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1 | Git User's Manual (for version 1.5.3 or newer) | |
2 | ______________________________________________ | |
3 | ||
4 | ||
5 | Git is a fast distributed revision control system. | |
6 | ||
7 | This manual is designed to be readable by someone with basic UNIX | |
8 | command-line skills, but no previous knowledge of git. | |
9 | ||
10 | <<repositories-and-branches>> and <<exploring-git-history>> explain how | |
11 | to fetch and study a project using git--read these chapters to learn how | |
12 | to build and test a particular version of a software project, search for | |
13 | regressions, and so on. | |
14 | ||
15 | People needing to do actual development will also want to read | |
16 | <<Developing-With-git>> and <<sharing-development>>. | |
17 | ||
18 | Further chapters cover more specialized topics. | |
19 | ||
20 | Comprehensive reference documentation is available through the man | |
21 | pages, or linkgit:git-help[1] command. For example, for the command | |
22 | "git clone <repo>", you can either use: | |
23 | ||
24 | ------------------------------------------------ | |
25 | $ man git-clone | |
26 | ------------------------------------------------ | |
27 | ||
28 | or: | |
29 | ||
30 | ------------------------------------------------ | |
31 | $ git help clone | |
32 | ------------------------------------------------ | |
33 | ||
34 | With the latter, you can use the manual viewer of your choice; see | |
35 | linkgit:git-help[1] for more information. | |
36 | ||
37 | See also <<git-quick-start>> for a brief overview of git commands, | |
38 | without any explanation. | |
39 | ||
40 | Finally, see <<todo>> for ways that you can help make this manual more | |
41 | complete. | |
42 | ||
43 | ||
44 | [[repositories-and-branches]] | |
45 | Repositories and Branches | |
46 | ========================= | |
47 | ||
48 | [[how-to-get-a-git-repository]] | |
49 | How to get a git repository | |
50 | --------------------------- | |
51 | ||
52 | It will be useful to have a git repository to experiment with as you | |
53 | read this manual. | |
54 | ||
55 | The best way to get one is by using the linkgit:git-clone[1] command to | |
56 | download a copy of an existing repository. If you don't already have a | |
57 | project in mind, here are some interesting examples: | |
58 | ||
59 | ------------------------------------------------ | |
60 | # git itself (approx. 10MB download): | |
61 | $ git clone git://git.kernel.org/pub/scm/git/git.git | |
62 | # the Linux kernel (approx. 150MB download): | |
63 | $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git | |
64 | ------------------------------------------------ | |
65 | ||
66 | The initial clone may be time-consuming for a large project, but you | |
67 | will only need to clone once. | |
68 | ||
69 | The clone command creates a new directory named after the project ("git" | |
70 | or "linux-2.6" in the examples above). After you cd into this | |
71 | directory, you will see that it contains a copy of the project files, | |
72 | called the <<def_working_tree,working tree>>, together with a special | |
73 | top-level directory named ".git", which contains all the information | |
74 | about the history of the project. | |
75 | ||
76 | [[how-to-check-out]] | |
77 | How to check out a different version of a project | |
78 | ------------------------------------------------- | |
79 | ||
80 | Git is best thought of as a tool for storing the history of a collection | |
81 | of files. It stores the history as a compressed collection of | |
82 | interrelated snapshots of the project's contents. In git each such | |
83 | version is called a <<def_commit,commit>>. | |
84 | ||
85 | Those snapshots aren't necessarily all arranged in a single line from | |
86 | oldest to newest; instead, work may simultaneously proceed along | |
87 | parallel lines of development, called <<def_branch,branches>>, which may | |
88 | merge and diverge. | |
89 | ||
90 | A single git repository can track development on multiple branches. It | |
91 | does this by keeping a list of <<def_head,heads>> which reference the | |
92 | latest commit on each branch; the linkgit:git-branch[1] command shows | |
93 | you the list of branch heads: | |
94 | ||
95 | ------------------------------------------------ | |
96 | $ git branch | |
97 | * master | |
98 | ------------------------------------------------ | |
99 | ||
100 | A freshly cloned repository contains a single branch head, by default | |
101 | named "master", with the working directory initialized to the state of | |
102 | the project referred to by that branch head. | |
103 | ||
104 | Most projects also use <<def_tag,tags>>. Tags, like heads, are | |
105 | references into the project's history, and can be listed using the | |
106 | linkgit:git-tag[1] command: | |
107 | ||
108 | ------------------------------------------------ | |
109 | $ git tag -l | |
110 | v2.6.11 | |
111 | v2.6.11-tree | |
112 | v2.6.12 | |
113 | v2.6.12-rc2 | |
114 | v2.6.12-rc3 | |
115 | v2.6.12-rc4 | |
116 | v2.6.12-rc5 | |
117 | v2.6.12-rc6 | |
118 | v2.6.13 | |
119 | ... | |
120 | ------------------------------------------------ | |
121 | ||
122 | Tags are expected to always point at the same version of a project, | |
123 | while heads are expected to advance as development progresses. | |
124 | ||
125 | Create a new branch head pointing to one of these versions and check it | |
126 | out using linkgit:git-checkout[1]: | |
127 | ||
128 | ------------------------------------------------ | |
129 | $ git checkout -b new v2.6.13 | |
130 | ------------------------------------------------ | |
131 | ||
132 | The working directory then reflects the contents that the project had | |
133 | when it was tagged v2.6.13, and linkgit:git-branch[1] shows two | |
134 | branches, with an asterisk marking the currently checked-out branch: | |
135 | ||
136 | ------------------------------------------------ | |
137 | $ git branch | |
138 | master | |
139 | * new | |
140 | ------------------------------------------------ | |
141 | ||
142 | If you decide that you'd rather see version 2.6.17, you can modify | |
143 | the current branch to point at v2.6.17 instead, with | |
144 | ||
145 | ------------------------------------------------ | |
146 | $ git reset --hard v2.6.17 | |
147 | ------------------------------------------------ | |
148 | ||
149 | Note that if the current branch head was your only reference to a | |
150 | particular point in history, then resetting that branch may leave you | |
151 | with no way to find the history it used to point to; so use this command | |
152 | carefully. | |
153 | ||
154 | [[understanding-commits]] | |
155 | Understanding History: Commits | |
156 | ------------------------------ | |
157 | ||
158 | Every change in the history of a project is represented by a commit. | |
159 | The linkgit:git-show[1] command shows the most recent commit on the | |
160 | current branch: | |
161 | ||
162 | ------------------------------------------------ | |
163 | $ git show | |
164 | commit 17cf781661e6d38f737f15f53ab552f1e95960d7 | |
165 | Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)> | |
166 | Date: Tue Apr 19 14:11:06 2005 -0700 | |
167 | ||
168 | Remove duplicate getenv(DB_ENVIRONMENT) call | |
169 | ||
170 | Noted by Tony Luck. | |
171 | ||
172 | diff --git a/init-db.c b/init-db.c | |
173 | index 65898fa..b002dc6 100644 | |
174 | --- a/init-db.c | |
175 | +++ b/init-db.c | |
176 | @@ -7,7 +7,7 @@ | |
177 | ||
178 | int main(int argc, char **argv) | |
179 | { | |
180 | - char *sha1_dir = getenv(DB_ENVIRONMENT), *path; | |
181 | + char *sha1_dir, *path; | |
182 | int len, i; | |
183 | ||
184 | if (mkdir(".git", 0755) < 0) { | |
185 | ------------------------------------------------ | |
186 | ||
187 | As you can see, a commit shows who made the latest change, what they | |
188 | did, and why. | |
189 | ||
190 | Every commit has a 40-hexdigit id, sometimes called the "object name" or the | |
191 | "SHA-1 id", shown on the first line of the "git show" output. You can usually | |
192 | refer to a commit by a shorter name, such as a tag or a branch name, but this | |
193 | longer name can also be useful. Most importantly, it is a globally unique | |
194 | name for this commit: so if you tell somebody else the object name (for | |
195 | example in email), then you are guaranteed that name will refer to the same | |
196 | commit in their repository that it does in yours (assuming their repository | |
197 | has that commit at all). Since the object name is computed as a hash over the | |
198 | contents of the commit, you are guaranteed that the commit can never change | |
199 | without its name also changing. | |
200 | ||
201 | In fact, in <<git-concepts>> we shall see that everything stored in git | |
202 | history, including file data and directory contents, is stored in an object | |
203 | with a name that is a hash of its contents. | |
204 | ||
205 | [[understanding-reachability]] | |
206 | Understanding history: commits, parents, and reachability | |
207 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
208 | ||
209 | Every commit (except the very first commit in a project) also has a | |
210 | parent commit which shows what happened before this commit. | |
211 | Following the chain of parents will eventually take you back to the | |
212 | beginning of the project. | |
213 | ||
214 | However, the commits do not form a simple list; git allows lines of | |
215 | development to diverge and then reconverge, and the point where two | |
216 | lines of development reconverge is called a "merge". The commit | |
217 | representing a merge can therefore have more than one parent, with | |
218 | each parent representing the most recent commit on one of the lines | |
219 | of development leading to that point. | |
220 | ||
221 | The best way to see how this works is using the linkgit:gitk[1] | |
222 | command; running gitk now on a git repository and looking for merge | |
223 | commits will help understand how the git organizes history. | |
224 | ||
225 | In the following, we say that commit X is "reachable" from commit Y | |
226 | if commit X is an ancestor of commit Y. Equivalently, you could say | |
227 | that Y is a descendant of X, or that there is a chain of parents | |
228 | leading from commit Y to commit X. | |
229 | ||
230 | [[history-diagrams]] | |
231 | Understanding history: History diagrams | |
232 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
233 | ||
234 | We will sometimes represent git history using diagrams like the one | |
235 | below. Commits are shown as "o", and the links between them with | |
236 | lines drawn with - / and \. Time goes left to right: | |
237 | ||
238 | ||
239 | ................................................ | |
240 | o--o--o <-- Branch A | |
241 | / | |
242 | o--o--o <-- master | |
243 | \ | |
244 | o--o--o <-- Branch B | |
245 | ................................................ | |
246 | ||
247 | If we need to talk about a particular commit, the character "o" may | |
248 | be replaced with another letter or number. | |
249 | ||
250 | [[what-is-a-branch]] | |
251 | Understanding history: What is a branch? | |
252 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
253 | ||
254 | When we need to be precise, we will use the word "branch" to mean a line | |
255 | of development, and "branch head" (or just "head") to mean a reference | |
256 | to the most recent commit on a branch. In the example above, the branch | |
257 | head named "A" is a pointer to one particular commit, but we refer to | |
258 | the line of three commits leading up to that point as all being part of | |
259 | "branch A". | |
260 | ||
261 | However, when no confusion will result, we often just use the term | |
262 | "branch" both for branches and for branch heads. | |
263 | ||
264 | [[manipulating-branches]] | |
265 | Manipulating branches | |
266 | --------------------- | |
267 | ||
268 | Creating, deleting, and modifying branches is quick and easy; here's | |
269 | a summary of the commands: | |
270 | ||
271 | git branch:: | |
272 | list all branches | |
273 | git branch <branch>:: | |
274 | create a new branch named <branch>, referencing the same | |
275 | point in history as the current branch | |
276 | git branch <branch> <start-point>:: | |
277 | create a new branch named <branch>, referencing | |
278 | <start-point>, which may be specified any way you like, | |
279 | including using a branch name or a tag name | |
280 | git branch -d <branch>:: | |
281 | delete the branch <branch>; if the branch you are deleting | |
282 | points to a commit which is not reachable from the current | |
283 | branch, this command will fail with a warning. | |
284 | git branch -D <branch>:: | |
285 | even if the branch points to a commit not reachable | |
286 | from the current branch, you may know that that commit | |
287 | is still reachable from some other branch or tag. In that | |
288 | case it is safe to use this command to force git to delete | |
289 | the branch. | |
290 | git checkout <branch>:: | |
291 | make the current branch <branch>, updating the working | |
292 | directory to reflect the version referenced by <branch> | |
293 | git checkout -b <new> <start-point>:: | |
294 | create a new branch <new> referencing <start-point>, and | |
295 | check it out. | |
296 | ||
297 | The special symbol "HEAD" can always be used to refer to the current | |
298 | branch. In fact, git uses a file named "HEAD" in the .git directory to | |
299 | remember which branch is current: | |
300 | ||
301 | ------------------------------------------------ | |
302 | $ cat .git/HEAD | |
303 | ref: refs/heads/master | |
304 | ------------------------------------------------ | |
305 | ||
306 | [[detached-head]] | |
307 | Examining an old version without creating a new branch | |
308 | ------------------------------------------------------ | |
309 | ||
310 | The `git checkout` command normally expects a branch head, but will also | |
311 | accept an arbitrary commit; for example, you can check out the commit | |
312 | referenced by a tag: | |
313 | ||
314 | ------------------------------------------------ | |
315 | $ git checkout v2.6.17 | |
316 | Note: moving to "v2.6.17" which isn't a local branch | |
317 | If you want to create a new branch from this checkout, you may do so | |
318 | (now or later) by using -b with the checkout command again. Example: | |
319 | git checkout -b <new_branch_name> | |
320 | HEAD is now at 427abfa... Linux v2.6.17 | |
321 | ------------------------------------------------ | |
322 | ||
323 | The HEAD then refers to the SHA-1 of the commit instead of to a branch, | |
324 | and git branch shows that you are no longer on a branch: | |
325 | ||
326 | ------------------------------------------------ | |
327 | $ cat .git/HEAD | |
328 | 427abfa28afedffadfca9dd8b067eb6d36bac53f | |
329 | $ git branch | |
330 | * (no branch) | |
331 | master | |
332 | ------------------------------------------------ | |
333 | ||
334 | In this case we say that the HEAD is "detached". | |
335 | ||
336 | This is an easy way to check out a particular version without having to | |
337 | make up a name for the new branch. You can still create a new branch | |
338 | (or tag) for this version later if you decide to. | |
339 | ||
340 | [[examining-remote-branches]] | |
341 | Examining branches from a remote repository | |
342 | ------------------------------------------- | |
343 | ||
344 | The "master" branch that was created at the time you cloned is a copy | |
345 | of the HEAD in the repository that you cloned from. That repository | |
346 | may also have had other branches, though, and your local repository | |
347 | keeps branches which track each of those remote branches, called | |
348 | remote-tracking branches, which you | |
349 | can view using the "-r" option to linkgit:git-branch[1]: | |
350 | ||
351 | ------------------------------------------------ | |
352 | $ git branch -r | |
353 | origin/HEAD | |
354 | origin/html | |
355 | origin/maint | |
356 | origin/man | |
357 | origin/master | |
358 | origin/next | |
359 | origin/pu | |
360 | origin/todo | |
361 | ------------------------------------------------ | |
362 | ||
363 | In this example, "origin" is called a remote repository, or "remote" | |
364 | for short. The branches of this repository are called "remote | |
365 | branches" from our point of view. The remote-tracking branches listed | |
366 | above were created based on the remote branches at clone time and will | |
367 | be updated by "git fetch" (hence "git pull") and "git push". See | |
368 | <<Updating-a-repository-With-git-fetch>> for details. | |
369 | ||
370 | You might want to build on one of these remote-tracking branches | |
371 | on a branch of your own, just as you would for a tag: | |
372 | ||
373 | ------------------------------------------------ | |
374 | $ git checkout -b my-todo-copy origin/todo | |
375 | ------------------------------------------------ | |
376 | ||
377 | You can also check out "origin/todo" directly to examine it or | |
378 | write a one-off patch. See <<detached-head,detached head>>. | |
379 | ||
380 | Note that the name "origin" is just the name that git uses by default | |
381 | to refer to the repository that you cloned from. | |
382 | ||
383 | [[how-git-stores-references]] | |
384 | Naming branches, tags, and other references | |
385 | ------------------------------------------- | |
386 | ||
387 | Branches, remote-tracking branches, and tags are all references to | |
388 | commits. All references are named with a slash-separated path name | |
389 | starting with "refs"; the names we've been using so far are actually | |
390 | shorthand: | |
391 | ||
392 | - The branch "test" is short for "refs/heads/test". | |
393 | - The tag "v2.6.18" is short for "refs/tags/v2.6.18". | |
394 | - "origin/master" is short for "refs/remotes/origin/master". | |
395 | ||
396 | The full name is occasionally useful if, for example, there ever | |
397 | exists a tag and a branch with the same name. | |
398 | ||
399 | (Newly created refs are actually stored in the .git/refs directory, | |
400 | under the path given by their name. However, for efficiency reasons | |
401 | they may also be packed together in a single file; see | |
402 | linkgit:git-pack-refs[1]). | |
403 | ||
404 | As another useful shortcut, the "HEAD" of a repository can be referred | |
405 | to just using the name of that repository. So, for example, "origin" | |
406 | is usually a shortcut for the HEAD branch in the repository "origin". | |
407 | ||
408 | For the complete list of paths which git checks for references, and | |
409 | the order it uses to decide which to choose when there are multiple | |
410 | references with the same shorthand name, see the "SPECIFYING | |
411 | REVISIONS" section of linkgit:gitrevisions[7]. | |
412 | ||
413 | [[Updating-a-repository-With-git-fetch]] | |
414 | Updating a repository with git fetch | |
415 | ------------------------------------ | |
416 | ||
417 | Eventually the developer cloned from will do additional work in her | |
418 | repository, creating new commits and advancing the branches to point | |
419 | at the new commits. | |
420 | ||
421 | The command "git fetch", with no arguments, will update all of the | |
422 | remote-tracking branches to the latest version found in her | |
423 | repository. It will not touch any of your own branches--not even the | |
424 | "master" branch that was created for you on clone. | |
425 | ||
426 | [[fetching-branches]] | |
427 | Fetching branches from other repositories | |
428 | ----------------------------------------- | |
429 | ||
430 | You can also track branches from repositories other than the one you | |
431 | cloned from, using linkgit:git-remote[1]: | |
432 | ||
433 | ------------------------------------------------- | |
434 | $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git | |
435 | $ git fetch linux-nfs | |
436 | * refs/remotes/linux-nfs/master: storing branch 'master' ... | |
437 | commit: bf81b46 | |
438 | ------------------------------------------------- | |
439 | ||
440 | New remote-tracking branches will be stored under the shorthand name | |
441 | that you gave "git remote add", in this case linux-nfs: | |
442 | ||
443 | ------------------------------------------------- | |
444 | $ git branch -r | |
445 | linux-nfs/master | |
446 | origin/master | |
447 | ------------------------------------------------- | |
448 | ||
449 | If you run "git fetch <remote>" later, the remote-tracking branches for the | |
450 | named <remote> will be updated. | |
451 | ||
452 | If you examine the file .git/config, you will see that git has added | |
453 | a new stanza: | |
454 | ||
455 | ------------------------------------------------- | |
456 | $ cat .git/config | |
457 | ... | |
458 | [remote "linux-nfs"] | |
459 | url = git://linux-nfs.org/pub/nfs-2.6.git | |
460 | fetch = +refs/heads/*:refs/remotes/linux-nfs/* | |
461 | ... | |
462 | ------------------------------------------------- | |
463 | ||
464 | This is what causes git to track the remote's branches; you may modify | |
465 | or delete these configuration options by editing .git/config with a | |
466 | text editor. (See the "CONFIGURATION FILE" section of | |
467 | linkgit:git-config[1] for details.) | |
468 | ||
469 | [[exploring-git-history]] | |
470 | Exploring git history | |
471 | ===================== | |
472 | ||
473 | Git is best thought of as a tool for storing the history of a | |
474 | collection of files. It does this by storing compressed snapshots of | |
475 | the contents of a file hierarchy, together with "commits" which show | |
476 | the relationships between these snapshots. | |
477 | ||
478 | Git provides extremely flexible and fast tools for exploring the | |
479 | history of a project. | |
480 | ||
481 | We start with one specialized tool that is useful for finding the | |
482 | commit that introduced a bug into a project. | |
483 | ||
484 | [[using-bisect]] | |
485 | How to use bisect to find a regression | |
486 | -------------------------------------- | |
487 | ||
488 | Suppose version 2.6.18 of your project worked, but the version at | |
489 | "master" crashes. Sometimes the best way to find the cause of such a | |
490 | regression is to perform a brute-force search through the project's | |
491 | history to find the particular commit that caused the problem. The | |
492 | linkgit:git-bisect[1] command can help you do this: | |
493 | ||
494 | ------------------------------------------------- | |
495 | $ git bisect start | |
496 | $ git bisect good v2.6.18 | |
497 | $ git bisect bad master | |
498 | Bisecting: 3537 revisions left to test after this | |
499 | [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6] | |
500 | ------------------------------------------------- | |
501 | ||
502 | If you run "git branch" at this point, you'll see that git has | |
503 | temporarily moved you in "(no branch)". HEAD is now detached from any | |
504 | branch and points directly to a commit (with commit id 65934...) that | |
505 | is reachable from "master" but not from v2.6.18. Compile and test it, | |
506 | and see whether it crashes. Assume it does crash. Then: | |
507 | ||
508 | ------------------------------------------------- | |
509 | $ git bisect bad | |
510 | Bisecting: 1769 revisions left to test after this | |
511 | [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings | |
512 | ------------------------------------------------- | |
513 | ||
514 | checks out an older version. Continue like this, telling git at each | |
515 | stage whether the version it gives you is good or bad, and notice | |
516 | that the number of revisions left to test is cut approximately in | |
517 | half each time. | |
518 | ||
519 | After about 13 tests (in this case), it will output the commit id of | |
520 | the guilty commit. You can then examine the commit with | |
521 | linkgit:git-show[1], find out who wrote it, and mail them your bug | |
522 | report with the commit id. Finally, run | |
523 | ||
524 | ------------------------------------------------- | |
525 | $ git bisect reset | |
526 | ------------------------------------------------- | |
527 | ||
528 | to return you to the branch you were on before. | |
529 | ||
530 | Note that the version which `git bisect` checks out for you at each | |
531 | point is just a suggestion, and you're free to try a different | |
532 | version if you think it would be a good idea. For example, | |
533 | occasionally you may land on a commit that broke something unrelated; | |
534 | run | |
535 | ||
536 | ------------------------------------------------- | |
537 | $ git bisect visualize | |
538 | ------------------------------------------------- | |
539 | ||
540 | which will run gitk and label the commit it chose with a marker that | |
541 | says "bisect". Choose a safe-looking commit nearby, note its commit | |
542 | id, and check it out with: | |
543 | ||
544 | ------------------------------------------------- | |
545 | $ git reset --hard fb47ddb2db... | |
546 | ------------------------------------------------- | |
547 | ||
548 | then test, run "bisect good" or "bisect bad" as appropriate, and | |
549 | continue. | |
550 | ||
551 | Instead of "git bisect visualize" and then "git reset --hard | |
552 | fb47ddb2db...", you might just want to tell git that you want to skip | |
553 | the current commit: | |
554 | ||
555 | ------------------------------------------------- | |
556 | $ git bisect skip | |
557 | ------------------------------------------------- | |
558 | ||
559 | In this case, though, git may not eventually be able to tell the first | |
560 | bad one between some first skipped commits and a later bad commit. | |
561 | ||
562 | There are also ways to automate the bisecting process if you have a | |
563 | test script that can tell a good from a bad commit. See | |
564 | linkgit:git-bisect[1] for more information about this and other "git | |
565 | bisect" features. | |
566 | ||
567 | [[naming-commits]] | |
568 | Naming commits | |
569 | -------------- | |
570 | ||
571 | We have seen several ways of naming commits already: | |
572 | ||
573 | - 40-hexdigit object name | |
574 | - branch name: refers to the commit at the head of the given | |
575 | branch | |
576 | - tag name: refers to the commit pointed to by the given tag | |
577 | (we've seen branches and tags are special cases of | |
578 | <<how-git-stores-references,references>>). | |
579 | - HEAD: refers to the head of the current branch | |
580 | ||
581 | There are many more; see the "SPECIFYING REVISIONS" section of the | |
582 | linkgit:gitrevisions[7] man page for the complete list of ways to | |
583 | name revisions. Some examples: | |
584 | ||
585 | ------------------------------------------------- | |
586 | $ git show fb47ddb2 # the first few characters of the object name | |
587 | # are usually enough to specify it uniquely | |
588 | $ git show HEAD^ # the parent of the HEAD commit | |
589 | $ git show HEAD^^ # the grandparent | |
590 | $ git show HEAD~4 # the great-great-grandparent | |
591 | ------------------------------------------------- | |
592 | ||
593 | Recall that merge commits may have more than one parent; by default, | |
594 | ^ and ~ follow the first parent listed in the commit, but you can | |
595 | also choose: | |
596 | ||
597 | ------------------------------------------------- | |
