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Christian Couder497c8332008-05-29 19:21:46 +02001gitcore-tutorial(7)
2===================
J. Bruce Fields927a5032006-01-22 23:57:25 -05003
Christian Couder497c8332008-05-29 19:21:46 +02004NAME
5----
Thomas Ackermann2de9b712013-01-21 20:17:53 +01006gitcore-tutorial - A Git core tutorial for developers
Christian Couder497c8332008-05-29 19:21:46 +02007
8SYNOPSIS
9--------
10git *
11
12DESCRIPTION
13-----------
J. Bruce Fields927a5032006-01-22 23:57:25 -050014
Thomas Ackermann2de9b712013-01-21 20:17:53 +010015This tutorial explains how to use the "core" Git commands to set up and
16work with a Git repository.
J. Bruce Fields927a5032006-01-22 23:57:25 -050017
Thomas Ackermann2de9b712013-01-21 20:17:53 +010018If you just need to use Git as a revision control system you may prefer
Thomas Ackermann48a8c262013-01-21 20:16:20 +010019to start with "A Tutorial Introduction to Git" (linkgit:gittutorial[7]) or
20link:user-manual.html[the Git User Manual].
J. Bruce Fieldsa85feca2007-09-03 10:34:27 -040021
22However, an understanding of these low-level tools can be helpful if
Thomas Ackermann2de9b712013-01-21 20:17:53 +010023you want to understand Git's internals.
J. Bruce Fields927a5032006-01-22 23:57:25 -050024
Thomas Ackermann2de9b712013-01-21 20:17:53 +010025The core Git is often called "plumbing", with the prettier user
J. Bruce Fields927a5032006-01-22 23:57:25 -050026interfaces on top of it called "porcelain". You may not want to use the
27plumbing directly very often, but it can be good to know what the
Kristoffer Haugsbakk47437fd2016-12-09 16:51:12 +010028plumbing does when the porcelain isn't flushing.
J. Bruce Fields927a5032006-01-22 23:57:25 -050029
Ramkumar Ramachandra52eb5172010-01-16 23:35:38 +053030Back when this document was originally written, many porcelain
31commands were shell scripts. For simplicity, it still uses them as
32examples to illustrate how plumbing is fit together to form the
33porcelain commands. The source tree includes some of these scripts in
34contrib/examples/ for reference. Although these are not implemented as
35shell scripts anymore, the description of what the plumbing layer
36commands do is still valid.
37
J. Bruce Fields927a5032006-01-22 23:57:25 -050038[NOTE]
J. Bruce Fieldsa85feca2007-09-03 10:34:27 -040039Deeper technical details are often marked as Notes, which you can
40skip on your first reading.
J. Bruce Fields927a5032006-01-22 23:57:25 -050041
42
Thomas Ackermann2de9b712013-01-21 20:17:53 +010043Creating a Git repository
J. Bruce Fields927a5032006-01-22 23:57:25 -050044-------------------------
45
Thomas Ackermann2de9b712013-01-21 20:17:53 +010046Creating a new Git repository couldn't be easier: all Git repositories start
J. Bruce Fields927a5032006-01-22 23:57:25 -050047out empty, and the only thing you need to do is find yourself a
48subdirectory that you want to use as a working tree - either an empty
49one for a totally new project, or an existing working tree that you want
Thomas Ackermann2de9b712013-01-21 20:17:53 +010050to import into Git.
J. Bruce Fields927a5032006-01-22 23:57:25 -050051
52For our first example, we're going to start a totally new repository from
Jonathan Niederba020ef2008-07-03 00:41:41 -050053scratch, with no pre-existing files, and we'll call it 'git-tutorial'.
J. Bruce Fields927a5032006-01-22 23:57:25 -050054To start up, create a subdirectory for it, change into that
Thomas Ackermann2de9b712013-01-21 20:17:53 +010055subdirectory, and initialize the Git infrastructure with 'git init':
J. Bruce Fields927a5032006-01-22 23:57:25 -050056
57------------------------------------------------
58$ mkdir git-tutorial
59$ cd git-tutorial
Jonathan Niederb1889c32008-06-30 01:09:04 -050060$ git init
J. Bruce Fields927a5032006-01-22 23:57:25 -050061------------------------------------------------
62
Thomas Ackermann2de9b712013-01-21 20:17:53 +010063to which Git will reply
J. Bruce Fields927a5032006-01-22 23:57:25 -050064
65----------------
Shawn O. Pearceef0a89a2006-12-15 00:44:58 -050066Initialized empty Git repository in .git/
J. Bruce Fields927a5032006-01-22 23:57:25 -050067----------------
68
Thomas Ackermann2de9b712013-01-21 20:17:53 +010069which is just Git's way of saying that you haven't been doing anything
J. Bruce Fields927a5032006-01-22 23:57:25 -050070strange, and that it will have created a local `.git` directory setup for
71your new project. You will now have a `.git` directory, and you can
Jonathan Nieder2fd02c92008-07-03 00:55:07 -050072inspect that with 'ls'. For your new empty project, it should show you
J. Bruce Fields927a5032006-01-22 23:57:25 -050073three entries, among other things:
74
Junio C Hamano960c7022006-02-06 12:27:33 -080075 - a file called `HEAD`, that has `ref: refs/heads/master` in it.
