | |
1954 | ||
1955 | ------------------------------------------------- | |
1956 | $ git checkout mywork | |
1957 | $ git rebase origin | |
1958 | ------------------------------------------------- | |
1959 | ||
b181d57f BF |
1960 | This will remove each of your commits from mywork, temporarily saving |
1961 | them as patches (in a directory named ".dotest"), update mywork to | |
1962 | point at the latest version of origin, then apply each of the saved | |
1963 | patches to the new mywork. The result will look like: | |
4c63ff45 BF |
1964 | |
1965 | ||
1966 | o--o--O--o--o--o <-- origin | |
1967 | \ | |
1968 | a'--b'--c' <-- mywork | |
1969 | ||
b181d57f BF |
1970 | In the process, it may discover conflicts. In that case it will stop |
1971 | and allow you to fix the conflicts; after fixing conflicts, use "git | |
1972 | add" to update the index with those contents, and then, instead of | |
1973 | running git-commit, just run | |
4c63ff45 BF |
1974 | |
1975 | ------------------------------------------------- | |
1976 | $ git rebase --continue | |
1977 | ------------------------------------------------- | |
1978 | ||
1979 | and git will continue applying the rest of the patches. | |
1980 | ||
1981 | At any point you may use the --abort option to abort this process and | |
1982 | return mywork to the state it had before you started the rebase: | |
1983 | ||
1984 | ------------------------------------------------- | |
1985 | $ git rebase --abort | |
1986 | ------------------------------------------------- | |
1987 | ||
365aa199 BF |
1988 | Modifying a single commit |
1989 | ------------------------- | |
1990 | ||
1991 | We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the | |
1992 | most recent commit using | |
1993 | ||
1994 | ------------------------------------------------- | |
1995 | $ git commit --amend | |
1996 | ------------------------------------------------- | |
1997 | ||
1998 | which will replace the old commit by a new commit incorporating your | |
1999 | changes, giving you a chance to edit the old commit message first. | |
2000 | ||
2001 | You can also use a combination of this and gitlink:git-rebase[1] to edit | |
2002 | commits further back in your history. First, tag the problematic commit with | |
2003 | ||
2004 | ------------------------------------------------- | |
2005 | $ git tag bad mywork~5 | |
2006 | ------------------------------------------------- | |
2007 | ||
2008 | (Either gitk or git-log may be useful for finding the commit.) | |
2009 | ||
2010 | Then check out a new branch at that commit, edit it, and rebase the rest of | |
2011 | the series on top of it: | |
2012 | ||
2013 | ------------------------------------------------- | |
2014 | $ git checkout -b TMP bad | |
2015 | $ # make changes here and update the index | |
2016 | $ git commit --amend | |
2017 | $ git rebase --onto TMP bad mywork | |
2018 | ------------------------------------------------- | |
2019 | ||
2020 | When you're done, you'll be left with mywork checked out, with the top patches | |
2021 | on mywork reapplied on top of the modified commit you created in TMP. You can | |
2022 | then clean up with | |
2023 | ||
2024 | ------------------------------------------------- | |
2025 | $ git branch -d TMP | |
2026 | $ git tag -d bad | |
2027 | ------------------------------------------------- | |
2028 | ||
2029 | Note that the immutable nature of git history means that you haven't really | |
2030 | "modified" existing commits; instead, you have replaced the old commits with | |
2031 | new commits having new object names. | |
2032 | ||
4c63ff45 BF |
2033 | Reordering or selecting from a patch series |
2034 | ------------------------------------------- | |
2035 | ||
b181d57f BF |
2036 | Given one existing commit, the gitlink:git-cherry-pick[1] command |
2037 | allows you to apply the change introduced by that commit and create a | |
2038 | new commit that records it. So, for example, if "mywork" points to a | |
2039 | series of patches on top of "origin", you might do something like: | |
2040 | ||
2041 | ------------------------------------------------- | |
2042 | $ git checkout -b mywork-new origin | |
2043 | $ gitk origin..mywork & | |
2044 | ------------------------------------------------- | |
2045 | ||
2046 | And browse through the list of patches in the mywork branch using gitk, | |
2047 | applying them (possibly in a different order) to mywork-new using | |
2048 | cherry-pick, and possibly modifying them as you go using commit | |
2049 | --amend. | |
2050 | ||
2051 | Another technique is to use git-format-patch to create a series of | |
2052 | patches, then reset the state to before the patches: | |
4c63ff45 | 2053 | |
b181d57f BF |
2054 | ------------------------------------------------- |
2055 | $ git format-patch origin | |
2056 | $ git reset --hard origin | |
2057 | ------------------------------------------------- | |
4c63ff45 | 2058 | |
b181d57f BF |
2059 | Then modify, reorder, or eliminate patches as preferred before applying |
2060 | them again with gitlink:git-am[1]. | |
4c63ff45 BF |
2061 | |
2062 | Other tools | |
2063 | ----------- | |
2064 | ||
b181d57f | 2065 | There are numerous other tools, such as stgit, which exist for the |
79c96c57 | 2066 | purpose of maintaining a patch series. These are outside of the scope of |
b181d57f | 2067 | this manual. |
4c63ff45 BF |
2068 | |
2069 | Problems with rewriting history | |
2070 | ------------------------------- | |
2071 | ||
b181d57f BF |
2072 | The primary problem with rewriting the history of a branch has to do |
2073 | with merging. Suppose somebody fetches your branch and merges it into | |
2074 | their branch, with a result something like this: | |
2075 | ||
2076 | o--o--O--o--o--o <-- origin | |
2077 | \ \ | |
2078 | t--t--t--m <-- their branch: | |
2079 | ||
2080 | Then suppose you modify the last three commits: | |
2081 | ||
2082 | o--o--o <-- new head of origin | |
2083 | / | |
2084 | o--o--O--o--o--o <-- old head of origin | |
2085 | ||
2086 | If we examined all this history together in one repository, it will | |
2087 | look like: | |
2088 | ||
2089 | o--o--o <-- new head of origin | |
2090 | / | |
2091 | o--o--O--o--o--o <-- old head of origin | |
2092 | \ \ | |
2093 | t--t--t--m <-- their branch: | |
2094 | ||
2095 | Git has no way of knowing that the new head is an updated version of | |
2096 | the old head; it treats this situation exactly the same as it would if | |
2097 | two developers had independently done the work on the old and new heads | |
2098 | in parallel. At this point, if someone attempts to merge the new head | |
2099 | in to their branch, git will attempt to merge together the two (old and | |
2100 | new) lines of development, instead of trying to replace the old by the | |
2101 | new. The results are likely to be unexpected. | |
2102 | ||
2103 | You may still choose to publish branches whose history is rewritten, | |
