1GITCORE-TUTORIAL(7)               Git Manual               GITCORE-TUTORIAL(7)


6       gitcore-tutorial - A Git core tutorial for developers


9       git *


12       This tutorial explains how to use the "core" Git commands to set up and
13       work with a Git repository.
15       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].
19       However, an understanding of these low-level tools can be helpful if
20       you want to understand Git’s internals.
22       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.
27       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.
34           Note
35           Deeper technical details are often marked as Notes, which you can
36           skip on your first reading.


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.
45       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:
50           $ mkdir git-tutorial
51           $ cd git-tutorial
52           $ git init
55       to which Git will reply
57           Initialized empty Git repository in .git/
60       which is just Git’s way of saying that you haven’t been doing anything
61       strange, and that it will have created a local .git directory setup for
62       your new project. You will now have a .git directory, and you can
63       inspect that with ls. For your new empty project, it should show you
64       three entries, among other things:
66       ·   a file called HEAD, that has ref: refs/heads/master in it. This is
67           similar to a symbolic link and points at refs/heads/master relative
68           to the HEAD file.
70           Don’t worry about the fact that the file that the HEAD link points
71           to doesn’t even exist yet — you haven’t created the commit that
72           will start your HEAD development branch yet.
74       ·   a subdirectory called objects, which will contain all the objects
75           of your project. You should never have any real reason to look at
76           the objects directly, but you might want to know that these objects
77           are what contains all the real data in your repository.
79       ·   a subdirectory called refs, which contains references to objects.
81       In particular, the refs subdirectory will contain two other
82       subdirectories, named heads and tags respectively. They do exactly what
83       their names imply: they contain references to any number of different
84       heads of development (aka branches), and to any tags that you have
85       created to name specific versions in your repository.
87       One note: the special master head is the default branch, which is why
88       the .git/HEAD file was created points to it even if it doesn’t yet
89       exist. Basically, the HEAD link is supposed to always point to the
90       branch you are working on right now, and you always start out expecting
91       to work on the master branch.
93       However, this is only a convention, and you can name your branches
94       anything you want, and don’t have to ever even have a master branch. A
95       number of the Git tools will assume that .git/HEAD is valid, though.
97           Note
98           An object is identified by its 160-bit SHA-1 hash, aka object name,
99           and a reference to an object is always the 40-byte hex
100           representation of that SHA-1 name. The files in the refs
101           subdirectory are expected to contain these hex references (usually
102           with a final \n at the end), and you should thus expect to see a
103           number of 41-byte files containing these references in these refs
104           subdirectories when you actually start populating your tree.
106           Note
107           An advanced user may want to take a look at gitrepository-layout(5)
108           after finishing this tutorial.
110       You have now created your first Git repository. Of course, since it’s
111       empty, that’s not very useful, so let’s start populating it with data.


114       We’ll keep this simple and stupid, so we’ll start off with populating a
115       few trivial files just to get a feel for it.
117       Start off with just creating any random files that you want to maintain
118       in your Git repository. We’ll start off with a few bad examples, just
119       to get a feel for how this works:
121           $ echo "Hello World" >hello
122           $ echo "Silly example" >example
125       you have now created two files in your working tree (aka working
126       directory), but to actually check in your hard work, you will have to
127       go through two steps:
129       ·   fill in the index file (aka cache) with the information about your
130           working tree state.
132       ·   commit that index file as an object.
134       The first step is trivial: when you want to tell Git about any changes
135       to your working tree, you use the git update-index program. That
136       program normally just takes a list of filenames you want to update, but
137       to avoid trivial mistakes, it refuses to add new entries to the index
138       (or remove existing ones) unless you explicitly tell it that you’re
139       adding a new entry with the --add flag (or removing an entry with the
140       --remove) flag.
142       So to populate the index with the two files you just created, you can
143       do
145           $ git update-index --add hello example
148       and you have now told Git to track those two files.
150       In fact, as you did that, if you now look into your object directory,
151       you’ll notice that Git will have added two new objects to the object
152       database. If you did exactly the steps above, you should now be able to
153       do
155           $ ls .git/objects/??/*
158       and see two files:
160           .git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
161           .git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
164       which correspond with the objects with names of 557db... and f24c7...
165       respectively.
167       If you want to, you can use git cat-file to look at those objects, but
168       you’ll have to use the object name, not the filename of the object:
170           $ git cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
173       where the -t tells git cat-file to tell you what the "type" of the
174       object is. Git will tell you that you have a "blob" object (i.e., just
175       a regular file), and you can see the contents with
177           $ git cat-file blob 557db03
180       which will print out "Hello World". The object 557db03 is nothing more
181       than the contents of your file hello.
183           Note
184           Don’t confuse that object with the file hello itself. The object is
185           literally just those specific contents of the file, and however
186           much you later change the contents in file hello, the object we
187           just looked at will never change. Objects are immutable.
189           Note
190           The second example demonstrates that you can abbreviate the object
191           name to only the first several hexadecimal digits in most places.
193       Anyway, as we mentioned previously, you normally never actually take a
194       look at the objects themselves, and typing long 40-character hex names
195       is not something you’d normally want to do. The above digression was
196       just to show that git update-index did something magical, and actually
197       saved away the contents of your files into the Git object database.
199       Updating the index did something else too: it created a .git/index
200       file. This is the index that describes your current working tree, and
201       something you should be very aware of. Again, you normally never worry
202       about the index file itself, but you should be aware of the fact that
203       you have not actually really "checked in" your files into Git so far,
204       you’ve only told Git about them.
206       However, since Git knows about them, you can now start using some of
207       the most basic Git commands to manipulate the files or look at their
208       status.
210       In particular, let’s not even check in the two files into Git yet,
211       we’ll start off by adding another line to hello first:
213           $ echo "It's a new day for git" >>hello
216       and you can now, since you told Git about the previous state of hello,
217       ask Git what has changed in the tree compared to your old index, using
218       the git diff-files command:
220           $ git diff-files
223       Oops. That wasn’t very readable. It just spit out its own internal
224       version of a diff, but that internal version really just tells you that
225       it has noticed that "hello" has been modified, and that the old object
226       contents it had have been replaced with something else.
228       To make it readable, we can tell git diff-files to output the
229       differences as a patch, using the -p flag:
231           $ git diff-files -p
232           diff --git a/hello b/hello
233           index 557db03..263414f 100644
234           --- a/hello
235           +++ b/hello
236           @@ -1 +1,2 @@
237            Hello World
238           +It's a new day for git
241       i.e. the diff of the change we caused by adding another line to hello.
243       In other words, git diff-files always shows us the difference between
244       what is recorded in the index, and what is currently in the working
245       tree. That’s very useful.
247       A common shorthand for git diff-files -p is to just write git diff,
248       which will do the same thing.
250           $ git diff
251           diff --git a/hello b/hello
252           index 557db03..263414f 100644
253           --- a/hello
254           +++ b/hello
255           @@ -1 +1,2 @@
256            Hello World
257           +It's a new day for git


