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0eb4f7cd | 1 | Git User's Manual (for version 1.5.3 or newer) |
71f4b183 | 2 | ______________________________________________ |
d19fbc3c | 3 | |
99eaefdd BF |
4 | |
5 | Git is a fast distributed revision control system. | |
6 | ||
02783075 | 7 | This manual is designed to be readable by someone with basic UNIX |
79c96c57 | 8 | command-line skills, but no previous knowledge of git. |
d19fbc3c | 9 | |
2624d9a5 BF |
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. | |
ef89f701 | 14 | |
2624d9a5 BF |
15 | People needing to do actual development will also want to read |
16 | <<Developing-with-git>> and <<sharing-development>>. | |
6bd9b682 BF |
17 | |
18 | Further chapters cover more specialized topics. | |
19 | ||
d19fbc3c BF |
20 | Comprehensive reference documentation is available through the man |
21 | pages. For a command such as "git clone", just use | |
22 | ||
23 | ------------------------------------------------ | |
24 | $ man git-clone | |
25 | ------------------------------------------------ | |
26 | ||
2624d9a5 BF |
27 | See also <<git-quick-start>> for a brief overview of git commands, |
28 | without any explanation. | |
b181d57f | 29 | |
99f171bb | 30 | Finally, see <<todo>> for ways that you can help make this manual more |
2624d9a5 | 31 | complete. |
b181d57f | 32 | |
b181d57f | 33 | |
e34caace | 34 | [[repositories-and-branches]] |
d19fbc3c BF |
35 | Repositories and Branches |
36 | ========================= | |
37 | ||
e34caace | 38 | [[how-to-get-a-git-repository]] |
d19fbc3c BF |
39 | How to get a git repository |
40 | --------------------------- | |
41 | ||
42 | It will be useful to have a git repository to experiment with as you | |
43 | read this manual. | |
44 | ||
a5f90f31 BF |
45 | The best way to get one is by using the gitlink:git-clone[1] command to |
46 | download a copy of an existing repository. If you don't already have a | |
47 | project in mind, here are some interesting examples: | |
d19fbc3c BF |
48 | |
49 | ------------------------------------------------ | |
50 | # git itself (approx. 10MB download): | |
51 | $ git clone git://git.kernel.org/pub/scm/git/git.git | |
52 | # the linux kernel (approx. 150MB download): | |
53 | $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git | |
54 | ------------------------------------------------ | |
55 | ||
56 | The initial clone may be time-consuming for a large project, but you | |
57 | will only need to clone once. | |
58 | ||
59 | The clone command creates a new directory named after the project | |
60 | ("git" or "linux-2.6" in the examples above). After you cd into this | |
61 | directory, you will see that it contains a copy of the project files, | |
62 | together with a special top-level directory named ".git", which | |
63 | contains all the information about the history of the project. | |
64 | ||
e34caace | 65 | [[how-to-check-out]] |
d19fbc3c BF |
66 | How to check out a different version of a project |
67 | ------------------------------------------------- | |
68 | ||
a2ef9d63 BF |
69 | Git is best thought of as a tool for storing the history of a collection |
70 | of files. It stores the history as a compressed collection of | |
71 | interrelated snapshots of the project's contents. In git each such | |
72 | version is called a <<def_commit,commit>>. | |
d19fbc3c | 73 | |
81b6c950 BF |
74 | A single git repository may contain multiple branches. It keeps track |
75 | of them by keeping a list of <<def_head,heads>> which reference the | |
a2ef9d63 | 76 | latest commit on each branch; the gitlink:git-branch[1] command shows |
81b6c950 | 77 | you the list of branch heads: |
d19fbc3c BF |
78 | |
79 | ------------------------------------------------ | |
80 | $ git branch | |
81 | * master | |
82 | ------------------------------------------------ | |
83 | ||
4f752407 BF |
84 | A freshly cloned repository contains a single branch head, by default |
85 | named "master", with the working directory initialized to the state of | |
86 | the project referred to by that branch head. | |
d19fbc3c | 87 | |
81b6c950 BF |
88 | Most projects also use <<def_tag,tags>>. Tags, like heads, are |
89 | references into the project's history, and can be listed using the | |
d19fbc3c BF |
90 | gitlink:git-tag[1] command: |
91 | ||
92 | ------------------------------------------------ | |
93 | $ git tag -l | |
94 | v2.6.11 | |
95 | v2.6.11-tree | |
96 | v2.6.12 | |
97 | v2.6.12-rc2 | |
98 | v2.6.12-rc3 | |
99 | v2.6.12-rc4 | |
100 | v2.6.12-rc5 | |
101 | v2.6.12-rc6 | |
102 | v2.6.13 | |
103 | ... | |
104 | ------------------------------------------------ | |
105 | ||
fe4b3e59 | 106 | Tags are expected to always point at the same version of a project, |
81b6c950 | 107 | while heads are expected to advance as development progresses. |
fe4b3e59 | 108 | |
81b6c950 | 109 | Create a new branch head pointing to one of these versions and check it |
d19fbc3c BF |
110 | out using gitlink:git-checkout[1]: |
111 | ||
112 | ------------------------------------------------ | |
113 | $ git checkout -b new v2.6.13 | |
114 | ------------------------------------------------ | |
115 | ||
116 | The working directory then reflects the contents that the project had | |
117 | when it was tagged v2.6.13, and gitlink:git-branch[1] shows two | |
118 | branches, with an asterisk marking the currently checked-out branch: | |
119 | ||
120 | ------------------------------------------------ | |
121 | $ git branch | |
122 | master | |
123 | * new | |
124 | ------------------------------------------------ | |
125 | ||
126 | If you decide that you'd rather see version 2.6.17, you can modify | |
127 | the current branch to point at v2.6.17 instead, with | |
128 | ||
129 | ------------------------------------------------ | |
130 | $ git reset --hard v2.6.17 | |
131 | ------------------------------------------------ | |
132 | ||
81b6c950 | 133 | Note that if the current branch head was your only reference to a |
d19fbc3c | 134 | particular point in history, then resetting that branch may leave you |
81b6c950 BF |
135 | with no way to find the history it used to point to; so use this command |
136 | carefully. | |
d19fbc3c | 137 | |
e34caace | 138 | [[understanding-commits]] |
d19fbc3c BF |
139 | Understanding History: Commits |
140 | ------------------------------ | |
141 | ||
142 | Every change in the history of a project is represented by a commit. | |
143 | The gitlink:git-show[1] command shows the most recent commit on the | |
144 | current branch: | |
145 | ||
146 | ------------------------------------------------ | |
147 | $ git show | |
e2618ff4 BF |
148 | commit 17cf781661e6d38f737f15f53ab552f1e95960d7 |
149 | Author: Linus Torvalds <torvalds@ppc970.osdl.org.(none)> | |
150 | Date: Tue Apr 19 14:11:06 2005 -0700 | |
151 | ||
152 | Remove duplicate getenv(DB_ENVIRONMENT) call | |
153 | ||
154 | Noted by Tony Luck. | |
155 | ||
156 | diff --git a/init-db.c b/init-db.c | |
157 | index 65898fa..b002dc6 100644 | |
158 | --- a/init-db.c | |
159 | +++ b/init-db.c | |
160 | @@ -7,7 +7,7 @@ | |
d19fbc3c | 161 | |
e2618ff4 BF |
162 | int main(int argc, char **argv) |
163 | { | |
164 | - char *sha1_dir = getenv(DB_ENVIRONMENT), *path; | |
165 | + char *sha1_dir, *path; | |
166 | int len, i; | |
167 | ||
168 | if (mkdir(".git", 0755) < 0) { | |
d19fbc3c BF |
169 | ------------------------------------------------ |
170 | ||
171 | As you can see, a commit shows who made the latest change, what they | |
172 | did, and why. | |
173 | ||
35121930 BF |
174 | Every commit has a 40-hexdigit id, sometimes called the "object name" or the |
175 | "SHA1 id", shown on the first line of the "git show" output. You can usually | |
176 | refer to a commit by a shorter name, such as a tag or a branch name, but this | |
177 | longer name can also be useful. Most importantly, it is a globally unique | |
178 | name for this commit: so if you tell somebody else the object name (for | |
179 | example in email), then you are guaranteed that name will refer to the same | |
180 | commit in their repository that it does in yours (assuming their repository | |
181 | has that commit at all). Since the object name is computed as a hash over the | |
182 | contents of the commit, you are guaranteed that the commit can never change | |
183 | without its name also changing. | |
184 | ||
036f8199 | 185 | In fact, in <<git-concepts>> we shall see that everything stored in git |
35121930 BF |
186 | history, including file data and directory contents, is stored in an object |
187 | with a name that is a hash of its contents. | |
d19fbc3c | 188 | |
e34caace | 189 | [[understanding-reachability]] |
d19fbc3c BF |
190 | Understanding history: commits, parents, and reachability |
191 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
192 | ||
193 | Every commit (except the very first commit in a project) also has a | |
194 | parent commit which shows what happened before this commit. | |
195 | Following the chain of parents will eventually take you back to the | |
196 | beginning of the project. | |
197 | ||
198 | However, the commits do not form a simple list; git allows lines of | |
199 | development to diverge and then reconverge, and the point where two | |
200 | lines of development reconverge is called a "merge". The commit | |
201 | representing a merge can therefore have more than one parent, with | |
202 | each parent representing the most recent commit on one of the lines | |
203 | of development leading to that point. | |
204 | ||
205 | The best way to see how this works is using the gitlink:gitk[1] | |
206 | command; running gitk now on a git repository and looking for merge | |
207 | commits will help understand how the git organizes history. | |
208 | ||
209 | In the following, we say that commit X is "reachable" from commit Y | |
210 | if commit X is an ancestor of commit Y. Equivalently, you could say | |
02783075 | 211 | that Y is a descendant of X, or that there is a chain of parents |
d19fbc3c BF |
212 | leading from commit Y to commit X. |
213 | ||
e34caace | 214 | [[history-diagrams]] |
3dff5379 PR |
215 | Understanding history: History diagrams |
216 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
d19fbc3c BF |
217 | |
218 | We will sometimes represent git history using diagrams like the one | |
219 | below. Commits are shown as "o", and the links between them with | |
220 | lines drawn with - / and \. Time goes left to right: | |
221 | ||
1dc71a91 BF |
222 | |
223 | ................................................ | |
d19fbc3c BF |
224 | o--o--o <-- Branch A |
225 | / | |
226 | o--o--o <-- master | |
227 | \ | |
228 | o--o--o <-- Branch B | |
1dc71a91 | 229 | ................................................ |
d19fbc3c BF |
230 | |
231 | If we need to talk about a particular commit, the character "o" may | |
232 | be replaced with another letter or number. | |
233 | ||
e34caace | 234 | [[what-is-a-branch]] |
d19fbc3c BF |
235 | Understanding history: What is a branch? |
236 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
237 | ||
81b6c950 BF |
238 | When we need to be precise, we will use the word "branch" to mean a line |
239 | of development, and "branch head" (or just "head") to mean a reference | |
240 | to the most recent commit on a branch. In the example above, the branch | |
241 | head named "A" is a pointer to one particular commit, but we refer to | |
242 | the line of three commits leading up to that point as all being part of | |
d19fbc3c BF |
243 | "branch A". |
244 | ||
81b6c950 BF |
245 | However, when no confusion will result, we often just use the term |
246 | "branch" both for branches and for branch heads. | |
d19fbc3c | 247 | |
e34caace | 248 | [[manipulating-branches]] |
d19fbc3c BF |
249 | Manipulating branches |
250 | --------------------- | |
251 | ||
252 | Creating, deleting, and modifying branches is quick and easy; here's | |
253 | a summary of the commands: | |
254 | ||
255 | git branch:: | |
256 | list all branches | |
257 | git branch <branch>:: | |
258 | create a new branch named <branch>, referencing the same | |
259 | point in history as the current branch | |
260 | git branch <branch> <start-point>:: | |
261 | create a new branch named <branch>, referencing | |
262 | <start-point>, which may be specified any way you like, | |
263 | including using a branch name or a tag name | |
264 | git branch -d <branch>:: | |
265 | delete the branch <branch>; if the branch you are deleting | |
c64415e2 BF |
266 | points to a commit which is not reachable from the current |
267 | branch, this command will fail with a warning. | |
d19fbc3c BF |
268 | git branch -D <branch>:: |
269 | even if the branch points to a commit not reachable | |
270 | from the current branch, you may know that that commit | |
271 | is still reachable from some other branch or tag. In that | |
272 | case it is safe to use this command to force git to delete | |
273 | the branch. | |
274 | git checkout <branch>:: | |
275 | make the current branch <branch>, updating the working | |
276 | directory to reflect the version referenced by <branch> | |
277 | git checkout -b <new> <start-point>:: | |
278 | create a new branch <new> referencing <start-point>, and | |
279 | check it out. | |
280 | ||
72a76c95 BF |
281 | The special symbol "HEAD" can always be used to refer to the current |
282 | branch. In fact, git uses a file named "HEAD" in the .git directory to | |
283 | remember which branch is current: | |
284 | ||
285 | ------------------------------------------------ | |
286 | $ cat .git/HEAD | |
287 | ref: refs/heads/master | |
288 | ------------------------------------------------ | |
289 | ||
25d9f3fa | 290 | [[detached-head]] |
72a76c95 BF |
291 | Examining an old version without creating a new branch |
292 | ------------------------------------------------------ | |
293 | ||
294 | The git-checkout command normally expects a branch head, but will also | |
295 | accept an arbitrary commit; for example, you can check out the commit | |
296 | referenced by a tag: | |
297 | ||
298 | ------------------------------------------------ | |
299 | $ git checkout v2.6.17 | |
300 | Note: moving to "v2.6.17" which isn't a local branch | |
301 | If you want to create a new branch from this checkout, you may do so | |
302 | (now or later) by using -b with the checkout command again. Example: | |
303 | git checkout -b <new_branch_name> | |
304 | HEAD is now at 427abfa... Linux v2.6.17 | |
305 | ------------------------------------------------ | |
306 | ||
307 | The HEAD then refers to the SHA1 of the commit instead of to a branch, | |
308 | and git branch shows that you are no longer on a branch: | |
309 | ||
310 | ------------------------------------------------ | |
311 | $ cat .git/HEAD | |
312 | 427abfa28afedffadfca9dd8b067eb6d36bac53f | |
953f3d6f | 313 | $ git branch |
72a76c95 BF |
314 | * (no branch) |
315 | master | |
316 | ------------------------------------------------ | |
317 | ||
318 | In this case we say that the HEAD is "detached". | |
319 | ||
953f3d6f BF |
320 | This is an easy way to check out a particular version without having to |
321 | make up a name for the new branch. You can still create a new branch | |
322 | (or tag) for this version later if you decide to. | |
d19fbc3c | 323 | |
e34caace | 324 | [[examining-remote-branches]] |
d19fbc3c BF |
325 | Examining branches from a remote repository |
326 | ------------------------------------------- | |
327 | ||
328 | The "master" branch that was created at the time you cloned is a copy | |
329 | of the HEAD in the repository that you cloned from. That repository | |
330 | may also have had other branches, though, and your local repository | |
331 | keeps branches which track each of those remote branches, which you | |
332 | can view using the "-r" option to gitlink:git-branch[1]: | |
333 | ||
334 | ------------------------------------------------ | |
335 | $ git branch -r | |
336 | origin/HEAD | |
337 | origin/html | |
338 | origin/maint | |
339 | origin/man | |
340 | origin/master | |
341 | origin/next | |
342 | origin/pu | |
343 | origin/todo | |
344 | ------------------------------------------------ | |
345 | ||
346 | You cannot check out these remote-tracking branches, but you can | |
347 | examine them on a branch of your own, just as you would a tag: | |
348 | ||
349 | ------------------------------------------------ | |
350 | $ git checkout -b my-todo-copy origin/todo | |
351 | ------------------------------------------------ | |
352 | ||
353 | Note that the name "origin" is just the name that git uses by default | |
354 | to refer to the repository that you cloned from. | |
355 | ||
356 | [[how-git-stores-references]] | |
f60b9642 BF |
357 | Naming branches, tags, and other references |
358 | ------------------------------------------- | |
d19fbc3c BF |
359 | |
360 | Branches, remote-tracking branches, and tags are all references to | |
f60b9642 BF |
361 | commits. All references are named with a slash-separated path name |
362 | starting with "refs"; the names we've been using so far are actually | |
363 | shorthand: | |
d19fbc3c | 364 | |
f60b9642 BF |
365 | - The branch "test" is short for "refs/heads/test". |
366 | - The tag "v2.6.18" is short for "refs/tags/v2.6.18". | |
367 | - "origin/master" is short for "refs/remotes/origin/master". | |
d19fbc3c | 368 | |
f60b9642 BF |
369 | The full name is occasionally useful if, for example, there ever |
370 | exists a tag and a branch with the same name. | |
d19fbc3c | 371 | |
c64415e2 BF |
372 | As another useful shortcut, the "HEAD" of a repository can be referred |
373 | to just using the name of that repository. So, for example, "origin" | |
374 | is usually a shortcut for the HEAD branch in the repository "origin". | |
d19fbc3c BF |
375 | |
376 | For the complete list of paths which git checks for references, and | |
f60b9642 BF |
377 | the order it uses to decide which to choose when there are multiple |
378 | references with the same shorthand name, see the "SPECIFYING | |
379 | REVISIONS" section of gitlink:git-rev-parse[1]. | |
d19fbc3c BF |
380 | |
381 | [[Updating-a-repository-with-git-fetch]] | |
382 | Updating a repository with git fetch | |
383 | ------------------------------------ | |
384 | ||
385 | Eventually the developer cloned from will do additional work in her | |
386 | repository, creating new commits and advancing the branches to point | |
387 | at the new commits. | |
388 | ||
389 | The command "git fetch", with no arguments, will update all of the | |
390 | remote-tracking branches to the latest version found in her | |
391 | repository. It will not touch any of your own branches--not even the | |
392 | "master" branch that was created for you on clone. | |
393 | ||
e34caace | 394 | [[fetching-branches]] |
d5cd5de4 BF |
395 | Fetching branches from other repositories |
396 | ----------------------------------------- | |
397 | ||
398 | You can also track branches from repositories other than the one you | |
399 | cloned from, using gitlink:git-remote[1]: | |
400 | ||
401 | ------------------------------------------------- | |
402 | $ git remote add linux-nfs git://linux-nfs.org/pub/nfs-2.6.git | |
04483524 | 403 | $ git fetch linux-nfs |
d5cd5de4 BF |
404 | * refs/remotes/linux-nfs/master: storing branch 'master' ... |
405 | commit: bf81b46 | |
406 | ------------------------------------------------- | |
407 | ||
408 | New remote-tracking branches will be stored under the shorthand name | |
409 | that you gave "git remote add", in this case linux-nfs: | |
410 | ||
411 | ------------------------------------------------- | |
412 | $ git branch -r | |
413 | linux-nfs/master | |
414 | origin/master | |
415 | ------------------------------------------------- | |
416 | ||
417 | If you run "git fetch <remote>" later, the tracking branches for the | |
418 | named <remote> will be updated. | |
419 | ||
420 | If you examine the file .git/config, you will see that git has added | |
421 | a new stanza: | |
422 | ||
423 | ------------------------------------------------- | |
424 | $ cat .git/config | |
425 | ... | |
426 | [remote "linux-nfs"] | |
923642fe BF |
427 | url = git://linux-nfs.org/pub/nfs-2.6.git |
428 | fetch = +refs/heads/*:refs/remotes/linux-nfs/* | |
d5cd5de4 BF |
429 | ... |
430 | ------------------------------------------------- | |
431 | ||
fc90c536 BF |
432 | This is what causes git to track the remote's branches; you may modify |
433 | or delete these configuration options by editing .git/config with a | |
434 | text editor. (See the "CONFIGURATION FILE" section of | |
435 | gitlink:git-config[1] for details.) | |
d5cd5de4 | 436 | |
e34caace | 437 | [[exploring-git-history]] |
d19fbc3c BF |
438 | Exploring git history |
439 | ===================== | |
440 | ||
441 | Git is best thought of as a tool for storing the history of a | |
442 | collection of files. It does this by storing compressed snapshots of | |
1130845b | 443 | the contents of a file hierarchy, together with "commits" which show |
d19fbc3c BF |
444 | the relationships between these snapshots. |
445 | ||
446 | Git provides extremely flexible and fast tools for exploring the | |
447 | history of a project. | |
448 | ||
aacd404e | 449 | We start with one specialized tool that is useful for finding the |
d19fbc3c BF |
450 | commit that introduced a bug into a project. |
451 | ||
e34caace | 452 | [[using-bisect]] |
d19fbc3c BF |
453 | How to use bisect to find a regression |
454 | -------------------------------------- | |
455 | ||
456 | Suppose version 2.6.18 of your project worked, but the version at | |
457 | "master" crashes. Sometimes the best way to find the cause of such a | |
458 | regression is to perform a brute-force search through the project's | |
459 | history to find the particular commit that caused the problem. The | |
460 | gitlink:git-bisect[1] command can help you do this: | |
461 | ||
462 | ------------------------------------------------- | |
463 | $ git bisect start | |
464 | $ git bisect good v2.6.18 | |
465 | $ git bisect bad master | |
466 | Bisecting: 3537 revisions left to test after this | |
467 | [65934a9a028b88e83e2b0f8b36618fe503349f8e] BLOCK: Make USB storage depend on SCSI rather than selecting it [try #6] | |
468 | ------------------------------------------------- | |
469 | ||
470 | If you run "git branch" at this point, you'll see that git has | |
471 | temporarily moved you to a new branch named "bisect". This branch | |
472 | points to a commit (with commit id 65934...) that is reachable from | |
473 | v2.6.19 but not from v2.6.18. Compile and test it, and see whether | |
474 | it crashes. Assume it does crash. Then: | |
475 | ||
476 | ------------------------------------------------- | |
477 | $ git bisect bad | |
478 | Bisecting: 1769 revisions left to test after this | |
479 | [7eff82c8b1511017ae605f0c99ac275a7e21b867] i2c-core: Drop useless bitmaskings | |
480 | ------------------------------------------------- | |
481 | ||
482 | checks out an older version. Continue like this, telling git at each | |
483 | stage whether the version it gives you is good or bad, and notice | |
484 | that the number of revisions left to test is cut approximately in | |
485 | half each time. | |
486 | ||
487 | After about 13 tests (in this case), it will output the commit id of | |
488 | the guilty commit. You can then examine the commit with | |
489 | gitlink:git-show[1], find out who wrote it, and mail them your bug | |
490 | report with the commit id. Finally, run | |
491 | ||
492 | ------------------------------------------------- | |
493 | $ git bisect reset | |
494 | ------------------------------------------------- | |
495 | ||
496 | to return you to the branch you were on before and delete the | |
497 | temporary "bisect" branch. | |
498 | ||
499 | Note that the version which git-bisect checks out for you at each | |
500 | point is just a suggestion, and you're free to try a different | |
501 | version if you think it would be a good idea. For example, | |
502 | occasionally you may land on a commit that broke something unrelated; | |
503 | run | |
504 | ||
505 | ------------------------------------------------- | |
04483524 | 506 | $ git bisect visualize |
d19fbc3c BF |
507 | ------------------------------------------------- |
508 | ||
509 | which will run gitk and label the commit it chose with a marker that | |
510 | says "bisect". Chose a safe-looking commit nearby, note its commit | |