2104 | and it may be useful for others to be able to fetch those branches in | |
2105 | order to examine or test them, but they should not attempt to pull such | |
2106 | branches into their own work. | |
2107 | ||
2108 | For true distributed development that supports proper merging, | |
2109 | published branches should never be rewritten. | |
2110 | ||
2111 | Advanced branch management | |
2112 | ========================== | |
4c63ff45 | 2113 | |
b181d57f BF |
2114 | Fetching individual branches |
2115 | ---------------------------- | |
2116 | ||
2117 | Instead of using gitlink:git-remote[1], you can also choose just | |
2118 | to update one branch at a time, and to store it locally under an | |
2119 | arbitrary name: | |
2120 | ||
2121 | ------------------------------------------------- | |
2122 | $ git fetch origin todo:my-todo-work | |
2123 | ------------------------------------------------- | |
2124 | ||
2125 | The first argument, "origin", just tells git to fetch from the | |
2126 | repository you originally cloned from. The second argument tells git | |
2127 | to fetch the branch named "todo" from the remote repository, and to | |
2128 | store it locally under the name refs/heads/my-todo-work. | |
2129 | ||
2130 | You can also fetch branches from other repositories; so | |
2131 | ||
2132 | ------------------------------------------------- | |
2133 | $ git fetch git://example.com/proj.git master:example-master | |
2134 | ------------------------------------------------- | |
2135 | ||
2136 | will create a new branch named "example-master" and store in it the | |
2137 | branch named "master" from the repository at the given URL. If you | |
2138 | already have a branch named example-master, it will attempt to | |
2139 | "fast-forward" to the commit given by example.com's master branch. So | |
2140 | next we explain what a fast-forward is: | |
2141 | ||
2142 | [[fast-forwards]] | |
2143 | Understanding git history: fast-forwards | |
2144 | ---------------------------------------- | |
2145 | ||
2146 | In the previous example, when updating an existing branch, "git | |
2147 | fetch" checks to make sure that the most recent commit on the remote | |
2148 | branch is a descendant of the most recent commit on your copy of the | |
2149 | branch before updating your copy of the branch to point at the new | |
2150 | commit. Git calls this process a "fast forward". | |
2151 | ||
2152 | A fast forward looks something like this: | |
2153 | ||
2154 | o--o--o--o <-- old head of the branch | |
2155 | \ | |
2156 | o--o--o <-- new head of the branch | |
2157 | ||
2158 | ||
2159 | In some cases it is possible that the new head will *not* actually be | |
2160 | a descendant of the old head. For example, the developer may have | |
2161 | realized she made a serious mistake, and decided to backtrack, | |
2162 | resulting in a situation like: | |
2163 | ||
2164 | o--o--o--o--a--b <-- old head of the branch | |
2165 | \ | |
2166 | o--o--o <-- new head of the branch | |
2167 | ||
2168 | ||
2169 | ||
2170 | In this case, "git fetch" will fail, and print out a warning. | |
2171 | ||
2172 | In that case, you can still force git to update to the new head, as | |
2173 | described in the following section. However, note that in the | |
2174 | situation above this may mean losing the commits labeled "a" and "b", | |
2175 | unless you've already created a reference of your own pointing to | |
2176 | them. | |
2177 | ||
2178 | Forcing git fetch to do non-fast-forward updates | |
2179 | ------------------------------------------------ | |
2180 | ||
2181 | If git fetch fails because the new head of a branch is not a | |
2182 | descendant of the old head, you may force the update with: | |
2183 | ||
2184 | ------------------------------------------------- | |
2185 | $ git fetch git://example.com/proj.git +master:refs/remotes/example/master | |
2186 | ------------------------------------------------- | |
2187 | ||
79c96c57 | 2188 | Note the addition of the "+" sign. Be aware that commits that the |
b181d57f BF |
2189 | old version of example/master pointed at may be lost, as we saw in |
2190 | the previous section. | |
2191 | ||
2192 | Configuring remote branches | |
2193 | --------------------------- | |
2194 | ||
2195 | We saw above that "origin" is just a shortcut to refer to the | |
79c96c57 | 2196 | repository that you originally cloned from. This information is |
b181d57f | 2197 | stored in git configuration variables, which you can see using |
9d13bda3 | 2198 | gitlink:git-config[1]: |
b181d57f BF |
2199 | |
2200 | ------------------------------------------------- | |
9d13bda3 | 2201 | $ git config -l |
b181d57f BF |
2202 | core.repositoryformatversion=0 |
2203 | core.filemode=true | |
2204 | core.logallrefupdates=true | |
2205 | remote.origin.url=git://git.kernel.org/pub/scm/git/git.git | |
2206 | remote.origin.fetch=+refs/heads/*:refs/remotes/origin/* | |
2207 | branch.master.remote=origin | |
2208 | branch.master.merge=refs/heads/master | |
2209 | ------------------------------------------------- | |
2210 | ||
2211 | If there are other repositories that you also use frequently, you can | |
2212 | create similar configuration options to save typing; for example, | |
2213 | after | |
2214 | ||
2215 | ------------------------------------------------- | |
9d13bda3 | 2216 | $ git config remote.example.url git://example.com/proj.git |
b181d57f BF |
2217 | ------------------------------------------------- |
2218 | ||
2219 | then the following two commands will do the same thing: | |
2220 | ||
2221 | ------------------------------------------------- | |
2222 | $ git fetch git://example.com/proj.git master:refs/remotes/example/master | |
2223 | $ git fetch example master:refs/remotes/example/master | |
2224 | ------------------------------------------------- | |
2225 | ||
2226 | Even better, if you add one more option: | |
2227 | ||
2228 | ------------------------------------------------- | |
9d13bda3 | 2229 | $ git config remote.example.fetch master:refs/remotes/example/master |
b181d57f BF |
2230 | ------------------------------------------------- |
2231 | ||
2232 | then the following commands will all do the same thing: | |
2233 | ||
2234 | ------------------------------------------------- | |
2235 | $ git fetch git://example.com/proj.git master:ref/remotes/example/master | |
2236 | $ git fetch example master:ref/remotes/example/master | |
2237 | $ git fetch example example/master | |
2238 | $ git fetch example | |
2239 | ------------------------------------------------- | |
2240 | ||
2241 | You can also add a "+" to force the update each time: | |
2242 | ||
2243 | ------------------------------------------------- | |
9d13bda3 | 2244 | $ git config remote.example.fetch +master:ref/remotes/example/master |
b181d57f BF |
2245 | ------------------------------------------------- |
2246 | ||
2247 | Don't do this unless you're sure you won't mind "git fetch" possibly | |