598 | $ git show HEAD^1 # show the first parent of HEAD | |
599 | $ git show HEAD^2 # show the second parent of HEAD | |
600 | ------------------------------------------------- | |
601 | ||
602 | In addition to HEAD, there are several other special names for | |
603 | commits: | |
604 | ||
605 | Merges (to be discussed later), as well as operations such as | |
606 | `git reset`, which change the currently checked-out commit, generally | |
607 | set ORIG_HEAD to the value HEAD had before the current operation. | |
608 | ||
609 | The `git fetch` operation always stores the head of the last fetched | |
610 | branch in FETCH_HEAD. For example, if you run `git fetch` without | |
611 | specifying a local branch as the target of the operation | |
612 | ||
613 | ------------------------------------------------- | |
614 | $ git fetch git://example.com/proj.git theirbranch | |
615 | ------------------------------------------------- | |
616 | ||
617 | the fetched commits will still be available from FETCH_HEAD. | |
618 | ||
619 | When we discuss merges we'll also see the special name MERGE_HEAD, | |
620 | which refers to the other branch that we're merging in to the current | |
621 | branch. | |
622 | ||
623 | The linkgit:git-rev-parse[1] command is a low-level command that is | |
624 | occasionally useful for translating some name for a commit to the object | |
625 | name for that commit: | |
626 | ||
627 | ------------------------------------------------- | |
628 | $ git rev-parse origin | |
629 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
630 | ------------------------------------------------- | |
631 | ||
632 | [[creating-tags]] | |
633 | Creating tags | |
634 | ------------- | |
635 | ||
636 | We can also create a tag to refer to a particular commit; after | |
637 | running | |
638 | ||
639 | ------------------------------------------------- | |
640 | $ git tag stable-1 1b2e1d63ff | |
641 | ------------------------------------------------- | |
642 | ||
643 | You can use stable-1 to refer to the commit 1b2e1d63ff. | |
644 | ||
645 | This creates a "lightweight" tag. If you would also like to include a | |
646 | comment with the tag, and possibly sign it cryptographically, then you | |
647 | should create a tag object instead; see the linkgit:git-tag[1] man page | |
648 | for details. | |
649 | ||
650 | [[browsing-revisions]] | |
651 | Browsing revisions | |
652 | ------------------ | |
653 | ||
654 | The linkgit:git-log[1] command can show lists of commits. On its | |
655 | own, it shows all commits reachable from the parent commit; but you | |
656 | can also make more specific requests: | |
657 | ||
658 | ------------------------------------------------- | |
659 | $ git log v2.5.. # commits since (not reachable from) v2.5 | |
660 | $ git log test..master # commits reachable from master but not test | |
661 | $ git log master..test # ...reachable from test but not master | |
662 | $ git log master...test # ...reachable from either test or master, | |
663 | # but not both | |
664 | $ git log --since="2 weeks ago" # commits from the last 2 weeks | |
665 | $ git log Makefile # commits which modify Makefile | |
666 | $ git log fs/ # ... which modify any file under fs/ | |
667 | $ git log -S'foo()' # commits which add or remove any file data | |
668 | # matching the string 'foo()' | |
669 | ------------------------------------------------- | |
670 | ||
671 | And of course you can combine all of these; the following finds | |
672 | commits since v2.5 which touch the Makefile or any file under fs: | |
673 | ||
674 | ------------------------------------------------- | |
675 | $ git log v2.5.. Makefile fs/ | |
676 | ------------------------------------------------- | |
677 | ||
678 | You can also ask git log to show patches: | |
679 | ||
680 | ------------------------------------------------- | |
681 | $ git log -p | |
682 | ------------------------------------------------- | |
683 | ||
684 | See the "--pretty" option in the linkgit:git-log[1] man page for more | |
685 | display options. | |
686 | ||
687 | Note that git log starts with the most recent commit and works | |
688 | backwards through the parents; however, since git history can contain | |
689 | multiple independent lines of development, the particular order that | |
690 | commits are listed in may be somewhat arbitrary. | |
691 | ||
692 | [[generating-diffs]] | |
693 | Generating diffs | |
694 | ---------------- | |
695 | ||
696 | You can generate diffs between any two versions using | |
697 | linkgit:git-diff[1]: | |
698 | ||
699 | ------------------------------------------------- | |
700 | $ git diff master..test | |
701 | ------------------------------------------------- | |
702 | ||
703 | That will produce the diff between the tips of the two branches. If | |
704 | you'd prefer to find the diff from their common ancestor to test, you | |
705 | can use three dots instead of two: | |
706 | ||
707 | ------------------------------------------------- | |
708 | $ git diff master...test | |
709 | ------------------------------------------------- | |
710 | ||
711 | Sometimes what you want instead is a set of patches; for this you can | |
712 | use linkgit:git-format-patch[1]: | |
713 | ||
714 | ------------------------------------------------- | |
715 | $ git format-patch master..test | |
716 | ------------------------------------------------- | |
717 | ||
718 | will generate a file with a patch for each commit reachable from test | |
719 | but not from master. | |
720 | ||
721 | [[viewing-old-file-versions]] | |
722 | Viewing old file versions | |
723 | ------------------------- | |
724 | ||
725 | You can always view an old version of a file by just checking out the | |
726 | correct revision first. But sometimes it is more convenient to be | |
727 | able to view an old version of a single file without checking | |
728 | anything out; this command does that: | |
729 | ||
730 | ------------------------------------------------- | |
731 | $ git show v2.5:fs/locks.c | |
732 | ------------------------------------------------- | |
733 | ||
734 | Before the colon may be anything that names a commit, and after it | |
735 | may be any path to a file tracked by git. | |
736 | ||
737 | [[history-examples]] | |
738 | Examples | |
739 | -------- | |
740 | ||
741 | [[counting-commits-on-a-branch]] | |
742 | Counting the number of commits on a branch | |
743 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
744 | ||
745 | Suppose you want to know how many commits you've made on "mybranch" | |
746 | since it diverged from "origin": | |
747 | ||
748 | ------------------------------------------------- | |
749 | $ git log --pretty=oneline origin..mybranch | wc -l | |
750 | ------------------------------------------------- | |
751 | ||
752 | Alternatively, you may often see this sort of thing done with the | |
753 | lower-level command linkgit:git-rev-list[1], which just lists the SHA-1's | |
754 | of all the given commits: | |
755 | ||
756 | ------------------------------------------------- | |
757 | $ git rev-list origin..mybranch | wc -l | |
758 | ------------------------------------------------- | |
759 | ||
760 | [[checking-for-equal-branches]] | |
761 | Check whether two branches point at the same history | |
762 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
763 | ||
764 | Suppose you want to check whether two branches point at the same point | |
765 | in history. | |
766 | ||
767 | ------------------------------------------------- | |
768 | $ git diff origin..master | |
769 | ------------------------------------------------- | |
770 | ||
771 | will tell you whether the contents of the project are the same at the | |
772 | two branches; in theory, however, it's possible that the same project | |
773 | contents could have been arrived at by two different historical | |
774 | routes. You could compare the object names: | |
775 | ||
776 | ------------------------------------------------- | |
777 | $ git rev-list origin | |
778 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
779 | $ git rev-list master | |
780 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
781 | ------------------------------------------------- | |
782 | ||
783 | Or you could recall that the ... operator selects all commits | |
784 | contained reachable from either one reference or the other but not | |
785 | both; so | |
786 | ||
787 | ------------------------------------------------- | |
788 | $ git log origin...master | |
789 | ------------------------------------------------- | |
790 | ||
791 | will return no commits when the two branches are equal. | |
792 | ||
793 | [[finding-tagged-descendants]] | |
794 | Find first tagged version including a given fix | |
795 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
796 | ||
797 | Suppose you know that the commit e05db0fd fixed a certain problem. | |
798 | You'd like to find the earliest tagged release that contains that | |
799 | fix. | |
800 | ||
801 | Of course, there may be more than one answer--if the history branched | |
802 | after commit e05db0fd, then there could be multiple "earliest" tagged | |
803 | releases. | |
804 | ||
805 | You could just visually inspect the commits since e05db0fd: | |
806 | ||
807 | ------------------------------------------------- | |
808 | $ gitk e05db0fd.. | |
809 | ------------------------------------------------- | |
810 | ||
811 | Or you can use linkgit:git-name-rev[1], which will give the commit a | |
812 | name based on any tag it finds pointing to one of the commit's | |
813 | descendants: | |
814 | ||
815 | ------------------------------------------------- | |
816 | $ git name-rev --tags e05db0fd | |
817 | e05db0fd tags/v1.5.0-rc1^0~23 | |
818 | ------------------------------------------------- | |
819 | ||
820 | The linkgit:git-describe[1] command does the opposite, naming the | |
821 | revision using a tag on which the given commit is based: | |
822 | ||
823 | ------------------------------------------------- | |
824 | $ git describe e05db0fd | |
825 | v1.5.0-rc0-260-ge05db0f | |
826 | ------------------------------------------------- | |
827 | ||
828 | but that may sometimes help you guess which tags might come after the | |
829 | given commit. | |
830 | ||
831 | If you just want to verify whether a given tagged version contains a | |
832 | given commit, you could use linkgit:git-merge-base[1]: | |
833 | ||
834 | ------------------------------------------------- | |
835 | $ git merge-base e05db0fd v1.5.0-rc1 | |
836 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
837 | ------------------------------------------------- | |
838 | ||
839 | The merge-base command finds a common ancestor of the given commits, | |
840 | and always returns one or the other in the case where one is a | |
841 | descendant of the other; so the above output shows that e05db0fd | |
842 | actually is an ancestor of v1.5.0-rc1. | |
843 | ||
844 | Alternatively, note that | |
845 | ||
846 | ------------------------------------------------- | |
847 | $ git log v1.5.0-rc1..e05db0fd | |
848 | ------------------------------------------------- | |
849 | ||
850 | will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, | |
851 | because it outputs only commits that are not reachable from v1.5.0-rc1. | |
852 | ||
853 | As yet another alternative, the linkgit:git-show-branch[1] command lists | |
854 | the commits reachable from its arguments with a display on the left-hand | |
855 | side that indicates which arguments that commit is reachable from. So, | |
856 | you can run something like | |
857 | ||
858 | ------------------------------------------------- | |
859 | $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 | |
860 | ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
861 | available | |
862 | ! [v1.5.0-rc0] GIT v1.5.0 preview | |
863 | ! [v1.5.0-rc1] GIT v1.5.0-rc1 | |
864 | ! [v1.5.0-rc2] GIT v1.5.0-rc2 | |
865 | ... | |
866 | ------------------------------------------------- | |
867 | ||
868 | then search for a line that looks like | |
869 | ||
870 | ------------------------------------------------- | |
871 | + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
872 | available | |
873 | ------------------------------------------------- | |
874 | ||
875 | Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and | |
876 | from v1.5.0-rc2, but not from v1.5.0-rc0. | |
877 | ||
878 | [[showing-commits-unique-to-a-branch]] | |
879 | Showing commits unique to a given branch | |
880 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
881 | ||
882 | Suppose you would like to see all the commits reachable from the branch | |
883 | head named "master" but not from any other head in your repository. | |
884 | ||
885 | We can list all the heads in this repository with | |
886 | linkgit:git-show-ref[1]: | |
887 | ||
888 | ------------------------------------------------- | |
889 | $ git show-ref --heads | |
890 | bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial | |
891 | db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint | |
892 | a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master | |
893 | 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2 | |
894 | 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes | |
895 | ------------------------------------------------- | |
896 | ||
897 | We can get just the branch-head names, and remove "master", with | |
898 | the help of the standard utilities cut and grep: | |
899 | ||
900 | ------------------------------------------------- | |
901 | $ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master' | |
902 | refs/heads/core-tutorial | |
903 | refs/heads/maint | |
904 | refs/heads/tutorial-2 | |
905 | refs/heads/tutorial-fixes | |
906 | ------------------------------------------------- | |
907 | ||
908 | And then we can ask to see all the commits reachable from master | |
909 | but not from these other heads: | |
910 | ||
911 | ------------------------------------------------- | |
912 | $ gitk master --not $( git show-ref --heads | cut -d' ' -f2 | | |
913 | grep -v '^refs/heads/master' ) | |
914 | ------------------------------------------------- | |
915 | ||
916 | Obviously, endless variations are possible; for example, to see all | |
917 | commits reachable from some head but not from any tag in the repository: | |
918 | ||
919 | ------------------------------------------------- | |
920 | $ gitk $( git show-ref --heads ) --not $( git show-ref --tags ) | |
921 | ------------------------------------------------- | |
922 | ||
923 | (See linkgit:gitrevisions[7] for explanations of commit-selecting | |
924 | syntax such as `--not`.) | |
925 | ||
926 | [[making-a-release]] | |
927 | Creating a changelog and tarball for a software release | |
928 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
929 | ||
930 | The linkgit:git-archive[1] command can create a tar or zip archive from | |
931 | any version of a project; for example: | |
932 | ||
933 | ------------------------------------------------- | |
934 | $ git archive -o latest.tar.gz --prefix=project/ HEAD | |
935 | ------------------------------------------------- | |
936 | ||
937 | will use HEAD to produce a gzipped tar archive in which each filename | |
938 | is preceded by `project/`. The output file format is inferred from | |
939 | the output file extension if possible, see linkgit:git-archive[1] for | |
940 | details. | |
941 | ||
942 | Versions of Git older than 1.7.7 don't know about the 'tar.gz' format, | |
943 | you'll need to use gzip explicitly: | |
944 | ||
945 | ------------------------------------------------- | |
946 | $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz | |
947 | ------------------------------------------------- | |
948 | ||
949 | If you're releasing a new version of a software project, you may want | |
950 | to simultaneously make a changelog to include in the release | |
951 | announcement. | |
952 | ||
953 | Linus Torvalds, for example, makes new kernel releases by tagging them, | |
954 | then running: | |
955 | ||
956 | ------------------------------------------------- | |
957 | $ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7 | |
958 | ------------------------------------------------- | |
959 | ||
960 | where release-script is a shell script that looks like: | |
961 | ||
962 | ------------------------------------------------- | |
963 | #!/bin/sh | |
964 | stable="$1" | |
965 | last="$2" | |
966 | new="$3" | |
967 | echo "# git tag v$new" | |
968 | echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz" | |
969 | echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz" | |
970 | echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new" | |
971 | echo "git shortlog --no-merges v$new ^v$last > ../ShortLog" | |
972 | echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new" | |
973 | ------------------------------------------------- | |
974 | ||
975 | and then he just cut-and-pastes the output commands after verifying that | |
976 | they look OK. | |
977 | ||
978 | [[Finding-commits-With-given-Content]] | |
979 | Finding commits referencing a file with given content | |
980 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
981 | ||
982 | Somebody hands you a copy of a file, and asks which commits modified a | |
983 | file such that it contained the given content either before or after the | |
984 | commit. You can find out with this: | |
985 | ||
986 | ------------------------------------------------- | |
987 | $ git log --raw --abbrev=40 --pretty=oneline | | |
988 | grep -B 1 `git hash-object filename` | |
989 | ------------------------------------------------- | |
990 | ||
991 | Figuring out why this works is left as an exercise to the (advanced) | |
992 | student. The linkgit:git-log[1], linkgit:git-diff-tree[1], and | |
993 | linkgit:git-hash-object[1] man pages may prove helpful. | |
994 | ||
995 | [[Developing-With-git]] | |
996 | Developing with git | |
997 | =================== | |
998 | ||
999 | [[telling-git-your-name]] | |
1000 | Telling git your name | |
1001 | --------------------- | |
1002 | ||
1003 | Before creating any commits, you should introduce yourself to Git. | |
1004 | The easiest way to do so is to use linkgit:git-config[1]: | |
1005 | ||
1006 | ------------------------------------------------ | |
1007 | $ git config --global user.name 'Your Name Comes Here' | |
1008 | $ git config --global user.email 'you@yourdomain.example.com' | |
1009 | ------------------------------------------------ | |
1010 | ||
1011 | Which will add the following to a file named `.gitconfig` in your | |
1012 | home directory: | |
1013 | ||
1014 | ------------------------------------------------ | |
1015 | [user] | |
1016 | name = Your Name Comes Here | |
1017 | email = you@yourdomain.example.com | |
1018 | ------------------------------------------------ | |
1019 | ||
1020 | See the "CONFIGURATION FILE" section of linkgit:git-config[1] for | |
1021 | details on the configuration file. The file is plain text, so you can | |
1022 | also edit it with your favorite editor. | |
1023 | ||
1024 | ||
1025 | [[creating-a-new-repository]] | |
1026 | Creating a new repository | |
1027 | ------------------------- | |
1028 | ||
1029 | Creating a new repository from scratch is very easy: | |
1030 | ||
1031 | ------------------------------------------------- | |
1032 | $ mkdir project | |
1033 | $ cd project | |
1034 | $ git init | |
1035 | ------------------------------------------------- | |
1036 | ||
1037 | If you have some initial content (say, a tarball): | |
1038 | ||
1039 | ------------------------------------------------- | |
1040 | $ tar xzvf project.tar.gz | |
1041 | $ cd project | |
1042 | $ git init | |
1043 | $ git add . # include everything below ./ in the first commit: | |
1044 | $ git commit | |
1045 | ------------------------------------------------- | |
1046 | ||
1047 | [[how-to-make-a-commit]] | |
1048 | How to make a commit | |
1049 | -------------------- | |
1050 | ||
1051 | Creating a new commit takes three steps: | |
1052 | ||
1053 | 1. Making some changes to the working directory using your | |
1054 | favorite editor. | |
1055 | 2. Telling git about your changes. | |
1056 | 3. Creating the commit using the content you told git about | |
1057 | in step 2. | |
1058 | ||
1059 | In practice, you can interleave and repeat steps 1 and 2 as many | |
1060 | times as you want: in order to keep track of what you want committed | |
1061 | at step 3, git maintains a snapshot of the tree's contents in a | |
1062 | special staging area called "the index." | |
1063 | ||
1064 | At the beginning, the content of the index will be identical to | |
1065 | that of the HEAD. The command "git diff --cached", which shows | |
1066 | the difference between the HEAD and the index, should therefore | |
1067 | produce no output at that point. | |
1068 | ||
1069 | Modifying the index is easy: | |
1070 | ||
1071 | To update the index with the new contents of a modified file, use | |
1072 | ||
1073 | ------------------------------------------------- | |
1074 | $ git add path/to/file | |
1075 | ------------------------------------------------- | |
1076 | ||
1077 | To add the contents of a new file to the index, use | |
1078 | ||
1079 | ------------------------------------------------- | |
1080 | $ git add path/to/file | |
1081 | ------------------------------------------------- | |
1082 | ||
1083 | To remove a file from the index and from the working tree, | |
1084 | ||
1085 | ------------------------------------------------- | |
1086 | $ git rm path/to/file | |
1087 | ------------------------------------------------- | |
1088 | ||
1089 | After each step you can verify that | |
1090 | ||
1091 | ------------------------------------------------- | |
1092 | $ git diff --cached | |
1093 | ------------------------------------------------- | |
1094 | ||
1095 | always shows the difference between the HEAD and the index file--this | |
1096 | is what you'd commit if you created the commit now--and that | |
1097 | ||
1098 | ------------------------------------------------- | |
1099 | $ git diff | |
1100 | ------------------------------------------------- | |
1101 | ||
1102 | shows the difference between the working tree and the index file. | |
1103 | ||
1104 | Note that "git add" always adds just the current contents of a file | |
1105 | to the index; further changes to the same file will be ignored unless | |
1106 | you run `git add` on the file again. | |
1107 | ||
1108 | When you're ready, just run | |
1109 | ||
1110 | ------------------------------------------------- | |
1111 | $ git commit | |
1112 | ------------------------------------------------- | |
1113 | ||
1114 | and git will prompt you for a commit message and then create the new | |
1115 | commit. Check to make sure it looks like what you expected with | |
1116 | ||
1117 | ------------------------------------------------- | |
1118 | $ git show | |
1119 | ------------------------------------------------- | |
1120 | ||
1121 | As a special shortcut, | |
1122 | ||
1123 | ------------------------------------------------- | |
1124 | $ git commit -a | |
1125 | ------------------------------------------------- | |
1126 | ||
1127 | will update the index with any files that you've modified or removed | |
1128 | and create a commit, all in one step. | |
1129 | ||
1130 | A number of commands are useful for keeping track of what you're | |
1131 | about to commit: | |
1132 | ||
1133 | ------------------------------------------------- | |
1134 | $ git diff --cached # difference between HEAD and the index; what | |
1135 | # would be committed if you ran "commit" now. | |
1136 | $ git diff # difference between the index file and your | |
1137 | # working directory; changes that would not | |
1138 | # be included if you ran "commit" now. | |
1139 | $ git diff HEAD # difference between HEAD and working tree; what | |
1140 | # would be committed if you ran "commit -a" now. | |
1141 | $ git status # a brief per-file summary of the above. | |
1142 | ------------------------------------------------- | |
1143 | ||
1144 | You can also use linkgit:git-gui[1] to create commits, view changes in | |
1145 | the index and the working tree files, and individually select diff hunks | |
1146 | for inclusion in the index (by right-clicking on the diff hunk and | |
1147 | choosing "Stage Hunk For Commit"). | |
1148 | ||
1149 | [[creating-good-commit-messages]] | |
1150 | Creating good commit messages | |
1151 | ----------------------------- | |
1152 | ||
1153 | Though not required, it's a good idea to begin the commit message | |
1154 | with a single short (less than 50 character) line summarizing the | |
1155 | change, followed by a blank line and then a more thorough | |
1156 | description. The text up to the first blank line in a commit | |
1157 | message is treated as the commit title, and that title is used | |
1158 | throughout git. For example, linkgit:git-format-patch[1] turns a | |
1159 | commit into email, and it uses the title on the Subject line and the | |
1160 | rest of the commit in the body. | |
1161 | ||
1162 | ||
1163 | [[ignoring-files]] | |
1164 | Ignoring files | |
1165 | -------------- | |
1166 | ||
1167 | A project will often generate files that you do 'not' want to track with git. | |
1168 | This typically includes files generated by a build process or temporary | |
1169 | backup files made by your editor. Of course, 'not' tracking files with git | |
1170 | is just a matter of 'not' calling `git add` on them. But it quickly becomes | |
1171 | annoying to have these untracked files lying around; e.g. they make | |
1172 | `git add .` practically useless, and they keep showing up in the output of | |
1173 | `git status`. | |
1174 | ||
1175 | You can tell git to ignore certain files by creating a file called .gitignore | |
1176 | in the top level of your working directory, with contents such as: | |
1177 | ||
1178 | ------------------------------------------------- | |
1179 | # Lines starting with '#' are considered comments. | |
1180 | # Ignore any file named foo.txt. | |
1181 | foo.txt | |
1182 | # Ignore (generated) html files, | |
1183 | *.html | |
1184 | # except foo.html which is maintained by hand. | |
1185 | !foo.html | |
1186 | # Ignore objects and archives. | |
1187 | *.[oa] | |
1188 | ------------------------------------------------- | |
1189 | ||
1190 | See linkgit:gitignore[5] for a detailed explanation of the syntax. You can | |
1191 | also place .gitignore files in other directories in your working tree, and they | |
1192 | will apply to those directories and their subdirectories. The `.gitignore` | |
1193 | files can be added to your repository like any other files (just run `git add | |
1194 | .gitignore` and `git commit`, as usual), which is convenient when the exclude | |
1195 | patterns (such as patterns matching build output files) would also make sense | |
1196 | for other users who clone your repository. | |
1197 | ||
1198 | If you wish the exclude patterns to affect only certain repositories | |
1199 | (instead of every repository for a given project), you may instead put | |
1200 | them in a file in your repository named .git/info/exclude, or in any file | |
1201 | specified by the `core.excludesfile` configuration variable. Some git | |
1202 | commands can also take exclude patterns directly on the command line. | |
1203 | See linkgit:gitignore[5] for the details. | |
1204 | ||
1205 | [[how-to-merge]] | |
1206 | How to merge | |