511 | id, and check it out with: | |
512 | ||
513 | ------------------------------------------------- | |
514 | $ git reset --hard fb47ddb2db... | |
515 | ------------------------------------------------- | |
516 | ||
517 | then test, run "bisect good" or "bisect bad" as appropriate, and | |
518 | continue. | |
519 | ||
e34caace | 520 | [[naming-commits]] |
d19fbc3c BF |
521 | Naming commits |
522 | -------------- | |
523 | ||
524 | We have seen several ways of naming commits already: | |
525 | ||
d55ae921 | 526 | - 40-hexdigit object name |
d19fbc3c BF |
527 | - branch name: refers to the commit at the head of the given |
528 | branch | |
529 | - tag name: refers to the commit pointed to by the given tag | |
530 | (we've seen branches and tags are special cases of | |
531 | <<how-git-stores-references,references>>). | |
532 | - HEAD: refers to the head of the current branch | |
533 | ||
eb6ae7f4 | 534 | There are many more; see the "SPECIFYING REVISIONS" section of the |
aec053bb | 535 | gitlink:git-rev-parse[1] man page for the complete list of ways to |
d19fbc3c BF |
536 | name revisions. Some examples: |
537 | ||
538 | ------------------------------------------------- | |
d55ae921 | 539 | $ git show fb47ddb2 # the first few characters of the object name |
d19fbc3c BF |
540 | # are usually enough to specify it uniquely |
541 | $ git show HEAD^ # the parent of the HEAD commit | |
542 | $ git show HEAD^^ # the grandparent | |
543 | $ git show HEAD~4 # the great-great-grandparent | |
544 | ------------------------------------------------- | |
545 | ||
546 | Recall that merge commits may have more than one parent; by default, | |
547 | ^ and ~ follow the first parent listed in the commit, but you can | |
548 | also choose: | |
549 | ||
550 | ------------------------------------------------- | |
551 | $ git show HEAD^1 # show the first parent of HEAD | |
552 | $ git show HEAD^2 # show the second parent of HEAD | |
553 | ------------------------------------------------- | |
554 | ||
555 | In addition to HEAD, there are several other special names for | |
556 | commits: | |
557 | ||
558 | Merges (to be discussed later), as well as operations such as | |
559 | git-reset, which change the currently checked-out commit, generally | |
560 | set ORIG_HEAD to the value HEAD had before the current operation. | |
561 | ||
562 | The git-fetch operation always stores the head of the last fetched | |
563 | branch in FETCH_HEAD. For example, if you run git fetch without | |
564 | specifying a local branch as the target of the operation | |
565 | ||
566 | ------------------------------------------------- | |
567 | $ git fetch git://example.com/proj.git theirbranch | |
568 | ------------------------------------------------- | |
569 | ||
570 | the fetched commits will still be available from FETCH_HEAD. | |
571 | ||
572 | When we discuss merges we'll also see the special name MERGE_HEAD, | |
573 | which refers to the other branch that we're merging in to the current | |
574 | branch. | |
575 | ||
aec053bb | 576 | The gitlink:git-rev-parse[1] command is a low-level command that is |
d55ae921 BF |
577 | occasionally useful for translating some name for a commit to the object |
578 | name for that commit: | |
aec053bb BF |
579 | |
580 | ------------------------------------------------- | |
581 | $ git rev-parse origin | |
582 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
583 | ------------------------------------------------- | |
584 | ||
e34caace | 585 | [[creating-tags]] |
d19fbc3c BF |
586 | Creating tags |
587 | ------------- | |
588 | ||
589 | We can also create a tag to refer to a particular commit; after | |
590 | running | |
591 | ||
592 | ------------------------------------------------- | |
04483524 | 593 | $ git tag stable-1 1b2e1d63ff |
d19fbc3c BF |
594 | ------------------------------------------------- |
595 | ||
596 | You can use stable-1 to refer to the commit 1b2e1d63ff. | |
597 | ||
c64415e2 BF |
598 | This creates a "lightweight" tag. If you would also like to include a |
599 | comment with the tag, and possibly sign it cryptographically, then you | |
600 | should create a tag object instead; see the gitlink:git-tag[1] man page | |
601 | for details. | |
d19fbc3c | 602 | |
e34caace | 603 | [[browsing-revisions]] |
d19fbc3c BF |
604 | Browsing revisions |
605 | ------------------ | |
606 | ||
607 | The gitlink:git-log[1] command can show lists of commits. On its | |
608 | own, it shows all commits reachable from the parent commit; but you | |
609 | can also make more specific requests: | |
610 | ||
611 | ------------------------------------------------- | |
612 | $ git log v2.5.. # commits since (not reachable from) v2.5 | |
613 | $ git log test..master # commits reachable from master but not test | |
614 | $ git log master..test # ...reachable from test but not master | |
615 | $ git log master...test # ...reachable from either test or master, | |
616 | # but not both | |
617 | $ git log --since="2 weeks ago" # commits from the last 2 weeks | |
618 | $ git log Makefile # commits which modify Makefile | |
619 | $ git log fs/ # ... which modify any file under fs/ | |
620 | $ git log -S'foo()' # commits which add or remove any file data | |
621 | # matching the string 'foo()' | |
622 | ------------------------------------------------- | |
623 | ||
624 | And of course you can combine all of these; the following finds | |
625 | commits since v2.5 which touch the Makefile or any file under fs: | |
626 | ||
627 | ------------------------------------------------- | |
628 | $ git log v2.5.. Makefile fs/ | |
629 | ------------------------------------------------- | |
630 | ||
631 | You can also ask git log to show patches: | |
632 | ||
633 | ------------------------------------------------- | |
634 | $ git log -p | |
635 | ------------------------------------------------- | |
636 | ||
637 | See the "--pretty" option in the gitlink:git-log[1] man page for more | |
638 | display options. | |
639 | ||
640 | Note that git log starts with the most recent commit and works | |
641 | backwards through the parents; however, since git history can contain | |
3dff5379 | 642 | multiple independent lines of development, the particular order that |
d19fbc3c BF |
643 | commits are listed in may be somewhat arbitrary. |
644 | ||
e34caace | 645 | [[generating-diffs]] |
d19fbc3c BF |
646 | Generating diffs |
647 | ---------------- | |
648 | ||
649 | You can generate diffs between any two versions using | |
650 | gitlink:git-diff[1]: | |
651 | ||
652 | ------------------------------------------------- | |
653 | $ git diff master..test | |
654 | ------------------------------------------------- | |
655 | ||
656 | Sometimes what you want instead is a set of patches: | |
657 | ||
658 | ------------------------------------------------- | |
659 | $ git format-patch master..test | |
660 | ------------------------------------------------- | |
661 | ||
662 | will generate a file with a patch for each commit reachable from test | |
663 | but not from master. Note that if master also has commits which are | |
664 | not reachable from test, then the combined result of these patches | |
665 | will not be the same as the diff produced by the git-diff example. | |
666 | ||
e34caace | 667 | [[viewing-old-file-versions]] |
d19fbc3c BF |
668 | Viewing old file versions |
669 | ------------------------- | |
670 | ||
671 | You can always view an old version of a file by just checking out the | |
672 | correct revision first. But sometimes it is more convenient to be | |
673 | able to view an old version of a single file without checking | |
674 | anything out; this command does that: | |
675 | ||
676 | ------------------------------------------------- | |
677 | $ git show v2.5:fs/locks.c | |
678 | ------------------------------------------------- | |
679 | ||
680 | Before the colon may be anything that names a commit, and after it | |
681 | may be any path to a file tracked by git. | |
682 | ||
e34caace | 683 | [[history-examples]] |
aec053bb BF |
684 | Examples |
685 | -------- | |
686 | ||
46acd3fa BF |
687 | [[counting-commits-on-a-branch]] |
688 | Counting the number of commits on a branch | |
689 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
690 | ||
691 | Suppose you want to know how many commits you've made on "mybranch" | |
692 | since it diverged from "origin": | |
693 | ||
694 | ------------------------------------------------- | |
695 | $ git log --pretty=oneline origin..mybranch | wc -l | |
696 | ------------------------------------------------- | |
697 | ||
698 | Alternatively, you may often see this sort of thing done with the | |
699 | lower-level command gitlink:git-rev-list[1], which just lists the SHA1's | |
700 | of all the given commits: | |
701 | ||
702 | ------------------------------------------------- | |
703 | $ git rev-list origin..mybranch | wc -l | |
704 | ------------------------------------------------- | |
705 | ||
e34caace | 706 | [[checking-for-equal-branches]] |
aec053bb | 707 | Check whether two branches point at the same history |
2f99710c | 708 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
aec053bb BF |
709 | |
710 | Suppose you want to check whether two branches point at the same point | |
711 | in history. | |
712 | ||
713 | ------------------------------------------------- | |
714 | $ git diff origin..master | |
715 | ------------------------------------------------- | |
716 | ||
69f7ad73 BF |
717 | will tell you whether the contents of the project are the same at the |
718 | two branches; in theory, however, it's possible that the same project | |
719 | contents could have been arrived at by two different historical | |
d55ae921 | 720 | routes. You could compare the object names: |
aec053bb BF |
721 | |
722 | ------------------------------------------------- | |
723 | $ git rev-list origin | |
724 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
725 | $ git rev-list master | |
726 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
727 | ------------------------------------------------- | |
728 | ||
69f7ad73 BF |
729 | Or you could recall that the ... operator selects all commits |
730 | contained reachable from either one reference or the other but not | |
731 | both: so | |
aec053bb BF |
732 | |
733 | ------------------------------------------------- | |
734 | $ git log origin...master | |
735 | ------------------------------------------------- | |
736 | ||
737 | will return no commits when the two branches are equal. | |
738 | ||
e34caace | 739 | [[finding-tagged-descendants]] |
b181d57f BF |
740 | Find first tagged version including a given fix |
741 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
aec053bb | 742 | |
69f7ad73 BF |
743 | Suppose you know that the commit e05db0fd fixed a certain problem. |
744 | You'd like to find the earliest tagged release that contains that | |
745 | fix. | |
746 | ||
747 | Of course, there may be more than one answer--if the history branched | |
748 | after commit e05db0fd, then there could be multiple "earliest" tagged | |
749 | releases. | |
750 | ||
751 | You could just visually inspect the commits since e05db0fd: | |
752 | ||
753 | ------------------------------------------------- | |
754 | $ gitk e05db0fd.. | |
755 | ------------------------------------------------- | |
756 | ||
b181d57f BF |
757 | Or you can use gitlink:git-name-rev[1], which will give the commit a |
758 | name based on any tag it finds pointing to one of the commit's | |
759 | descendants: | |
760 | ||
761 | ------------------------------------------------- | |
04483524 | 762 | $ git name-rev --tags e05db0fd |
b181d57f BF |
763 | e05db0fd tags/v1.5.0-rc1^0~23 |
764 | ------------------------------------------------- | |
765 | ||
766 | The gitlink:git-describe[1] command does the opposite, naming the | |
767 | revision using a tag on which the given commit is based: | |
768 | ||
769 | ------------------------------------------------- | |
770 | $ git describe e05db0fd | |
04483524 | 771 | v1.5.0-rc0-260-ge05db0f |
b181d57f BF |
772 | ------------------------------------------------- |
773 | ||
774 | but that may sometimes help you guess which tags might come after the | |
775 | given commit. | |
776 | ||
777 | If you just want to verify whether a given tagged version contains a | |
778 | given commit, you could use gitlink:git-merge-base[1]: | |
779 | ||
780 | ------------------------------------------------- | |
781 | $ git merge-base e05db0fd v1.5.0-rc1 | |
782 | e05db0fd4f31dde7005f075a84f96b360d05984b | |
783 | ------------------------------------------------- | |
784 | ||
785 | The merge-base command finds a common ancestor of the given commits, | |
786 | and always returns one or the other in the case where one is a | |
787 | descendant of the other; so the above output shows that e05db0fd | |
788 | actually is an ancestor of v1.5.0-rc1. | |
789 | ||
790 | Alternatively, note that | |
791 | ||
792 | ------------------------------------------------- | |
4a7979ca | 793 | $ git log v1.5.0-rc1..e05db0fd |
b181d57f BF |
794 | ------------------------------------------------- |
795 | ||
4a7979ca | 796 | will produce empty output if and only if v1.5.0-rc1 includes e05db0fd, |
b181d57f | 797 | because it outputs only commits that are not reachable from v1.5.0-rc1. |
aec053bb | 798 | |
4a7979ca BF |
799 | As yet another alternative, the gitlink:git-show-branch[1] command lists |
800 | the commits reachable from its arguments with a display on the left-hand | |
801 | side that indicates which arguments that commit is reachable from. So, | |
802 | you can run something like | |
803 | ||
804 | ------------------------------------------------- | |
805 | $ git show-branch e05db0fd v1.5.0-rc0 v1.5.0-rc1 v1.5.0-rc2 | |
806 | ! [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
807 | available | |
808 | ! [v1.5.0-rc0] GIT v1.5.0 preview | |
809 | ! [v1.5.0-rc1] GIT v1.5.0-rc1 | |
810 | ! [v1.5.0-rc2] GIT v1.5.0-rc2 | |
811 | ... | |
812 | ------------------------------------------------- | |
813 | ||
814 | then search for a line that looks like | |
815 | ||
816 | ------------------------------------------------- | |
817 | + ++ [e05db0fd] Fix warnings in sha1_file.c - use C99 printf format if | |
818 | available | |
819 | ------------------------------------------------- | |
820 | ||
821 | Which shows that e05db0fd is reachable from itself, from v1.5.0-rc1, and | |
822 | from v1.5.0-rc2, but not from v1.5.0-rc0. | |
823 | ||
629d9f78 BF |
824 | [[showing-commits-unique-to-a-branch]] |
825 | Showing commits unique to a given branch | |
826 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
4a7979ca | 827 | |
629d9f78 BF |
828 | Suppose you would like to see all the commits reachable from the branch |
829 | head named "master" but not from any other head in your repository. | |
d19fbc3c | 830 | |
629d9f78 BF |
831 | We can list all the heads in this repository with |
832 | gitlink:git-show-ref[1]: | |
d19fbc3c | 833 | |
629d9f78 BF |
834 | ------------------------------------------------- |
835 | $ git show-ref --heads | |
836 | bf62196b5e363d73353a9dcf094c59595f3153b7 refs/heads/core-tutorial | |
837 | db768d5504c1bb46f63ee9d6e1772bd047e05bf9 refs/heads/maint | |
838 | a07157ac624b2524a059a3414e99f6f44bebc1e7 refs/heads/master | |
839 | 24dbc180ea14dc1aebe09f14c8ecf32010690627 refs/heads/tutorial-2 | |
840 | 1e87486ae06626c2f31eaa63d26fc0fd646c8af2 refs/heads/tutorial-fixes | |
841 | ------------------------------------------------- | |
d19fbc3c | 842 | |
629d9f78 BF |
843 | We can get just the branch-head names, and remove "master", with |
844 | the help of the standard utilities cut and grep: | |
845 | ||
846 | ------------------------------------------------- | |
847 | $ git show-ref --heads | cut -d' ' -f2 | grep -v '^refs/heads/master' | |
848 | refs/heads/core-tutorial | |
849 | refs/heads/maint | |
850 | refs/heads/tutorial-2 | |
851 | refs/heads/tutorial-fixes | |
852 | ------------------------------------------------- | |
853 | ||
854 | And then we can ask to see all the commits reachable from master | |
855 | but not from these other heads: | |
856 | ||
857 | ------------------------------------------------- | |
858 | $ gitk master --not $( git show-ref --heads | cut -d' ' -f2 | | |
859 | grep -v '^refs/heads/master' ) | |
860 | ------------------------------------------------- | |
861 | ||
862 | Obviously, endless variations are possible; for example, to see all | |
863 | commits reachable from some head but not from any tag in the repository: | |
864 | ||
865 | ------------------------------------------------- | |
c78974f7 | 866 | $ gitk $( git show-ref --heads ) --not $( git show-ref --tags ) |
629d9f78 BF |
867 | ------------------------------------------------- |
868 | ||
869 | (See gitlink:git-rev-parse[1] for explanations of commit-selecting | |
870 | syntax such as `--not`.) | |
871 | ||
82c8bf28 BF |
872 | [[making-a-release]] |
873 | Creating a changelog and tarball for a software release | |
874 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
875 | ||
876 | The gitlink:git-archive[1] command can create a tar or zip archive from | |
877 | any version of a project; for example: | |
878 | ||
879 | ------------------------------------------------- | |
880 | $ git archive --format=tar --prefix=project/ HEAD | gzip >latest.tar.gz | |
881 | ------------------------------------------------- | |
882 | ||
883 | will use HEAD to produce a tar archive in which each filename is | |
ccd71866 | 884 | preceded by "project/". |
82c8bf28 BF |
885 | |
886 | If you're releasing a new version of a software project, you may want | |
887 | to simultaneously make a changelog to include in the release | |
888 | announcement. | |
889 | ||
890 | Linus Torvalds, for example, makes new kernel releases by tagging them, | |
891 | then running: | |
892 | ||
893 | ------------------------------------------------- | |
894 | $ release-script 2.6.12 2.6.13-rc6 2.6.13-rc7 | |
895 | ------------------------------------------------- | |
896 | ||
897 | where release-script is a shell script that looks like: | |
898 | ||
899 | ------------------------------------------------- | |
900 | #!/bin/sh | |
901 | stable="$1" | |
902 | last="$2" | |
903 | new="$3" | |
904 | echo "# git tag v$new" | |
905 | echo "git archive --prefix=linux-$new/ v$new | gzip -9 > ../linux-$new.tar.gz" | |
906 | echo "git diff v$stable v$new | gzip -9 > ../patch-$new.gz" | |
907 | echo "git log --no-merges v$new ^v$last > ../ChangeLog-$new" | |
908 | echo "git shortlog --no-merges v$new ^v$last > ../ShortLog" | |
909 | echo "git diff --stat --summary -M v$last v$new > ../diffstat-$new" | |
910 | ------------------------------------------------- | |
911 | ||
912 | and then he just cut-and-pastes the output commands after verifying that | |
913 | they look OK. | |
4a7979ca | 914 | |
8ceca74a | 915 | [[Finding-comments-with-given-content]] |
187b0d80 | 916 | Finding commits referencing a file with given content |
d5821de2 | 917 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
187b0d80 BF |
918 | |
919 | Somebody hands you a copy of a file, and asks which commits modified a | |
920 | file such that it contained the given content either before or after the | |
921 | commit. You can find out with this: | |
922 | ||
923 | ------------------------------------------------- | |
170c0438 | 924 | $ git log --raw --abbrev=40 --pretty=oneline -- filename | |
187b0d80 BF |
925 | grep -B 1 `git hash-object filename` |
926 | ------------------------------------------------- | |
927 | ||
928 | Figuring out why this works is left as an exercise to the (advanced) | |
929 | student. The gitlink:git-log[1], gitlink:git-diff-tree[1], and | |
930 | gitlink:git-hash-object[1] man pages may prove helpful. | |
931 | ||
e34caace | 932 | [[Developing-with-git]] |
d19fbc3c BF |
933 | Developing with git |
934 | =================== | |
935 | ||
e34caace | 936 | [[telling-git-your-name]] |
d19fbc3c BF |
937 | Telling git your name |
938 | --------------------- | |
939 | ||
940 | Before creating any commits, you should introduce yourself to git. The | |
58c19d1f BF |
941 | easiest way to do so is to make sure the following lines appear in a |
942 | file named .gitconfig in your home directory: | |
d19fbc3c BF |
943 | |
944 | ------------------------------------------------ | |
d19fbc3c BF |
945 | [user] |
946 | name = Your Name Comes Here | |
947 | email = you@yourdomain.example.com | |
d19fbc3c BF |
948 | ------------------------------------------------ |
949 | ||
fc90c536 BF |
950 | (See the "CONFIGURATION FILE" section of gitlink:git-config[1] for |
951 | details on the configuration file.) | |
952 | ||
d19fbc3c | 953 | |
e34caace | 954 | [[creating-a-new-repository]] |
d19fbc3c BF |
955 | Creating a new repository |
956 | ------------------------- | |
957 | ||
958 | Creating a new repository from scratch is very easy: | |
959 | ||
960 | ------------------------------------------------- | |
961 | $ mkdir project | |
962 | $ cd project | |
f1d2b477 | 963 | $ git init |
d19fbc3c BF |
964 | ------------------------------------------------- |
965 | ||
966 | If you have some initial content (say, a tarball): | |
967 | ||
968 | ------------------------------------------------- | |
969 | $ tar -xzvf project.tar.gz | |
970 | $ cd project | |
f1d2b477 | 971 | $ git init |
d19fbc3c BF |
972 | $ git add . # include everything below ./ in the first commit: |
973 | $ git commit | |
974 | ------------------------------------------------- | |
975 | ||
976 | [[how-to-make-a-commit]] | |
ae25c67a | 977 | How to make a commit |
d19fbc3c BF |
978 | -------------------- |
979 | ||
980 | Creating a new commit takes three steps: | |
981 | ||
982 | 1. Making some changes to the working directory using your | |
983 | favorite editor. | |
984 | 2. Telling git about your changes. | |
985 | 3. Creating the commit using the content you told git about | |
986 | in step 2. | |
987 | ||
988 | In practice, you can interleave and repeat steps 1 and 2 as many | |
989 | times as you want: in order to keep track of what you want committed | |
990 | at step 3, git maintains a snapshot of the tree's contents in a | |
991 | special staging area called "the index." | |
992 | ||
01997b4a BF |
993 | At the beginning, the content of the index will be identical to |
994 | that of the HEAD. The command "git diff --cached", which shows | |
995 | the difference between the HEAD and the index, should therefore | |
996 | produce no output at that point. | |
eb6ae7f4 | 997 | |
d19fbc3c BF |
998 | Modifying the index is easy: |
999 | ||
1000 | To update the index with the new contents of a modified file, use | |
1001 | ||
1002 | ------------------------------------------------- | |
1003 | $ git add path/to/file | |
1004 | ------------------------------------------------- | |
1005 | ||
1006 | To add the contents of a new file to the index, use | |
1007 | ||
1008 | ------------------------------------------------- | |
1009 | $ git add path/to/file | |
1010 | ------------------------------------------------- | |
1011 | ||
eb6ae7f4 | 1012 | To remove a file from the index and from the working tree, |
d19fbc3c BF |
1013 | |
1014 | ------------------------------------------------- | |
1015 | $ git rm path/to/file | |
1016 | ------------------------------------------------- | |
1017 | ||
1018 | After each step you can verify that | |
1019 | ||
1020 | ------------------------------------------------- | |
1021 | $ git diff --cached | |
1022 | ------------------------------------------------- | |
1023 | ||
1024 | always shows the difference between the HEAD and the index file--this | |
1025 | is what you'd commit if you created the commit now--and that | |
1026 | ||
1027 | ------------------------------------------------- | |
1028 | $ git diff | |
1029 | ------------------------------------------------- | |
1030 | ||
1031 | shows the difference between the working tree and the index file. | |
1032 | ||
1033 | Note that "git add" always adds just the current contents of a file | |
1034 | to the index; further changes to the same file will be ignored unless | |
1035 | you run git-add on the file again. | |
1036 | ||
1037 | When you're ready, just run | |
1038 | ||
1039 | ------------------------------------------------- | |
1040 | $ git commit | |
1041 | ------------------------------------------------- | |
1042 | ||