2248 | throwing away commits on mybranch. | |
2249 | ||
2250 | Also note that all of the above configuration can be performed by | |
2251 | directly editing the file .git/config instead of using | |
9d13bda3 | 2252 | gitlink:git-config[1]. |
b181d57f | 2253 | |
9d13bda3 | 2254 | See gitlink:git-config[1] for more details on the configuration |
b181d57f | 2255 | options mentioned above. |
d19fbc3c | 2256 | |
d19fbc3c | 2257 | |
35121930 | 2258 | [[git-internals]] |
d19fbc3c BF |
2259 | Git internals |
2260 | ============= | |
2261 | ||
b181d57f BF |
2262 | There are two object abstractions: the "object database", and the |
2263 | "current directory cache" aka "index". | |
2264 | ||
2265 | The Object Database | |
2266 | ------------------- | |
2267 | ||
2268 | The object database is literally just a content-addressable collection | |
2269 | of objects. All objects are named by their content, which is | |
2270 | approximated by the SHA1 hash of the object itself. Objects may refer | |
2271 | to other objects (by referencing their SHA1 hash), and so you can | |
2272 | build up a hierarchy of objects. | |
2273 | ||
2274 | All objects have a statically determined "type" aka "tag", which is | |
2275 | determined at object creation time, and which identifies the format of | |
2276 | the object (i.e. how it is used, and how it can refer to other | |
2277 | objects). There are currently four different object types: "blob", | |
2278 | "tree", "commit" and "tag". | |
2279 | ||
2280 | A "blob" object cannot refer to any other object, and is, like the type | |
2281 | implies, a pure storage object containing some user data. It is used to | |
2282 | actually store the file data, i.e. a blob object is associated with some | |
2283 | particular version of some file. | |
2284 | ||
2285 | A "tree" object is an object that ties one or more "blob" objects into a | |
2286 | directory structure. In addition, a tree object can refer to other tree | |
2287 | objects, thus creating a directory hierarchy. | |
2288 | ||
2289 | A "commit" object ties such directory hierarchies together into | |
2290 | a DAG of revisions - each "commit" is associated with exactly one tree | |
2291 | (the directory hierarchy at the time of the commit). In addition, a | |
2292 | "commit" refers to one or more "parent" commit objects that describe the | |
2293 | history of how we arrived at that directory hierarchy. | |
2294 | ||
2295 | As a special case, a commit object with no parents is called the "root" | |
2296 | object, and is the point of an initial project commit. Each project | |
2297 | must have at least one root, and while you can tie several different | |
2298 | root objects together into one project by creating a commit object which | |
2299 | has two or more separate roots as its ultimate parents, that's probably | |
2300 | just going to confuse people. So aim for the notion of "one root object | |
2301 | per project", even if git itself does not enforce that. | |
2302 | ||
2303 | A "tag" object symbolically identifies and can be used to sign other | |
2304 | objects. It contains the identifier and type of another object, a | |
2305 | symbolic name (of course!) and, optionally, a signature. | |
2306 | ||
2307 | Regardless of object type, all objects share the following | |
2308 | characteristics: they are all deflated with zlib, and have a header | |
2309 | that not only specifies their type, but also provides size information | |
2310 | about the data in the object. It's worth noting that the SHA1 hash | |
2311 | that is used to name the object is the hash of the original data | |
2312 | plus this header, so `sha1sum` 'file' does not match the object name | |
2313 | for 'file'. | |
2314 | (Historical note: in the dawn of the age of git the hash | |
2315 | was the sha1 of the 'compressed' object.) | |
2316 | ||
2317 | As a result, the general consistency of an object can always be tested | |
2318 | independently of the contents or the type of the object: all objects can | |
2319 | be validated by verifying that (a) their hashes match the content of the | |
2320 | file and (b) the object successfully inflates to a stream of bytes that | |
2321 | forms a sequence of <ascii type without space> + <space> + <ascii decimal | |
2322 | size> + <byte\0> + <binary object data>. | |
2323 | ||
2324 | The structured objects can further have their structure and | |
2325 | connectivity to other objects verified. This is generally done with | |
04e50e94 | 2326 | the `git-fsck` program, which generates a full dependency graph |
b181d57f BF |
2327 | of all objects, and verifies their internal consistency (in addition |
2328 | to just verifying their superficial consistency through the hash). | |
2329 | ||
2330 | The object types in some more detail: | |
2331 | ||
2332 | Blob Object | |
2333 | ----------- | |
2334 | ||
2335 | A "blob" object is nothing but a binary blob of data, and doesn't | |
2336 | refer to anything else. There is no signature or any other | |
2337 | verification of the data, so while the object is consistent (it 'is' | |
2338 | indexed by its sha1 hash, so the data itself is certainly correct), it | |
2339 | has absolutely no other attributes. No name associations, no | |
2340 | permissions. It is purely a blob of data (i.e. normally "file | |
2341 | contents"). | |
2342 | ||
2343 | In particular, since the blob is entirely defined by its data, if two | |
2344 | files in a directory tree (or in multiple different versions of the | |
2345 | repository) have the same contents, they will share the same blob | |
2346 | object. The object is totally independent of its location in the | |
2347 | directory tree, and renaming a file does not change the object that | |
2348 | file is associated with in any way. | |
2349 | ||
2350 | A blob is typically created when gitlink:git-update-index[1] | |
2351 | is run, and its data can be accessed by gitlink:git-cat-file[1]. | |
2352 | ||
2353 | Tree Object | |
2354 | ----------- | |
2355 | ||
2356 | The next hierarchical object type is the "tree" object. A tree object | |
2357 | is a list of mode/name/blob data, sorted by name. Alternatively, the | |
2358 | mode data may specify a directory mode, in which case instead of | |
2359 | naming a blob, that name is associated with another TREE object. | |
2360 | ||
2361 | Like the "blob" object, a tree object is uniquely determined by the | |
2362 | set contents, and so two separate but identical trees will always | |
2363 | share the exact same object. This is true at all levels, i.e. it's | |
2364 | true for a "leaf" tree (which does not refer to any other trees, only | |
2365 | blobs) as well as for a whole subdirectory. | |
2366 | ||
2367 | For that reason a "tree" object is just a pure data abstraction: it | |
2368 | has no history, no signatures, no verification of validity, except | |
2369 | that since the contents are again protected by the hash itself, we can | |
