1GITCORE-TUTORIAL(7) Git Manual GITCORE-TUTORIAL(7)
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6 gitcore-tutorial - A Git core tutorial for developers
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9 git *
10
12 This tutorial explains how to use the "core" Git commands to set up and
13 work with a Git repository.
14 If you just need to use Git as a revision control system you may prefer
16 to start with "A Tutorial Introduction to Git" (gittutorial(7)) or the
17 Git User Manual[1].
18 However, an understanding of these low-level tools can be helpful if
20 you want to understand Git’s internals.
21 The core Git is often called "plumbing", with the prettier user
23 interfaces on top of it called "porcelain". You may not want to use the
24 plumbing directly very often, but it can be good to know what the
25 plumbing does when the porcelain isn’t flushing.
26 Back when this document was originally written, many porcelain commands
28 were shell scripts. For simplicity, it still uses them as examples to
29 illustrate how plumbing is fit together to form the porcelain commands.
30 The source tree includes some of these scripts in contrib/examples/ for
31 reference. Although these are not implemented as shell scripts anymore,
32 the description of what the plumbing layer commands do is still valid.
33 Note
35 Deeper technical details are often marked as Notes, which you can
36 skip on your first reading.
37
39 Creating a new Git repository couldn’t be easier: all Git repositories
40 start out empty, and the only thing you need to do is find yourself a
41 subdirectory that you want to use as a working tree - either an empty
42 one for a totally new project, or an existing working tree that you
43 want to import into Git.
44 For our first example, we’re going to start a totally new repository
46 from scratch, with no pre-existing files, and we’ll call it
47 git-tutorial. To start up, create a subdirectory for it, change into
48 that subdirectory, and initialize the Git infrastructure with git init:
49 $ mkdir git-tutorial
51 $ cd git-tutorial
52 $ git init
53 to which Git will reply
55 Initialized empty Git repository in .git/
57 which is just Git’s way of saying that you haven’t been doing anything
59 strange, and that it will have created a local .git directory setup for
60 your new project. You will now have a .git directory, and you can
61 inspect that with ls. For your new empty project, it should show you
62 three entries, among other things:
63 · a file called HEAD, that has ref: refs/heads/master in it. This is
65 similar to a symbolic link and points at refs/heads/master relative
66 to the HEAD file.
67 Don’t worry about the fact that the file that the HEAD link points
69 to doesn’t even exist yet — you haven’t created the commit that
70 will start your HEAD development branch yet.
71 · a subdirectory called objects, which will contain all the objects
73 of your project. You should never have any real reason to look at
74 the objects directly, but you might want to know that these objects
75 are what contains all the real data in your repository.
76 · a subdirectory called refs, which contains references to objects.
78 In particular, the refs subdirectory will contain two other
80 subdirectories, named heads and tags respectively. They do exactly what
81 their names imply: they contain references to any number of different
82 heads of development (aka branches), and to any tags that you have
83 created to name specific versions in your repository.
84 One note: the special master head is the default branch, which is why
86 the .git/HEAD file was created points to it even if it doesn’t yet
87 exist. Basically, the HEAD link is supposed to always point to the
88 branch you are working on right now, and you always start out expecting
89 to work on the master branch.
90 However, this is only a convention, and you can name your branches
92 anything you want, and don’t have to ever even have a master branch. A
93 number of the Git tools will assume that .git/HEAD is valid, though.
94 Note
96 An object is identified by its 160-bit SHA-1 hash, aka object name,
97 and a reference to an object is always the 40-byte hex
98 representation of that SHA-1 name. The files in the refs
99 subdirectory are expected to contain these hex references (usually
100 with a final \n at the end), and you should thus expect to see a
101 number of 41-byte files containing these references in these refs
102 subdirectories when you actually start populating your tree.
103 Note
105 An advanced user may want to take a look at gitrepository-layout(5)
106 after finishing this tutorial.
107 You have now created your first Git repository. Of course, since it’s
109 empty, that’s not very useful, so let’s start populating it with data.
110
112 We’ll keep this simple and stupid, so we’ll start off with populating a
113 few trivial files just to get a feel for it.
114 Start off with just creating any random files that you want to maintain
116 in your Git repository. We’ll start off with a few bad examples, just
117 to get a feel for how this works:
118 $ echo "Hello World" >hello
120 $ echo "Silly example" >example
121 you have now created two files in your working tree (aka working
123 directory), but to actually check in your hard work, you will have to
124 go through two steps:
125 · fill in the index file (aka cache) with the information about your
127 working tree state.
128 · commit that index file as an object.
130 The first step is trivial: when you want to tell Git about any changes
132 to your working tree, you use the git update-index program. That
133 program normally just takes a list of filenames you want to update, but
134 to avoid trivial mistakes, it refuses to add new entries to the index
135 (or remove existing ones) unless you explicitly tell it that you’re
136 adding a new entry with the --add flag (or removing an entry with the
137 --remove) flag.
138 So to populate the index with the two files you just created, you can
140 do
141 $ git update-index --add hello example
143 and you have now told Git to track those two files.
145 In fact, as you did that, if you now look into your object directory,
147 you’ll notice that Git will have added two new objects to the object
148 database. If you did exactly the steps above, you should now be able to
149 do
150 $ ls .git/objects/??/*
152 and see two files:
154 .git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
156 .git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
157 which correspond with the objects with names of 557db... and f24c7...
159 respectively.
160 If you want to, you can use git cat-file to look at those objects, but
162 you’ll have to use the object name, not the filename of the object:
163 $ git cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
165 where the -t tells git cat-file to tell you what the "type" of the
167 object is. Git will tell you that you have a "blob" object (i.e., just
168 a regular file), and you can see the contents with
169 $ git cat-file blob 557db03
171 which will print out "Hello World". The object 557db03 is nothing more
173 than the contents of your file hello.
174 Note
176 Don’t confuse that object with the file hello itself. The object is
177 literally just those specific contents of the file, and however
178 much you later change the contents in file hello, the object we
179 just looked at will never change. Objects are immutable.
180 Note
182 The second example demonstrates that you can abbreviate the object
183 name to only the first several hexadecimal digits in most places.
184 Anyway, as we mentioned previously, you normally never actually take a
186 look at the objects themselves, and typing long 40-character hex names
187 is not something you’d normally want to do. The above digression was
188 just to show that git update-index did something magical, and actually
189 saved away the contents of your files into the Git object database.