1207 | ------------ | |
1208 | ||
1209 | You can rejoin two diverging branches of development using | |
1210 | linkgit:git-merge[1]: | |
1211 | ||
1212 | ------------------------------------------------- | |
1213 | $ git merge branchname | |
1214 | ------------------------------------------------- | |
1215 | ||
1216 | merges the development in the branch "branchname" into the current | |
1217 | branch. | |
1218 | ||
1219 | A merge is made by combining the changes made in "branchname" and the | |
1220 | changes made up to the latest commit in your current branch since | |
1221 | their histories forked. The work tree is overwritten by the result of | |
1222 | the merge when this combining is done cleanly, or overwritten by a | |
1223 | half-merged results when this combining results in conflicts. | |
1224 | Therefore, if you have uncommitted changes touching the same files as | |
1225 | the ones impacted by the merge, Git will refuse to proceed. Most of | |
1226 | the time, you will want to commit your changes before you can merge, | |
1227 | and if you don't, then linkgit:git-stash[1] can take these changes | |
1228 | away while you're doing the merge, and reapply them afterwards. | |
1229 | ||
1230 | If the changes are independent enough, Git will automatically complete | |
1231 | the merge and commit the result (or reuse an existing commit in case | |
1232 | of <<fast-forwards,fast-forward>>, see below). On the other hand, | |
1233 | if there are conflicts--for example, if the same file is | |
1234 | modified in two different ways in the remote branch and the local | |
1235 | branch--then you are warned; the output may look something like this: | |
1236 | ||
1237 | ------------------------------------------------- | |
1238 | $ git merge next | |
1239 | 100% (4/4) done | |
1240 | Auto-merged file.txt | |
1241 | CONFLICT (content): Merge conflict in file.txt | |
1242 | Automatic merge failed; fix conflicts and then commit the result. | |
1243 | ------------------------------------------------- | |
1244 | ||
1245 | Conflict markers are left in the problematic files, and after | |
1246 | you resolve the conflicts manually, you can update the index | |
1247 | with the contents and run git commit, as you normally would when | |
1248 | creating a new file. | |
1249 | ||
1250 | If you examine the resulting commit using gitk, you will see that it | |
1251 | has two parents, one pointing to the top of the current branch, and | |
1252 | one to the top of the other branch. | |
1253 | ||
1254 | [[resolving-a-merge]] | |
1255 | Resolving a merge | |
1256 | ----------------- | |
1257 | ||
1258 | When a merge isn't resolved automatically, git leaves the index and | |
1259 | the working tree in a special state that gives you all the | |
1260 | information you need to help resolve the merge. | |
1261 | ||
1262 | Files with conflicts are marked specially in the index, so until you | |
1263 | resolve the problem and update the index, linkgit:git-commit[1] will | |
1264 | fail: | |
1265 | ||
1266 | ------------------------------------------------- | |
1267 | $ git commit | |
1268 | file.txt: needs merge | |
1269 | ------------------------------------------------- | |
1270 | ||
1271 | Also, linkgit:git-status[1] will list those files as "unmerged", and the | |
1272 | files with conflicts will have conflict markers added, like this: | |
1273 | ||
1274 | ------------------------------------------------- | |
1275 | <<<<<<< HEAD:file.txt | |
1276 | Hello world | |
1277 | ======= | |
1278 | Goodbye | |
1279 | >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt | |
1280 | ------------------------------------------------- | |
1281 | ||
1282 | All you need to do is edit the files to resolve the conflicts, and then | |
1283 | ||
1284 | ------------------------------------------------- | |
1285 | $ git add file.txt | |
1286 | $ git commit | |
1287 | ------------------------------------------------- | |
1288 | ||
1289 | Note that the commit message will already be filled in for you with | |
1290 | some information about the merge. Normally you can just use this | |
1291 | default message unchanged, but you may add additional commentary of | |
1292 | your own if desired. | |
1293 | ||
1294 | The above is all you need to know to resolve a simple merge. But git | |
1295 | also provides more information to help resolve conflicts: | |
1296 | ||
1297 | [[conflict-resolution]] | |
1298 | Getting conflict-resolution help during a merge | |
1299 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1300 | ||
1301 | All of the changes that git was able to merge automatically are | |
1302 | already added to the index file, so linkgit:git-diff[1] shows only | |
1303 | the conflicts. It uses an unusual syntax: | |
1304 | ||
1305 | ------------------------------------------------- | |
1306 | $ git diff | |
1307 | diff --cc file.txt | |
1308 | index 802992c,2b60207..0000000 | |
1309 | --- a/file.txt | |
1310 | +++ b/file.txt | |
1311 | @@@ -1,1 -1,1 +1,5 @@@ | |
1312 | ++<<<<<<< HEAD:file.txt | |
1313 | +Hello world | |
1314 | ++======= | |
1315 | + Goodbye | |
1316 | ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt | |
1317 | ------------------------------------------------- | |
1318 | ||
1319 | Recall that the commit which will be committed after we resolve this | |
1320 | conflict will have two parents instead of the usual one: one parent | |
1321 | will be HEAD, the tip of the current branch; the other will be the | |
1322 | tip of the other branch, which is stored temporarily in MERGE_HEAD. | |
1323 | ||
1324 | During the merge, the index holds three versions of each file. Each of | |
1325 | these three "file stages" represents a different version of the file: | |
1326 | ||
1327 | ------------------------------------------------- | |
1328 | $ git show :1:file.txt # the file in a common ancestor of both branches | |
1329 | $ git show :2:file.txt # the version from HEAD. | |
1330 | $ git show :3:file.txt # the version from MERGE_HEAD. | |
1331 | ------------------------------------------------- | |
1332 | ||
1333 | When you ask linkgit:git-diff[1] to show the conflicts, it runs a | |
1334 | three-way diff between the conflicted merge results in the work tree with | |
1335 | stages 2 and 3 to show only hunks whose contents come from both sides, | |
1336 | mixed (in other words, when a hunk's merge results come only from stage 2, | |
1337 | that part is not conflicting and is not shown. Same for stage 3). | |
1338 | ||
1339 | The diff above shows the differences between the working-tree version of | |
1340 | file.txt and the stage 2 and stage 3 versions. So instead of preceding | |
1341 | each line by a single "+" or "-", it now uses two columns: the first | |
1342 | column is used for differences between the first parent and the working | |
1343 | directory copy, and the second for differences between the second parent | |
1344 | and the working directory copy. (See the "COMBINED DIFF FORMAT" section | |
1345 | of linkgit:git-diff-files[1] for a details of the format.) | |
1346 | ||
1347 | After resolving the conflict in the obvious way (but before updating the | |
1348 | index), the diff will look like: | |
1349 | ||
1350 | ------------------------------------------------- | |
1351 | $ git diff | |
1352 | diff --cc file.txt | |
1353 | index 802992c,2b60207..0000000 | |
1354 | --- a/file.txt | |
1355 | +++ b/file.txt | |
1356 | @@@ -1,1 -1,1 +1,1 @@@ | |
1357 | - Hello world | |
1358 | -Goodbye | |
1359 | ++Goodbye world | |
1360 | ------------------------------------------------- | |
1361 | ||
1362 | This shows that our resolved version deleted "Hello world" from the | |
1363 | first parent, deleted "Goodbye" from the second parent, and added | |
1364 | "Goodbye world", which was previously absent from both. | |
1365 | ||
1366 | Some special diff options allow diffing the working directory against | |
1367 | any of these stages: | |
1368 | ||
1369 | ------------------------------------------------- | |
1370 | $ git diff -1 file.txt # diff against stage 1 | |
1371 | $ git diff --base file.txt # same as the above | |
1372 | $ git diff -2 file.txt # diff against stage 2 | |
1373 | $ git diff --ours file.txt # same as the above | |
1374 | $ git diff -3 file.txt # diff against stage 3 | |
1375 | $ git diff --theirs file.txt # same as the above. | |
1376 | ------------------------------------------------- | |
1377 | ||
1378 | The linkgit:git-log[1] and linkgit:gitk[1] commands also provide special help | |
1379 | for merges: | |
1380 | ||
1381 | ------------------------------------------------- | |
1382 | $ git log --merge | |
1383 | $ gitk --merge | |
1384 | ------------------------------------------------- | |
1385 | ||
1386 | These will display all commits which exist only on HEAD or on | |
1387 | MERGE_HEAD, and which touch an unmerged file. | |
1388 | ||
1389 | You may also use linkgit:git-mergetool[1], which lets you merge the | |
1390 | unmerged files using external tools such as Emacs or kdiff3. | |
1391 | ||
1392 | Each time you resolve the conflicts in a file and update the index: | |
1393 | ||
1394 | ------------------------------------------------- | |
1395 | $ git add file.txt | |
1396 | ------------------------------------------------- | |
1397 | ||
1398 | the different stages of that file will be "collapsed", after which | |
1399 | `git diff` will (by default) no longer show diffs for that file. | |
1400 | ||
1401 | [[undoing-a-merge]] | |
1402 | Undoing a merge | |
1403 | --------------- | |
1404 | ||
1405 | If you get stuck and decide to just give up and throw the whole mess | |
1406 | away, you can always return to the pre-merge state with | |
1407 | ||
1408 | ------------------------------------------------- | |
1409 | $ git reset --hard HEAD | |
1410 | ------------------------------------------------- | |
1411 | ||
1412 | Or, if you've already committed the merge that you want to throw away, | |
1413 | ||
1414 | ------------------------------------------------- | |
1415 | $ git reset --hard ORIG_HEAD | |
1416 | ------------------------------------------------- | |
1417 | ||
1418 | However, this last command can be dangerous in some cases--never | |
1419 | throw away a commit you have already committed if that commit may | |
1420 | itself have been merged into another branch, as doing so may confuse | |
1421 | further merges. | |
1422 | ||
1423 | [[fast-forwards]] | |
1424 | Fast-forward merges | |
1425 | ------------------- | |
1426 | ||
1427 | There is one special case not mentioned above, which is treated | |
1428 | differently. Normally, a merge results in a merge commit, with two | |
1429 | parents, one pointing at each of the two lines of development that | |
1430 | were merged. | |
1431 | ||
1432 | However, if the current branch is a descendant of the other--so every | |
1433 | commit present in the one is already contained in the other--then git | |
1434 | just performs a "fast-forward"; the head of the current branch is moved | |
1435 | forward to point at the head of the merged-in branch, without any new | |
1436 | commits being created. | |
1437 | ||
1438 | [[fixing-mistakes]] | |
1439 | Fixing mistakes | |
1440 | --------------- | |
1441 | ||
1442 | If you've messed up the working tree, but haven't yet committed your | |
1443 | mistake, you can return the entire working tree to the last committed | |
1444 | state with | |
1445 | ||
1446 | ------------------------------------------------- | |
1447 | $ git reset --hard HEAD | |
1448 | ------------------------------------------------- | |
1449 | ||
1450 | If you make a commit that you later wish you hadn't, there are two | |
1451 | fundamentally different ways to fix the problem: | |
1452 | ||
1453 | 1. You can create a new commit that undoes whatever was done | |
1454 | by the old commit. This is the correct thing if your | |
1455 | mistake has already been made public. | |
1456 | ||
1457 | 2. You can go back and modify the old commit. You should | |
1458 | never do this if you have already made the history public; | |
1459 | git does not normally expect the "history" of a project to | |
1460 | change, and cannot correctly perform repeated merges from | |
1461 | a branch that has had its history changed. | |
1462 | ||
1463 | [[reverting-a-commit]] | |
1464 | Fixing a mistake with a new commit | |
1465 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1466 | ||
1467 | Creating a new commit that reverts an earlier change is very easy; | |
1468 | just pass the linkgit:git-revert[1] command a reference to the bad | |
1469 | commit; for example, to revert the most recent commit: | |
1470 | ||
1471 | ------------------------------------------------- | |
1472 | $ git revert HEAD | |
1473 | ------------------------------------------------- | |
1474 | ||
1475 | This will create a new commit which undoes the change in HEAD. You | |
1476 | will be given a chance to edit the commit message for the new commit. | |
1477 | ||
1478 | You can also revert an earlier change, for example, the next-to-last: | |
1479 | ||
1480 | ------------------------------------------------- | |
1481 | $ git revert HEAD^ | |
1482 | ------------------------------------------------- | |
1483 | ||
1484 | In this case git will attempt to undo the old change while leaving | |
1485 | intact any changes made since then. If more recent changes overlap | |
1486 | with the changes to be reverted, then you will be asked to fix | |
1487 | conflicts manually, just as in the case of <<resolving-a-merge, | |
1488 | resolving a merge>>. | |
1489 | ||
1490 | [[fixing-a-mistake-by-rewriting-history]] | |
1491 | Fixing a mistake by rewriting history | |
1492 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1493 | ||
1494 | If the problematic commit is the most recent commit, and you have not | |
1495 | yet made that commit public, then you may just | |
1496 | <<undoing-a-merge,destroy it using `git reset`>>. | |
1497 | ||
1498 | Alternatively, you | |
1499 | can edit the working directory and update the index to fix your | |
1500 | mistake, just as if you were going to <<how-to-make-a-commit,create a | |
1501 | new commit>>, then run | |
1502 | ||
1503 | ------------------------------------------------- | |
1504 | $ git commit --amend | |
1505 | ------------------------------------------------- | |
1506 | ||
1507 | which will replace the old commit by a new commit incorporating your | |
1508 | changes, giving you a chance to edit the old commit message first. | |
1509 | ||
1510 | Again, you should never do this to a commit that may already have | |
1511 | been merged into another branch; use linkgit:git-revert[1] instead in | |
1512 | that case. | |
1513 | ||
1514 | It is also possible to replace commits further back in the history, but | |
1515 | this is an advanced topic to be left for | |
1516 | <<cleaning-up-history,another chapter>>. | |
1517 | ||
1518 | [[checkout-of-path]] | |
1519 | Checking out an old version of a file | |
1520 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1521 | ||
1522 | In the process of undoing a previous bad change, you may find it | |
1523 | useful to check out an older version of a particular file using | |
1524 | linkgit:git-checkout[1]. We've used `git checkout` before to switch | |
1525 | branches, but it has quite different behavior if it is given a path | |
1526 | name: the command | |
1527 | ||
1528 | ------------------------------------------------- | |
1529 | $ git checkout HEAD^ path/to/file | |
1530 | ------------------------------------------------- | |
1531 | ||
1532 | replaces path/to/file by the contents it had in the commit HEAD^, and | |
1533 | also updates the index to match. It does not change branches. | |
1534 | ||
1535 | If you just want to look at an old version of the file, without | |
1536 | modifying the working directory, you can do that with | |
1537 | linkgit:git-show[1]: | |
1538 | ||
1539 | ------------------------------------------------- | |
1540 | $ git show HEAD^:path/to/file | |
1541 | ------------------------------------------------- | |
1542 | ||
1543 | which will display the given version of the file. | |
1544 | ||
1545 | [[interrupted-work]] | |
1546 | Temporarily setting aside work in progress | |
1547 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1548 | ||
1549 | While you are in the middle of working on something complicated, you | |
1550 | find an unrelated but obvious and trivial bug. You would like to fix it | |
1551 | before continuing. You can use linkgit:git-stash[1] to save the current | |
1552 | state of your work, and after fixing the bug (or, optionally after doing | |
1553 | so on a different branch and then coming back), unstash the | |
1554 | work-in-progress changes. | |
1555 | ||
1556 | ------------------------------------------------ | |
1557 | $ git stash save "work in progress for foo feature" | |
1558 | ------------------------------------------------ | |
1559 | ||
1560 | This command will save your changes away to the `stash`, and | |
1561 | reset your working tree and the index to match the tip of your | |
1562 | current branch. Then you can make your fix as usual. | |
1563 | ||
1564 | ------------------------------------------------ | |
1565 | ... edit and test ... | |
1566 | $ git commit -a -m "blorpl: typofix" | |
1567 | ------------------------------------------------ | |
1568 | ||
1569 | After that, you can go back to what you were working on with | |
1570 | `git stash pop`: | |
1571 | ||
1572 | ------------------------------------------------ | |
1573 | $ git stash pop | |
1574 | ------------------------------------------------ | |
1575 | ||
1576 | ||
1577 | [[ensuring-good-performance]] | |
1578 | Ensuring good performance | |
1579 | ------------------------- | |
1580 | ||
1581 | On large repositories, Git depends on compression to keep the history | |
1582 | information from taking up too much space on disk or in memory. Some | |
1583 | git commands may automatically run linkgit:git-gc[1], so you don't | |
1584 | have to worry about running it manually. However, compressing a large | |
1585 | repository may take a while, so you may want to call `gc` explicitly | |
1586 | to avoid automatic compression kicking in when it is not convenient. | |
1587 | ||
1588 | ||
1589 | [[ensuring-reliability]] | |
1590 | Ensuring reliability | |
1591 | -------------------- | |
1592 | ||
1593 | [[checking-for-corruption]] | |
1594 | Checking the repository for corruption | |
1595 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1596 | ||
1597 | The linkgit:git-fsck[1] command runs a number of self-consistency checks | |
1598 | on the repository, and reports on any problems. This may take some | |
1599 | time. | |
1600 | ||
1601 | ------------------------------------------------- | |
1602 | $ git fsck | |
1603 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 | |
1604 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1605 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1606 | dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb | |
1607 | dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f | |
1608 | dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e | |
1609 | dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 | |
1610 | dangling tree b24c2473f1fd3d91352a624795be026d64c8841f | |
1611 | ... | |
1612 | ------------------------------------------------- | |
1613 | ||
1614 | You will see informational messages on dangling objects. They are objects | |
1615 | that still exist in the repository but are no longer referenced by any of | |
1616 | your branches, and can (and will) be removed after a while with "gc". | |
1617 | You can run `git fsck --no-dangling` to suppress these messages, and still | |
1618 | view real errors. | |
1619 | ||
1620 | [[recovering-lost-changes]] | |
1621 | Recovering lost changes | |
1622 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
1623 | ||
1624 | [[reflogs]] | |
1625 | Reflogs | |
1626 | ^^^^^^^ | |
1627 | ||
1628 | Say you modify a branch with +linkgit:git-reset[1] \--hard+, and then | |
1629 | realize that the branch was the only reference you had to that point in | |
1630 | history. | |
1631 | ||
1632 | Fortunately, git also keeps a log, called a "reflog", of all the | |
1633 | previous values of each branch. So in this case you can still find the | |
1634 | old history using, for example, | |
1635 | ||
1636 | ------------------------------------------------- | |
1637 | $ git log master@{1} | |
1638 | ------------------------------------------------- | |
1639 | ||
1640 | This lists the commits reachable from the previous version of the | |
1641 | "master" branch head. This syntax can be used with any git command | |
1642 | that accepts a commit, not just with git log. Some other examples: | |
1643 | ||
1644 | ------------------------------------------------- | |
1645 | $ git show master@{2} # See where the branch pointed 2, | |
1646 | $ git show master@{3} # 3, ... changes ago. | |
1647 | $ gitk master@{yesterday} # See where it pointed yesterday, | |
1648 | $ gitk master@{"1 week ago"} # ... or last week | |
1649 | $ git log --walk-reflogs master # show reflog entries for master | |
1650 | ------------------------------------------------- | |
1651 | ||
1652 | A separate reflog is kept for the HEAD, so | |
1653 | ||
1654 | ------------------------------------------------- | |
1655 | $ git show HEAD@{"1 week ago"} | |
1656 | ------------------------------------------------- | |
1657 | ||
1658 | will show what HEAD pointed to one week ago, not what the current branch | |
1659 | pointed to one week ago. This allows you to see the history of what | |
1660 | you've checked out. | |
1661 | ||
1662 | The reflogs are kept by default for 30 days, after which they may be | |
1663 | pruned. See linkgit:git-reflog[1] and linkgit:git-gc[1] to learn | |
1664 | how to control this pruning, and see the "SPECIFYING REVISIONS" | |
1665 | section of linkgit:gitrevisions[7] for details. | |
1666 | ||
1667 | Note that the reflog history is very different from normal git history. | |
1668 | While normal history is shared by every repository that works on the | |
1669 | same project, the reflog history is not shared: it tells you only about | |
1670 | how the branches in your local repository have changed over time. | |
1671 | ||
1672 | [[dangling-object-recovery]] | |
1673 | Examining dangling objects | |
1674 | ^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
1675 | ||
1676 | In some situations the reflog may not be able to save you. For example, | |
1677 | suppose you delete a branch, then realize you need the history it | |
1678 | contained. The reflog is also deleted; however, if you have not yet | |
1679 | pruned the repository, then you may still be able to find the lost | |
1680 | commits in the dangling objects that `git fsck` reports. See | |
1681 | <<dangling-objects>> for the details. | |
1682 | ||
1683 | ------------------------------------------------- | |
1684 | $ git fsck | |
1685 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 | |
1686 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1687 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1688 | ... | |
1689 | ------------------------------------------------- | |
1690 | ||
1691 | You can examine | |
1692 | one of those dangling commits with, for example, | |
1693 | ||
1694 | ------------------------------------------------ | |
1695 | $ gitk 7281251ddd --not --all | |
1696 | ------------------------------------------------ | |
1697 | ||
1698 | which does what it sounds like: it says that you want to see the commit | |
1699 | history that is described by the dangling commit(s), but not the | |
1700 | history that is described by all your existing branches and tags. Thus | |
1701 | you get exactly the history reachable from that commit that is lost. | |
1702 | (And notice that it might not be just one commit: we only report the | |
1703 | "tip of the line" as being dangling, but there might be a whole deep | |
1704 | and complex commit history that was dropped.) | |
1705 | ||
1706 | If you decide you want the history back, you can always create a new | |
1707 | reference pointing to it, for example, a new branch: | |
1708 | ||
1709 | ------------------------------------------------ | |
1710 | $ git branch recovered-branch 7281251ddd | |
1711 | ------------------------------------------------ | |
1712 | ||
1713 | Other types of dangling objects (blobs and trees) are also possible, and | |
1714 | dangling objects can arise in other situations. | |
1715 | ||
1716 | ||
1717 | [[sharing-development]] | |
1718 | Sharing development with others | |
1719 | =============================== | |
1720 | ||
1721 | [[getting-updates-With-git-pull]] | |
1722 | Getting updates with git pull | |
1723 | ----------------------------- | |
1724 | ||
1725 | After you clone a repository and commit a few changes of your own, you | |
1726 | may wish to check the original repository for updates and merge them | |
1727 | into your own work. | |
1728 | ||
1729 | We have already seen <<Updating-a-repository-With-git-fetch,how to | |
1730 | keep remote-tracking branches up to date>> with linkgit:git-fetch[1], | |
1731 | and how to merge two branches. So you can merge in changes from the | |
1732 | original repository's master branch with: | |
1733 | ||
1734 | ------------------------------------------------- | |
1735 | $ git fetch | |
1736 | $ git merge origin/master | |
1737 | ------------------------------------------------- | |
1738 | ||
1739 | However, the linkgit:git-pull[1] command provides a way to do this in | |
1740 | one step: | |
1741 | ||
1742 | ------------------------------------------------- | |
1743 | $ git pull origin master | |
1744 | ------------------------------------------------- | |
1745 | ||
1746 | In fact, if you have "master" checked out, then this branch has been | |
1747 | configured by "git clone" to get changes from the HEAD branch of the | |
1748 | origin repository. So often you can | |
1749 | accomplish the above with just a simple | |
1750 | ||
1751 | ------------------------------------------------- | |
1752 | $ git pull | |
1753 | ------------------------------------------------- | |
1754 | ||
1755 | This command will fetch changes from the remote branches to your | |
1756 | remote-tracking branches `origin/*`, and merge the default branch into | |
1757 | the current branch. | |
1758 | ||
1759 | More generally, a branch that is created from a remote-tracking branch | |
1760 | will pull | |
1761 | by default from that branch. See the descriptions of the | |
1762 | branch.<name>.remote and branch.<name>.merge options in | |
1763 | linkgit:git-config[1], and the discussion of the `--track` option in | |
1764 | linkgit:git-checkout[1], to learn how to control these defaults. | |
1765 | ||
1766 | In addition to saving you keystrokes, "git pull" also helps you by | |
1767 | producing a default commit message documenting the branch and | |
1768 | repository that you pulled from. | |
1769 | ||
1770 | (But note that no such commit will be created in the case of a | |
1771 | <<fast-forwards,fast-forward>>; instead, your branch will just be | |
1772 | updated to point to the latest commit from the upstream branch.) | |
1773 | ||
1774 | The `git pull` command can also be given "." as the "remote" repository, | |
1775 | in which case it just merges in a branch from the current repository; so | |
1776 | the commands | |
1777 | ||
