Merge git://
[git/git.git] / Documentation / core-tutorial.txt
1 A short git tutorial
2 ====================
4 Introduction
5 ------------
7 This is trying to be a short tutorial on setting up and using a git
8 repository, mainly because being hands-on and using explicit examples is
9 often the best way of explaining what is going on.
11 In normal life, most people wouldn't use the "core" git programs
12 directly, but rather script around them to make them more palatable.
13 Understanding the core git stuff may help some people get those scripts
14 done, though, and it may also be instructive in helping people
15 understand what it is that the higher-level helper scripts are actually
16 doing.
18 The core git is often called "plumbing", with the prettier user
19 interfaces on top of it called "porcelain". You may not want to use the
20 plumbing directly very often, but it can be good to know what the
21 plumbing does for when the porcelain isn't flushing.
23 The material presented here often goes deep describing how things
24 work internally. If you are mostly interested in using git as a
25 SCM, you can skip them during your first pass.
27 [NOTE]
28 And those "too deep" descriptions are often marked as Note.
30 [NOTE]
31 If you are already familiar with another version control system,
32 like CVS, you may want to take a look at
33 link:everyday.html[Everyday GIT in 20 commands or so] first
34 before reading this.
37 Creating a git repository
38 -------------------------
40 Creating a new git repository couldn't be easier: all git repositories start
41 out empty, and the only thing you need to do is find yourself a
42 subdirectory that you want to use as a working tree - either an empty
43 one for a totally new project, or an existing working tree that you want
44 to import into git.
46 For our first example, we're going to start a totally new repository from
47 scratch, with no pre-existing files, and we'll call it `git-tutorial`.
48 To start up, create a subdirectory for it, change into that
49 subdirectory, and initialize the git infrastructure with `git-init-db`:
51 ------------------------------------------------
52 $ mkdir git-tutorial
53 $ cd git-tutorial
54 $ git-init-db
55 ------------------------------------------------
57 to which git will reply
59 ----------------
60 defaulting to local storage area
61 ----------------
63 which is just git's way of saying that you haven't been doing anything
64 strange, and that it will have created a local `.git` directory setup for
65 your new project. You will now have a `.git` directory, and you can
66 inspect that with `ls`. For your new empty project, it should show you
67 three entries, among other things:
69 - a file called `HEAD`, that has `ref: refs/heads/master` in it.
70 This is similar to a symbolic link and points at
71 `refs/heads/master` relative to the `HEAD` file.
72 +
73 Don't worry about the fact that the file that the `HEAD` link points to
74 doesn't even exist yet -- you haven't created the commit that will
75 start your `HEAD` development branch yet.
77 - a subdirectory called `objects`, which will contain all the
78 objects of your project. You should never have any real reason to
79 look at the objects directly, but you might want to know that these
80 objects are what contains all the real 'data' in your repository.
82 - a subdirectory called `refs`, which contains references to objects.
84 In particular, the `refs` subdirectory will contain two other
85 subdirectories, named `heads` and `tags` respectively. They do
86 exactly what their names imply: they contain references to any number
87 of different 'heads' of development (aka 'branches'), and to any
88 'tags' that you have created to name specific versions in your
89 repository.
91 One note: the special `master` head is the default branch, which is
92 why the `.git/HEAD` file was created points to it even if it
93 doesn't yet exist. Basically, the `HEAD` link is supposed to always
94 point to the branch you are working on right now, and you always
95 start out expecting to work on the `master` branch.
97 However, this is only a convention, and you can name your branches
98 anything you want, and don't have to ever even 'have' a `master`
99 branch. A number of the git tools will assume that `.git/HEAD` is
100 valid, though.
102 [NOTE]
103 An 'object' is identified by its 160-bit SHA1 hash, aka 'object name',
104 and a reference to an object is always the 40-byte hex
105 representation of that SHA1 name. The files in the `refs`
106 subdirectory are expected to contain these hex references
107 (usually with a final `\'\n\'` at the end), and you should thus
108 expect to see a number of 41-byte files containing these
109 references in these `refs` subdirectories when you actually start
110 populating your tree.
112 [NOTE]
113 An advanced user may want to take a look at the
114 link:repository-layout.html[repository layout] document
115 after finishing this tutorial.
117 You have now created your first git repository. Of course, since it's
118 empty, that's not very useful, so let's start populating it with data.
121 Populating a git repository
122 ---------------------------
124 We'll keep this simple and stupid, so we'll start off with populating a
125 few trivial files just to get a feel for it.
127 Start off with just creating any random files that you want to maintain
128 in your git repository. We'll start off with a few bad examples, just to
129 get a feel for how this works:
131 ------------------------------------------------
132 $ echo "Hello World" >hello
133 $ echo "Silly example" >example
134 ------------------------------------------------
136 you have now created two files in your working tree (aka 'working directory'),
137 but to actually check in your hard work, you will have to go through two steps:
139 - fill in the 'index' file (aka 'cache') with the information about your
140 working tree state.
142 - commit that index file as an object.
144 The first step is trivial: when you want to tell git about any changes
145 to your working tree, you use the `git-update-index` program. That
146 program normally just takes a list of filenames you want to update, but
147 to avoid trivial mistakes, it refuses to add new entries to the index
148 (or remove existing ones) unless you explicitly tell it that you're
149 adding a new entry with the `\--add` flag (or removing an entry with the
150 `\--remove`) flag.
152 So to populate the index with the two files you just created, you can do
154 ------------------------------------------------
155 $ git-update-index --add hello example
156 ------------------------------------------------
158 and you have now told git to track those two files.
160 In fact, as you did that, if you now look into your object directory,
161 you'll notice that git will have added two new objects to the object
162 database. If you did exactly the steps above, you should now be able to do
165 ----------------
166 $ ls .git/objects/??/*
167 ----------------
169 and see two files:
171 ----------------
172 .git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
173 .git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
174 ----------------
176 which correspond with the objects with names of `557db...` and
177 `f24c7...` respectively.
179 If you want to, you can use `git-cat-file` to look at those objects, but
180 you'll have to use the object name, not the filename of the object:
182 ----------------
183 $ git-cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
184 ----------------
186 where the `-t` tells `git-cat-file` to tell you what the "type" of the
187 object is. git will tell you that you have a "blob" object (ie just a
188 regular file), and you can see the contents with
190 ----------------
191 $ git-cat-file "blob" 557db03
192 ----------------
194 which will print out "Hello World". The object `557db03` is nothing
195 more than the contents of your file `hello`.
197 [NOTE]
198 Don't confuse that object with the file `hello` itself. The
199 object is literally just those specific *contents* of the file, and
200 however much you later change the contents in file `hello`, the object
201 we just looked at will never change. Objects are immutable.
203 [NOTE]
204 The second example demonstrates that you can
205 abbreviate the object name to only the first several
206 hexadecimal digits in most places.
208 Anyway, as we mentioned previously, you normally never actually take a
209 look at the objects themselves, and typing long 40-character hex
210 names is not something you'd normally want to do. The above digression
211 was just to show that `git-update-index` did something magical, and
212 actually saved away the contents of your files into the git object
213 database.
215 Updating the index did something else too: it created a `.git/index`
216 file. This is the index that describes your current working tree, and
217 something you should be very aware of. Again, you normally never worry
218 about the index file itself, but you should be aware of the fact that
219 you have not actually really "checked in" your files into git so far,
220 you've only *told* git about them.