190 Updating the index did something else too: it created a .git/index
192 file. This is the index that describes your current working tree, and
193 something you should be very aware of. Again, you normally never worry
194 about the index file itself, but you should be aware of the fact that
195 you have not actually really "checked in" your files into Git so far,
196 you’ve only told Git about them.
197 However, since Git knows about them, you can now start using some of
199 the most basic Git commands to manipulate the files or look at their
200 status.
201 In particular, let’s not even check in the two files into Git yet,
203 we’ll start off by adding another line to hello first:
204 $ echo "It's a new day for git" >>hello
206 and you can now, since you told Git about the previous state of hello,
208 ask Git what has changed in the tree compared to your old index, using
209 the git diff-files command:
210 $ git diff-files
212 Oops. That wasn’t very readable. It just spit out its own internal
214 version of a diff, but that internal version really just tells you that
215 it has noticed that "hello" has been modified, and that the old object
216 contents it had have been replaced with something else.
217 To make it readable, we can tell git diff-files to output the
219 differences as a patch, using the -p flag:
220 $ git diff-files -p
222 diff --git a/hello b/hello
223 index 557db03..263414f 100644
224 --- a/hello
225 +++ b/hello
226 @@ -1 +1,2 @@
227 Hello World
228 +It's a new day for git
229 i.e. the diff of the change we caused by adding another line to hello.
231 In other words, git diff-files always shows us the difference between
233 what is recorded in the index, and what is currently in the working
234 tree. That’s very useful.
235 A common shorthand for git diff-files -p is to just write git diff,
237 which will do the same thing.
238 $ git diff
240 diff --git a/hello b/hello
241 index 557db03..263414f 100644
242 --- a/hello
243 +++ b/hello
244 @@ -1 +1,2 @@
245 Hello World
246 +It's a new day for git
247
249 Now, we want to go to the next stage in Git, which is to take the files
250 that Git knows about in the index, and commit them as a real tree. We
251 do that in two phases: creating a tree object, and committing that tree
252 object as a commit object together with an explanation of what the tree
253 was all about, along with information of how we came to that state.
254 Creating a tree object is trivial, and is done with git write-tree.
256 There are no options or other input: git write-tree will take the
257 current index state, and write an object that describes that whole
258 index. In other words, we’re now tying together all the different
259 filenames with their contents (and their permissions), and we’re
260 creating the equivalent of a Git "directory" object:
261 $ git write-tree
263 and this will just output the name of the resulting tree, in this case
265 (if you have done exactly as I’ve described) it should be
266 8988da15d077d4829fc51d8544c097def6644dbb
268 which is another incomprehensible object name. Again, if you want to,
270 you can use git cat-file -t 8988d... to see that this time the object
271 is not a "blob" object, but a "tree" object (you can also use git
272 cat-file to actually output the raw object contents, but you’ll see
273 mainly a binary mess, so that’s less interesting).
274 However — normally you’d never use git write-tree on its own, because
276 normally you always commit a tree into a commit object using the git
277 commit-tree command. In fact, it’s easier to not actually use git
278 write-tree on its own at all, but to just pass its result in as an
279 argument to git commit-tree.
280 git commit-tree normally takes several arguments — it wants to know
282 what the parent of a commit was, but since this is the first commit
283 ever in this new repository, and it has no parents, we only need to
284 pass in the object name of the tree. However, git commit-tree also
285 wants to get a commit message on its standard input, and it will write
286 out the resulting object name for the commit to its standard output.
287 And this is where we create the .git/refs/heads/master file which is
289 pointed at by HEAD. This file is supposed to contain the reference to
290 the top-of-tree of the master branch, and since that’s exactly what git
291 commit-tree spits out, we can do this all with a sequence of simple
292 shell commands:
293 $ tree=$(git write-tree)
295 $ commit=$(echo 'Initial commit' | git commit-tree $tree)
296 $ git update-ref HEAD $commit
297 In this case this creates a totally new commit that is not related to
299 anything else. Normally you do this only once for a project ever, and
300 all later commits will be parented on top of an earlier commit.
301 Again, normally you’d never actually do this by hand. There is a
303 helpful script called git commit that will do all of this for you. So
304 you could have just written git commit instead, and it would have done
305 the above magic scripting for you.
306
308 Remember how we did the git update-index on file hello and then we
309 changed hello afterward, and could compare the new state of hello with
310 the state we saved in the index file?
311 Further, remember how I said that git write-tree writes the contents of
313 the index file to the tree, and thus what we just committed was in fact
314 the original contents of the file hello, not the new ones. We did that
315 on purpose, to show the difference between the index state, and the
316 state in the working tree, and how they don’t have to match, even when
317 we commit things.
318 As before, if we do git diff-files -p in our git-tutorial project,
320 we’ll still see the same difference we saw last time: the index file
321 hasn’t changed by the act of committing anything. However, now that we
322 have committed something, we can also learn to use a new command: git
323 diff-index.
324 Unlike git diff-files, which showed the difference between the index
326 file and the working tree, git diff-index shows the differences between
327 a committed tree and either the index file or the working tree. In
328 other words, git diff-index wants a tree to be diffed against, and
329 before we did the commit, we couldn’t do that, because we didn’t have
330 anything to diff against.
331 But now we can do
333 $ git diff-index -p HEAD
335 (where -p has the same meaning as it did in git diff-files), and it
337 will show us the same difference, but for a totally different reason.
338 Now we’re comparing the working tree not against the index file, but
339 against the tree we just wrote. It just so happens that those two are
340 obviously the same, so we get the same result.
341 Again, because this is a common operation, you can also just shorthand
343 it with
344 $ git diff HEAD
346 which ends up doing the above for you.
348 In other words, git diff-index normally compares a tree against the
350 working tree, but when given the --cached flag, it is told to instead
351 compare against just the index cache contents, and ignore the current
352 working tree state entirely. Since we just wrote the index file to
353 HEAD, doing git diff-index --cached -p HEAD should thus return an empty
354 set of differences, and that’s exactly what it does.
355 Note
357 git diff-index really always uses the index for its comparisons,
358 and saying that it compares a tree against the working tree is thus
359 not strictly accurate. In particular, the list of files to compare
360 (the "meta-data") always comes from the index file, regardless of
361 whether the --cached flag is used or not. The --cached flag really
362 only determines whether the file contents to be compared come from
363 the working tree or not.
