Merge branch 'ks/maint-mailinfo-folded'
[git/git.git] / Documentation / gitcore-tutorial.txt
1 gitcore-tutorial(7)
2 ===================
3
4 NAME
5 ----
6 gitcore-tutorial - A git core tutorial for developers
7
8 SYNOPSIS
9 --------
10 git *
11
12 DESCRIPTION
13 -----------
14
15 This tutorial explains how to use the "core" git programs to set up and
16 work with a git repository.
17
18 If you just need to use git as a revision control system you may prefer
19 to start with "A Tutorial Introduction to GIT" (linkgit:gittutorial[7]) or
20 link:user-manual.html[the GIT User Manual].
21
22 However, an understanding of these low-level tools can be helpful if
23 you want to understand git's internals.
24
25 The core git is often called "plumbing", with the prettier user
26 interfaces on top of it called "porcelain". You may not want to use the
27 plumbing directly very often, but it can be good to know what the
28 plumbing does for when the porcelain isn't flushing.
29
30 [NOTE]
31 Deeper technical details are often marked as Notes, which you can
32 skip on your first reading.
33
34
35 Creating a git repository
36 -------------------------
37
38 Creating a new git repository couldn't be easier: all git repositories start
39 out empty, and the only thing you need to do is find yourself a
40 subdirectory that you want to use as a working tree - either an empty
41 one for a totally new project, or an existing working tree that you want
42 to import into git.
43
44 For our first example, we're going to start a totally new repository from
45 scratch, with no pre-existing files, and we'll call it 'git-tutorial'.
46 To start up, create a subdirectory for it, change into that
47 subdirectory, and initialize the git infrastructure with 'git-init':
48
49 ------------------------------------------------
50 $ mkdir git-tutorial
51 $ cd git-tutorial
52 $ git init
53 ------------------------------------------------
54
55 to which git will reply
56
57 ----------------
58 Initialized empty Git repository in .git/
59 ----------------
60
61 which is just git's way of saying that you haven't been doing anything
62 strange, and that it will have created a local `.git` directory setup for
63 your new project. You will now have a `.git` directory, and you can
64 inspect that with 'ls'. For your new empty project, it should show you
65 three entries, among other things:
66
67 - a file called `HEAD`, that has `ref: refs/heads/master` in it.
68 This is similar to a symbolic link and points at
69 `refs/heads/master` relative to the `HEAD` file.
70 +
71 Don't worry about the fact that the file that the `HEAD` link points to
72 doesn't even exist yet -- you haven't created the commit that will
73 start your `HEAD` development branch yet.
74
75 - a subdirectory called `objects`, which will contain all the
76 objects of your project. You should never have any real reason to
77 look at the objects directly, but you might want to know that these
78 objects are what contains all the real 'data' in your repository.
79
80 - a subdirectory called `refs`, which contains references to objects.
81
82 In particular, the `refs` subdirectory will contain two other
83 subdirectories, named `heads` and `tags` respectively. They do
84 exactly what their names imply: they contain references to any number
85 of different 'heads' of development (aka 'branches'), and to any
86 'tags' that you have created to name specific versions in your
87 repository.
88
89 One note: the special `master` head is the default branch, which is
90 why the `.git/HEAD` file was created points to it even if it
91 doesn't yet exist. Basically, the `HEAD` link is supposed to always
92 point to the branch you are working on right now, and you always
93 start out expecting to work on the `master` branch.
94
95 However, this is only a convention, and you can name your branches
96 anything you want, and don't have to ever even 'have' a `master`
97 branch. A number of the git tools will assume that `.git/HEAD` is
98 valid, though.
99
100 [NOTE]
101 An 'object' is identified by its 160-bit SHA1 hash, aka 'object name',
102 and a reference to an object is always the 40-byte hex
103 representation of that SHA1 name. The files in the `refs`
104 subdirectory are expected to contain these hex references
105 (usually with a final `\'\n\'` at the end), and you should thus
106 expect to see a number of 41-byte files containing these
107 references in these `refs` subdirectories when you actually start
108 populating your tree.
109
110 [NOTE]
111 An advanced user may want to take a look at linkgit:gitrepository-layout[5]
112 after finishing this tutorial.
113
114 You have now created your first git repository. Of course, since it's
115 empty, that's not very useful, so let's start populating it with data.
116
117
118 Populating a git repository
119 ---------------------------
120
121 We'll keep this simple and stupid, so we'll start off with populating a
122 few trivial files just to get a feel for it.
123
124 Start off with just creating any random files that you want to maintain
125 in your git repository. We'll start off with a few bad examples, just to
126 get a feel for how this works:
127
128 ------------------------------------------------
129 $ echo "Hello World" >hello
130 $ echo "Silly example" >example
131 ------------------------------------------------
132
133 you have now created two files in your working tree (aka 'working directory'),
134 but to actually check in your hard work, you will have to go through two steps:
135
136 - fill in the 'index' file (aka 'cache') with the information about your
137 working tree state.
138
139 - commit that index file as an object.
140
141 The first step is trivial: when you want to tell git about any changes
142 to your working tree, you use the 'git-update-index' program. That
143 program normally just takes a list of filenames you want to update, but
144 to avoid trivial mistakes, it refuses to add new entries to the index
145 (or remove existing ones) unless you explicitly tell it that you're
146 adding a new entry with the `\--add` flag (or removing an entry with the
147 `\--remove`) flag.
148
149 So to populate the index with the two files you just created, you can do
150
151 ------------------------------------------------
152 $ git update-index --add hello example
153 ------------------------------------------------
154
155 and you have now told git to track those two files.
156
157 In fact, as you did that, if you now look into your object directory,
158 you'll notice that git will have added two new objects to the object
159 database. If you did exactly the steps above, you should now be able to do
160
161
162 ----------------
163 $ ls .git/objects/??/*
164 ----------------
165
166 and see two files:
167
168 ----------------
169 .git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
170 .git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
171 ----------------
172
173 which correspond with the objects with names of `557db...` and
174 `f24c7...` respectively.
175
176 If you want to, you can use 'git-cat-file' to look at those objects, but
177 you'll have to use the object name, not the filename of the object:
178
179 ----------------
180 $ git cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
181 ----------------
182
183 where the `-t` tells 'git-cat-file' to tell you what the "type" of the
184 object is. git will tell you that you have a "blob" object (i.e., just a
185 regular file), and you can see the contents with
186
187 ----------------
188 $ git cat-file "blob" 557db03
189 ----------------
190
191 which will print out "Hello World". The object `557db03` is nothing
192 more than the contents of your file `hello`.
193
194 [NOTE]
195 Don't confuse that object with the file `hello` itself. The
196 object is literally just those specific *contents* of the file, and
197 however much you later change the contents in file `hello`, the object
198 we just looked at will never change. Objects are immutable.
199
200 [NOTE]
201 The second example demonstrates that you can
202 abbreviate the object name to only the first several
203 hexadecimal digits in most places.
204
205 Anyway, as we mentioned previously, you normally never actually take a
206 look at the objects themselves, and typing long 40-character hex
207 names is not something you'd normally want to do. The above digression
208 was just to show that 'git-update-index' did something magical, and
209 actually saved away the contents of your files into the git object
210 database.
211
212 Updating the index did something else too: it created a `.git/index`
213 file. This is the index that describes your current working tree, and
214 something you should be very aware of. Again, you normally never worry
215 about the index file itself, but you should be aware of the fact that
216 you have not actually really "checked in" your files into git so far,
217 you've only *told* git about them.
218
219 However, since git knows about them, you can now start using some of the
220 most basic git commands to manipulate the files or look at their status.