76 This is similar to a symbolic link and points at
77 `refs/heads/master` relative to the `HEAD` file.
J. Bruce Fields927a5032006-01-22 23:57:25 -050078+
79Don't worry about the fact that the file that the `HEAD` link points to
80doesn't even exist yet -- you haven't created the commit that will
81start your `HEAD` development branch yet.
82
83 - a subdirectory called `objects`, which will contain all the
84 objects of your project. You should never have any real reason to
85 look at the objects directly, but you might want to know that these
86 objects are what contains all the real 'data' in your repository.
87
88 - a subdirectory called `refs`, which contains references to objects.
89
90In particular, the `refs` subdirectory will contain two other
91subdirectories, named `heads` and `tags` respectively. They do
92exactly what their names imply: they contain references to any number
93of different 'heads' of development (aka 'branches'), and to any
94'tags' that you have created to name specific versions in your
95repository.
96
97One note: the special `master` head is the default branch, which is
Junio C Hamano960c7022006-02-06 12:27:33 -080098why the `.git/HEAD` file was created points to it even if it
J. Bruce Fields927a5032006-01-22 23:57:25 -050099doesn't yet exist. Basically, the `HEAD` link is supposed to always
100point to the branch you are working on right now, and you always
101start out expecting to work on the `master` branch.
102
103However, this is only a convention, and you can name your branches
104anything you want, and don't have to ever even 'have' a `master`
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100105branch. A number of the Git tools will assume that `.git/HEAD` is
J. Bruce Fields927a5032006-01-22 23:57:25 -0500106valid, though.
107
108[NOTE]
Thomas Ackermannd5fa1f12013-04-15 19:49:04 +0200109An 'object' is identified by its 160-bit SHA-1 hash, aka 'object name',
J. Bruce Fields927a5032006-01-22 23:57:25 -0500110and a reference to an object is always the 40-byte hex
Thomas Ackermannd5fa1f12013-04-15 19:49:04 +0200111representation of that SHA-1 name. The files in the `refs`
J. Bruce Fields927a5032006-01-22 23:57:25 -0500112subdirectory are expected to contain these hex references
Jonathan Nieder70676e62010-08-20 05:37:51 -0500113(usually with a final `\n` at the end), and you should thus
J. Bruce Fields927a5032006-01-22 23:57:25 -0500114expect to see a number of 41-byte files containing these
115references in these `refs` subdirectories when you actually start
116populating your tree.
117
118[NOTE]
Jonathan Nieder6998e4d2008-06-30 17:01:21 -0500119An advanced user may want to take a look at linkgit:gitrepository-layout[5]
J. Bruce Fields927a5032006-01-22 23:57:25 -0500120after finishing this tutorial.
121
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100122You have now created your first Git repository. Of course, since it's
J. Bruce Fields927a5032006-01-22 23:57:25 -0500123empty, that's not very useful, so let's start populating it with data.
124
125
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100126Populating a Git repository
J. Bruce Fields927a5032006-01-22 23:57:25 -0500127---------------------------
128
129We'll keep this simple and stupid, so we'll start off with populating a
130few trivial files just to get a feel for it.
131
132Start off with just creating any random files that you want to maintain
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100133in your Git repository. We'll start off with a few bad examples, just to
J. Bruce Fields927a5032006-01-22 23:57:25 -0500134get a feel for how this works:
135
136------------------------------------------------
137$ echo "Hello World" >hello
138$ echo "Silly example" >example
139------------------------------------------------
140
Junio C Hamano960c7022006-02-06 12:27:33 -0800141you have now created two files in your working tree (aka 'working directory'),
142but to actually check in your hard work, you will have to go through two steps:
J. Bruce Fields927a5032006-01-22 23:57:25 -0500143
144 - fill in the 'index' file (aka 'cache') with the information about your
145 working tree state.
146
147 - commit that index file as an object.