222 However, since git knows about them, you can now start using some of the
223 most basic git commands to manipulate the files or look at their status.
225 In particular, let's not even check in the two files into git yet, we'll
226 start off by adding another line to `hello` first:
228 ------------------------------------------------
229 $ echo "It's a new day for git" >>hello
230 ------------------------------------------------
232 and you can now, since you told git about the previous state of `hello`, ask
233 git what has changed in the tree compared to your old index, using the
234 `git-diff-files` command:
236 ------------
237 $ git-diff-files
238 ------------
240 Oops. That wasn't very readable. It just spit out its own internal
241 version of a `diff`, but that internal version really just tells you
242 that it has noticed that "hello" has been modified, and that the old object
243 contents it had have been replaced with something else.
245 To make it readable, we can tell git-diff-files to output the
246 differences as a patch, using the `-p` flag:
248 ------------
249 $ git-diff-files -p
250 diff --git a/hello b/hello
251 index 557db03..263414f 100644
252 --- a/hello
253 +++ b/hello
254 @@ -1 +1,2 @@
255 Hello World
256 +It's a new day for git
257 ----
259 i.e. the diff of the change we caused by adding another line to `hello`.
261 In other words, `git-diff-files` always shows us the difference between
262 what is recorded in the index, and what is currently in the working
263 tree. That's very useful.
265 A common shorthand for `git-diff-files -p` is to just write `git
266 diff`, which will do the same thing.
268 ------------
269 $ git diff
270 diff --git a/hello b/hello
271 index 557db03..263414f 100644
272 --- a/hello
273 +++ b/hello
274 @@ -1 +1,2 @@
275 Hello World
276 +It's a new day for git
277 ------------
280 Committing git state
281 --------------------
283 Now, we want to go to the next stage in git, which is to take the files
284 that git knows about in the index, and commit them as a real tree. We do
285 that in two phases: creating a 'tree' object, and committing that 'tree'
286 object as a 'commit' object together with an explanation of what the
287 tree was all about, along with information of how we came to that state.
289 Creating a tree object is trivial, and is done with `git-write-tree`.
290 There are no options or other input: git-write-tree will take the
291 current index state, and write an object that describes that whole
292 index. In other words, we're now tying together all the different
293 filenames with their contents (and their permissions), and we're
294 creating the equivalent of a git "directory" object:
296 ------------------------------------------------
297 $ git-write-tree
298 ------------------------------------------------
300 and this will just output the name of the resulting tree, in this case
301 (if you have done exactly as I've described) it should be
303 ----------------
304 8988da15d077d4829fc51d8544c097def6644dbb
305 ----------------
307 which is another incomprehensible object name. Again, if you want to,
308 you can use `git-cat-file -t 8988d\...` to see that this time the object
309 is not a "blob" object, but a "tree" object (you can also use
310 `git-cat-file` to actually output the raw object contents, but you'll see
311 mainly a binary mess, so that's less interesting).
313 However -- normally you'd never use `git-write-tree` on its own, because
314 normally you always commit a tree into a commit object using the
315 `git-commit-tree` command. In fact, it's easier to not actually use
316 `git-write-tree` on its own at all, but to just pass its result in as an
317 argument to `git-commit-tree`.
319 `git-commit-tree` normally takes several arguments -- it wants to know
320 what the 'parent' of a commit was, but since this is the first commit
321 ever in this new repository, and it has no parents, we only need to pass in
322 the object name of the tree. However, `git-commit-tree`
323 also wants to get a commit message
324 on its standard input, and it will write out the resulting object name for the
325 commit to its standard output.
327 And this is where we create the `.git/refs/heads/master` file
328 which is pointed at by `HEAD`. This file is supposed to contain
329 the reference to the top-of-tree of the master branch, and since
330 that's exactly what `git-commit-tree` spits out, we can do this
331 all with a sequence of simple shell commands:
333 ------------------------------------------------
334 $ tree=$(git-write-tree)
335 $ commit=$(echo 'Initial commit' | git-commit-tree $tree)
336 $ git-update-ref HEAD $commit
337 ------------------------------------------------
339 which will say:
341 ----------------
342 Committing initial tree 8988da15d077d4829fc51d8544c097def6644dbb
343 ----------------
345 just to warn you about the fact that it created a totally new commit
346 that is not related to anything else. Normally you do this only *once*
347 for a project ever, and all later commits will be parented on top of an
348 earlier commit, and you'll never see this "Committing initial tree"
349 message ever again.
351 Again, normally you'd never actually do this by hand. There is a
352 helpful script called `git commit` that will do all of this for you. So
353 you could have just written `git commit`
354 instead, and it would have done the above magic scripting for you.
357 Making a change
358 ---------------
360 Remember how we did the `git-update-index` on file `hello` and then we
361 changed `hello` afterward, and could compare the new state of `hello` with the
362 state we saved in the index file?
364 Further, remember how I said that `git-write-tree` writes the contents
365 of the *index* file to the tree, and thus what we just committed was in
366 fact the *original* contents of the file `hello`, not the new ones. We did
367 that on purpose, to show the difference between the index state, and the
368 state in the working tree, and how they don't have to match, even
369 when we commit things.
371 As before, if we do `git-diff-files -p` in our git-tutorial project,
372 we'll still see the same difference we saw last time: the index file
373 hasn't changed by the act of committing anything. However, now that we
374 have committed something, we can also learn to use a new command:
375 `git-diff-index`.
377 Unlike `git-diff-files`, which showed the difference between the index
378 file and the working tree, `git-diff-index` shows the differences
379 between a committed *tree* and either the index file or the working
380 tree. In other words, `git-diff-index` wants a tree to be diffed
381 against, and before we did the commit, we couldn't do that, because we
382 didn't have anything to diff against.
384 But now we can do
386 ----------------
387 $ git-diff-index -p HEAD
388 ----------------
390 (where `-p` has the same meaning as it did in `git-diff-files`), and it
391 will show us the same difference, but for a totally different reason.
392 Now we're comparing the working tree not against the index file,
393 but against the tree we just wrote. It just so happens that those two
394 are obviously the same, so we get the same result.
396 Again, because this is a common operation, you can also just shorthand
397 it with
399 ----------------
400 $ git diff HEAD
401 ----------------
403 which ends up doing the above for you.
405 In other words, `git-diff-index` normally compares a tree against the
406 working tree, but when given the `\--cached` flag, it is told to
407 instead compare against just the index cache contents, and ignore the
408 current working tree state entirely. Since we just wrote the index
409 file to HEAD, doing `git-diff-index \--cached -p HEAD` should thus return
410 an empty set of differences, and that's exactly what it does.
412 [NOTE]
413 ================
414 `git-diff-index` really always uses the index for its
415 comparisons, and saying that it compares a tree against the working
416 tree is thus not strictly accurate. In particular, the list of
417 files to compare (the "meta-data") *always* comes from the index file,
418 regardless of whether the `\--cached` flag is used or not. The `\--cached`
419 flag really only determines whether the file *contents* to be compared
420 come from the working tree or not.
422 This is not hard to understand, as soon as you realize that git simply
423 never knows (or cares) about files that it is not told about
424 explicitly. git will never go *looking* for files to compare, it
425 expects you to tell it what the files are, and that's what the index
426 is there for.