221
222 In particular, let's not even check in the two files into git yet, we'll
223 start off by adding another line to `hello` first:
224
225 ------------------------------------------------
226 $ echo "It's a new day for git" >>hello
227 ------------------------------------------------
228
229 and you can now, since you told git about the previous state of `hello`, ask
230 git what has changed in the tree compared to your old index, using the
231 'git-diff-files' command:
232
233 ------------
234 $ git diff-files
235 ------------
236
237 Oops. That wasn't very readable. It just spit out its own internal
238 version of a 'diff', but that internal version really just tells you
239 that it has noticed that "hello" has been modified, and that the old object
240 contents it had have been replaced with something else.
241
242 To make it readable, we can tell 'git-diff-files' to output the
243 differences as a patch, using the `-p` flag:
244
245 ------------
246 $ git diff-files -p
247 diff --git a/hello b/hello
248 index 557db03..263414f 100644
249 --- a/hello
250 +++ b/hello
251 @@ -1 +1,2 @@
252 Hello World
253 +It's a new day for git
254 ----
255
256 i.e. the diff of the change we caused by adding another line to `hello`.
257
258 In other words, 'git-diff-files' always shows us the difference between
259 what is recorded in the index, and what is currently in the working
260 tree. That's very useful.
261
262 A common shorthand for `git diff-files -p` is to just write `git
263 diff`, which will do the same thing.
264
265 ------------
266 $ git diff
267 diff --git a/hello b/hello
268 index 557db03..263414f 100644
269 --- a/hello
270 +++ b/hello
271 @@ -1 +1,2 @@
272 Hello World
273 +It's a new day for git
274 ------------
275
276
277 Committing git state
278 --------------------
279
280 Now, we want to go to the next stage in git, which is to take the files
281 that git knows about in the index, and commit them as a real tree. We do
282 that in two phases: creating a 'tree' object, and committing that 'tree'
283 object as a 'commit' object together with an explanation of what the
284 tree was all about, along with information of how we came to that state.
285
286 Creating a tree object is trivial, and is done with 'git-write-tree'.
287 There are no options or other input: `git write-tree` will take the
288 current index state, and write an object that describes that whole
289 index. In other words, we're now tying together all the different
290 filenames with their contents (and their permissions), and we're
291 creating the equivalent of a git "directory" object:
292
293 ------------------------------------------------
294 $ git write-tree
295 ------------------------------------------------
296
297 and this will just output the name of the resulting tree, in this case
298 (if you have done exactly as I've described) it should be
299
300 ----------------
301 8988da15d077d4829fc51d8544c097def6644dbb
302 ----------------
303
304 which is another incomprehensible object name. Again, if you want to,
305 you can use `git cat-file -t 8988d\...` to see that this time the object
306 is not a "blob" object, but a "tree" object (you can also use
307 `git cat-file` to actually output the raw object contents, but you'll see
308 mainly a binary mess, so that's less interesting).
309
310 However -- normally you'd never use 'git-write-tree' on its own, because
311 normally you always commit a tree into a commit object using the
312 'git-commit-tree' command. In fact, it's easier to not actually use
313 'git-write-tree' on its own at all, but to just pass its result in as an
314 argument to 'git-commit-tree'.
315
316 'git-commit-tree' normally takes several arguments -- it wants to know
317 what the 'parent' of a commit was, but since this is the first commit
318 ever in this new repository, and it has no parents, we only need to pass in
319 the object name of the tree. However, 'git-commit-tree' also wants to get a
320 commit message on its standard input, and it will write out the resulting
321 object name for the commit to its standard output.
322
323 And this is where we create the `.git/refs/heads/master` file
324 which is pointed at by `HEAD`. This file is supposed to contain
325 the reference to the top-of-tree of the master branch, and since
326 that's exactly what 'git-commit-tree' spits out, we can do this
327 all with a sequence of simple shell commands:
328
329 ------------------------------------------------
330 $ tree=$(git write-tree)
331 $ commit=$(echo 'Initial commit' | git commit-tree $tree)
332 $ git update-ref HEAD $commit
333 ------------------------------------------------
334
335 In this case this creates a totally new commit that is not related to
336 anything else. Normally you do this only *once* for a project ever, and
337 all later commits will be parented on top of an earlier commit.
338
339 Again, normally you'd never actually do this by hand. There is a
340 helpful script called `git commit` that will do all of this for you. So
341 you could have just written `git commit`
342 instead, and it would have done the above magic scripting for you.
343
344
345 Making a change
346 ---------------
347
348 Remember how we did the 'git-update-index' on file `hello` and then we
349 changed `hello` afterward, and could compare the new state of `hello` with the
350 state we saved in the index file?
351
352 Further, remember how I said that 'git-write-tree' writes the contents
353 of the *index* file to the tree, and thus what we just committed was in
354 fact the *original* contents of the file `hello`, not the new ones. We did
355 that on purpose, to show the difference between the index state, and the
356 state in the working tree, and how they don't have to match, even
357 when we commit things.
358
359 As before, if we do `git diff-files -p` in our git-tutorial project,
360 we'll still see the same difference we saw last time: the index file
361 hasn't changed by the act of committing anything. However, now that we
362 have committed something, we can also learn to use a new command:
363 'git-diff-index'.
364
365 Unlike 'git-diff-files', which showed the difference between the index
366 file and the working tree, 'git-diff-index' shows the differences
367 between a committed *tree* and either the index file or the working
368 tree. In other words, 'git-diff-index' wants a tree to be diffed
369 against, and before we did the commit, we couldn't do that, because we
370 didn't have anything to diff against.
371
372 But now we can do
373
374 ----------------
375 $ git diff-index -p HEAD
376 ----------------
377
378 (where `-p` has the same meaning as it did in 'git-diff-files'), and it
379 will show us the same difference, but for a totally different reason.
380 Now we're comparing the working tree not against the index file,
381 but against the tree we just wrote. It just so happens that those two
382 are obviously the same, so we get the same result.
383
384 Again, because this is a common operation, you can also just shorthand
385 it with
386
387 ----------------
388 $ git diff HEAD
389 ----------------
390
391 which ends up doing the above for you.
392
393 In other words, 'git-diff-index' normally compares a tree against the
394 working tree, but when given the `\--cached` flag, it is told to
395 instead compare against just the index cache contents, and ignore the
396 current working tree state entirely. Since we just wrote the index
397 file to HEAD, doing `git diff-index \--cached -p HEAD` should thus return
398 an empty set of differences, and that's exactly what it does.
399
400 [NOTE]
401 ================
402 'git-diff-index' really always uses the index for its
403 comparisons, and saying that it compares a tree against the working
404 tree is thus not strictly accurate. In particular, the list of
405 files to compare (the "meta-data") *always* comes from the index file,
406 regardless of whether the `\--cached` flag is used or not. The `\--cached`
407 flag really only determines whether the file *contents* to be compared
408 come from the working tree or not.
409
410 This is not hard to understand, as soon as you realize that git simply
411 never knows (or cares) about files that it is not told about
412 explicitly. git will never go *looking* for files to compare, it
413 expects you to tell it what the files are, and that's what the index
414 is there for.
415 ================
416
417 However, our next step is to commit the *change* we did, and again, to
418 understand what's going on, keep in mind the difference between "working
419 tree contents", "index file" and "committed tree". We have changes
420 in the working tree that we want to commit, and we always have to
421 work through the index file, so the first thing we need to do is to
422 update the index cache:
423
424 ------------------------------------------------
425 $ git update-index hello
426 ------------------------------------------------
427
428 (note how we didn't need the `\--add` flag this time, since git knew
429 about the file already).