364 This is not hard to understand, as soon as you realize that Git
366 simply never knows (or cares) about files that it is not told about
367 explicitly. Git will never go looking for files to compare, it
368 expects you to tell it what the files are, and that’s what the
369 index is there for.
370 However, our next step is to commit the change we did, and again, to
372 understand what’s going on, keep in mind the difference between
373 "working tree contents", "index file" and "committed tree". We have
374 changes in the working tree that we want to commit, and we always have
375 to work through the index file, so the first thing we need to do is to
376 update the index cache:
377 $ git update-index hello
379 (note how we didn’t need the --add flag this time, since Git knew about
381 the file already).
382 Note what happens to the different git diff-* versions here. After
384 we’ve updated hello in the index, git diff-files -p now shows no
385 differences, but git diff-index -p HEAD still does show that the
386 current state is different from the state we committed. In fact, now
387 git diff-index shows the same difference whether we use the --cached
388 flag or not, since now the index is coherent with the working tree.
389 Now, since we’ve updated hello in the index, we can commit the new
391 version. We could do it by writing the tree by hand again, and
392 committing the tree (this time we’d have to use the -p HEAD flag to
393 tell commit that the HEAD was the parent of the new commit, and that
394 this wasn’t an initial commit any more), but you’ve done that once
395 already, so let’s just use the helpful script this time:
396 $ git commit
398 which starts an editor for you to write the commit message and tells
400 you a bit about what you have done.
401 Write whatever message you want, and all the lines that start with #
403 will be pruned out, and the rest will be used as the commit message for
404 the change. If you decide you don’t want to commit anything after all
405 at this point (you can continue to edit things and update the index),
406 you can just leave an empty message. Otherwise git commit will commit
407 the change for you.
408 You’ve now made your first real Git commit. And if you’re interested in
410 looking at what git commit really does, feel free to investigate: it’s
411 a few very simple shell scripts to generate the helpful (?) commit
412 message headers, and a few one-liners that actually do the commit
413 itself (git commit).
414
416 While creating changes is useful, it’s even more useful if you can tell
417 later what changed. The most useful command for this is another of the
418 diff family, namely git diff-tree.
419 git diff-tree can be given two arbitrary trees, and it will tell you
421 the differences between them. Perhaps even more commonly, though, you
422 can give it just a single commit object, and it will figure out the
423 parent of that commit itself, and show the difference directly. Thus,
424 to get the same diff that we’ve already seen several times, we can now
425 do
426 $ git diff-tree -p HEAD
428 (again, -p means to show the difference as a human-readable patch), and
430 it will show what the last commit (in HEAD) actually changed.
431 Note
433 Here is an ASCII art by Jon Loeliger that illustrates how various
434 diff-* commands compare things.
435 diff-tree
437 +----+
438 | |
439 | |
440 V V
441 +-----------+
442 | Object DB |
443 | Backing |
444 | Store |
445 +-----------+
446 ^ ^
447 | |
448 | | diff-index --cached
449 | |
450 diff-index | V
451 | +-----------+
452 | | Index |
453 | | "cache" |
454 | +-----------+
455 | ^
456 | |
457 | | diff-files
458 | |
459 V V
460 +-----------+
461 | Working |
462 | Directory |
463 +-----------+
464 More interestingly, you can also give git diff-tree the --pretty flag,
466 which tells it to also show the commit message and author and date of
467 the commit, and you can tell it to show a whole series of diffs.
468 Alternatively, you can tell it to be "silent", and not show the diffs
469 at all, but just show the actual commit message.
470 In fact, together with the git rev-list program (which generates a list
472 of revisions), git diff-tree ends up being a veritable fount of
473 changes. You can emulate git log, git log -p, etc. with a trivial
474 script that pipes the output of git rev-list to git diff-tree --stdin,
475 which was exactly how early versions of git log were implemented.
476
478 In Git, there are two kinds of tags, a "light" one, and an "annotated
479 tag".
480 A "light" tag is technically nothing more than a branch, except we put
482 it in the .git/refs/tags/ subdirectory instead of calling it a head. So
483 the simplest form of tag involves nothing more than
484 $ git tag my-first-tag
486 which just writes the current HEAD into the .git/refs/tags/my-first-tag
488 file, after which point you can then use this symbolic name for that
489 particular state. You can, for example, do
490 $ git diff my-first-tag
492 to diff your current state against that tag which at this point will
494 obviously be an empty diff, but if you continue to develop and commit
495 stuff, you can use your tag as an "anchor-point" to see what has
496 changed since you tagged it.
497 An "annotated tag" is actually a real Git object, and contains not only
499 a pointer to the state you want to tag, but also a small tag name and
500 message, along with optionally a PGP signature that says that yes, you
501 really did that tag. You create these annotated tags with either the -a
502 or -s flag to git tag:
503 $ git tag -s <tagname>
505 which will sign the current HEAD (but you can also give it another
507 argument that specifies the thing to tag, e.g., you could have tagged
508 the current mybranch point by using git tag <tagname> mybranch).
509 You normally only do signed tags for major releases or things like
511 that, while the light-weight tags are useful for any marking you want
512 to do — any time you decide that you want to remember a certain point,
513 just create a private tag for it, and you have a nice symbolic name for
514 the state at that point.
515
517 Git repositories are normally totally self-sufficient and relocatable.
518 Unlike CVS, for example, there is no separate notion of "repository"
519 and "working tree". A Git repository normally is the working tree, with
520 the local Git information hidden in the .git subdirectory. There is
521 nothing else. What you see is what you got.
522 Note
524 You can tell Git to split the Git internal information from the
525 directory that it tracks, but we’ll ignore that for now: it’s not
526 how normal projects work, and it’s really only meant for special
527 uses. So the mental model of "the Git information is always tied
528 directly to the working tree that it describes" may not be
529 technically 100% accurate, but it’s a good model for all normal
530 use.
531 This has two implications:
533 · if you grow bored with the tutorial repository you created (or
535 you’ve made a mistake and want to start all over), you can just do
536 simple
537 $ rm -rf git-tutorial
539 and it will be gone. There’s no external repository, and there’s no
541 history outside the project you created.
542 · if you want to move or duplicate a Git repository, you can do so.
544 There is git clone command, but if all you want to do is just to
545 create a copy of your repository (with all the full history that
546 went along with it), you can do so with a regular cp -a
547 git-tutorial new-git-tutorial.