427 ================
429 However, our next step is to commit the *change* we did, and again, to
430 understand what's going on, keep in mind the difference between "working
431 tree contents", "index file" and "committed tree". We have changes
432 in the working tree that we want to commit, and we always have to
433 work through the index file, so the first thing we need to do is to
434 update the index cache:
436 ------------------------------------------------
437 $ git-update-index hello
438 ------------------------------------------------
440 (note how we didn't need the `\--add` flag this time, since git knew
441 about the file already).
443 Note what happens to the different `git-diff-\*` versions here. After
444 we've updated `hello` in the index, `git-diff-files -p` now shows no
445 differences, but `git-diff-index -p HEAD` still *does* show that the
446 current state is different from the state we committed. In fact, now
447 `git-diff-index` shows the same difference whether we use the `--cached`
448 flag or not, since now the index is coherent with the working tree.
450 Now, since we've updated `hello` in the index, we can commit the new
451 version. We could do it by writing the tree by hand again, and
452 committing the tree (this time we'd have to use the `-p HEAD` flag to
453 tell commit that the HEAD was the *parent* of the new commit, and that
454 this wasn't an initial commit any more), but you've done that once
455 already, so let's just use the helpful script this time:
457 ------------------------------------------------
458 $ git commit
459 ------------------------------------------------
461 which starts an editor for you to write the commit message and tells you
462 a bit about what you have done.
464 Write whatever message you want, and all the lines that start with '#'
465 will be pruned out, and the rest will be used as the commit message for
466 the change. If you decide you don't want to commit anything after all at
467 this point (you can continue to edit things and update the index), you
468 can just leave an empty message. Otherwise `git commit` will commit
469 the change for you.
471 You've now made your first real git commit. And if you're interested in
472 looking at what `git commit` really does, feel free to investigate:
473 it's a few very simple shell scripts to generate the helpful (?) commit
474 message headers, and a few one-liners that actually do the
475 commit itself (`git-commit`).
478 Inspecting Changes
479 ------------------
481 While creating changes is useful, it's even more useful if you can tell
482 later what changed. The most useful command for this is another of the
483 `diff` family, namely `git-diff-tree`.
485 `git-diff-tree` can be given two arbitrary trees, and it will tell you the
486 differences between them. Perhaps even more commonly, though, you can
487 give it just a single commit object, and it will figure out the parent
488 of that commit itself, and show the difference directly. Thus, to get
489 the same diff that we've already seen several times, we can now do
491 ----------------
492 $ git-diff-tree -p HEAD
493 ----------------
495 (again, `-p` means to show the difference as a human-readable patch),
496 and it will show what the last commit (in `HEAD`) actually changed.
498 [NOTE]
499 ============
500 Here is an ASCII art by Jon Loeliger that illustrates how
501 various diff-\* commands compare things.
503 diff-tree
504 +----+
505 | |
506 | |
507 V V
508 +-----------+
509 | Object DB |
510 | Backing |
511 | Store |
512 +-----------+
513 ^ ^
514 | |
515 | | diff-index --cached
516 | |
517 diff-index | V
518 | +-----------+
519 | | Index |
520 | | "cache" |
521 | +-----------+
522 | ^
523 | |
524 | | diff-files
525 | |
526 V V
527 +-----------+
528 | Working |
529 | Directory |
530 +-----------+
531 ============
533 More interestingly, you can also give `git-diff-tree` the `--pretty` flag,
534 which tells it to also show the commit message and author and date of the
535 commit, and you can tell it to show a whole series of diffs.
536 Alternatively, you can tell it to be "silent", and not show the diffs at
537 all, but just show the actual commit message.
539 In fact, together with the `git-rev-list` program (which generates a
540 list of revisions), `git-diff-tree` ends up being a veritable fount of
541 changes. A trivial (but very useful) script called `git-whatchanged` is
542 included with git which does exactly this, and shows a log of recent
543 activities.
545 To see the whole history of our pitiful little git-tutorial project, you
546 can do
548 ----------------
549 $ git log
550 ----------------
552 which shows just the log messages, or if we want to see the log together
553 with the associated patches use the more complex (and much more
554 powerful)
556 ----------------
557 $ git-whatchanged -p --root
558 ----------------
560 and you will see exactly what has changed in the repository over its
561 short history.
563 [NOTE]
564 The `\--root` flag is a flag to `git-diff-tree` to tell it to
565 show the initial aka 'root' commit too. Normally you'd probably not
566 want to see the initial import diff, but since the tutorial project
567 was started from scratch and is so small, we use it to make the result
568 a bit more interesting.
570 With that, you should now be having some inkling of what git does, and
571 can explore on your own.
573 [NOTE]
574 Most likely, you are not directly using the core
575 git Plumbing commands, but using Porcelain like Cogito on top
576 of it. Cogito works a bit differently and you usually do not
577 have to run `git-update-index` yourself for changed files (you
578 do tell underlying git about additions and removals via
579 `cg-add` and `cg-rm` commands). Just before you make a commit
580 with `cg-commit`, Cogito figures out which files you modified,
581 and runs `git-update-index` on them for you.
584 Tagging a version
585 -----------------
587 In git, there are two kinds of tags, a "light" one, and an "annotated tag".
589 A "light" tag is technically nothing more than a branch, except we put
590 it in the `.git/refs/tags/` subdirectory instead of calling it a `head`.
591 So the simplest form of tag involves nothing more than
593 ------------------------------------------------
594 $ git tag my-first-tag
595 ------------------------------------------------
597 which just writes the current `HEAD` into the `.git/refs/tags/my-first-tag`
598 file, after which point you can then use this symbolic name for that
599 particular state. You can, for example, do
601 ----------------
602 $ git diff my-first-tag
603 ----------------
605 to diff your current state against that tag (which at this point will
606 obviously be an empty diff, but if you continue to develop and commit
607 stuff, you can use your tag as an "anchor-point" to see what has changed
608 since you tagged it.
610 An "annotated tag" is actually a real git object, and contains not only a
611 pointer to the state you want to tag, but also a small tag name and
612 message, along with optionally a PGP signature that says that yes,
613 you really did
614 that tag. You create these annotated tags with either the `-a` or
615 `-s` flag to `git tag`:
617 ----------------
618 $ git tag -s <tagname>
619 ----------------
621 which will sign the current `HEAD` (but you can also give it another
622 argument that specifies the thing to tag, ie you could have tagged the
623 current `mybranch` point by using `git tag <tagname> mybranch`).
625 You normally only do signed tags for major releases or things
626 like that, while the light-weight tags are useful for any marking you
627 want to do -- any time you decide that you want to remember a certain
628 point, just create a private tag for it, and you have a nice symbolic
629 name for the state at that point.
632 Copying repositories
633 --------------------
635 git repositories are normally totally self-sufficient and relocatable
636 Unlike CVS, for example, there is no separate notion of
637 "repository" and "working tree". A git repository normally *is* the
638 working tree, with the local git information hidden in the `.git`
639 subdirectory. There is nothing else. What you see is what you got.
641 [NOTE]
642 You can tell git to split the git internal information from
643 the directory that it tracks, but we'll ignore that for now: it's not
644 how normal projects work, and it's really only meant for special uses.
645 So the mental model of "the git information is always tied directly to
646 the working tree that it describes" may not be technically 100%
647 accurate, but it's a good model for all normal use.