430
431 Note what happens to the different 'git-diff-\*' versions here. After
432 we've updated `hello` in the index, `git diff-files -p` now shows no
433 differences, but `git diff-index -p HEAD` still *does* show that the
434 current state is different from the state we committed. In fact, now
435 'git-diff-index' shows the same difference whether we use the `--cached`
436 flag or not, since now the index is coherent with the working tree.
437
438 Now, since we've updated `hello` in the index, we can commit the new
439 version. We could do it by writing the tree by hand again, and
440 committing the tree (this time we'd have to use the `-p HEAD` flag to
441 tell commit that the HEAD was the *parent* of the new commit, and that
442 this wasn't an initial commit any more), but you've done that once
443 already, so let's just use the helpful script this time:
444
445 ------------------------------------------------
446 $ git commit
447 ------------------------------------------------
448
449 which starts an editor for you to write the commit message and tells you
450 a bit about what you have done.
451
452 Write whatever message you want, and all the lines that start with '#'
453 will be pruned out, and the rest will be used as the commit message for
454 the change. If you decide you don't want to commit anything after all at
455 this point (you can continue to edit things and update the index), you
456 can just leave an empty message. Otherwise `git commit` will commit
457 the change for you.
458
459 You've now made your first real git commit. And if you're interested in
460 looking at what `git commit` really does, feel free to investigate:
461 it's a few very simple shell scripts to generate the helpful (?) commit
462 message headers, and a few one-liners that actually do the
463 commit itself ('git-commit').
464
465
466 Inspecting Changes
467 ------------------
468
469 While creating changes is useful, it's even more useful if you can tell
470 later what changed. The most useful command for this is another of the
471 'diff' family, namely 'git-diff-tree'.
472
473 'git-diff-tree' can be given two arbitrary trees, and it will tell you the
474 differences between them. Perhaps even more commonly, though, you can
475 give it just a single commit object, and it will figure out the parent
476 of that commit itself, and show the difference directly. Thus, to get
477 the same diff that we've already seen several times, we can now do
478
479 ----------------
480 $ git diff-tree -p HEAD
481 ----------------
482
483 (again, `-p` means to show the difference as a human-readable patch),
484 and it will show what the last commit (in `HEAD`) actually changed.
485
486 [NOTE]
487 ============
488 Here is an ASCII art by Jon Loeliger that illustrates how
489 various diff-\* commands compare things.
490
491 diff-tree
492 +----+
493 | |
494 | |
495 V V
496 +-----------+
497 | Object DB |
498 | Backing |
499 | Store |
500 +-----------+
501 ^ ^
502 | |
503 | | diff-index --cached
504 | |
505 diff-index | V
506 | +-----------+
507 | | Index |
508 | | "cache" |
509 | +-----------+
510 | ^
511 | |
512 | | diff-files
513 | |
514 V V
515 +-----------+
516 | Working |
517 | Directory |
518 +-----------+
519 ============
520
521 More interestingly, you can also give 'git-diff-tree' the `--pretty` flag,
522 which tells it to also show the commit message and author and date of the
523 commit, and you can tell it to show a whole series of diffs.
524 Alternatively, you can tell it to be "silent", and not show the diffs at
525 all, but just show the actual commit message.
526
527 In fact, together with the 'git-rev-list' program (which generates a
528 list of revisions), 'git-diff-tree' ends up being a veritable fount of
529 changes. A trivial (but very useful) script called 'git-whatchanged' is
530 included with git which does exactly this, and shows a log of recent
531 activities.
532
533 To see the whole history of our pitiful little git-tutorial project, you
534 can do
535
536 ----------------
537 $ git log
538 ----------------
539
540 which shows just the log messages, or if we want to see the log together
541 with the associated patches use the more complex (and much more
542 powerful)
543
544 ----------------
545 $ git whatchanged -p
546 ----------------
547
548 and you will see exactly what has changed in the repository over its
549 short history.
550
551 [NOTE]
552 When using the above two commands, the initial commit will be shown.
553 If this is a problem because it is huge, you can hide it by setting
554 the log.showroot configuration variable to false. Having this, you
555 can still show it for each command just adding the `\--root` option,
556 which is a flag for 'git-diff-tree' accepted by both commands.
557
558 With that, you should now be having some inkling of what git does, and
559 can explore on your own.
560
561 [NOTE]
562 Most likely, you are not directly using the core
563 git Plumbing commands, but using Porcelain such as 'git-add', `git-rm'
564 and `git-commit'.
565
566
567 Tagging a version
568 -----------------
569
570 In git, there are two kinds of tags, a "light" one, and an "annotated tag".
571
572 A "light" tag is technically nothing more than a branch, except we put
573 it in the `.git/refs/tags/` subdirectory instead of calling it a `head`.
574 So the simplest form of tag involves nothing more than
575
576 ------------------------------------------------
577 $ git tag my-first-tag
578 ------------------------------------------------
579
580 which just writes the current `HEAD` into the `.git/refs/tags/my-first-tag`
581 file, after which point you can then use this symbolic name for that
582 particular state. You can, for example, do
583
584 ----------------
585 $ git diff my-first-tag
586 ----------------
587
588 to diff your current state against that tag which at this point will
589 obviously be an empty diff, but if you continue to develop and commit
590 stuff, you can use your tag as an "anchor-point" to see what has changed
591 since you tagged it.
592
593 An "annotated tag" is actually a real git object, and contains not only a
594 pointer to the state you want to tag, but also a small tag name and
595 message, along with optionally a PGP signature that says that yes,
596 you really did
597 that tag. You create these annotated tags with either the `-a` or
598 `-s` flag to 'git-tag':
599
600 ----------------
601 $ git tag -s <tagname>
602 ----------------
603
604 which will sign the current `HEAD` (but you can also give it another
605 argument that specifies the thing to tag, i.e., you could have tagged the
606 current `mybranch` point by using `git tag <tagname> mybranch`).
607
608 You normally only do signed tags for major releases or things
609 like that, while the light-weight tags are useful for any marking you
610 want to do -- any time you decide that you want to remember a certain
611 point, just create a private tag for it, and you have a nice symbolic
612 name for the state at that point.
613
614
615 Copying repositories
616 --------------------
617
618 git repositories are normally totally self-sufficient and relocatable.
619 Unlike CVS, for example, there is no separate notion of
620 "repository" and "working tree". A git repository normally *is* the
621 working tree, with the local git information hidden in the `.git`
622 subdirectory. There is nothing else. What you see is what you got.
623
624 [NOTE]
625 You can tell git to split the git internal information from
626 the directory that it tracks, but we'll ignore that for now: it's not
627 how normal projects work, and it's really only meant for special uses.
628 So the mental model of "the git information is always tied directly to
629 the working tree that it describes" may not be technically 100%
630 accurate, but it's a good model for all normal use.
631
632 This has two implications:
633
634 - if you grow bored with the tutorial repository you created (or you've
635 made a mistake and want to start all over), you can just do simple
636 +
637 ----------------
638 $ rm -rf git-tutorial
639 ----------------
640 +
641 and it will be gone. There's no external repository, and there's no
642 history outside the project you created.
643
644 - if you want to move or duplicate a git repository, you can do so. There
645 is 'git-clone' command, but if all you want to do is just to
646 create a copy of your repository (with all the full history that
647 went along with it), you can do so with a regular
648 `cp -a git-tutorial new-git-tutorial`.
649 +
650 Note that when you've moved or copied a git repository, your git index
651 file (which caches various information, notably some of the "stat"
652 information for the files involved) will likely need to be refreshed.