548 Note that when you’ve moved or copied a Git repository, your Git
550 index file (which caches various information, notably some of the
551 "stat" information for the files involved) will likely need to be
552 refreshed. So after you do a cp -a to create a new copy, you’ll
553 want to do
554 $ git update-index --refresh
556 in the new repository to make sure that the index file is up to
558 date.
559 Note that the second point is true even across machines. You can
561 duplicate a remote Git repository with any regular copy mechanism, be
562 it scp, rsync or wget.
563 When copying a remote repository, you’ll want to at a minimum update
565 the index cache when you do this, and especially with other peoples'
566 repositories you often want to make sure that the index cache is in
567 some known state (you don’t know what they’ve done and not yet checked
568 in), so usually you’ll precede the git update-index with a
569 $ git read-tree --reset HEAD
571 $ git update-index --refresh
572 which will force a total index re-build from the tree pointed to by
574 HEAD. It resets the index contents to HEAD, and then the git
575 update-index makes sure to match up all index entries with the
576 checked-out files. If the original repository had uncommitted changes
577 in its working tree, git update-index --refresh notices them and tells
578 you they need to be updated.
579 The above can also be written as simply
581 $ git reset
583 and in fact a lot of the common Git command combinations can be
585 scripted with the git xyz interfaces. You can learn things by just
586 looking at what the various git scripts do. For example, git reset used
587 to be the above two lines implemented in git reset, but some things
588 like git status and git commit are slightly more complex scripts around
589 the basic Git commands.
590 Many (most?) public remote repositories will not contain any of the
592 checked out files or even an index file, and will only contain the
593 actual core Git files. Such a repository usually doesn’t even have the
594 .git subdirectory, but has all the Git files directly in the
595 repository.
596 To create your own local live copy of such a "raw" Git repository,
598 you’d first create your own subdirectory for the project, and then copy
599 the raw repository contents into the .git directory. For example, to
600 create your own copy of the Git repository, you’d do the following
601 $ mkdir my-git
603 $ cd my-git
604 $ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
605 followed by
607 $ git read-tree HEAD
609 to populate the index. However, now you have populated the index, and
611 you have all the Git internal files, but you will notice that you don’t
612 actually have any of the working tree files to work on. To get those,
613 you’d check them out with
614 $ git checkout-index -u -a
616 where the -u flag means that you want the checkout to keep the index up
618 to date (so that you don’t have to refresh it afterward), and the -a
619 flag means "check out all files" (if you have a stale copy or an older
620 version of a checked out tree you may also need to add the -f flag
621 first, to tell git checkout-index to force overwriting of any old
622 files).
623 Again, this can all be simplified with
625 $ git clone git://git.kernel.org/pub/scm/git/git.git/ my-git
627 $ cd my-git
628 $ git checkout
629 which will end up doing all of the above for you.
631 You have now successfully copied somebody else’s (mine) remote
633 repository, and checked it out.
634
636 Branches in Git are really nothing more than pointers into the Git
637 object database from within the .git/refs/ subdirectory, and as we
638 already discussed, the HEAD branch is nothing but a symlink to one of
639 these object pointers.
640 You can at any time create a new branch by just picking an arbitrary
642 point in the project history, and just writing the SHA-1 name of that
643 object into a file under .git/refs/heads/. You can use any filename you
644 want (and indeed, subdirectories), but the convention is that the
645 "normal" branch is called master. That’s just a convention, though, and
646 nothing enforces it.
647 To show that as an example, let’s go back to the git-tutorial
649 repository we used earlier, and create a branch in it. You do that by
650 simply just saying that you want to check out a new branch:
651 $ git switch -c mybranch
653 will create a new branch based at the current HEAD position, and switch
655 to it.
656 Note
658 If you make the decision to start your new branch at some other
659 point in the history than the current HEAD, you can do so by just
660 telling git switch what the base of the checkout would be. In other
661 words, if you have an earlier tag or branch, you’d just do
662 $ git switch -c mybranch earlier-commit
664 and it would create the new branch mybranch at the earlier commit,
666 and check out the state at that time.
667 You can always just jump back to your original master branch by doing
669 $ git switch master
671 (or any other branch-name, for that matter) and if you forget which
673 branch you happen to be on, a simple
674 $ cat .git/HEAD
676 will tell you where it’s pointing. To get the list of branches you
678 have, you can say
679 $ git branch
681 which used to be nothing more than a simple script around ls
683 .git/refs/heads. There will be an asterisk in front of the branch you
684 are currently on.
685 Sometimes you may wish to create a new branch without actually checking
687 it out and switching to it. If so, just use the command
688 $ git branch <branchname> [startingpoint]
690 which will simply create the branch, but will not do anything further.
692 You can then later — once you decide that you want to actually develop
693 on that branch — switch to that branch with a regular git switch with
694 the branchname as the argument.
695
697 One of the ideas of having a branch is that you do some (possibly
698 experimental) work in it, and eventually merge it back to the main
699 branch. So assuming you created the above mybranch that started out
700 being the same as the original master branch, let’s make sure we’re in
701 that branch, and do some work there.
702 $ git switch mybranch
704 $ echo "Work, work, work" >>hello
705 $ git commit -m "Some work." -i hello
706 Here, we just added another line to hello, and we used a shorthand for
708 doing both git update-index hello and git commit by just giving the
709 filename directly to git commit, with an -i flag (it tells Git to
710 include that file in addition to what you have done to the index file
711 so far when making the commit). The -m flag is to give the commit log
712 message from the command line.
713 Now, to make it a bit more interesting, let’s assume that somebody else
715 does some work in the original branch, and simulate that by going back
716 to the master branch, and editing the same file differently there:
717 $ git switch master
719 Here, take a moment to look at the contents of hello, and notice how
721 they don’t contain the work we just did in mybranch — because that work
722 hasn’t happened in the master branch at all. Then do
723 $ echo "Play, play, play" >>hello
725 $ echo "Lots of fun" >>example
726 $ git commit -m "Some fun." -i hello example
727 since the master branch is obviously in a much better mood.
729 Now, you’ve got two branches, and you decide that you want to merge the
731 work done. Before we do that, let’s introduce a cool graphical tool
732 that helps you view what’s going on:
733 $ gitk --all
735 will show you graphically both of your branches (that’s what the --all
737 means: normally it will just show you your current HEAD) and their
738 histories. You can also see exactly how they came to be from a common
739 source.