261       Now, we want to go to the next stage in Git, which is to take the files
262       that Git knows about in the index, and commit them as a real tree. We
263       do that in two phases: creating a tree object, and committing that tree
264       object as a commit object together with an explanation of what the tree
265       was all about, along with information of how we came to that state.
267       Creating a tree object is trivial, and is done with git write-tree.
268       There are no options or other input: git write-tree will take the
269       current index state, and write an object that describes that whole
270       index. In other words, we’re now tying together all the different
271       filenames with their contents (and their permissions), and we’re
272       creating the equivalent of a Git "directory" object:
274           $ git write-tree
277       and this will just output the name of the resulting tree, in this case
278       (if you have done exactly as I’ve described) it should be
280           8988da15d077d4829fc51d8544c097def6644dbb
283       which is another incomprehensible object name. Again, if you want to,
284       you can use git cat-file -t 8988d... to see that this time the object
285       is not a "blob" object, but a "tree" object (you can also use git
286       cat-file to actually output the raw object contents, but you’ll see
287       mainly a binary mess, so that’s less interesting).
289       However — normally you’d never use git write-tree on its own, because
290       normally you always commit a tree into a commit object using the git
291       commit-tree command. In fact, it’s easier to not actually use git
292       write-tree on its own at all, but to just pass its result in as an
293       argument to git commit-tree.
295       git commit-tree normally takes several arguments — it wants to know
296       what the parent of a commit was, but since this is the first commit
297       ever in this new repository, and it has no parents, we only need to
298       pass in the object name of the tree. However, git commit-tree also
299       wants to get a commit message on its standard input, and it will write
300       out the resulting object name for the commit to its standard output.
302       And this is where we create the .git/refs/heads/master file which is
303       pointed at by HEAD. This file is supposed to contain the reference to
304       the top-of-tree of the master branch, and since that’s exactly what git
305       commit-tree spits out, we can do this all with a sequence of simple
306       shell commands:
308           $ tree=$(git write-tree)
309           $ commit=$(echo 'Initial commit' | git commit-tree $tree)
310           $ git update-ref HEAD $commit
313       In this case this creates a totally new commit that is not related to
314       anything else. Normally you do this only once for a project ever, and
315       all later commits will be parented on top of an earlier commit.
317       Again, normally you’d never actually do this by hand. There is a
318       helpful script called git commit that will do all of this for you. So
319       you could have just written git commit instead, and it would have done
320       the above magic scripting for you.


323       Remember how we did the git update-index on file hello and then we
324       changed hello afterward, and could compare the new state of hello with
325       the state we saved in the index file?
327       Further, remember how I said that git write-tree writes the contents of
328       the index file to the tree, and thus what we just committed was in fact
329       the original contents of the file hello, not the new ones. We did that
330       on purpose, to show the difference between the index state, and the
331       state in the working tree, and how they don’t have to match, even when
332       we commit things.
334       As before, if we do git diff-files -p in our git-tutorial project,
335       we’ll still see the same difference we saw last time: the index file
336       hasn’t changed by the act of committing anything. However, now that we
337       have committed something, we can also learn to use a new command: git
338       diff-index.
340       Unlike git diff-files, which showed the difference between the index
341       file and the working tree, git diff-index shows the differences between
342       a committed tree and either the index file or the working tree. In
343       other words, git diff-index wants a tree to be diffed against, and
344       before we did the commit, we couldn’t do that, because we didn’t have
345       anything to diff against.
347       But now we can do
349           $ git diff-index -p HEAD
352       (where -p has the same meaning as it did in git diff-files), and it
353       will show us the same difference, but for a totally different reason.
354       Now we’re comparing the working tree not against the index file, but
355       against the tree we just wrote. It just so happens that those two are
356       obviously the same, so we get the same result.
358       Again, because this is a common operation, you can also just shorthand
359       it with
361           $ git diff HEAD
364       which ends up doing the above for you.
366       In other words, git diff-index normally compares a tree against the
367       working tree, but when given the --cached flag, it is told to instead
368       compare against just the index cache contents, and ignore the current
369       working tree state entirely. Since we just wrote the index file to
370       HEAD, doing git diff-index --cached -p HEAD should thus return an empty
371       set of differences, and that’s exactly what it does.
373           Note
374           git diff-index really always uses the index for its comparisons,
375           and saying that it compares a tree against the working tree is thus
376           not strictly accurate. In particular, the list of files to compare
377           (the "meta-data") always comes from the index file, regardless of
378           whether the --cached flag is used or not. The --cached flag really
379           only determines whether the file contents to be compared come from
380           the working tree or not.
382           This is not hard to understand, as soon as you realize that Git
383           simply never knows (or cares) about files that it is not told about
384           explicitly. Git will never go looking for files to compare, it
385           expects you to tell it what the files are, and that’s what the
386           index is there for.
388       However, our next step is to commit the change we did, and again, to
389       understand what’s going on, keep in mind the difference between
390       "working tree contents", "index file" and "committed tree". We have
391       changes in the working tree that we want to commit, and we always have
392       to work through the index file, so the first thing we need to do is to
393       update the index cache:
395           $ git update-index hello
398       (note how we didn’t need the --add flag this time, since Git knew about
399       the file already).
401       Note what happens to the different git diff-* versions here. After
402       we’ve updated hello in the index, git diff-files -p now shows no
403       differences, but git diff-index -p HEAD still does show that the
404       current state is different from the state we committed. In fact, now
405       git diff-index shows the same difference whether we use the --cached
406       flag or not, since now the index is coherent with the working tree.
408       Now, since we’ve updated hello in the index, we can commit the new
409       version. We could do it by writing the tree by hand again, and
410       committing the tree (this time we’d have to use the -p HEAD flag to
411       tell commit that the HEAD was the parent of the new commit, and that
412       this wasn’t an initial commit any more), but you’ve done that once
413       already, so let’s just use the helpful script this time:
415           $ git commit
418       which starts an editor for you to write the commit message and tells
419       you a bit about what you have done.
421       Write whatever message you want, and all the lines that start with #
422       will be pruned out, and the rest will be used as the commit message for
423       the change. If you decide you don’t want to commit anything after all
424       at this point (you can continue to edit things and update the index),
425       you can just leave an empty message. Otherwise git commit will commit
426       the change for you.
428       You’ve now made your first real Git commit. And if you’re interested in
429       looking at what git commit really does, feel free to investigate: it’s
430       a few very simple shell scripts to generate the helpful (?) commit
431       message headers, and a few one-liners that actually do the commit
432       itself (git commit).