1043 | and git will prompt you for a commit message and then create the new | |
3dff5379 | 1044 | commit. Check to make sure it looks like what you expected with |
d19fbc3c BF |
1045 | |
1046 | ------------------------------------------------- | |
1047 | $ git show | |
1048 | ------------------------------------------------- | |
1049 | ||
1050 | As a special shortcut, | |
a6080a0a | 1051 | |
d19fbc3c BF |
1052 | ------------------------------------------------- |
1053 | $ git commit -a | |
1054 | ------------------------------------------------- | |
1055 | ||
1056 | will update the index with any files that you've modified or removed | |
1057 | and create a commit, all in one step. | |
1058 | ||
1059 | A number of commands are useful for keeping track of what you're | |
1060 | about to commit: | |
1061 | ||
1062 | ------------------------------------------------- | |
1063 | $ git diff --cached # difference between HEAD and the index; what | |
1130845b | 1064 | # would be committed if you ran "commit" now. |
d19fbc3c BF |
1065 | $ git diff # difference between the index file and your |
1066 | # working directory; changes that would not | |
1067 | # be included if you ran "commit" now. | |
c64415e2 BF |
1068 | $ git diff HEAD # difference between HEAD and working tree; what |
1069 | # would be committed if you ran "commit -a" now. | |
d19fbc3c BF |
1070 | $ git status # a brief per-file summary of the above. |
1071 | ------------------------------------------------- | |
1072 | ||
407c0c87 BF |
1073 | You can also use gitlink:git-gui[1] to create commits, view changes in |
1074 | the index and the working tree files, and individually select diff hunks | |
1075 | for inclusion in the index (by right-clicking on the diff hunk and | |
1076 | choosing "Stage Hunk For Commit"). | |
1077 | ||
e34caace | 1078 | [[creating-good-commit-messages]] |
ae25c67a | 1079 | Creating good commit messages |
d19fbc3c BF |
1080 | ----------------------------- |
1081 | ||
1082 | Though not required, it's a good idea to begin the commit message | |
1083 | with a single short (less than 50 character) line summarizing the | |
1084 | change, followed by a blank line and then a more thorough | |
1085 | description. Tools that turn commits into email, for example, use | |
1086 | the first line on the Subject line and the rest of the commit in the | |
1087 | body. | |
1088 | ||
2dc53617 JH |
1089 | [[ignoring-files]] |
1090 | Ignoring files | |
1091 | -------------- | |
1092 | ||
1093 | A project will often generate files that you do 'not' want to track with git. | |
1094 | This typically includes files generated by a build process or temporary | |
1095 | backup files made by your editor. Of course, 'not' tracking files with git | |
1096 | is just a matter of 'not' calling "`git add`" on them. But it quickly becomes | |
1097 | annoying to have these untracked files lying around; e.g. they make | |
1098 | "`git add .`" and "`git commit -a`" practically useless, and they keep | |
464a8a7a | 1099 | showing up in the output of "`git status`". |
2dc53617 | 1100 | |
464a8a7a BF |
1101 | You can tell git to ignore certain files by creating a file called .gitignore |
1102 | in the top level of your working directory, with contents such as: | |
2dc53617 JH |
1103 | |
1104 | ------------------------------------------------- | |
1105 | # Lines starting with '#' are considered comments. | |
464a8a7a | 1106 | # Ignore any file named foo.txt. |
2dc53617 JH |
1107 | foo.txt |
1108 | # Ignore (generated) html files, | |
1109 | *.html | |
1110 | # except foo.html which is maintained by hand. | |
1111 | !foo.html | |
1112 | # Ignore objects and archives. | |
1113 | *.[oa] | |
1114 | ------------------------------------------------- | |
1115 | ||
464a8a7a BF |
1116 | See gitlink:gitignore[5] for a detailed explanation of the syntax. You can |
1117 | also place .gitignore files in other directories in your working tree, and they | |
1118 | will apply to those directories and their subdirectories. The `.gitignore` | |
1119 | files can be added to your repository like any other files (just run `git add | |
1120 | .gitignore` and `git commit`, as usual), which is convenient when the exclude | |
1121 | patterns (such as patterns matching build output files) would also make sense | |
1122 | for other users who clone your repository. | |
1123 | ||
1124 | If you wish the exclude patterns to affect only certain repositories | |
1125 | (instead of every repository for a given project), you may instead put | |
1126 | them in a file in your repository named .git/info/exclude, or in any file | |
1127 | specified by the `core.excludesfile` configuration variable. Some git | |
1128 | commands can also take exclude patterns directly on the command line. | |
1129 | See gitlink:gitignore[5] for the details. | |
2dc53617 | 1130 | |
e34caace | 1131 | [[how-to-merge]] |
ae25c67a | 1132 | How to merge |
d19fbc3c BF |
1133 | ------------ |
1134 | ||
1135 | You can rejoin two diverging branches of development using | |
1136 | gitlink:git-merge[1]: | |
1137 | ||
1138 | ------------------------------------------------- | |
1139 | $ git merge branchname | |
1140 | ------------------------------------------------- | |
1141 | ||
1142 | merges the development in the branch "branchname" into the current | |
1143 | branch. If there are conflicts--for example, if the same file is | |
1144 | modified in two different ways in the remote branch and the local | |
1145 | branch--then you are warned; the output may look something like this: | |
1146 | ||
1147 | ------------------------------------------------- | |
fabbd8f6 BF |
1148 | $ git merge next |
1149 | 100% (4/4) done | |
1150 | Auto-merged file.txt | |
d19fbc3c BF |
1151 | CONFLICT (content): Merge conflict in file.txt |
1152 | Automatic merge failed; fix conflicts and then commit the result. | |
1153 | ------------------------------------------------- | |
1154 | ||
1155 | Conflict markers are left in the problematic files, and after | |
1156 | you resolve the conflicts manually, you can update the index | |
1157 | with the contents and run git commit, as you normally would when | |
1158 | creating a new file. | |
1159 | ||
1160 | If you examine the resulting commit using gitk, you will see that it | |
1161 | has two parents, one pointing to the top of the current branch, and | |
1162 | one to the top of the other branch. | |
1163 | ||
d19fbc3c BF |
1164 | [[resolving-a-merge]] |
1165 | Resolving a merge | |
1166 | ----------------- | |
1167 | ||
1168 | When a merge isn't resolved automatically, git leaves the index and | |
1169 | the working tree in a special state that gives you all the | |
1170 | information you need to help resolve the merge. | |
1171 | ||
1172 | Files with conflicts are marked specially in the index, so until you | |
ef561ac7 BF |
1173 | resolve the problem and update the index, gitlink:git-commit[1] will |
1174 | fail: | |
d19fbc3c BF |
1175 | |
1176 | ------------------------------------------------- | |
1177 | $ git commit | |
1178 | file.txt: needs merge | |
1179 | ------------------------------------------------- | |
1180 | ||
ef561ac7 BF |
1181 | Also, gitlink:git-status[1] will list those files as "unmerged", and the |
1182 | files with conflicts will have conflict markers added, like this: | |
1183 | ||
1184 | ------------------------------------------------- | |
1185 | <<<<<<< HEAD:file.txt | |
1186 | Hello world | |
1187 | ======= | |
1188 | Goodbye | |
1189 | >>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt | |
1190 | ------------------------------------------------- | |
1191 | ||
1192 | All you need to do is edit the files to resolve the conflicts, and then | |
1193 | ||
1194 | ------------------------------------------------- | |
1195 | $ git add file.txt | |
1196 | $ git commit | |
1197 | ------------------------------------------------- | |
1198 | ||
1199 | Note that the commit message will already be filled in for you with | |
1200 | some information about the merge. Normally you can just use this | |
1201 | default message unchanged, but you may add additional commentary of | |
1202 | your own if desired. | |
1203 | ||
1204 | The above is all you need to know to resolve a simple merge. But git | |
1205 | also provides more information to help resolve conflicts: | |
1206 | ||
e34caace | 1207 | [[conflict-resolution]] |
ef561ac7 BF |
1208 | Getting conflict-resolution help during a merge |
1209 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
d19fbc3c BF |
1210 | |
1211 | All of the changes that git was able to merge automatically are | |
1212 | already added to the index file, so gitlink:git-diff[1] shows only | |
ef561ac7 | 1213 | the conflicts. It uses an unusual syntax: |
d19fbc3c BF |
1214 | |
1215 | ------------------------------------------------- | |
1216 | $ git diff | |
1217 | diff --cc file.txt | |
1218 | index 802992c,2b60207..0000000 | |
1219 | --- a/file.txt | |
1220 | +++ b/file.txt | |
1221 | @@@ -1,1 -1,1 +1,5 @@@ | |
1222 | ++<<<<<<< HEAD:file.txt | |
1223 | +Hello world | |
1224 | ++======= | |
1225 | + Goodbye | |
1226 | ++>>>>>>> 77976da35a11db4580b80ae27e8d65caf5208086:file.txt | |
1227 | ------------------------------------------------- | |
1228 | ||
1130845b | 1229 | Recall that the commit which will be committed after we resolve this |
d19fbc3c BF |
1230 | conflict will have two parents instead of the usual one: one parent |
1231 | will be HEAD, the tip of the current branch; the other will be the | |
1232 | tip of the other branch, which is stored temporarily in MERGE_HEAD. | |
1233 | ||
ef561ac7 BF |
1234 | During the merge, the index holds three versions of each file. Each of |
1235 | these three "file stages" represents a different version of the file: | |
1236 | ||
1237 | ------------------------------------------------- | |
1238 | $ git show :1:file.txt # the file in a common ancestor of both branches | |
1239 | $ git show :2:file.txt # the version from HEAD, but including any | |
1240 | # nonconflicting changes from MERGE_HEAD | |
1241 | $ git show :3:file.txt # the version from MERGE_HEAD, but including any | |
1242 | # nonconflicting changes from HEAD. | |
1243 | ------------------------------------------------- | |
1244 | ||
1245 | Since the stage 2 and stage 3 versions have already been updated with | |
1246 | nonconflicting changes, the only remaining differences between them are | |
1247 | the important ones; thus gitlink:git-diff[1] can use the information in | |
1248 | the index to show only those conflicts. | |
1249 | ||
1250 | The diff above shows the differences between the working-tree version of | |
1251 | file.txt and the stage 2 and stage 3 versions. So instead of preceding | |
1252 | each line by a single "+" or "-", it now uses two columns: the first | |
1253 | column is used for differences between the first parent and the working | |
1254 | directory copy, and the second for differences between the second parent | |
1255 | and the working directory copy. (See the "COMBINED DIFF FORMAT" section | |
1256 | of gitlink:git-diff-files[1] for a details of the format.) | |
1257 | ||
1258 | After resolving the conflict in the obvious way (but before updating the | |
1259 | index), the diff will look like: | |
d19fbc3c BF |
1260 | |
1261 | ------------------------------------------------- | |
1262 | $ git diff | |
1263 | diff --cc file.txt | |
1264 | index 802992c,2b60207..0000000 | |
1265 | --- a/file.txt | |
1266 | +++ b/file.txt | |
1267 | @@@ -1,1 -1,1 +1,1 @@@ | |
1268 | - Hello world | |
1269 | -Goodbye | |
1270 | ++Goodbye world | |
1271 | ------------------------------------------------- | |
1272 | ||
1273 | This shows that our resolved version deleted "Hello world" from the | |
1274 | first parent, deleted "Goodbye" from the second parent, and added | |
1275 | "Goodbye world", which was previously absent from both. | |
1276 | ||
ef561ac7 BF |
1277 | Some special diff options allow diffing the working directory against |
1278 | any of these stages: | |
1279 | ||
1280 | ------------------------------------------------- | |
1281 | $ git diff -1 file.txt # diff against stage 1 | |
1282 | $ git diff --base file.txt # same as the above | |
1283 | $ git diff -2 file.txt # diff against stage 2 | |
1284 | $ git diff --ours file.txt # same as the above | |
1285 | $ git diff -3 file.txt # diff against stage 3 | |
1286 | $ git diff --theirs file.txt # same as the above. | |
1287 | ------------------------------------------------- | |
1288 | ||
1289 | The gitlink:git-log[1] and gitk[1] commands also provide special help | |
1290 | for merges: | |
d19fbc3c BF |
1291 | |
1292 | ------------------------------------------------- | |
1293 | $ git log --merge | |
ef561ac7 | 1294 | $ gitk --merge |
d19fbc3c BF |
1295 | ------------------------------------------------- |
1296 | ||
ef561ac7 BF |
1297 | These will display all commits which exist only on HEAD or on |
1298 | MERGE_HEAD, and which touch an unmerged file. | |
d19fbc3c | 1299 | |
61d72564 | 1300 | You may also use gitlink:git-mergetool[1], which lets you merge the |
c64415e2 BF |
1301 | unmerged files using external tools such as emacs or kdiff3. |
1302 | ||
ef561ac7 | 1303 | Each time you resolve the conflicts in a file and update the index: |
d19fbc3c BF |
1304 | |
1305 | ------------------------------------------------- | |
1306 | $ git add file.txt | |
d19fbc3c BF |
1307 | ------------------------------------------------- |
1308 | ||
ef561ac7 BF |
1309 | the different stages of that file will be "collapsed", after which |
1310 | git-diff will (by default) no longer show diffs for that file. | |
d19fbc3c BF |
1311 | |
1312 | [[undoing-a-merge]] | |
ae25c67a | 1313 | Undoing a merge |
d19fbc3c BF |
1314 | --------------- |
1315 | ||
1316 | If you get stuck and decide to just give up and throw the whole mess | |
1317 | away, you can always return to the pre-merge state with | |
1318 | ||
1319 | ------------------------------------------------- | |
1320 | $ git reset --hard HEAD | |
1321 | ------------------------------------------------- | |
1322 | ||
1130845b | 1323 | Or, if you've already committed the merge that you want to throw away, |
d19fbc3c BF |
1324 | |
1325 | ------------------------------------------------- | |
1c73bb0e | 1326 | $ git reset --hard ORIG_HEAD |
d19fbc3c BF |
1327 | ------------------------------------------------- |
1328 | ||
1329 | However, this last command can be dangerous in some cases--never | |
1330 | throw away a commit you have already committed if that commit may | |
1331 | itself have been merged into another branch, as doing so may confuse | |
1332 | further merges. | |
1333 | ||
e34caace | 1334 | [[fast-forwards]] |
d19fbc3c BF |
1335 | Fast-forward merges |
1336 | ------------------- | |
1337 | ||
1338 | There is one special case not mentioned above, which is treated | |
1339 | differently. Normally, a merge results in a merge commit, with two | |
1340 | parents, one pointing at each of the two lines of development that | |
1341 | were merged. | |
1342 | ||
59723040 BF |
1343 | However, if the current branch is a descendant of the other--so every |
1344 | commit present in the one is already contained in the other--then git | |
1345 | just performs a "fast forward"; the head of the current branch is moved | |
1346 | forward to point at the head of the merged-in branch, without any new | |
1347 | commits being created. | |
d19fbc3c | 1348 | |
e34caace | 1349 | [[fixing-mistakes]] |
b684f830 BF |
1350 | Fixing mistakes |
1351 | --------------- | |
1352 | ||
1353 | If you've messed up the working tree, but haven't yet committed your | |
1354 | mistake, you can return the entire working tree to the last committed | |
1355 | state with | |
1356 | ||
1357 | ------------------------------------------------- | |
1358 | $ git reset --hard HEAD | |
1359 | ------------------------------------------------- | |
1360 | ||
1361 | If you make a commit that you later wish you hadn't, there are two | |
1362 | fundamentally different ways to fix the problem: | |
1363 | ||
1364 | 1. You can create a new commit that undoes whatever was done | |
1365 | by the previous commit. This is the correct thing if your | |
1366 | mistake has already been made public. | |
1367 | ||
1368 | 2. You can go back and modify the old commit. You should | |
1369 | never do this if you have already made the history public; | |
1370 | git does not normally expect the "history" of a project to | |
1371 | change, and cannot correctly perform repeated merges from | |
1372 | a branch that has had its history changed. | |
1373 | ||
e34caace | 1374 | [[reverting-a-commit]] |
b684f830 BF |
1375 | Fixing a mistake with a new commit |
1376 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1377 | ||
1378 | Creating a new commit that reverts an earlier change is very easy; | |
1379 | just pass the gitlink:git-revert[1] command a reference to the bad | |
1380 | commit; for example, to revert the most recent commit: | |
1381 | ||
1382 | ------------------------------------------------- | |
1383 | $ git revert HEAD | |
1384 | ------------------------------------------------- | |
1385 | ||
1386 | This will create a new commit which undoes the change in HEAD. You | |
1387 | will be given a chance to edit the commit message for the new commit. | |
1388 | ||
1389 | You can also revert an earlier change, for example, the next-to-last: | |
1390 | ||
1391 | ------------------------------------------------- | |
1392 | $ git revert HEAD^ | |
1393 | ------------------------------------------------- | |
1394 | ||
1395 | In this case git will attempt to undo the old change while leaving | |
1396 | intact any changes made since then. If more recent changes overlap | |
1397 | with the changes to be reverted, then you will be asked to fix | |
1398 | conflicts manually, just as in the case of <<resolving-a-merge, | |
1399 | resolving a merge>>. | |
1400 | ||
365aa199 | 1401 | [[fixing-a-mistake-by-editing-history]] |
b684f830 BF |
1402 | Fixing a mistake by editing history |
1403 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1404 | ||
1405 | If the problematic commit is the most recent commit, and you have not | |
1406 | yet made that commit public, then you may just | |
1407 | <<undoing-a-merge,destroy it using git-reset>>. | |
1408 | ||
1409 | Alternatively, you | |
1410 | can edit the working directory and update the index to fix your | |
1411 | mistake, just as if you were going to <<how-to-make-a-commit,create a | |
1412 | new commit>>, then run | |
1413 | ||
1414 | ------------------------------------------------- | |
1415 | $ git commit --amend | |
1416 | ------------------------------------------------- | |
1417 | ||
1418 | which will replace the old commit by a new commit incorporating your | |
1419 | changes, giving you a chance to edit the old commit message first. | |
1420 | ||
1421 | Again, you should never do this to a commit that may already have | |
1422 | been merged into another branch; use gitlink:git-revert[1] instead in | |
1423 | that case. | |
1424 | ||
1425 | It is also possible to edit commits further back in the history, but | |
1426 | this is an advanced topic to be left for | |
1427 | <<cleaning-up-history,another chapter>>. | |
1428 | ||
e34caace | 1429 | [[checkout-of-path]] |
b684f830 BF |
1430 | Checking out an old version of a file |
1431 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1432 | ||
1433 | In the process of undoing a previous bad change, you may find it | |
1434 | useful to check out an older version of a particular file using | |
1435 | gitlink:git-checkout[1]. We've used git checkout before to switch | |
1436 | branches, but it has quite different behavior if it is given a path | |
1437 | name: the command | |
1438 | ||
1439 | ------------------------------------------------- | |
1440 | $ git checkout HEAD^ path/to/file | |
1441 | ------------------------------------------------- | |
1442 | ||
1443 | replaces path/to/file by the contents it had in the commit HEAD^, and | |
1444 | also updates the index to match. It does not change branches. | |
1445 | ||
1446 | If you just want to look at an old version of the file, without | |
1447 | modifying the working directory, you can do that with | |
1448 | gitlink:git-show[1]: | |
1449 | ||
1450 | ------------------------------------------------- | |
ed4eb0d8 | 1451 | $ git show HEAD^:path/to/file |
b684f830 BF |
1452 | ------------------------------------------------- |
1453 | ||
1454 | which will display the given version of the file. | |
1455 | ||
7a7cc594 JH |
1456 | [[interrupted-work]] |
1457 | Temporarily setting aside work in progress | |
1458 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1459 | ||
1460 | While you are in the middle of working on something complicated, you | |
1461 | find an unrelated but obvious and trivial bug. You would like to fix it | |
1462 | before continuing. You can use gitlink:git-stash[1] to save the current | |
1463 | state of your work, and after fixing the bug (or, optionally after doing | |
1464 | so on a different branch and then coming back), unstash the | |
1465 | work-in-progress changes. | |
1466 | ||
1467 | ------------------------------------------------ | |
1468 | $ git stash "work in progress for foo feature" | |
1469 | ------------------------------------------------ | |
1470 | ||
1471 | This command will save your changes away to the `stash`, and | |
1472 | reset your working tree and the index to match the tip of your | |
1473 | current branch. Then you can make your fix as usual. | |
1474 | ||
1475 | ------------------------------------------------ | |
1476 | ... edit and test ... | |
1477 | $ git commit -a -m "blorpl: typofix" | |
1478 | ------------------------------------------------ | |
1479 | ||
1480 | After that, you can go back to what you were working on with | |
1481 | `git stash apply`: | |
1482 | ||
1483 | ------------------------------------------------ | |
1484 | $ git stash apply | |
1485 | ------------------------------------------------ | |
1486 | ||
1487 | ||
e34caace | 1488 | [[ensuring-good-performance]] |
d19fbc3c BF |
1489 | Ensuring good performance |
1490 | ------------------------- | |
1491 | ||
1492 | On large repositories, git depends on compression to keep the history | |
1493 | information from taking up to much space on disk or in memory. | |
1494 | ||
1495 | This compression is not performed automatically. Therefore you | |
17217090 | 1496 | should occasionally run gitlink:git-gc[1]: |
d19fbc3c BF |
1497 | |
1498 | ------------------------------------------------- | |
1499 | $ git gc | |
1500 | ------------------------------------------------- | |
1501 | ||
17217090 BF |
1502 | to recompress the archive. This can be very time-consuming, so |
1503 | you may prefer to run git-gc when you are not doing other work. | |
d19fbc3c | 1504 | |
e34caace BF |
1505 | |
1506 | [[ensuring-reliability]] | |
11e016a3 BF |
1507 | Ensuring reliability |
1508 | -------------------- | |
1509 | ||
e34caace | 1510 | [[checking-for-corruption]] |
11e016a3 BF |
1511 | Checking the repository for corruption |
1512 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1513 | ||
1191ee18 BF |
1514 | The gitlink:git-fsck[1] command runs a number of self-consistency checks |
1515 | on the repository, and reports on any problems. This may take some | |
21dcb3b7 BF |
1516 | time. The most common warning by far is about "dangling" objects: |
1517 | ||
1518 | ------------------------------------------------- | |
04e50e94 | 1519 | $ git fsck |
21dcb3b7 BF |
1520 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 |
1521 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1522 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1523 | dangling blob 218761f9d90712d37a9c5e36f406f92202db07eb | |
1524 | dangling commit bf093535a34a4d35731aa2bd90fe6b176302f14f | |
1525 | dangling commit 8e4bec7f2ddaa268bef999853c25755452100f8e | |
1526 | dangling tree d50bb86186bf27b681d25af89d3b5b68382e4085 | |
1527 | dangling tree b24c2473f1fd3d91352a624795be026d64c8841f | |
1528 | ... | |
1529 | ------------------------------------------------- | |
1530 | ||
59723040 | 1531 | Dangling objects are not a problem. At worst they may take up a little |
54782859 AP |
1532 | extra disk space. They can sometimes provide a last-resort method for |
1533 | recovering lost work--see <<dangling-objects>> for details. However, if | |
1534 | you wish, you can remove them with gitlink:git-prune[1] or the --prune | |