148
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100149The first step is trivial: when you want to tell Git about any changes
Thomas Rast0b444cd2010-01-10 00:33:00 +0100150to your working tree, you use the 'git update-index' program. That
J. Bruce Fields927a5032006-01-22 23:57:25 -0500151program normally just takes a list of filenames you want to update, but
152to avoid trivial mistakes, it refuses to add new entries to the index
153(or remove existing ones) unless you explicitly tell it that you're
Jeff King6cf378f2012-04-26 04:51:57 -0400154adding a new entry with the `--add` flag (or removing an entry with the
155`--remove`) flag.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500156
157So to populate the index with the two files you just created, you can do
158
159------------------------------------------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500160$ git update-index --add hello example
J. Bruce Fields927a5032006-01-22 23:57:25 -0500161------------------------------------------------
162
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100163and you have now told Git to track those two files.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500164
165In fact, as you did that, if you now look into your object directory,
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100166you'll notice that Git will have added two new objects to the object
J. Bruce Fields927a5032006-01-22 23:57:25 -0500167database. If you did exactly the steps above, you should now be able to do
168
169
170----------------
171$ ls .git/objects/??/*
172----------------
173
174and see two files:
175
176----------------
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700177.git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
J. Bruce Fields927a5032006-01-22 23:57:25 -0500178.git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
179----------------
180
Junio C Hamano960c7022006-02-06 12:27:33 -0800181which correspond with the objects with names of `557db...` and
182`f24c7...` respectively.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500183
Thomas Rast0b444cd2010-01-10 00:33:00 +0100184If you want to, you can use 'git cat-file' to look at those objects, but
J. Bruce Fields927a5032006-01-22 23:57:25 -0500185you'll have to use the object name, not the filename of the object:
186
187----------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500188$ git cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
J. Bruce Fields927a5032006-01-22 23:57:25 -0500189----------------
190
Thomas Rast0b444cd2010-01-10 00:33:00 +0100191where the `-t` tells 'git cat-file' to tell you what the "type" of the
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100192object is. Git will tell you that you have a "blob" object (i.e., just a
J. Bruce Fields927a5032006-01-22 23:57:25 -0500193regular file), and you can see the contents with
194
195----------------
Stephen Boyd7c5858a2009-11-04 22:33:53 -0800196$ git cat-file blob 557db03
J. Bruce Fields927a5032006-01-22 23:57:25 -0500197----------------
198
Junio C Hamano960c7022006-02-06 12:27:33 -0800199which will print out "Hello World". The object `557db03` is nothing
J. Bruce Fields927a5032006-01-22 23:57:25 -0500200more than the contents of your file `hello`.
201
202[NOTE]
203Don't confuse that object with the file `hello` itself. The
204object is literally just those specific *contents* of the file, and
205however much you later change the contents in file `hello`, the object
206we just looked at will never change. Objects are immutable.
207
208[NOTE]
209The second example demonstrates that you can
210abbreviate the object name to only the first several
211hexadecimal digits in most places.
212
213Anyway, as we mentioned previously, you normally never actually take a
214look at the objects themselves, and typing long 40-character hex
215names is not something you'd normally want to do. The above digression
Thomas Rast0b444cd2010-01-10 00:33:00 +0100216was just to show that 'git update-index' did something magical, and
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100217actually saved away the contents of your files into the Git object
J. Bruce Fields927a5032006-01-22 23:57:25 -0500218database.
219
220Updating the index did something else too: it created a `.git/index`
221file. This is the index that describes your current working tree, and
222something you should be very aware of. Again, you normally never worry
223about the index file itself, but you should be aware of the fact that
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100224you have not actually really "checked in" your files into Git so far,
225you've only *told* Git about them.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500226
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100227However, since Git knows about them, you can now start using some of the
228most basic Git commands to manipulate the files or look at their status.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500229
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100230In particular, let's not even check in the two files into Git yet, we'll
J. Bruce Fields927a5032006-01-22 23:57:25 -0500231start off by adding another line to `hello` first:
232
233------------------------------------------------
234$ echo "It's a new day for git" >>hello
235------------------------------------------------
236
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100237and you can now, since you told Git about the previous state of `hello`, ask
238Git what has changed in the tree compared to your old index, using the
Thomas Rast0b444cd2010-01-10 00:33:00 +0100239'git diff-files' command:
J. Bruce Fields927a5032006-01-22 23:57:25 -0500240
241------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500242$ git diff-files
J. Bruce Fields927a5032006-01-22 23:57:25 -0500243------------
244
245Oops. That wasn't very readable. It just spit out its own internal
Jonathan Nieder5833d732008-07-03 00:59:09 -0500246version of a 'diff', but that internal version really just tells you
J. Bruce Fields927a5032006-01-22 23:57:25 -0500247that it has noticed that "hello" has been modified, and that the old object
248contents it had have been replaced with something else.