653 So after you do a `cp -a` to create a new copy, you'll want to do
654 +
655 ----------------
656 $ git update-index --refresh
657 ----------------
658 +
659 in the new repository to make sure that the index file is up-to-date.
660
661 Note that the second point is true even across machines. You can
662 duplicate a remote git repository with *any* regular copy mechanism, be it
663 'scp', 'rsync' or 'wget'.
664
665 When copying a remote repository, you'll want to at a minimum update the
666 index cache when you do this, and especially with other peoples'
667 repositories you often want to make sure that the index cache is in some
668 known state (you don't know *what* they've done and not yet checked in),
669 so usually you'll precede the 'git-update-index' with a
670
671 ----------------
672 $ git read-tree --reset HEAD
673 $ git update-index --refresh
674 ----------------
675
676 which will force a total index re-build from the tree pointed to by `HEAD`.
677 It resets the index contents to `HEAD`, and then the 'git-update-index'
678 makes sure to match up all index entries with the checked-out files.
679 If the original repository had uncommitted changes in its
680 working tree, `git update-index --refresh` notices them and
681 tells you they need to be updated.
682
683 The above can also be written as simply
684
685 ----------------
686 $ git reset
687 ----------------
688
689 and in fact a lot of the common git command combinations can be scripted
690 with the `git xyz` interfaces. You can learn things by just looking
691 at what the various git scripts do. For example, `git reset` used to be
692 the above two lines implemented in 'git-reset', but some things like
693 'git-status' and 'git-commit' are slightly more complex scripts around
694 the basic git commands.
695
696 Many (most?) public remote repositories will not contain any of
697 the checked out files or even an index file, and will *only* contain the
698 actual core git files. Such a repository usually doesn't even have the
699 `.git` subdirectory, but has all the git files directly in the
700 repository.
701
702 To create your own local live copy of such a "raw" git repository, you'd
703 first create your own subdirectory for the project, and then copy the
704 raw repository contents into the `.git` directory. For example, to
705 create your own copy of the git repository, you'd do the following
706
707 ----------------
708 $ mkdir my-git
709 $ cd my-git
710 $ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
711 ----------------
712
713 followed by
714
715 ----------------
716 $ git read-tree HEAD
717 ----------------
718
719 to populate the index. However, now you have populated the index, and
720 you have all the git internal files, but you will notice that you don't
721 actually have any of the working tree files to work on. To get
722 those, you'd check them out with
723
724 ----------------
725 $ git checkout-index -u -a
726 ----------------
727
728 where the `-u` flag means that you want the checkout to keep the index
729 up-to-date (so that you don't have to refresh it afterward), and the
730 `-a` flag means "check out all files" (if you have a stale copy or an
731 older version of a checked out tree you may also need to add the `-f`
732 flag first, to tell 'git-checkout-index' to *force* overwriting of any old
733 files).
734
735 Again, this can all be simplified with
736
737 ----------------
738 $ git clone rsync://rsync.kernel.org/pub/scm/git/git.git/ my-git
739 $ cd my-git
740 $ git checkout
741 ----------------
742
743 which will end up doing all of the above for you.
744
745 You have now successfully copied somebody else's (mine) remote
746 repository, and checked it out.
747
748
749 Creating a new branch
750 ---------------------
751
752 Branches in git are really nothing more than pointers into the git
753 object database from within the `.git/refs/` subdirectory, and as we
754 already discussed, the `HEAD` branch is nothing but a symlink to one of
755 these object pointers.
756
757 You can at any time create a new branch by just picking an arbitrary
758 point in the project history, and just writing the SHA1 name of that
759 object into a file under `.git/refs/heads/`. You can use any filename you
760 want (and indeed, subdirectories), but the convention is that the
761 "normal" branch is called `master`. That's just a convention, though,
762 and nothing enforces it.
763
764 To show that as an example, let's go back to the git-tutorial repository we
765 used earlier, and create a branch in it. You do that by simply just
766 saying that you want to check out a new branch:
767
768 ------------
769 $ git checkout -b mybranch
770 ------------
771
772 will create a new branch based at the current `HEAD` position, and switch
773 to it.
774
775 [NOTE]
776 ================================================
777 If you make the decision to start your new branch at some
778 other point in the history than the current `HEAD`, you can do so by
779 just telling 'git-checkout' what the base of the checkout would be.
780 In other words, if you have an earlier tag or branch, you'd just do
781
782 ------------
783 $ git checkout -b mybranch earlier-commit
784 ------------
785
786 and it would create the new branch `mybranch` at the earlier commit,
787 and check out the state at that time.
788 ================================================
789
790 You can always just jump back to your original `master` branch by doing
791
792 ------------
793 $ git checkout master
794 ------------
795
796 (or any other branch-name, for that matter) and if you forget which
797 branch you happen to be on, a simple
798
799 ------------
800 $ cat .git/HEAD
801 ------------
802
803 will tell you where it's pointing. To get the list of branches
804 you have, you can say
805
806 ------------
807 $ git branch
808 ------------
809
810 which used to be nothing more than a simple script around `ls .git/refs/heads`.
811 There will be an asterisk in front of the branch you are currently on.
812
813 Sometimes you may wish to create a new branch _without_ actually
814 checking it out and switching to it. If so, just use the command
815
816 ------------
817 $ git branch <branchname> [startingpoint]
818 ------------
819
820 which will simply _create_ the branch, but will not do anything further.
821 You can then later -- once you decide that you want to actually develop
822 on that branch -- switch to that branch with a regular 'git-checkout'
823 with the branchname as the argument.
824
825
826 Merging two branches
827 --------------------
828
829 One of the ideas of having a branch is that you do some (possibly
830 experimental) work in it, and eventually merge it back to the main
831 branch. So assuming you created the above `mybranch` that started out
832 being the same as the original `master` branch, let's make sure we're in
833 that branch, and do some work there.
834
835 ------------------------------------------------
836 $ git checkout mybranch
837 $ echo "Work, work, work" >>hello
838 $ git commit -m "Some work." -i hello
839 ------------------------------------------------
840
841 Here, we just added another line to `hello`, and we used a shorthand for
842 doing both `git update-index hello` and `git commit` by just giving the
843 filename directly to `git commit`, with an `-i` flag (it tells
844 git to 'include' that file in addition to what you have done to
845 the index file so far when making the commit). The `-m` flag is to give the
846 commit log message from the command line.
847
848 Now, to make it a bit more interesting, let's assume that somebody else
849 does some work in the original branch, and simulate that by going back
850 to the master branch, and editing the same file differently there:
851
852 ------------
853 $ git checkout master
854 ------------
855
856 Here, take a moment to look at the contents of `hello`, and notice how they
857 don't contain the work we just did in `mybranch` -- because that work
858 hasn't happened in the `master` branch at all. Then do
859
860 ------------
861 $ echo "Play, play, play" >>hello
862 $ echo "Lots of fun" >>example
863 $ git commit -m "Some fun." -i hello example
864 ------------
865
866 since the master branch is obviously in a much better mood.
867
868 Now, you've got two branches, and you decide that you want to merge the
869 work done. Before we do that, let's introduce a cool graphical tool that
870 helps you view what's going on:
871
872 ----------------
873 $ gitk --all
874 ----------------
875
876 will show you graphically both of your branches (that's what the `\--all`
877 means: normally it will just show you your current `HEAD`) and their
878 histories. You can also see exactly how they came to be from a common
879 source.