1191ee18 | 1535 | option to gitlink:git-gc[1]: |
21dcb3b7 BF |
1536 | |
1537 | ------------------------------------------------- | |
1538 | $ git gc --prune | |
1539 | ------------------------------------------------- | |
1540 | ||
1191ee18 BF |
1541 | This may be time-consuming. Unlike most other git operations (including |
1542 | git-gc when run without any options), it is not safe to prune while | |
1543 | other git operations are in progress in the same repository. | |
21dcb3b7 | 1544 | |
e34caace | 1545 | [[recovering-lost-changes]] |
11e016a3 BF |
1546 | Recovering lost changes |
1547 | ~~~~~~~~~~~~~~~~~~~~~~~ | |
1548 | ||
e34caace | 1549 | [[reflogs]] |
559e4d7a BF |
1550 | Reflogs |
1551 | ^^^^^^^ | |
1552 | ||
1553 | Say you modify a branch with gitlink:git-reset[1] --hard, and then | |
1554 | realize that the branch was the only reference you had to that point in | |
1555 | history. | |
1556 | ||
1557 | Fortunately, git also keeps a log, called a "reflog", of all the | |
1558 | previous values of each branch. So in this case you can still find the | |
a6080a0a | 1559 | old history using, for example, |
559e4d7a BF |
1560 | |
1561 | ------------------------------------------------- | |
1562 | $ git log master@{1} | |
1563 | ------------------------------------------------- | |
1564 | ||
1565 | This lists the commits reachable from the previous version of the head. | |
1566 | This syntax can be used to with any git command that accepts a commit, | |
1567 | not just with git log. Some other examples: | |
1568 | ||
1569 | ------------------------------------------------- | |
1570 | $ git show master@{2} # See where the branch pointed 2, | |
1571 | $ git show master@{3} # 3, ... changes ago. | |
1572 | $ gitk master@{yesterday} # See where it pointed yesterday, | |
1573 | $ gitk master@{"1 week ago"} # ... or last week | |
953f3d6f BF |
1574 | $ git log --walk-reflogs master # show reflog entries for master |
1575 | ------------------------------------------------- | |
1576 | ||
1577 | A separate reflog is kept for the HEAD, so | |
1578 | ||
1579 | ------------------------------------------------- | |
1580 | $ git show HEAD@{"1 week ago"} | |
559e4d7a BF |
1581 | ------------------------------------------------- |
1582 | ||
953f3d6f BF |
1583 | will show what HEAD pointed to one week ago, not what the current branch |
1584 | pointed to one week ago. This allows you to see the history of what | |
1585 | you've checked out. | |
1586 | ||
559e4d7a | 1587 | The reflogs are kept by default for 30 days, after which they may be |
036be17e | 1588 | pruned. See gitlink:git-reflog[1] and gitlink:git-gc[1] to learn |
559e4d7a BF |
1589 | how to control this pruning, and see the "SPECIFYING REVISIONS" |
1590 | section of gitlink:git-rev-parse[1] for details. | |
1591 | ||
1592 | Note that the reflog history is very different from normal git history. | |
1593 | While normal history is shared by every repository that works on the | |
1594 | same project, the reflog history is not shared: it tells you only about | |
1595 | how the branches in your local repository have changed over time. | |
1596 | ||
59723040 | 1597 | [[dangling-object-recovery]] |
559e4d7a BF |
1598 | Examining dangling objects |
1599 | ^^^^^^^^^^^^^^^^^^^^^^^^^^ | |
1600 | ||
59723040 BF |
1601 | In some situations the reflog may not be able to save you. For example, |
1602 | suppose you delete a branch, then realize you need the history it | |
1603 | contained. The reflog is also deleted; however, if you have not yet | |
1604 | pruned the repository, then you may still be able to find the lost | |
1605 | commits in the dangling objects that git-fsck reports. See | |
1606 | <<dangling-objects>> for the details. | |
559e4d7a BF |
1607 | |
1608 | ------------------------------------------------- | |
1609 | $ git fsck | |
1610 | dangling commit 7281251ddd2a61e38657c827739c57015671a6b3 | |
1611 | dangling commit 2706a059f258c6b245f298dc4ff2ccd30ec21a63 | |
1612 | dangling commit 13472b7c4b80851a1bc551779171dcb03655e9b5 | |
1613 | ... | |
1614 | ------------------------------------------------- | |
1615 | ||
aacd404e | 1616 | You can examine |
559e4d7a BF |
1617 | one of those dangling commits with, for example, |
1618 | ||
1619 | ------------------------------------------------ | |
1620 | $ gitk 7281251ddd --not --all | |
1621 | ------------------------------------------------ | |
1622 | ||
1623 | which does what it sounds like: it says that you want to see the commit | |
1624 | history that is described by the dangling commit(s), but not the | |
1625 | history that is described by all your existing branches and tags. Thus | |
1626 | you get exactly the history reachable from that commit that is lost. | |
1627 | (And notice that it might not be just one commit: we only report the | |
1628 | "tip of the line" as being dangling, but there might be a whole deep | |
79c96c57 | 1629 | and complex commit history that was dropped.) |
559e4d7a BF |
1630 | |
1631 | If you decide you want the history back, you can always create a new | |
1632 | reference pointing to it, for example, a new branch: | |
1633 | ||
1634 | ------------------------------------------------ | |
a6080a0a | 1635 | $ git branch recovered-branch 7281251ddd |
559e4d7a BF |
1636 | ------------------------------------------------ |
1637 | ||
59723040 BF |
1638 | Other types of dangling objects (blobs and trees) are also possible, and |
1639 | dangling objects can arise in other situations. | |
1640 | ||
11e016a3 | 1641 | |
e34caace | 1642 | [[sharing-development]] |
d19fbc3c | 1643 | Sharing development with others |
b684f830 | 1644 | =============================== |
d19fbc3c BF |
1645 | |
1646 | [[getting-updates-with-git-pull]] | |
1647 | Getting updates with git pull | |
b684f830 | 1648 | ----------------------------- |
d19fbc3c BF |
1649 | |
1650 | After you clone a repository and make a few changes of your own, you | |
1651 | may wish to check the original repository for updates and merge them | |
1652 | into your own work. | |
1653 | ||
1654 | We have already seen <<Updating-a-repository-with-git-fetch,how to | |
1655 | keep remote tracking branches up to date>> with gitlink:git-fetch[1], | |
1656 | and how to merge two branches. So you can merge in changes from the | |
1657 | original repository's master branch with: | |
1658 | ||
1659 | ------------------------------------------------- | |
1660 | $ git fetch | |
1661 | $ git merge origin/master | |
1662 | ------------------------------------------------- | |
1663 | ||
1664 | However, the gitlink:git-pull[1] command provides a way to do this in | |
1665 | one step: | |
1666 | ||
1667 | ------------------------------------------------- | |
1668 | $ git pull origin master | |
1669 | ------------------------------------------------- | |
1670 | ||
0eb4f7cd BF |
1671 | In fact, if you have "master" checked out, then by default "git pull" |
1672 | merges from the HEAD branch of the origin repository. So often you can | |
1673 | accomplish the above with just a simple | |
d19fbc3c BF |
1674 | |
1675 | ------------------------------------------------- | |
1676 | $ git pull | |
1677 | ------------------------------------------------- | |
1678 | ||
0eb4f7cd BF |
1679 | More generally, a branch that is created from a remote branch will pull |
1680 | by default from that branch. See the descriptions of the | |
1681 | branch.<name>.remote and branch.<name>.merge options in | |
1682 | gitlink:git-config[1], and the discussion of the --track option in | |
1683 | gitlink:git-checkout[1], to learn how to control these defaults. | |
d19fbc3c BF |
1684 | |
1685 | In addition to saving you keystrokes, "git pull" also helps you by | |
1686 | producing a default commit message documenting the branch and | |
1687 | repository that you pulled from. | |
1688 | ||
1689 | (But note that no such commit will be created in the case of a | |
1690 | <<fast-forwards,fast forward>>; instead, your branch will just be | |
79c96c57 | 1691 | updated to point to the latest commit from the upstream branch.) |
d19fbc3c | 1692 | |
1191ee18 BF |
1693 | The git-pull command can also be given "." as the "remote" repository, |
1694 | in which case it just merges in a branch from the current repository; so | |
4c63ff45 BF |
1695 | the commands |
1696 | ||
1697 | ------------------------------------------------- | |
1698 | $ git pull . branch | |
1699 | $ git merge branch | |
1700 | ------------------------------------------------- | |
1701 | ||
1702 | are roughly equivalent. The former is actually very commonly used. | |
1703 | ||
e34caace | 1704 | [[submitting-patches]] |
d19fbc3c | 1705 | Submitting patches to a project |
b684f830 | 1706 | ------------------------------- |
d19fbc3c BF |
1707 | |
1708 | If you just have a few changes, the simplest way to submit them may | |
1709 | just be to send them as patches in email: | |
1710 | ||
036be17e | 1711 | First, use gitlink:git-format-patch[1]; for example: |
d19fbc3c BF |
1712 | |
1713 | ------------------------------------------------- | |
eb6ae7f4 | 1714 | $ git format-patch origin |
d19fbc3c BF |
1715 | ------------------------------------------------- |
1716 | ||
1717 | will produce a numbered series of files in the current directory, one | |
1718 | for each patch in the current branch but not in origin/HEAD. | |
1719 | ||
1720 | You can then import these into your mail client and send them by | |
1721 | hand. However, if you have a lot to send at once, you may prefer to | |
1722 | use the gitlink:git-send-email[1] script to automate the process. | |
1723 | Consult the mailing list for your project first to determine how they | |
1724 | prefer such patches be handled. | |
1725 | ||
e34caace | 1726 | [[importing-patches]] |
d19fbc3c | 1727 | Importing patches to a project |
b684f830 | 1728 | ------------------------------ |
d19fbc3c BF |
1729 | |
1730 | Git also provides a tool called gitlink:git-am[1] (am stands for | |
1731 | "apply mailbox"), for importing such an emailed series of patches. | |
1732 | Just save all of the patch-containing messages, in order, into a | |
1733 | single mailbox file, say "patches.mbox", then run | |
1734 | ||
1735 | ------------------------------------------------- | |
eb6ae7f4 | 1736 | $ git am -3 patches.mbox |
d19fbc3c BF |
1737 | ------------------------------------------------- |
1738 | ||
1739 | Git will apply each patch in order; if any conflicts are found, it | |
1740 | will stop, and you can fix the conflicts as described in | |
01997b4a BF |
1741 | "<<resolving-a-merge,Resolving a merge>>". (The "-3" option tells |
1742 | git to perform a merge; if you would prefer it just to abort and | |
1743 | leave your tree and index untouched, you may omit that option.) | |
1744 | ||
1745 | Once the index is updated with the results of the conflict | |
1746 | resolution, instead of creating a new commit, just run | |
d19fbc3c BF |
1747 | |
1748 | ------------------------------------------------- | |
1749 | $ git am --resolved | |
1750 | ------------------------------------------------- | |
1751 | ||
1752 | and git will create the commit for you and continue applying the | |
1753 | remaining patches from the mailbox. | |
1754 | ||
1755 | The final result will be a series of commits, one for each patch in | |
1756 | the original mailbox, with authorship and commit log message each | |
1757 | taken from the message containing each patch. | |
1758 | ||
eda69449 BF |
1759 | [[public-repositories]] |
1760 | Public git repositories | |
1761 | ----------------------- | |
d19fbc3c | 1762 | |
6e30fb0c DK |
1763 | Another way to submit changes to a project is to tell the maintainer |
1764 | of that project to pull the changes from your repository using | |
1765 | gitlink:git-pull[1]. In the section "<<getting-updates-with-git-pull, | |
1766 | Getting updates with git pull>>" we described this as a way to get | |
1767 | updates from the "main" repository, but it works just as well in the | |
1768 | other direction. | |
d19fbc3c | 1769 | |
eda69449 BF |
1770 | If you and the maintainer both have accounts on the same machine, then |
1771 | you can just pull changes from each other's repositories directly; | |
11d51533 | 1772 | commands that accept repository URLs as arguments will also accept a |
eda69449 | 1773 | local directory name: |
d19fbc3c BF |
1774 | |
1775 | ------------------------------------------------- | |
1776 | $ git clone /path/to/repository | |
1777 | $ git pull /path/to/other/repository | |
1778 | ------------------------------------------------- | |
1779 | ||
11d51533 BF |
1780 | or an ssh url: |
1781 | ||
1782 | ------------------------------------------------- | |
1783 | $ git clone ssh://yourhost/~you/repository | |
1784 | ------------------------------------------------- | |
1785 | ||
1786 | For projects with few developers, or for synchronizing a few private | |
1787 | repositories, this may be all you need. | |
1788 | ||
eda69449 BF |
1789 | However, the more common way to do this is to maintain a separate public |
1790 | repository (usually on a different host) for others to pull changes | |
1791 | from. This is usually more convenient, and allows you to cleanly | |
1792 | separate private work in progress from publicly visible work. | |
d19fbc3c BF |
1793 | |
1794 | You will continue to do your day-to-day work in your personal | |
1795 | repository, but periodically "push" changes from your personal | |
1796 | repository into your public repository, allowing other developers to | |
1797 | pull from that repository. So the flow of changes, in a situation | |
1798 | where there is one other developer with a public repository, looks | |
1799 | like this: | |
1800 | ||
1801 | you push | |
1802 | your personal repo ------------------> your public repo | |
a6080a0a | 1803 | ^ | |
d19fbc3c BF |
1804 | | | |
1805 | | you pull | they pull | |
1806 | | | | |
1807 | | | | |
1808 | | they push V | |
1809 | their public repo <------------------- their repo | |
1810 | ||
11d51533 BF |
1811 | We explain how to do this in the following sections. |
1812 | ||
eda69449 BF |
1813 | [[setting-up-a-public-repository]] |
1814 | Setting up a public repository | |
1815 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1816 | ||
1817 | Assume your personal repository is in the directory ~/proj. We | |
1818 | first create a new clone of the repository and tell git-daemon that it | |
1819 | is meant to be public: | |
d19fbc3c BF |
1820 | |
1821 | ------------------------------------------------- | |
52c80037 | 1822 | $ git clone --bare ~/proj proj.git |
eda69449 | 1823 | $ touch proj.git/git-daemon-export-ok |
d19fbc3c BF |
1824 | ------------------------------------------------- |
1825 | ||
52c80037 | 1826 | The resulting directory proj.git contains a "bare" git repository--it is |
eda69449 BF |
1827 | just the contents of the ".git" directory, without any files checked out |
1828 | around it. | |
d19fbc3c | 1829 | |
c64415e2 | 1830 | Next, copy proj.git to the server where you plan to host the |
d19fbc3c BF |
1831 | public repository. You can use scp, rsync, or whatever is most |
1832 | convenient. | |
1833 | ||
eda69449 BF |
1834 | [[exporting-via-git]] |
1835 | Exporting a git repository via the git protocol | |
1836 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1837 | ||
1838 | This is the preferred method. | |
1839 | ||
1840 | If someone else administers the server, they should tell you what | |
1841 | directory to put the repository in, and what git:// url it will appear | |
1842 | at. You can then skip to the section | |
d19fbc3c BF |
1843 | "<<pushing-changes-to-a-public-repository,Pushing changes to a public |
1844 | repository>>", below. | |
1845 | ||
eda69449 BF |
1846 | Otherwise, all you need to do is start gitlink:git-daemon[1]; it will |
1847 | listen on port 9418. By default, it will allow access to any directory | |
1848 | that looks like a git directory and contains the magic file | |
1849 | git-daemon-export-ok. Passing some directory paths as git-daemon | |
1850 | arguments will further restrict the exports to those paths. | |
1851 | ||
1852 | You can also run git-daemon as an inetd service; see the | |
1853 | gitlink:git-daemon[1] man page for details. (See especially the | |
1854 | examples section.) | |
d19fbc3c BF |
1855 | |
1856 | [[exporting-via-http]] | |
1857 | Exporting a git repository via http | |
eda69449 | 1858 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
d19fbc3c BF |
1859 | |
1860 | The git protocol gives better performance and reliability, but on a | |
1861 | host with a web server set up, http exports may be simpler to set up. | |
1862 | ||
1863 | All you need to do is place the newly created bare git repository in | |
1864 | a directory that is exported by the web server, and make some | |
1865 | adjustments to give web clients some extra information they need: | |
1866 | ||
1867 | ------------------------------------------------- | |
1868 | $ mv proj.git /home/you/public_html/proj.git | |
1869 | $ cd proj.git | |
c64415e2 | 1870 | $ git --bare update-server-info |
d19fbc3c BF |
1871 | $ chmod a+x hooks/post-update |
1872 | ------------------------------------------------- | |
1873 | ||
1874 | (For an explanation of the last two lines, see | |
1875 | gitlink:git-update-server-info[1], and the documentation | |
a2983cb7 | 1876 | link:hooks.html[Hooks used by git].) |
d19fbc3c BF |
1877 | |
1878 | Advertise the url of proj.git. Anybody else should then be able to | |
02783075 | 1879 | clone or pull from that url, for example with a command line like: |
d19fbc3c BF |
1880 | |
1881 | ------------------------------------------------- | |
1882 | $ git clone http://yourserver.com/~you/proj.git | |
1883 | ------------------------------------------------- | |
1884 | ||
1885 | (See also | |
1886 | link:howto/setup-git-server-over-http.txt[setup-git-server-over-http] | |
1887 | for a slightly more sophisticated setup using WebDAV which also | |
1888 | allows pushing over http.) | |
1889 | ||
d19fbc3c BF |
1890 | [[pushing-changes-to-a-public-repository]] |
1891 | Pushing changes to a public repository | |
eda69449 | 1892 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
d19fbc3c | 1893 | |
eda69449 | 1894 | Note that the two techniques outlined above (exporting via |
d19fbc3c BF |
1895 | <<exporting-via-http,http>> or <<exporting-via-git,git>>) allow other |
1896 | maintainers to fetch your latest changes, but they do not allow write | |
1897 | access, which you will need to update the public repository with the | |
1898 | latest changes created in your private repository. | |
1899 | ||
1900 | The simplest way to do this is using gitlink:git-push[1] and ssh; to | |
1901 | update the remote branch named "master" with the latest state of your | |
1902 | branch named "master", run | |
1903 | ||
1904 | ------------------------------------------------- | |
1905 | $ git push ssh://yourserver.com/~you/proj.git master:master | |
1906 | ------------------------------------------------- | |
1907 | ||
1908 | or just | |
1909 | ||
1910 | ------------------------------------------------- | |
1911 | $ git push ssh://yourserver.com/~you/proj.git master | |
1912 | ------------------------------------------------- | |
1913 | ||
1914 | As with git-fetch, git-push will complain if this does not result in | |
1915 | a <<fast-forwards,fast forward>>. Normally this is a sign of | |
1916 | something wrong. However, if you are sure you know what you're | |
1917 | doing, you may force git-push to perform the update anyway by | |
1918 | proceeding the branch name by a plus sign: | |
1919 | ||
1920 | ------------------------------------------------- | |
1921 | $ git push ssh://yourserver.com/~you/proj.git +master | |
1922 | ------------------------------------------------- | |
1923 | ||
11d51533 BF |
1924 | Note that the target of a "push" is normally a |
1925 | <<def_bare_repository,bare>> repository. You can also push to a | |
1926 | repository that has a checked-out working tree, but the working tree | |
1927 | will not be updated by the push. This may lead to unexpected results if | |
1928 | the branch you push to is the currently checked-out branch! | |
1929 | ||
d19fbc3c BF |
1930 | As with git-fetch, you may also set up configuration options to |
1931 | save typing; so, for example, after | |
1932 | ||
1933 | ------------------------------------------------- | |
c64415e2 | 1934 | $ cat >>.git/config <<EOF |
d19fbc3c BF |
1935 | [remote "public-repo"] |
1936 | url = ssh://yourserver.com/~you/proj.git | |
1937 | EOF | |
1938 | ------------------------------------------------- | |
1939 | ||
1940 | you should be able to perform the above push with just | |
1941 | ||
1942 | ------------------------------------------------- | |
1943 | $ git push public-repo master | |
1944 | ------------------------------------------------- | |
1945 | ||
1946 | See the explanations of the remote.<name>.url, branch.<name>.remote, | |
9d13bda3 | 1947 | and remote.<name>.push options in gitlink:git-config[1] for |
d19fbc3c BF |
1948 | details. |
1949 | ||
e34caace | 1950 | [[setting-up-a-shared-repository]] |
d19fbc3c | 1951 | Setting up a shared repository |
eda69449 | 1952 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ |
d19fbc3c BF |
1953 | |
1954 | Another way to collaborate is by using a model similar to that | |
1955 | commonly used in CVS, where several developers with special rights | |
1956 | all push to and pull from a single shared repository. See | |
a2983cb7 | 1957 | link:cvs-migration.html[git for CVS users] for instructions on how to |
d19fbc3c BF |
1958 | set this up. |
1959 | ||
8fae2225 BF |
1960 | However, while there is nothing wrong with git's support for shared |
1961 | repositories, this mode of operation is not generally recommended, | |
1962 | simply because the mode of collaboration that git supports--by | |
1963 | exchanging patches and pulling from public repositories--has so many | |
1964 | advantages over the central shared repository: | |
1965 | ||
1966 | - Git's ability to quickly import and merge patches allows a | |
1967 | single maintainer to process incoming changes even at very | |
1968 | high rates. And when that becomes too much, git-pull provides | |
1969 | an easy way for that maintainer to delegate this job to other | |
1970 | maintainers while still allowing optional review of incoming | |
1971 | changes. | |
1972 | - Since every developer's repository has the same complete copy | |
1973 | of the project history, no repository is special, and it is | |
1974 | trivial for another developer to take over maintenance of a | |
1975 | project, either by mutual agreement, or because a maintainer | |
1976 | becomes unresponsive or difficult to work with. | |
1977 | - The lack of a central group of "committers" means there is | |
1978 | less need for formal decisions about who is "in" and who is | |
1979 | "out". | |
1980 | ||
e34caace | 1981 | [[setting-up-gitweb]] |
eda69449 BF |
1982 | Allowing web browsing of a repository |
1983 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
d19fbc3c | 1984 | |
a8cd1402 BF |
1985 | The gitweb cgi script provides users an easy way to browse your |
1986 | project's files and history without having to install git; see the file | |
04483524 | 1987 | gitweb/INSTALL in the git source tree for instructions on setting it up. |
d19fbc3c | 1988 | |
e34caace | 1989 | [[sharing-development-examples]] |
b684f830 BF |
1990 | Examples |
1991 | -------- | |
d19fbc3c | 1992 | |
9e2163ea BF |
1993 | [[maintaining-topic-branches]] |
1994 | Maintaining topic branches for a Linux subsystem maintainer | |
1995 | ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
1996 | ||
1997 | This describes how Tony Luck uses git in his role as maintainer of the | |
1998 | IA64 architecture for the Linux kernel. | |
1999 | ||
2000 | He uses two public branches: | |
2001 | ||
2002 | - A "test" tree into which patches are initially placed so that they | |
2003 | can get some exposure when integrated with other ongoing development. | |
2004 | This tree is available to Andrew for pulling into -mm whenever he | |
2005 | wants. | |
2006 | ||
2007 | - A "release" tree into which tested patches are moved for final sanity | |
2008 | checking, and as a vehicle to send them upstream to Linus (by sending | |
2009 | him a "please pull" request.) | |
2010 | ||