249
Thomas Rast0b444cd2010-01-10 00:33:00 +0100250To make it readable, we can tell 'git diff-files' to output the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500251differences as a patch, using the `-p` flag:
252
253------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500254$ git diff-files -p
J. Bruce Fields927a5032006-01-22 23:57:25 -0500255diff --git a/hello b/hello
256index 557db03..263414f 100644
257--- a/hello
258+++ b/hello
259@@ -1 +1,2 @@
260 Hello World
261+It's a new day for git
Jean-Noel Avila975e3822015-05-12 19:23:20 +0200262------------
J. Bruce Fields927a5032006-01-22 23:57:25 -0500263
264i.e. the diff of the change we caused by adding another line to `hello`.
265
Thomas Rast0b444cd2010-01-10 00:33:00 +0100266In other words, 'git diff-files' always shows us the difference between
J. Bruce Fields927a5032006-01-22 23:57:25 -0500267what is recorded in the index, and what is currently in the working
268tree. That's very useful.
269
Jonathan Niederb1889c32008-06-30 01:09:04 -0500270A common shorthand for `git diff-files -p` is to just write `git
J. Bruce Fields927a5032006-01-22 23:57:25 -0500271diff`, which will do the same thing.
272
273------------
274$ git diff
275diff --git a/hello b/hello
276index 557db03..263414f 100644
277--- a/hello
278+++ b/hello
279@@ -1 +1,2 @@
280 Hello World
281+It's a new day for git
282------------
283
284
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100285Committing Git state
J. Bruce Fields927a5032006-01-22 23:57:25 -0500286--------------------
287
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100288Now, we want to go to the next stage in Git, which is to take the files
289that Git knows about in the index, and commit them as a real tree. We do
J. Bruce Fields927a5032006-01-22 23:57:25 -0500290that in two phases: creating a 'tree' object, and committing that 'tree'
291object as a 'commit' object together with an explanation of what the
292tree was all about, along with information of how we came to that state.
293
Thomas Rast0b444cd2010-01-10 00:33:00 +0100294Creating a tree object is trivial, and is done with 'git write-tree'.
Jonathan Nieder483bc4f2008-06-30 13:56:34 -0500295There are no options or other input: `git write-tree` will take the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500296current index state, and write an object that describes that whole
297index. In other words, we're now tying together all the different
298filenames with their contents (and their permissions), and we're
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100299creating the equivalent of a Git "directory" object:
J. Bruce Fields927a5032006-01-22 23:57:25 -0500300
301------------------------------------------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500302$ git write-tree
J. Bruce Fields927a5032006-01-22 23:57:25 -0500303------------------------------------------------
304
305and this will just output the name of the resulting tree, in this case
306(if you have done exactly as I've described) it should be
307
308----------------
3098988da15d077d4829fc51d8544c097def6644dbb
310----------------
311
312which is another incomprehensible object name. Again, if you want to,
Jonathan Nieder70676e62010-08-20 05:37:51 -0500313you can use `git cat-file -t 8988d...` to see that this time the object
J. Bruce Fields927a5032006-01-22 23:57:25 -0500314is not a "blob" object, but a "tree" object (you can also use
Jonathan Niederb1889c32008-06-30 01:09:04 -0500315`git cat-file` to actually output the raw object contents, but you'll see