1778 | ------------------------------------------------- | |
1779 | $ git pull . branch | |
1780 | $ git merge branch | |
1781 | ------------------------------------------------- | |
1782 | ||
1783 | are roughly equivalent. The former is actually very commonly used. | |
1784 | ||
1785 | [[submitting-patches]] | |
1786 | Submitting patches to a project | |
1787 | ------------------------------- | |
1788 | ||
1789 | If you just have a few changes, the simplest way to submit them may | |
1790 | just be to send them as patches in email: | |
1791 | ||
1792 | First, use linkgit:git-format-patch[1]; for example: | |
1793 | ||
1794 | ------------------------------------------------- | |
1795 | $ git format-patch origin | |
1796 | ------------------------------------------------- | |
1797 | ||
1798 | will produce a numbered series of files in the current directory, one | |
1799 | for each patch in the current branch but not in origin/HEAD. | |
1800 | ||
1801 | `git format-patch` can include an initial "cover letter". You can insert | |
1802 | commentary on individual patches after the three dash line which | |
1803 | `format-patch` places after the commit message but before the patch | |
1804 | itself. If you use `git notes` to track your cover letter material, | |
1805 | `git format-patch --notes` will include the commit's notes in a similar | |
1806 | manner. | |
1807 | ||
1808 | You can then import these into your mail client and send them by | |
1809 | hand. However, if you have a lot to send at once, you may prefer to | |
1810 | use the linkgit:git-send-email[1] script to automate the process. | |
1811 | Consult the mailing list for your project first to determine how they | |
1812 | prefer such patches be handled. | |
1813 | ||
1814 | [[importing-patches]] | |
1815 | Importing patches to a project | |
1816 | ------------------------------ | |
1817 | ||
1818 | Git also provides a tool called linkgit:git-am[1] (am stands for | |
1819 | "apply mailbox"), for importing such an emailed series of patches. | |
1820 | Just save all of the patch-containing messages, in order, into a | |
1821 | single mailbox file, say "patches.mbox", then run | |
1822 | ||
1823 | ------------------------------------------------- | |
1824 | $ git am -3 patches.mbox | |
1825 | ------------------------------------------------- | |
1826 | ||
1827 | Git will apply each patch in order; if any conflicts are found, it | |
1828 | will stop, and you can fix the conflicts as described in | |
1829 | "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells | |
1830 | git to perform a merge; if you would prefer it just to abort and | |
1831 | leave your tree and index untouched, you may omit that option.) | |
1832 | ||
1833 | Once the index is updated with the results of the conflict | |
1834 | resolution, instead of creating a new commit, just run | |
1835 | ||
1836 | ------------------------------------------------- | |
1837 | $ git am --resolved | |
1838 | ------------------------------------------------- | |
1839 | ||
1840 | and git will create the commit for you and continue applying the | |
1841 | remaining patches from the mailbox. | |
1842 | ||
1843 | The final result will be a series of commits, one for each patch in | |
1844 | the original mailbox, with authorship and commit log message each | |
1845 | taken from the message containing each patch. | |
1846 | ||
1847 | [[public-repositories]] | |
1848 | Public git repositories | |
1849 | ----------------------- | |
1850 | ||
1851 | Another way to submit changes to a project is to tell the maintainer | |
1852 | of that project to pull the changes from your repository using | |
1853 | linkgit:git-pull[1]. In the section "<<getting-updates-With-git-pull, | |
1854 | Getting updates with `git pull`>>" we described this as a way to get | |
1855 | updates from the "main" repository, but it works just as well in the | |
1856 | other direction. | |
1857 | ||
1858 | If you and the maintainer both have accounts on the same machine, then | |
1859 | you can just pull changes from each other's repositories directly; | |
1860 | commands that accept repository URLs as arguments will also accept a | |
1861 | local directory name: | |
1862 | ||
1863 | ------------------------------------------------- | |
1864 | $ git clone /path/to/repository | |
1865 | $ git pull /path/to/other/repository | |
1866 | ------------------------------------------------- | |
1867 | ||
1868 | or an ssh URL: | |
1869 | ||
1870 | ------------------------------------------------- | |
1871 | $ git clone ssh://yourhost/~you/repository | |
1872 | ------------------------------------------------- | |
1873 | ||
1874 | For projects with few developers, or for synchronizing a few private | |
1875 | repositories, this may be all you need. | |
1876 | ||
1877 | However, the more common way to do this is to maintain a separate public | |
1878 | repository (usually on a different host) for others to pull changes | |
1879 | from. This is usually more convenient, and allows you to cleanly | |
1880 | separate private work in progress from publicly visible work. | |
1881 | ||
1882 | You will continue to do your day-to-day work in your personal | |
1883 | repository, but periodically "push" changes from your personal | |
1884 | repository into your public repository, allowing other developers to | |
1885 | pull from that repository. So the flow of changes, in a situation | |
1886 | where there is one other developer with a public repository, looks | |
1887 | like this: | |
1888 | ||
1889 | you push | |
1890 | your personal repo ------------------> your public repo | |
1891 | ^ | | |
1892 | | | | |
1893 | | you pull | they pull | |
1894 | | | | |
1895 | | | | |
1896 | | they push V | |
1897 | their public repo <------------------- their repo | |
1898 | ||
1899 | We explain how to do this in the following sections. | |
1900 | ||
1901 | [[setting-up-a-public-repository]] | |
1902 | Setting up a public repository | |
1903 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1904 | ||
1905 | Assume your personal repository is in the directory ~/proj. We | |
1906 | first create a new clone of the repository and tell `git daemon` that it | |
1907 | is meant to be public: | |
1908 | ||
1909 | ------------------------------------------------- | |
1910 | $ git clone --bare ~/proj proj.git | |
1911 | $ touch proj.git/git-daemon-export-ok | |
1912 | ------------------------------------------------- | |
1913 | ||
1914 | The resulting directory proj.git contains a "bare" git repository--it is | |
1915 | just the contents of the ".git" directory, without any files checked out | |
1916 | around it. | |
1917 | ||
1918 | Next, copy proj.git to the server where you plan to host the | |
1919 | public repository. You can use scp, rsync, or whatever is most | |
1920 | convenient. | |
1921 | ||
1922 | [[exporting-via-git]] | |
1923 | Exporting a git repository via the git protocol | |
1924 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1925 | ||
1926 | This is the preferred method. | |
1927 | ||
1928 | If someone else administers the server, they should tell you what | |
1929 | directory to put the repository in, and what git:// URL it will appear | |
1930 | at. You can then skip to the section | |
1931 | "<<pushing-changes-to-a-public-repository,Pushing changes to a public | |
1932 | repository>>", below. | |
1933 | ||
1934 | Otherwise, all you need to do is start linkgit:git-daemon[1]; it will | |
1935 | listen on port 9418. By default, it will allow access to any directory | |
1936 | that looks like a git directory and contains the magic file | |
1937 | git-daemon-export-ok. Passing some directory paths as `git daemon` | |
1938 | arguments will further restrict the exports to those paths. | |
1939 | ||
1940 | You can also run `git daemon` as an inetd service; see the | |
1941 | linkgit:git-daemon[1] man page for details. (See especially the | |
1942 | examples section.) | |
1943 | ||
1944 | [[exporting-via-http]] | |
1945 | Exporting a git repository via HTTP | |
1946 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1947 | ||
1948 | The git protocol gives better performance and reliability, but on a | |
1949 | host with a web server set up, HTTP exports may be simpler to set up. | |
1950 | ||
1951 | All you need to do is place the newly created bare git repository in | |
1952 | a directory that is exported by the web server, and make some | |
1953 | adjustments to give web clients some extra information they need: | |
1954 | ||
1955 | ------------------------------------------------- | |
1956 | $ mv proj.git /home/you/public_html/proj.git | |
1957 | $ cd proj.git | |
1958 | $ git --bare update-server-info | |
1959 | $ mv hooks/post-update.sample hooks/post-update | |
1960 | ------------------------------------------------- | |
1961 | ||
1962 | (For an explanation of the last two lines, see | |
1963 | linkgit:git-update-server-info[1] and linkgit:githooks[5].) | |
1964 | ||
1965 | Advertise the URL of proj.git. Anybody else should then be able to | |
1966 | clone or pull from that URL, for example with a command line like: | |
1967 | ||
1968 | ------------------------------------------------- | |
1969 | $ git clone http://yourserver.com/~you/proj.git | |
1970 | ------------------------------------------------- | |
1971 | ||
1972 | (See also | |
1973 | link:howto/setup-git-server-over-http.txt[setup-git-server-over-http] | |
1974 | for a slightly more sophisticated setup using WebDAV which also | |
1975 | allows pushing over HTTP.) | |
1976 | ||
1977 | [[pushing-changes-to-a-public-repository]] | |
1978 | Pushing changes to a public repository | |
1979 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1980 | ||
1981 | Note that the two techniques outlined above (exporting via | |
1982 | <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other | |
1983 | maintainers to fetch your latest changes, but they do not allow write | |
1984 | access, which you will need to update the public repository with the | |
1985 | latest changes created in your private repository. | |
1986 | ||
1987 | The simplest way to do this is using linkgit:git-push[1] and ssh; to | |
1988 | update the remote branch named "master" with the latest state of your | |
1989 | branch named "master", run | |
1990 | ||
1991 | ------------------------------------------------- | |
1992 | $ git push ssh://yourserver.com/~you/proj.git master:master | |
1993 | ------------------------------------------------- | |
1994 | ||
1995 | or just | |
1996 | ||
1997 | ------------------------------------------------- | |
1998 | $ git push ssh://yourserver.com/~you/proj.git master | |
1999 | ------------------------------------------------- | |
2000 | ||
2001 | As with `git fetch`, `git push` will complain if this does not result in a | |
2002 | <<fast-forwards,fast-forward>>; see the following section for details on | |
2003 | handling this case. | |
2004 | ||
2005 | Note that the target of a "push" is normally a | |
2006 | <<def_bare_repository,bare>> repository. You can also push to a | |
2007 | repository that has a checked-out working tree, but the working tree | |
2008 | will not be updated by the push. This may lead to unexpected results if | |
2009 | the branch you push to is the currently checked-out branch! | |
2010 | ||
2011 | As with `git fetch`, you may also set up configuration options to | |
2012 | save typing; so, for example: | |
2013 | ||
2014 | ------------------------------------------------- | |
2015 | $ git remote add public-repo ssh://yourserver.com/~you/proj.git | |
2016 | ------------------------------------------------- | |
2017 | ||
2018 | adds the following to `.git/config`: | |
2019 | ||
2020 | ------------------------------------------------- | |
2021 | [remote "public-repo"] | |
2022 | url = yourserver.com:proj.git | |
2023 | fetch = +refs/heads/*:refs/remotes/example/* | |
2024 | ------------------------------------------------- | |
2025 | ||
2026 | which lets you do the same push with just | |
2027 | ||
2028 | ------------------------------------------------- | |
2029 | $ git push public-repo master | |
2030 | ------------------------------------------------- | |
2031 | ||
2032 | See the explanations of the remote.<name>.url, branch.<name>.remote, | |
2033 | and remote.<name>.push options in linkgit:git-config[1] for | |
2034 | details. | |
2035 | ||
2036 | [[forcing-push]] | |
2037 | What to do when a push fails | |
2038 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2039 | ||
2040 | If a push would not result in a <<fast-forwards,fast-forward>> of the | |
2041 | remote branch, then it will fail with an error like: | |
2042 | ||
2043 | ------------------------------------------------- | |
2044 | error: remote 'refs/heads/master' is not an ancestor of | |
2045 | local 'refs/heads/master'. | |
2046 | Maybe you are not up-to-date and need to pull first? | |
2047 | error: failed to push to 'ssh://yourserver.com/~you/proj.git' | |
2048 | ------------------------------------------------- | |
2049 | ||
2050 | This can happen, for example, if you: | |
2051 | ||
2052 | - use `git reset --hard` to remove already-published commits, or | |
2053 | - use `git commit --amend` to replace already-published commits | |
2054 | (as in <<fixing-a-mistake-by-rewriting-history>>), or | |
2055 | - use `git rebase` to rebase any already-published commits (as | |
2056 | in <<using-git-rebase>>). | |
2057 | ||
2058 | You may force `git push` to perform the update anyway by preceding the | |
2059 | branch name with a plus sign: | |
2060 | ||
2061 | ------------------------------------------------- | |
2062 | $ git push ssh://yourserver.com/~you/proj.git +master | |
2063 | ------------------------------------------------- | |
2064 | ||
2065 | Note the addition of the `+` sign. Alternatively, you can use the | |
2066 | `-f` flag to force the remote update, as in: | |
2067 | ||
2068 | ------------------------------------------------- | |
2069 | $ git push -f ssh://yourserver.com/~you/proj.git master | |
2070 | ------------------------------------------------- | |
2071 | ||
2072 | Normally whenever a branch head in a public repository is modified, it | |
2073 | is modified to point to a descendant of the commit that it pointed to | |
2074 | before. By forcing a push in this situation, you break that convention. | |
2075 | (See <<problems-With-rewriting-history>>.) | |
2076 | ||
2077 | Nevertheless, this is a common practice for people that need a simple | |
2078 | way to publish a work-in-progress patch series, and it is an acceptable | |
2079 | compromise as long as you warn other developers that this is how you | |
2080 | intend to manage the branch. | |
2081 | ||
2082 | It's also possible for a push to fail in this way when other people have | |
2083 | the right to push to the same repository. In that case, the correct | |
2084 | solution is to retry the push after first updating your work: either by a | |
2085 | pull, or by a fetch followed by a rebase; see the | |
2086 | <<setting-up-a-shared-repository,next section>> and | |
2087 | linkgit:gitcvs-migration[7] for more. | |
2088 | ||
2089 | [[setting-up-a-shared-repository]] | |
2090 | Setting up a shared repository | |
2091 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2092 | ||
2093 | Another way to collaborate is by using a model similar to that | |
2094 | commonly used in CVS, where several developers with special rights | |
2095 | all push to and pull from a single shared repository. See | |
2096 | linkgit:gitcvs-migration[7] for instructions on how to | |
2097 | set this up. | |
2098 | ||
2099 | However, while there is nothing wrong with git's support for shared | |
2100 | repositories, this mode of operation is not generally recommended, | |
2101 | simply because the mode of collaboration that git supports--by | |
2102 | exchanging patches and pulling from public repositories--has so many | |
2103 | advantages over the central shared repository: | |
2104 | ||
2105 | - Git's ability to quickly import and merge patches allows a | |
2106 | single maintainer to process incoming changes even at very | |
2107 | high rates. And when that becomes too much, `git pull` provides | |
2108 | an easy way for that maintainer to delegate this job to other | |
2109 | maintainers while still allowing optional review of incoming | |
2110 | changes. | |
2111 | - Since every developer's repository has the same complete copy | |
2112 | of the project history, no repository is special, and it is | |
2113 | trivial for another developer to take over maintenance of a | |
2114 | project, either by mutual agreement, or because a maintainer | |
2115 | becomes unresponsive or difficult to work with. | |
2116 | - The lack of a central group of "committers" means there is | |
2117 | less need for formal decisions about who is "in" and who is | |
2118 | "out". | |
2119 | ||
2120 | [[setting-up-gitweb]] | |
2121 | Allowing web browsing of a repository | |
2122 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2123 | ||
2124 | The gitweb cgi script provides users an easy way to browse your | |
2125 | project's files and history without having to install git; see the file | |
2126 | gitweb/INSTALL in the git source tree for instructions on setting it up. | |
2127 | ||
2128 | [[sharing-development-examples]] | |
2129 | Examples | |
2130 | -------- | |
2131 | ||
2132 | [[maintaining-topic-branches]] | |
2133 | Maintaining topic branches for a Linux subsystem maintainer | |
2134 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2135 | ||
2136 | This describes how Tony Luck uses git in his role as maintainer of the | |
2137 | IA64 architecture for the Linux kernel. | |
2138 | ||
2139 | He uses two public branches: | |
2140 | ||
2141 | - A "test" tree into which patches are initially placed so that they | |
2142 | can get some exposure when integrated with other ongoing development. | |
2143 | This tree is available to Andrew for pulling into -mm whenever he | |
2144 | wants. | |
2145 | ||
2146 | - A "release" tree into which tested patches are moved for final sanity | |
2147 | checking, and as a vehicle to send them upstream to Linus (by sending | |
2148 | him a "please pull" request.) | |
2149 | ||
2150 | He also uses a set of temporary branches ("topic branches"), each | |
2151 | containing a logical grouping of patches. | |
2152 | ||
2153 | To set this up, first create your work tree by cloning Linus's public | |
2154 | tree: | |
2155 | ||
2156 | ------------------------------------------------- | |
2157 | $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work | |
2158 | $ cd work | |
2159 | ------------------------------------------------- | |
2160 | ||
2161 | Linus's tree will be stored in the remote-tracking branch named origin/master, | |
2162 | and can be updated using linkgit:git-fetch[1]; you can track other | |
2163 | public trees using linkgit:git-remote[1] to set up a "remote" and | |
2164 | linkgit:git-fetch[1] to keep them up-to-date; see | |
2165 | <<repositories-and-branches>>. | |
2166 | ||
2167 | Now create the branches in which you are going to work; these start out | |
2168 | at the current tip of origin/master branch, and should be set up (using | |
2169 | the --track option to linkgit:git-branch[1]) to merge changes in from | |
2170 | Linus by default. | |
2171 | ||
2172 | ------------------------------------------------- | |
2173 | $ git branch --track test origin/master | |
2174 | $ git branch --track release origin/master | |
2175 | ------------------------------------------------- | |
2176 | ||
2177 | These can be easily kept up to date using linkgit:git-pull[1]. | |
2178 | ||
2179 | ------------------------------------------------- | |
2180 | $ git checkout test && git pull | |
2181 | $ git checkout release && git pull | |
2182 | ------------------------------------------------- | |
2183 | ||
2184 | Important note! If you have any local changes in these branches, then | |
2185 | this merge will create a commit object in the history (with no local | |
2186 | changes git will simply do a "fast-forward" merge). Many people dislike | |
2187 | the "noise" that this creates in the Linux history, so you should avoid | |
2188 | doing this capriciously in the "release" branch, as these noisy commits | |
2189 | will become part of the permanent history when you ask Linus to pull | |
2190 | from the release branch. | |
2191 | ||
2192 | A few configuration variables (see linkgit:git-config[1]) can | |
2193 | make it easy to push both branches to your public tree. (See | |
2194 | <<setting-up-a-public-repository>>.) | |
2195 | ||
2196 | ------------------------------------------------- | |
2197 | $ cat >> .git/config <<EOF | |
2198 | [remote "mytree"] | |
2199 | url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git | |
2200 | push = release | |
2201 | push = test | |
2202 | EOF | |
2203 | ------------------------------------------------- | |
2204 | ||
2205 | Then you can push both the test and release trees using | |
2206 | linkgit:git-push[1]: | |
2207 | ||
2208 | ------------------------------------------------- | |
2209 | $ git push mytree | |
2210 | ------------------------------------------------- | |
2211 | ||
2212 | or push just one of the test and release branches using: | |
2213 | ||
2214 | ------------------------------------------------- | |
2215 | $ git push mytree test | |
2216 | ------------------------------------------------- | |
2217 | ||
2218 | or | |
2219 | ||
2220 | ------------------------------------------------- | |
2221 | $ git push mytree release | |
2222 | ------------------------------------------------- | |
2223 | ||
2224 | Now to apply some patches from the community. Think of a short | |
2225 | snappy name for a branch to hold this patch (or related group of | |
2226 | patches), and create a new branch from a recent stable tag of | |
2227 | Linus's branch. Picking a stable base for your branch will: | |
2228 | 1) help you: by avoiding inclusion of unrelated and perhaps lightly | |
2229 | tested changes | |
2230 | 2) help future bug hunters that use "git bisect" to find problems | |
2231 | ||
2232 | ------------------------------------------------- | |
2233 | $ git checkout -b speed-up-spinlocks v2.6.35 | |
2234 | ------------------------------------------------- | |
2235 | ||
2236 | Now you apply the patch(es), run some tests, and commit the change(s). If | |
2237 | the patch is a multi-part series, then you should apply each as a separate | |
2238 | commit to this branch. | |
2239 | ||
2240 | ------------------------------------------------- | |
2241 | $ ... patch ... test ... commit [ ... patch ... test ... commit ]* | |
2242 | ------------------------------------------------- | |
2243 | ||
2244 | When you are happy with the state of this change, you can pull it into the | |
2245 | "test" branch in preparation to make it public: | |
2246 | ||
2247 | ------------------------------------------------- | |
2248 | $ git checkout test && git pull . speed-up-spinlocks | |
2249 | ------------------------------------------------- | |
2250 | ||
2251 | It is unlikely that you would have any conflicts here ... but you might if you | |
2252 | spent a while on this step and had also pulled new versions from upstream. | |
2253 | ||
2254 | Some time later when enough time has passed and testing done, you can pull the | |
2255 | same branch into the "release" tree ready to go upstream. This is where you | |
2256 | see the value of keeping each patch (or patch series) in its own branch. It | |
2257 | means that the patches can be moved into the "release" tree in any order. | |
2258 | ||
2259 | ------------------------------------------------- | |
2260 | $ git checkout release && git pull . speed-up-spinlocks | |
2261 | ------------------------------------------------- | |
2262 | ||
2263 | After a while, you will have a number of branches, and despite the | |
2264 | well chosen names you picked for each of them, you may forget what | |
2265 | they are for, or what status they are in. To get a reminder of what | |
2266 | changes are in a specific branch, use: | |
2267 | ||
2268 | ------------------------------------------------- | |
2269 | $ git log linux..branchname | git shortlog | |
2270 | ------------------------------------------------- | |
2271 | ||
2272 | To see whether it has already been merged into the test or release branches, | |
2273 | use: | |
2274 | ||
2275 | ------------------------------------------------- | |
2276 | $ git log test..branchname | |
2277 | ------------------------------------------------- | |
2278 | ||
2279 | or | |
2280 | ||
2281 | ------------------------------------------------- | |
2282 | $ git log release..branchname | |
2283 | ------------------------------------------------- | |
2284 | ||
2285 | (If this branch has not yet been merged, you will see some log entries. | |
2286 | If it has been merged, then there will be no output.) | |
2287 | ||
2288 | Once a patch completes the great cycle (moving from test to release, | |
2289 | then pulled by Linus, and finally coming back into your local | |
2290 | "origin/master" branch), the branch for this change is no longer needed. | |
2291 | You detect this when the output from: | |
2292 | ||
2293 | ------------------------------------------------- | |
2294 | $ git log origin..branchname | |
2295 | ------------------------------------------------- | |
2296 | ||
2297 | is empty. At this point the branch can be deleted: | |
2298 | ||
2299 | ------------------------------------------------- | |
2300 | $ git branch -d branchname | |
2301 | ------------------------------------------------- | |
2302 | ||
2303 | Some changes are so trivial that it is not necessary to create a separate | |
2304 | branch and then merge into each of the test and release branches. For | |
2305 | these changes, just apply directly to the "release" branch, and then | |
2306 | merge that into the "test" branch. | |
2307 | ||
2308 | To create diffstat and shortlog summaries of changes to include in a "please | |
2309 | pull" request to Linus you can use: | |
2310 | ||
2311 | ------------------------------------------------- | |
2312 | $ git diff --stat origin..release | |
2313 | ------------------------------------------------- | |
2314 | ||
2315 | and | |
2316 | ||
2317 | ------------------------------------------------- | |
2318 | $ git log -p origin..release | git shortlog | |
2319 | ------------------------------------------------- | |
2320 | ||
2321 | Here are some of the scripts that simplify all this even further. | |
2322 | ||
2323 | ------------------------------------------------- | |
2324 | ==== update script ==== | |
2325 | # Update a branch in my GIT tree. If the branch to be updated | |
2326 | # is origin, then pull from kernel.org. Otherwise merge | |
2327 | # origin/master branch into test|release branch | |
2328 | ||
2329 | case "$1" in | |
2330 | test|release) | |
2331 | git checkout $1 && git pull . origin | |
2332 | ;; | |
2333 | origin) | |
2334 | before=$(git rev-parse refs/remotes/origin/master) | |
2335 | git fetch origin | |
2336 | after=$(git rev-parse refs/remotes/origin/master) | |
2337 | if [ $before != $after ] | |
2338 | then | |
2339 | git log $before..$after | git shortlog | |
2340 | fi | |
2341 | ;; | |
2342 | *) | |
2343 | echo "Usage: $0 origin|test|release" 1>&2 | |
2344 | exit 1 | |
2345 | ;; | |
2346 | esac | |
2347 | ------------------------------------------------- | |