740 Anyway, let’s exit gitk (^Q or the File menu), and decide that we want
742 to merge the work we did on the mybranch branch into the master branch
743 (which is currently our HEAD too). To do that, there’s a nice script
744 called git merge, which wants to know which branches you want to
745 resolve and what the merge is all about:
746 $ git merge -m "Merge work in mybranch" mybranch
748 where the first argument is going to be used as the commit message if
750 the merge can be resolved automatically.
751 Now, in this case we’ve intentionally created a situation where the
753 merge will need to be fixed up by hand, though, so Git will do as much
754 of it as it can automatically (which in this case is just merge the
755 example file, which had no differences in the mybranch branch), and
756 say:
757 Auto-merging hello
759 CONFLICT (content): Merge conflict in hello
760 Automatic merge failed; fix conflicts and then commit the result.
761 It tells you that it did an "Automatic merge", which failed due to
763 conflicts in hello.
764 Not to worry. It left the (trivial) conflict in hello in the same form
766 you should already be well used to if you’ve ever used CVS, so let’s
767 just open hello in our editor (whatever that may be), and fix it up
768 somehow. I’d suggest just making it so that hello contains all four
769 lines:
770 Hello World
772 It's a new day for git
773 Play, play, play
774 Work, work, work
775 and once you’re happy with your manual merge, just do a
777 $ git commit -i hello
779 which will very loudly warn you that you’re now committing a merge
781 (which is correct, so never mind), and you can write a small merge
782 message about your adventures in git merge-land.
783 After you’re done, start up gitk --all to see graphically what the
785 history looks like. Notice that mybranch still exists, and you can
786 switch to it, and continue to work with it if you want to. The mybranch
787 branch will not contain the merge, but next time you merge it from the
788 master branch, Git will know how you merged it, so you’ll not have to
789 do that merge again.
790 Another useful tool, especially if you do not always work in X-Window
792 environment, is git show-branch.
793 $ git show-branch --topo-order --more=1 master mybranch
795 * [master] Merge work in mybranch
796 ! [mybranch] Some work.
797 --
798 - [master] Merge work in mybranch
799 *+ [mybranch] Some work.
800 * [master^] Some fun.
801 The first two lines indicate that it is showing the two branches with
803 the titles of their top-of-the-tree commits, you are currently on
804 master branch (notice the asterisk * character), and the first column
805 for the later output lines is used to show commits contained in the
806 master branch, and the second column for the mybranch branch. Three
807 commits are shown along with their titles. All of them have non blank
808 characters in the first column (* shows an ordinary commit on the
809 current branch, - is a merge commit), which means they are now part of
810 the master branch. Only the "Some work" commit has the plus + character
811 in the second column, because mybranch has not been merged to
812 incorporate these commits from the master branch. The string inside
813 brackets before the commit log message is a short name you can use to
814 name the commit. In the above example, master and mybranch are branch
815 heads. master^ is the first parent of master branch head. Please see
816 gitrevisions(7) if you want to see more complex cases.
817 Note
819 Without the --more=1 option, git show-branch would not output the
820 [master^] commit, as [mybranch] commit is a common ancestor of both
821 master and mybranch tips. Please see git-show-branch(1) for
822 details.
823 Note
825 If there were more commits on the master branch after the merge,
826 the merge commit itself would not be shown by git show-branch by
827 default. You would need to provide --sparse option to make the
828 merge commit visible in this case.
829 Now, let’s pretend you are the one who did all the work in mybranch,
831 and the fruit of your hard work has finally been merged to the master
832 branch. Let’s go back to mybranch, and run git merge to get the
833 "upstream changes" back to your branch.
834 $ git switch mybranch
836 $ git merge -m "Merge upstream changes." master
837 This outputs something like this (the actual commit object names would
839 be different)
840 Updating from ae3a2da... to a80b4aa....
842 Fast-forward (no commit created; -m option ignored)
843 example | 1 +
844 hello | 1 +
845 2 files changed, 2 insertions(+)
846 Because your branch did not contain anything more than what had already
848 been merged into the master branch, the merge operation did not
849 actually do a merge. Instead, it just updated the top of the tree of
850 your branch to that of the master branch. This is often called
851 fast-forward merge.
852 You can run gitk --all again to see how the commit ancestry looks like,
854 or run show-branch, which tells you this.
855 $ git show-branch master mybranch
857 ! [master] Merge work in mybranch
858 * [mybranch] Merge work in mybranch
859 --
860 -- [master] Merge work in mybranch
861
863 It’s usually much more common that you merge with somebody else than
864 merging with your own branches, so it’s worth pointing out that Git
865 makes that very easy too, and in fact, it’s not that different from
866 doing a git merge. In fact, a remote merge ends up being nothing more
867 than "fetch the work from a remote repository into a temporary tag"
868 followed by a git merge.
869 Fetching from a remote repository is done by, unsurprisingly, git
871 fetch:
872 $ git fetch <remote-repository>
874 One of the following transports can be used to name the repository to
876 download from:
877 SSH
879 remote.machine:/path/to/repo.git/ or
880 ssh://remote.machine/path/to/repo.git/
882 This transport can be used for both uploading and downloading, and
884 requires you to have a log-in privilege over ssh to the remote
885 machine. It finds out the set of objects the other side lacks by
886 exchanging the head commits both ends have and transfers (close to)
887 minimum set of objects. It is by far the most efficient way to
888 exchange Git objects between repositories.
889 Local directory
891 /path/to/repo.git/
892 This transport is the same as SSH transport but uses sh to run both
894 ends on the local machine instead of running other end on the
895 remote machine via ssh.
896 Git Native
898 git://remote.machine/path/to/repo.git/
899 This transport was designed for anonymous downloading. Like SSH
901 transport, it finds out the set of objects the downstream side
902 lacks and transfers (close to) minimum set of objects.
903 HTTP(S)
905 http://remote.machine/path/to/repo.git/
906 Downloader from http and https URL first obtains the topmost commit
908 object name from the remote site by looking at the specified
909 refname under repo.git/refs/ directory, and then tries to obtain
910 the commit object by downloading from repo.git/objects/xx/xxx...
911 using the object name of that commit object. Then it reads the
912 commit object to find out its parent commits and the associate tree
913 object; it repeats this process until it gets all the necessary
914 objects. Because of this behavior, they are sometimes also called
915 commit walkers.