J. Bruce Fields927a5032006-01-22 23:57:25 -0500316mainly a binary mess, so that's less interesting).
317
Thomas Rast0b444cd2010-01-10 00:33:00 +0100318However -- normally you'd never use 'git write-tree' on its own, because
J. Bruce Fields927a5032006-01-22 23:57:25 -0500319normally you always commit a tree into a commit object using the
Thomas Rast0b444cd2010-01-10 00:33:00 +0100320'git commit-tree' command. In fact, it's easier to not actually use
321'git write-tree' on its own at all, but to just pass its result in as an
322argument to 'git commit-tree'.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500323
Thomas Rast0b444cd2010-01-10 00:33:00 +0100324'git commit-tree' normally takes several arguments -- it wants to know
J. Bruce Fields927a5032006-01-22 23:57:25 -0500325what the 'parent' of a commit was, but since this is the first commit
326ever in this new repository, and it has no parents, we only need to pass in
Thomas Rast0b444cd2010-01-10 00:33:00 +0100327the object name of the tree. However, 'git commit-tree' also wants to get a
Luiz Fernando N. Capitulino79dbbed2007-04-25 11:18:28 -0300328commit message on its standard input, and it will write out the resulting
329object name for the commit to its standard output.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500330
331And this is where we create the `.git/refs/heads/master` file
332which is pointed at by `HEAD`. This file is supposed to contain
333the reference to the top-of-tree of the master branch, and since
Thomas Rast0b444cd2010-01-10 00:33:00 +0100334that's exactly what 'git commit-tree' spits out, we can do this
J. Bruce Fields927a5032006-01-22 23:57:25 -0500335all with a sequence of simple shell commands:
336
337------------------------------------------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500338$ tree=$(git write-tree)
339$ commit=$(echo 'Initial commit' | git commit-tree $tree)
340$ git update-ref HEAD $commit
J. Bruce Fields927a5032006-01-22 23:57:25 -0500341------------------------------------------------
342
Nicolas Pitreebd124c2006-12-14 23:15:44 -0500343In this case this creates a totally new commit that is not related to
344anything else. Normally you do this only *once* for a project ever, and
345all later commits will be parented on top of an earlier commit.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500346
347Again, normally you'd never actually do this by hand. There is a
348helpful script called `git commit` that will do all of this for you. So
349you could have just written `git commit`
350instead, and it would have done the above magic scripting for you.
351
352
353Making a change
354---------------
355
Thomas Rast0b444cd2010-01-10 00:33:00 +0100356Remember how we did the 'git update-index' on file `hello` and then we
J. Bruce Fields927a5032006-01-22 23:57:25 -0500357changed `hello` afterward, and could compare the new state of `hello` with the
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700358state we saved in the index file?
J. Bruce Fields927a5032006-01-22 23:57:25 -0500359
Thomas Rast0b444cd2010-01-10 00:33:00 +0100360Further, remember how I said that 'git write-tree' writes the contents
J. Bruce Fields927a5032006-01-22 23:57:25 -0500361of the *index* file to the tree, and thus what we just committed was in
362fact the *original* contents of the file `hello`, not the new ones. We did
363that on purpose, to show the difference between the index state, and the
364state in the working tree, and how they don't have to match, even
365when we commit things.
366
Jonathan Niederb1889c32008-06-30 01:09:04 -0500367As before, if we do `git diff-files -p` in our git-tutorial project,
J. Bruce Fields927a5032006-01-22 23:57:25 -0500368we'll still see the same difference we saw last time: the index file
369hasn't changed by the act of committing anything. However, now that we
370have committed something, we can also learn to use a new command:
Thomas Rast0b444cd2010-01-10 00:33:00 +0100371'git diff-index'.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500372
Thomas Rast0b444cd2010-01-10 00:33:00 +0100373Unlike 'git diff-files', which showed the difference between the index
374file and the working tree, 'git diff-index' shows the differences
J. Bruce Fields927a5032006-01-22 23:57:25 -0500375between a committed *tree* and either the index file or the working
Thomas Rast0b444cd2010-01-10 00:33:00 +0100376tree. In other words, 'git diff-index' wants a tree to be diffed
J. Bruce Fields927a5032006-01-22 23:57:25 -0500377against, and before we did the commit, we couldn't do that, because we
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700378didn't have anything to diff against.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500379
380But now we can do
381
382----------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500383$ git diff-index -p HEAD
J. Bruce Fields927a5032006-01-22 23:57:25 -0500384----------------
385
Thomas Rast0b444cd2010-01-10 00:33:00 +0100386(where `-p` has the same meaning as it did in 'git diff-files'), and it
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700387will show us the same difference, but for a totally different reason.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500388Now we're comparing the working tree not against the index file,
389but against the tree we just wrote. It just so happens that those two
390are obviously the same, so we get the same result.
391
392Again, because this is a common operation, you can also just shorthand
393it with
394
395----------------
396$ git diff HEAD
397----------------
398
399which ends up doing the above for you.
400
Thomas Rast0b444cd2010-01-10 00:33:00 +0100401In other words, 'git diff-index' normally compares a tree against the
Jeff King6cf378f2012-04-26 04:51:57 -0400402working tree, but when given the `--cached` flag, it is told to
J. Bruce Fields927a5032006-01-22 23:57:25 -0500403instead compare against just the index cache contents, and ignore the
404current working tree state entirely. Since we just wrote the index
Jeff King6cf378f2012-04-26 04:51:57 -0400405file to HEAD, doing `git diff-index --cached -p HEAD` should thus return
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700406an empty set of differences, and that's exactly what it does.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500407
408[NOTE]
409================
Thomas Rast0b444cd2010-01-10 00:33:00 +0100410'git diff-index' really always uses the index for its
J. Bruce Fields927a5032006-01-22 23:57:25 -0500411comparisons, and saying that it compares a tree against the working
412tree is thus not strictly accurate. In particular, the list of
413files to compare (the "meta-data") *always* comes from the index file,
Jeff King6cf378f2012-04-26 04:51:57 -0400414regardless of whether the `--cached` flag is used or not. The `--cached`
J. Bruce Fields927a5032006-01-22 23:57:25 -0500415flag really only determines whether the file *contents* to be compared
416come from the working tree or not.