2370 | trust that the tree is immutable and its contents never change. | |
2371 | ||
2372 | So you can trust the contents of a tree to be valid, the same way you | |
2373 | can trust the contents of a blob, but you don't know where those | |
2374 | contents 'came' from. | |
2375 | ||
2376 | Side note on trees: since a "tree" object is a sorted list of | |
2377 | "filename+content", you can create a diff between two trees without | |
2378 | actually having to unpack two trees. Just ignore all common parts, | |
2379 | and your diff will look right. In other words, you can effectively | |
2380 | (and efficiently) tell the difference between any two random trees by | |
2381 | O(n) where "n" is the size of the difference, rather than the size of | |
2382 | the tree. | |
2383 | ||
2384 | Side note 2 on trees: since the name of a "blob" depends entirely and | |
2385 | exclusively on its contents (i.e. there are no names or permissions | |
2386 | involved), you can see trivial renames or permission changes by | |
2387 | noticing that the blob stayed the same. However, renames with data | |
2388 | changes need a smarter "diff" implementation. | |
2389 | ||
2390 | A tree is created with gitlink:git-write-tree[1] and | |
2391 | its data can be accessed by gitlink:git-ls-tree[1]. | |
2392 | Two trees can be compared with gitlink:git-diff-tree[1]. | |
2393 | ||
2394 | Commit Object | |
2395 | ------------- | |
2396 | ||
2397 | The "commit" object is an object that introduces the notion of | |
2398 | history into the picture. In contrast to the other objects, it | |
2399 | doesn't just describe the physical state of a tree, it describes how | |
2400 | we got there, and why. | |
2401 | ||
2402 | A "commit" is defined by the tree-object that it results in, the | |
2403 | parent commits (zero, one or more) that led up to that point, and a | |
2404 | comment on what happened. Again, a commit is not trusted per se: | |
2405 | the contents are well-defined and "safe" due to the cryptographically | |
2406 | strong signatures at all levels, but there is no reason to believe | |
2407 | that the tree is "good" or that the merge information makes sense. | |
2408 | The parents do not have to actually have any relationship with the | |
2409 | result, for example. | |
2410 | ||
2411 | Note on commits: unlike real SCM's, commits do not contain | |
2412 | rename information or file mode change information. All of that is | |
2413 | implicit in the trees involved (the result tree, and the result trees | |
2414 | of the parents), and describing that makes no sense in this idiotic | |
2415 | file manager. | |
2416 | ||
2417 | A commit is created with gitlink:git-commit-tree[1] and | |
2418 | its data can be accessed by gitlink:git-cat-file[1]. | |
2419 | ||
2420 | Trust | |
2421 | ----- | |
2422 | ||
2423 | An aside on the notion of "trust". Trust is really outside the scope | |
2424 | of "git", but it's worth noting a few things. First off, since | |
2425 | everything is hashed with SHA1, you 'can' trust that an object is | |
2426 | intact and has not been messed with by external sources. So the name | |
2427 | of an object uniquely identifies a known state - just not a state that | |
2428 | you may want to trust. | |
2429 | ||
2430 | Furthermore, since the SHA1 signature of a commit refers to the | |
2431 | SHA1 signatures of the tree it is associated with and the signatures | |
2432 | of the parent, a single named commit specifies uniquely a whole set | |
2433 | of history, with full contents. You can't later fake any step of the | |
2434 | way once you have the name of a commit. | |
2435 | ||
2436 | So to introduce some real trust in the system, the only thing you need | |
2437 | to do is to digitally sign just 'one' special note, which includes the | |
2438 | name of a top-level commit. Your digital signature shows others | |
2439 | that you trust that commit, and the immutability of the history of | |
2440 | commits tells others that they can trust the whole history. | |
2441 | ||
2442 | In other words, you can easily validate a whole archive by just | |
2443 | sending out a single email that tells the people the name (SHA1 hash) | |
2444 | of the top commit, and digitally sign that email using something | |
2445 | like GPG/PGP. | |
2446 | ||
2447 | To assist in this, git also provides the tag object... | |
2448 | ||
2449 | Tag Object | |
2450 | ---------- | |
2451 | ||
2452 | Git provides the "tag" object to simplify creating, managing and | |
2453 | exchanging symbolic and signed tokens. The "tag" object at its | |
2454 | simplest simply symbolically identifies another object by containing | |
2455 | the sha1, type and symbolic name. | |
2456 | ||
2457 | However it can optionally contain additional signature information | |
2458 | (which git doesn't care about as long as there's less than 8k of | |
2459 | it). This can then be verified externally to git. | |
2460 | ||
2461 | Note that despite the tag features, "git" itself only handles content | |
2462 | integrity; the trust framework (and signature provision and | |
2463 | verification) has to come from outside. | |
2464 | ||
2465 | A tag is created with gitlink:git-mktag[1], | |
2466 | its data can be accessed by gitlink:git-cat-file[1], | |
2467 | and the signature can be verified by | |
2468 | gitlink:git-verify-tag[1]. | |
2469 | ||
2470 | ||
2471 | The "index" aka "Current Directory Cache" | |
2472 | ----------------------------------------- | |
2473 | ||
2474 | The index is a simple binary file, which contains an efficient | |
2475 | representation of a virtual directory content at some random time. It | |
2476 | does so by a simple array that associates a set of names, dates, | |
2477 | permissions and content (aka "blob") objects together. The cache is | |
2478 | always kept ordered by name, and names are unique (with a few very | |
2479 | specific rules) at any point in time, but the cache has no long-term | |
2480 | meaning, and can be partially updated at any time. | |
2481 | ||
2482 | In particular, the index certainly does not need to be consistent with | |
2483 | the current directory contents (in fact, most operations will depend on | |
2484 | different ways to make the index 'not' be consistent with the directory | |
2485 | hierarchy), but it has three very important attributes: | |
2486 | ||
2487 | '(a) it can re-generate the full state it caches (not just the | |
2488 | directory structure: it contains pointers to the "blob" objects so | |
2489 | that it can regenerate the data too)' | |
2490 | ||
2491 | As a special case, there is a clear and unambiguous one-way mapping | |
2492 | from a current directory cache to a "tree object", which can be | |
2493 | efficiently created from just the current directory cache without | |
2494 | actually looking at any other data. So a directory cache at any one | |
2495 | time uniquely specifies one and only one "tree" object (but has | |