916 The commit walkers are sometimes also called dumb transports,
918 because they do not require any Git aware smart server like Git
919 Native transport does. Any stock HTTP server that does not even
920 support directory index would suffice. But you must prepare your
921 repository with git update-server-info to help dumb transport
922 downloaders.
923 Once you fetch from the remote repository, you merge that with your
925 current branch.
926 However — it’s such a common thing to fetch and then immediately merge,
928 that it’s called git pull, and you can simply do
929 $ git pull <remote-repository>
931 and optionally give a branch-name for the remote end as a second
933 argument.
934 Note
936 You could do without using any branches at all, by keeping as many
937 local repositories as you would like to have branches, and merging
938 between them with git pull, just like you merge between branches.
939 The advantage of this approach is that it lets you keep a set of
940 files for each branch checked out and you may find it easier to
941 switch back and forth if you juggle multiple lines of development
942 simultaneously. Of course, you will pay the price of more disk
943 usage to hold multiple working trees, but disk space is cheap these
944 days.
945 It is likely that you will be pulling from the same remote repository
947 from time to time. As a short hand, you can store the remote repository
948 URL in the local repository’s config file like this:
949 $ git config remote.linus.url http://www.kernel.org/pub/scm/git/git.git/
951 and use the "linus" keyword with git pull instead of the full URL.
953 Examples.
955 1. git pull linus
957 2. git pull linus tag v0.99.1
959 the above are equivalent to:
961 1. git pull http://www.kernel.org/pub/scm/git/git.git/ HEAD
963 2. git pull http://www.kernel.org/pub/scm/git/git.git/ tag v0.99.1
965
967 We said this tutorial shows what plumbing does to help you cope with
968 the porcelain that isn’t flushing, but we so far did not talk about how
969 the merge really works. If you are following this tutorial the first
970 time, I’d suggest to skip to "Publishing your work" section and come
971 back here later.
972 OK, still with me? To give us an example to look at, let’s go back to
974 the earlier repository with "hello" and "example" file, and bring
975 ourselves back to the pre-merge state:
976 $ git show-branch --more=2 master mybranch
978 ! [master] Merge work in mybranch
979 * [mybranch] Merge work in mybranch
980 --
981 -- [master] Merge work in mybranch
982 +* [master^2] Some work.
983 +* [master^] Some fun.
984 Remember, before running git merge, our master head was at "Some fun."
986 commit, while our mybranch head was at "Some work." commit.
987 $ git switch -C mybranch master^2
989 $ git switch master
990 $ git reset --hard master^
991 After rewinding, the commit structure should look like this:
993 $ git show-branch
995 * [master] Some fun.
996 ! [mybranch] Some work.
997 --
998 * [master] Some fun.
999 + [mybranch] Some work.
1000 *+ [master^] Initial commit
1001 Now we are ready to experiment with the merge by hand.
1003 git merge command, when merging two branches, uses 3-way merge
1005 algorithm. First, it finds the common ancestor between them. The
1006 command it uses is git merge-base:
1007 $ mb=$(git merge-base HEAD mybranch)
1009 The command writes the commit object name of the common ancestor to the
1011 standard output, so we captured its output to a variable, because we
1012 will be using it in the next step. By the way, the common ancestor
1013 commit is the "Initial commit" commit in this case. You can tell it by:
1014 $ git name-rev --name-only --tags $mb
1016 my-first-tag
1017 After finding out a common ancestor commit, the second step is this:
1019 $ git read-tree -m -u $mb HEAD mybranch
1021 This is the same git read-tree command we have already seen, but it
1023 takes three trees, unlike previous examples. This reads the contents of
1024 each tree into different stage in the index file (the first tree goes
1025 to stage 1, the second to stage 2, etc.). After reading three trees
1026 into three stages, the paths that are the same in all three stages are
1027 collapsed into stage 0. Also paths that are the same in two of three
1028 stages are collapsed into stage 0, taking the SHA-1 from either stage 2
1029 or stage 3, whichever is different from stage 1 (i.e. only one side
1030 changed from the common ancestor).
1031 After collapsing operation, paths that are different in three trees are
1033 left in non-zero stages. At this point, you can inspect the index file
1034 with this command:
1035 $ git ls-files --stage
1037 100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
1038 100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1 hello
1039 100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2 hello
1040 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1041 In our example of only two files, we did not have unchanged files so
1043 only example resulted in collapsing. But in real-life large projects,
1044 when only a small number of files change in one commit, this collapsing
1045 tends to trivially merge most of the paths fairly quickly, leaving only
1046 a handful of real changes in non-zero stages.
1047 To look at only non-zero stages, use --unmerged flag:
1049 $ git ls-files --unmerged
1051 100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1 hello
1052 100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2 hello
1053 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1054 The next step of merging is to merge these three versions of the file,
1056 using 3-way merge. This is done by giving git merge-one-file command as
1057 one of the arguments to git merge-index command:
1058 $ git merge-index git-merge-one-file hello
1060 Auto-merging hello
1061 ERROR: Merge conflict in hello
1062 fatal: merge program failed
1063 git merge-one-file script is called with parameters to describe those
1065 three versions, and is responsible to leave the merge results in the
1066 working tree. It is a fairly straightforward shell script, and
1067 eventually calls merge program from RCS suite to perform a file-level
1068 3-way merge. In this case, merge detects conflicts, and the merge
1069 result with conflict marks is left in the working tree.. This can be
1070 seen if you run ls-files --stage again at this point:
1071 $ git ls-files --stage
1073 100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
1074 100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1 hello
1075 100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2 hello
1076 100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1077 This is the state of the index file and the working file after git
1079 merge returns control back to you, leaving the conflicting merge for
1080 you to resolve. Notice that the path hello is still unmerged, and what
1081 you see with git diff at this point is differences since stage 2 (i.e.
1082 your version).
1083
1085 So, we can use somebody else’s work from a remote repository, but how
1086 can you prepare a repository to let other people pull from it?
1087 You do your real work in your working tree that has your primary
1089 repository hanging under it as its .git subdirectory. You could make
1090 that repository accessible remotely and ask people to pull from it, but
1091 in practice that is not the way things are usually done. A recommended
1092 way is to have a public repository, make it reachable by other people,
1093 and when the changes you made in your primary working tree are in good
1094 shape, update the public repository from it. This is often called
1095 pushing.