2348 | ||
2349 | ------------------------------------------------- | |
2350 | ==== merge script ==== | |
2351 | # Merge a branch into either the test or release branch | |
2352 | ||
2353 | pname=$0 | |
2354 | ||
2355 | usage() | |
2356 | { | |
2357 | echo "Usage: $pname branch test|release" 1>&2 | |
2358 | exit 1 | |
2359 | } | |
2360 | ||
2361 | git show-ref -q --verify -- refs/heads/"$1" || { | |
2362 | echo "Can't see branch <$1>" 1>&2 | |
2363 | usage | |
2364 | } | |
2365 | ||
2366 | case "$2" in | |
2367 | test|release) | |
2368 | if [ $(git log $2..$1 | wc -c) -eq 0 ] | |
2369 | then | |
2370 | echo $1 already merged into $2 1>&2 | |
2371 | exit 1 | |
2372 | fi | |
2373 | git checkout $2 && git pull . $1 | |
2374 | ;; | |
2375 | *) | |
2376 | usage | |
2377 | ;; | |
2378 | esac | |
2379 | ------------------------------------------------- | |
2380 | ||
2381 | ------------------------------------------------- | |
2382 | ==== status script ==== | |
2383 | # report on status of my ia64 GIT tree | |
2384 | ||
2385 | gb=$(tput setab 2) | |
2386 | rb=$(tput setab 1) | |
2387 | restore=$(tput setab 9) | |
2388 | ||
2389 | if [ `git rev-list test..release | wc -c` -gt 0 ] | |
2390 | then | |
2391 | echo $rb Warning: commits in release that are not in test $restore | |
2392 | git log test..release | |
2393 | fi | |
2394 | ||
2395 | for branch in `git show-ref --heads | sed 's|^.*/||'` | |
2396 | do | |
2397 | if [ $branch = test -o $branch = release ] | |
2398 | then | |
2399 | continue | |
2400 | fi | |
2401 | ||
2402 | echo -n $gb ======= $branch ====== $restore " " | |
2403 | status= | |
2404 | for ref in test release origin/master | |
2405 | do | |
2406 | if [ `git rev-list $ref..$branch | wc -c` -gt 0 ] | |
2407 | then | |
2408 | status=$status${ref:0:1} | |
2409 | fi | |
2410 | done | |
2411 | case $status in | |
2412 | trl) | |
2413 | echo $rb Need to pull into test $restore | |
2414 | ;; | |
2415 | rl) | |
2416 | echo "In test" | |
2417 | ;; | |
2418 | l) | |
2419 | echo "Waiting for linus" | |
2420 | ;; | |
2421 | "") | |
2422 | echo $rb All done $restore | |
2423 | ;; | |
2424 | *) | |
2425 | echo $rb "<$status>" $restore | |
2426 | ;; | |
2427 | esac | |
2428 | git log origin/master..$branch | git shortlog | |
2429 | done | |
2430 | ------------------------------------------------- | |
2431 | ||
2432 | ||
2433 | [[cleaning-up-history]] | |
2434 | Rewriting history and maintaining patch series | |
2435 | ============================================== | |
2436 | ||
2437 | Normally commits are only added to a project, never taken away or | |
2438 | replaced. Git is designed with this assumption, and violating it will | |
2439 | cause git's merge machinery (for example) to do the wrong thing. | |
2440 | ||
2441 | However, there is a situation in which it can be useful to violate this | |
2442 | assumption. | |
2443 | ||
2444 | [[patch-series]] | |
2445 | Creating the perfect patch series | |
2446 | --------------------------------- | |
2447 | ||
2448 | Suppose you are a contributor to a large project, and you want to add a | |
2449 | complicated feature, and to present it to the other developers in a way | |
2450 | that makes it easy for them to read your changes, verify that they are | |
2451 | correct, and understand why you made each change. | |
2452 | ||
2453 | If you present all of your changes as a single patch (or commit), they | |
2454 | may find that it is too much to digest all at once. | |
2455 | ||
2456 | If you present them with the entire history of your work, complete with | |
2457 | mistakes, corrections, and dead ends, they may be overwhelmed. | |
2458 | ||
2459 | So the ideal is usually to produce a series of patches such that: | |
2460 | ||
2461 | 1. Each patch can be applied in order. | |
2462 | ||
2463 | 2. Each patch includes a single logical change, together with a | |
2464 | message explaining the change. | |
2465 | ||
2466 | 3. No patch introduces a regression: after applying any initial | |
2467 | part of the series, the resulting project still compiles and | |
2468 | works, and has no bugs that it didn't have before. | |
2469 | ||
2470 | 4. The complete series produces the same end result as your own | |
2471 | (probably much messier!) development process did. | |
2472 | ||
2473 | We will introduce some tools that can help you do this, explain how to | |
2474 | use them, and then explain some of the problems that can arise because | |
2475 | you are rewriting history. | |
2476 | ||
2477 | [[using-git-rebase]] | |
2478 | Keeping a patch series up to date using git rebase | |
2479 | -------------------------------------------------- | |
2480 | ||
2481 | Suppose that you create a branch "mywork" on a remote-tracking branch | |
2482 | "origin", and create some commits on top of it: | |
2483 | ||
2484 | ------------------------------------------------- | |
2485 | $ git checkout -b mywork origin | |
2486 | $ vi file.txt | |
2487 | $ git commit | |
2488 | $ vi otherfile.txt | |
2489 | $ git commit | |
2490 | ... | |
2491 | ------------------------------------------------- | |
2492 | ||
2493 | You have performed no merges into mywork, so it is just a simple linear | |
2494 | sequence of patches on top of "origin": | |
2495 | ||
2496 | ................................................ | |
2497 | o--o--O <-- origin | |
2498 | \ | |
2499 | a--b--c <-- mywork | |
2500 | ................................................ | |
2501 | ||
2502 | Some more interesting work has been done in the upstream project, and | |
2503 | "origin" has advanced: | |
2504 | ||
2505 | ................................................ | |
2506 | o--o--O--o--o--o <-- origin | |
2507 | \ | |
2508 | a--b--c <-- mywork | |
2509 | ................................................ | |
2510 | ||
2511 | At this point, you could use "pull" to merge your changes back in; | |
2512 | the result would create a new merge commit, like this: | |
2513 | ||
2514 | ................................................ | |
2515 | o--o--O--o--o--o <-- origin | |
2516 | \ \ | |
2517 | a--b--c--m <-- mywork | |
2518 | ................................................ | |
2519 | ||
2520 | However, if you prefer to keep the history in mywork a simple series of | |
2521 | commits without any merges, you may instead choose to use | |
2522 | linkgit:git-rebase[1]: | |
2523 | ||
2524 | ------------------------------------------------- | |
2525 | $ git checkout mywork | |
2526 | $ git rebase origin | |
2527 | ------------------------------------------------- | |
2528 | ||
2529 | This will remove each of your commits from mywork, temporarily saving | |
2530 | them as patches (in a directory named ".git/rebase-apply"), update mywork to | |
2531 | point at the latest version of origin, then apply each of the saved | |
2532 | patches to the new mywork. The result will look like: | |
2533 | ||
2534 | ||
2535 | ................................................ | |
2536 | o--o--O--o--o--o <-- origin | |
2537 | \ | |
2538 | a'--b'--c' <-- mywork | |
2539 | ................................................ | |
2540 | ||
2541 | In the process, it may discover conflicts. In that case it will stop | |
2542 | and allow you to fix the conflicts; after fixing conflicts, use `git add` | |
2543 | to update the index with those contents, and then, instead of | |
2544 | running `git commit`, just run | |
2545 | ||
2546 | ------------------------------------------------- | |
2547 | $ git rebase --continue | |
2548 | ------------------------------------------------- | |
2549 | ||
2550 | and git will continue applying the rest of the patches. | |
2551 | ||
2552 | At any point you may use the `--abort` option to abort this process and | |
2553 | return mywork to the state it had before you started the rebase: | |
2554 | ||
2555 | ------------------------------------------------- | |
2556 | $ git rebase --abort | |
2557 | ------------------------------------------------- | |
2558 | ||
2559 | If you need to reorder or edit a number of commits in a branch, it may | |
2560 | be easier to use `git rebase -i`, which allows you to reorder and | |
2561 | squash commits, as well as marking them for individual editing during | |
2562 | the rebase. See <<interactive-rebase>> for details, and | |
2563 | <<reordering-patch-series>> for alternatives. | |
2564 | ||
2565 | [[rewriting-one-commit]] | |
2566 | Rewriting a single commit | |
2567 | ------------------------- | |
2568 | ||
2569 | We saw in <<fixing-a-mistake-by-rewriting-history>> that you can replace the | |
2570 | most recent commit using | |
2571 | ||
2572 | ------------------------------------------------- | |
2573 | $ git commit --amend | |
2574 | ------------------------------------------------- | |
2575 | ||
2576 | which will replace the old commit by a new commit incorporating your | |
2577 | changes, giving you a chance to edit the old commit message first. | |
2578 | This is useful for fixing typos in your last commit, or for adjusting | |
2579 | the patch contents of a poorly staged commit. | |
2580 | ||
2581 | If you need to amend commits from deeper in your history, you can | |
2582 | use <<interactive-rebase,interactive rebase's `edit` instruction>>. | |
2583 | ||
2584 | [[reordering-patch-series]] | |
2585 | Reordering or selecting from a patch series | |
2586 | ------------------------------------------- | |
2587 | ||
2588 | Sometimes you want to edit a commit deeper in your history. One | |
2589 | approach is to use `git format-patch` to create a series of patches | |
2590 | and then reset the state to before the patches: | |
2591 | ||
2592 | ------------------------------------------------- | |
2593 | $ git format-patch origin | |
2594 | $ git reset --hard origin | |
2595 | ------------------------------------------------- | |
2596 | ||
2597 | Then modify, reorder, or eliminate patches as needed before applying | |
2598 | them again with linkgit:git-am[1]: | |
2599 | ||
2600 | ------------------------------------------------- | |
2601 | $ git am *.patch | |
2602 | ------------------------------------------------- | |
2603 | ||
2604 | [[interactive-rebase]] | |
2605 | Using interactive rebases | |
2606 | ------------------------- | |
2607 | ||
2608 | You can also edit a patch series with an interactive rebase. This is | |
2609 | the same as <<reordering-patch-series,reordering a patch series using | |
2610 | `format-patch`>>, so use whichever interface you like best. | |
2611 | ||
2612 | Rebase your current HEAD on the last commit you want to retain as-is. | |
2613 | For example, if you want to reorder the last 5 commits, use: | |
2614 | ||
2615 | ------------------------------------------------- | |
2616 | $ git rebase -i HEAD~5 | |
2617 | ------------------------------------------------- | |
2618 | ||
2619 | This will open your editor with a list of steps to be taken to perform | |
2620 | your rebase. | |
2621 | ||
2622 | ------------------------------------------------- | |
2623 | pick deadbee The oneline of this commit | |
2624 | pick fa1afe1 The oneline of the next commit | |
2625 | ... | |
2626 | ||
2627 | # Rebase c0ffeee..deadbee onto c0ffeee | |
2628 | # | |
2629 | # Commands: | |
2630 | # p, pick = use commit | |
2631 | # r, reword = use commit, but edit the commit message | |
2632 | # e, edit = use commit, but stop for amending | |
2633 | # s, squash = use commit, but meld into previous commit | |
2634 | # f, fixup = like "squash", but discard this commit's log message | |
2635 | # x, exec = run command (the rest of the line) using shell | |
2636 | # | |
2637 | # These lines can be re-ordered; they are executed from top to bottom. | |
2638 | # | |
2639 | # If you remove a line here THAT COMMIT WILL BE LOST. | |
2640 | # | |
2641 | # However, if you remove everything, the rebase will be aborted. | |
2642 | # | |
2643 | # Note that empty commits are commented out | |
2644 | ------------------------------------------------- | |
2645 | ||
2646 | As explained in the comments, you can reorder commits, squash them | |
2647 | together, edit commit messages, etc. by editing the list. Once you | |
2648 | are satisfied, save the list and close your editor, and the rebase | |
2649 | will begin. | |
2650 | ||
2651 | The rebase will stop where `pick` has been replaced with `edit` or | |
2652 | when a step in the list fails to mechanically resolve conflicts and | |
2653 | needs your help. When you are done editing and/or resolving conflicts | |
2654 | you can continue with `git rebase --continue`. If you decide that | |
2655 | things are getting too hairy, you can always bail out with `git rebase | |
2656 | --abort`. Even after the rebase is complete, you can still recover | |
2657 | the original branch by using the <<reflogs,reflog>>. | |
2658 | ||
2659 | For a more detailed discussion of the procedure and additional tips, | |
2660 | see the "INTERACTIVE MODE" section of linkgit:git-rebase[1]. | |
2661 | ||
2662 | [[patch-series-tools]] | |
2663 | Other tools | |
2664 | ----------- | |
2665 | ||
2666 | There are numerous other tools, such as StGit, which exist for the | |
2667 | purpose of maintaining a patch series. These are outside of the scope of | |
2668 | this manual. | |
2669 | ||
2670 | [[problems-With-rewriting-history]] | |
2671 | Problems with rewriting history | |
2672 | ------------------------------- | |
2673 | ||
2674 | The primary problem with rewriting the history of a branch has to do | |
2675 | with merging. Suppose somebody fetches your branch and merges it into | |
2676 | their branch, with a result something like this: | |
2677 | ||
2678 | ................................................ | |
2679 | o--o--O--o--o--o <-- origin | |
2680 | \ \ | |
2681 | t--t--t--m <-- their branch: | |
2682 | ................................................ | |
2683 | ||
2684 | Then suppose you modify the last three commits: | |
2685 | ||
2686 | ................................................ | |
2687 | o--o--o <-- new head of origin | |
2688 | / | |
2689 | o--o--O--o--o--o <-- old head of origin | |
2690 | ................................................ | |
2691 | ||
2692 | If we examined all this history together in one repository, it will | |
2693 | look like: | |
2694 | ||
2695 | ................................................ | |
2696 | o--o--o <-- new head of origin | |
2697 | / | |
2698 | o--o--O--o--o--o <-- old head of origin | |
2699 | \ \ | |
2700 | t--t--t--m <-- their branch: | |
2701 | ................................................ | |
2702 | ||
2703 | Git has no way of knowing that the new head is an updated version of | |
2704 | the old head; it treats this situation exactly the same as it would if | |
2705 | two developers had independently done the work on the old and new heads | |
2706 | in parallel. At this point, if someone attempts to merge the new head | |
2707 | in to their branch, git will attempt to merge together the two (old and | |
2708 | new) lines of development, instead of trying to replace the old by the | |
2709 | new. The results are likely to be unexpected. | |
2710 | ||
2711 | You may still choose to publish branches whose history is rewritten, | |
2712 | and it may be useful for others to be able to fetch those branches in | |
2713 | order to examine or test them, but they should not attempt to pull such | |
2714 | branches into their own work. | |
2715 | ||
2716 | For true distributed development that supports proper merging, | |
2717 | published branches should never be rewritten. | |
2718 | ||
2719 | [[bisect-merges]] | |
2720 | Why bisecting merge commits can be harder than bisecting linear history | |
2721 | ----------------------------------------------------------------------- | |
2722 | ||
2723 | The linkgit:git-bisect[1] command correctly handles history that | |
2724 | includes merge commits. However, when the commit that it finds is a | |
2725 | merge commit, the user may need to work harder than usual to figure out | |
2726 | why that commit introduced a problem. | |
2727 | ||
2728 | Imagine this history: | |
2729 | ||
2730 | ................................................ | |
2731 | ---Z---o---X---...---o---A---C---D | |
2732 | \ / | |
2733 | o---o---Y---...---o---B | |
2734 | ................................................ | |
2735 | ||
2736 | Suppose that on the upper line of development, the meaning of one | |
2737 | of the functions that exists at Z is changed at commit X. The | |
2738 | commits from Z leading to A change both the function's | |
2739 | implementation and all calling sites that exist at Z, as well | |
2740 | as new calling sites they add, to be consistent. There is no | |
2741 | bug at A. | |
2742 | ||
2743 | Suppose that in the meantime on the lower line of development somebody | |
2744 | adds a new calling site for that function at commit Y. The | |
2745 | commits from Z leading to B all assume the old semantics of that | |
2746 | function and the callers and the callee are consistent with each | |
2747 | other. There is no bug at B, either. | |
2748 | ||
2749 | Suppose further that the two development lines merge cleanly at C, | |
2750 | so no conflict resolution is required. | |
2751 | ||
2752 | Nevertheless, the code at C is broken, because the callers added | |
2753 | on the lower line of development have not been converted to the new | |
2754 | semantics introduced on the upper line of development. So if all | |
2755 | you know is that D is bad, that Z is good, and that | |
2756 | linkgit:git-bisect[1] identifies C as the culprit, how will you | |
2757 | figure out that the problem is due to this change in semantics? | |
2758 | ||
2759 | When the result of a `git bisect` is a non-merge commit, you should | |
2760 | normally be able to discover the problem by examining just that commit. | |
2761 | Developers can make this easy by breaking their changes into small | |
2762 | self-contained commits. That won't help in the case above, however, | |
2763 | because the problem isn't obvious from examination of any single | |
2764 | commit; instead, a global view of the development is required. To | |
2765 | make matters worse, the change in semantics in the problematic | |
2766 | function may be just one small part of the changes in the upper | |
2767 | line of development. | |
2768 | ||
2769 | On the other hand, if instead of merging at C you had rebased the | |
2770 | history between Z to B on top of A, you would have gotten this | |
2771 | linear history: | |
2772 | ||
2773 | ................................................................ | |
2774 | ---Z---o---X--...---o---A---o---o---Y*--...---o---B*--D* | |
2775 | ................................................................ | |
2776 | ||
2777 | Bisecting between Z and D* would hit a single culprit commit Y*, | |
2778 | and understanding why Y* was broken would probably be easier. | |
2779 | ||
2780 | Partly for this reason, many experienced git users, even when | |
2781 | working on an otherwise merge-heavy project, keep the history | |
2782 | linear by rebasing against the latest upstream version before | |
2783 | publishing. | |
2784 | ||
2785 | [[advanced-branch-management]] | |
2786 | Advanced branch management | |
2787 | ========================== | |
2788 | ||
2789 | [[fetching-individual-branches]] | |
2790 | Fetching individual branches | |
2791 | ---------------------------- | |
2792 | ||
2793 | Instead of using linkgit:git-remote[1], you can also choose just | |
2794 | to update one branch at a time, and to store it locally under an | |
2795 | arbitrary name: | |
2796 | ||
2797 | ------------------------------------------------- | |
2798 | $ git fetch origin todo:my-todo-work | |
2799 | ------------------------------------------------- | |
2800 | ||
2801 | The first argument, "origin", just tells git to fetch from the | |
2802 | repository you originally cloned from. The second argument tells git | |
2803 | to fetch the branch named "todo" from the remote repository, and to | |
2804 | store it locally under the name refs/heads/my-todo-work. | |
2805 | ||
2806 | You can also fetch branches from other repositories; so | |
2807 | ||
2808 | ------------------------------------------------- | |
2809 | $ git fetch git://example.com/proj.git master:example-master | |
2810 | ------------------------------------------------- | |
2811 | ||
2812 | will create a new branch named "example-master" and store in it the | |
2813 | branch named "master" from the repository at the given URL. If you | |
2814 | already have a branch named example-master, it will attempt to | |
2815 | <<fast-forwards,fast-forward>> to the commit given by example.com's | |
2816 | master branch. In more detail: | |
2817 | ||
2818 | [[fetch-fast-forwards]] | |
2819 | git fetch and fast-forwards | |
2820 | --------------------------- | |
2821 | ||
2822 | In the previous example, when updating an existing branch, "git fetch" | |
2823 | checks to make sure that the most recent commit on the remote | |
2824 | branch is a descendant of the most recent commit on your copy of the | |
2825 | branch before updating your copy of the branch to point at the new | |
2826 | commit. Git calls this process a <<fast-forwards,fast-forward>>. | |
2827 | ||
2828 | A fast-forward looks something like this: | |
2829 | ||
2830 | ................................................ | |
2831 | o--o--o--o <-- old head of the branch | |
2832 | \ | |
2833 | o--o--o <-- new head of the branch | |
2834 | ................................................ | |
2835 | ||
2836 | ||
2837 | In some cases it is possible that the new head will *not* actually be | |
2838 | a descendant of the old head. For example, the developer may have | |
2839 | realized she made a serious mistake, and decided to backtrack, | |
2840 | resulting in a situation like: | |
2841 | ||
2842 | ................................................ | |
2843 | o--o--o--o--a--b <-- old head of the branch | |
2844 | \ | |
2845 | o--o--o <-- new head of the branch | |
2846 | ................................................ | |
2847 | ||
2848 | In this case, "git fetch" will fail, and print out a warning. | |
2849 | ||
2850 | In that case, you can still force git to update to the new head, as | |
2851 | described in the following section. However, note that in the | |
2852 | situation above this may mean losing the commits labeled "a" and "b", | |
2853 | unless you've already created a reference of your own pointing to | |
2854 | them. | |
2855 | ||
2856 | [[forcing-fetch]] | |
2857 | Forcing git fetch to do non-fast-forward updates | |
2858 | ------------------------------------------------ | |
2859 | ||
2860 | If git fetch fails because the new head of a branch is not a | |
2861 | descendant of the old head, you may force the update with: | |
2862 | ||
2863 | ------------------------------------------------- | |
2864 | $ git fetch git://example.com/proj.git +master:refs/remotes/example/master | |
2865 | ------------------------------------------------- | |
2866 | ||
2867 | Note the addition of the "+" sign. Alternatively, you can use the "-f" | |
2868 | flag to force updates of all the fetched branches, as in: | |
2869 | ||
2870 | ------------------------------------------------- | |
2871 | $ git fetch -f origin | |
2872 | ------------------------------------------------- | |
2873 | ||
2874 | Be aware that commits that the old version of example/master pointed at | |
2875 | may be lost, as we saw in the previous section. | |
2876 | ||
2877 | [[remote-branch-configuration]] | |
2878 | Configuring remote-tracking branches | |
2879 | ------------------------------------ | |
2880 | ||
2881 | We saw above that "origin" is just a shortcut to refer to the | |
2882 | repository that you originally cloned from. This information is | |
2883 | stored in git configuration variables, which you can see using | |
2884 | linkgit:git-config[1]: | |
2885 | ||
2886 | ------------------------------------------------- | |
2887 | $ git config -l | |
2888 | core.repositoryformatversion=0 | |
2889 | core.filemode=true | |
2890 | core.logallrefupdates=true | |
2891 | remote.origin.url=git://git.kernel.org/pub/scm/git/git.git | |
2892 | remote.origin.fetch=+refs/heads/*:refs/remotes/origin/* | |
2893 | branch.master.remote=origin | |
2894 | branch.master.merge=refs/heads/master | |
2895 | ------------------------------------------------- | |
2896 | ||
2897 | If there are other repositories that you also use frequently, you can | |
2898 | create similar configuration options to save typing; for example, | |
2899 | ||
2900 | ------------------------------------------------- | |
2901 | $ git remote add example git://example.com/proj.git | |
2902 | ------------------------------------------------- | |
2903 | ||
2904 | adds the following to `.git/config`: | |
2905 | ||
2906 | ------------------------------------------------- | |
2907 | [remote "example"] | |
2908 | url = git://example.com/proj.git | |
2909 | fetch = +refs/heads/*:refs/remotes/example/* | |
2910 | ------------------------------------------------- | |
2911 | ||
2912 | Also note that the above configuration can be performed by directly | |
2913 | editing the file `.git/config` instead of using linkgit:git-remote[1]. | |
2914 | ||
2915 | After configuring the remote, the following three commands will do the | |
2916 | same thing: | |
2917 | ||
2918 | ------------------------------------------------- | |
2919 | $ git fetch git://example.com/proj.git +refs/heads/*:refs/remotes/example/* | |
2920 | $ git fetch example +refs/heads/*:refs/remotes/example/* | |
2921 | $ git fetch example | |
2922 | ------------------------------------------------- | |
2923 | ||
2924 | See linkgit:git-config[1] for more details on the configuration | |
2925 | options mentioned above and linkgit:git-fetch[1] for more details on | |
2926 | the refspec syntax. | |
2927 | ||
2928 | ||
2929 | [[git-concepts]] | |
2930 | Git concepts | |
2931 | ============ | |
2932 | ||
2933 | Git is built on a small number of simple but powerful ideas. While it | |
2934 | is possible to get things done without understanding them, you will find | |
2935 | git much more intuitive if you do. | |
2936 | ||
2937 | We start with the most important, the <<def_object_database,object | |
2938 | database>> and the <<def_index,index>>. | |
2939 | ||
2940 | [[the-object-database]] | |
2941 | The Object Database | |
2942 | ------------------- | |
2943 | ||
2944 | ||
2945 | We already saw in <<understanding-commits>> that all commits are stored | |
2946 | under a 40-digit "object name". In fact, all the information needed to | |
2947 | represent the history of a project is stored in objects with such names. | |
2948 | In each case the name is calculated by taking the SHA-1 hash of the | |
2949 | contents of the object. The SHA-1 hash is a cryptographic hash function. | |
2950 | What that means to us is that it is impossible to find two different | |
2951 | objects with the same name. This has a number of advantages; among | |
2952 | others: | |
2953 | ||
2954 | - Git can quickly determine whether two objects are identical or not, | |
2955 | just by comparing names. | |
2956 | - Since object names are computed the same way in every repository, the | |
2957 | same content stored in two repositories will always be stored under | |
2958 | the same name. | |
2959 | - Git can detect errors when it reads an object, by checking that the | |
2960 | object's name is still the SHA-1 hash of its contents. | |
2961 | ||