435       While creating changes is useful, it’s even more useful if you can tell
436       later what changed. The most useful command for this is another of the
437       diff family, namely git diff-tree.
439       git diff-tree can be given two arbitrary trees, and it will tell you
440       the differences between them. Perhaps even more commonly, though, you
441       can give it just a single commit object, and it will figure out the
442       parent of that commit itself, and show the difference directly. Thus,
443       to get the same diff that we’ve already seen several times, we can now
444       do
446           $ git diff-tree -p HEAD
449       (again, -p means to show the difference as a human-readable patch), and
450       it will show what the last commit (in HEAD) actually changed.
452           Note
453           Here is an ASCII art by Jon Loeliger that illustrates how various
454           diff-* commands compare things.
456                           diff-tree
457                            +----+
458                            |    |
459                            |    |
460                            V    V
461                         +-----------+
462                         | Object DB |
463                         |  Backing  |
464                         |   Store   |
465                         +-----------+
466                           ^    ^
467                           |    |
468                           |    |  diff-index --cached
469                           |    |
470               diff-index  |    V
471                           |  +-----------+
472                           |  |   Index   |
473                           |  |  "cache"  |
474                           |  +-----------+
475                           |    ^
476                           |    |
477                           |    |  diff-files
478                           |    |
479                           V    V
480                         +-----------+
481                         |  Working  |
482                         | Directory |
483                         +-----------+
485       More interestingly, you can also give git diff-tree the --pretty flag,
486       which tells it to also show the commit message and author and date of
487       the commit, and you can tell it to show a whole series of diffs.
488       Alternatively, you can tell it to be "silent", and not show the diffs
489       at all, but just show the actual commit message.
491       In fact, together with the git rev-list program (which generates a list
492       of revisions), git diff-tree ends up being a veritable fount of
493       changes. You can emulate git log, git log -p, etc. with a trivial
494       script that pipes the output of git rev-list to git diff-tree --stdin,
495       which was exactly how early versions of git log were implemented.


498       In Git, there are two kinds of tags, a "light" one, and an "annotated
499       tag".
501       A "light" tag is technically nothing more than a branch, except we put
502       it in the .git/refs/tags/ subdirectory instead of calling it a head. So
503       the simplest form of tag involves nothing more than
505           $ git tag my-first-tag
508       which just writes the current HEAD into the .git/refs/tags/my-first-tag
509       file, after which point you can then use this symbolic name for that
510       particular state. You can, for example, do
512           $ git diff my-first-tag
515       to diff your current state against that tag which at this point will
516       obviously be an empty diff, but if you continue to develop and commit
517       stuff, you can use your tag as an "anchor-point" to see what has
518       changed since you tagged it.
520       An "annotated tag" is actually a real Git object, and contains not only
521       a pointer to the state you want to tag, but also a small tag name and
522       message, along with optionally a PGP signature that says that yes, you
523       really did that tag. You create these annotated tags with either the -a
524       or -s flag to git tag:
526           $ git tag -s <tagname>
529       which will sign the current HEAD (but you can also give it another
530       argument that specifies the thing to tag, e.g., you could have tagged
531       the current mybranch point by using git tag <tagname> mybranch).
533       You normally only do signed tags for major releases or things like
534       that, while the light-weight tags are useful for any marking you want
535       to do — any time you decide that you want to remember a certain point,
536       just create a private tag for it, and you have a nice symbolic name for
537       the state at that point.