1096 Note
1098 This public repository could further be mirrored, and that is how
1099 Git repositories at kernel.org are managed.
1100 Publishing the changes from your local (private) repository to your
1102 remote (public) repository requires a write privilege on the remote
1103 machine. You need to have an SSH account there to run a single command,
1104 git-receive-pack.
1105 First, you need to create an empty repository on the remote machine
1107 that will house your public repository. This empty repository will be
1108 populated and be kept up to date by pushing into it later. Obviously,
1109 this repository creation needs to be done only once.
1110 Note
1112 git push uses a pair of commands, git send-pack on your local
1113 machine, and git-receive-pack on the remote machine. The
1114 communication between the two over the network internally uses an
1115 SSH connection.
1116 Your private repository’s Git directory is usually .git, but your
1118 public repository is often named after the project name, i.e.
1119 <project>.git. Let’s create such a public repository for project
1120 my-git. After logging into the remote machine, create an empty
1121 directory:
1122 $ mkdir my-git.git
1124 Then, make that directory into a Git repository by running git init,
1126 but this time, since its name is not the usual .git, we do things
1127 slightly differently:
1128 $ GIT_DIR=my-git.git git init
1130 Make sure this directory is available for others you want your changes
1132 to be pulled via the transport of your choice. Also you need to make
1133 sure that you have the git-receive-pack program on the $PATH.
1134 Note
1136 Many installations of sshd do not invoke your shell as the login
1137 shell when you directly run programs; what this means is that if
1138 your login shell is bash, only .bashrc is read and not
1139 .bash_profile. As a workaround, make sure .bashrc sets up $PATH so
1140 that you can run git-receive-pack program.
1141 Note
1143 If you plan to publish this repository to be accessed over http,
1144 you should do mv my-git.git/hooks/post-update.sample
1145 my-git.git/hooks/post-update at this point. This makes sure that
1146 every time you push into this repository, git update-server-info is
1147 run.
1148 Your "public repository" is now ready to accept your changes. Come back
1150 to the machine you have your private repository. From there, run this
1151 command:
1152 $ git push <public-host>:/path/to/my-git.git master
1154 This synchronizes your public repository to match the named branch head
1156 (i.e. master in this case) and objects reachable from them in your
1157 current repository.
1158 As a real example, this is how I update my public Git repository.
1160 Kernel.org mirror network takes care of the propagation to other
1161 publicly visible machines:
1162 $ git push master.kernel.org:/pub/scm/git/git.git/
1164
1166 Earlier, we saw that one file under .git/objects/??/ directory is
1167 stored for each Git object you create. This representation is efficient
1168 to create atomically and safely, but not so convenient to transport
1169 over the network. Since Git objects are immutable once they are
1170 created, there is a way to optimize the storage by "packing them
1171 together". The command
1172 $ git repack
1174 will do it for you. If you followed the tutorial examples, you would
1176 have accumulated about 17 objects in .git/objects/??/ directories by
1177 now. git repack tells you how many objects it packed, and stores the
1178 packed file in the .git/objects/pack directory.
1179 Note
1181 You will see two files, pack-*.pack and pack-*.idx, in
1182 .git/objects/pack directory. They are closely related to each
1183 other, and if you ever copy them by hand to a different repository
1184 for whatever reason, you should make sure you copy them together.
1185 The former holds all the data from the objects in the pack, and the
1186 latter holds the index for random access.
1187 If you are paranoid, running git verify-pack command would detect if
1189 you have a corrupt pack, but do not worry too much. Our programs are
1190 always perfect ;-).
1191 Once you have packed objects, you do not need to leave the unpacked
1193 objects that are contained in the pack file anymore.
1194 $ git prune-packed
1196 would remove them for you.
1198 You can try running find .git/objects -type f before and after you run
1200 git prune-packed if you are curious. Also git count-objects would tell
1201 you how many unpacked objects are in your repository and how much space
1202 they are consuming.
1203 Note
1205 git pull is slightly cumbersome for HTTP transport, as a packed
1206 repository may contain relatively few objects in a relatively large
1207 pack. If you expect many HTTP pulls from your public repository you
1208 might want to repack & prune often, or never.
1209 If you run git repack again at this point, it will say "Nothing new to
1211 pack.". Once you continue your development and accumulate the changes,
1212 running git repack again will create a new pack, that contains objects
1213 created since you packed your repository the last time. We recommend
1214 that you pack your project soon after the initial import (unless you
1215 are starting your project from scratch), and then run git repack every
1216 once in a while, depending on how active your project is.
1217 When a repository is synchronized via git push and git pull objects
1219 packed in the source repository are usually stored unpacked in the
1220 destination. While this allows you to use different packing strategies
1221 on both ends, it also means you may need to repack both repositories
1222 every once in a while.
1223
1225 Although Git is a truly distributed system, it is often convenient to
1226 organize your project with an informal hierarchy of developers. Linux
1227 kernel development is run this way. There is a nice illustration (page
1228 17, "Merges to Mainline") in Randy Dunlap’s presentation[2].
1229 It should be stressed that this hierarchy is purely informal. There is
1231 nothing fundamental in Git that enforces the "chain of patch flow" this
1232 hierarchy implies. You do not have to pull from only one remote
1233 repository.
1234 A recommended workflow for a "project lead" goes like this:
1236 1. Prepare your primary repository on your local machine. Your work is
1238 done there.
1239 2. Prepare a public repository accessible to others.
1241 If other people are pulling from your repository over dumb
1243 transport protocols (HTTP), you need to keep this repository dumb
1244 transport friendly. After git init,
1245 $GIT_DIR/hooks/post-update.sample copied from the standard
1246 templates would contain a call to git update-server-info but you
1247 need to manually enable the hook with mv post-update.sample
1248 post-update. This makes sure git update-server-info keeps the
1249 necessary files up to date.
1250 3. Push into the public repository from your primary repository.
1252 4. git repack the public repository. This establishes a big pack that
1254 contains the initial set of objects as the baseline, and possibly
1255 git prune if the transport used for pulling from your repository
1256 supports packed repositories.
1257 5. Keep working in your primary repository. Your changes include
1259 modifications of your own, patches you receive via e-mails, and
1260 merges resulting from pulling the "public" repositories of your
1261 "subsystem maintainers".
1262 You can repack this private repository whenever you feel like.
1264 6. Push your changes to the public repository, and announce it to the
1266 public.
1267 7. Every once in a while, git repack the public repository. Go back to
1269 step 5. and continue working.