2011 | He also uses a set of temporary branches ("topic branches"), each | |
2012 | containing a logical grouping of patches. | |
2013 | ||
2014 | To set this up, first create your work tree by cloning Linus's public | |
2015 | tree: | |
2016 | ||
2017 | ------------------------------------------------- | |
2018 | $ git clone git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6.git work | |
2019 | $ cd work | |
2020 | ------------------------------------------------- | |
2021 | ||
2022 | Linus's tree will be stored in the remote branch named origin/master, | |
2023 | and can be updated using gitlink:git-fetch[1]; you can track other | |
2024 | public trees using gitlink:git-remote[1] to set up a "remote" and | |
6e30fb0c DK |
2025 | gitlink:git-fetch[1] to keep them up-to-date; see |
2026 | <<repositories-and-branches>>. | |
9e2163ea BF |
2027 | |
2028 | Now create the branches in which you are going to work; these start out | |
2029 | at the current tip of origin/master branch, and should be set up (using | |
2030 | the --track option to gitlink:git-branch[1]) to merge changes in from | |
2031 | Linus by default. | |
2032 | ||
2033 | ------------------------------------------------- | |
2034 | $ git branch --track test origin/master | |
2035 | $ git branch --track release origin/master | |
2036 | ------------------------------------------------- | |
2037 | ||
2038 | These can be easily kept up to date using gitlink:git-pull[1] | |
2039 | ||
2040 | ------------------------------------------------- | |
2041 | $ git checkout test && git pull | |
2042 | $ git checkout release && git pull | |
2043 | ------------------------------------------------- | |
2044 | ||
2045 | Important note! If you have any local changes in these branches, then | |
2046 | this merge will create a commit object in the history (with no local | |
2047 | changes git will simply do a "Fast forward" merge). Many people dislike | |
2048 | the "noise" that this creates in the Linux history, so you should avoid | |
2049 | doing this capriciously in the "release" branch, as these noisy commits | |
2050 | will become part of the permanent history when you ask Linus to pull | |
2051 | from the release branch. | |
2052 | ||
2053 | A few configuration variables (see gitlink:git-config[1]) can | |
2054 | make it easy to push both branches to your public tree. (See | |
2055 | <<setting-up-a-public-repository>>.) | |
2056 | ||
2057 | ------------------------------------------------- | |
2058 | $ cat >> .git/config <<EOF | |
2059 | [remote "mytree"] | |
2060 | url = master.kernel.org:/pub/scm/linux/kernel/git/aegl/linux-2.6.git | |
2061 | push = release | |
2062 | push = test | |
2063 | EOF | |
2064 | ------------------------------------------------- | |
2065 | ||
2066 | Then you can push both the test and release trees using | |
2067 | gitlink:git-push[1]: | |
2068 | ||
2069 | ------------------------------------------------- | |
2070 | $ git push mytree | |
2071 | ------------------------------------------------- | |
2072 | ||
2073 | or push just one of the test and release branches using: | |
2074 | ||
2075 | ------------------------------------------------- | |
2076 | $ git push mytree test | |
2077 | ------------------------------------------------- | |
2078 | ||
2079 | or | |
2080 | ||
2081 | ------------------------------------------------- | |
2082 | $ git push mytree release | |
2083 | ------------------------------------------------- | |
2084 | ||
2085 | Now to apply some patches from the community. Think of a short | |
2086 | snappy name for a branch to hold this patch (or related group of | |
2087 | patches), and create a new branch from the current tip of Linus's | |
2088 | branch: | |
2089 | ||
2090 | ------------------------------------------------- | |
2091 | $ git checkout -b speed-up-spinlocks origin | |
2092 | ------------------------------------------------- | |
2093 | ||
2094 | Now you apply the patch(es), run some tests, and commit the change(s). If | |
2095 | the patch is a multi-part series, then you should apply each as a separate | |
2096 | commit to this branch. | |
2097 | ||
2098 | ------------------------------------------------- | |
2099 | $ ... patch ... test ... commit [ ... patch ... test ... commit ]* | |
2100 | ------------------------------------------------- | |
2101 | ||
2102 | When you are happy with the state of this change, you can pull it into the | |
2103 | "test" branch in preparation to make it public: | |
2104 | ||
2105 | ------------------------------------------------- | |
2106 | $ git checkout test && git pull . speed-up-spinlocks | |
2107 | ------------------------------------------------- | |
2108 | ||
2109 | It is unlikely that you would have any conflicts here ... but you might if you | |
2110 | spent a while on this step and had also pulled new versions from upstream. | |
2111 | ||
2112 | Some time later when enough time has passed and testing done, you can pull the | |
2113 | same branch into the "release" tree ready to go upstream. This is where you | |
2114 | see the value of keeping each patch (or patch series) in its own branch. It | |
2115 | means that the patches can be moved into the "release" tree in any order. | |
2116 | ||
2117 | ------------------------------------------------- | |
2118 | $ git checkout release && git pull . speed-up-spinlocks | |
2119 | ------------------------------------------------- | |
2120 | ||
2121 | After a while, you will have a number of branches, and despite the | |
2122 | well chosen names you picked for each of them, you may forget what | |
2123 | they are for, or what status they are in. To get a reminder of what | |
2124 | changes are in a specific branch, use: | |
2125 | ||
2126 | ------------------------------------------------- | |
2127 | $ git log linux..branchname | git-shortlog | |
2128 | ------------------------------------------------- | |
2129 | ||
2130 | To see whether it has already been merged into the test or release branches | |
2131 | use: | |
2132 | ||
2133 | ------------------------------------------------- | |
2134 | $ git log test..branchname | |
2135 | ------------------------------------------------- | |
2136 | ||
2137 | or | |
2138 | ||
2139 | ------------------------------------------------- | |
2140 | $ git log release..branchname | |
2141 | ------------------------------------------------- | |
2142 | ||
2143 | (If this branch has not yet been merged you will see some log entries. | |
2144 | If it has been merged, then there will be no output.) | |
2145 | ||
2146 | Once a patch completes the great cycle (moving from test to release, | |
2147 | then pulled by Linus, and finally coming back into your local | |
2148 | "origin/master" branch) the branch for this change is no longer needed. | |
2149 | You detect this when the output from: | |
2150 | ||
2151 | ------------------------------------------------- | |
2152 | $ git log origin..branchname | |
2153 | ------------------------------------------------- | |
2154 | ||
2155 | is empty. At this point the branch can be deleted: | |
2156 | ||
2157 | ------------------------------------------------- | |
2158 | $ git branch -d branchname | |
2159 | ------------------------------------------------- | |
2160 | ||
2161 | Some changes are so trivial that it is not necessary to create a separate | |
2162 | branch and then merge into each of the test and release branches. For | |
2163 | these changes, just apply directly to the "release" branch, and then | |
2164 | merge that into the "test" branch. | |
2165 | ||
2166 | To create diffstat and shortlog summaries of changes to include in a "please | |
2167 | pull" request to Linus you can use: | |
2168 | ||
2169 | ------------------------------------------------- | |
2170 | $ git diff --stat origin..release | |
2171 | ------------------------------------------------- | |
2172 | ||
2173 | and | |
2174 | ||
2175 | ------------------------------------------------- | |
2176 | $ git log -p origin..release | git shortlog | |
2177 | ------------------------------------------------- | |
2178 | ||
2179 | Here are some of the scripts that simplify all this even further. | |
2180 | ||
2181 | ------------------------------------------------- | |
2182 | ==== update script ==== | |
2183 | # Update a branch in my GIT tree. If the branch to be updated | |
2184 | # is origin, then pull from kernel.org. Otherwise merge | |
2185 | # origin/master branch into test|release branch | |
2186 | ||
2187 | case "$1" in | |
2188 | test|release) | |
2189 | git checkout $1 && git pull . origin | |
2190 | ;; | |
2191 | origin) | |
2192 | before=$(cat .git/refs/remotes/origin/master) | |
2193 | git fetch origin | |
2194 | after=$(cat .git/refs/remotes/origin/master) | |
2195 | if [ $before != $after ] | |
2196 | then | |
2197 | git log $before..$after | git shortlog | |
2198 | fi | |
2199 | ;; | |
2200 | *) | |
2201 | echo "Usage: $0 origin|test|release" 1>&2 | |
2202 | exit 1 | |
2203 | ;; | |
2204 | esac | |
2205 | ------------------------------------------------- | |
2206 | ||
2207 | ------------------------------------------------- | |
2208 | ==== merge script ==== | |
2209 | # Merge a branch into either the test or release branch | |
2210 | ||
2211 | pname=$0 | |
2212 | ||
2213 | usage() | |
2214 | { | |
2215 | echo "Usage: $pname branch test|release" 1>&2 | |
2216 | exit 1 | |
2217 | } | |
2218 | ||
2219 | if [ ! -f .git/refs/heads/"$1" ] | |
2220 | then | |
2221 | echo "Can't see branch <$1>" 1>&2 | |
2222 | usage | |
2223 | fi | |
2224 | ||
2225 | case "$2" in | |
2226 | test|release) | |
2227 | if [ $(git log $2..$1 | wc -c) -eq 0 ] | |
2228 | then | |
2229 | echo $1 already merged into $2 1>&2 | |
2230 | exit 1 | |
2231 | fi | |
2232 | git checkout $2 && git pull . $1 | |
2233 | ;; | |
2234 | *) | |
2235 | usage | |
2236 | ;; | |
2237 | esac | |
2238 | ------------------------------------------------- | |
2239 | ||
2240 | ------------------------------------------------- | |
2241 | ==== status script ==== | |
2242 | # report on status of my ia64 GIT tree | |
2243 | ||
2244 | gb=$(tput setab 2) | |
2245 | rb=$(tput setab 1) | |
2246 | restore=$(tput setab 9) | |
2247 | ||
2248 | if [ `git rev-list test..release | wc -c` -gt 0 ] | |
2249 | then | |
2250 | echo $rb Warning: commits in release that are not in test $restore | |
2251 | git log test..release | |
2252 | fi | |
2253 | ||
2254 | for branch in `ls .git/refs/heads` | |
2255 | do | |
2256 | if [ $branch = test -o $branch = release ] | |
2257 | then | |
2258 | continue | |
2259 | fi | |
2260 | ||
2261 | echo -n $gb ======= $branch ====== $restore " " | |
2262 | status= | |
2263 | for ref in test release origin/master | |
2264 | do | |
2265 | if [ `git rev-list $ref..$branch | wc -c` -gt 0 ] | |
2266 | then | |
2267 | status=$status${ref:0:1} | |
2268 | fi | |
2269 | done | |
2270 | case $status in | |
2271 | trl) | |
2272 | echo $rb Need to pull into test $restore | |
2273 | ;; | |
2274 | rl) | |
2275 | echo "In test" | |
2276 | ;; | |
2277 | l) | |
2278 | echo "Waiting for linus" | |
2279 | ;; | |
2280 | "") | |
2281 | echo $rb All done $restore | |
2282 | ;; | |
2283 | *) | |
2284 | echo $rb "<$status>" $restore | |
2285 | ;; | |
2286 | esac | |
2287 | git log origin/master..$branch | git shortlog | |
2288 | done | |
2289 | ------------------------------------------------- | |
d19fbc3c | 2290 | |
d19fbc3c | 2291 | |
d19fbc3c | 2292 | [[cleaning-up-history]] |
4c63ff45 BF |
2293 | Rewriting history and maintaining patch series |
2294 | ============================================== | |
2295 | ||
2296 | Normally commits are only added to a project, never taken away or | |
2297 | replaced. Git is designed with this assumption, and violating it will | |
2298 | cause git's merge machinery (for example) to do the wrong thing. | |
2299 | ||
2300 | However, there is a situation in which it can be useful to violate this | |
2301 | assumption. | |
2302 | ||
e34caace | 2303 | [[patch-series]] |
4c63ff45 BF |
2304 | Creating the perfect patch series |
2305 | --------------------------------- | |
2306 | ||
2307 | Suppose you are a contributor to a large project, and you want to add a | |
2308 | complicated feature, and to present it to the other developers in a way | |
2309 | that makes it easy for them to read your changes, verify that they are | |
2310 | correct, and understand why you made each change. | |
2311 | ||
b181d57f | 2312 | If you present all of your changes as a single patch (or commit), they |
79c96c57 | 2313 | may find that it is too much to digest all at once. |
4c63ff45 BF |
2314 | |
2315 | If you present them with the entire history of your work, complete with | |
2316 | mistakes, corrections, and dead ends, they may be overwhelmed. | |
2317 | ||
2318 | So the ideal is usually to produce a series of patches such that: | |
2319 | ||
2320 | 1. Each patch can be applied in order. | |
2321 | ||
2322 | 2. Each patch includes a single logical change, together with a | |
2323 | message explaining the change. | |
2324 | ||
2325 | 3. No patch introduces a regression: after applying any initial | |
2326 | part of the series, the resulting project still compiles and | |
2327 | works, and has no bugs that it didn't have before. | |
2328 | ||
2329 | 4. The complete series produces the same end result as your own | |
2330 | (probably much messier!) development process did. | |
2331 | ||
b181d57f BF |
2332 | We will introduce some tools that can help you do this, explain how to |
2333 | use them, and then explain some of the problems that can arise because | |
2334 | you are rewriting history. | |
4c63ff45 | 2335 | |
e34caace | 2336 | [[using-git-rebase]] |
4c63ff45 BF |
2337 | Keeping a patch series up to date using git-rebase |
2338 | -------------------------------------------------- | |
2339 | ||
79c96c57 MC |
2340 | Suppose that you create a branch "mywork" on a remote-tracking branch |
2341 | "origin", and create some commits on top of it: | |
4c63ff45 BF |
2342 | |
2343 | ------------------------------------------------- | |
2344 | $ git checkout -b mywork origin | |
2345 | $ vi file.txt | |
2346 | $ git commit | |
2347 | $ vi otherfile.txt | |
2348 | $ git commit | |
2349 | ... | |
2350 | ------------------------------------------------- | |
2351 | ||
2352 | You have performed no merges into mywork, so it is just a simple linear | |
2353 | sequence of patches on top of "origin": | |
2354 | ||
1dc71a91 | 2355 | ................................................ |
4c63ff45 BF |
2356 | o--o--o <-- origin |
2357 | \ | |
2358 | o--o--o <-- mywork | |
1dc71a91 | 2359 | ................................................ |
4c63ff45 BF |
2360 | |
2361 | Some more interesting work has been done in the upstream project, and | |
2362 | "origin" has advanced: | |
2363 | ||
1dc71a91 | 2364 | ................................................ |
4c63ff45 BF |
2365 | o--o--O--o--o--o <-- origin |
2366 | \ | |
2367 | a--b--c <-- mywork | |
1dc71a91 | 2368 | ................................................ |
4c63ff45 BF |
2369 | |
2370 | At this point, you could use "pull" to merge your changes back in; | |
2371 | the result would create a new merge commit, like this: | |
2372 | ||
1dc71a91 | 2373 | ................................................ |
4c63ff45 BF |
2374 | o--o--O--o--o--o <-- origin |
2375 | \ \ | |
2376 | a--b--c--m <-- mywork | |
1dc71a91 | 2377 | ................................................ |
a6080a0a | 2378 | |
4c63ff45 BF |
2379 | However, if you prefer to keep the history in mywork a simple series of |
2380 | commits without any merges, you may instead choose to use | |
2381 | gitlink:git-rebase[1]: | |
2382 | ||
2383 | ------------------------------------------------- | |
2384 | $ git checkout mywork | |
2385 | $ git rebase origin | |
2386 | ------------------------------------------------- | |
2387 | ||
b181d57f BF |
2388 | This will remove each of your commits from mywork, temporarily saving |
2389 | them as patches (in a directory named ".dotest"), update mywork to | |
2390 | point at the latest version of origin, then apply each of the saved | |
2391 | patches to the new mywork. The result will look like: | |
4c63ff45 BF |
2392 | |
2393 | ||
1dc71a91 | 2394 | ................................................ |
4c63ff45 BF |
2395 | o--o--O--o--o--o <-- origin |
2396 | \ | |
2397 | a'--b'--c' <-- mywork | |
1dc71a91 | 2398 | ................................................ |
4c63ff45 | 2399 | |
b181d57f BF |
2400 | In the process, it may discover conflicts. In that case it will stop |
2401 | and allow you to fix the conflicts; after fixing conflicts, use "git | |
2402 | add" to update the index with those contents, and then, instead of | |
2403 | running git-commit, just run | |
4c63ff45 BF |
2404 | |
2405 | ------------------------------------------------- | |
2406 | $ git rebase --continue | |
2407 | ------------------------------------------------- | |
2408 | ||
2409 | and git will continue applying the rest of the patches. | |
2410 | ||
2411 | At any point you may use the --abort option to abort this process and | |
2412 | return mywork to the state it had before you started the rebase: | |
2413 | ||
2414 | ------------------------------------------------- | |
2415 | $ git rebase --abort | |
2416 | ------------------------------------------------- | |
2417 | ||
e34caace | 2418 | [[modifying-one-commit]] |
365aa199 BF |
2419 | Modifying a single commit |
2420 | ------------------------- | |
2421 | ||
2422 | We saw in <<fixing-a-mistake-by-editing-history>> that you can replace the | |
2423 | most recent commit using | |
2424 | ||
2425 | ------------------------------------------------- | |
2426 | $ git commit --amend | |
2427 | ------------------------------------------------- | |
2428 | ||
2429 | which will replace the old commit by a new commit incorporating your | |
2430 | changes, giving you a chance to edit the old commit message first. | |
2431 | ||
2432 | You can also use a combination of this and gitlink:git-rebase[1] to edit | |
2433 | commits further back in your history. First, tag the problematic commit with | |
2434 | ||
2435 | ------------------------------------------------- | |
2436 | $ git tag bad mywork~5 | |
2437 | ------------------------------------------------- | |
2438 | ||
2439 | (Either gitk or git-log may be useful for finding the commit.) | |
2440 | ||
25d9f3fa BF |
2441 | Then check out that commit, edit it, and rebase the rest of the series |
2442 | on top of it (note that we could check out the commit on a temporary | |
2443 | branch, but instead we're using a <<detached-head,detached head>>): | |
365aa199 BF |
2444 | |
2445 | ------------------------------------------------- | |
25d9f3fa | 2446 | $ git checkout bad |
365aa199 BF |
2447 | $ # make changes here and update the index |
2448 | $ git commit --amend | |
25d9f3fa | 2449 | $ git rebase --onto HEAD bad mywork |
365aa199 BF |
2450 | ------------------------------------------------- |
2451 | ||
25d9f3fa BF |
2452 | When you're done, you'll be left with mywork checked out, with the top |
2453 | patches on mywork reapplied on top of your modified commit. You can | |
365aa199 BF |
2454 | then clean up with |
2455 | ||
2456 | ------------------------------------------------- | |
365aa199 BF |
2457 | $ git tag -d bad |
2458 | ------------------------------------------------- | |
2459 | ||
2460 | Note that the immutable nature of git history means that you haven't really | |
2461 | "modified" existing commits; instead, you have replaced the old commits with | |
2462 | new commits having new object names. | |
2463 | ||
e34caace | 2464 | [[reordering-patch-series]] |
4c63ff45 BF |
2465 | Reordering or selecting from a patch series |
2466 | ------------------------------------------- | |
2467 | ||
b181d57f BF |
2468 | Given one existing commit, the gitlink:git-cherry-pick[1] command |
2469 | allows you to apply the change introduced by that commit and create a | |
2470 | new commit that records it. So, for example, if "mywork" points to a | |
2471 | series of patches on top of "origin", you might do something like: | |
2472 | ||
2473 | ------------------------------------------------- | |
2474 | $ git checkout -b mywork-new origin | |
2475 | $ gitk origin..mywork & | |
2476 | ------------------------------------------------- | |
2477 | ||
2478 | And browse through the list of patches in the mywork branch using gitk, | |
2479 | applying them (possibly in a different order) to mywork-new using | |
407c0c87 | 2480 | cherry-pick, and possibly modifying them as you go using commit --amend. |
6e30fb0c DK |
2481 | The gitlink:git-gui[1] command may also help as it allows you to |
2482 | individually select diff hunks for inclusion in the index (by | |
2483 | right-clicking on the diff hunk and choosing "Stage Hunk for Commit"). | |
b181d57f BF |
2484 | |
2485 | Another technique is to use git-format-patch to create a series of | |
2486 | patches, then reset the state to before the patches: | |
4c63ff45 | 2487 | |
b181d57f BF |
2488 | ------------------------------------------------- |
2489 | $ git format-patch origin | |
2490 | $ git reset --hard origin | |
2491 | ------------------------------------------------- | |
4c63ff45 | 2492 | |
b181d57f BF |
2493 | Then modify, reorder, or eliminate patches as preferred before applying |
2494 | them again with gitlink:git-am[1]. | |
4c63ff45 | 2495 | |
e34caace | 2496 | [[patch-series-tools]] |
4c63ff45 BF |
2497 | Other tools |
2498 | ----------- | |
2499 | ||
02783075 | 2500 | There are numerous other tools, such as StGIT, which exist for the |
79c96c57 | 2501 | purpose of maintaining a patch series. These are outside of the scope of |
b181d57f | 2502 | this manual. |
4c63ff45 | 2503 | |
e34caace | 2504 | [[problems-with-rewriting-history]] |
4c63ff45 BF |
2505 | Problems with rewriting history |
2506 | ------------------------------- | |
2507 | ||
b181d57f BF |
2508 | The primary problem with rewriting the history of a branch has to do |
2509 | with merging. Suppose somebody fetches your branch and merges it into | |
2510 | their branch, with a result something like this: | |
2511 | ||
1dc71a91 | 2512 | ................................................ |
b181d57f BF |
2513 | o--o--O--o--o--o <-- origin |
2514 | \ \ | |
2515 | t--t--t--m <-- their branch: | |
1dc71a91 | 2516 | ................................................ |
b181d57f BF |
2517 | |
2518 | Then suppose you modify the last three commits: | |
2519 | ||
1dc71a91 | 2520 | ................................................ |
b181d57f BF |
2521 | o--o--o <-- new head of origin |
2522 | / | |
2523 | o--o--O--o--o--o <-- old head of origin | |
1dc71a91 | 2524 | ................................................ |
b181d57f BF |
2525 | |
2526 | If we examined all this history together in one repository, it will | |
2527 | look like: | |
2528 | ||
1dc71a91 | 2529 | ................................................ |
b181d57f BF |
2530 | o--o--o <-- new head of origin |
2531 | / | |
2532 | o--o--O--o--o--o <-- old head of origin | |
2533 | \ \ | |
2534 | t--t--t--m <-- their branch: | |
1dc71a91 | 2535 | ................................................ |
b181d57f BF |
2536 | |
2537 | Git has no way of knowing that the new head is an updated version of | |
2538 | the old head; it treats this situation exactly the same as it would if | |
2539 | two developers had independently done the work on the old and new heads | |
2540 | in parallel. At this point, if someone attempts to merge the new head | |
2541 | in to their branch, git will attempt to merge together the two (old and | |
2542 | new) lines of development, instead of trying to replace the old by the | |
2543 | new. The results are likely to be unexpected. | |
2544 | ||
2545 | You may still choose to publish branches whose history is rewritten, | |
2546 | and it may be useful for others to be able to fetch those branches in | |
2547 | order to examine or test them, but they should not attempt to pull such | |
2548 | branches into their own work. | |
2549 | ||
2550 | For true distributed development that supports proper merging, | |
2551 | published branches should never be rewritten. | |
2552 | ||
e34caace | 2553 | [[advanced-branch-management]] |
b181d57f BF |
2554 | Advanced branch management |
2555 | ========================== | |
4c63ff45 | 2556 | |
e34caace | 2557 | [[fetching-individual-branches]] |
b181d57f BF |
2558 | Fetching individual branches |