2962 | (See <<object-details>> for the details of the object formatting and | |
2963 | SHA-1 calculation.) | |
2964 | ||
2965 | There are four different types of objects: "blob", "tree", "commit", and | |
2966 | "tag". | |
2967 | ||
2968 | - A <<def_blob_object,"blob" object>> is used to store file data. | |
2969 | - A <<def_tree_object,"tree" object>> ties one or more | |
2970 | "blob" objects into a directory structure. In addition, a tree object | |
2971 | can refer to other tree objects, thus creating a directory hierarchy. | |
2972 | - A <<def_commit_object,"commit" object>> ties such directory hierarchies | |
2973 | together into a <<def_DAG,directed acyclic graph>> of revisions--each | |
2974 | commit contains the object name of exactly one tree designating the | |
2975 | directory hierarchy at the time of the commit. In addition, a commit | |
2976 | refers to "parent" commit objects that describe the history of how we | |
2977 | arrived at that directory hierarchy. | |
2978 | - A <<def_tag_object,"tag" object>> symbolically identifies and can be | |
2979 | used to sign other objects. It contains the object name and type of | |
2980 | another object, a symbolic name (of course!) and, optionally, a | |
2981 | signature. | |
2982 | ||
2983 | The object types in some more detail: | |
2984 | ||
2985 | [[commit-object]] | |
2986 | Commit Object | |
2987 | ~~~~~~~~~~~~~ | |
2988 | ||
2989 | The "commit" object links a physical state of a tree with a description | |
2990 | of how we got there and why. Use the --pretty=raw option to | |
2991 | linkgit:git-show[1] or linkgit:git-log[1] to examine your favorite | |
2992 | commit: | |
2993 | ||
2994 | ------------------------------------------------ | |
2995 | $ git show -s --pretty=raw 2be7fcb476 | |
2996 | commit 2be7fcb4764f2dbcee52635b91fedb1b3dcf7ab4 | |
2997 | tree fb3a8bdd0ceddd019615af4d57a53f43d8cee2bf | |
2998 | parent 257a84d9d02e90447b149af58b271c19405edb6a | |
2999 | author Dave Watson <dwatson@mimvista.com> 1187576872 -0400 | |
3000 | committer Junio C Hamano <gitster@pobox.com> 1187591163 -0700 | |
3001 | ||
3002 | Fix misspelling of 'suppress' in docs | |
3003 | ||
3004 | Signed-off-by: Junio C Hamano <gitster@pobox.com> | |
3005 | ------------------------------------------------ | |
3006 | ||
3007 | As you can see, a commit is defined by: | |
3008 | ||
3009 | - a tree: The SHA-1 name of a tree object (as defined below), representing | |
3010 | the contents of a directory at a certain point in time. | |
3011 | - parent(s): The SHA-1 name(s) of some number of commits which represent the | |
3012 | immediately previous step(s) in the history of the project. The | |
3013 | example above has one parent; merge commits may have more than | |
3014 | one. A commit with no parents is called a "root" commit, and | |
3015 | represents the initial revision of a project. Each project must have | |
3016 | at least one root. A project can also have multiple roots, though | |
3017 | that isn't common (or necessarily a good idea). | |
3018 | - an author: The name of the person responsible for this change, together | |
3019 | with its date. | |
3020 | - a committer: The name of the person who actually created the commit, | |
3021 | with the date it was done. This may be different from the author, for | |
3022 | example, if the author was someone who wrote a patch and emailed it | |
3023 | to the person who used it to create the commit. | |
3024 | - a comment describing this commit. | |
3025 | ||
3026 | Note that a commit does not itself contain any information about what | |
3027 | actually changed; all changes are calculated by comparing the contents | |
3028 | of the tree referred to by this commit with the trees associated with | |
3029 | its parents. In particular, git does not attempt to record file renames | |
3030 | explicitly, though it can identify cases where the existence of the same | |
3031 | file data at changing paths suggests a rename. (See, for example, the | |
3032 | -M option to linkgit:git-diff[1]). | |
3033 | ||
3034 | A commit is usually created by linkgit:git-commit[1], which creates a | |
3035 | commit whose parent is normally the current HEAD, and whose tree is | |
3036 | taken from the content currently stored in the index. | |
3037 | ||
3038 | [[tree-object]] | |
3039 | Tree Object | |
3040 | ~~~~~~~~~~~ | |
3041 | ||
3042 | The ever-versatile linkgit:git-show[1] command can also be used to | |
3043 | examine tree objects, but linkgit:git-ls-tree[1] will give you more | |
3044 | details: | |
3045 | ||
3046 | ------------------------------------------------ | |
3047 | $ git ls-tree fb3a8bdd0ce | |
3048 | 100644 blob 63c918c667fa005ff12ad89437f2fdc80926e21c .gitignore | |
3049 | 100644 blob 5529b198e8d14decbe4ad99db3f7fb632de0439d .mailmap | |
3050 | 100644 blob 6ff87c4664981e4397625791c8ea3bbb5f2279a3 COPYING | |
3051 | 040000 tree 2fb783e477100ce076f6bf57e4a6f026013dc745 Documentation | |
3052 | 100755 blob 3c0032cec592a765692234f1cba47dfdcc3a9200 GIT-VERSION-GEN | |
3053 | 100644 blob 289b046a443c0647624607d471289b2c7dcd470b INSTALL | |
3054 | 100644 blob 4eb463797adc693dc168b926b6932ff53f17d0b1 Makefile | |
3055 | 100644 blob 548142c327a6790ff8821d67c2ee1eff7a656b52 README | |
3056 | ... | |
3057 | ------------------------------------------------ | |
3058 | ||
3059 | As you can see, a tree object contains a list of entries, each with a | |
3060 | mode, object type, SHA-1 name, and name, sorted by name. It represents | |
3061 | the contents of a single directory tree. | |
3062 | ||
3063 | The object type may be a blob, representing the contents of a file, or | |
3064 | another tree, representing the contents of a subdirectory. Since trees | |
3065 | and blobs, like all other objects, are named by the SHA-1 hash of their | |
3066 | contents, two trees have the same SHA-1 name if and only if their | |
3067 | contents (including, recursively, the contents of all subdirectories) | |
3068 | are identical. This allows git to quickly determine the differences | |
3069 | between two related tree objects, since it can ignore any entries with | |
3070 | identical object names. | |
3071 | ||
3072 | (Note: in the presence of submodules, trees may also have commits as | |
3073 | entries. See <<submodules>> for documentation.) | |
3074 | ||
3075 | Note that the files all have mode 644 or 755: git actually only pays | |
3076 | attention to the executable bit. | |
3077 | ||
3078 | [[blob-object]] | |
3079 | Blob Object | |
3080 | ~~~~~~~~~~~ | |
3081 | ||
3082 | You can use linkgit:git-show[1] to examine the contents of a blob; take, | |
3083 | for example, the blob in the entry for "COPYING" from the tree above: | |
3084 | ||
3085 | ------------------------------------------------ | |
3086 | $ git show 6ff87c4664 | |
3087 | ||
3088 | Note that the only valid version of the GPL as far as this project | |
3089 | is concerned is _this_ particular version of the license (ie v2, not | |
3090 | v2.2 or v3.x or whatever), unless explicitly otherwise stated. | |
3091 | ... | |
3092 | ------------------------------------------------ | |
3093 | ||
3094 | A "blob" object is nothing but a binary blob of data. It doesn't refer | |
3095 | to anything else or have attributes of any kind. | |
3096 | ||
3097 | Since the blob is entirely defined by its data, if two files in a | |
3098 | directory tree (or in multiple different versions of the repository) | |
3099 | have the same contents, they will share the same blob object. The object | |
3100 | is totally independent of its location in the directory tree, and | |
3101 | renaming a file does not change the object that file is associated with. | |
3102 | ||
3103 | Note that any tree or blob object can be examined using | |
3104 | linkgit:git-show[1] with the <revision>:<path> syntax. This can | |
3105 | sometimes be useful for browsing the contents of a tree that is not | |
3106 | currently checked out. | |
3107 | ||
3108 | [[trust]] | |
3109 | Trust | |
3110 | ~~~~~ | |
3111 | ||
3112 | If you receive the SHA-1 name of a blob from one source, and its contents | |
3113 | from another (possibly untrusted) source, you can still trust that those | |
3114 | contents are correct as long as the SHA-1 name agrees. This is because | |
3115 | the SHA-1 is designed so that it is infeasible to find different contents | |
3116 | that produce the same hash. | |
3117 | ||
3118 | Similarly, you need only trust the SHA-1 name of a top-level tree object | |
3119 | to trust the contents of the entire directory that it refers to, and if | |
3120 | you receive the SHA-1 name of a commit from a trusted source, then you | |
3121 | can easily verify the entire history of commits reachable through | |
3122 | parents of that commit, and all of those contents of the trees referred | |
3123 | to by those commits. | |
3124 | ||
3125 | So to introduce some real trust in the system, the only thing you need | |
3126 | to do is to digitally sign just 'one' special note, which includes the | |
3127 | name of a top-level commit. Your digital signature shows others | |
3128 | that you trust that commit, and the immutability of the history of | |
3129 | commits tells others that they can trust the whole history. | |
3130 | ||
3131 | In other words, you can easily validate a whole archive by just | |
3132 | sending out a single email that tells the people the name (SHA-1 hash) | |
3133 | of the top commit, and digitally sign that email using something | |
3134 | like GPG/PGP. | |
3135 | ||
3136 | To assist in this, git also provides the tag object... | |
3137 | ||
3138 | [[tag-object]] | |
3139 | Tag Object | |
3140 | ~~~~~~~~~~ | |
3141 | ||
3142 | A tag object contains an object, object type, tag name, the name of the | |
3143 | person ("tagger") who created the tag, and a message, which may contain | |
3144 | a signature, as can be seen using linkgit:git-cat-file[1]: | |
3145 | ||
3146 | ------------------------------------------------ | |
3147 | $ git cat-file tag v1.5.0 | |
3148 | object 437b1b20df4b356c9342dac8d38849f24ef44f27 | |
3149 | type commit | |
3150 | tag v1.5.0 | |
3151 | tagger Junio C Hamano <junkio@cox.net> 1171411200 +0000 | |
3152 | ||
3153 | GIT 1.5.0 | |
3154 | -----BEGIN PGP SIGNATURE----- | |
3155 | Version: GnuPG v1.4.6 (GNU/Linux) | |
3156 | ||
3157 | iD8DBQBF0lGqwMbZpPMRm5oRAuRiAJ9ohBLd7s2kqjkKlq1qqC57SbnmzQCdG4ui | |
3158 | nLE/L9aUXdWeTFPron96DLA= | |
3159 | =2E+0 | |
3160 | -----END PGP SIGNATURE----- | |
3161 | ------------------------------------------------ | |
3162 | ||
3163 | See the linkgit:git-tag[1] command to learn how to create and verify tag | |
3164 | objects. (Note that linkgit:git-tag[1] can also be used to create | |
3165 | "lightweight tags", which are not tag objects at all, but just simple | |
3166 | references whose names begin with "refs/tags/"). | |
3167 | ||
3168 | [[pack-files]] | |
3169 | How git stores objects efficiently: pack files | |
3170 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3171 | ||
3172 | Newly created objects are initially created in a file named after the | |
3173 | object's SHA-1 hash (stored in .git/objects). | |
3174 | ||
3175 | Unfortunately this system becomes inefficient once a project has a | |
3176 | lot of objects. Try this on an old project: | |
3177 | ||
3178 | ------------------------------------------------ | |
3179 | $ git count-objects | |
3180 | 6930 objects, 47620 kilobytes | |
3181 | ------------------------------------------------ | |
3182 | ||
3183 | The first number is the number of objects which are kept in | |
3184 | individual files. The second is the amount of space taken up by | |
3185 | those "loose" objects. | |
3186 | ||
3187 | You can save space and make git faster by moving these loose objects in | |
3188 | to a "pack file", which stores a group of objects in an efficient | |
3189 | compressed format; the details of how pack files are formatted can be | |
3190 | found in link:technical/pack-format.txt[technical/pack-format.txt]. | |
3191 | ||
3192 | To put the loose objects into a pack, just run git repack: | |
3193 | ||
3194 | ------------------------------------------------ | |
3195 | $ git repack | |
3196 | Generating pack... | |
3197 | Done counting 6020 objects. | |
3198 | Deltifying 6020 objects. | |
3199 | 100% (6020/6020) done | |
3200 | Writing 6020 objects. | |
3201 | 100% (6020/6020) done | |
3202 | Total 6020, written 6020 (delta 4070), reused 0 (delta 0) | |
3203 | Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created. | |
3204 | ------------------------------------------------ | |
3205 | ||
3206 | You can then run | |
3207 | ||
3208 | ------------------------------------------------ | |
3209 | $ git prune | |
3210 | ------------------------------------------------ | |
3211 | ||
3212 | to remove any of the "loose" objects that are now contained in the | |
3213 | pack. This will also remove any unreferenced objects (which may be | |
3214 | created when, for example, you use "git reset" to remove a commit). | |
3215 | You can verify that the loose objects are gone by looking at the | |
3216 | .git/objects directory or by running | |
3217 | ||
3218 | ------------------------------------------------ | |
3219 | $ git count-objects | |
3220 | 0 objects, 0 kilobytes | |
3221 | ------------------------------------------------ | |
3222 | ||
3223 | Although the object files are gone, any commands that refer to those | |
3224 | objects will work exactly as they did before. | |
3225 | ||
3226 | The linkgit:git-gc[1] command performs packing, pruning, and more for | |
3227 | you, so is normally the only high-level command you need. | |
3228 | ||
3229 | [[dangling-objects]] | |
3230 | Dangling objects | |
3231 | ~~~~~~~~~~~~~~~~ | |
3232 | ||
3233 | The linkgit:git-fsck[1] command will sometimes complain about dangling | |
3234 | objects. They are not a problem. | |
3235 | ||
3236 | The most common cause of dangling objects is that you've rebased a | |
3237 | branch, or you have pulled from somebody else who rebased a branch--see | |
3238 | <<cleaning-up-history>>. In that case, the old head of the original | |
3239 | branch still exists, as does everything it pointed to. The branch | |
3240 | pointer itself just doesn't, since you replaced it with another one. | |
3241 | ||
3242 | There are also other situations that cause dangling objects. For | |
3243 | example, a "dangling blob" may arise because you did a "git add" of a | |
3244 | file, but then, before you actually committed it and made it part of the | |
3245 | bigger picture, you changed something else in that file and committed | |
3246 | that *updated* thing--the old state that you added originally ends up | |
3247 | not being pointed to by any commit or tree, so it's now a dangling blob | |
3248 | object. | |
3249 | ||
3250 | Similarly, when the "recursive" merge strategy runs, and finds that | |
3251 | there are criss-cross merges and thus more than one merge base (which is | |
3252 | fairly unusual, but it does happen), it will generate one temporary | |
3253 | midway tree (or possibly even more, if you had lots of criss-crossing | |
3254 | merges and more than two merge bases) as a temporary internal merge | |
3255 | base, and again, those are real objects, but the end result will not end | |
3256 | up pointing to them, so they end up "dangling" in your repository. | |
3257 | ||
3258 | Generally, dangling objects aren't anything to worry about. They can | |
3259 | even be very useful: if you screw something up, the dangling objects can | |
3260 | be how you recover your old tree (say, you did a rebase, and realized | |
3261 | that you really didn't want to--you can look at what dangling objects | |
3262 | you have, and decide to reset your head to some old dangling state). | |
3263 | ||
3264 | For commits, you can just use: | |
3265 | ||
3266 | ------------------------------------------------ | |
3267 | $ gitk <dangling-commit-sha-goes-here> --not --all | |
3268 | ------------------------------------------------ | |
3269 | ||
3270 | This asks for all the history reachable from the given commit but not | |
3271 | from any branch, tag, or other reference. If you decide it's something | |
3272 | you want, you can always create a new reference to it, e.g., | |
3273 | ||
3274 | ------------------------------------------------ | |
3275 | $ git branch recovered-branch <dangling-commit-sha-goes-here> | |
3276 | ------------------------------------------------ | |
3277 | ||
3278 | For blobs and trees, you can't do the same, but you can still examine | |
3279 | them. You can just do | |
3280 | ||
3281 | ------------------------------------------------ | |
3282 | $ git show <dangling-blob/tree-sha-goes-here> | |
3283 | ------------------------------------------------ | |
3284 | ||
3285 | to show what the contents of the blob were (or, for a tree, basically | |
3286 | what the "ls" for that directory was), and that may give you some idea | |
3287 | of what the operation was that left that dangling object. | |
3288 | ||
3289 | Usually, dangling blobs and trees aren't very interesting. They're | |
3290 | almost always the result of either being a half-way mergebase (the blob | |
3291 | will often even have the conflict markers from a merge in it, if you | |
3292 | have had conflicting merges that you fixed up by hand), or simply | |
3293 | because you interrupted a "git fetch" with ^C or something like that, | |
3294 | leaving _some_ of the new objects in the object database, but just | |
3295 | dangling and useless. | |
3296 | ||
3297 | Anyway, once you are sure that you're not interested in any dangling | |
3298 | state, you can just prune all unreachable objects: | |
3299 | ||
3300 | ------------------------------------------------ | |
3301 | $ git prune | |
3302 | ------------------------------------------------ | |
3303 | ||
3304 | and they'll be gone. But you should only run "git prune" on a quiescent | |
3305 | repository--it's kind of like doing a filesystem fsck recovery: you | |
3306 | don't want to do that while the filesystem is mounted. | |
3307 | ||
3308 | (The same is true of "git fsck" itself, btw, but since | |
3309 | `git fsck` never actually *changes* the repository, it just reports | |
3310 | on what it found, `git fsck` itself is never 'dangerous' to run. | |
3311 | Running it while somebody is actually changing the repository can cause | |
3312 | confusing and scary messages, but it won't actually do anything bad. In | |
3313 | contrast, running "git prune" while somebody is actively changing the | |
3314 | repository is a *BAD* idea). | |
3315 | ||
3316 | [[recovering-from-repository-corruption]] | |
3317 | Recovering from repository corruption | |
3318 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3319 | ||
3320 | By design, git treats data trusted to it with caution. However, even in | |
3321 | the absence of bugs in git itself, it is still possible that hardware or | |
3322 | operating system errors could corrupt data. | |
3323 | ||
3324 | The first defense against such problems is backups. You can back up a | |
3325 | git directory using clone, or just using cp, tar, or any other backup | |
3326 | mechanism. | |
3327 | ||
3328 | As a last resort, you can search for the corrupted objects and attempt | |
3329 | to replace them by hand. Back up your repository before attempting this | |
3330 | in case you corrupt things even more in the process. | |
3331 | ||
3332 | We'll assume that the problem is a single missing or corrupted blob, | |
3333 | which is sometimes a solvable problem. (Recovering missing trees and | |
3334 | especially commits is *much* harder). | |
3335 | ||
3336 | Before starting, verify that there is corruption, and figure out where | |
3337 | it is with linkgit:git-fsck[1]; this may be time-consuming. | |
3338 | ||
3339 | Assume the output looks like this: | |
3340 | ||
3341 | ------------------------------------------------ | |
3342 | $ git fsck --full --no-dangling | |
3343 | broken link from tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 | |
3344 | to blob 4b9458b3786228369c63936db65827de3cc06200 | |
3345 | missing blob 4b9458b3786228369c63936db65827de3cc06200 | |
3346 | ------------------------------------------------ | |
3347 | ||
3348 | Now you know that blob 4b9458b3 is missing, and that the tree 2d9263c6 | |
3349 | points to it. If you could find just one copy of that missing blob | |
3350 | object, possibly in some other repository, you could move it into | |
3351 | .git/objects/4b/9458b3... and be done. Suppose you can't. You can | |
3352 | still examine the tree that pointed to it with linkgit:git-ls-tree[1], | |
3353 | which might output something like: | |
3354 | ||
3355 | ------------------------------------------------ | |
3356 | $ git ls-tree 2d9263c6d23595e7cb2a21e5ebbb53655278dff8 | |
3357 | 100644 blob 8d14531846b95bfa3564b58ccfb7913a034323b8 .gitignore | |
3358 | 100644 blob ebf9bf84da0aab5ed944264a5db2a65fe3a3e883 .mailmap | |
3359 | 100644 blob ca442d313d86dc67e0a2e5d584b465bd382cbf5c COPYING | |
3360 | ... | |
3361 | 100644 blob 4b9458b3786228369c63936db65827de3cc06200 myfile | |
3362 | ... | |
3363 | ------------------------------------------------ | |
3364 | ||
3365 | So now you know that the missing blob was the data for a file named | |
3366 | "myfile". And chances are you can also identify the directory--let's | |
3367 | say it's in "somedirectory". If you're lucky the missing copy might be | |
3368 | the same as the copy you have checked out in your working tree at | |
3369 | "somedirectory/myfile"; you can test whether that's right with | |
3370 | linkgit:git-hash-object[1]: | |
3371 | ||
3372 | ------------------------------------------------ | |
3373 | $ git hash-object -w somedirectory/myfile | |
3374 | ------------------------------------------------ | |
3375 | ||
3376 | which will create and store a blob object with the contents of | |
3377 | somedirectory/myfile, and output the SHA-1 of that object. if you're | |
3378 | extremely lucky it might be 4b9458b3786228369c63936db65827de3cc06200, in | |
3379 | which case you've guessed right, and the corruption is fixed! | |
3380 | ||
3381 | Otherwise, you need more information. How do you tell which version of | |
3382 | the file has been lost? | |
3383 | ||
3384 | The easiest way to do this is with: | |
3385 | ||
3386 | ------------------------------------------------ | |
3387 | $ git log --raw --all --full-history -- somedirectory/myfile | |
3388 | ------------------------------------------------ | |
3389 | ||
3390 | Because you're asking for raw output, you'll now get something like | |
3391 | ||
3392 | ------------------------------------------------ | |
3393 | commit abc | |
3394 | Author: | |
3395 | Date: | |
3396 | ... | |
3397 | :100644 100644 4b9458b... newsha... M somedirectory/myfile | |
3398 | ||
3399 | ||
3400 | commit xyz | |
3401 | Author: | |
3402 | Date: | |
3403 | ||
3404 | ... | |
3405 | :100644 100644 oldsha... 4b9458b... M somedirectory/myfile | |
3406 | ------------------------------------------------ | |
3407 | ||
3408 | This tells you that the immediately following version of the file was | |
3409 | "newsha", and that the immediately preceding version was "oldsha". | |
3410 | You also know the commit messages that went with the change from oldsha | |
3411 | to 4b9458b and with the change from 4b9458b to newsha. | |
3412 | ||
3413 | If you've been committing small enough changes, you may now have a good | |
3414 | shot at reconstructing the contents of the in-between state 4b9458b. | |
3415 | ||
3416 | If you can do that, you can now recreate the missing object with | |
3417 | ||
3418 | ------------------------------------------------ | |
3419 | $ git hash-object -w <recreated-file> | |
3420 | ------------------------------------------------ | |
3421 | ||
3422 | and your repository is good again! | |
3423 | ||
3424 | (Btw, you could have ignored the fsck, and started with doing a | |
3425 | ||
3426 | ------------------------------------------------ | |
3427 | $ git log --raw --all | |
3428 | ------------------------------------------------ | |
3429 | ||
3430 | and just looked for the sha of the missing object (4b9458b..) in that | |
3431 | whole thing. It's up to you--Git does *have* a lot of information, it is | |
3432 | just missing one particular blob version. | |
3433 | ||
3434 | [[the-index]] | |
3435 | The index | |
3436 | ----------- | |
3437 | ||
3438 | The index is a binary file (generally kept in .git/index) containing a | |
3439 | sorted list of path names, each with permissions and the SHA-1 of a blob | |
3440 | object; linkgit:git-ls-files[1] can show you the contents of the index: | |
3441 | ||
3442 | ------------------------------------------------- | |
3443 | $ git ls-files --stage | |
3444 | 100644 63c918c667fa005ff12ad89437f2fdc80926e21c 0 .gitignore | |
3445 | 100644 5529b198e8d14decbe4ad99db3f7fb632de0439d 0 .mailmap | |
3446 | 100644 6ff87c4664981e4397625791c8ea3bbb5f2279a3 0 COPYING | |
3447 | 100644 a37b2152bd26be2c2289e1f57a292534a51a93c7 0 Documentation/.gitignore | |
3448 | 100644 fbefe9a45b00a54b58d94d06eca48b03d40a50e0 0 Documentation/Makefile | |
3449 | ... | |
3450 | 100644 2511aef8d89ab52be5ec6a5e46236b4b6bcd07ea 0 xdiff/xtypes.h | |
3451 | 100644 2ade97b2574a9f77e7ae4002a4e07a6a38e46d07 0 xdiff/xutils.c | |
3452 | 100644 d5de8292e05e7c36c4b68857c1cf9855e3d2f70a 0 xdiff/xutils.h | |
3453 | ------------------------------------------------- | |
3454 | ||
3455 | Note that in older documentation you may see the index called the | |
3456 | "current directory cache" or just the "cache". It has three important | |
3457 | properties: | |
3458 | ||
3459 | 1. The index contains all the information necessary to generate a single | |
3460 | (uniquely determined) tree object. | |
3461 | + | |
3462 | For example, running linkgit:git-commit[1] generates this tree object | |
3463 | from the index, stores it in the object database, and uses it as the | |
3464 | tree object associated with the new commit. | |
3465 | ||
3466 | 2. The index enables fast comparisons between the tree object it defines | |
3467 | and the working tree. | |
3468 | + | |
3469 | It does this by storing some additional data for each entry (such as | |
3470 | the last modified time). This data is not displayed above, and is not | |
3471 | stored in the created tree object, but it can be used to determine | |
3472 | quickly which files in the working directory differ from what was | |
3473 | stored in the index, and thus save git from having to read all of the | |
3474 | data from such files to look for changes. | |
3475 | ||
3476 | 3. It can efficiently represent information about merge conflicts | |
3477 | between different tree objects, allowing each pathname to be | |
3478 | associated with sufficient information about the trees involved that | |
3479 | you can create a three-way merge between them. | |
3480 | + | |
3481 | We saw in <<conflict-resolution>> that during a merge the index can | |
3482 | store multiple versions of a single file (called "stages"). The third | |
3483 | column in the linkgit:git-ls-files[1] output above is the stage | |
3484 | number, and will take on values other than 0 for files with merge | |
3485 | conflicts. | |
3486 | ||
3487 | The index is thus a sort of temporary staging area, which is filled with | |
3488 | a tree which you are in the process of working on. | |
3489 | ||
3490 | If you blow the index away entirely, you generally haven't lost any | |