2496 | additional data to make it easy to match up that tree object with what | |
2497 | has happened in the directory) | |
2498 | ||
2499 | '(b) it has efficient methods for finding inconsistencies between that | |
2500 | cached state ("tree object waiting to be instantiated") and the | |
2501 | current state.' | |
2502 | ||
2503 | '(c) it can additionally efficiently represent information about merge | |
2504 | conflicts between different tree objects, allowing each pathname to be | |
2505 | associated with sufficient information about the trees involved that | |
2506 | you can create a three-way merge between them.' | |
2507 | ||
79c96c57 | 2508 | Those are the ONLY three things that the directory cache does. It's a |
b181d57f BF |
2509 | cache, and the normal operation is to re-generate it completely from a |
2510 | known tree object, or update/compare it with a live tree that is being | |
2511 | developed. If you blow the directory cache away entirely, you generally | |
2512 | haven't lost any information as long as you have the name of the tree | |
2513 | that it described. | |
2514 | ||
2515 | At the same time, the index is at the same time also the | |
2516 | staging area for creating new trees, and creating a new tree always | |
2517 | involves a controlled modification of the index file. In particular, | |
2518 | the index file can have the representation of an intermediate tree that | |
2519 | has not yet been instantiated. So the index can be thought of as a | |
2520 | write-back cache, which can contain dirty information that has not yet | |
2521 | been written back to the backing store. | |
2522 | ||
2523 | ||
2524 | ||
2525 | The Workflow | |
2526 | ------------ | |
2527 | ||
2528 | Generally, all "git" operations work on the index file. Some operations | |
2529 | work *purely* on the index file (showing the current state of the | |
2530 | index), but most operations move data to and from the index file. Either | |
2531 | from the database or from the working directory. Thus there are four | |
2532 | main combinations: | |
2533 | ||
2534 | working directory -> index | |
2535 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2536 | ||
2537 | You update the index with information from the working directory with | |
2538 | the gitlink:git-update-index[1] command. You | |
2539 | generally update the index information by just specifying the filename | |
2540 | you want to update, like so: | |
2541 | ||
2542 | ------------------------------------------------- | |
2543 | $ git-update-index filename | |
2544 | ------------------------------------------------- | |
2545 | ||
2546 | but to avoid common mistakes with filename globbing etc, the command | |
2547 | will not normally add totally new entries or remove old entries, | |
2548 | i.e. it will normally just update existing cache entries. | |
2549 | ||
2550 | To tell git that yes, you really do realize that certain files no | |
2551 | longer exist, or that new files should be added, you | |
2552 | should use the `--remove` and `--add` flags respectively. | |
2553 | ||
2554 | NOTE! A `--remove` flag does 'not' mean that subsequent filenames will | |
2555 | necessarily be removed: if the files still exist in your directory | |
2556 | structure, the index will be updated with their new status, not | |
2557 | removed. The only thing `--remove` means is that update-cache will be | |
2558 | considering a removed file to be a valid thing, and if the file really | |
2559 | does not exist any more, it will update the index accordingly. | |
2560 | ||
2561 | As a special case, you can also do `git-update-index --refresh`, which | |
2562 | will refresh the "stat" information of each index to match the current | |
2563 | stat information. It will 'not' update the object status itself, and | |
2564 | it will only update the fields that are used to quickly test whether | |
2565 | an object still matches its old backing store object. | |
2566 | ||
2567 | index -> object database | |
2568 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
2569 | ||
2570 | You write your current index file to a "tree" object with the program | |
2571 | ||
2572 | ------------------------------------------------- | |
2573 | $ git-write-tree | |
2574 | ------------------------------------------------- | |
2575 | ||
2576 | that doesn't come with any options - it will just write out the | |
2577 | current index into the set of tree objects that describe that state, | |
2578 | and it will return the name of the resulting top-level tree. You can | |
2579 | use that tree to re-generate the index at any time by going in the | |
2580 | other direction: | |
2581 | ||
2582 | object database -> index | |
2583 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
2584 | ||
2585 | You read a "tree" file from the object database, and use that to | |
2586 | populate (and overwrite - don't do this if your index contains any | |
2587 | unsaved state that you might want to restore later!) your current | |
2588 | index. Normal operation is just | |
2589 | ||
2590 | ------------------------------------------------- | |
2591 | $ git-read-tree <sha1 of tree> | |
2592 | ------------------------------------------------- | |
2593 | ||
2594 | and your index file will now be equivalent to the tree that you saved | |
2595 | earlier. However, that is only your 'index' file: your working | |
2596 | directory contents have not been modified. | |
2597 | ||
2598 | index -> working directory | |
2599 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2600 | ||
2601 | You update your working directory from the index by "checking out" | |
2602 | files. This is not a very common operation, since normally you'd just | |
2603 | keep your files updated, and rather than write to your working | |
2604 | directory, you'd tell the index files about the changes in your | |
2605 | working directory (i.e. `git-update-index`). | |
2606 | ||
2607 | However, if you decide to jump to a new version, or check out somebody | |
2608 | else's version, or just restore a previous tree, you'd populate your | |
2609 | index file with read-tree, and then you need to check out the result | |
2610 | with | |
2611 | ||
2612 | ------------------------------------------------- | |
2613 | $ git-checkout-index filename | |
2614 | ------------------------------------------------- | |
2615 | ||
2616 | or, if you want to check out all of the index, use `-a`. | |
2617 | ||
2618 | NOTE! git-checkout-index normally refuses to overwrite old files, so | |
2619 | if you have an old version of the tree already checked out, you will | |
2620 | need to use the "-f" flag ('before' the "-a" flag or the filename) to | |
2621 | 'force' the checkout. | |
2622 | ||
2623 | ||
2624 | Finally, there are a few odds and ends which are not purely moving | |
2625 | from one representation to the other: | |
2626 | ||
2627 | Tying it all together | |
2628 | ~~~~~~~~~~~~~~~~~~~~~ | |
2629 | ||