2559 | ---------------------------- | |
2560 | ||
2561 | Instead of using gitlink:git-remote[1], you can also choose just | |
2562 | to update one branch at a time, and to store it locally under an | |
2563 | arbitrary name: | |
2564 | ||
2565 | ------------------------------------------------- | |
2566 | $ git fetch origin todo:my-todo-work | |
2567 | ------------------------------------------------- | |
2568 | ||
2569 | The first argument, "origin", just tells git to fetch from the | |
2570 | repository you originally cloned from. The second argument tells git | |
2571 | to fetch the branch named "todo" from the remote repository, and to | |
2572 | store it locally under the name refs/heads/my-todo-work. | |
2573 | ||
2574 | You can also fetch branches from other repositories; so | |
2575 | ||
2576 | ------------------------------------------------- | |
2577 | $ git fetch git://example.com/proj.git master:example-master | |
2578 | ------------------------------------------------- | |
2579 | ||
2580 | will create a new branch named "example-master" and store in it the | |
2581 | branch named "master" from the repository at the given URL. If you | |
2582 | already have a branch named example-master, it will attempt to | |
59723040 BF |
2583 | <<fast-forwards,fast-forward>> to the commit given by example.com's |
2584 | master branch. In more detail: | |
b181d57f | 2585 | |
59723040 BF |
2586 | [[fetch-fast-forwards]] |
2587 | git fetch and fast-forwards | |
2588 | --------------------------- | |
b181d57f BF |
2589 | |
2590 | In the previous example, when updating an existing branch, "git | |
2591 | fetch" checks to make sure that the most recent commit on the remote | |
2592 | branch is a descendant of the most recent commit on your copy of the | |
2593 | branch before updating your copy of the branch to point at the new | |
59723040 | 2594 | commit. Git calls this process a <<fast-forwards,fast forward>>. |
b181d57f BF |
2595 | |
2596 | A fast forward looks something like this: | |
2597 | ||
1dc71a91 | 2598 | ................................................ |
b181d57f BF |
2599 | o--o--o--o <-- old head of the branch |
2600 | \ | |
2601 | o--o--o <-- new head of the branch | |
1dc71a91 | 2602 | ................................................ |
b181d57f BF |
2603 | |
2604 | ||
2605 | In some cases it is possible that the new head will *not* actually be | |
2606 | a descendant of the old head. For example, the developer may have | |
2607 | realized she made a serious mistake, and decided to backtrack, | |
2608 | resulting in a situation like: | |
2609 | ||
1dc71a91 | 2610 | ................................................ |
b181d57f BF |
2611 | o--o--o--o--a--b <-- old head of the branch |
2612 | \ | |
2613 | o--o--o <-- new head of the branch | |
1dc71a91 | 2614 | ................................................ |
b181d57f BF |
2615 | |
2616 | In this case, "git fetch" will fail, and print out a warning. | |
2617 | ||
2618 | In that case, you can still force git to update to the new head, as | |
2619 | described in the following section. However, note that in the | |
2620 | situation above this may mean losing the commits labeled "a" and "b", | |
2621 | unless you've already created a reference of your own pointing to | |
2622 | them. | |
2623 | ||
e34caace | 2624 | [[forcing-fetch]] |
b181d57f BF |
2625 | Forcing git fetch to do non-fast-forward updates |
2626 | ------------------------------------------------ | |
2627 | ||
2628 | If git fetch fails because the new head of a branch is not a | |
2629 | descendant of the old head, you may force the update with: | |
2630 | ||
2631 | ------------------------------------------------- | |
2632 | $ git fetch git://example.com/proj.git +master:refs/remotes/example/master | |
2633 | ------------------------------------------------- | |
2634 | ||
c64415e2 BF |
2635 | Note the addition of the "+" sign. Alternatively, you can use the "-f" |
2636 | flag to force updates of all the fetched branches, as in: | |
2637 | ||
2638 | ------------------------------------------------- | |
2639 | $ git fetch -f origin | |
2640 | ------------------------------------------------- | |
2641 | ||
2642 | Be aware that commits that the old version of example/master pointed at | |
2643 | may be lost, as we saw in the previous section. | |
b181d57f | 2644 | |
e34caace | 2645 | [[remote-branch-configuration]] |
b181d57f BF |
2646 | Configuring remote branches |
2647 | --------------------------- | |
2648 | ||
2649 | We saw above that "origin" is just a shortcut to refer to the | |
79c96c57 | 2650 | repository that you originally cloned from. This information is |
b181d57f | 2651 | stored in git configuration variables, which you can see using |
9d13bda3 | 2652 | gitlink:git-config[1]: |
b181d57f BF |
2653 | |
2654 | ------------------------------------------------- | |
9d13bda3 | 2655 | $ git config -l |
b181d57f BF |
2656 | core.repositoryformatversion=0 |
2657 | core.filemode=true | |
2658 | core.logallrefupdates=true | |
2659 | remote.origin.url=git://git.kernel.org/pub/scm/git/git.git | |
2660 | remote.origin.fetch=+refs/heads/*:refs/remotes/origin/* | |
2661 | branch.master.remote=origin | |
2662 | branch.master.merge=refs/heads/master | |
2663 | ------------------------------------------------- | |
2664 | ||
2665 | If there are other repositories that you also use frequently, you can | |
2666 | create similar configuration options to save typing; for example, | |
2667 | after | |
2668 | ||
2669 | ------------------------------------------------- | |
9d13bda3 | 2670 | $ git config remote.example.url git://example.com/proj.git |
b181d57f BF |
2671 | ------------------------------------------------- |
2672 | ||
2673 | then the following two commands will do the same thing: | |
2674 | ||
2675 | ------------------------------------------------- | |
2676 | $ git fetch git://example.com/proj.git master:refs/remotes/example/master | |
2677 | $ git fetch example master:refs/remotes/example/master | |
2678 | ------------------------------------------------- | |
2679 | ||
2680 | Even better, if you add one more option: | |
2681 | ||
2682 | ------------------------------------------------- | |
9d13bda3 | 2683 | $ git config remote.example.fetch master:refs/remotes/example/master |
b181d57f BF |
2684 | ------------------------------------------------- |
2685 | ||
2686 | then the following commands will all do the same thing: | |
2687 | ||
2688 | ------------------------------------------------- | |
52c80037 BF |
2689 | $ git fetch git://example.com/proj.git master:refs/remotes/example/master |
2690 | $ git fetch example master:refs/remotes/example/master | |
b181d57f BF |
2691 | $ git fetch example |
2692 | ------------------------------------------------- | |
2693 | ||
2694 | You can also add a "+" to force the update each time: | |
2695 | ||
2696 | ------------------------------------------------- | |
9d13bda3 | 2697 | $ git config remote.example.fetch +master:ref/remotes/example/master |
b181d57f BF |
2698 | ------------------------------------------------- |
2699 | ||
2700 | Don't do this unless you're sure you won't mind "git fetch" possibly | |
2701 | throwing away commits on mybranch. | |
2702 | ||
2703 | Also note that all of the above configuration can be performed by | |
2704 | directly editing the file .git/config instead of using | |
9d13bda3 | 2705 | gitlink:git-config[1]. |
b181d57f | 2706 | |
9d13bda3 | 2707 | See gitlink:git-config[1] for more details on the configuration |
b181d57f | 2708 | options mentioned above. |
d19fbc3c | 2709 | |
d19fbc3c | 2710 | |
036f8199 BF |
2711 | [[git-concepts]] |
2712 | Git concepts | |
2713 | ============ | |
d19fbc3c | 2714 | |
036f8199 BF |
2715 | Git is built on a small number of simple but powerful ideas. While it |
2716 | is possible to get things done without understanding them, you will find | |
2717 | git much more intuitive if you do. | |
2718 | ||
2719 | We start with the most important, the <<def_object_database,object | |
2720 | database>> and the <<def_index,index>>. | |
b181d57f | 2721 | |
e34caace | 2722 | [[the-object-database]] |
b181d57f BF |
2723 | The Object Database |
2724 | ------------------- | |
2725 | ||
2726 | The object database is literally just a content-addressable collection | |
2727 | of objects. All objects are named by their content, which is | |
2728 | approximated by the SHA1 hash of the object itself. Objects may refer | |
2729 | to other objects (by referencing their SHA1 hash), and so you can | |
2730 | build up a hierarchy of objects. | |
2731 | ||
c64415e2 | 2732 | All objects have a statically determined "type" which is |
b181d57f BF |
2733 | determined at object creation time, and which identifies the format of |
2734 | the object (i.e. how it is used, and how it can refer to other | |
2735 | objects). There are currently four different object types: "blob", | |
a536b08b | 2736 | "tree", "commit", and "tag". |
b181d57f | 2737 | |
a536b08b BF |
2738 | A <<def_blob_object,"blob" object>> cannot refer to any other object, |
2739 | and is, as the name implies, a pure storage object containing some | |
2740 | user data. It is used to actually store the file data, i.e. a blob | |
2741 | object is associated with some particular version of some file. | |
b181d57f | 2742 | |
a536b08b BF |
2743 | A <<def_tree_object,"tree" object>> is an object that ties one or more |
2744 | "blob" objects into a directory structure. In addition, a tree object | |
2745 | can refer to other tree objects, thus creating a directory hierarchy. | |
b181d57f | 2746 | |
a536b08b BF |
2747 | A <<def_commit_object,"commit" object>> ties such directory hierarchies |
2748 | together into a <<def_DAG,directed acyclic graph>> of revisions - each | |
2749 | "commit" is associated with exactly one tree (the directory hierarchy at | |
2750 | the time of the commit). In addition, a "commit" refers to one or more | |
2751 | "parent" commit objects that describe the history of how we arrived at | |
2752 | that directory hierarchy. | |
b181d57f BF |
2753 | |
2754 | As a special case, a commit object with no parents is called the "root" | |
c64415e2 | 2755 | commit, and is the point of an initial project commit. Each project |
b181d57f BF |
2756 | must have at least one root, and while you can tie several different |
2757 | root objects together into one project by creating a commit object which | |
2758 | has two or more separate roots as its ultimate parents, that's probably | |
2759 | just going to confuse people. So aim for the notion of "one root object | |
a6080a0a | 2760 | per project", even if git itself does not enforce that. |
b181d57f | 2761 | |
a536b08b BF |
2762 | A <<def_tag_object,"tag" object>> symbolically identifies and can be |
2763 | used to sign other objects. It contains the identifier and type of | |
2764 | another object, a symbolic name (of course!) and, optionally, a | |
2765 | signature. | |
b181d57f | 2766 | |
b181d57f BF |
2767 | The object types in some more detail: |
2768 | ||
e34caace | 2769 | [[blob-object]] |
b181d57f | 2770 | Blob Object |
971aa71f | 2771 | ~~~~~~~~~~~ |
b181d57f BF |
2772 | |
2773 | A "blob" object is nothing but a binary blob of data, and doesn't | |
2774 | refer to anything else. There is no signature or any other | |
2775 | verification of the data, so while the object is consistent (it 'is' | |
2776 | indexed by its sha1 hash, so the data itself is certainly correct), it | |
2777 | has absolutely no other attributes. No name associations, no | |
2778 | permissions. It is purely a blob of data (i.e. normally "file | |
2779 | contents"). | |
2780 | ||
2781 | In particular, since the blob is entirely defined by its data, if two | |
2782 | files in a directory tree (or in multiple different versions of the | |
2783 | repository) have the same contents, they will share the same blob | |
2784 | object. The object is totally independent of its location in the | |
2785 | directory tree, and renaming a file does not change the object that | |
2786 | file is associated with in any way. | |
2787 | ||
2788 | A blob is typically created when gitlink:git-update-index[1] | |
2789 | is run, and its data can be accessed by gitlink:git-cat-file[1]. | |
2790 | ||
e34caace | 2791 | [[tree-object]] |
b181d57f | 2792 | Tree Object |
971aa71f | 2793 | ~~~~~~~~~~~ |
b181d57f BF |
2794 | |
2795 | The next hierarchical object type is the "tree" object. A tree object | |
2796 | is a list of mode/name/blob data, sorted by name. Alternatively, the | |
2797 | mode data may specify a directory mode, in which case instead of | |
2798 | naming a blob, that name is associated with another TREE object. | |
2799 | ||
2800 | Like the "blob" object, a tree object is uniquely determined by the | |
2801 | set contents, and so two separate but identical trees will always | |
2802 | share the exact same object. This is true at all levels, i.e. it's | |
2803 | true for a "leaf" tree (which does not refer to any other trees, only | |
2804 | blobs) as well as for a whole subdirectory. | |
2805 | ||
2806 | For that reason a "tree" object is just a pure data abstraction: it | |
2807 | has no history, no signatures, no verification of validity, except | |
2808 | that since the contents are again protected by the hash itself, we can | |
2809 | trust that the tree is immutable and its contents never change. | |
2810 | ||
2811 | So you can trust the contents of a tree to be valid, the same way you | |
2812 | can trust the contents of a blob, but you don't know where those | |
2813 | contents 'came' from. | |
2814 | ||
2815 | Side note on trees: since a "tree" object is a sorted list of | |
2816 | "filename+content", you can create a diff between two trees without | |
2817 | actually having to unpack two trees. Just ignore all common parts, | |
2818 | and your diff will look right. In other words, you can effectively | |
2819 | (and efficiently) tell the difference between any two random trees by | |
2820 | O(n) where "n" is the size of the difference, rather than the size of | |
2821 | the tree. | |
2822 | ||
2823 | Side note 2 on trees: since the name of a "blob" depends entirely and | |
2824 | exclusively on its contents (i.e. there are no names or permissions | |
2825 | involved), you can see trivial renames or permission changes by | |
2826 | noticing that the blob stayed the same. However, renames with data | |
2827 | changes need a smarter "diff" implementation. | |
2828 | ||
2829 | A tree is created with gitlink:git-write-tree[1] and | |
2830 | its data can be accessed by gitlink:git-ls-tree[1]. | |
2831 | Two trees can be compared with gitlink:git-diff-tree[1]. | |
2832 | ||
e34caace | 2833 | [[commit-object]] |
b181d57f | 2834 | Commit Object |
971aa71f | 2835 | ~~~~~~~~~~~~~ |
b181d57f BF |
2836 | |
2837 | The "commit" object is an object that introduces the notion of | |
2838 | history into the picture. In contrast to the other objects, it | |
2839 | doesn't just describe the physical state of a tree, it describes how | |
2840 | we got there, and why. | |
2841 | ||
2842 | A "commit" is defined by the tree-object that it results in, the | |
2843 | parent commits (zero, one or more) that led up to that point, and a | |
2844 | comment on what happened. Again, a commit is not trusted per se: | |
2845 | the contents are well-defined and "safe" due to the cryptographically | |
2846 | strong signatures at all levels, but there is no reason to believe | |
2847 | that the tree is "good" or that the merge information makes sense. | |
2848 | The parents do not have to actually have any relationship with the | |
2849 | result, for example. | |
2850 | ||
c64415e2 | 2851 | Note on commits: unlike some SCM's, commits do not contain |
b181d57f BF |
2852 | rename information or file mode change information. All of that is |
2853 | implicit in the trees involved (the result tree, and the result trees | |
2854 | of the parents), and describing that makes no sense in this idiotic | |
2855 | file manager. | |
2856 | ||
2857 | A commit is created with gitlink:git-commit-tree[1] and | |
2858 | its data can be accessed by gitlink:git-cat-file[1]. | |
2859 | ||
e34caace | 2860 | [[trust]] |
b181d57f | 2861 | Trust |
971aa71f | 2862 | ~~~~~ |
b181d57f BF |
2863 | |
2864 | An aside on the notion of "trust". Trust is really outside the scope | |
2865 | of "git", but it's worth noting a few things. First off, since | |
2866 | everything is hashed with SHA1, you 'can' trust that an object is | |
2867 | intact and has not been messed with by external sources. So the name | |
2868 | of an object uniquely identifies a known state - just not a state that | |
2869 | you may want to trust. | |
2870 | ||
2871 | Furthermore, since the SHA1 signature of a commit refers to the | |
2872 | SHA1 signatures of the tree it is associated with and the signatures | |
2873 | of the parent, a single named commit specifies uniquely a whole set | |
2874 | of history, with full contents. You can't later fake any step of the | |
2875 | way once you have the name of a commit. | |
2876 | ||
2877 | So to introduce some real trust in the system, the only thing you need | |
2878 | to do is to digitally sign just 'one' special note, which includes the | |
2879 | name of a top-level commit. Your digital signature shows others | |
2880 | that you trust that commit, and the immutability of the history of | |
2881 | commits tells others that they can trust the whole history. | |
2882 | ||
2883 | In other words, you can easily validate a whole archive by just | |
2884 | sending out a single email that tells the people the name (SHA1 hash) | |
2885 | of the top commit, and digitally sign that email using something | |
2886 | like GPG/PGP. | |
2887 | ||
2888 | To assist in this, git also provides the tag object... | |
2889 | ||
e34caace | 2890 | [[tag-object]] |
b181d57f | 2891 | Tag Object |
971aa71f | 2892 | ~~~~~~~~~~ |
b181d57f BF |
2893 | |
2894 | Git provides the "tag" object to simplify creating, managing and | |
2895 | exchanging symbolic and signed tokens. The "tag" object at its | |
2896 | simplest simply symbolically identifies another object by containing | |
2897 | the sha1, type and symbolic name. | |
2898 | ||
2899 | However it can optionally contain additional signature information | |
2900 | (which git doesn't care about as long as there's less than 8k of | |
2901 | it). This can then be verified externally to git. | |
2902 | ||
2903 | Note that despite the tag features, "git" itself only handles content | |
2904 | integrity; the trust framework (and signature provision and | |
2905 | verification) has to come from outside. | |
2906 | ||
2907 | A tag is created with gitlink:git-mktag[1], | |
2908 | its data can be accessed by gitlink:git-cat-file[1], | |
2909 | and the signature can be verified by | |
2910 | gitlink:git-verify-tag[1]. | |
2911 | ||
2912 | ||
e34caace | 2913 | [[the-index]] |
b181d57f BF |
2914 | The "index" aka "Current Directory Cache" |
2915 | ----------------------------------------- | |
2916 | ||
2917 | The index is a simple binary file, which contains an efficient | |
c64415e2 | 2918 | representation of the contents of a virtual directory. It |
b181d57f BF |
2919 | does so by a simple array that associates a set of names, dates, |
2920 | permissions and content (aka "blob") objects together. The cache is | |
2921 | always kept ordered by name, and names are unique (with a few very | |
2922 | specific rules) at any point in time, but the cache has no long-term | |
2923 | meaning, and can be partially updated at any time. | |
2924 | ||
2925 | In particular, the index certainly does not need to be consistent with | |
2926 | the current directory contents (in fact, most operations will depend on | |
2927 | different ways to make the index 'not' be consistent with the directory | |
2928 | hierarchy), but it has three very important attributes: | |
2929 | ||
2930 | '(a) it can re-generate the full state it caches (not just the | |
2931 | directory structure: it contains pointers to the "blob" objects so | |
2932 | that it can regenerate the data too)' | |
2933 | ||
2934 | As a special case, there is a clear and unambiguous one-way mapping | |
2935 | from a current directory cache to a "tree object", which can be | |
2936 | efficiently created from just the current directory cache without | |
2937 | actually looking at any other data. So a directory cache at any one | |
2938 | time uniquely specifies one and only one "tree" object (but has | |
2939 | additional data to make it easy to match up that tree object with what | |
2940 | has happened in the directory) | |
2941 | ||
2942 | '(b) it has efficient methods for finding inconsistencies between that | |
2943 | cached state ("tree object waiting to be instantiated") and the | |
2944 | current state.' | |
2945 | ||
2946 | '(c) it can additionally efficiently represent information about merge | |
2947 | conflicts between different tree objects, allowing each pathname to be | |
2948 | associated with sufficient information about the trees involved that | |
2949 | you can create a three-way merge between them.' | |
2950 | ||
79c96c57 | 2951 | Those are the ONLY three things that the directory cache does. It's a |
b181d57f BF |
2952 | cache, and the normal operation is to re-generate it completely from a |
2953 | known tree object, or update/compare it with a live tree that is being | |
2954 | developed. If you blow the directory cache away entirely, you generally | |
2955 | haven't lost any information as long as you have the name of the tree | |
a6080a0a | 2956 | that it described. |
b181d57f | 2957 | |
48389181 MF |
2958 | At the same time, the index is also the staging area for creating |
2959 | new trees, and creating a new tree always involves a controlled | |
2960 | modification of the index file. In particular, the index file can | |
2961 | have the representation of an intermediate tree that has not yet been | |
2962 | instantiated. So the index can be thought of as a write-back cache, | |
2963 | which can contain dirty information that has not yet been written back | |
2964 | to the backing store. | |
b181d57f | 2965 | |
1c6045ff BF |
2966 | [[low-level-operations]] |
2967 | Low-level git operations | |
2968 | ======================== | |
b181d57f | 2969 | |
1c6045ff BF |
2970 | Many of the higher-level commands were originally implemented as shell |
2971 | scripts using a smaller core of low-level git commands. These can still | |
2972 | be useful when doing unusual things with git, or just as a way to | |
2973 | understand its inner workings. | |
b181d57f | 2974 | |
e34caace | 2975 | [[the-workflow]] |
b181d57f BF |
2976 | The Workflow |
2977 | ------------ | |
2978 | ||
1c6045ff BF |
2979 | High-level operations such as gitlink:git-commit[1], |
2980 | gitlink:git-checkout[1] and git-reset[1] work by moving data between the | |
2981 | working tree, the index, and the object database. Git provides | |
2982 | low-level operations which perform each of these steps individually. | |
2983 | ||
b181d57f BF |
2984 | Generally, all "git" operations work on the index file. Some operations |
2985 | work *purely* on the index file (showing the current state of the | |
1c6045ff BF |
2986 | index), but most operations move data between the index file and either |
2987 | the database or the working directory. Thus there are four main | |
2988 | combinations: | |
b181d57f | 2989 | |
e34caace | 2990 | [[working-directory-to-index]] |
b181d57f BF |
2991 | working directory -> index |
2992 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
2993 | ||
1c6045ff BF |
2994 | The gitlink:git-update-index[1] command updates the index with |
2995 | information from the working directory. You generally update the | |
2996 | index information by just specifying the filename you want to update, | |
2997 | like so: | |
b181d57f BF |
2998 | |
2999 | ------------------------------------------------- | |
1c6045ff | 3000 | $ git update-index filename |
b181d57f BF |
3001 | ------------------------------------------------- |
3002 | ||
3003 | but to avoid common mistakes with filename globbing etc, the command | |
3004 | will not normally add totally new entries or remove old entries, | |
3005 | i.e. it will normally just update existing cache entries. | |
3006 | ||
3007 | To tell git that yes, you really do realize that certain files no | |
3008 | longer exist, or that new files should be added, you | |