3491 | information as long as you have the name of the tree that it described. | |
3492 | ||
3493 | [[submodules]] | |
3494 | Submodules | |
3495 | ========== | |
3496 | ||
3497 | Large projects are often composed of smaller, self-contained modules. For | |
3498 | example, an embedded Linux distribution's source tree would include every | |
3499 | piece of software in the distribution with some local modifications; a movie | |
3500 | player might need to build against a specific, known-working version of a | |
3501 | decompression library; several independent programs might all share the same | |
3502 | build scripts. | |
3503 | ||
3504 | With centralized revision control systems this is often accomplished by | |
3505 | including every module in one single repository. Developers can check out | |
3506 | all modules or only the modules they need to work with. They can even modify | |
3507 | files across several modules in a single commit while moving things around | |
3508 | or updating APIs and translations. | |
3509 | ||
3510 | Git does not allow partial checkouts, so duplicating this approach in Git | |
3511 | would force developers to keep a local copy of modules they are not | |
3512 | interested in touching. Commits in an enormous checkout would be slower | |
3513 | than you'd expect as Git would have to scan every directory for changes. | |
3514 | If modules have a lot of local history, clones would take forever. | |
3515 | ||
3516 | On the plus side, distributed revision control systems can much better | |
3517 | integrate with external sources. In a centralized model, a single arbitrary | |
3518 | snapshot of the external project is exported from its own revision control | |
3519 | and then imported into the local revision control on a vendor branch. All | |
3520 | the history is hidden. With distributed revision control you can clone the | |
3521 | entire external history and much more easily follow development and re-merge | |
3522 | local changes. | |
3523 | ||
3524 | Git's submodule support allows a repository to contain, as a subdirectory, a | |
3525 | checkout of an external project. Submodules maintain their own identity; | |
3526 | the submodule support just stores the submodule repository location and | |
3527 | commit ID, so other developers who clone the containing project | |
3528 | ("superproject") can easily clone all the submodules at the same revision. | |
3529 | Partial checkouts of the superproject are possible: you can tell Git to | |
3530 | clone none, some or all of the submodules. | |
3531 | ||
3532 | The linkgit:git-submodule[1] command is available since Git 1.5.3. Users | |
3533 | with Git 1.5.2 can look up the submodule commits in the repository and | |
3534 | manually check them out; earlier versions won't recognize the submodules at | |
3535 | all. | |
3536 | ||
3537 | To see how submodule support works, create (for example) four example | |
3538 | repositories that can be used later as a submodule: | |
3539 | ||
3540 | ------------------------------------------------- | |
3541 | $ mkdir ~/git | |
3542 | $ cd ~/git | |
3543 | $ for i in a b c d | |
3544 | do | |
3545 | mkdir $i | |
3546 | cd $i | |
3547 | git init | |
3548 | echo "module $i" > $i.txt | |
3549 | git add $i.txt | |
3550 | git commit -m "Initial commit, submodule $i" | |
3551 | cd .. | |
3552 | done | |
3553 | ------------------------------------------------- | |
3554 | ||
3555 | Now create the superproject and add all the submodules: | |
3556 | ||
3557 | ------------------------------------------------- | |
3558 | $ mkdir super | |
3559 | $ cd super | |
3560 | $ git init | |
3561 | $ for i in a b c d | |
3562 | do | |
3563 | git submodule add ~/git/$i $i | |
3564 | done | |
3565 | ------------------------------------------------- | |
3566 | ||
3567 | NOTE: Do not use local URLs here if you plan to publish your superproject! | |
3568 | ||
3569 | See what files `git submodule` created: | |
3570 | ||
3571 | ------------------------------------------------- | |
3572 | $ ls -a | |
3573 | . .. .git .gitmodules a b c d | |
3574 | ------------------------------------------------- | |
3575 | ||
3576 | The `git submodule add <repo> <path>` command does a couple of things: | |
3577 | ||
3578 | - It clones the submodule from <repo> to the given <path> under the | |
3579 | current directory and by default checks out the master branch. | |
3580 | - It adds the submodule's clone path to the linkgit:gitmodules[5] file and | |
3581 | adds this file to the index, ready to be committed. | |
3582 | - It adds the submodule's current commit ID to the index, ready to be | |
3583 | committed. | |
3584 | ||
3585 | Commit the superproject: | |
3586 | ||
3587 | ------------------------------------------------- | |
3588 | $ git commit -m "Add submodules a, b, c and d." | |
3589 | ------------------------------------------------- | |
3590 | ||
3591 | Now clone the superproject: | |
3592 | ||
3593 | ------------------------------------------------- | |
3594 | $ cd .. | |
3595 | $ git clone super cloned | |
3596 | $ cd cloned | |
3597 | ------------------------------------------------- | |
3598 | ||
3599 | The submodule directories are there, but they're empty: | |
3600 | ||
3601 | ------------------------------------------------- | |
3602 | $ ls -a a | |
3603 | . .. | |
3604 | $ git submodule status | |
3605 | -d266b9873ad50488163457f025db7cdd9683d88b a | |
3606 | -e81d457da15309b4fef4249aba9b50187999670d b | |
3607 | -c1536a972b9affea0f16e0680ba87332dc059146 c | |
3608 | -d96249ff5d57de5de093e6baff9e0aafa5276a74 d | |
3609 | ------------------------------------------------- | |
3610 | ||
3611 | NOTE: The commit object names shown above would be different for you, but they | |
3612 | should match the HEAD commit object names of your repositories. You can check | |
3613 | it by running `git ls-remote ../a`. | |
3614 | ||
3615 | Pulling down the submodules is a two-step process. First run `git submodule | |
3616 | init` to add the submodule repository URLs to `.git/config`: | |
3617 | ||
3618 | ------------------------------------------------- | |
3619 | $ git submodule init | |
3620 | ------------------------------------------------- | |
3621 | ||
3622 | Now use `git submodule update` to clone the repositories and check out the | |
3623 | commits specified in the superproject: | |
3624 | ||
3625 | ------------------------------------------------- | |
3626 | $ git submodule update | |
3627 | $ cd a | |
3628 | $ ls -a | |
3629 | . .. .git a.txt | |
3630 | ------------------------------------------------- | |
3631 | ||
3632 | One major difference between `git submodule update` and `git submodule add` is | |
3633 | that `git submodule update` checks out a specific commit, rather than the tip | |
3634 | of a branch. It's like checking out a tag: the head is detached, so you're not | |
3635 | working on a branch. | |
3636 | ||
3637 | ------------------------------------------------- | |
3638 | $ git branch | |
3639 | * (no branch) | |
3640 | master | |
3641 | ------------------------------------------------- | |
3642 | ||
3643 | If you want to make a change within a submodule and you have a detached head, | |
3644 | then you should create or checkout a branch, make your changes, publish the | |
3645 | change within the submodule, and then update the superproject to reference the | |
3646 | new commit: | |
3647 | ||
3648 | ------------------------------------------------- | |
3649 | $ git checkout master | |
3650 | ------------------------------------------------- | |
3651 | ||
3652 | or | |
3653 | ||
3654 | ------------------------------------------------- | |
3655 | $ git checkout -b fix-up | |
3656 | ------------------------------------------------- | |
3657 | ||
3658 | then | |
3659 | ||
3660 | ------------------------------------------------- | |
3661 | $ echo "adding a line again" >> a.txt | |
3662 | $ git commit -a -m "Updated the submodule from within the superproject." | |
3663 | $ git push | |
3664 | $ cd .. | |
3665 | $ git diff | |
3666 | diff --git a/a b/a | |
3667 | index d266b98..261dfac 160000 | |
3668 | --- a/a | |
3669 | +++ b/a | |
3670 | @@ -1 +1 @@ | |
3671 | -Subproject commit d266b9873ad50488163457f025db7cdd9683d88b | |
3672 | +Subproject commit 261dfac35cb99d380eb966e102c1197139f7fa24 | |
3673 | $ git add a | |
3674 | $ git commit -m "Updated submodule a." | |
3675 | $ git push | |
3676 | ------------------------------------------------- | |
3677 | ||
3678 | You have to run `git submodule update` after `git pull` if you want to update | |
3679 | submodules, too. | |
3680 | ||
3681 | Pitfalls with submodules | |
3682 | ------------------------ | |
3683 | ||
3684 | Always publish the submodule change before publishing the change to the | |
3685 | superproject that references it. If you forget to publish the submodule change, | |
3686 | others won't be able to clone the repository: | |
3687 | ||
3688 | ------------------------------------------------- | |
3689 | $ cd ~/git/super/a | |
3690 | $ echo i added another line to this file >> a.txt | |
3691 | $ git commit -a -m "doing it wrong this time" | |
3692 | $ cd .. | |
3693 | $ git add a | |
3694 | $ git commit -m "Updated submodule a again." | |
3695 | $ git push | |
3696 | $ cd ~/git/cloned | |
3697 | $ git pull | |
3698 | $ git submodule update | |
3699 | error: pathspec '261dfac35cb99d380eb966e102c1197139f7fa24' did not match any file(s) known to git. | |
3700 | Did you forget to 'git add'? | |
3701 | Unable to checkout '261dfac35cb99d380eb966e102c1197139f7fa24' in submodule path 'a' | |
3702 | ------------------------------------------------- | |
3703 | ||
3704 | In older git versions it could be easily forgotten to commit new or modified | |
3705 | files in a submodule, which silently leads to similar problems as not pushing | |
3706 | the submodule changes. Starting with git 1.7.0 both "git status" and "git diff" | |
3707 | in the superproject show submodules as modified when they contain new or | |
3708 | modified files to protect against accidentally committing such a state. "git | |
3709 | diff" will also add a "-dirty" to the work tree side when generating patch | |
3710 | output or used with the --submodule option: | |
3711 | ||
3712 | ------------------------------------------------- | |
3713 | $ git diff | |
3714 | diff --git a/sub b/sub | |
3715 | --- a/sub | |
3716 | +++ b/sub | |
3717 | @@ -1 +1 @@ | |
3718 | -Subproject commit 3f356705649b5d566d97ff843cf193359229a453 | |
3719 | +Subproject commit 3f356705649b5d566d97ff843cf193359229a453-dirty | |
3720 | $ git diff --submodule | |
3721 | Submodule sub 3f35670..3f35670-dirty: | |
3722 | ------------------------------------------------- | |
3723 | ||
3724 | You also should not rewind branches in a submodule beyond commits that were | |
3725 | ever recorded in any superproject. | |
3726 | ||
3727 | It's not safe to run `git submodule update` if you've made and committed | |
3728 | changes within a submodule without checking out a branch first. They will be | |
3729 | silently overwritten: | |
3730 | ||
3731 | ------------------------------------------------- | |
3732 | $ cat a.txt | |
3733 | module a | |
3734 | $ echo line added from private2 >> a.txt | |
3735 | $ git commit -a -m "line added inside private2" | |
3736 | $ cd .. | |
3737 | $ git submodule update | |
3738 | Submodule path 'a': checked out 'd266b9873ad50488163457f025db7cdd9683d88b' | |
3739 | $ cd a | |
3740 | $ cat a.txt | |
3741 | module a | |
3742 | ------------------------------------------------- | |
3743 | ||
3744 | NOTE: The changes are still visible in the submodule's reflog. | |
3745 | ||
3746 | This is not the case if you did not commit your changes. | |
3747 | ||
3748 | [[low-level-operations]] | |
3749 | Low-level git operations | |
3750 | ======================== | |
3751 | ||
3752 | Many of the higher-level commands were originally implemented as shell | |
3753 | scripts using a smaller core of low-level git commands. These can still | |
3754 | be useful when doing unusual things with git, or just as a way to | |
3755 | understand its inner workings. | |
3756 | ||
3757 | [[object-manipulation]] | |
3758 | Object access and manipulation | |
3759 | ------------------------------ | |
3760 | ||
3761 | The linkgit:git-cat-file[1] command can show the contents of any object, | |
3762 | though the higher-level linkgit:git-show[1] is usually more useful. | |
3763 | ||
3764 | The linkgit:git-commit-tree[1] command allows constructing commits with | |
3765 | arbitrary parents and trees. | |
3766 | ||
3767 | A tree can be created with linkgit:git-write-tree[1] and its data can be | |
3768 | accessed by linkgit:git-ls-tree[1]. Two trees can be compared with | |
3769 | linkgit:git-diff-tree[1]. | |
3770 | ||
3771 | A tag is created with linkgit:git-mktag[1], and the signature can be | |
3772 | verified by linkgit:git-verify-tag[1], though it is normally simpler to | |
3773 | use linkgit:git-tag[1] for both. | |
3774 | ||
3775 | [[the-workflow]] | |
3776 | The Workflow | |
3777 | ------------ | |
3778 | ||
3779 | High-level operations such as linkgit:git-commit[1], | |
3780 | linkgit:git-checkout[1] and linkgit:git-reset[1] work by moving data | |
3781 | between the working tree, the index, and the object database. Git | |
3782 | provides low-level operations which perform each of these steps | |
3783 | individually. | |
3784 | ||
3785 | Generally, all "git" operations work on the index file. Some operations | |
3786 | work *purely* on the index file (showing the current state of the | |
3787 | index), but most operations move data between the index file and either | |
3788 | the database or the working directory. Thus there are four main | |
3789 | combinations: | |
3790 | ||
3791 | [[working-directory-to-index]] | |
3792 | working directory -> index | |
3793 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3794 | ||
3795 | The linkgit:git-update-index[1] command updates the index with | |
3796 | information from the working directory. You generally update the | |
3797 | index information by just specifying the filename you want to update, | |
3798 | like so: | |
3799 | ||
3800 | ------------------------------------------------- | |
3801 | $ git update-index filename | |
3802 | ------------------------------------------------- | |
3803 | ||
3804 | but to avoid common mistakes with filename globbing etc, the command | |
3805 | will not normally add totally new entries or remove old entries, | |
3806 | i.e. it will normally just update existing cache entries. | |
3807 | ||
3808 | To tell git that yes, you really do realize that certain files no | |
3809 | longer exist, or that new files should be added, you | |
3810 | should use the `--remove` and `--add` flags respectively. | |
3811 | ||
3812 | NOTE! A `--remove` flag does 'not' mean that subsequent filenames will | |
3813 | necessarily be removed: if the files still exist in your directory | |
3814 | structure, the index will be updated with their new status, not | |
3815 | removed. The only thing `--remove` means is that update-index will be | |
3816 | considering a removed file to be a valid thing, and if the file really | |
3817 | does not exist any more, it will update the index accordingly. | |
3818 | ||
3819 | As a special case, you can also do `git update-index --refresh`, which | |
3820 | will refresh the "stat" information of each index to match the current | |
3821 | stat information. It will 'not' update the object status itself, and | |
3822 | it will only update the fields that are used to quickly test whether | |
3823 | an object still matches its old backing store object. | |
3824 | ||
3825 | The previously introduced linkgit:git-add[1] is just a wrapper for | |
3826 | linkgit:git-update-index[1]. | |
3827 | ||
3828 | [[index-to-object-database]] | |
3829 | index -> object database | |
3830 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
3831 | ||
3832 | You write your current index file to a "tree" object with the program | |
3833 | ||
3834 | ------------------------------------------------- | |
3835 | $ git write-tree | |
3836 | ------------------------------------------------- | |
3837 | ||
3838 | that doesn't come with any options--it will just write out the | |
3839 | current index into the set of tree objects that describe that state, | |
3840 | and it will return the name of the resulting top-level tree. You can | |
3841 | use that tree to re-generate the index at any time by going in the | |
3842 | other direction: | |
3843 | ||
3844 | [[object-database-to-index]] | |
3845 | object database -> index | |
3846 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
3847 | ||
3848 | You read a "tree" file from the object database, and use that to | |
3849 | populate (and overwrite--don't do this if your index contains any | |
3850 | unsaved state that you might want to restore later!) your current | |
3851 | index. Normal operation is just | |
3852 | ||
3853 | ------------------------------------------------- | |
3854 | $ git read-tree <SHA-1 of tree> | |
3855 | ------------------------------------------------- | |
3856 | ||
3857 | and your index file will now be equivalent to the tree that you saved | |
3858 | earlier. However, that is only your 'index' file: your working | |
3859 | directory contents have not been modified. | |
3860 | ||
3861 | [[index-to-working-directory]] | |
3862 | index -> working directory | |
3863 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3864 | ||
3865 | You update your working directory from the index by "checking out" | |
3866 | files. This is not a very common operation, since normally you'd just | |
3867 | keep your files updated, and rather than write to your working | |
3868 | directory, you'd tell the index files about the changes in your | |
3869 | working directory (i.e. `git update-index`). | |
3870 | ||
3871 | However, if you decide to jump to a new version, or check out somebody | |
3872 | else's version, or just restore a previous tree, you'd populate your | |
3873 | index file with read-tree, and then you need to check out the result | |
3874 | with | |
3875 | ||
3876 | ------------------------------------------------- | |
3877 | $ git checkout-index filename | |
3878 | ------------------------------------------------- | |
3879 | ||
3880 | or, if you want to check out all of the index, use `-a`. | |
3881 | ||
3882 | NOTE! `git checkout-index` normally refuses to overwrite old files, so | |
3883 | if you have an old version of the tree already checked out, you will | |
3884 | need to use the "-f" flag ('before' the "-a" flag or the filename) to | |
3885 | 'force' the checkout. | |
3886 | ||
3887 | ||
3888 | Finally, there are a few odds and ends which are not purely moving | |
3889 | from one representation to the other: | |
3890 | ||
3891 | [[tying-it-all-together]] | |
3892 | Tying it all together | |
3893 | ~~~~~~~~~~~~~~~~~~~~~ | |
3894 | ||
3895 | To commit a tree you have instantiated with "git write-tree", you'd | |
3896 | create a "commit" object that refers to that tree and the history | |
3897 | behind it--most notably the "parent" commits that preceded it in | |
3898 | history. | |
3899 | ||
3900 | Normally a "commit" has one parent: the previous state of the tree | |
3901 | before a certain change was made. However, sometimes it can have two | |
3902 | or more parent commits, in which case we call it a "merge", due to the | |
3903 | fact that such a commit brings together ("merges") two or more | |
3904 | previous states represented by other commits. | |
3905 | ||
3906 | In other words, while a "tree" represents a particular directory state | |
3907 | of a working directory, a "commit" represents that state in "time", | |
3908 | and explains how we got there. | |
3909 | ||
3910 | You create a commit object by giving it the tree that describes the | |
3911 | state at the time of the commit, and a list of parents: | |
3912 | ||
3913 | ------------------------------------------------- | |
3914 | $ git commit-tree <tree> -p <parent> [(-p <parent2>)...] | |
3915 | ------------------------------------------------- | |
3916 | ||
3917 | and then giving the reason for the commit on stdin (either through | |
3918 | redirection from a pipe or file, or by just typing it at the tty). | |
3919 | ||
3920 | `git commit-tree` will return the name of the object that represents | |
3921 | that commit, and you should save it away for later use. Normally, | |
3922 | you'd commit a new `HEAD` state, and while git doesn't care where you | |
3923 | save the note about that state, in practice we tend to just write the | |
3924 | result to the file pointed at by `.git/HEAD`, so that we can always see | |
3925 | what the last committed state was. | |
3926 | ||
3927 | Here is an ASCII art by Jon Loeliger that illustrates how | |
3928 | various pieces fit together. | |
3929 | ||
3930 | ------------ | |
3931 | ||
3932 | commit-tree | |
3933 | commit obj | |
3934 | +----+ | |
3935 | | | | |
3936 | | | | |
3937 | V V | |
3938 | +-----------+ | |
3939 | | Object DB | | |
3940 | | Backing | | |
3941 | | Store | | |
3942 | +-----------+ | |
3943 | ^ | |
3944 | write-tree | | | |
3945 | tree obj | | | |
3946 | | | read-tree | |
3947 | | | tree obj | |
3948 | V | |
3949 | +-----------+ | |
3950 | | Index | | |
3951 | | "cache" | | |
3952 | +-----------+ | |
3953 | update-index ^ | |
3954 | blob obj | | | |
3955 | | | | |
3956 | checkout-index -u | | checkout-index | |
3957 | stat | | blob obj | |
3958 | V | |
3959 | +-----------+ | |
3960 | | Working | | |
3961 | | Directory | | |
3962 | +-----------+ | |
3963 | ||
3964 | ------------ | |
3965 | ||
3966 | ||
3967 | [[examining-the-data]] | |
3968 | Examining the data | |
3969 | ------------------ | |
3970 | ||
3971 | You can examine the data represented in the object database and the | |
3972 | index with various helper tools. For every object, you can use | |
3973 | linkgit:git-cat-file[1] to examine details about the | |
3974 | object: | |
3975 | ||
3976 | ------------------------------------------------- | |
3977 | $ git cat-file -t <objectname> | |
3978 | ------------------------------------------------- | |
3979 | ||
3980 | shows the type of the object, and once you have the type (which is | |
3981 | usually implicit in where you find the object), you can use | |
3982 | ||
3983 | ------------------------------------------------- | |
3984 | $ git cat-file blob|tree|commit|tag <objectname> | |
3985 | ------------------------------------------------- | |
3986 | ||
3987 | to show its contents. NOTE! Trees have binary content, and as a result | |
3988 | there is a special helper for showing that content, called | |
3989 | `git ls-tree`, which turns the binary content into a more easily | |
3990 | readable form. | |
3991 | ||
3992 | It's especially instructive to look at "commit" objects, since those | |
3993 | tend to be small and fairly self-explanatory. In particular, if you | |
3994 | follow the convention of having the top commit name in `.git/HEAD`, | |
3995 | you can do | |
3996 | ||
3997 | ------------------------------------------------- | |
3998 | $ git cat-file commit HEAD | |
3999 | ------------------------------------------------- | |
4000 | ||
4001 | to see what the top commit was. | |
4002 | ||
4003 | [[merging-multiple-trees]] | |
4004 | Merging multiple trees | |
4005 | ---------------------- | |
4006 | ||
4007 | Git helps you do a three-way merge, which you can expand to n-way by | |
4008 | repeating the merge procedure arbitrary times until you finally | |
4009 | "commit" the state. The normal situation is that you'd only do one | |
4010 | three-way merge (two parents), and commit it, but if you like to, you | |
4011 | can do multiple parents in one go. | |
4012 | ||
4013 | To do a three-way merge, you need the two sets of "commit" objects | |
4014 | that you want to merge, use those to find the closest common parent (a | |
4015 | third "commit" object), and then use those commit objects to find the | |
4016 | state of the directory ("tree" object) at these points. | |
4017 | ||
4018 | To get the "base" for the merge, you first look up the common parent | |
4019 | of two commits with | |
4020 | ||
4021 | ------------------------------------------------- | |
4022 | $ git merge-base <commit1> <commit2> | |
4023 | ------------------------------------------------- | |
4024 | ||
4025 | which will return you the commit they are both based on. You should | |
4026 | now look up the "tree" objects of those commits, which you can easily | |
4027 | do with (for example) | |
4028 | ||
4029 | ------------------------------------------------- | |
4030 | $ git cat-file commit <commitname> | head -1 | |
4031 | ------------------------------------------------- | |
4032 | ||
4033 | since the tree object information is always the first line in a commit | |
4034 | object. | |
4035 | ||
4036 | Once you know the three trees you are going to merge (the one "original" | |
4037 | tree, aka the common tree, and the two "result" trees, aka the branches | |
4038 | you want to merge), you do a "merge" read into the index. This will | |
4039 | complain if it has to throw away your old index contents, so you should | |
4040 | make sure that you've committed those--in fact you would normally | |
4041 | always do a merge against your last commit (which should thus match what | |
4042 | you have in your current index anyway). | |
4043 | ||
4044 | To do the merge, do | |
4045 | ||
4046 | ------------------------------------------------- | |
4047 | $ git read-tree -m -u <origtree> <yourtree> <targettree> | |
4048 | ------------------------------------------------- | |
4049 | ||
4050 | which will do all trivial merge operations for you directly in the | |
4051 | index file, and you can just write the result out with | |
4052 | `git write-tree`. | |
4053 | ||
4054 | ||
4055 | [[merging-multiple-trees-2]] | |
4056 | Merging multiple trees, continued | |
4057 | --------------------------------- | |
4058 | ||
4059 | Sadly, many merges aren't trivial. If there are files that have | |
4060 | been added, moved or removed, or if both branches have modified the | |
4061 | same file, you will be left with an index tree that contains "merge | |
4062 | entries" in it. Such an index tree can 'NOT' be written out to a tree | |
4063 | object, and you will have to resolve any such merge clashes using | |
4064 | other tools before you can write out the result. | |
4065 | ||
4066 | You can examine such index state with `git ls-files --unmerged` | |
4067 | command. An example: | |
4068 | ||
4069 | ------------------------------------------------ | |
4070 | $ git read-tree -m $orig HEAD $target | |
4071 | $ git ls-files --unmerged | |
4072 | 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c | |
4073 | 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c | |
4074 | 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c | |
4075 | ------------------------------------------------ | |
4076 | ||
4077 | Each line of the `git ls-files --unmerged` output begins with | |
4078 | the blob mode bits, blob SHA-1, 'stage number', and the | |
4079 | filename. The 'stage number' is git's way to say which tree it | |
4080 | came from: stage 1 corresponds to the `$orig` tree, stage 2 to | |
4081 | the `HEAD` tree, and stage 3 to the `$target` tree. | |
4082 | ||
4083 | Earlier we said that trivial merges are done inside | |
4084 | `git read-tree -m`. For example, if the file did not change | |