649 This has two implications:
651 - if you grow bored with the tutorial repository you created (or you've
652 made a mistake and want to start all over), you can just do simple
653 +
654 ----------------
655 $ rm -rf git-tutorial
656 ----------------
657 +
658 and it will be gone. There's no external repository, and there's no
659 history outside the project you created.
661 - if you want to move or duplicate a git repository, you can do so. There
662 is `git clone` command, but if all you want to do is just to
663 create a copy of your repository (with all the full history that
664 went along with it), you can do so with a regular
665 `cp -a git-tutorial new-git-tutorial`.
666 +
667 Note that when you've moved or copied a git repository, your git index
668 file (which caches various information, notably some of the "stat"
669 information for the files involved) will likely need to be refreshed.
670 So after you do a `cp -a` to create a new copy, you'll want to do
671 +
672 ----------------
673 $ git-update-index --refresh
674 ----------------
675 +
676 in the new repository to make sure that the index file is up-to-date.
678 Note that the second point is true even across machines. You can
679 duplicate a remote git repository with *any* regular copy mechanism, be it
680 `scp`, `rsync` or `wget`.
682 When copying a remote repository, you'll want to at a minimum update the
683 index cache when you do this, and especially with other peoples'
684 repositories you often want to make sure that the index cache is in some
685 known state (you don't know *what* they've done and not yet checked in),
686 so usually you'll precede the `git-update-index` with a
688 ----------------
689 $ git-read-tree --reset HEAD
690 $ git-update-index --refresh
691 ----------------
693 which will force a total index re-build from the tree pointed to by `HEAD`.
694 It resets the index contents to `HEAD`, and then the `git-update-index`
695 makes sure to match up all index entries with the checked-out files.
696 If the original repository had uncommitted changes in its
697 working tree, `git-update-index --refresh` notices them and
698 tells you they need to be updated.
700 The above can also be written as simply
702 ----------------
703 $ git reset
704 ----------------
706 and in fact a lot of the common git command combinations can be scripted
707 with the `git xyz` interfaces. You can learn things by just looking
708 at what the various git scripts do. For example, `git reset` is the
709 above two lines implemented in `git-reset`, but some things like
710 `git status` and `git commit` are slightly more complex scripts around
711 the basic git commands.
713 Many (most?) public remote repositories will not contain any of
714 the checked out files or even an index file, and will *only* contain the
715 actual core git files. Such a repository usually doesn't even have the
716 `.git` subdirectory, but has all the git files directly in the
717 repository.
719 To create your own local live copy of such a "raw" git repository, you'd
720 first create your own subdirectory for the project, and then copy the
721 raw repository contents into the `.git` directory. For example, to
722 create your own copy of the git repository, you'd do the following
724 ----------------
725 $ mkdir my-git
726 $ cd my-git
727 $ rsync -rL rsync:// .git
728 ----------------
730 followed by
732 ----------------
733 $ git-read-tree HEAD
734 ----------------
736 to populate the index. However, now you have populated the index, and
737 you have all the git internal files, but you will notice that you don't
738 actually have any of the working tree files to work on. To get
739 those, you'd check them out with
741 ----------------
742 $ git-checkout-index -u -a
743 ----------------
745 where the `-u` flag means that you want the checkout to keep the index
746 up-to-date (so that you don't have to refresh it afterward), and the
747 `-a` flag means "check out all files" (if you have a stale copy or an
748 older version of a checked out tree you may also need to add the `-f`
749 flag first, to tell git-checkout-index to *force* overwriting of any old
750 files).
752 Again, this can all be simplified with
754 ----------------
755 $ git clone rsync:// my-git
756 $ cd my-git
757 $ git checkout
758 ----------------
760 which will end up doing all of the above for you.
762 You have now successfully copied somebody else's (mine) remote
763 repository, and checked it out.
766 Creating a new branch
767 ---------------------
769 Branches in git are really nothing more than pointers into the git
770 object database from within the `.git/refs/` subdirectory, and as we
771 already discussed, the `HEAD` branch is nothing but a symlink to one of
772 these object pointers.
774 You can at any time create a new branch by just picking an arbitrary
775 point in the project history, and just writing the SHA1 name of that
776 object into a file under `.git/refs/heads/`. You can use any filename you
777 want (and indeed, subdirectories), but the convention is that the
778 "normal" branch is called `master`. That's just a convention, though,
779 and nothing enforces it.
781 To show that as an example, let's go back to the git-tutorial repository we
782 used earlier, and create a branch in it. You do that by simply just
783 saying that you want to check out a new branch:
785 ------------
786 $ git checkout -b mybranch
787 ------------
789 will create a new branch based at the current `HEAD` position, and switch
790 to it.
792 [NOTE]
793 ================================================
794 If you make the decision to start your new branch at some
795 other point in the history than the current `HEAD`, you can do so by
796 just telling `git checkout` what the base of the checkout would be.
797 In other words, if you have an earlier tag or branch, you'd just do
799 ------------
800 $ git checkout -b mybranch earlier-commit
801 ------------
803 and it would create the new branch `mybranch` at the earlier commit,
804 and check out the state at that time.
805 ================================================
807 You can always just jump back to your original `master` branch by doing
809 ------------
810 $ git checkout master
811 ------------
813 (or any other branch-name, for that matter) and if you forget which
814 branch you happen to be on, a simple
816 ------------
817 $ cat .git/HEAD
818 ------------
820 will tell you where it's pointing. To get the list of branches
821 you have, you can say
823 ------------
824 $ git branch
825 ------------
827 which is nothing more than a simple script around `ls .git/refs/heads`.
828 There will be asterisk in front of the branch you are currently on.
830 Sometimes you may wish to create a new branch _without_ actually
831 checking it out and switching to it. If so, just use the command
833 ------------
834 $ git branch <branchname> [startingpoint]
835 ------------
837 which will simply _create_ the branch, but will not do anything further.
838 You can then later -- once you decide that you want to actually develop
839 on that branch -- switch to that branch with a regular `git checkout`
840 with the branchname as the argument.
843 Merging two branches
844 --------------------
846 One of the ideas of having a branch is that you do some (possibly
847 experimental) work in it, and eventually merge it back to the main
848 branch. So assuming you created the above `mybranch` that started out
849 being the same as the original `master` branch, let's make sure we're in
850 that branch, and do some work there.
852 ------------------------------------------------
853 $ git checkout mybranch
854 $ echo "Work, work, work" >>hello
855 $ git commit -m 'Some work.' -i hello
856 ------------------------------------------------
858 Here, we just added another line to `hello`, and we used a shorthand for
859 doing both `git-update-index hello` and `git commit` by just giving the
860 filename directly to `git commit`, with an `-i` flag (it tells
861 git to 'include' that file in addition to what you have done to
862 the index file so far when making the commit). The `-m` flag is to give the
863 commit log message from the command line.
865 Now, to make it a bit more interesting, let's assume that somebody else
866 does some work in the original branch, and simulate that by going back
867 to the master branch, and editing the same file differently there:
869 ------------
870 $ git checkout master
871 ------------
873 Here, take a moment to look at the contents of `hello`, and notice how they
874 don't contain the work we just did in `mybranch` -- because that work
875 hasn't happened in the `master` branch at all. Then do
877 ------------
878 $ echo "Play, play, play" >>hello
879 $ echo "Lots of fun" >>example
880 $ git commit -m 'Some fun.' -i hello example
881 ------------
883 since the master branch is obviously in a much better mood.