417
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100418This is not hard to understand, as soon as you realize that Git simply
J. Bruce Fields927a5032006-01-22 23:57:25 -0500419never knows (or cares) about files that it is not told about
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100420explicitly. Git will never go *looking* for files to compare, it
J. Bruce Fields927a5032006-01-22 23:57:25 -0500421expects you to tell it what the files are, and that's what the index
422is there for.
423================
424
425However, our next step is to commit the *change* we did, and again, to
426understand what's going on, keep in mind the difference between "working
427tree contents", "index file" and "committed tree". We have changes
428in the working tree that we want to commit, and we always have to
429work through the index file, so the first thing we need to do is to
430update the index cache:
431
432------------------------------------------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500433$ git update-index hello
J. Bruce Fields927a5032006-01-22 23:57:25 -0500434------------------------------------------------
435
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100436(note how we didn't need the `--add` flag this time, since Git knew
J. Bruce Fields927a5032006-01-22 23:57:25 -0500437about the file already).
438
Jonathan Nieder70676e62010-08-20 05:37:51 -0500439Note what happens to the different 'git diff-{asterisk}' versions here.
440After we've updated `hello` in the index, `git diff-files -p` now shows no
Jonathan Niederb1889c32008-06-30 01:09:04 -0500441differences, but `git diff-index -p HEAD` still *does* show that the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500442current state is different from the state we committed. In fact, now
Thomas Rast0b444cd2010-01-10 00:33:00 +0100443'git diff-index' shows the same difference whether we use the `--cached`
J. Bruce Fields927a5032006-01-22 23:57:25 -0500444flag or not, since now the index is coherent with the working tree.
445
446Now, since we've updated `hello` in the index, we can commit the new
447version. We could do it by writing the tree by hand again, and
448committing the tree (this time we'd have to use the `-p HEAD` flag to
449tell commit that the HEAD was the *parent* of the new commit, and that
450this wasn't an initial commit any more), but you've done that once
451already, so let's just use the helpful script this time:
452
453------------------------------------------------
454$ git commit
455------------------------------------------------
456
457which starts an editor for you to write the commit message and tells you
458a bit about what you have done.
459
460Write whatever message you want, and all the lines that start with '#'
461will be pruned out, and the rest will be used as the commit message for
462the change. If you decide you don't want to commit anything after all at
463this point (you can continue to edit things and update the index), you
464can just leave an empty message. Otherwise `git commit` will commit
465the change for you.
466
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100467You've now made your first real Git commit. And if you're interested in
J. Bruce Fields927a5032006-01-22 23:57:25 -0500468looking at what `git commit` really does, feel free to investigate:
469it's a few very simple shell scripts to generate the helpful (?) commit
470message headers, and a few one-liners that actually do the
Thomas Rast0b444cd2010-01-10 00:33:00 +0100471commit itself ('git commit').
J. Bruce Fields927a5032006-01-22 23:57:25 -0500472
473
474Inspecting Changes
475------------------
476
477While creating changes is useful, it's even more useful if you can tell
478later what changed. The most useful command for this is another of the
Thomas Rast0b444cd2010-01-10 00:33:00 +0100479'diff' family, namely 'git diff-tree'.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500480
Thomas Rast0b444cd2010-01-10 00:33:00 +0100481'git diff-tree' can be given two arbitrary trees, and it will tell you the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500482differences between them. Perhaps even more commonly, though, you can
483give it just a single commit object, and it will figure out the parent
484of that commit itself, and show the difference directly. Thus, to get
485the same diff that we've already seen several times, we can now do
486
487----------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500488$ git diff-tree -p HEAD
J. Bruce Fields927a5032006-01-22 23:57:25 -0500489----------------
490
491(again, `-p` means to show the difference as a human-readable patch),
492and it will show what the last commit (in `HEAD`) actually changed.