2630 | To commit a tree you have instantiated with "git-write-tree", you'd | |
2631 | create a "commit" object that refers to that tree and the history | |
2632 | behind it - most notably the "parent" commits that preceded it in | |
2633 | history. | |
2634 | ||
2635 | Normally a "commit" has one parent: the previous state of the tree | |
2636 | before a certain change was made. However, sometimes it can have two | |
2637 | or more parent commits, in which case we call it a "merge", due to the | |
2638 | fact that such a commit brings together ("merges") two or more | |
2639 | previous states represented by other commits. | |
2640 | ||
2641 | In other words, while a "tree" represents a particular directory state | |
2642 | of a working directory, a "commit" represents that state in "time", | |
2643 | and explains how we got there. | |
2644 | ||
2645 | You create a commit object by giving it the tree that describes the | |
2646 | state at the time of the commit, and a list of parents: | |
2647 | ||
2648 | ------------------------------------------------- | |
2649 | $ git-commit-tree <tree> -p <parent> [-p <parent2> ..] | |
2650 | ------------------------------------------------- | |
2651 | ||
2652 | and then giving the reason for the commit on stdin (either through | |
2653 | redirection from a pipe or file, or by just typing it at the tty). | |
2654 | ||
2655 | git-commit-tree will return the name of the object that represents | |
2656 | that commit, and you should save it away for later use. Normally, | |
2657 | you'd commit a new `HEAD` state, and while git doesn't care where you | |
2658 | save the note about that state, in practice we tend to just write the | |
2659 | result to the file pointed at by `.git/HEAD`, so that we can always see | |
2660 | what the last committed state was. | |
2661 | ||
2662 | Here is an ASCII art by Jon Loeliger that illustrates how | |
2663 | various pieces fit together. | |
2664 | ||
2665 | ------------ | |
2666 | ||
2667 | commit-tree | |
2668 | commit obj | |
2669 | +----+ | |
2670 | | | | |
2671 | | | | |
2672 | V V | |
2673 | +-----------+ | |
2674 | | Object DB | | |
2675 | | Backing | | |
2676 | | Store | | |
2677 | +-----------+ | |
2678 | ^ | |
2679 | write-tree | | | |
2680 | tree obj | | | |
2681 | | | read-tree | |
2682 | | | tree obj | |
2683 | V | |
2684 | +-----------+ | |
2685 | | Index | | |
2686 | | "cache" | | |
2687 | +-----------+ | |
2688 | update-index ^ | |
2689 | blob obj | | | |
2690 | | | | |
2691 | checkout-index -u | | checkout-index | |
2692 | stat | | blob obj | |
2693 | V | |
2694 | +-----------+ | |
2695 | | Working | | |
2696 | | Directory | | |
2697 | +-----------+ | |
2698 | ||
2699 | ------------ | |
2700 | ||
2701 | ||
2702 | Examining the data | |
2703 | ------------------ | |
2704 | ||
2705 | You can examine the data represented in the object database and the | |
2706 | index with various helper tools. For every object, you can use | |
2707 | gitlink:git-cat-file[1] to examine details about the | |
2708 | object: | |
2709 | ||
2710 | ------------------------------------------------- | |
2711 | $ git-cat-file -t <objectname> | |
2712 | ------------------------------------------------- | |
2713 | ||
2714 | shows the type of the object, and once you have the type (which is | |
2715 | usually implicit in where you find the object), you can use | |
2716 | ||
2717 | ------------------------------------------------- | |
2718 | $ git-cat-file blob|tree|commit|tag <objectname> | |
2719 | ------------------------------------------------- | |
2720 | ||
2721 | to show its contents. NOTE! Trees have binary content, and as a result | |
2722 | there is a special helper for showing that content, called | |
2723 | `git-ls-tree`, which turns the binary content into a more easily | |
2724 | readable form. | |
2725 | ||
2726 | It's especially instructive to look at "commit" objects, since those | |
2727 | tend to be small and fairly self-explanatory. In particular, if you | |
2728 | follow the convention of having the top commit name in `.git/HEAD`, | |
2729 | you can do | |
2730 | ||
2731 | ------------------------------------------------- | |
2732 | $ git-cat-file commit HEAD | |
2733 | ------------------------------------------------- | |
2734 | ||
2735 | to see what the top commit was. | |
2736 | ||
2737 | Merging multiple trees | |
d19fbc3c BF |
2738 | ---------------------- |
2739 | ||
b181d57f BF |
2740 | Git helps you do a three-way merge, which you can expand to n-way by |
2741 | repeating the merge procedure arbitrary times until you finally | |
2742 | "commit" the state. The normal situation is that you'd only do one | |
2743 | three-way merge (two parents), and commit it, but if you like to, you | |
2744 | can do multiple parents in one go. | |
2745 | ||
2746 | To do a three-way merge, you need the two sets of "commit" objects | |
2747 | that you want to merge, use those to find the closest common parent (a | |
2748 | third "commit" object), and then use those commit objects to find the | |
2749 | state of the directory ("tree" object) at these points. | |
2750 | ||
2751 | To get the "base" for the merge, you first look up the common parent | |
2752 | of two commits with | |
2753 | ||
2754 | ------------------------------------------------- | |
2755 | $ git-merge-base <commit1> <commit2> | |
2756 | ------------------------------------------------- | |
2757 | ||
2758 | which will return you the commit they are both based on. You should | |
2759 | now look up the "tree" objects of those commits, which you can easily | |
2760 | do with (for example) | |
2761 | ||
2762 | ------------------------------------------------- | |
2763 | $ git-cat-file commit <commitname> | head -1 | |
2764 | ------------------------------------------------- | |
2765 | ||
2766 | since the tree object information is always the first line in a commit | |
2767 | object. | |
2768 | ||
1191ee18 BF |
2769 | Once you know the three trees you are going to merge (the one "original" |
2770 | tree, aka the common case, and the two "result" trees, aka the branches | |
2771 | you want to merge), you do a "merge" read into the index. This will | |
2772 | complain if it has to throw away your old index contents, so you should | |
b181d57f | 2773 | make sure that you've committed those - in fact you would normally |
1191ee18 BF |
2774 | always do a merge against your last commit (which should thus match what |
2775 | you have in your current index anyway). | |
b181d57f BF |
2776 | |
2777 | To do the merge, do | |
2778 | ||
2779 | ------------------------------------------------- | |
2780 | $ git-read-tree -m -u <origtree> <yourtree> <targettree> | |
2781 | ------------------------------------------------- | |
2782 | ||
2783 | which will do all trivial merge operations for you directly in the | |
2784 | index file, and you can just write the result out with | |
2785 | `git-write-tree`. | |
2786 | ||