3009 | should use the `--remove` and `--add` flags respectively. | |
3010 | ||
3011 | NOTE! A `--remove` flag does 'not' mean that subsequent filenames will | |
3012 | necessarily be removed: if the files still exist in your directory | |
3013 | structure, the index will be updated with their new status, not | |
3014 | removed. The only thing `--remove` means is that update-cache will be | |
3015 | considering a removed file to be a valid thing, and if the file really | |
3016 | does not exist any more, it will update the index accordingly. | |
3017 | ||
3018 | As a special case, you can also do `git-update-index --refresh`, which | |
3019 | will refresh the "stat" information of each index to match the current | |
3020 | stat information. It will 'not' update the object status itself, and | |
3021 | it will only update the fields that are used to quickly test whether | |
3022 | an object still matches its old backing store object. | |
3023 | ||
1c6045ff BF |
3024 | The previously introduced gitlink:git-add[1] is just a wrapper for |
3025 | gitlink:git-update-index[1]. | |
3026 | ||
e34caace | 3027 | [[index-to-object-database]] |
b181d57f BF |
3028 | index -> object database |
3029 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
3030 | ||
3031 | You write your current index file to a "tree" object with the program | |
3032 | ||
3033 | ------------------------------------------------- | |
1c6045ff | 3034 | $ git write-tree |
b181d57f BF |
3035 | ------------------------------------------------- |
3036 | ||
3037 | that doesn't come with any options - it will just write out the | |
3038 | current index into the set of tree objects that describe that state, | |
3039 | and it will return the name of the resulting top-level tree. You can | |
3040 | use that tree to re-generate the index at any time by going in the | |
3041 | other direction: | |
3042 | ||
e34caace | 3043 | [[object-database-to-index]] |
b181d57f BF |
3044 | object database -> index |
3045 | ~~~~~~~~~~~~~~~~~~~~~~~~ | |
3046 | ||
3047 | You read a "tree" file from the object database, and use that to | |
3048 | populate (and overwrite - don't do this if your index contains any | |
3049 | unsaved state that you might want to restore later!) your current | |
3050 | index. Normal operation is just | |
3051 | ||
3052 | ------------------------------------------------- | |
3053 | $ git-read-tree <sha1 of tree> | |
3054 | ------------------------------------------------- | |
3055 | ||
3056 | and your index file will now be equivalent to the tree that you saved | |
3057 | earlier. However, that is only your 'index' file: your working | |
3058 | directory contents have not been modified. | |
3059 | ||
e34caace | 3060 | [[index-to-working-directory]] |
b181d57f BF |
3061 | index -> working directory |
3062 | ~~~~~~~~~~~~~~~~~~~~~~~~~~ | |
3063 | ||
3064 | You update your working directory from the index by "checking out" | |
3065 | files. This is not a very common operation, since normally you'd just | |
3066 | keep your files updated, and rather than write to your working | |
3067 | directory, you'd tell the index files about the changes in your | |
3068 | working directory (i.e. `git-update-index`). | |
3069 | ||
3070 | However, if you decide to jump to a new version, or check out somebody | |
3071 | else's version, or just restore a previous tree, you'd populate your | |
3072 | index file with read-tree, and then you need to check out the result | |
3073 | with | |
3074 | ||
3075 | ------------------------------------------------- | |
3076 | $ git-checkout-index filename | |
3077 | ------------------------------------------------- | |
3078 | ||
3079 | or, if you want to check out all of the index, use `-a`. | |
3080 | ||
3081 | NOTE! git-checkout-index normally refuses to overwrite old files, so | |
3082 | if you have an old version of the tree already checked out, you will | |
3083 | need to use the "-f" flag ('before' the "-a" flag or the filename) to | |
3084 | 'force' the checkout. | |
3085 | ||
3086 | ||
3087 | Finally, there are a few odds and ends which are not purely moving | |
3088 | from one representation to the other: | |
3089 | ||
e34caace | 3090 | [[tying-it-all-together]] |
b181d57f BF |
3091 | Tying it all together |
3092 | ~~~~~~~~~~~~~~~~~~~~~ | |
3093 | ||
3094 | To commit a tree you have instantiated with "git-write-tree", you'd | |
3095 | create a "commit" object that refers to that tree and the history | |
3096 | behind it - most notably the "parent" commits that preceded it in | |
3097 | history. | |
3098 | ||
3099 | Normally a "commit" has one parent: the previous state of the tree | |
3100 | before a certain change was made. However, sometimes it can have two | |
3101 | or more parent commits, in which case we call it a "merge", due to the | |
3102 | fact that such a commit brings together ("merges") two or more | |
3103 | previous states represented by other commits. | |
3104 | ||
3105 | In other words, while a "tree" represents a particular directory state | |
3106 | of a working directory, a "commit" represents that state in "time", | |
3107 | and explains how we got there. | |
3108 | ||
3109 | You create a commit object by giving it the tree that describes the | |
3110 | state at the time of the commit, and a list of parents: | |
3111 | ||
3112 | ------------------------------------------------- | |
3113 | $ git-commit-tree <tree> -p <parent> [-p <parent2> ..] | |
3114 | ------------------------------------------------- | |
3115 | ||
3116 | and then giving the reason for the commit on stdin (either through | |
3117 | redirection from a pipe or file, or by just typing it at the tty). | |
3118 | ||
3119 | git-commit-tree will return the name of the object that represents | |
3120 | that commit, and you should save it away for later use. Normally, | |
3121 | you'd commit a new `HEAD` state, and while git doesn't care where you | |
3122 | save the note about that state, in practice we tend to just write the | |
3123 | result to the file pointed at by `.git/HEAD`, so that we can always see | |
3124 | what the last committed state was. | |
3125 | ||
3126 | Here is an ASCII art by Jon Loeliger that illustrates how | |
3127 | various pieces fit together. | |
3128 | ||
3129 | ------------ | |
3130 | ||
3131 | commit-tree | |
3132 | commit obj | |
3133 | +----+ | |
3134 | | | | |
3135 | | | | |
3136 | V V | |
3137 | +-----------+ | |
3138 | | Object DB | | |
3139 | | Backing | | |
3140 | | Store | | |
3141 | +-----------+ | |
3142 | ^ | |
3143 | write-tree | | | |
3144 | tree obj | | | |
3145 | | | read-tree | |
3146 | | | tree obj | |
3147 | V | |
3148 | +-----------+ | |
3149 | | Index | | |
3150 | | "cache" | | |
3151 | +-----------+ | |
3152 | update-index ^ | |
3153 | blob obj | | | |
3154 | | | | |
3155 | checkout-index -u | | checkout-index | |
3156 | stat | | blob obj | |
3157 | V | |
3158 | +-----------+ | |
3159 | | Working | | |
3160 | | Directory | | |
3161 | +-----------+ | |
3162 | ||
3163 | ------------ | |
3164 | ||
3165 | ||
e34caace | 3166 | [[examining-the-data]] |
b181d57f BF |
3167 | Examining the data |
3168 | ------------------ | |
3169 | ||
3170 | You can examine the data represented in the object database and the | |
3171 | index with various helper tools. For every object, you can use | |
3172 | gitlink:git-cat-file[1] to examine details about the | |
3173 | object: | |
3174 | ||
3175 | ------------------------------------------------- | |
3176 | $ git-cat-file -t <objectname> | |
3177 | ------------------------------------------------- | |
3178 | ||
3179 | shows the type of the object, and once you have the type (which is | |
3180 | usually implicit in where you find the object), you can use | |
3181 | ||
3182 | ------------------------------------------------- | |
3183 | $ git-cat-file blob|tree|commit|tag <objectname> | |
3184 | ------------------------------------------------- | |
3185 | ||
3186 | to show its contents. NOTE! Trees have binary content, and as a result | |
3187 | there is a special helper for showing that content, called | |
3188 | `git-ls-tree`, which turns the binary content into a more easily | |
3189 | readable form. | |
3190 | ||
3191 | It's especially instructive to look at "commit" objects, since those | |
3192 | tend to be small and fairly self-explanatory. In particular, if you | |
3193 | follow the convention of having the top commit name in `.git/HEAD`, | |
3194 | you can do | |
3195 | ||
3196 | ------------------------------------------------- | |
3197 | $ git-cat-file commit HEAD | |
3198 | ------------------------------------------------- | |
3199 | ||
3200 | to see what the top commit was. | |
3201 | ||
e34caace | 3202 | [[merging-multiple-trees]] |
b181d57f | 3203 | Merging multiple trees |
d19fbc3c BF |
3204 | ---------------------- |
3205 | ||
b181d57f BF |
3206 | Git helps you do a three-way merge, which you can expand to n-way by |
3207 | repeating the merge procedure arbitrary times until you finally | |
3208 | "commit" the state. The normal situation is that you'd only do one | |
3209 | three-way merge (two parents), and commit it, but if you like to, you | |
3210 | can do multiple parents in one go. | |
3211 | ||
3212 | To do a three-way merge, you need the two sets of "commit" objects | |
3213 | that you want to merge, use those to find the closest common parent (a | |
3214 | third "commit" object), and then use those commit objects to find the | |
3215 | state of the directory ("tree" object) at these points. | |
3216 | ||
3217 | To get the "base" for the merge, you first look up the common parent | |
3218 | of two commits with | |
3219 | ||
3220 | ------------------------------------------------- | |
3221 | $ git-merge-base <commit1> <commit2> | |
3222 | ------------------------------------------------- | |
3223 | ||
3224 | which will return you the commit they are both based on. You should | |
3225 | now look up the "tree" objects of those commits, which you can easily | |
3226 | do with (for example) | |
3227 | ||
3228 | ------------------------------------------------- | |
3229 | $ git-cat-file commit <commitname> | head -1 | |
3230 | ------------------------------------------------- | |
3231 | ||
3232 | since the tree object information is always the first line in a commit | |
3233 | object. | |
3234 | ||
1191ee18 | 3235 | Once you know the three trees you are going to merge (the one "original" |
c64415e2 | 3236 | tree, aka the common tree, and the two "result" trees, aka the branches |
1191ee18 BF |
3237 | you want to merge), you do a "merge" read into the index. This will |
3238 | complain if it has to throw away your old index contents, so you should | |
b181d57f | 3239 | make sure that you've committed those - in fact you would normally |
1191ee18 BF |
3240 | always do a merge against your last commit (which should thus match what |
3241 | you have in your current index anyway). | |
b181d57f BF |
3242 | |
3243 | To do the merge, do | |
3244 | ||
3245 | ------------------------------------------------- | |
3246 | $ git-read-tree -m -u <origtree> <yourtree> <targettree> | |
3247 | ------------------------------------------------- | |
3248 | ||
3249 | which will do all trivial merge operations for you directly in the | |
3250 | index file, and you can just write the result out with | |
3251 | `git-write-tree`. | |
3252 | ||
3253 | ||
e34caace | 3254 | [[merging-multiple-trees-2]] |
b181d57f BF |
3255 | Merging multiple trees, continued |
3256 | --------------------------------- | |
3257 | ||
3258 | Sadly, many merges aren't trivial. If there are files that have | |
3259 | been added.moved or removed, or if both branches have modified the | |
3260 | same file, you will be left with an index tree that contains "merge | |
3261 | entries" in it. Such an index tree can 'NOT' be written out to a tree | |
3262 | object, and you will have to resolve any such merge clashes using | |
3263 | other tools before you can write out the result. | |
3264 | ||
3265 | You can examine such index state with `git-ls-files --unmerged` | |
3266 | command. An example: | |
3267 | ||
3268 | ------------------------------------------------ | |
3269 | $ git-read-tree -m $orig HEAD $target | |
3270 | $ git-ls-files --unmerged | |
3271 | 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello.c | |
3272 | 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello.c | |
3273 | 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello.c | |
3274 | ------------------------------------------------ | |
3275 | ||
3276 | Each line of the `git-ls-files --unmerged` output begins with | |
3277 | the blob mode bits, blob SHA1, 'stage number', and the | |
3278 | filename. The 'stage number' is git's way to say which tree it | |
3279 | came from: stage 1 corresponds to `$orig` tree, stage 2 `HEAD` | |
3280 | tree, and stage3 `$target` tree. | |
3281 | ||
3282 | Earlier we said that trivial merges are done inside | |
3283 | `git-read-tree -m`. For example, if the file did not change | |
3284 | from `$orig` to `HEAD` nor `$target`, or if the file changed | |
3285 | from `$orig` to `HEAD` and `$orig` to `$target` the same way, | |
3286 | obviously the final outcome is what is in `HEAD`. What the | |
3287 | above example shows is that file `hello.c` was changed from | |
3288 | `$orig` to `HEAD` and `$orig` to `$target` in a different way. | |
3289 | You could resolve this by running your favorite 3-way merge | |
c64415e2 BF |
3290 | program, e.g. `diff3`, `merge`, or git's own merge-file, on |
3291 | the blob objects from these three stages yourself, like this: | |
b181d57f BF |
3292 | |
3293 | ------------------------------------------------ | |
3294 | $ git-cat-file blob 263414f... >hello.c~1 | |
3295 | $ git-cat-file blob 06fa6a2... >hello.c~2 | |
3296 | $ git-cat-file blob cc44c73... >hello.c~3 | |
c64415e2 | 3297 | $ git merge-file hello.c~2 hello.c~1 hello.c~3 |
b181d57f BF |
3298 | ------------------------------------------------ |
3299 | ||
3300 | This would leave the merge result in `hello.c~2` file, along | |
3301 | with conflict markers if there are conflicts. After verifying | |
3302 | the merge result makes sense, you can tell git what the final | |
3303 | merge result for this file is by: | |
3304 | ||
3305 | ------------------------------------------------- | |
3306 | $ mv -f hello.c~2 hello.c | |
3307 | $ git-update-index hello.c | |
3308 | ------------------------------------------------- | |
3309 | ||
3310 | When a path is in unmerged state, running `git-update-index` for | |
3311 | that path tells git to mark the path resolved. | |
3312 | ||
3313 | The above is the description of a git merge at the lowest level, | |
3314 | to help you understand what conceptually happens under the hood. | |
3315 | In practice, nobody, not even git itself, uses three `git-cat-file` | |
3316 | for this. There is `git-merge-index` program that extracts the | |
3317 | stages to temporary files and calls a "merge" script on it: | |
3318 | ||
3319 | ------------------------------------------------- | |
3320 | $ git-merge-index git-merge-one-file hello.c | |
3321 | ------------------------------------------------- | |
3322 | ||
207dfa07 | 3323 | and that is what higher level `git merge -s resolve` is implemented with. |
b181d57f | 3324 | |
e34caace | 3325 | [[pack-files]] |
b181d57f BF |
3326 | How git stores objects efficiently: pack files |
3327 | ---------------------------------------------- | |
3328 | ||
3329 | We've seen how git stores each object in a file named after the | |
3330 | object's SHA1 hash. | |
3331 | ||
3332 | Unfortunately this system becomes inefficient once a project has a | |
3333 | lot of objects. Try this on an old project: | |
3334 | ||
3335 | ------------------------------------------------ | |
3336 | $ git count-objects | |
3337 | 6930 objects, 47620 kilobytes | |
3338 | ------------------------------------------------ | |
3339 | ||
3340 | The first number is the number of objects which are kept in | |
3341 | individual files. The second is the amount of space taken up by | |
3342 | those "loose" objects. | |
3343 | ||
3344 | You can save space and make git faster by moving these loose objects in | |
3345 | to a "pack file", which stores a group of objects in an efficient | |
3346 | compressed format; the details of how pack files are formatted can be | |
3347 | found in link:technical/pack-format.txt[technical/pack-format.txt]. | |
3348 | ||
3349 | To put the loose objects into a pack, just run git repack: | |
3350 | ||
3351 | ------------------------------------------------ | |
3352 | $ git repack | |
3353 | Generating pack... | |
3354 | Done counting 6020 objects. | |
3355 | Deltifying 6020 objects. | |
3356 | 100% (6020/6020) done | |
3357 | Writing 6020 objects. | |
3358 | 100% (6020/6020) done | |
3359 | Total 6020, written 6020 (delta 4070), reused 0 (delta 0) | |
3360 | Pack pack-3e54ad29d5b2e05838c75df582c65257b8d08e1c created. | |
3361 | ------------------------------------------------ | |
3362 | ||
3363 | You can then run | |
3364 | ||
3365 | ------------------------------------------------ | |
3366 | $ git prune | |
3367 | ------------------------------------------------ | |
3368 | ||
3369 | to remove any of the "loose" objects that are now contained in the | |
3370 | pack. This will also remove any unreferenced objects (which may be | |
3371 | created when, for example, you use "git reset" to remove a commit). | |
3372 | You can verify that the loose objects are gone by looking at the | |
3373 | .git/objects directory or by running | |
3374 | ||
3375 | ------------------------------------------------ | |
3376 | $ git count-objects | |
3377 | 0 objects, 0 kilobytes | |
3378 | ------------------------------------------------ | |
3379 | ||
3380 | Although the object files are gone, any commands that refer to those | |
3381 | objects will work exactly as they did before. | |
3382 | ||
3383 | The gitlink:git-gc[1] command performs packing, pruning, and more for | |
3384 | you, so is normally the only high-level command you need. | |
d19fbc3c | 3385 | |
59723040 | 3386 | [[dangling-objects]] |
21dcb3b7 | 3387 | Dangling objects |
61b41790 | 3388 | ---------------- |
21dcb3b7 | 3389 | |
04e50e94 | 3390 | The gitlink:git-fsck[1] command will sometimes complain about dangling |
21dcb3b7 BF |
3391 | objects. They are not a problem. |
3392 | ||
1191ee18 BF |
3393 | The most common cause of dangling objects is that you've rebased a |
3394 | branch, or you have pulled from somebody else who rebased a branch--see | |
3395 | <<cleaning-up-history>>. In that case, the old head of the original | |
59723040 BF |
3396 | branch still exists, as does everything it pointed to. The branch |
3397 | pointer itself just doesn't, since you replaced it with another one. | |
1191ee18 | 3398 | |
59723040 | 3399 | There are also other situations that cause dangling objects. For |
1191ee18 BF |
3400 | example, a "dangling blob" may arise because you did a "git add" of a |
3401 | file, but then, before you actually committed it and made it part of the | |
3402 | bigger picture, you changed something else in that file and committed | |
3403 | that *updated* thing - the old state that you added originally ends up | |
3404 | not being pointed to by any commit or tree, so it's now a dangling blob | |
3405 | object. | |
3406 | ||
3407 | Similarly, when the "recursive" merge strategy runs, and finds that | |
3408 | there are criss-cross merges and thus more than one merge base (which is | |
3409 | fairly unusual, but it does happen), it will generate one temporary | |
3410 | midway tree (or possibly even more, if you had lots of criss-crossing | |
3411 | merges and more than two merge bases) as a temporary internal merge | |
3412 | base, and again, those are real objects, but the end result will not end | |
3413 | up pointing to them, so they end up "dangling" in your repository. | |
3414 | ||
3415 | Generally, dangling objects aren't anything to worry about. They can | |
3416 | even be very useful: if you screw something up, the dangling objects can | |
3417 | be how you recover your old tree (say, you did a rebase, and realized | |
3418 | that you really didn't want to - you can look at what dangling objects | |
3419 | you have, and decide to reset your head to some old dangling state). | |
21dcb3b7 | 3420 | |
59723040 | 3421 | For commits, you can just use: |
21dcb3b7 BF |
3422 | |
3423 | ------------------------------------------------ | |
3424 | $ gitk <dangling-commit-sha-goes-here> --not --all | |
3425 | ------------------------------------------------ | |
3426 | ||
59723040 BF |
3427 | This asks for all the history reachable from the given commit but not |
3428 | from any branch, tag, or other reference. If you decide it's something | |
3429 | you want, you can always create a new reference to it, e.g., | |
3430 | ||
3431 | ------------------------------------------------ | |
3432 | $ git branch recovered-branch <dangling-commit-sha-goes-here> | |
3433 | ------------------------------------------------ | |
3434 | ||
3435 | For blobs and trees, you can't do the same, but you can still examine | |
3436 | them. You can just do | |
21dcb3b7 BF |
3437 | |
3438 | ------------------------------------------------ | |
3439 | $ git show <dangling-blob/tree-sha-goes-here> | |
3440 | ------------------------------------------------ | |
3441 | ||
1191ee18 BF |
3442 | to show what the contents of the blob were (or, for a tree, basically |
3443 | what the "ls" for that directory was), and that may give you some idea | |
3444 | of what the operation was that left that dangling object. | |
21dcb3b7 | 3445 | |
1191ee18 BF |
3446 | Usually, dangling blobs and trees aren't very interesting. They're |
3447 | almost always the result of either being a half-way mergebase (the blob | |
3448 | will often even have the conflict markers from a merge in it, if you | |
3449 | have had conflicting merges that you fixed up by hand), or simply | |
3450 | because you interrupted a "git fetch" with ^C or something like that, | |
3451 | leaving _some_ of the new objects in the object database, but just | |
3452 | dangling and useless. | |
21dcb3b7 | 3453 | |
a6080a0a | 3454 | Anyway, once you are sure that you're not interested in any dangling |
21dcb3b7 BF |
3455 | state, you can just prune all unreachable objects: |
3456 | ||
3457 | ------------------------------------------------ | |
3458 | $ git prune | |
3459 | ------------------------------------------------ | |
3460 | ||
1191ee18 BF |
3461 | and they'll be gone. But you should only run "git prune" on a quiescent |
3462 | repository - it's kind of like doing a filesystem fsck recovery: you | |
3463 | don't want to do that while the filesystem is mounted. | |
21dcb3b7 | 3464 | |
a6080a0a JH |
3465 | (The same is true of "git-fsck" itself, btw - but since |
3466 | git-fsck never actually *changes* the repository, it just reports | |
3467 | on what it found, git-fsck itself is never "dangerous" to run. | |
3468 | Running it while somebody is actually changing the repository can cause | |
3469 | confusing and scary messages, but it won't actually do anything bad. In | |
3470 | contrast, running "git prune" while somebody is actively changing the | |
21dcb3b7 BF |
3471 | repository is a *BAD* idea). |
3472 | ||
971aa71f BF |
3473 | [[hacking-git]] |
3474 | Hacking git | |
3475 | =========== | |
3476 | ||
3477 | This chapter covers internal details of the git implementation which | |
3478 | probably only git developers need to understand. | |
3479 | ||
f2327c6c BF |
3480 | [[object-details]] |
3481 | Object storage format | |
3482 | --------------------- | |
3483 | ||
3484 | All objects have a statically determined "type" which identifies the | |
3485 | format of the object (i.e. how it is used, and how it can refer to other | |
3486 | objects). There are currently four different object types: "blob", | |
3487 | "tree", "commit", and "tag". | |
3488 | ||
3489 | Regardless of object type, all objects share the following | |
3490 | characteristics: they are all deflated with zlib, and have a header | |
3491 | that not only specifies their type, but also provides size information | |
3492 | about the data in the object. It's worth noting that the SHA1 hash | |
3493 | that is used to name the object is the hash of the original data | |
3494 | plus this header, so `sha1sum` 'file' does not match the object name | |
3495 | for 'file'. | |