540       Git repositories are normally totally self-sufficient and relocatable.
541       Unlike CVS, for example, there is no separate notion of "repository"
542       and "working tree". A Git repository normally is the working tree, with
543       the local Git information hidden in the .git subdirectory. There is
544       nothing else. What you see is what you got.
546           Note
547           You can tell Git to split the Git internal information from the
548           directory that it tracks, but we’ll ignore that for now: it’s not
549           how normal projects work, and it’s really only meant for special
550           uses. So the mental model of "the Git information is always tied
551           directly to the working tree that it describes" may not be
552           technically 100% accurate, but it’s a good model for all normal
553           use.
555       This has two implications:
557       ·   if you grow bored with the tutorial repository you created (or
558           you’ve made a mistake and want to start all over), you can just do
559           simple
561               $ rm -rf git-tutorial
563           and it will be gone. There’s no external repository, and there’s no
564           history outside the project you created.
566       ·   if you want to move or duplicate a Git repository, you can do so.
567           There is git clone command, but if all you want to do is just to
568           create a copy of your repository (with all the full history that
569           went along with it), you can do so with a regular cp -a
570           git-tutorial new-git-tutorial.
572           Note that when you’ve moved or copied a Git repository, your Git
573           index file (which caches various information, notably some of the
574           "stat" information for the files involved) will likely need to be
575           refreshed. So after you do a cp -a to create a new copy, you’ll
576           want to do
578               $ git update-index --refresh
580           in the new repository to make sure that the index file is up to
581           date.
583       Note that the second point is true even across machines. You can
584       duplicate a remote Git repository with any regular copy mechanism, be
585       it scp, rsync or wget.
587       When copying a remote repository, you’ll want to at a minimum update
588       the index cache when you do this, and especially with other peoples'
589       repositories you often want to make sure that the index cache is in
590       some known state (you don’t know what they’ve done and not yet checked
591       in), so usually you’ll precede the git update-index with a
593           $ git read-tree --reset HEAD
594           $ git update-index --refresh
597       which will force a total index re-build from the tree pointed to by
598       HEAD. It resets the index contents to HEAD, and then the git
599       update-index makes sure to match up all index entries with the
600       checked-out files. If the original repository had uncommitted changes
601       in its working tree, git update-index --refresh notices them and tells
602       you they need to be updated.
604       The above can also be written as simply
606           $ git reset
609       and in fact a lot of the common Git command combinations can be
610       scripted with the git xyz interfaces. You can learn things by just
611       looking at what the various git scripts do. For example, git reset used
612       to be the above two lines implemented in git reset, but some things
613       like git status and git commit are slightly more complex scripts around
614       the basic Git commands.
616       Many (most?) public remote repositories will not contain any of the
617       checked out files or even an index file, and will only contain the
618       actual core Git files. Such a repository usually doesn’t even have the
619       .git subdirectory, but has all the Git files directly in the
620       repository.
622       To create your own local live copy of such a "raw" Git repository,
623       you’d first create your own subdirectory for the project, and then copy
624       the raw repository contents into the .git directory. For example, to
625       create your own copy of the Git repository, you’d do the following
627           $ mkdir my-git
628           $ cd my-git
629           $ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
632       followed by
634           $ git read-tree HEAD
637       to populate the index. However, now you have populated the index, and
638       you have all the Git internal files, but you will notice that you don’t
639       actually have any of the working tree files to work on. To get those,
640       you’d check them out with
642           $ git checkout-index -u -a
645       where the -u flag means that you want the checkout to keep the index up
646       to date (so that you don’t have to refresh it afterward), and the -a
647       flag means "check out all files" (if you have a stale copy or an older
648       version of a checked out tree you may also need to add the -f flag
649       first, to tell git checkout-index to force overwriting of any old
650       files).
652       Again, this can all be simplified with
654           $ git clone git://git.kernel.org/pub/scm/git/git.git/ my-git
655           $ cd my-git
656           $ git checkout
659       which will end up doing all of the above for you.
661       You have now successfully copied somebody else’s (mine) remote
662       repository, and checked it out.


665       Branches in Git are really nothing more than pointers into the Git
666       object database from within the .git/refs/ subdirectory, and as we
667       already discussed, the HEAD branch is nothing but a symlink to one of
668       these object pointers.
670       You can at any time create a new branch by just picking an arbitrary
671       point in the project history, and just writing the SHA-1 name of that
672       object into a file under .git/refs/heads/. You can use any filename you
673       want (and indeed, subdirectories), but the convention is that the
674       "normal" branch is called master. That’s just a convention, though, and
675       nothing enforces it.
677       To show that as an example, let’s go back to the git-tutorial
678       repository we used earlier, and create a branch in it. You do that by
679       simply just saying that you want to check out a new branch:
681           $ git checkout -b mybranch
684       will create a new branch based at the current HEAD position, and switch
685       to it.
687           Note
688           If you make the decision to start your new branch at some other
689           point in the history than the current HEAD, you can do so by just
690           telling git checkout what the base of the checkout would be. In
691           other words, if you have an earlier tag or branch, you’d just do
693               $ git checkout -b mybranch earlier-commit
696           and it would create the new branch mybranch at the earlier commit,
697           and check out the state at that time.
699       You can always just jump back to your original master branch by doing
701           $ git checkout master
704       (or any other branch-name, for that matter) and if you forget which
705       branch you happen to be on, a simple
707           $ cat .git/HEAD
710       will tell you where it’s pointing. To get the list of branches you
711       have, you can say
713           $ git branch
716       which used to be nothing more than a simple script around ls
717       .git/refs/heads. There will be an asterisk in front of the branch you
718       are currently on.
720       Sometimes you may wish to create a new branch without actually checking
721       it out and switching to it. If so, just use the command
723           $ git branch <branchname> [startingpoint]
726       which will simply create the branch, but will not do anything further.
727       You can then later — once you decide that you want to actually develop
728       on that branch — switch to that branch with a regular git checkout with
729       the branchname as the argument.