880
881 Anyway, let's exit 'gitk' (`^Q` or the File menu), and decide that we want
882 to merge the work we did on the `mybranch` branch into the `master`
883 branch (which is currently our `HEAD` too). To do that, there's a nice
884 script called 'git-merge', which wants to know which branches you want
885 to resolve and what the merge is all about:
886
887 ------------
888 $ git merge -m "Merge work in mybranch" mybranch
889 ------------
890
891 where the first argument is going to be used as the commit message if
892 the merge can be resolved automatically.
893
894 Now, in this case we've intentionally created a situation where the
895 merge will need to be fixed up by hand, though, so git will do as much
896 of it as it can automatically (which in this case is just merge the `example`
897 file, which had no differences in the `mybranch` branch), and say:
898
899 ----------------
900 Auto-merging hello
901 CONFLICT (content): Merge conflict in hello
902 Automatic merge failed; fix conflicts and then commit the result.
903 ----------------
904
905 It tells you that it did an "Automatic merge", which
906 failed due to conflicts in `hello`.
907
908 Not to worry. It left the (trivial) conflict in `hello` in the same form you
909 should already be well used to if you've ever used CVS, so let's just
910 open `hello` in our editor (whatever that may be), and fix it up somehow.
911 I'd suggest just making it so that `hello` contains all four lines:
912
913 ------------
914 Hello World
915 It's a new day for git
916 Play, play, play
917 Work, work, work
918 ------------
919
920 and once you're happy with your manual merge, just do a
921
922 ------------
923 $ git commit -i hello
924 ------------
925
926 which will very loudly warn you that you're now committing a merge
927 (which is correct, so never mind), and you can write a small merge
928 message about your adventures in 'git-merge'-land.
929
930 After you're done, start up `gitk \--all` to see graphically what the
931 history looks like. Notice that `mybranch` still exists, and you can
932 switch to it, and continue to work with it if you want to. The
933 `mybranch` branch will not contain the merge, but next time you merge it
934 from the `master` branch, git will know how you merged it, so you'll not
935 have to do _that_ merge again.
936
937 Another useful tool, especially if you do not always work in X-Window
938 environment, is `git show-branch`.
939
940 ------------------------------------------------
941 $ git show-branch --topo-order --more=1 master mybranch
942 * [master] Merge work in mybranch
943 ! [mybranch] Some work.
944 --
945 - [master] Merge work in mybranch
946 *+ [mybranch] Some work.
947 * [master^] Some fun.
948 ------------------------------------------------
949
950 The first two lines indicate that it is showing the two branches
951 and the first line of the commit log message from their
952 top-of-the-tree commits, you are currently on `master` branch
953 (notice the asterisk `\*` character), and the first column for
954 the later output lines is used to show commits contained in the
955 `master` branch, and the second column for the `mybranch`
956 branch. Three commits are shown along with their log messages.
957 All of them have non blank characters in the first column (`*`
958 shows an ordinary commit on the current branch, `-` is a merge commit), which
959 means they are now part of the `master` branch. Only the "Some
960 work" commit has the plus `+` character in the second column,
961 because `mybranch` has not been merged to incorporate these
962 commits from the master branch. The string inside brackets
963 before the commit log message is a short name you can use to
964 name the commit. In the above example, 'master' and 'mybranch'
965 are branch heads. 'master^' is the first parent of 'master'
966 branch head. Please see linkgit:git-rev-parse[1] if you want to
967 see more complex cases.
968
969 [NOTE]
970 Without the '--more=1' option, 'git-show-branch' would not output the
971 '[master^]' commit, as '[mybranch]' commit is a common ancestor of
972 both 'master' and 'mybranch' tips. Please see linkgit:git-show-branch[1]
973 for details.
974
975 [NOTE]
976 If there were more commits on the 'master' branch after the merge, the
977 merge commit itself would not be shown by 'git-show-branch' by
978 default. You would need to provide '--sparse' option to make the
979 merge commit visible in this case.
980
981 Now, let's pretend you are the one who did all the work in
982 `mybranch`, and the fruit of your hard work has finally been merged
983 to the `master` branch. Let's go back to `mybranch`, and run
984 'git-merge' to get the "upstream changes" back to your branch.
985
986 ------------
987 $ git checkout mybranch
988 $ git merge -m "Merge upstream changes." master
989 ------------
990
991 This outputs something like this (the actual commit object names
992 would be different)
993
994 ----------------
995 Updating from ae3a2da... to a80b4aa....
996 Fast forward (no commit created; -m option ignored)
997 example | 1 +
998 hello | 1 +
999 2 files changed, 2 insertions(+), 0 deletions(-)
1000 ----------------
1001
1002 Because your branch did not contain anything more than what had
1003 already been merged into the `master` branch, the merge operation did
1004 not actually do a merge. Instead, it just updated the top of
1005 the tree of your branch to that of the `master` branch. This is
1006 often called 'fast forward' merge.
1007
1008 You can run `gitk \--all` again to see how the commit ancestry
1009 looks like, or run 'show-branch', which tells you this.
1010
1011 ------------------------------------------------
1012 $ git show-branch master mybranch
1013 ! [master] Merge work in mybranch
1014 * [mybranch] Merge work in mybranch
1015 --
1016 -- [master] Merge work in mybranch
1017 ------------------------------------------------
1018
1019
1020 Merging external work
1021 ---------------------
1022
1023 It's usually much more common that you merge with somebody else than
1024 merging with your own branches, so it's worth pointing out that git
1025 makes that very easy too, and in fact, it's not that different from
1026 doing a 'git-merge'. In fact, a remote merge ends up being nothing
1027 more than "fetch the work from a remote repository into a temporary tag"
1028 followed by a 'git-merge'.
1029
1030 Fetching from a remote repository is done by, unsurprisingly,
1031 'git-fetch':
1032
1033 ----------------
1034 $ git fetch <remote-repository>
1035 ----------------
1036
1037 One of the following transports can be used to name the
1038 repository to download from:
1039
1040 Rsync::
1041 `rsync://remote.machine/path/to/repo.git/`
1042 +
1043 Rsync transport is usable for both uploading and downloading,
1044 but is completely unaware of what git does, and can produce
1045 unexpected results when you download from the public repository
1046 while the repository owner is uploading into it via `rsync`
1047 transport. Most notably, it could update the files under
1048 `refs/` which holds the object name of the topmost commits
1049 before uploading the files in `objects/` -- the downloader would
1050 obtain head commit object name while that object itself is still
1051 not available in the repository. For this reason, it is
1052 considered deprecated.
1053
1054 SSH::
1055 `remote.machine:/path/to/repo.git/` or
1056 +
1057 `ssh://remote.machine/path/to/repo.git/`
1058 +
1059 This transport can be used for both uploading and downloading,
1060 and requires you to have a log-in privilege over `ssh` to the
1061 remote machine. It finds out the set of objects the other side
1062 lacks by exchanging the head commits both ends have and
1063 transfers (close to) minimum set of objects. It is by far the
1064 most efficient way to exchange git objects between repositories.
1065
1066 Local directory::
1067 `/path/to/repo.git/`
1068 +
1069 This transport is the same as SSH transport but uses 'sh' to run
1070 both ends on the local machine instead of running other end on
1071 the remote machine via 'ssh'.
1072
1073 git Native::
1074 `git://remote.machine/path/to/repo.git/`
1075 +
1076 This transport was designed for anonymous downloading. Like SSH
1077 transport, it finds out the set of objects the downstream side
1078 lacks and transfers (close to) minimum set of objects.