885 Now, you've got two branches, and you decide that you want to merge the
886 work done. Before we do that, let's introduce a cool graphical tool that
887 helps you view what's going on:
889 ----------------
890 $ gitk --all
891 ----------------
893 will show you graphically both of your branches (that's what the `\--all`
894 means: normally it will just show you your current `HEAD`) and their
895 histories. You can also see exactly how they came to be from a common
896 source.
898 Anyway, let's exit `gitk` (`^Q` or the File menu), and decide that we want
899 to merge the work we did on the `mybranch` branch into the `master`
900 branch (which is currently our `HEAD` too). To do that, there's a nice
901 script called `git merge`, which wants to know which branches you want
902 to resolve and what the merge is all about:
904 ------------
905 $ git merge "Merge work in mybranch" HEAD mybranch
906 ------------
908 where the first argument is going to be used as the commit message if
909 the merge can be resolved automatically.
911 Now, in this case we've intentionally created a situation where the
912 merge will need to be fixed up by hand, though, so git will do as much
913 of it as it can automatically (which in this case is just merge the `example`
914 file, which had no differences in the `mybranch` branch), and say:
916 ----------------
917 Trying really trivial in-index merge...
918 fatal: Merge requires file-level merging
919 Nope.
920 ...
921 Auto-merging hello
922 CONFLICT (content): Merge conflict in hello
923 Automatic merge failed; fix up by hand
924 ----------------
926 which is way too verbose, but it basically tells you that it failed the
927 really trivial merge ("Simple merge") and did an "Automatic merge"
928 instead, but that too failed due to conflicts in `hello`.
930 Not to worry. It left the (trivial) conflict in `hello` in the same form you
931 should already be well used to if you've ever used CVS, so let's just
932 open `hello` in our editor (whatever that may be), and fix it up somehow.
933 I'd suggest just making it so that `hello` contains all four lines:
935 ------------
936 Hello World
937 It's a new day for git
938 Play, play, play
939 Work, work, work
940 ------------
942 and once you're happy with your manual merge, just do a
944 ------------
945 $ git commit -i hello
946 ------------
948 which will very loudly warn you that you're now committing a merge
949 (which is correct, so never mind), and you can write a small merge
950 message about your adventures in git-merge-land.
952 After you're done, start up `gitk \--all` to see graphically what the
953 history looks like. Notice that `mybranch` still exists, and you can
954 switch to it, and continue to work with it if you want to. The
955 `mybranch` branch will not contain the merge, but next time you merge it
956 from the `master` branch, git will know how you merged it, so you'll not
957 have to do _that_ merge again.
959 Another useful tool, especially if you do not always work in X-Window
960 environment, is `git show-branch`.
962 ------------------------------------------------
963 $ git show-branch --topo-order master mybranch
964 * [master] Merge work in mybranch
965 ! [mybranch] Some work.
966 --
967 - [master] Merge work in mybranch
968 *+ [mybranch] Some work.
969 ------------------------------------------------
971 The first two lines indicate that it is showing the two branches
972 and the first line of the commit log message from their
973 top-of-the-tree commits, you are currently on `master` branch
974 (notice the asterisk `*` character), and the first column for
975 the later output lines is used to show commits contained in the
976 `master` branch, and the second column for the `mybranch`
977 branch. Three commits are shown along with their log messages.
978 All of them have non blank characters in the first column (`*`
979 shows an ordinary commit on the current branch, `.` is a merge commit), which
980 means they are now part of the `master` branch. Only the "Some
981 work" commit has the plus `+` character in the second column,
982 because `mybranch` has not been merged to incorporate these
983 commits from the master branch. The string inside brackets
984 before the commit log message is a short name you can use to
985 name the commit. In the above example, 'master' and 'mybranch'
986 are branch heads. 'master~1' is the first parent of 'master'
987 branch head. Please see 'git-rev-parse' documentation if you
988 see more complex cases.
990 Now, let's pretend you are the one who did all the work in
991 `mybranch`, and the fruit of your hard work has finally been merged
992 to the `master` branch. Let's go back to `mybranch`, and run
993 resolve to get the "upstream changes" back to your branch.
995 ------------
996 $ git checkout mybranch
997 $ git merge "Merge upstream changes." HEAD master
998 ------------
1000 This outputs something like this (the actual commit object names
1001 would be different)
1003 ----------------
1004 Updating from ae3a2da... to a80b4aa....
1005 Fast forward
1006 example | 1 +
1007 hello | 1 +
1008 2 files changed, 2 insertions(+), 0 deletions(-)
1009 ----------------
1011 Because your branch did not contain anything more than what are
1012 already merged into the `master` branch, the resolve operation did
1013 not actually do a merge. Instead, it just updated the top of
1014 the tree of your branch to that of the `master` branch. This is
1015 often called 'fast forward' merge.
1017 You can run `gitk \--all` again to see how the commit ancestry
1018 looks like, or run `show-branch`, which tells you this.
1020 ------------------------------------------------
1021 $ git show-branch master mybranch
1022 ! [master] Merge work in mybranch
1023 * [mybranch] Merge work in mybranch
1024 --
1025 -- [master] Merge work in mybranch
1026 ------------------------------------------------
1029 Merging external work
1030 ---------------------
1032 It's usually much more common that you merge with somebody else than
1033 merging with your own branches, so it's worth pointing out that git
1034 makes that very easy too, and in fact, it's not that different from
1035 doing a `git merge`. In fact, a remote merge ends up being nothing
1036 more than "fetch the work from a remote repository into a temporary tag"
1037 followed by a `git merge`.
1039 Fetching from a remote repository is done by, unsurprisingly,
1040 `git fetch`:
1042 ----------------
1043 $ git fetch <remote-repository>
1044 ----------------
1046 One of the following transports can be used to name the
1047 repository to download from:
1049 Rsync::
1050 `rsync://remote.machine/path/to/repo.git/`
1051 +
1052 Rsync transport is usable for both uploading and downloading,
1053 but is completely unaware of what git does, and can produce
1054 unexpected results when you download from the public repository
1055 while the repository owner is uploading into it via `rsync`
1056 transport. Most notably, it could update the files under
1057 `refs/` which holds the object name of the topmost commits
1058 before uploading the files in `objects/` -- the downloader would
1059 obtain head commit object name while that object itself is still
1060 not available in the repository. For this reason, it is
1061 considered deprecated.
1063 SSH::
1064 `remote.machine:/path/to/repo.git/` or
1065 +
1066 `ssh://remote.machine/path/to/repo.git/`
1067 +
1068 This transport can be used for both uploading and downloading,
1069 and requires you to have a log-in privilege over `ssh` to the
1070 remote machine. It finds out the set of objects the other side
1071 lacks by exchanging the head commits both ends have and
1072 transfers (close to) minimum set of objects. It is by far the
1073 most efficient way to exchange git objects between repositories.
1075 Local directory::
1076 `/path/to/repo.git/`
1077 +
1078 This transport is the same as SSH transport but uses `sh` to run
1079 both ends on the local machine instead of running other end on
1080 the remote machine via `ssh`.
1082 git Native::
1083 `git://remote.machine/path/to/repo.git/`
1084 +
1085 This transport was designed for anonymous downloading. Like SSH
1086 transport, it finds out the set of objects the downstream side
1087 lacks and transfers (close to) minimum set of objects.