732       One of the ideas of having a branch is that you do some (possibly
733       experimental) work in it, and eventually merge it back to the main
734       branch. So assuming you created the above mybranch that started out
735       being the same as the original master branch, let’s make sure we’re in
736       that branch, and do some work there.
738           $ git checkout mybranch
739           $ echo "Work, work, work" >>hello
740           $ git commit -m "Some work." -i hello
743       Here, we just added another line to hello, and we used a shorthand for
744       doing both git update-index hello and git commit by just giving the
745       filename directly to git commit, with an -i flag (it tells Git to
746       include that file in addition to what you have done to the index file
747       so far when making the commit). The -m flag is to give the commit log
748       message from the command line.
750       Now, to make it a bit more interesting, let’s assume that somebody else
751       does some work in the original branch, and simulate that by going back
752       to the master branch, and editing the same file differently there:
754           $ git checkout master
757       Here, take a moment to look at the contents of hello, and notice how
758       they don’t contain the work we just did in mybranch — because that work
759       hasn’t happened in the master branch at all. Then do
761           $ echo "Play, play, play" >>hello
762           $ echo "Lots of fun" >>example
763           $ git commit -m "Some fun." -i hello example
766       since the master branch is obviously in a much better mood.
768       Now, you’ve got two branches, and you decide that you want to merge the
769       work done. Before we do that, let’s introduce a cool graphical tool
770       that helps you view what’s going on:
772           $ gitk --all
775       will show you graphically both of your branches (that’s what the --all
776       means: normally it will just show you your current HEAD) and their
777       histories. You can also see exactly how they came to be from a common
778       source.
780       Anyway, let’s exit gitk (^Q or the File menu), and decide that we want
781       to merge the work we did on the mybranch branch into the master branch
782       (which is currently our HEAD too). To do that, there’s a nice script
783       called git merge, which wants to know which branches you want to
784       resolve and what the merge is all about:
786           $ git merge -m "Merge work in mybranch" mybranch
789       where the first argument is going to be used as the commit message if
790       the merge can be resolved automatically.
792       Now, in this case we’ve intentionally created a situation where the
793       merge will need to be fixed up by hand, though, so Git will do as much
794       of it as it can automatically (which in this case is just merge the
795       example file, which had no differences in the mybranch branch), and
796       say:
798                   Auto-merging hello
799                   CONFLICT (content): Merge conflict in hello
800                   Automatic merge failed; fix conflicts and then commit the result.
803       It tells you that it did an "Automatic merge", which failed due to
804       conflicts in hello.
806       Not to worry. It left the (trivial) conflict in hello in the same form
807       you should already be well used to if you’ve ever used CVS, so let’s
808       just open hello in our editor (whatever that may be), and fix it up
809       somehow. I’d suggest just making it so that hello contains all four
810       lines:
812           Hello World
813           It's a new day for git
814           Play, play, play
815           Work, work, work
818       and once you’re happy with your manual merge, just do a
820           $ git commit -i hello
823       which will very loudly warn you that you’re now committing a merge
824       (which is correct, so never mind), and you can write a small merge
825       message about your adventures in git merge-land.
827       After you’re done, start up gitk --all to see graphically what the
828       history looks like. Notice that mybranch still exists, and you can
829       switch to it, and continue to work with it if you want to. The mybranch
830       branch will not contain the merge, but next time you merge it from the
831       master branch, Git will know how you merged it, so you’ll not have to
832       do that merge again.
834       Another useful tool, especially if you do not always work in X-Window
835       environment, is git show-branch.
837           $ git show-branch --topo-order --more=1 master mybranch
838           * [master] Merge work in mybranch
839            ! [mybranch] Some work.
840           --
841           -  [master] Merge work in mybranch
842           *+ [mybranch] Some work.
843           *  [master^] Some fun.
846       The first two lines indicate that it is showing the two branches with
847       the titles of their top-of-the-tree commits, you are currently on
848       master branch (notice the asterisk * character), and the first column
849       for the later output lines is used to show commits contained in the
850       master branch, and the second column for the mybranch branch. Three
851       commits are shown along with their titles. All of them have non blank
852       characters in the first column (* shows an ordinary commit on the
853       current branch, - is a merge commit), which means they are now part of
854       the master branch. Only the "Some work" commit has the plus + character
855       in the second column, because mybranch has not been merged to
856       incorporate these commits from the master branch. The string inside
857       brackets before the commit log message is a short name you can use to
858       name the commit. In the above example, master and mybranch are branch
859       heads. master^ is the first parent of master branch head. Please see
860       gitrevisions(7) if you want to see more complex cases.
862           Note
863           Without the --more=1 option, git show-branch would not output the
864           [master^] commit, as [mybranch] commit is a common ancestor of both
865           master and mybranch tips. Please see git-show-branch(1) for
866           details.
868           Note
869           If there were more commits on the master branch after the merge,
870           the merge commit itself would not be shown by git show-branch by
871           default. You would need to provide --sparse option to make the
872           merge commit visible in this case.
874       Now, let’s pretend you are the one who did all the work in mybranch,
875       and the fruit of your hard work has finally been merged to the master
876       branch. Let’s go back to mybranch, and run git merge to get the
877       "upstream changes" back to your branch.
879           $ git checkout mybranch
880           $ git merge -m "Merge upstream changes." master
883       This outputs something like this (the actual commit object names would
884       be different)
886           Updating from ae3a2da... to a80b4aa....
887           Fast-forward (no commit created; -m option ignored)
888            example | 1 +
889            hello   | 1 +
890            2 files changed, 2 insertions(+)
893       Because your branch did not contain anything more than what had already
894       been merged into the master branch, the merge operation did not
895       actually do a merge. Instead, it just updated the top of the tree of
896       your branch to that of the master branch. This is often called
897       fast-forward merge.
899       You can run gitk --all again to see how the commit ancestry looks like,
900       or run show-branch, which tells you this.
902           $ git show-branch master mybranch
903           ! [master] Merge work in mybranch
904            * [mybranch] Merge work in mybranch
905           --
906           -- [master] Merge work in mybranch


910       It’s usually much more common that you merge with somebody else than
911       merging with your own branches, so it’s worth pointing out that Git
912       makes that very easy too, and in fact, it’s not that different from
913       doing a git merge. In fact, a remote merge ends up being nothing more
914       than "fetch the work from a remote repository into a temporary tag"
915       followed by a git merge.
917       Fetching from a remote repository is done by, unsurprisingly, git
918       fetch:
920           $ git fetch <remote-repository>
923       One of the following transports can be used to name the repository to
924       download from:
926       SSH
927           remote.machine:/path/to/repo.git/ or
929           ssh://remote.machine/path/to/repo.git/
931           This transport can be used for both uploading and downloading, and
932           requires you to have a log-in privilege over ssh to the remote
933           machine. It finds out the set of objects the other side lacks by
934           exchanging the head commits both ends have and transfers (close to)
935           minimum set of objects. It is by far the most efficient way to
936           exchange Git objects between repositories.
938       Local directory
939           /path/to/repo.git/
941           This transport is the same as SSH transport but uses sh to run both
942           ends on the local machine instead of running other end on the
943           remote machine via ssh.
945       Git Native
946           git://remote.machine/path/to/repo.git/
948           This transport was designed for anonymous downloading. Like SSH
949           transport, it finds out the set of objects the downstream side
950           lacks and transfers (close to) minimum set of objects.
952       HTTP(S)
953           http://remote.machine/path/to/repo.git/
955           Downloader from http and https URL first obtains the topmost commit
956           object name from the remote site by looking at the specified
957           refname under repo.git/refs/ directory, and then tries to obtain
958           the commit object by downloading from repo.git/objects/xx/xxx...
959           using the object name of that commit object. Then it reads the
960           commit object to find out its parent commits and the associate tree
961           object; it repeats this process until it gets all the necessary
962           objects. Because of this behavior, they are sometimes also called
963           commit walkers.
965           The commit walkers are sometimes also called dumb transports,
966           because they do not require any Git aware smart server like Git
967           Native transport does. Any stock HTTP server that does not even
968           support directory index would suffice. But you must prepare your
969           repository with git update-server-info to help dumb transport
970           downloaders.
972       Once you fetch from the remote repository, you merge that with your
973       current branch.
975       However — it’s such a common thing to fetch and then immediately merge,
976       that it’s called git pull, and you can simply do
978           $ git pull <remote-repository>
981       and optionally give a branch-name for the remote end as a second
982       argument.
984           Note
985           You could do without using any branches at all, by keeping as many
986           local repositories as you would like to have branches, and merging
987           between them with git pull, just like you merge between branches.
988           The advantage of this approach is that it lets you keep a set of
989           files for each branch checked out and you may find it easier to
990           switch back and forth if you juggle multiple lines of development
991           simultaneously. Of course, you will pay the price of more disk
992           usage to hold multiple working trees, but disk space is cheap these
993           days.
995       It is likely that you will be pulling from the same remote repository
996       from time to time. As a short hand, you can store the remote repository
997       URL in the local repository’s config file like this:
999           $ git config remote.linus.url http://www.kernel.org/pub/scm/git/git.git/
1002       and use the "linus" keyword with git pull instead of the full URL.
1004       Examples.
1006        1. git pull linus
1008        2. git pull linus tag v0.99.1
1010       the above are equivalent to:
1012        1. git pull http://www.kernel.org/pub/scm/git/git.git/ HEAD
1014        2. git pull http://www.kernel.org/pub/scm/git/git.git/ tag v0.99.1