1270 A recommended work cycle for a "subsystem maintainer" who works on that
1272 project and has an own "public repository" goes like this:
1273 1. Prepare your work repository, by running git clone on the public
1275 repository of the "project lead". The URL used for the initial
1276 cloning is stored in the remote.origin.url configuration variable.
1277 2. Prepare a public repository accessible to others, just like the
1279 "project lead" person does.
1280 3. Copy over the packed files from "project lead" public repository to
1282 your public repository, unless the "project lead" repository lives
1283 on the same machine as yours. In the latter case, you can use
1284 objects/info/alternates file to point at the repository you are
1285 borrowing from.
1286 4. Push into the public repository from your primary repository. Run
1288 git repack, and possibly git prune if the transport used for
1289 pulling from your repository supports packed repositories.
1290 5. Keep working in your primary repository. Your changes include
1292 modifications of your own, patches you receive via e-mails, and
1293 merges resulting from pulling the "public" repositories of your
1294 "project lead" and possibly your "sub-subsystem maintainers".
1295 You can repack this private repository whenever you feel like.
1297 6. Push your changes to your public repository, and ask your "project
1299 lead" and possibly your "sub-subsystem maintainers" to pull from
1300 it.
1301 7. Every once in a while, git repack the public repository. Go back to
1303 step 5. and continue working.
1304 A recommended work cycle for an "individual developer" who does not
1306 have a "public" repository is somewhat different. It goes like this:
1307 1. Prepare your work repository, by git clone the public repository of
1309 the "project lead" (or a "subsystem maintainer", if you work on a
1310 subsystem). The URL used for the initial cloning is stored in the
1311 remote.origin.url configuration variable.
1312 2. Do your work in your repository on master branch.
1314 3. Run git fetch origin from the public repository of your upstream
1316 every once in a while. This does only the first half of git pull
1317 but does not merge. The head of the public repository is stored in
1318 .git/refs/remotes/origin/master.
1319 4. Use git cherry origin to see which ones of your patches were
1321 accepted, and/or use git rebase origin to port your unmerged
1322 changes forward to the updated upstream.
1323 5. Use git format-patch origin to prepare patches for e-mail
1325 submission to your upstream and send it out. Go back to step 2. and
1326 continue.
1327
1329 If you are coming from a CVS background, the style of cooperation
1330 suggested in the previous section may be new to you. You do not have to
1331 worry. Git supports the "shared public repository" style of cooperation
1332 you are probably more familiar with as well.
1333 See gitcvs-migration(7) for the details.
1335
1337 It is likely that you will be working on more than one thing at a time.
1338 It is easy to manage those more-or-less independent tasks using
1339 branches with Git.
1340 We have already seen how branches work previously, with "fun and work"
1342 example using two branches. The idea is the same if there are more than
1343 two branches. Let’s say you started out from "master" head, and have
1344 some new code in the "master" branch, and two independent fixes in the
1345 "commit-fix" and "diff-fix" branches:
1346 $ git show-branch
1348 ! [commit-fix] Fix commit message normalization.
1349 ! [diff-fix] Fix rename detection.
1350 * [master] Release candidate #1
1351 ---
1352 + [diff-fix] Fix rename detection.
1353 + [diff-fix~1] Better common substring algorithm.
1354 + [commit-fix] Fix commit message normalization.
1355 * [master] Release candidate #1
1356 ++* [diff-fix~2] Pretty-print messages.
1357 Both fixes are tested well, and at this point, you want to merge in
1359 both of them. You could merge in diff-fix first and then commit-fix
1360 next, like this:
1361 $ git merge -m "Merge fix in diff-fix" diff-fix
1363 $ git merge -m "Merge fix in commit-fix" commit-fix
1364 Which would result in:
1366 $ git show-branch
1368 ! [commit-fix] Fix commit message normalization.
1369 ! [diff-fix] Fix rename detection.
1370 * [master] Merge fix in commit-fix
1371 ---
1372 - [master] Merge fix in commit-fix
1373 + * [commit-fix] Fix commit message normalization.
1374 - [master~1] Merge fix in diff-fix
1375 +* [diff-fix] Fix rename detection.
1376 +* [diff-fix~1] Better common substring algorithm.
1377 * [master~2] Release candidate #1
1378 ++* [master~3] Pretty-print messages.
1379 However, there is no particular reason to merge in one branch first and
1381 the other next, when what you have are a set of truly independent
1382 changes (if the order mattered, then they are not independent by
1383 definition). You could instead merge those two branches into the
1384 current branch at once. First let’s undo what we just did and start
1385 over. We would want to get the master branch before these two merges by
1386 resetting it to master~2:
1387 $ git reset --hard master~2
1389 You can make sure git show-branch matches the state before those two
1391 git merge you just did. Then, instead of running two git merge commands
1392 in a row, you would merge these two branch heads (this is known as
1393 making an Octopus):
1394 $ git merge commit-fix diff-fix
1396 $ git show-branch
1397 ! [commit-fix] Fix commit message normalization.
1398 ! [diff-fix] Fix rename detection.
1399 * [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1400 ---
1401 - [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1402 + * [commit-fix] Fix commit message normalization.
1403 +* [diff-fix] Fix rename detection.
1404 +* [diff-fix~1] Better common substring algorithm.
1405 * [master~1] Release candidate #1
1406 ++* [master~2] Pretty-print messages.
1407 Note that you should not do Octopus just because you can. An octopus is
1409 a valid thing to do and often makes it easier to view the commit
1410 history if you are merging more than two independent changes at the
1411 same time. However, if you have merge conflicts with any of the
1412 branches you are merging in and need to hand resolve, that is an
1413 indication that the development happened in those branches were not
1414 independent after all, and you should merge two at a time, documenting
1415 how you resolved the conflicts, and the reason why you preferred
1416 changes made in one side over the other. Otherwise it would make the
1417 project history harder to follow, not easier.
1418
1420 gittutorial(7), gittutorial-2(7), gitcvs-migration(7), git-help(1),
1421 giteveryday(7), The Git User’s Manual[1]
1422
1424 Part of the git(1) suite
1425
1427 1. the Git User Manual
1428 file:///usr/share/doc/git/user-manual.html
1429 2. Randy Dunlap’s presentation
1431 https://web.archive.org/web/20120915203609/http://www.xenotime.net/linux/mentor/linux-mentoring-2006.pdf
1432Git 2.26.2 2020-04-20 GITCORE-TUTORIAL(7)