4085 | from `$orig` to `HEAD` nor `$target`, or if the file changed | |
4086 | from `$orig` to `HEAD` and `$orig` to `$target` the same way, | |
4087 | obviously the final outcome is what is in `HEAD`. What the | |
4088 | above example shows is that file `hello.c` was changed from | |
4089 | `$orig` to `HEAD` and `$orig` to `$target` in a different way. | |
4090 | You could resolve this by running your favorite 3-way merge | |
4091 | program, e.g. `diff3`, `merge`, or git's own merge-file, on | |
4092 | the blob objects from these three stages yourself, like this: | |
4093 | ||
4094 | ------------------------------------------------ | |
4095 | $ git cat-file blob 263414f... >hello.c~1 | |
4096 | $ git cat-file blob 06fa6a2... >hello.c~2 | |
4097 | $ git cat-file blob cc44c73... >hello.c~3 | |
4098 | $ git merge-file hello.c~2 hello.c~1 hello.c~3 | |
4099 | ------------------------------------------------ | |
4100 | ||
4101 | This would leave the merge result in `hello.c~2` file, along | |
4102 | with conflict markers if there are conflicts. After verifying | |
4103 | the merge result makes sense, you can tell git what the final | |
4104 | merge result for this file is by: | |
4105 | ||
4106 | ------------------------------------------------- | |
4107 | $ mv -f hello.c~2 hello.c | |
4108 | $ git update-index hello.c | |
4109 | ------------------------------------------------- | |
4110 | ||
4111 | When a path is in the "unmerged" state, running `git update-index` for | |
4112 | that path tells git to mark the path resolved. | |
4113 | ||
4114 | The above is the description of a git merge at the lowest level, | |
4115 | to help you understand what conceptually happens under the hood. | |
4116 | In practice, nobody, not even git itself, runs `git cat-file` three times | |
4117 | for this. There is a `git merge-index` program that extracts the | |
4118 | stages to temporary files and calls a "merge" script on it: | |
4119 | ||
4120 | ------------------------------------------------- | |
4121 | $ git merge-index git-merge-one-file hello.c | |
4122 | ------------------------------------------------- | |
4123 | ||
4124 | and that is what higher level `git merge -s resolve` is implemented with. | |
4125 | ||
4126 | [[hacking-git]] | |
4127 | Hacking git | |
4128 | =========== | |
4129 | ||
4130 | This chapter covers internal details of the git implementation which | |
4131 | probably only git developers need to understand. | |
4132 | ||
4133 | [[object-details]] | |
4134 | Object storage format | |
4135 | --------------------- | |
4136 | ||
4137 | All objects have a statically determined "type" which identifies the | |
4138 | format of the object (i.e. how it is used, and how it can refer to other | |
4139 | objects). There are currently four different object types: "blob", | |
4140 | "tree", "commit", and "tag". | |
4141 | ||
4142 | Regardless of object type, all objects share the following | |
4143 | characteristics: they are all deflated with zlib, and have a header | |
4144 | that not only specifies their type, but also provides size information | |
4145 | about the data in the object. It's worth noting that the SHA-1 hash | |
4146 | that is used to name the object is the hash of the original data | |
4147 | plus this header, so `sha1sum` 'file' does not match the object name | |
4148 | for 'file'. | |
4149 | (Historical note: in the dawn of the age of git the hash | |
4150 | was the SHA-1 of the 'compressed' object.) | |
4151 | ||
4152 | As a result, the general consistency of an object can always be tested | |
4153 | independently of the contents or the type of the object: all objects can | |
4154 | be validated by verifying that (a) their hashes match the content of the | |
4155 | file and (b) the object successfully inflates to a stream of bytes that | |
4156 | forms a sequence of <ascii type without space> {plus} <space> {plus} <ascii decimal | |
4157 | size> {plus} <byte\0> {plus} <binary object data>. | |
4158 | ||
4159 | The structured objects can further have their structure and | |
4160 | connectivity to other objects verified. This is generally done with | |
4161 | the `git fsck` program, which generates a full dependency graph | |
4162 | of all objects, and verifies their internal consistency (in addition | |
4163 | to just verifying their superficial consistency through the hash). | |
4164 | ||
4165 | [[birdview-on-the-source-code]] | |
4166 | A birds-eye view of Git's source code | |
4167 | ------------------------------------- | |
4168 | ||
4169 | It is not always easy for new developers to find their way through Git's | |
4170 | source code. This section gives you a little guidance to show where to | |
4171 | start. | |
4172 | ||
4173 | A good place to start is with the contents of the initial commit, with: | |
4174 | ||
4175 | ---------------------------------------------------- | |
4176 | $ git checkout e83c5163 | |
4177 | ---------------------------------------------------- | |
4178 | ||
4179 | The initial revision lays the foundation for almost everything git has | |
4180 | today, but is small enough to read in one sitting. | |
4181 | ||
4182 | Note that terminology has changed since that revision. For example, the | |
4183 | README in that revision uses the word "changeset" to describe what we | |
4184 | now call a <<def_commit_object,commit>>. | |
4185 | ||
4186 | Also, we do not call it "cache" any more, but rather "index"; however, the | |
4187 | file is still called `cache.h`. Remark: Not much reason to change it now, | |
4188 | especially since there is no good single name for it anyway, because it is | |
4189 | basically _the_ header file which is included by _all_ of Git's C sources. | |
4190 | ||
4191 | If you grasp the ideas in that initial commit, you should check out a | |
4192 | more recent version and skim `cache.h`, `object.h` and `commit.h`. | |
4193 | ||
4194 | In the early days, Git (in the tradition of UNIX) was a bunch of programs | |
4195 | which were extremely simple, and which you used in scripts, piping the | |
4196 | output of one into another. This turned out to be good for initial | |
4197 | development, since it was easier to test new things. However, recently | |
4198 | many of these parts have become builtins, and some of the core has been | |
4199 | "libified", i.e. put into libgit.a for performance, portability reasons, | |
4200 | and to avoid code duplication. | |
4201 | ||
4202 | By now, you know what the index is (and find the corresponding data | |
4203 | structures in `cache.h`), and that there are just a couple of object types | |
4204 | (blobs, trees, commits and tags) which inherit their common structure from | |
4205 | `struct object`, which is their first member (and thus, you can cast e.g. | |
4206 | `(struct object *)commit` to achieve the _same_ as `&commit->object`, i.e. | |
4207 | get at the object name and flags). | |
4208 | ||
4209 | Now is a good point to take a break to let this information sink in. | |
4210 | ||
4211 | Next step: get familiar with the object naming. Read <<naming-commits>>. | |
4212 | There are quite a few ways to name an object (and not only revisions!). | |
4213 | All of these are handled in `sha1_name.c`. Just have a quick look at | |
4214 | the function `get_sha1()`. A lot of the special handling is done by | |
4215 | functions like `get_sha1_basic()` or the likes. | |
4216 | ||
4217 | This is just to get you into the groove for the most libified part of Git: | |
4218 | the revision walker. | |
4219 | ||
4220 | Basically, the initial version of `git log` was a shell script: | |
4221 | ||
4222 | ---------------------------------------------------------------- | |
4223 | $ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \ | |
4224 | LESS=-S ${PAGER:-less} | |
4225 | ---------------------------------------------------------------- | |
4226 | ||
4227 | What does this mean? | |
4228 | ||
4229 | `git rev-list` is the original version of the revision walker, which | |
4230 | _always_ printed a list of revisions to stdout. It is still functional, | |
4231 | and needs to, since most new Git commands start out as scripts using | |
4232 | `git rev-list`. | |
4233 | ||
4234 | `git rev-parse` is not as important any more; it was only used to filter out | |
4235 | options that were relevant for the different plumbing commands that were | |
4236 | called by the script. | |
4237 | ||
4238 | Most of what `git rev-list` did is contained in `revision.c` and | |
4239 | `revision.h`. It wraps the options in a struct named `rev_info`, which | |
4240 | controls how and what revisions are walked, and more. | |
4241 | ||
4242 | The original job of `git rev-parse` is now taken by the function | |
4243 | `setup_revisions()`, which parses the revisions and the common command line | |
4244 | options for the revision walker. This information is stored in the struct | |
4245 | `rev_info` for later consumption. You can do your own command line option | |
4246 | parsing after calling `setup_revisions()`. After that, you have to call | |
4247 | `prepare_revision_walk()` for initialization, and then you can get the | |
4248 | commits one by one with the function `get_revision()`. | |
4249 | ||
4250 | If you are interested in more details of the revision walking process, | |
4251 | just have a look at the first implementation of `cmd_log()`; call | |
4252 | `git show v1.3.0~155^2~4` and scroll down to that function (note that you | |
4253 | no longer need to call `setup_pager()` directly). | |
4254 | ||
4255 | Nowadays, `git log` is a builtin, which means that it is _contained_ in the | |
4256 | command `git`. The source side of a builtin is | |
4257 | ||
4258 | - a function called `cmd_<bla>`, typically defined in `builtin-<bla>.c`, | |
4259 | and declared in `builtin.h`, | |
4260 | ||
4261 | - an entry in the `commands[]` array in `git.c`, and | |
4262 | ||
4263 | - an entry in `BUILTIN_OBJECTS` in the `Makefile`. | |
4264 | ||
4265 | Sometimes, more than one builtin is contained in one source file. For | |
4266 | example, `cmd_whatchanged()` and `cmd_log()` both reside in `builtin-log.c`, | |
4267 | since they share quite a bit of code. In that case, the commands which are | |
4268 | _not_ named like the `.c` file in which they live have to be listed in | |
4269 | `BUILT_INS` in the `Makefile`. | |
4270 | ||
4271 | `git log` looks more complicated in C than it does in the original script, | |
4272 | but that allows for a much greater flexibility and performance. | |
4273 | ||
4274 | Here again it is a good point to take a pause. | |
4275 | ||
4276 | Lesson three is: study the code. Really, it is the best way to learn about | |
4277 | the organization of Git (after you know the basic concepts). | |
4278 | ||
4279 | So, think about something which you are interested in, say, "how can I | |
4280 | access a blob just knowing the object name of it?". The first step is to | |
4281 | find a Git command with which you can do it. In this example, it is either | |
4282 | `git show` or `git cat-file`. | |
4283 | ||
4284 | For the sake of clarity, let's stay with `git cat-file`, because it | |
4285 | ||
4286 | - is plumbing, and | |
4287 | ||
4288 | - was around even in the initial commit (it literally went only through | |
4289 | some 20 revisions as `cat-file.c`, was renamed to `builtin-cat-file.c` | |
4290 | when made a builtin, and then saw less than 10 versions). | |
4291 | ||
4292 | So, look into `builtin-cat-file.c`, search for `cmd_cat_file()` and look what | |
4293 | it does. | |
4294 | ||
4295 | ------------------------------------------------------------------ | |
4296 | git_config(git_default_config); | |
4297 | if (argc != 3) | |
4298 | usage("git cat-file [-t|-s|-e|-p|<type>] <sha1>"); | |
4299 | if (get_sha1(argv[2], sha1)) | |
4300 | die("Not a valid object name %s", argv[2]); | |
4301 | ------------------------------------------------------------------ | |
4302 | ||
4303 | Let's skip over the obvious details; the only really interesting part | |
4304 | here is the call to `get_sha1()`. It tries to interpret `argv[2]` as an | |
4305 | object name, and if it refers to an object which is present in the current | |
4306 | repository, it writes the resulting SHA-1 into the variable `sha1`. | |
4307 | ||
4308 | Two things are interesting here: | |
4309 | ||
4310 | - `get_sha1()` returns 0 on _success_. This might surprise some new | |
4311 | Git hackers, but there is a long tradition in UNIX to return different | |
4312 | negative numbers in case of different errors--and 0 on success. | |
4313 | ||
4314 | - the variable `sha1` in the function signature of `get_sha1()` is `unsigned | |
4315 | char *`, but is actually expected to be a pointer to `unsigned | |
4316 | char[20]`. This variable will contain the 160-bit SHA-1 of the given | |
4317 | commit. Note that whenever a SHA-1 is passed as `unsigned char *`, it | |
4318 | is the binary representation, as opposed to the ASCII representation in | |
4319 | hex characters, which is passed as `char *`. | |
4320 | ||
4321 | You will see both of these things throughout the code. | |
4322 | ||
4323 | Now, for the meat: | |
4324 | ||
4325 | ----------------------------------------------------------------------------- | |
4326 | case 0: | |
4327 | buf = read_object_with_reference(sha1, argv[1], &size, NULL); | |
4328 | ----------------------------------------------------------------------------- | |
4329 | ||
4330 | This is how you read a blob (actually, not only a blob, but any type of | |
4331 | object). To know how the function `read_object_with_reference()` actually | |
4332 | works, find the source code for it (something like `git grep | |
4333 | read_object_with | grep ":[a-z]"` in the git repository), and read | |
4334 | the source. | |
4335 | ||
4336 | To find out how the result can be used, just read on in `cmd_cat_file()`: | |
4337 | ||
4338 | ----------------------------------- | |
4339 | write_or_die(1, buf, size); | |
4340 | ----------------------------------- | |
4341 | ||
4342 | Sometimes, you do not know where to look for a feature. In many such cases, | |
4343 | it helps to search through the output of `git log`, and then `git show` the | |
4344 | corresponding commit. | |
4345 | ||
4346 | Example: If you know that there was some test case for `git bundle`, but | |
4347 | do not remember where it was (yes, you _could_ `git grep bundle t/`, but that | |
4348 | does not illustrate the point!): | |
4349 | ||
4350 | ------------------------ | |
4351 | $ git log --no-merges t/ | |
4352 | ------------------------ | |
4353 | ||
4354 | In the pager (`less`), just search for "bundle", go a few lines back, | |
4355 | and see that it is in commit 18449ab0... Now just copy this object name, | |
4356 | and paste it into the command line | |
4357 | ||
4358 | ------------------- | |
4359 | $ git show 18449ab0 | |
4360 | ------------------- | |
4361 | ||
4362 | Voila. | |
4363 | ||
4364 | Another example: Find out what to do in order to make some script a | |
4365 | builtin: | |
4366 | ||
4367 | ------------------------------------------------- | |
4368 | $ git log --no-merges --diff-filter=A builtin-*.c | |
4369 | ------------------------------------------------- | |
4370 | ||
4371 | You see, Git is actually the best tool to find out about the source of Git | |
4372 | itself! | |
4373 | ||
4374 | [[glossary]] | |
4375 | Git Glossary | |
4376 | ============ | |
4377 | ||
4378 | include::glossary-content.txt[] | |
4379 | ||
4380 | [[git-quick-start]] | |
4381 | Appendix A: Git Quick Reference | |
4382 | =============================== | |
4383 | ||
4384 | This is a quick summary of the major commands; the previous chapters | |
4385 | explain how these work in more detail. | |
4386 | ||
4387 | [[quick-creating-a-new-repository]] | |
4388 | Creating a new repository | |
4389 | ------------------------- | |
4390 | ||
4391 | From a tarball: | |
4392 | ||
4393 | ----------------------------------------------- | |
4394 | $ tar xzf project.tar.gz | |
4395 | $ cd project | |
4396 | $ git init | |
4397 | Initialized empty Git repository in .git/ | |
4398 | $ git add . | |
4399 | $ git commit | |
4400 | ----------------------------------------------- | |
4401 | ||
4402 | From a remote repository: | |
4403 | ||
4404 | ----------------------------------------------- | |
4405 | $ git clone git://example.com/pub/project.git | |
4406 | $ cd project | |
4407 | ----------------------------------------------- | |
4408 | ||
4409 | [[managing-branches]] | |
4410 | Managing branches | |
4411 | ----------------- | |
4412 | ||
4413 | ----------------------------------------------- | |
4414 | $ git branch # list all local branches in this repo | |
4415 | $ git checkout test # switch working directory to branch "test" | |
4416 | $ git branch new # create branch "new" starting at current HEAD | |
4417 | $ git branch -d new # delete branch "new" | |
4418 | ----------------------------------------------- | |
4419 | ||
4420 | Instead of basing a new branch on current HEAD (the default), use: | |
4421 | ||
4422 | ----------------------------------------------- | |
4423 | $ git branch new test # branch named "test" | |
4424 | $ git branch new v2.6.15 # tag named v2.6.15 | |
4425 | $ git branch new HEAD^ # commit before the most recent | |
4426 | $ git branch new HEAD^^ # commit before that | |
4427 | $ git branch new test~10 # ten commits before tip of branch "test" | |
4428 | ----------------------------------------------- | |
4429 | ||
4430 | Create and switch to a new branch at the same time: | |
4431 | ||
4432 | ----------------------------------------------- | |
4433 | $ git checkout -b new v2.6.15 | |
4434 | ----------------------------------------------- | |
4435 | ||
4436 | Update and examine branches from the repository you cloned from: | |
4437 | ||
4438 | ----------------------------------------------- | |
4439 | $ git fetch # update | |
4440 | $ git branch -r # list | |
4441 | origin/master | |
4442 | origin/next | |
4443 | ... | |
4444 | $ git checkout -b masterwork origin/master | |
4445 | ----------------------------------------------- | |
4446 | ||
4447 | Fetch a branch from a different repository, and give it a new | |
4448 | name in your repository: | |
4449 | ||
4450 | ----------------------------------------------- | |
4451 | $ git fetch git://example.com/project.git theirbranch:mybranch | |
4452 | $ git fetch git://example.com/project.git v2.6.15:mybranch | |
4453 | ----------------------------------------------- | |
4454 | ||
4455 | Keep a list of repositories you work with regularly: | |
4456 | ||
4457 | ----------------------------------------------- | |
4458 | $ git remote add example git://example.com/project.git | |
4459 | $ git remote # list remote repositories | |
4460 | example | |
4461 | origin | |
4462 | $ git remote show example # get details | |
4463 | * remote example | |
4464 | URL: git://example.com/project.git | |
4465 | Tracked remote branches | |
4466 | master | |
4467 | next | |
4468 | ... | |
4469 | $ git fetch example # update branches from example | |
4470 | $ git branch -r # list all remote branches | |
4471 | ----------------------------------------------- | |
4472 | ||
4473 | ||
4474 | [[exploring-history]] | |
4475 | Exploring history | |
4476 | ----------------- | |
4477 | ||
4478 | ----------------------------------------------- | |
4479 | $ gitk # visualize and browse history | |
4480 | $ git log # list all commits | |
4481 | $ git log src/ # ...modifying src/ | |
4482 | $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15 | |
4483 | $ git log master..test # ...in branch test, not in branch master | |
4484 | $ git log test..master # ...in branch master, but not in test | |
4485 | $ git log test...master # ...in one branch, not in both | |
4486 | $ git log -S'foo()' # ...where difference contain "foo()" | |
4487 | $ git log --since="2 weeks ago" | |
4488 | $ git log -p # show patches as well | |
4489 | $ git show # most recent commit | |
4490 | $ git diff v2.6.15..v2.6.16 # diff between two tagged versions | |
4491 | $ git diff v2.6.15..HEAD # diff with current head | |
4492 | $ git grep "foo()" # search working directory for "foo()" | |
4493 | $ git grep v2.6.15 "foo()" # search old tree for "foo()" | |
4494 | $ git show v2.6.15:a.txt # look at old version of a.txt | |
4495 | ----------------------------------------------- | |
4496 | ||
4497 | Search for regressions: | |
4498 | ||
4499 | ----------------------------------------------- | |
4500 | $ git bisect start | |
4501 | $ git bisect bad # current version is bad | |
4502 | $ git bisect good v2.6.13-rc2 # last known good revision | |
4503 | Bisecting: 675 revisions left to test after this | |
4504 | # test here, then: | |
4505 | $ git bisect good # if this revision is good, or | |
4506 | $ git bisect bad # if this revision is bad. | |
4507 | # repeat until done. | |
4508 | ----------------------------------------------- | |
4509 | ||
4510 | [[making-changes]] | |
4511 | Making changes | |
4512 | -------------- | |
4513 | ||
4514 | Make sure git knows who to blame: | |
4515 | ||
4516 | ------------------------------------------------ | |
4517 | $ cat >>~/.gitconfig <<\EOF | |
4518 | [user] | |
4519 | name = Your Name Comes Here | |
4520 | email = you@yourdomain.example.com | |
4521 | EOF | |
4522 | ------------------------------------------------ | |
4523 | ||
4524 | Select file contents to include in the next commit, then make the | |
4525 | commit: | |
4526 | ||
4527 | ----------------------------------------------- | |
4528 | $ git add a.txt # updated file | |
4529 | $ git add b.txt # new file | |
4530 | $ git rm c.txt # old file | |
4531 | $ git commit | |
4532 | ----------------------------------------------- | |
4533 | ||
4534 | Or, prepare and create the commit in one step: | |
4535 | ||
4536 | ----------------------------------------------- | |
4537 | $ git commit d.txt # use latest content only of d.txt | |
4538 | $ git commit -a # use latest content of all tracked files | |
4539 | ----------------------------------------------- | |
4540 | ||
4541 | [[merging]] | |
4542 | Merging | |
4543 | ------- | |
4544 | ||
4545 | ----------------------------------------------- | |
4546 | $ git merge test # merge branch "test" into the current branch | |
4547 | $ git pull git://example.com/project.git master | |
4548 | # fetch and merge in remote branch | |
4549 | $ git pull . test # equivalent to git merge test | |
4550 | ----------------------------------------------- | |
4551 | ||
4552 | [[sharing-your-changes]] | |
4553 | Sharing your changes | |
4554 | -------------------- | |
4555 | ||
4556 | Importing or exporting patches: | |
4557 | ||
4558 | ----------------------------------------------- | |
4559 | $ git format-patch origin..HEAD # format a patch for each commit | |
4560 | # in HEAD but not in origin | |
4561 | $ git am mbox # import patches from the mailbox "mbox" | |
4562 | ----------------------------------------------- | |
4563 | ||
4564 | Fetch a branch in a different git repository, then merge into the | |
4565 | current branch: | |
4566 | ||
4567 | ----------------------------------------------- | |
4568 | $ git pull git://example.com/project.git theirbranch | |
4569 | ----------------------------------------------- | |
4570 | ||
4571 | Store the fetched branch into a local branch before merging into the | |
4572 | current branch: | |
4573 | ||
4574 | ----------------------------------------------- | |
4575 | $ git pull git://example.com/project.git theirbranch:mybranch | |
4576 | ----------------------------------------------- | |
4577 | ||
4578 | After creating commits on a local branch, update the remote | |
4579 | branch with your commits: | |
4580 | ||
4581 | ----------------------------------------------- | |
4582 | $ git push ssh://example.com/project.git mybranch:theirbranch | |
4583 | ----------------------------------------------- | |
4584 | ||
4585 | When remote and local branch are both named "test": | |
4586 | ||
4587 | ----------------------------------------------- | |
4588 | $ git push ssh://example.com/project.git test | |
4589 | ----------------------------------------------- | |
4590 | ||
4591 | Shortcut version for a frequently used remote repository: | |
4592 | ||
4593 | ----------------------------------------------- | |
4594 | $ git remote add example ssh://example.com/project.git | |
4595 | $ git push example test | |
4596 | ----------------------------------------------- | |
4597 | ||
4598 | [[repository-maintenance]] | |
4599 | Repository maintenance | |
4600 | ---------------------- | |
4601 | ||
4602 | Check for corruption: | |
4603 | ||
4604 | ----------------------------------------------- | |
4605 | $ git fsck | |
4606 | ----------------------------------------------- | |
4607 | ||
4608 | Recompress, remove unused cruft: | |
4609 | ||
4610 | ----------------------------------------------- | |
4611 | $ git gc | |
4612 | ----------------------------------------------- | |
4613 | ||
4614 | ||
4615 | [[todo]] | |
4616 | Appendix B: Notes and todo list for this manual | |
4617 | =============================================== | |
4618 | ||
4619 | This is a work in progress. | |
4620 | ||
4621 | The basic requirements: | |
4622 | ||
4623 | - It must be readable in order, from beginning to end, by someone | |
4624 | intelligent with a basic grasp of the UNIX command line, but without | |
4625 | any special knowledge of git. If necessary, any other prerequisites | |
4626 | should be specifically mentioned as they arise. | |
4627 | - Whenever possible, section headings should clearly describe the task | |
4628 | they explain how to do, in language that requires no more knowledge | |
4629 | than necessary: for example, "importing patches into a project" rather | |
4630 | than "the `git am` command" | |
4631 | ||
4632 | Think about how to create a clear chapter dependency graph that will | |
4633 | allow people to get to important topics without necessarily reading | |
4634 | everything in between. | |
4635 | ||
4636 | Scan Documentation/ for other stuff left out; in particular: | |
4637 | ||
4638 | - howto's | |
4639 | - some of technical/? | |
4640 | - hooks | |
4641 | - list of commands in linkgit:git[1] | |
4642 | ||
4643 | Scan email archives for other stuff left out | |
4644 | ||
4645 | Scan man pages to see if any assume more background than this manual | |
4646 | provides. | |
4647 | ||
4648 | Simplify beginning by suggesting disconnected head instead of | |
4649 | temporary branch creation? | |
4650 | ||
4651 | Add more good examples. Entire sections of just cookbook examples | |
4652 | might be a good idea; maybe make an "advanced examples" section a | |
4653 | standard end-of-chapter section? | |
4654 | ||
4655 | Include cross-references to the glossary, where appropriate. | |
4656 | ||
4657 | Document shallow clones? See draft 1.5.0 release notes for some | |
4658 | documentation. | |
4659 | ||
4660 | Add a section on working with other version control systems, including | |
4661 | CVS, Subversion, and just imports of series of release tarballs. | |
4662 | ||
4663 | More details on gitweb? | |
4664 | ||
4665 | Write a chapter on using plumbing and writing scripts. | |
4666 | ||
4667 | Alternates, clone -reference, etc. | |
4668 | ||
4669 | More on recovery from repository corruption. See: | |
4670 | http://marc.theaimsgroup.com/?l=git&m=117263864820799&w=2 | |
4671 | http://marc.theaimsgroup.com/?l=git&m=117147855503798&w=2 |