1089 HTTP(S)::
1090 `http://remote.machine/path/to/repo.git/`
1091 +
1092 Downloader from http and https URL
1093 first obtains the topmost commit object name from the remote site
1094 by looking at the specified refname under `repo.git/refs/` directory,
1095 and then tries to obtain the
1096 commit object by downloading from `repo.git/objects/xx/xxx\...`
1097 using the object name of that commit object. Then it reads the
1098 commit object to find out its parent commits and the associate
1099 tree object; it repeats this process until it gets all the
1100 necessary objects. Because of this behaviour, they are
1101 sometimes also called 'commit walkers'.
1102 +
1103 The 'commit walkers' are sometimes also called 'dumb
1104 transports', because they do not require any git aware smart
1105 server like git Native transport does. Any stock HTTP server
1106 that does not even support directory index would suffice. But
1107 you must prepare your repository with `git-update-server-info`
1108 to help dumb transport downloaders.
1109 +
1110 There are (confusingly enough) `git-ssh-fetch` and `git-ssh-upload`
1111 programs, which are 'commit walkers'; they outlived their
1112 usefulness when git Native and SSH transports were introduced,
1113 and not used by `git pull` or `git push` scripts.
1115 Once you fetch from the remote repository, you `resolve` that
1116 with your current branch.
1118 However -- it's such a common thing to `fetch` and then
1119 immediately `resolve`, that it's called `git pull`, and you can
1120 simply do
1122 ----------------
1123 $ git pull <remote-repository>
1124 ----------------
1126 and optionally give a branch-name for the remote end as a second
1127 argument.
1129 [NOTE]
1130 You could do without using any branches at all, by
1131 keeping as many local repositories as you would like to have
1132 branches, and merging between them with `git pull`, just like
1133 you merge between branches. The advantage of this approach is
1134 that it lets you keep set of files for each `branch` checked
1135 out and you may find it easier to switch back and forth if you
1136 juggle multiple lines of development simultaneously. Of
1137 course, you will pay the price of more disk usage to hold
1138 multiple working trees, but disk space is cheap these days.
1140 [NOTE]
1141 You could even pull from your own repository by
1142 giving '.' as <remote-repository> parameter to `git pull`. This
1143 is useful when you want to merge a local branch (or more, if you
1144 are making an Octopus) into the current branch.
1146 It is likely that you will be pulling from the same remote
1147 repository from time to time. As a short hand, you can store
1148 the remote repository URL in a file under .git/remotes/
1149 directory, like this:
1151 ------------------------------------------------
1152 $ mkdir -p .git/remotes/
1153 $ cat >.git/remotes/linus <<\EOF
1154 URL:
1155 EOF
1156 ------------------------------------------------
1158 and use the filename to `git pull` instead of the full URL.
1159 The URL specified in such file can even be a prefix
1160 of a full URL, like this:
1162 ------------------------------------------------
1163 $ cat >.git/remotes/jgarzik <<\EOF
1164 URL:
1165 EOF
1166 ------------------------------------------------
1169 Examples.
1171 . `git pull linus`
1172 . `git pull linus tag v0.99.1`
1173 . `git pull jgarzik/netdev-2.6.git/ e100`
1175 the above are equivalent to:
1177 . `git pull HEAD`
1178 . `git pull tag v0.99.1`
1179 . `git pull e100`
1182 How does the merge work?
1183 ------------------------
1185 We said this tutorial shows what plumbing does to help you cope
1186 with the porcelain that isn't flushing, but we so far did not
1187 talk about how the merge really works. If you are following
1188 this tutorial the first time, I'd suggest to skip to "Publishing
1189 your work" section and come back here later.
1191 OK, still with me? To give us an example to look at, let's go
1192 back to the earlier repository with "hello" and "example" file,
1193 and bring ourselves back to the pre-merge state:
1195 ------------
1196 $ git show-branch --more=3 master mybranch
1197 ! [master] Merge work in mybranch
1198 * [mybranch] Merge work in mybranch
1199 --
1200 -- [master] Merge work in mybranch
1201 +* [master^2] Some work.
1202 +* [master^] Some fun.
1203 ------------
1205 Remember, before running `git merge`, our `master` head was at
1206 "Some fun." commit, while our `mybranch` head was at "Some
1207 work." commit.
1209 ------------
1210 $ git checkout mybranch
1211 $ git reset --hard master^2
1212 $ git checkout master
1213 $ git reset --hard master^
1214 ------------
1216 After rewinding, the commit structure should look like this:
1218 ------------
1219 $ git show-branch
1220 * [master] Some fun.
1221 ! [mybranch] Some work.
1222 --
1223 + [mybranch] Some work.
1224 * [master] Some fun.
1225 *+ [mybranch^] New day.
1226 ------------
1228 Now we are ready to experiment with the merge by hand.
1230 `git merge` command, when merging two branches, uses 3-way merge
1231 algorithm. First, it finds the common ancestor between them.
1232 The command it uses is `git-merge-base`:
1234 ------------
1235 $ mb=$(git-merge-base HEAD mybranch)
1236 ------------
1238 The command writes the commit object name of the common ancestor
1239 to the standard output, so we captured its output to a variable,
1240 because we will be using it in the next step. BTW, the common
1241 ancestor commit is the "New day." commit in this case. You can
1242 tell it by:
1244 ------------
1245 $ git-name-rev $mb
1246 my-first-tag
1247 ------------
1249 After finding out a common ancestor commit, the second step is
1250 this:
1252 ------------
1253 $ git-read-tree -m -u $mb HEAD mybranch
1254 ------------
1256 This is the same `git-read-tree` command we have already seen,
1257 but it takes three trees, unlike previous examples. This reads
1258 the contents of each tree into different 'stage' in the index
1259 file (the first tree goes to stage 1, the second stage 2,
1260 etc.). After reading three trees into three stages, the paths
1261 that are the same in all three stages are 'collapsed' into stage
1262 0. Also paths that are the same in two of three stages are
1263 collapsed into stage 0, taking the SHA1 from either stage 2 or
1264 stage 3, whichever is different from stage 1 (i.e. only one side
1265 changed from the common ancestor).
1267 After 'collapsing' operation, paths that are different in three
1268 trees are left in non-zero stages. At this point, you can
1269 inspect the index file with this command:
1271 ------------
1272 $ git-ls-files --stage
1273 100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
1274 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1275 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1276 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1277 ------------
1279 In our example of only two files, we did not have unchanged
1280 files so only 'example' resulted in collapsing, but in real-life
1281 large projects, only small number of files change in one commit,
1282 and this 'collapsing' tends to trivially merge most of the paths
1283 fairly quickly, leaving only a handful the real changes in non-zero
1284 stages.
1286 To look at only non-zero stages, use `\--unmerged` flag:
1288 ------------
1289 $ git-ls-files --unmerged
1290 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1291 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1292 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1293 ------------
1295 The next step of merging is to merge these three versions of the
1296 file, using 3-way merge. This is done by giving
1297 `git-merge-one-file` command as one of the arguments to
1298 `git-merge-index` command:
1300 ------------
1301 $ git-merge-index git-merge-one-file hello
1302 Auto-merging hello.
1303 merge: warning: conflicts during merge
1304 ERROR: Merge conflict in hello.
1305 fatal: merge program failed
1306 ------------
1308 `git-merge-one-file` script is called with parameters to
1309 describe those three versions, and is responsible to leave the
1310 merge results in the working tree.