493
494[NOTE]
495============
496Here is an ASCII art by Jon Loeliger that illustrates how
Jonathan Nieder70676e62010-08-20 05:37:51 -0500497various 'diff-{asterisk}' commands compare things.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500498
499 diff-tree
500 +----+
501 | |
502 | |
503 V V
504 +-----------+
505 | Object DB |
506 | Backing |
507 | Store |
508 +-----------+
509 ^ ^
510 | |
511 | | diff-index --cached
512 | |
513 diff-index | V
514 | +-----------+
515 | | Index |
516 | | "cache" |
517 | +-----------+
518 | ^
519 | |
520 | | diff-files
521 | |
522 V V
523 +-----------+
524 | Working |
525 | Directory |
526 +-----------+
527============
528
Thomas Rast0b444cd2010-01-10 00:33:00 +0100529More interestingly, you can also give 'git diff-tree' the `--pretty` flag,
Junio C Hamano960c7022006-02-06 12:27:33 -0800530which tells it to also show the commit message and author and date of the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500531commit, and you can tell it to show a whole series of diffs.
532Alternatively, you can tell it to be "silent", and not show the diffs at
533all, but just show the actual commit message.
534
Thomas Rast0b444cd2010-01-10 00:33:00 +0100535In fact, together with the 'git rev-list' program (which generates a
536list of revisions), 'git diff-tree' ends up being a veritable fount of
Junio C Hamano627a8b82013-08-09 10:28:53 -0700537changes. You can emulate `git log`, `git log -p`, etc. with a trivial
538script that pipes the output of `git rev-list` to `git diff-tree --stdin`,
539which was exactly how early versions of `git log` were implemented.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500540
541
542Tagging a version
543-----------------
544
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100545In Git, there are two kinds of tags, a "light" one, and an "annotated tag".
J. Bruce Fields927a5032006-01-22 23:57:25 -0500546
547A "light" tag is technically nothing more than a branch, except we put
548it in the `.git/refs/tags/` subdirectory instead of calling it a `head`.
549So the simplest form of tag involves nothing more than
550
551------------------------------------------------
552$ git tag my-first-tag
553------------------------------------------------
554
555which just writes the current `HEAD` into the `.git/refs/tags/my-first-tag`
556file, after which point you can then use this symbolic name for that
557particular state. You can, for example, do
558
559----------------
560$ git diff my-first-tag
561----------------
562
Thomas Zander5221ecb2008-01-16 23:48:21 +0100563to diff your current state against that tag which at this point will
J. Bruce Fields927a5032006-01-22 23:57:25 -0500564obviously be an empty diff, but if you continue to develop and commit
565stuff, you can use your tag as an "anchor-point" to see what has changed
566since you tagged it.
567
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100568An "annotated tag" is actually a real Git object, and contains not only a
J. Bruce Fields927a5032006-01-22 23:57:25 -0500569pointer to the state you want to tag, but also a small tag name and
570message, along with optionally a PGP signature that says that yes,
571you really did
572that tag. You create these annotated tags with either the `-a` or
Thomas Rast0b444cd2010-01-10 00:33:00 +0100573`-s` flag to 'git tag':
J. Bruce Fields927a5032006-01-22 23:57:25 -0500574
575----------------
576$ git tag -s <tagname>
577----------------
578
579which will sign the current `HEAD` (but you can also give it another
Michael J Gruber3c652d12009-12-01 10:19:05 +0100580argument that specifies the thing to tag, e.g., you could have tagged the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500581current `mybranch` point by using `git tag <tagname> mybranch`).
582
583You normally only do signed tags for major releases or things
584like that, while the light-weight tags are useful for any marking you
585want to do -- any time you decide that you want to remember a certain
586point, just create a private tag for it, and you have a nice symbolic
587name for the state at that point.
588
589
590Copying repositories
591--------------------
592
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100593Git repositories are normally totally self-sufficient and relocatable.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500594Unlike CVS, for example, there is no separate notion of
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100595"repository" and "working tree". A Git repository normally *is* the
596working tree, with the local Git information hidden in the `.git`
J. Bruce Fields927a5032006-01-22 23:57:25 -0500597subdirectory. There is nothing else. What you see is what you got.
598
599[NOTE]
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100600You can tell Git to split the Git internal information from
J. Bruce Fields927a5032006-01-22 23:57:25 -0500601the directory that it tracks, but we'll ignore that for now: it's not
602how normal projects work, and it's really only meant for special uses.
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100603So the mental model of "the Git information is always tied directly to
J. Bruce Fields927a5032006-01-22 23:57:25 -0500604the working tree that it describes" may not be technically 100%
605accurate, but it's a good model for all normal use.
606
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700607This has two implications:
J. Bruce Fields927a5032006-01-22 23:57:25 -0500608
609 - if you grow bored with the tutorial repository you created (or you've
610 made a mistake and want to start all over), you can just do simple
611+
612----------------
613$ rm -rf git-tutorial
614----------------
615+
616and it will be gone. There's no external repository, and there's no
617history outside the project you created.