1017       We said this tutorial shows what plumbing does to help you cope with
1018       the porcelain that isn’t flushing, but we so far did not talk about how
1019       the merge really works. If you are following this tutorial the first
1020       time, I’d suggest to skip to "Publishing your work" section and come
1021       back here later.
1023       OK, still with me? To give us an example to look at, let’s go back to
1024       the earlier repository with "hello" and "example" file, and bring
1025       ourselves back to the pre-merge state:
1027           $ git show-branch --more=2 master mybranch
1028           ! [master] Merge work in mybranch
1029            * [mybranch] Merge work in mybranch
1030           --
1031           -- [master] Merge work in mybranch
1032           +* [master^2] Some work.
1033           +* [master^] Some fun.
1036       Remember, before running git merge, our master head was at "Some fun."
1037       commit, while our mybranch head was at "Some work." commit.
1039           $ git checkout mybranch
1040           $ git reset --hard master^2
1041           $ git checkout master
1042           $ git reset --hard master^
1045       After rewinding, the commit structure should look like this:
1047           $ git show-branch
1048           * [master] Some fun.
1049            ! [mybranch] Some work.
1050           --
1051           *  [master] Some fun.
1052            + [mybranch] Some work.
1053           *+ [master^] Initial commit
1056       Now we are ready to experiment with the merge by hand.
1058       git merge command, when merging two branches, uses 3-way merge
1059       algorithm. First, it finds the common ancestor between them. The
1060       command it uses is git merge-base:
1062           $ mb=$(git merge-base HEAD mybranch)
1065       The command writes the commit object name of the common ancestor to the
1066       standard output, so we captured its output to a variable, because we
1067       will be using it in the next step. By the way, the common ancestor
1068       commit is the "Initial commit" commit in this case. You can tell it by:
1070           $ git name-rev --name-only --tags $mb
1071           my-first-tag
1074       After finding out a common ancestor commit, the second step is this:
1076           $ git read-tree -m -u $mb HEAD mybranch
1079       This is the same git read-tree command we have already seen, but it
1080       takes three trees, unlike previous examples. This reads the contents of
1081       each tree into different stage in the index file (the first tree goes
1082       to stage 1, the second to stage 2, etc.). After reading three trees
1083       into three stages, the paths that are the same in all three stages are
1084       collapsed into stage 0. Also paths that are the same in two of three
1085       stages are collapsed into stage 0, taking the SHA-1 from either stage 2
1086       or stage 3, whichever is different from stage 1 (i.e. only one side
1087       changed from the common ancestor).
1089       After collapsing operation, paths that are different in three trees are
1090       left in non-zero stages. At this point, you can inspect the index file
1091       with this command:
1093           $ git ls-files --stage
1094           100644 7f8b141b65fdcee47321e399a2598a235a032422 0       example
1095           100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1       hello
1096           100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2       hello
1097           100644 cc44c73eb783565da5831b4d820c962954019b69 3       hello
1100       In our example of only two files, we did not have unchanged files so
1101       only example resulted in collapsing. But in real-life large projects,
1102       when only a small number of files change in one commit, this collapsing
1103       tends to trivially merge most of the paths fairly quickly, leaving only
1104       a handful of real changes in non-zero stages.
1106       To look at only non-zero stages, use --unmerged flag:
1108           $ git ls-files --unmerged
1109           100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1       hello
1110           100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2       hello
1111           100644 cc44c73eb783565da5831b4d820c962954019b69 3       hello
1114       The next step of merging is to merge these three versions of the file,
1115       using 3-way merge. This is done by giving git merge-one-file command as
1116       one of the arguments to git merge-index command:
1118           $ git merge-index git-merge-one-file hello
1119           Auto-merging hello
1120           ERROR: Merge conflict in hello
1121           fatal: merge program failed
1124       git merge-one-file script is called with parameters to describe those
1125       three versions, and is responsible to leave the merge results in the
1126       working tree. It is a fairly straightforward shell script, and
1127       eventually calls merge program from RCS suite to perform a file-level
1128       3-way merge. In this case, merge detects conflicts, and the merge
1129       result with conflict marks is left in the working tree.. This can be
1130       seen if you run ls-files --stage again at this point:
1132           $ git ls-files --stage
1133           100644 7f8b141b65fdcee47321e399a2598a235a032422 0       example
1134           100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1       hello
1135           100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2       hello
1136           100644 cc44c73eb783565da5831b4d820c962954019b69 3       hello
1139       This is the state of the index file and the working file after git
1140       merge returns control back to you, leaving the conflicting merge for
1141       you to resolve. Notice that the path hello is still unmerged, and what
1142       you see with git diff at this point is differences since stage 2 (i.e.
1143       your version).