1311 It is a fairly straightforward shell script, and
1312 eventually calls `merge` program from RCS suite to perform a
1313 file-level 3-way merge. In this case, `merge` detects
1314 conflicts, and the merge result with conflict marks is left in
1315 the working tree.. This can be seen if you run `ls-files
1316 --stage` again at this point:
1318 ------------
1319 $ git-ls-files --stage
1320 100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
1321 100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1322 100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1323 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1324 ------------
1326 This is the state of the index file and the working file after
1327 `git merge` returns control back to you, leaving the conflicting
1328 merge for you to resolve. Notice that the path `hello` is still
1329 unmerged, and what you see with `git diff` at this point is
1330 differences since stage 2 (i.e. your version).
1333 Publishing your work
1334 --------------------
1336 So we can use somebody else's work from a remote repository; but
1337 how can *you* prepare a repository to let other people pull from
1338 it?
1340 Your do your real work in your working tree that has your
1341 primary repository hanging under it as its `.git` subdirectory.
1342 You *could* make that repository accessible remotely and ask
1343 people to pull from it, but in practice that is not the way
1344 things are usually done. A recommended way is to have a public
1345 repository, make it reachable by other people, and when the
1346 changes you made in your primary working tree are in good shape,
1347 update the public repository from it. This is often called
1348 'pushing'.
1350 [NOTE]
1351 This public repository could further be mirrored, and that is
1352 how git repositories at `` are managed.
1354 Publishing the changes from your local (private) repository to
1355 your remote (public) repository requires a write privilege on
1356 the remote machine. You need to have an SSH account there to
1357 run a single command, `git-receive-pack`.
1359 First, you need to create an empty repository on the remote
1360 machine that will house your public repository. This empty
1361 repository will be populated and be kept up-to-date by pushing
1362 into it later. Obviously, this repository creation needs to be
1363 done only once.
1365 [NOTE]
1366 `git push` uses a pair of programs,
1367 `git-send-pack` on your local machine, and `git-receive-pack`
1368 on the remote machine. The communication between the two over
1369 the network internally uses an SSH connection.
1371 Your private repository's git directory is usually `.git`, but
1372 your public repository is often named after the project name,
1373 i.e. `<project>.git`. Let's create such a public repository for
1374 project `my-git`. After logging into the remote machine, create
1375 an empty directory:
1377 ------------
1378 $ mkdir my-git.git
1379 ------------
1381 Then, make that directory into a git repository by running
1382 `git init-db`, but this time, since its name is not the usual
1383 `.git`, we do things slightly differently:
1385 ------------
1386 $ GIT_DIR=my-git.git git-init-db
1387 ------------
1389 Make sure this directory is available for others you want your
1390 changes to be pulled by via the transport of your choice. Also
1391 you need to make sure that you have the `git-receive-pack`
1392 program on the `$PATH`.
1394 [NOTE]
1395 Many installations of sshd do not invoke your shell as the login
1396 shell when you directly run programs; what this means is that if
1397 your login shell is `bash`, only `.bashrc` is read and not
1398 `.bash_profile`. As a workaround, make sure `.bashrc` sets up
1399 `$PATH` so that you can run `git-receive-pack` program.
1401 [NOTE]
1402 If you plan to publish this repository to be accessed over http,
1403 you should do `chmod +x my-git.git/hooks/post-update` at this
1404 point. This makes sure that every time you push into this
1405 repository, `git-update-server-info` is run.
1407 Your "public repository" is now ready to accept your changes.
1408 Come back to the machine you have your private repository. From
1409 there, run this command:
1411 ------------
1412 $ git push <public-host>:/path/to/my-git.git master
1413 ------------
1415 This synchronizes your public repository to match the named
1416 branch head (i.e. `master` in this case) and objects reachable
1417 from them in your current repository.
1419 As a real example, this is how I update my public git
1420 repository. mirror network takes care of the
1421 propagation to other publicly visible machines:
1423 ------------
1424 $ git push
1425 ------------
1428 Packing your repository
1429 -----------------------
1431 Earlier, we saw that one file under `.git/objects/??/` directory
1432 is stored for each git object you create. This representation
1433 is efficient to create atomically and safely, but
1434 not so convenient to transport over the network. Since git objects are
1435 immutable once they are created, there is a way to optimize the
1436 storage by "packing them together". The command
1438 ------------
1439 $ git repack
1440 ------------
1442 will do it for you. If you followed the tutorial examples, you
1443 would have accumulated about 17 objects in `.git/objects/??/`
1444 directories by now. `git repack` tells you how many objects it
1445 packed, and stores the packed file in `.git/objects/pack`
1446 directory.
1448 [NOTE]
1449 You will see two files, `pack-\*.pack` and `pack-\*.idx`,
1450 in `.git/objects/pack` directory. They are closely related to
1451 each other, and if you ever copy them by hand to a different
1452 repository for whatever reason, you should make sure you copy
1453 them together. The former holds all the data from the objects
1454 in the pack, and the latter holds the index for random
1455 access.
1457 If you are paranoid, running `git-verify-pack` command would
1458 detect if you have a corrupt pack, but do not worry too much.
1459 Our programs are always perfect ;-).
1461 Once you have packed objects, you do not need to leave the
1462 unpacked objects that are contained in the pack file anymore.
1464 ------------
1465 $ git prune-packed
1466 ------------
1468 would remove them for you.
1470 You can try running `find .git/objects -type f` before and after
1471 you run `git prune-packed` if you are curious. Also `git
1472 count-objects` would tell you how many unpacked objects are in
1473 your repository and how much space they are consuming.
1475 [NOTE]
1476 `git pull` is slightly cumbersome for HTTP transport, as a
1477 packed repository may contain relatively few objects in a
1478 relatively large pack. If you expect many HTTP pulls from your
1479 public repository you might want to repack & prune often, or
1480 never.
1482 If you run `git repack` again at this point, it will say
1483 "Nothing to pack". Once you continue your development and
1484 accumulate the changes, running `git repack` again will create a
1485 new pack, that contains objects created since you packed your
1486 repository the last time. We recommend that you pack your project
1487 soon after the initial import (unless you are starting your
1488 project from scratch), and then run `git repack` every once in a
1489 while, depending on how active your project is.
1491 When a repository is synchronized via `git push` and `git pull`
1492 objects packed in the source repository are usually stored
1493 unpacked in the destination, unless rsync transport is used.
1494 While this allows you to use different packing strategies on
1495 both ends, it also means you may need to repack both
1496 repositories every once in a while.
1499 Working with Others
1500 -------------------
1502 Although git is a truly distributed system, it is often
1503 convenient to organize your project with an informal hierarchy
1504 of developers. Linux kernel development is run this way. There
1505 is a nice illustration (page 17, "Merges to Mainline") in Randy
1506 Dunlap's presentation (``).
1508 It should be stressed that this hierarchy is purely *informal*.
1509 There is nothing fundamental in git that enforces the "chain of
1510 patch flow" this hierarchy implies. You do not have to pull
1511 from only one remote repository.
1513 A recommended workflow for a "project lead" goes like this:
1515 1. Prepare your primary repository on your local machine. Your
1516 work is done there.
1518 2. Prepare a public repository accessible to others.