1079
1080 HTTP(S)::
1081 `http://remote.machine/path/to/repo.git/`
1082 +
1083 Downloader from http and https URL
1084 first obtains the topmost commit object name from the remote site
1085 by looking at the specified refname under `repo.git/refs/` directory,
1086 and then tries to obtain the
1087 commit object by downloading from `repo.git/objects/xx/xxx\...`
1088 using the object name of that commit object. Then it reads the
1089 commit object to find out its parent commits and the associate
1090 tree object; it repeats this process until it gets all the
1091 necessary objects. Because of this behavior, they are
1092 sometimes also called 'commit walkers'.
1093 +
1094 The 'commit walkers' are sometimes also called 'dumb
1095 transports', because they do not require any git aware smart
1096 server like git Native transport does. Any stock HTTP server
1097 that does not even support directory index would suffice. But
1098 you must prepare your repository with 'git-update-server-info'
1099 to help dumb transport downloaders.
1100
1101 Once you fetch from the remote repository, you `merge` that
1102 with your current branch.
1103
1104 However -- it's such a common thing to `fetch` and then
1105 immediately `merge`, that it's called `git pull`, and you can
1106 simply do
1107
1108 ----------------
1109 $ git pull <remote-repository>
1110 ----------------
1111
1112 and optionally give a branch-name for the remote end as a second
1113 argument.
1114
1115 [NOTE]
1116 You could do without using any branches at all, by
1117 keeping as many local repositories as you would like to have
1118 branches, and merging between them with 'git-pull', just like
1119 you merge between branches. The advantage of this approach is
1120 that it lets you keep a set of files for each `branch` checked
1121 out and you may find it easier to switch back and forth if you
1122 juggle multiple lines of development simultaneously. Of
1123 course, you will pay the price of more disk usage to hold
1124 multiple working trees, but disk space is cheap these days.
1125
1126 It is likely that you will be pulling from the same remote
1127 repository from time to time. As a short hand, you can store
1128 the remote repository URL in the local repository's config file
1129 like this:
1130
1131 ------------------------------------------------
1132 $ git config remote.linus.url http://www.kernel.org/pub/scm/git/git.git/
1133 ------------------------------------------------
1134
1135 and use the "linus" keyword with 'git-pull' instead of the full URL.
1136
1137 Examples.
1138
1139 . `git pull linus`
1140 . `git pull linus tag v0.99.1`
1141
1142 the above are equivalent to:
1143
1144 . `git pull http://www.kernel.org/pub/scm/git/git.git/ HEAD`
1145 . `git pull http://www.kernel.org/pub/scm/git/git.git/ tag v0.99.1`
1146
1147
1148 How does the merge work?
1149 ------------------------
1150
1151 We said this tutorial shows what plumbing does to help you cope
1152 with the porcelain that isn't flushing, but we so far did not
1153 talk about how the merge really works. If you are following
1154 this tutorial the first time, I'd suggest to skip to "Publishing
1155 your work" section and come back here later.
1156
1157 OK, still with me? To give us an example to look at, let's go
1158 back to the earlier repository with "hello" and "example" file,
1159 and bring ourselves back to the pre-merge state:
1160
1161 ------------
1162 $ git show-branch --more=2 master mybranch
1163 ! [master] Merge work in mybranch
1164 * [mybranch] Merge work in mybranch
1165 --
1166 -- [master] Merge work in mybranch
1167 +* [master^2] Some work.
1168 +* [master^] Some fun.
1169 ------------
1170
1171 Remember, before running 'git-merge', our `master` head was at
1172 "Some fun." commit, while our `mybranch` head was at "Some
1173 work." commit.
1174
1175 ------------
1176 $ git checkout mybranch
1177 $ git reset --hard master^2
1178 $ git checkout master
1179 $ git reset --hard master^
1180 ------------
1181
1182 After rewinding, the commit structure should look like this:
1183
1184 ------------
1185 $ git show-branch
1186 * [master] Some fun.
1187 ! [mybranch] Some work.
1188 --
1189 + [mybranch] Some work.
1190 * [master] Some fun.
1191 *+ [mybranch^] New day.
1192 ------------
1193
1194 Now we are ready to experiment with the merge by hand.
1195
1196 `git merge` command, when merging two branches, uses 3-way merge
1197 algorithm. First, it finds the common ancestor between them.
1198 The command it uses is 'git-merge-base':
1199
1200 ------------
1201 $ mb=$(git merge-base HEAD mybranch)
1202 ------------
1203
1204 The command writes the commit object name of the common ancestor
1205 to the standard output, so we captured its output to a variable,
1206 because we will be using it in the next step. By the way, the common
1207 ancestor commit is the "New day." commit in this case. You can
1208 tell it by:
1209
1210 ------------
1211 $ git name-rev $mb
1212 my-first-tag
1213 ------------
1214
1215 After finding out a common ancestor commit, the second step is
1216 this:
1217
1218 ------------
1219 $ git read-tree -m -u $mb HEAD mybranch
1220 ------------
1221
1222 This is the same 'git-read-tree' command we have already seen,
1223 but it takes three trees, unlike previous examples. This reads
1224 the contents of each tree into different 'stage' in the index
1225 file (the first tree goes to stage 1, the second to stage 2,
1226 etc.). After reading three trees into three stages, the paths
1227 that are the same in all three stages are 'collapsed' into stage
1228 0. Also paths that are the same in two of three stages are
1229 collapsed into stage 0, taking the SHA1 from either stage 2 or
1230 stage 3, whichever is different from stage 1 (i.e. only one side
1231 changed from the common ancestor).
1232
1233 After 'collapsing' operation, paths that are different in three
1234 trees are left in non-zero stages. At this point, you can
1235 inspect the index file with this command:
1236
1237 ------------
1238 $ git ls-files --stage
1239 100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
1240 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1241 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1242 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1243 ------------
1244
1245 In our example of only two files, we did not have unchanged
1246 files so only 'example' resulted in collapsing. But in real-life
1247 large projects, when only a small number of files change in one commit,
1248 this 'collapsing' tends to trivially merge most of the paths
1249 fairly quickly, leaving only a handful of real changes in non-zero
1250 stages.
1251
1252 To look at only non-zero stages, use `\--unmerged` flag:
1253
1254 ------------
1255 $ git ls-files --unmerged
1256 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1257 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1258 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1259 ------------
1260
1261 The next step of merging is to merge these three versions of the
1262 file, using 3-way merge. This is done by giving
1263 'git-merge-one-file' command as one of the arguments to
1264 'git-merge-index' command:
1265
1266 ------------
1267 $ git merge-index git-merge-one-file hello
1268 Auto-merging hello
1269 ERROR: Merge conflict in hello
1270 fatal: merge program failed
1271 ------------
1272
1273 'git-merge-one-file' script is called with parameters to
1274 describe those three versions, and is responsible to leave the
1275 merge results in the working tree.
1276 It is a fairly straightforward shell script, and
1277 eventually calls 'merge' program from RCS suite to perform a
1278 file-level 3-way merge. In this case, 'merge' detects
1279 conflicts, and the merge result with conflict marks is left in
1280 the working tree.. This can be seen if you run `ls-files
1281 --stage` again at this point:
1282
1283 ------------
1284 $ git ls-files --stage
1285 100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
1286 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1287 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1288 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1289 ------------
1290
1291 This is the state of the index file and the working file after
1292 'git-merge' returns control back to you, leaving the conflicting
1293 merge for you to resolve. Notice that the path `hello` is still
1294 unmerged, and what you see with 'git-diff' at this point is
1295 differences since stage 2 (i.e. your version).
1296
1297
1298 Publishing your work
1299 --------------------
1300
1301 So, we can use somebody else's work from a remote repository, but
1302 how can *you* prepare a repository to let other people pull from
1303 it?