1146       So, we can use somebody else’s work from a remote repository, but how
1147       can you prepare a repository to let other people pull from it?
1149       You do your real work in your working tree that has your primary
1150       repository hanging under it as its .git subdirectory. You could make
1151       that repository accessible remotely and ask people to pull from it, but
1152       in practice that is not the way things are usually done. A recommended
1153       way is to have a public repository, make it reachable by other people,
1154       and when the changes you made in your primary working tree are in good
1155       shape, update the public repository from it. This is often called
1156       pushing.
1158           Note
1159           This public repository could further be mirrored, and that is how
1160           Git repositories at kernel.org are managed.
1162       Publishing the changes from your local (private) repository to your
1163       remote (public) repository requires a write privilege on the remote
1164       machine. You need to have an SSH account there to run a single command,
1165       git-receive-pack.
1167       First, you need to create an empty repository on the remote machine
1168       that will house your public repository. This empty repository will be
1169       populated and be kept up to date by pushing into it later. Obviously,
1170       this repository creation needs to be done only once.
1172           Note
1173           git push uses a pair of commands, git send-pack on your local
1174           machine, and git-receive-pack on the remote machine. The
1175           communication between the two over the network internally uses an
1176           SSH connection.
1178       Your private repository’s Git directory is usually .git, but your
1179       public repository is often named after the project name, i.e.
1180       <project>.git. Let’s create such a public repository for project
1181       my-git. After logging into the remote machine, create an empty
1182       directory:
1184           $ mkdir my-git.git
1187       Then, make that directory into a Git repository by running git init,
1188       but this time, since its name is not the usual .git, we do things
1189       slightly differently:
1191           $ GIT_DIR=my-git.git git init
1194       Make sure this directory is available for others you want your changes
1195       to be pulled via the transport of your choice. Also you need to make
1196       sure that you have the git-receive-pack program on the $PATH.
1198           Note
1199           Many installations of sshd do not invoke your shell as the login
1200           shell when you directly run programs; what this means is that if
1201           your login shell is bash, only .bashrc is read and not
1202           .bash_profile. As a workaround, make sure .bashrc sets up $PATH so
1203           that you can run git-receive-pack program.
1205           Note
1206           If you plan to publish this repository to be accessed over http,
1207           you should do mv my-git.git/hooks/post-update.sample
1208           my-git.git/hooks/post-update at this point. This makes sure that
1209           every time you push into this repository, git update-server-info is
1210           run.
1212       Your "public repository" is now ready to accept your changes. Come back
1213       to the machine you have your private repository. From there, run this
1214       command:
1216           $ git push <public-host>:/path/to/my-git.git master
1219       This synchronizes your public repository to match the named branch head
1220       (i.e. master in this case) and objects reachable from them in your
1221       current repository.
1223       As a real example, this is how I update my public Git repository.
1224       Kernel.org mirror network takes care of the propagation to other
1225       publicly visible machines:
1227           $ git push master.kernel.org:/pub/scm/git/git.git/


1231       Earlier, we saw that one file under .git/objects/??/ directory is
1232       stored for each Git object you create. This representation is efficient
1233       to create atomically and safely, but not so convenient to transport
1234       over the network. Since Git objects are immutable once they are
1235       created, there is a way to optimize the storage by "packing them
1236       together". The command
1238           $ git repack
1241       will do it for you. If you followed the tutorial examples, you would
1242       have accumulated about 17 objects in .git/objects/??/ directories by
1243       now. git repack tells you how many objects it packed, and stores the
1244       packed file in the .git/objects/pack directory.
1246           Note
1247           You will see two files, pack-*.pack and pack-*.idx, in
1248           .git/objects/pack directory. They are closely related to each
1249           other, and if you ever copy them by hand to a different repository
1250           for whatever reason, you should make sure you copy them together.
1251           The former holds all the data from the objects in the pack, and the
1252           latter holds the index for random access.
1254       If you are paranoid, running git verify-pack command would detect if
1255       you have a corrupt pack, but do not worry too much. Our programs are
1256       always perfect ;-).
1258       Once you have packed objects, you do not need to leave the unpacked
1259       objects that are contained in the pack file anymore.
1261           $ git prune-packed
1264       would remove them for you.
1266       You can try running find .git/objects -type f before and after you run
1267       git prune-packed if you are curious. Also git count-objects would tell
1268       you how many unpacked objects are in your repository and how much space
1269       they are consuming.
1271           Note
1272           git pull is slightly cumbersome for HTTP transport, as a packed
1273           repository may contain relatively few objects in a relatively large
1274           pack. If you expect many HTTP pulls from your public repository you
1275           might want to repack & prune often, or never.
1277       If you run git repack again at this point, it will say "Nothing new to
1278       pack.". Once you continue your development and accumulate the changes,
1279       running git repack again will create a new pack, that contains objects
1280       created since you packed your repository the last time. We recommend
1281       that you pack your project soon after the initial import (unless you
1282       are starting your project from scratch), and then run git repack every
1283       once in a while, depending on how active your project is.
1285       When a repository is synchronized via git push and git pull objects
1286       packed in the source repository are usually stored unpacked in the
1287       destination. While this allows you to use different packing strategies
1288       on both ends, it also means you may need to repack both repositories
1289       every once in a while.