1519 +
1520 If other people are pulling from your repository over dumb
1521 transport protocols (HTTP), you need to keep this repository
1522 'dumb transport friendly'. After `git init-db`,
1523 `$GIT_DIR/hooks/post-update` copied from the standard templates
1524 would contain a call to `git-update-server-info` but the
1525 `post-update` hook itself is disabled by default -- enable it
1526 with `chmod +x post-update`. This makes sure `git-update-server-info`
1527 keeps the necessary files up-to-date.
1529 3. Push into the public repository from your primary
1530 repository.
1532 4. `git repack` the public repository. This establishes a big
1533 pack that contains the initial set of objects as the
1534 baseline, and possibly `git prune` if the transport
1535 used for pulling from your repository supports packed
1536 repositories.
1538 5. Keep working in your primary repository. Your changes
1539 include modifications of your own, patches you receive via
1540 e-mails, and merges resulting from pulling the "public"
1541 repositories of your "subsystem maintainers".
1542 +
1543 You can repack this private repository whenever you feel like.
1545 6. Push your changes to the public repository, and announce it
1546 to the public.
1548 7. Every once in a while, "git repack" the public repository.
1549 Go back to step 5. and continue working.
1552 A recommended work cycle for a "subsystem maintainer" who works
1553 on that project and has an own "public repository" goes like this:
1555 1. Prepare your work repository, by `git clone` the public
1556 repository of the "project lead". The URL used for the
1557 initial cloning is stored in `.git/remotes/origin`.
1559 2. Prepare a public repository accessible to others, just like
1560 the "project lead" person does.
1562 3. Copy over the packed files from "project lead" public
1563 repository to your public repository, unless the "project
1564 lead" repository lives on the same machine as yours. In the
1565 latter case, you can use `objects/info/alternates` file to
1566 point at the repository you are borrowing from.
1568 4. Push into the public repository from your primary
1569 repository. Run `git repack`, and possibly `git prune` if the
1570 transport used for pulling from your repository supports
1571 packed repositories.
1573 5. Keep working in your primary repository. Your changes
1574 include modifications of your own, patches you receive via
1575 e-mails, and merges resulting from pulling the "public"
1576 repositories of your "project lead" and possibly your
1577 "sub-subsystem maintainers".
1578 +
1579 You can repack this private repository whenever you feel
1580 like.
1582 6. Push your changes to your public repository, and ask your
1583 "project lead" and possibly your "sub-subsystem
1584 maintainers" to pull from it.
1586 7. Every once in a while, `git repack` the public repository.
1587 Go back to step 5. and continue working.
1590 A recommended work cycle for an "individual developer" who does
1591 not have a "public" repository is somewhat different. It goes
1592 like this:
1594 1. Prepare your work repository, by `git clone` the public
1595 repository of the "project lead" (or a "subsystem
1596 maintainer", if you work on a subsystem). The URL used for
1597 the initial cloning is stored in `.git/remotes/origin`.
1599 2. Do your work in your repository on 'master' branch.
1601 3. Run `git fetch origin` from the public repository of your
1602 upstream every once in a while. This does only the first
1603 half of `git pull` but does not merge. The head of the
1604 public repository is stored in `.git/refs/heads/origin`.
1606 4. Use `git cherry origin` to see which ones of your patches
1607 were accepted, and/or use `git rebase origin` to port your
1608 unmerged changes forward to the updated upstream.
1610 5. Use `git format-patch origin` to prepare patches for e-mail
1611 submission to your upstream and send it out. Go back to
1612 step 2. and continue.
1615 Working with Others, Shared Repository Style
1616 --------------------------------------------
1618 If you are coming from CVS background, the style of cooperation
1619 suggested in the previous section may be new to you. You do not
1620 have to worry. git supports "shared public repository" style of
1621 cooperation you are probably more familiar with as well.
1623 See link:cvs-migration.txt[git for CVS users] for the details.
1625 Bundling your work together
1626 ---------------------------
1628 It is likely that you will be working on more than one thing at
1629 a time. It is easy to manage those more-or-less independent tasks
1630 using branches with git.
1632 We have already seen how branches work previously,
1633 with "fun and work" example using two branches. The idea is the
1634 same if there are more than two branches. Let's say you started
1635 out from "master" head, and have some new code in the "master"
1636 branch, and two independent fixes in the "commit-fix" and
1637 "diff-fix" branches:
1639 ------------
1640 $ git show-branch
1641 ! [commit-fix] Fix commit message normalization.
1642 ! [diff-fix] Fix rename detection.
1643 * [master] Release candidate #1
1644 ---
1645 + [diff-fix] Fix rename detection.
1646 + [diff-fix~1] Better common substring algorithm.
1647 + [commit-fix] Fix commit message normalization.
1648 * [master] Release candidate #1
1649 ++* [diff-fix~2] Pretty-print messages.
1650 ------------
1652 Both fixes are tested well, and at this point, you want to merge
1653 in both of them. You could merge in 'diff-fix' first and then
1654 'commit-fix' next, like this:
1656 ------------
1657 $ git merge 'Merge fix in diff-fix' master diff-fix
1658 $ git merge 'Merge fix in commit-fix' master commit-fix
1659 ------------
1661 Which would result in:
1663 ------------
1664 $ git show-branch
1665 ! [commit-fix] Fix commit message normalization.
1666 ! [diff-fix] Fix rename detection.
1667 * [master] Merge fix in commit-fix
1668 ---
1669 - [master] Merge fix in commit-fix
1670 + * [commit-fix] Fix commit message normalization.
1671 - [master~1] Merge fix in diff-fix
1672 +* [diff-fix] Fix rename detection.
1673 +* [diff-fix~1] Better common substring algorithm.
1674 * [master~2] Release candidate #1
1675 ++* [master~3] Pretty-print messages.
1676 ------------
1678 However, there is no particular reason to merge in one branch
1679 first and the other next, when what you have are a set of truly
1680 independent changes (if the order mattered, then they are not
1681 independent by definition). You could instead merge those two
1682 branches into the current branch at once. First let's undo what
1683 we just did and start over. We would want to get the master
1684 branch before these two merges by resetting it to 'master~2':
1686 ------------
1687 $ git reset --hard master~2
1688 ------------
1690 You can make sure 'git show-branch' matches the state before
1691 those two 'git merge' you just did. Then, instead of running
1692 two 'git merge' commands in a row, you would pull these two
1693 branch heads (this is known as 'making an Octopus'):
1695 ------------
1696 $ git pull . commit-fix diff-fix
1697 $ git show-branch
1698 ! [commit-fix] Fix commit message normalization.
1699 ! [diff-fix] Fix rename detection.
1700 * [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1701 ---
1702 - [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1703 + * [commit-fix] Fix commit message normalization.
1704 +* [diff-fix] Fix rename detection.
1705 +* [diff-fix~1] Better common substring algorithm.
1706 * [master~1] Release candidate #1
1707 ++* [master~2] Pretty-print messages.
1708 ------------
1710 Note that you should not do Octopus because you can. An octopus
1711 is a valid thing to do and often makes it easier to view the
1712 commit history if you are pulling more than two independent
1713 changes at the same time. However, if you have merge conflicts
1714 with any of the branches you are merging in and need to hand
1715 resolve, that is an indication that the development happened in
1716 those branches were not independent after all, and you should
1717 merge two at a time, documenting how you resolved the conflicts,
1718 and the reason why you preferred changes made in one side over
1719 the other. Otherwise it would make the project history harder
1720 to follow, not easier.
1722 [ to be continued.. cvsimports ]