1304
1305 You do your real work in your working tree that has your
1306 primary repository hanging under it as its `.git` subdirectory.
1307 You *could* make that repository accessible remotely and ask
1308 people to pull from it, but in practice that is not the way
1309 things are usually done. A recommended way is to have a public
1310 repository, make it reachable by other people, and when the
1311 changes you made in your primary working tree are in good shape,
1312 update the public repository from it. This is often called
1313 'pushing'.
1314
1315 [NOTE]
1316 This public repository could further be mirrored, and that is
1317 how git repositories at `kernel.org` are managed.
1318
1319 Publishing the changes from your local (private) repository to
1320 your remote (public) repository requires a write privilege on
1321 the remote machine. You need to have an SSH account there to
1322 run a single command, 'git-receive-pack'.
1323
1324 First, you need to create an empty repository on the remote
1325 machine that will house your public repository. This empty
1326 repository will be populated and be kept up-to-date by pushing
1327 into it later. Obviously, this repository creation needs to be
1328 done only once.
1329
1330 [NOTE]
1331 'git-push' uses a pair of programs,
1332 'git-send-pack' on your local machine, and 'git-receive-pack'
1333 on the remote machine. The communication between the two over
1334 the network internally uses an SSH connection.
1335
1336 Your private repository's git directory is usually `.git`, but
1337 your public repository is often named after the project name,
1338 i.e. `<project>.git`. Let's create such a public repository for
1339 project `my-git`. After logging into the remote machine, create
1340 an empty directory:
1341
1342 ------------
1343 $ mkdir my-git.git
1344 ------------
1345
1346 Then, make that directory into a git repository by running
1347 'git-init', but this time, since its name is not the usual
1348 `.git`, we do things slightly differently:
1349
1350 ------------
1351 $ GIT_DIR=my-git.git git init
1352 ------------
1353
1354 Make sure this directory is available for others you want your
1355 changes to be pulled via the transport of your choice. Also
1356 you need to make sure that you have the 'git-receive-pack'
1357 program on the `$PATH`.
1358
1359 [NOTE]
1360 Many installations of sshd do not invoke your shell as the login
1361 shell when you directly run programs; what this means is that if
1362 your login shell is 'bash', only `.bashrc` is read and not
1363 `.bash_profile`. As a workaround, make sure `.bashrc` sets up
1364 `$PATH` so that you can run 'git-receive-pack' program.
1365
1366 [NOTE]
1367 If you plan to publish this repository to be accessed over http,
1368 you should do `mv my-git.git/hooks/post-update.sample
1369 my-git.git/hooks/post-update` at this point.
1370 This makes sure that every time you push into this
1371 repository, `git update-server-info` is run.
1372
1373 Your "public repository" is now ready to accept your changes.
1374 Come back to the machine you have your private repository. From
1375 there, run this command:
1376
1377 ------------
1378 $ git push <public-host>:/path/to/my-git.git master
1379 ------------
1380
1381 This synchronizes your public repository to match the named
1382 branch head (i.e. `master` in this case) and objects reachable
1383 from them in your current repository.
1384
1385 As a real example, this is how I update my public git
1386 repository. Kernel.org mirror network takes care of the
1387 propagation to other publicly visible machines:
1388
1389 ------------
1390 $ git push master.kernel.org:/pub/scm/git/git.git/
1391 ------------
1392
1393
1394 Packing your repository
1395 -----------------------
1396
1397 Earlier, we saw that one file under `.git/objects/??/` directory
1398 is stored for each git object you create. This representation
1399 is efficient to create atomically and safely, but
1400 not so convenient to transport over the network. Since git objects are
1401 immutable once they are created, there is a way to optimize the
1402 storage by "packing them together". The command
1403
1404 ------------
1405 $ git repack
1406 ------------
1407
1408 will do it for you. If you followed the tutorial examples, you
1409 would have accumulated about 17 objects in `.git/objects/??/`
1410 directories by now. 'git-repack' tells you how many objects it
1411 packed, and stores the packed file in `.git/objects/pack`
1412 directory.
1413
1414 [NOTE]
1415 You will see two files, `pack-\*.pack` and `pack-\*.idx`,
1416 in `.git/objects/pack` directory. They are closely related to
1417 each other, and if you ever copy them by hand to a different
1418 repository for whatever reason, you should make sure you copy
1419 them together. The former holds all the data from the objects
1420 in the pack, and the latter holds the index for random
1421 access.
1422
1423 If you are paranoid, running 'git-verify-pack' command would
1424 detect if you have a corrupt pack, but do not worry too much.
1425 Our programs are always perfect ;-).
1426
1427 Once you have packed objects, you do not need to leave the
1428 unpacked objects that are contained in the pack file anymore.
1429
1430 ------------
1431 $ git prune-packed
1432 ------------
1433
1434 would remove them for you.
1435
1436 You can try running `find .git/objects -type f` before and after
1437 you run `git prune-packed` if you are curious. Also `git
1438 count-objects` would tell you how many unpacked objects are in
1439 your repository and how much space they are consuming.
1440
1441 [NOTE]
1442 `git pull` is slightly cumbersome for HTTP transport, as a
1443 packed repository may contain relatively few objects in a
1444 relatively large pack. If you expect many HTTP pulls from your
1445 public repository you might want to repack & prune often, or
1446 never.
1447
1448 If you run `git repack` again at this point, it will say
1449 "Nothing new to pack.". Once you continue your development and
1450 accumulate the changes, running `git repack` again will create a
1451 new pack, that contains objects created since you packed your
1452 repository the last time. We recommend that you pack your project
1453 soon after the initial import (unless you are starting your
1454 project from scratch), and then run `git repack` every once in a
1455 while, depending on how active your project is.
1456
1457 When a repository is synchronized via `git push` and `git pull`
1458 objects packed in the source repository are usually stored
1459 unpacked in the destination, unless rsync transport is used.
1460 While this allows you to use different packing strategies on
1461 both ends, it also means you may need to repack both
1462 repositories every once in a while.
1463
1464
1465 Working with Others
1466 -------------------
1467
1468 Although git is a truly distributed system, it is often
1469 convenient to organize your project with an informal hierarchy
1470 of developers. Linux kernel development is run this way. There
1471 is a nice illustration (page 17, "Merges to Mainline") in
1472 link:http://www.xenotime.net/linux/mentor/linux-mentoring-2006.pdf[Randy Dunlap's presentation].
1473
1474 It should be stressed that this hierarchy is purely *informal*.
1475 There is nothing fundamental in git that enforces the "chain of
1476 patch flow" this hierarchy implies. You do not have to pull
1477 from only one remote repository.
1478
1479 A recommended workflow for a "project lead" goes like this:
1480
1481 1. Prepare your primary repository on your local machine. Your
1482 work is done there.
1483
1484 2. Prepare a public repository accessible to others.
1485 +
1486 If other people are pulling from your repository over dumb
1487 transport protocols (HTTP), you need to keep this repository
1488 'dumb transport friendly'. After `git init`,
1489 `$GIT_DIR/hooks/post-update.sample` copied from the standard templates
1490 would contain a call to 'git-update-server-info'
1491 but you need to manually enable the hook with
1492 `mv post-update.sample post-update`. This makes sure
1493 'git-update-server-info' keeps the necessary files up-to-date.
1494
1495 3. Push into the public repository from your primary
1496 repository.
1497
1498 4. 'git-repack' the public repository. This establishes a big
1499 pack that contains the initial set of objects as the
1500 baseline, and possibly 'git-prune' if the transport
1501 used for pulling from your repository supports packed
1502 repositories.