1292       Although Git is a truly distributed system, it is often convenient to
1293       organize your project with an informal hierarchy of developers. Linux
1294       kernel development is run this way. There is a nice illustration (page
1295       17, "Merges to Mainline") in Randy Dunlap’s presentation[2].
1297       It should be stressed that this hierarchy is purely informal. There is
1298       nothing fundamental in Git that enforces the "chain of patch flow" this
1299       hierarchy implies. You do not have to pull from only one remote
1300       repository.
1302       A recommended workflow for a "project lead" goes like this:
1304        1. Prepare your primary repository on your local machine. Your work is
1305           done there.
1307        2. Prepare a public repository accessible to others.
1309           If other people are pulling from your repository over dumb
1310           transport protocols (HTTP), you need to keep this repository dumb
1311           transport friendly. After git init,
1312           $GIT_DIR/hooks/post-update.sample copied from the standard
1313           templates would contain a call to git update-server-info but you
1314           need to manually enable the hook with mv post-update.sample
1315           post-update. This makes sure git update-server-info keeps the
1316           necessary files up to date.
1318        3. Push into the public repository from your primary repository.
1320        4. git repack the public repository. This establishes a big pack that
1321           contains the initial set of objects as the baseline, and possibly
1322           git prune if the transport used for pulling from your repository
1323           supports packed repositories.
1325        5. Keep working in your primary repository. Your changes include
1326           modifications of your own, patches you receive via e-mails, and
1327           merges resulting from pulling the "public" repositories of your
1328           "subsystem maintainers".
1330           You can repack this private repository whenever you feel like.
1332        6. Push your changes to the public repository, and announce it to the
1333           public.
1335        7. Every once in a while, git repack the public repository. Go back to
1336           step 5. and continue working.
1338       A recommended work cycle for a "subsystem maintainer" who works on that
1339       project and has an own "public repository" goes like this:
1341        1. Prepare your work repository, by running git clone on the public
1342           repository of the "project lead". The URL used for the initial
1343           cloning is stored in the remote.origin.url configuration variable.
1345        2. Prepare a public repository accessible to others, just like the
1346           "project lead" person does.
1348        3. Copy over the packed files from "project lead" public repository to
1349           your public repository, unless the "project lead" repository lives
1350           on the same machine as yours. In the latter case, you can use
1351           objects/info/alternates file to point at the repository you are
1352           borrowing from.
1354        4. Push into the public repository from your primary repository. Run
1355           git repack, and possibly git prune if the transport used for
1356           pulling from your repository supports packed repositories.
1358        5. Keep working in your primary repository. Your changes include
1359           modifications of your own, patches you receive via e-mails, and
1360           merges resulting from pulling the "public" repositories of your
1361           "project lead" and possibly your "sub-subsystem maintainers".
1363           You can repack this private repository whenever you feel like.
1365        6. Push your changes to your public repository, and ask your "project
1366           lead" and possibly your "sub-subsystem maintainers" to pull from
1367           it.
1369        7. Every once in a while, git repack the public repository. Go back to
1370           step 5. and continue working.
1372       A recommended work cycle for an "individual developer" who does not
1373       have a "public" repository is somewhat different. It goes like this:
1375        1. Prepare your work repository, by git clone the public repository of
1376           the "project lead" (or a "subsystem maintainer", if you work on a
1377           subsystem). The URL used for the initial cloning is stored in the
1378           remote.origin.url configuration variable.
1380        2. Do your work in your repository on master branch.
1382        3. Run git fetch origin from the public repository of your upstream
1383           every once in a while. This does only the first half of git pull
1384           but does not merge. The head of the public repository is stored in
1385           .git/refs/remotes/origin/master.
1387        4. Use git cherry origin to see which ones of your patches were
1388           accepted, and/or use git rebase origin to port your unmerged
1389           changes forward to the updated upstream.
1391        5. Use git format-patch origin to prepare patches for e-mail
1392           submission to your upstream and send it out. Go back to step 2. and
1393           continue.


1396       If you are coming from a CVS background, the style of cooperation
1397       suggested in the previous section may be new to you. You do not have to
1398       worry. Git supports the "shared public repository" style of cooperation
1399       you are probably more familiar with as well.
1401       See gitcvs-migration(7) for the details.


1404       It is likely that you will be working on more than one thing at a time.
1405       It is easy to manage those more-or-less independent tasks using
1406       branches with Git.
1408       We have already seen how branches work previously, with "fun and work"
1409       example using two branches. The idea is the same if there are more than
1410       two branches. Let’s say you started out from "master" head, and have
1411       some new code in the "master" branch, and two independent fixes in the
1412       "commit-fix" and "diff-fix" branches:
1414           $ git show-branch
1415           ! [commit-fix] Fix commit message normalization.
1416            ! [diff-fix] Fix rename detection.
1417             * [master] Release candidate #1
1418           ---
1419            +  [diff-fix] Fix rename detection.
1420            +  [diff-fix~1] Better common substring algorithm.
1421           +   [commit-fix] Fix commit message normalization.
1422             * [master] Release candidate #1
1423           ++* [diff-fix~2] Pretty-print messages.
1426       Both fixes are tested well, and at this point, you want to merge in
1427       both of them. You could merge in diff-fix first and then commit-fix
1428       next, like this:
1430           $ git merge -m "Merge fix in diff-fix" diff-fix
1431           $ git merge -m "Merge fix in commit-fix" commit-fix
1434       Which would result in:
1436           $ git show-branch
1437           ! [commit-fix] Fix commit message normalization.
1438            ! [diff-fix] Fix rename detection.
1439             * [master] Merge fix in commit-fix
1440           ---
1441             - [master] Merge fix in commit-fix
1442           + * [commit-fix] Fix commit message normalization.
1443             - [master~1] Merge fix in diff-fix
1444            +* [diff-fix] Fix rename detection.
1445            +* [diff-fix~1] Better common substring algorithm.
1446             * [master~2] Release candidate #1
1447           ++* [master~3] Pretty-print messages.
1450       However, there is no particular reason to merge in one branch first and
1451       the other next, when what you have are a set of truly independent
1452       changes (if the order mattered, then they are not independent by
1453       definition). You could instead merge those two branches into the
1454       current branch at once. First let’s undo what we just did and start
1455       over. We would want to get the master branch before these two merges by
1456       resetting it to master~2:
1458           $ git reset --hard master~2
1461       You can make sure git show-branch matches the state before those two
1462       git merge you just did. Then, instead of running two git merge commands
1463       in a row, you would merge these two branch heads (this is known as
1464       making an Octopus):
1466           $ git merge commit-fix diff-fix
1467           $ git show-branch
1468           ! [commit-fix] Fix commit message normalization.
1469            ! [diff-fix] Fix rename detection.
1470             * [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1471           ---
1472             - [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1473           + * [commit-fix] Fix commit message normalization.
1474            +* [diff-fix] Fix rename detection.
1475            +* [diff-fix~1] Better common substring algorithm.
1476             * [master~1] Release candidate #1
1477           ++* [master~2] Pretty-print messages.
1480       Note that you should not do Octopus just because you can. An octopus is
1481       a valid thing to do and often makes it easier to view the commit
1482       history if you are merging more than two independent changes at the
1483       same time. However, if you have merge conflicts with any of the
1484       branches you are merging in and need to hand resolve, that is an
1485       indication that the development happened in those branches were not
1486       independent after all, and you should merge two at a time, documenting
1487       how you resolved the conflicts, and the reason why you preferred
1488       changes made in one side over the other. Otherwise it would make the
1489       project history harder to follow, not easier.


1492       gittutorial(7), gittutorial-2(7), gitcvs-migration(7), git-help(1),
1493       giteveryday(7), The Git User’s Manual[1]


1496       Part of the git(1) suite


1499        1. the Git User Manual
1500           file:///usr/share/doc/git/user-manual.html
1502        2. Randy Dunlap’s presentation
1503           https://web.archive.org/web/20120915203609/http://www.xenotime.net/linux/mentor/linux-mentoring-2006.pdf
1507Git 2.18.1                        05/14/2019               GITCORE-TUTORIAL(7)