2787 | ||
2788 | Merging multiple trees, continued | |
2789 | --------------------------------- | |
2790 | ||
2791 | Sadly, many merges aren't trivial. If there are files that have | |
2792 | been added.moved or removed, or if both branches have modified the | |
2793 | same file, you will be left with an index tree that contains "merge | |
2794 | entries" in it. Such an index tree can 'NOT' be written out to a tree | |
2795 | object, and you will have to resolve any such merge clashes using | |
2796 | other tools before you can write out the result. | |
2797 | ||
2798 | You can examine such index state with `git-ls-files --unmerged` | |
2799 | command. An example: | |
2800 | ||
2801 | ------------------------------------------------ | |
2802 | $ git-read-tree -m $orig HEAD $target | |
2803 | $ git-ls-files --unmerged | |
2804 | 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c | |
2805 | 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c | |
2806 | 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c | |
2807 | ------------------------------------------------ | |
2808 | ||
2809 | Each line of the `git-ls-files --unmerged` output begins with | |
2810 | the blob mode bits, blob SHA1, 'stage number', and the | |
2811 | filename. The 'stage number' is git's way to say which tree it | |
2812 | came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD` | |
2813 | tree, and stage3 `$target` tree. | |
2814 | ||
2815 | Earlier we said that trivial merges are done inside | |
2816 | `git-read-tree -m`. For example, if the file did not change | |
2817 | from `$orig` to `HEAD` nor `$target`, or if the file changed | |
2818 | from `$orig` to `HEAD` and `$orig` to `$target` the same way, | |
2819 | obviously the final outcome is what is in `HEAD`. What the | |
2820 | above example shows is that file `hello.c` was changed from | |
2821 | `$orig` to `HEAD` and `$orig` to `$target` in a different way. | |
2822 | You could resolve this by running your favorite 3-way merge | |
2823 | program, e.g. `diff3` or `merge`, on the blob objects from | |
2824 | these three stages yourself, like this: | |
2825 | ||
2826 | ------------------------------------------------ | |
2827 | $ git-cat-file blob 263414f... >hello.c~1 | |
2828 | $ git-cat-file blob 06fa6a2... >hello.c~2 | |
2829 | $ git-cat-file blob cc44c73... >hello.c~3 | |
2830 | $ merge hello.c~2 hello.c~1 hello.c~3 | |
2831 | ------------------------------------------------ | |
2832 | ||
2833 | This would leave the merge result in `hello.c~2` file, along | |
2834 | with conflict markers if there are conflicts. After verifying | |
2835 | the merge result makes sense, you can tell git what the final | |
2836 | merge result for this file is by: | |
2837 | ||
2838 | ------------------------------------------------- | |
2839 | $ mv -f hello.c~2 hello.c | |
2840 | $ git-update-index hello.c | |
2841 | ------------------------------------------------- | |
2842 | ||
2843 | When a path is in unmerged state, running `git-update-index` for | |
2844 | that path tells git to mark the path resolved. | |
2845 | ||
2846 | The above is the description of a git merge at the lowest level, | |
2847 | to help you understand what conceptually happens under the hood. | |
2848 | In practice, nobody, not even git itself, uses three `git-cat-file` | |
2849 | for this. There is `git-merge-index` program that extracts the | |
2850 | stages to temporary files and calls a "merge" script on it: | |
2851 | ||
2852 | ------------------------------------------------- | |
2853 | $ git-merge-index git-merge-one-file hello.c | |
2854 | ------------------------------------------------- | |
2855 | ||
2856 | and that is what higher level `git resolve` is implemented with. | |
2857 | ||
2858 | How git stores objects efficiently: pack files | |
2859 | ---------------------------------------------- | |
2860 | ||
2861 | We've seen how git stores each object in a file named after the | |
2862 | object's SHA1 hash. | |
2863 | ||
2864 | Unfortunately this system becomes inefficient once a project has a | |
2865 | lot of objects. Try this on an old project: | |
2866 | ||
2867 | ------------------------------------------------ | |
2868 | $ git count-objects | |
2869 | 6930 objects, 47620 kilobytes | |
2870 | ------------------------------------------------ | |
2871 | ||
2872 | The first number is the number of objects which are kept in | |
2873 | individual files. The second is the amount of space taken up by | |
2874 | those "loose" objects. | |
2875 | ||
2876 | You can save space and make git faster by moving these loose objects in | |
2877 | to a "pack file", which stores a group of objects in an efficient | |
2878 | compressed format; the details of how pack files are formatted can be | |
2879 | found in link:technical/pack-format.txt[technical/pack-format.txt]. | |
2880 | ||
2881 | To put the loose objects into a pack, just run git repack: | |
2882 | ||
2883 | ------------------------------------------------ | |
2884 | $ git repack | |
2885 | Generating pack... | |
2886 | Done counting 6020 objects. | |
2887 | Deltifying 6020 objects. | |
2888 | 100% (6020/6020) done | |
2889 | Writing 6020 objects. | |
2890 | 100% (6020/6020) done | |
2891 | Total 6020, written 6020 (delta 4070), reused 0 (delta 0) | |
2892 | Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created. | |
2893 | ------------------------------------------------ | |
2894 | ||
2895 | You can then run | |
2896 | ||
2897 | ------------------------------------------------ | |
2898 | $ git prune | |
2899 | ------------------------------------------------ | |
2900 | ||
2901 | to remove any of the "loose" objects that are now contained in the | |
2902 | pack. This will also remove any unreferenced objects (which may be | |
2903 | created when, for example, you use "git reset" to remove a commit). | |
2904 | You can verify that the loose objects are gone by looking at the | |
2905 | .git/objects directory or by running | |
2906 | ||
2907 | ------------------------------------------------ | |
2908 | $ git count-objects | |
2909 | 0 objects, 0 kilobytes | |
2910 | ------------------------------------------------ | |
2911 | ||
2912 | Although the object files are gone, any commands that refer to those | |
2913 | objects will work exactly as they did before. | |
2914 | ||
2915 | The gitlink:git-gc[1] command performs packing, pruning, and more for | |
2916 | you, so is normally the only high-level command you need. | |
d19fbc3c | 2917 | |
21dcb3b7 BF |
2918 | [[dangling-objects]] |
2919 | Dangling objects | |
61b41790 | 2920 | ---------------- |
21dcb3b7 | 2921 | |
04e50e94 | 2922 | The gitlink:git-fsck[1] command will sometimes complain about dangling |
21dcb3b7 BF |
2923 | objects. They are not a problem. |
2924 | ||
1191ee18 BF |
2925 | The most common cause of dangling objects is that you've rebased a |
2926 | branch, or you have pulled from somebody else who rebased a branch--see | |