1503
1504 5. Keep working in your primary repository. Your changes
1505 include modifications of your own, patches you receive via
1506 e-mails, and merges resulting from pulling the "public"
1507 repositories of your "subsystem maintainers".
1508 +
1509 You can repack this private repository whenever you feel like.
1510
1511 6. Push your changes to the public repository, and announce it
1512 to the public.
1513
1514 7. Every once in a while, 'git-repack' the public repository.
1515 Go back to step 5. and continue working.
1516
1517
1518 A recommended work cycle for a "subsystem maintainer" who works
1519 on that project and has an own "public repository" goes like this:
1520
1521 1. Prepare your work repository, by 'git-clone' the public
1522 repository of the "project lead". The URL used for the
1523 initial cloning is stored in the remote.origin.url
1524 configuration variable.
1525
1526 2. Prepare a public repository accessible to others, just like
1527 the "project lead" person does.
1528
1529 3. Copy over the packed files from "project lead" public
1530 repository to your public repository, unless the "project
1531 lead" repository lives on the same machine as yours. In the
1532 latter case, you can use `objects/info/alternates` file to
1533 point at the repository you are borrowing from.
1534
1535 4. Push into the public repository from your primary
1536 repository. Run 'git-repack', and possibly 'git-prune' if the
1537 transport used for pulling from your repository supports
1538 packed repositories.
1539
1540 5. Keep working in your primary repository. Your changes
1541 include modifications of your own, patches you receive via
1542 e-mails, and merges resulting from pulling the "public"
1543 repositories of your "project lead" and possibly your
1544 "sub-subsystem maintainers".
1545 +
1546 You can repack this private repository whenever you feel
1547 like.
1548
1549 6. Push your changes to your public repository, and ask your
1550 "project lead" and possibly your "sub-subsystem
1551 maintainers" to pull from it.
1552
1553 7. Every once in a while, 'git-repack' the public repository.
1554 Go back to step 5. and continue working.
1555
1556
1557 A recommended work cycle for an "individual developer" who does
1558 not have a "public" repository is somewhat different. It goes
1559 like this:
1560
1561 1. Prepare your work repository, by 'git-clone' the public
1562 repository of the "project lead" (or a "subsystem
1563 maintainer", if you work on a subsystem). The URL used for
1564 the initial cloning is stored in the remote.origin.url
1565 configuration variable.
1566
1567 2. Do your work in your repository on 'master' branch.
1568
1569 3. Run `git fetch origin` from the public repository of your
1570 upstream every once in a while. This does only the first
1571 half of `git pull` but does not merge. The head of the
1572 public repository is stored in `.git/refs/remotes/origin/master`.
1573
1574 4. Use `git cherry origin` to see which ones of your patches
1575 were accepted, and/or use `git rebase origin` to port your
1576 unmerged changes forward to the updated upstream.
1577
1578 5. Use `git format-patch origin` to prepare patches for e-mail
1579 submission to your upstream and send it out. Go back to
1580 step 2. and continue.
1581
1582
1583 Working with Others, Shared Repository Style
1584 --------------------------------------------
1585
1586 If you are coming from CVS background, the style of cooperation
1587 suggested in the previous section may be new to you. You do not
1588 have to worry. git supports "shared public repository" style of
1589 cooperation you are probably more familiar with as well.
1590
1591 See linkgit:gitcvs-migration[7] for the details.
1592
1593 Bundling your work together
1594 ---------------------------
1595
1596 It is likely that you will be working on more than one thing at
1597 a time. It is easy to manage those more-or-less independent tasks
1598 using branches with git.
1599
1600 We have already seen how branches work previously,
1601 with "fun and work" example using two branches. The idea is the
1602 same if there are more than two branches. Let's say you started
1603 out from "master" head, and have some new code in the "master"
1604 branch, and two independent fixes in the "commit-fix" and
1605 "diff-fix" branches:
1606
1607 ------------
1608 $ git show-branch
1609 ! [commit-fix] Fix commit message normalization.
1610 ! [diff-fix] Fix rename detection.
1611 * [master] Release candidate #1
1612 ---
1613 + [diff-fix] Fix rename detection.
1614 + [diff-fix~1] Better common substring algorithm.
1615 + [commit-fix] Fix commit message normalization.
1616 * [master] Release candidate #1
1617 ++* [diff-fix~2] Pretty-print messages.
1618 ------------
1619
1620 Both fixes are tested well, and at this point, you want to merge
1621 in both of them. You could merge in 'diff-fix' first and then
1622 'commit-fix' next, like this:
1623
1624 ------------
1625 $ git merge -m "Merge fix in diff-fix" diff-fix
1626 $ git merge -m "Merge fix in commit-fix" commit-fix
1627 ------------
1628
1629 Which would result in:
1630
1631 ------------
1632 $ git show-branch
1633 ! [commit-fix] Fix commit message normalization.
1634 ! [diff-fix] Fix rename detection.
1635 * [master] Merge fix in commit-fix
1636 ---
1637 - [master] Merge fix in commit-fix
1638 + * [commit-fix] Fix commit message normalization.
1639 - [master~1] Merge fix in diff-fix
1640 +* [diff-fix] Fix rename detection.
1641 +* [diff-fix~1] Better common substring algorithm.
1642 * [master~2] Release candidate #1
1643 ++* [master~3] Pretty-print messages.
1644 ------------
1645
1646 However, there is no particular reason to merge in one branch
1647 first and the other next, when what you have are a set of truly
1648 independent changes (if the order mattered, then they are not
1649 independent by definition). You could instead merge those two
1650 branches into the current branch at once. First let's undo what
1651 we just did and start over. We would want to get the master
1652 branch before these two merges by resetting it to 'master~2':
1653
1654 ------------
1655 $ git reset --hard master~2
1656 ------------
1657
1658 You can make sure `git show-branch` matches the state before
1659 those two 'git-merge' you just did. Then, instead of running
1660 two 'git-merge' commands in a row, you would merge these two
1661 branch heads (this is known as 'making an Octopus'):
1662
1663 ------------
1664 $ git merge commit-fix diff-fix
1665 $ git show-branch
1666 ! [commit-fix] Fix commit message normalization.
1667 ! [diff-fix] Fix rename detection.
1668 * [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1669 ---
1670 - [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1671 + * [commit-fix] Fix commit message normalization.
1672 +* [diff-fix] Fix rename detection.
1673 +* [diff-fix~1] Better common substring algorithm.
1674 * [master~1] Release candidate #1
1675 ++* [master~2] Pretty-print messages.
1676 ------------
1677
1678 Note that you should not do Octopus because you can. An octopus
1679 is a valid thing to do and often makes it easier to view the
1680 commit history if you are merging more than two independent
1681 changes at the same time. However, if you have merge conflicts
1682 with any of the branches you are merging in and need to hand
1683 resolve, that is an indication that the development happened in
1684 those branches were not independent after all, and you should
1685 merge two at a time, documenting how you resolved the conflicts,
1686 and the reason why you preferred changes made in one side over
1687 the other. Otherwise it would make the project history harder
1688 to follow, not easier.
1689
1690 SEE ALSO
1691 --------
1692 linkgit:gittutorial[7],
1693 linkgit:gittutorial-2[7],
1694 linkgit:gitcvs-migration[7],
1695 linkgit:git-help[1],
1696 link:everyday.html[Everyday git],
1697 link:user-manual.html[The Git User's Manual]
1698
1699 GIT
1700 ---
1701 Part of the linkgit:git[1] suite.