3496 | (Historical note: in the dawn of the age of git the hash | |
3497 | was the sha1 of the 'compressed' object.) | |
3498 | ||
3499 | As a result, the general consistency of an object can always be tested | |
3500 | independently of the contents or the type of the object: all objects can | |
3501 | be validated by verifying that (a) their hashes match the content of the | |
3502 | file and (b) the object successfully inflates to a stream of bytes that | |
3503 | forms a sequence of <ascii type without space> {plus} <space> {plus} <ascii decimal | |
3504 | size> {plus} <byte\0> {plus} <binary object data>. | |
3505 | ||
3506 | The structured objects can further have their structure and | |
3507 | connectivity to other objects verified. This is generally done with | |
3508 | the `git-fsck` program, which generates a full dependency graph | |
3509 | of all objects, and verifies their internal consistency (in addition | |
3510 | to just verifying their superficial consistency through the hash). | |
3511 | ||
126640af | 3512 | [[birdview-on-the-source-code]] |
a5fc33b4 BF |
3513 | A birds-eye view of Git's source code |
3514 | ------------------------------------- | |
126640af | 3515 | |
a5fc33b4 BF |
3516 | It is not always easy for new developers to find their way through Git's |
3517 | source code. This section gives you a little guidance to show where to | |
3518 | start. | |
126640af | 3519 | |
a5fc33b4 | 3520 | A good place to start is with the contents of the initial commit, with: |
126640af JS |
3521 | |
3522 | ---------------------------------------------------- | |
a5fc33b4 | 3523 | $ git checkout e83c5163 |
126640af JS |
3524 | ---------------------------------------------------- |
3525 | ||
a5fc33b4 BF |
3526 | The initial revision lays the foundation for almost everything git has |
3527 | today, but is small enough to read in one sitting. | |
126640af | 3528 | |
a5fc33b4 BF |
3529 | Note that terminology has changed since that revision. For example, the |
3530 | README in that revision uses the word "changeset" to describe what we | |
3531 | now call a <<def_commit_object,commit>>. | |
126640af | 3532 | |
a5fc33b4 | 3533 | Also, we do not call it "cache" any more, but "index", however, the |
126640af JS |
3534 | file is still called `cache.h`. Remark: Not much reason to change it now, |
3535 | especially since there is no good single name for it anyway, because it is | |
3536 | basically _the_ header file which is included by _all_ of Git's C sources. | |
3537 | ||
a5fc33b4 BF |
3538 | If you grasp the ideas in that initial commit, you should check out a |
3539 | more recent version and skim `cache.h`, `object.h` and `commit.h`. | |
126640af JS |
3540 | |
3541 | In the early days, Git (in the tradition of UNIX) was a bunch of programs | |
3542 | which were extremely simple, and which you used in scripts, piping the | |
3543 | output of one into another. This turned out to be good for initial | |
3544 | development, since it was easier to test new things. However, recently | |
3545 | many of these parts have become builtins, and some of the core has been | |
3546 | "libified", i.e. put into libgit.a for performance, portability reasons, | |
3547 | and to avoid code duplication. | |
3548 | ||
3549 | By now, you know what the index is (and find the corresponding data | |
3550 | structures in `cache.h`), and that there are just a couple of object types | |
3551 | (blobs, trees, commits and tags) which inherit their common structure from | |
3552 | `struct object`, which is their first member (and thus, you can cast e.g. | |
3553 | `(struct object *)commit` to achieve the _same_ as `&commit->object`, i.e. | |
3554 | get at the object name and flags). | |
3555 | ||
3556 | Now is a good point to take a break to let this information sink in. | |
3557 | ||
3558 | Next step: get familiar with the object naming. Read <<naming-commits>>. | |
3559 | There are quite a few ways to name an object (and not only revisions!). | |
3560 | All of these are handled in `sha1_name.c`. Just have a quick look at | |
3561 | the function `get_sha1()`. A lot of the special handling is done by | |
3562 | functions like `get_sha1_basic()` or the likes. | |
3563 | ||
3564 | This is just to get you into the groove for the most libified part of Git: | |
3565 | the revision walker. | |
3566 | ||
3567 | Basically, the initial version of `git log` was a shell script: | |
3568 | ||
3569 | ---------------------------------------------------------------- | |
3570 | $ git-rev-list --pretty $(git-rev-parse --default HEAD "$@") | \ | |
3571 | LESS=-S ${PAGER:-less} | |
3572 | ---------------------------------------------------------------- | |
3573 | ||
3574 | What does this mean? | |
3575 | ||
3576 | `git-rev-list` is the original version of the revision walker, which | |
3577 | _always_ printed a list of revisions to stdout. It is still functional, | |
3578 | and needs to, since most new Git programs start out as scripts using | |
3579 | `git-rev-list`. | |
3580 | ||
3581 | `git-rev-parse` is not as important any more; it was only used to filter out | |
3582 | options that were relevant for the different plumbing commands that were | |
3583 | called by the script. | |
3584 | ||
3585 | Most of what `git-rev-list` did is contained in `revision.c` and | |
3586 | `revision.h`. It wraps the options in a struct named `rev_info`, which | |
3587 | controls how and what revisions are walked, and more. | |
3588 | ||
3589 | The original job of `git-rev-parse` is now taken by the function | |
3590 | `setup_revisions()`, which parses the revisions and the common command line | |
3591 | options for the revision walker. This information is stored in the struct | |
3592 | `rev_info` for later consumption. You can do your own command line option | |
3593 | parsing after calling `setup_revisions()`. After that, you have to call | |
3594 | `prepare_revision_walk()` for initialization, and then you can get the | |
3595 | commits one by one with the function `get_revision()`. | |
3596 | ||
3597 | If you are interested in more details of the revision walking process, | |
3598 | just have a look at the first implementation of `cmd_log()`; call | |
3599 | `git-show v1.3.0~155^2~4` and scroll down to that function (note that you | |
3600 | no longer need to call `setup_pager()` directly). | |
3601 | ||
3602 | Nowadays, `git log` is a builtin, which means that it is _contained_ in the | |
3603 | command `git`. The source side of a builtin is | |
3604 | ||
3605 | - a function called `cmd_<bla>`, typically defined in `builtin-<bla>.c`, | |
3606 | and declared in `builtin.h`, | |
3607 | ||
3608 | - an entry in the `commands[]` array in `git.c`, and | |
3609 | ||
3610 | - an entry in `BUILTIN_OBJECTS` in the `Makefile`. | |
3611 | ||
3612 | Sometimes, more than one builtin is contained in one source file. For | |
3613 | example, `cmd_whatchanged()` and `cmd_log()` both reside in `builtin-log.c`, | |
3614 | since they share quite a bit of code. In that case, the commands which are | |
3615 | _not_ named like the `.c` file in which they live have to be listed in | |
3616 | `BUILT_INS` in the `Makefile`. | |
3617 | ||
3618 | `git log` looks more complicated in C than it does in the original script, | |
3619 | but that allows for a much greater flexibility and performance. | |
3620 | ||
3621 | Here again it is a good point to take a pause. | |
3622 | ||
3623 | Lesson three is: study the code. Really, it is the best way to learn about | |
3624 | the organization of Git (after you know the basic concepts). | |
3625 | ||
3626 | So, think about something which you are interested in, say, "how can I | |
3627 | access a blob just knowing the object name of it?". The first step is to | |
3628 | find a Git command with which you can do it. In this example, it is either | |
3629 | `git show` or `git cat-file`. | |
3630 | ||
3631 | For the sake of clarity, let's stay with `git cat-file`, because it | |
3632 | ||
3633 | - is plumbing, and | |
3634 | ||
3635 | - was around even in the initial commit (it literally went only through | |
3636 | some 20 revisions as `cat-file.c`, was renamed to `builtin-cat-file.c` | |
3637 | when made a builtin, and then saw less than 10 versions). | |
3638 | ||
3639 | So, look into `builtin-cat-file.c`, search for `cmd_cat_file()` and look what | |
3640 | it does. | |
3641 | ||
3642 | ------------------------------------------------------------------ | |
3643 | git_config(git_default_config); | |
3644 | if (argc != 3) | |
3645 | usage("git-cat-file [-t|-s|-e|-p|<type>] <sha1>"); | |
3646 | if (get_sha1(argv[2], sha1)) | |
3647 | die("Not a valid object name %s", argv[2]); | |
3648 | ------------------------------------------------------------------ | |
3649 | ||
3650 | Let's skip over the obvious details; the only really interesting part | |
3651 | here is the call to `get_sha1()`. It tries to interpret `argv[2]` as an | |
3652 | object name, and if it refers to an object which is present in the current | |
3653 | repository, it writes the resulting SHA-1 into the variable `sha1`. | |
3654 | ||
3655 | Two things are interesting here: | |
3656 | ||
3657 | - `get_sha1()` returns 0 on _success_. This might surprise some new | |
3658 | Git hackers, but there is a long tradition in UNIX to return different | |
3659 | negative numbers in case of different errors -- and 0 on success. | |
3660 | ||
3661 | - the variable `sha1` in the function signature of `get_sha1()` is `unsigned | |
a5fc33b4 | 3662 | char \*`, but is actually expected to be a pointer to `unsigned |
126640af | 3663 | char[20]`. This variable will contain the 160-bit SHA-1 of the given |
a5fc33b4 | 3664 | commit. Note that whenever a SHA-1 is passed as `unsigned char \*`, it |
126640af | 3665 | is the binary representation, as opposed to the ASCII representation in |
a5fc33b4 | 3666 | hex characters, which is passed as `char *`. |
126640af JS |
3667 | |
3668 | You will see both of these things throughout the code. | |
3669 | ||
3670 | Now, for the meat: | |
3671 | ||
3672 | ----------------------------------------------------------------------------- | |
3673 | case 0: | |
3674 | buf = read_object_with_reference(sha1, argv[1], &size, NULL); | |
3675 | ----------------------------------------------------------------------------- | |
3676 | ||
3677 | This is how you read a blob (actually, not only a blob, but any type of | |
3678 | object). To know how the function `read_object_with_reference()` actually | |
3679 | works, find the source code for it (something like `git grep | |
3680 | read_object_with | grep ":[a-z]"` in the git repository), and read | |
3681 | the source. | |
3682 | ||
3683 | To find out how the result can be used, just read on in `cmd_cat_file()`: | |
3684 | ||
3685 | ----------------------------------- | |
3686 | write_or_die(1, buf, size); | |
3687 | ----------------------------------- | |
3688 | ||
3689 | Sometimes, you do not know where to look for a feature. In many such cases, | |
3690 | it helps to search through the output of `git log`, and then `git show` the | |
3691 | corresponding commit. | |
3692 | ||
3693 | Example: If you know that there was some test case for `git bundle`, but | |
3694 | do not remember where it was (yes, you _could_ `git grep bundle t/`, but that | |
3695 | does not illustrate the point!): | |
3696 | ||
3697 | ------------------------ | |
3698 | $ git log --no-merges t/ | |
3699 | ------------------------ | |
3700 | ||
3701 | In the pager (`less`), just search for "bundle", go a few lines back, | |
3702 | and see that it is in commit 18449ab0... Now just copy this object name, | |
3703 | and paste it into the command line | |
3704 | ||
3705 | ------------------- | |
3706 | $ git show 18449ab0 | |
3707 | ------------------- | |
3708 | ||
3709 | Voila. | |
3710 | ||
3711 | Another example: Find out what to do in order to make some script a | |
3712 | builtin: | |
3713 | ||
3714 | ------------------------------------------------- | |
3715 | $ git log --no-merges --diff-filter=A builtin-*.c | |
3716 | ------------------------------------------------- | |
3717 | ||
3718 | You see, Git is actually the best tool to find out about the source of Git | |
3719 | itself! | |
3720 | ||
e34caace | 3721 | [[glossary]] |
d19fbc3c BF |
3722 | include::glossary.txt[] |
3723 | ||
2624d9a5 | 3724 | [[git-quick-start]] |
99f171bb BF |
3725 | Appendix A: Git Quick Reference |
3726 | =============================== | |
2624d9a5 | 3727 | |
99f171bb BF |
3728 | This is a quick summary of the major commands; the previous chapters |
3729 | explain how these work in more detail. | |
2624d9a5 BF |
3730 | |
3731 | [[quick-creating-a-new-repository]] | |
3732 | Creating a new repository | |
3733 | ------------------------- | |
3734 | ||
3735 | From a tarball: | |
3736 | ||
3737 | ----------------------------------------------- | |
3738 | $ tar xzf project.tar.gz | |
3739 | $ cd project | |
3740 | $ git init | |
3741 | Initialized empty Git repository in .git/ | |
3742 | $ git add . | |
3743 | $ git commit | |
3744 | ----------------------------------------------- | |
3745 | ||
3746 | From a remote repository: | |
3747 | ||
3748 | ----------------------------------------------- | |
3749 | $ git clone git://example.com/pub/project.git | |
3750 | $ cd project | |
3751 | ----------------------------------------------- | |
3752 | ||
3753 | [[managing-branches]] | |
3754 | Managing branches | |
3755 | ----------------- | |
3756 | ||
3757 | ----------------------------------------------- | |
3758 | $ git branch # list all local branches in this repo | |
3759 | $ git checkout test # switch working directory to branch "test" | |
3760 | $ git branch new # create branch "new" starting at current HEAD | |
3761 | $ git branch -d new # delete branch "new" | |
3762 | ----------------------------------------------- | |
3763 | ||
3764 | Instead of basing new branch on current HEAD (the default), use: | |
3765 | ||
3766 | ----------------------------------------------- | |
3767 | $ git branch new test # branch named "test" | |
3768 | $ git branch new v2.6.15 # tag named v2.6.15 | |
3769 | $ git branch new HEAD^ # commit before the most recent | |
3770 | $ git branch new HEAD^^ # commit before that | |
3771 | $ git branch new test~10 # ten commits before tip of branch "test" | |
3772 | ----------------------------------------------- | |
3773 | ||
3774 | Create and switch to a new branch at the same time: | |
3775 | ||
3776 | ----------------------------------------------- | |
3777 | $ git checkout -b new v2.6.15 | |
3778 | ----------------------------------------------- | |
3779 | ||
3780 | Update and examine branches from the repository you cloned from: | |
3781 | ||
3782 | ----------------------------------------------- | |
3783 | $ git fetch # update | |
3784 | $ git branch -r # list | |
3785 | origin/master | |
3786 | origin/next | |
3787 | ... | |
3788 | $ git checkout -b masterwork origin/master | |
3789 | ----------------------------------------------- | |
3790 | ||
3791 | Fetch a branch from a different repository, and give it a new | |
3792 | name in your repository: | |
3793 | ||
3794 | ----------------------------------------------- | |
3795 | $ git fetch git://example.com/project.git theirbranch:mybranch | |
3796 | $ git fetch git://example.com/project.git v2.6.15:mybranch | |
3797 | ----------------------------------------------- | |
3798 | ||
3799 | Keep a list of repositories you work with regularly: | |
3800 | ||
3801 | ----------------------------------------------- | |
3802 | $ git remote add example git://example.com/project.git | |
3803 | $ git remote # list remote repositories | |
3804 | example | |
3805 | origin | |
3806 | $ git remote show example # get details | |
3807 | * remote example | |
3808 | URL: git://example.com/project.git | |
3809 | Tracked remote branches | |
3810 | master next ... | |
3811 | $ git fetch example # update branches from example | |
3812 | $ git branch -r # list all remote branches | |
3813 | ----------------------------------------------- | |
3814 | ||
3815 | ||
3816 | [[exploring-history]] | |
3817 | Exploring history | |
3818 | ----------------- | |
3819 | ||
3820 | ----------------------------------------------- | |
3821 | $ gitk # visualize and browse history | |
3822 | $ git log # list all commits | |
3823 | $ git log src/ # ...modifying src/ | |
3824 | $ git log v2.6.15..v2.6.16 # ...in v2.6.16, not in v2.6.15 | |
3825 | $ git log master..test # ...in branch test, not in branch master | |
3826 | $ git log test..master # ...in branch master, but not in test | |
3827 | $ git log test...master # ...in one branch, not in both | |
3828 | $ git log -S'foo()' # ...where difference contain "foo()" | |
3829 | $ git log --since="2 weeks ago" | |
3830 | $ git log -p # show patches as well | |
3831 | $ git show # most recent commit | |
3832 | $ git diff v2.6.15..v2.6.16 # diff between two tagged versions | |
3833 | $ git diff v2.6.15..HEAD # diff with current head | |
3834 | $ git grep "foo()" # search working directory for "foo()" | |
3835 | $ git grep v2.6.15 "foo()" # search old tree for "foo()" | |
3836 | $ git show v2.6.15:a.txt # look at old version of a.txt | |
3837 | ----------------------------------------------- | |
3838 | ||
3839 | Search for regressions: | |
3840 | ||
3841 | ----------------------------------------------- | |
3842 | $ git bisect start | |
3843 | $ git bisect bad # current version is bad | |
3844 | $ git bisect good v2.6.13-rc2 # last known good revision | |
3845 | Bisecting: 675 revisions left to test after this | |
3846 | # test here, then: | |
3847 | $ git bisect good # if this revision is good, or | |
3848 | $ git bisect bad # if this revision is bad. | |
3849 | # repeat until done. | |
3850 | ----------------------------------------------- | |
3851 | ||
3852 | [[making-changes]] | |
3853 | Making changes | |
3854 | -------------- | |
3855 | ||
3856 | Make sure git knows who to blame: | |
3857 | ||
3858 | ------------------------------------------------ | |
3859 | $ cat >>~/.gitconfig <<\EOF | |
3860 | [user] | |
3861 | name = Your Name Comes Here | |
3862 | email = you@yourdomain.example.com | |
3863 | EOF | |
3864 | ------------------------------------------------ | |
3865 | ||
3866 | Select file contents to include in the next commit, then make the | |
3867 | commit: | |
3868 | ||
3869 | ----------------------------------------------- | |
3870 | $ git add a.txt # updated file | |
3871 | $ git add b.txt # new file | |
3872 | $ git rm c.txt # old file | |
3873 | $ git commit | |
3874 | ----------------------------------------------- | |
3875 | ||
3876 | Or, prepare and create the commit in one step: | |
3877 | ||
3878 | ----------------------------------------------- | |
3879 | $ git commit d.txt # use latest content only of d.txt | |
3880 | $ git commit -a # use latest content of all tracked files | |
3881 | ----------------------------------------------- | |
3882 | ||
3883 | [[merging]] | |
3884 | Merging | |
3885 | ------- | |
3886 | ||
3887 | ----------------------------------------------- | |
3888 | $ git merge test # merge branch "test" into the current branch | |
3889 | $ git pull git://example.com/project.git master | |
3890 | # fetch and merge in remote branch | |
3891 | $ git pull . test # equivalent to git merge test | |
3892 | ----------------------------------------------- | |
3893 | ||
3894 | [[sharing-your-changes]] | |
3895 | Sharing your changes | |
3896 | -------------------- | |
3897 | ||
3898 | Importing or exporting patches: | |
3899 | ||
3900 | ----------------------------------------------- | |
3901 | $ git format-patch origin..HEAD # format a patch for each commit | |
3902 | # in HEAD but not in origin | |
3903 | $ git am mbox # import patches from the mailbox "mbox" | |
3904 | ----------------------------------------------- | |
3905 | ||
3906 | Fetch a branch in a different git repository, then merge into the | |
3907 | current branch: | |
3908 | ||
3909 | ----------------------------------------------- | |
3910 | $ git pull git://example.com/project.git theirbranch | |
3911 | ----------------------------------------------- | |
3912 | ||
3913 | Store the fetched branch into a local branch before merging into the | |
3914 | current branch: | |
3915 | ||
3916 | ----------------------------------------------- | |
3917 | $ git pull git://example.com/project.git theirbranch:mybranch | |
3918 | ----------------------------------------------- | |
3919 | ||
3920 | After creating commits on a local branch, update the remote | |
3921 | branch with your commits: | |
3922 | ||
3923 | ----------------------------------------------- | |
3924 | $ git push ssh://example.com/project.git mybranch:theirbranch | |
3925 | ----------------------------------------------- | |
3926 | ||
3927 | When remote and local branch are both named "test": | |
3928 | ||
3929 | ----------------------------------------------- | |
3930 | $ git push ssh://example.com/project.git test | |
3931 | ----------------------------------------------- | |
3932 | ||
3933 | Shortcut version for a frequently used remote repository: | |
3934 | ||
3935 | ----------------------------------------------- | |
3936 | $ git remote add example ssh://example.com/project.git | |
3937 | $ git push example test | |
3938 | ----------------------------------------------- | |
3939 | ||
3940 | [[repository-maintenance]] | |
3941 | Repository maintenance | |
3942 | ---------------------- | |
3943 | ||
3944 | Check for corruption: | |
3945 | ||
3946 | ----------------------------------------------- | |
3947 | $ git fsck | |
3948 | ----------------------------------------------- | |
3949 | ||
3950 | Recompress, remove unused cruft: | |
3951 | ||
3952 | ----------------------------------------------- | |
3953 | $ git gc | |
3954 | ----------------------------------------------- | |
3955 | ||
3956 | ||
e34caace | 3957 | [[todo]] |
2624d9a5 BF |
3958 | Appendix B: Notes and todo list for this manual |
3959 | =============================================== | |
6bd9b682 BF |
3960 | |
3961 | This is a work in progress. | |
3962 | ||
3963 | The basic requirements: | |
2f99710c | 3964 | - It must be readable in order, from beginning to end, by |
02783075 BH |
3965 | someone intelligent with a basic grasp of the UNIX |
3966 | command line, but without any special knowledge of git. If | |
2f99710c BF |
3967 | necessary, any other prerequisites should be specifically |
3968 | mentioned as they arise. | |
3969 | - Whenever possible, section headings should clearly describe | |
3970 | the task they explain how to do, in language that requires | |
3971 | no more knowledge than necessary: for example, "importing | |
3972 | patches into a project" rather than "the git-am command" | |
6bd9b682 | 3973 | |
d5cd5de4 BF |
3974 | Think about how to create a clear chapter dependency graph that will |
3975 | allow people to get to important topics without necessarily reading | |
3976 | everything in between. | |
d19fbc3c BF |
3977 | |
3978 | Scan Documentation/ for other stuff left out; in particular: | |
3979 | howto's | |
d19fbc3c BF |
3980 | some of technical/? |
3981 | hooks | |
0b375ab0 | 3982 | list of commands in gitlink:git[1] |
d19fbc3c BF |
3983 | |
3984 | Scan email archives for other stuff left out | |
3985 | ||
3986 | Scan man pages to see if any assume more background than this manual | |
3987 | provides. | |
3988 | ||
2f99710c | 3989 | Simplify beginning by suggesting disconnected head instead of |
b181d57f | 3990 | temporary branch creation? |
d19fbc3c | 3991 | |
2f99710c BF |
3992 | Add more good examples. Entire sections of just cookbook examples |
3993 | might be a good idea; maybe make an "advanced examples" section a | |
3994 | standard end-of-chapter section? | |
d19fbc3c BF |
3995 | |
3996 | Include cross-references to the glossary, where appropriate. | |
3997 | ||
9a241220 BF |
3998 | Document shallow clones? See draft 1.5.0 release notes for some |
3999 | documentation. | |
4000 | ||
3dff5379 | 4001 | Add a section on working with other version control systems, including |
9a241220 BF |
4002 | CVS, Subversion, and just imports of series of release tarballs. |
4003 | ||
a8cd1402 | 4004 | More details on gitweb? |
0b375ab0 BF |
4005 | |
4006 | Write a chapter on using plumbing and writing scripts. | |
d9bd321c BF |
4007 | |
4008 | Alternates, clone -reference, etc. | |
4009 | ||
4010 | git unpack-objects -r for recovery |