2927 | <<cleaning-up-history>>. In that case, the old head of the original | |
2928 | branch still exists, as does obviously everything it pointed to. The | |
2929 | branch pointer itself just doesn't, since you replaced it with another | |
2930 | one. | |
2931 | ||
2932 | There are also other situations too that cause dangling objects. For | |
2933 | example, a "dangling blob" may arise because you did a "git add" of a | |
2934 | file, but then, before you actually committed it and made it part of the | |
2935 | bigger picture, you changed something else in that file and committed | |
2936 | that *updated* thing - the old state that you added originally ends up | |
2937 | not being pointed to by any commit or tree, so it's now a dangling blob | |
2938 | object. | |
2939 | ||
2940 | Similarly, when the "recursive" merge strategy runs, and finds that | |
2941 | there are criss-cross merges and thus more than one merge base (which is | |
2942 | fairly unusual, but it does happen), it will generate one temporary | |
2943 | midway tree (or possibly even more, if you had lots of criss-crossing | |
2944 | merges and more than two merge bases) as a temporary internal merge | |
2945 | base, and again, those are real objects, but the end result will not end | |
2946 | up pointing to them, so they end up "dangling" in your repository. | |
2947 | ||
2948 | Generally, dangling objects aren't anything to worry about. They can | |
2949 | even be very useful: if you screw something up, the dangling objects can | |
2950 | be how you recover your old tree (say, you did a rebase, and realized | |
2951 | that you really didn't want to - you can look at what dangling objects | |
2952 | you have, and decide to reset your head to some old dangling state). | |
21dcb3b7 | 2953 | |
559e4d7a BF |
2954 | For commits, the most useful thing to do with dangling objects tends to |
2955 | be to do a simple | |
21dcb3b7 BF |
2956 | |
2957 | ------------------------------------------------ | |
2958 | $ gitk <dangling-commit-sha-goes-here> --not --all | |
2959 | ------------------------------------------------ | |
2960 | ||
1191ee18 BF |
2961 | For blobs and trees, you can't do the same, but you can examine them. |
2962 | You can just do | |
21dcb3b7 BF |
2963 | |
2964 | ------------------------------------------------ | |
2965 | $ git show <dangling-blob/tree-sha-goes-here> | |
2966 | ------------------------------------------------ | |
2967 | ||
1191ee18 BF |
2968 | to show what the contents of the blob were (or, for a tree, basically |
2969 | what the "ls" for that directory was), and that may give you some idea | |
2970 | of what the operation was that left that dangling object. | |
21dcb3b7 | 2971 | |
1191ee18 BF |
2972 | Usually, dangling blobs and trees aren't very interesting. They're |
2973 | almost always the result of either being a half-way mergebase (the blob | |
2974 | will often even have the conflict markers from a merge in it, if you | |
2975 | have had conflicting merges that you fixed up by hand), or simply | |
2976 | because you interrupted a "git fetch" with ^C or something like that, | |
2977 | leaving _some_ of the new objects in the object database, but just | |
2978 | dangling and useless. | |
21dcb3b7 BF |
2979 | |
2980 | Anyway, once you are sure that you're not interested in any dangling | |
2981 | state, you can just prune all unreachable objects: | |
2982 | ||
2983 | ------------------------------------------------ | |
2984 | $ git prune | |
2985 | ------------------------------------------------ | |
2986 | ||
1191ee18 BF |
2987 | and they'll be gone. But you should only run "git prune" on a quiescent |
2988 | repository - it's kind of like doing a filesystem fsck recovery: you | |
2989 | don't want to do that while the filesystem is mounted. | |
21dcb3b7 | 2990 | |
04e50e94 BF |
2991 | (The same is true of "git-fsck" itself, btw - but since |
2992 | git-fsck never actually *changes* the repository, it just reports | |
2993 | on what it found, git-fsck itself is never "dangerous" to run. | |
21dcb3b7 BF |
2994 | Running it while somebody is actually changing the repository can cause |
2995 | confusing and scary messages, but it won't actually do anything bad. In | |
2996 | contrast, running "git prune" while somebody is actively changing the | |
2997 | repository is a *BAD* idea). | |
2998 | ||
d19fbc3c BF |
2999 | Glossary of git terms |
3000 | ===================== | |
3001 | ||
3002 | include::glossary.txt[] | |
3003 | ||
6bd9b682 BF |
3004 | Notes and todo list for this manual |
3005 | =================================== | |
3006 | ||
3007 | This is a work in progress. | |
3008 | ||
3009 | The basic requirements: | |
2f99710c BF |
3010 | - It must be readable in order, from beginning to end, by |
3011 | someone intelligent with a basic grasp of the unix | |
3012 | commandline, but without any special knowledge of git. If | |
3013 | necessary, any other prerequisites should be specifically | |
3014 | mentioned as they arise. | |
3015 | - Whenever possible, section headings should clearly describe | |
3016 | the task they explain how to do, in language that requires | |
3017 | no more knowledge than necessary: for example, "importing | |
3018 | patches into a project" rather than "the git-am command" | |
6bd9b682 | 3019 | |
d5cd5de4 BF |
3020 | Think about how to create a clear chapter dependency graph that will |
3021 | allow people to get to important topics without necessarily reading | |
3022 | everything in between. | |
d19fbc3c | 3023 | |
aacd404e MC |
3024 | Say something about .gitignore. |
3025 | ||
d19fbc3c BF |
3026 | Scan Documentation/ for other stuff left out; in particular: |
3027 | howto's | |
d19fbc3c BF |
3028 | some of technical/? |
3029 | hooks | |
0b375ab0 | 3030 | list of commands in gitlink:git[1] |
d19fbc3c BF |
3031 | |
3032 | Scan email archives for other stuff left out | |
3033 | ||
3034 | Scan man pages to see if any assume more background than this manual | |
3035 | provides. | |
3036 | ||
2f99710c | 3037 | Simplify beginning by suggesting disconnected head instead of |
b181d57f | 3038 | temporary branch creation? |
d19fbc3c | 3039 | |
2f99710c BF |
3040 | Add more good examples. Entire sections of just cookbook examples |
3041 | might be a good idea; maybe make an "advanced examples" section a | |
3042 | standard end-of-chapter section? | |
d19fbc3c BF |
3043 | |
3044 | Include cross-references to the glossary, where appropriate. | |
3045 | ||
9a241220 BF |
3046 | Document shallow clones? See draft 1.5.0 release notes for some |
3047 | documentation. | |
3048 | ||
3dff5379 | 3049 | Add a section on working with other version control systems, including |
9a241220 BF |
3050 | CVS, Subversion, and just imports of series of release tarballs. |
3051 | ||
a8cd1402 | 3052 | More details on gitweb? |
0b375ab0 BF |
3053 | |
3054 | Write a chapter on using plumbing and writing scripts. |