618
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100619 - if you want to move or duplicate a Git repository, you can do so. There
Thomas Rast0b444cd2010-01-10 00:33:00 +0100620 is 'git clone' command, but if all you want to do is just to
J. Bruce Fields927a5032006-01-22 23:57:25 -0500621 create a copy of your repository (with all the full history that
622 went along with it), you can do so with a regular
623 `cp -a git-tutorial new-git-tutorial`.
624+
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100625Note that when you've moved or copied a Git repository, your Git index
J. Bruce Fields927a5032006-01-22 23:57:25 -0500626file (which caches various information, notably some of the "stat"
627information for the files involved) will likely need to be refreshed.
628So after you do a `cp -a` to create a new copy, you'll want to do
629+
630----------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500631$ git update-index --refresh
J. Bruce Fields927a5032006-01-22 23:57:25 -0500632----------------
633+
Martin Ågren7560f542017-08-23 19:49:35 +0200634in the new repository to make sure that the index file is up to date.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500635
636Note that the second point is true even across machines. You can
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100637duplicate a remote Git repository with *any* regular copy mechanism, be it
Jonathan Nieder2fd02c92008-07-03 00:55:07 -0500638'scp', 'rsync' or 'wget'.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500639
640When copying a remote repository, you'll want to at a minimum update the
641index cache when you do this, and especially with other peoples'
642repositories you often want to make sure that the index cache is in some
643known state (you don't know *what* they've done and not yet checked in),
Thomas Rast0b444cd2010-01-10 00:33:00 +0100644so usually you'll precede the 'git update-index' with a
J. Bruce Fields927a5032006-01-22 23:57:25 -0500645
646----------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500647$ git read-tree --reset HEAD
648$ git update-index --refresh
J. Bruce Fields927a5032006-01-22 23:57:25 -0500649----------------
650
651which will force a total index re-build from the tree pointed to by `HEAD`.
Thomas Rast0b444cd2010-01-10 00:33:00 +0100652It resets the index contents to `HEAD`, and then the 'git update-index'
J. Bruce Fields927a5032006-01-22 23:57:25 -0500653makes sure to match up all index entries with the checked-out files.
654If the original repository had uncommitted changes in its
Jonathan Niederb1889c32008-06-30 01:09:04 -0500655working tree, `git update-index --refresh` notices them and
J. Bruce Fields927a5032006-01-22 23:57:25 -0500656tells you they need to be updated.
657
658The above can also be written as simply
659
660----------------
661$ git reset
662----------------
663
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100664and in fact a lot of the common Git command combinations can be scripted
J. Bruce Fields927a5032006-01-22 23:57:25 -0500665with the `git xyz` interfaces. You can learn things by just looking
Benoit Sigoure3b274282007-10-29 08:00:32 +0100666at what the various git scripts do. For example, `git reset` used to be
Thomas Rast0b444cd2010-01-10 00:33:00 +0100667the above two lines implemented in 'git reset', but some things like
668'git status' and 'git commit' are slightly more complex scripts around
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100669the basic Git commands.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500670
671Many (most?) public remote repositories will not contain any of
672the checked out files or even an index file, and will *only* contain the
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100673actual core Git files. Such a repository usually doesn't even have the
674`.git` subdirectory, but has all the Git files directly in the
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700675repository.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500676
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100677To create your own local live copy of such a "raw" Git repository, you'd
J. Bruce Fields927a5032006-01-22 23:57:25 -0500678first create your own subdirectory for the project, and then copy the
679raw repository contents into the `.git` directory. For example, to
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100680create your own copy of the Git repository, you'd do the following
J. Bruce Fields927a5032006-01-22 23:57:25 -0500681
682----------------
683$ mkdir my-git
684$ cd my-git
685$ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
686----------------
687
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700688followed by
J. Bruce Fields927a5032006-01-22 23:57:25 -0500689
690----------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500691$ git read-tree HEAD
J. Bruce Fields927a5032006-01-22 23:57:25 -0500692----------------
693
694to populate the index. However, now you have populated the index, and
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100695you have all the Git internal files, but you will notice that you don't
J. Bruce Fields927a5032006-01-22 23:57:25 -0500696actually have any of the working tree files to work on. To get
697those, you'd check them out with
698
699----------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500700$ git checkout-index -u -a
J. Bruce Fields927a5032006-01-22 23:57:25 -0500701----------------
702
703where the `-u` flag means that you want the checkout to keep the index
Martin Ågren7560f542017-08-23 19:49:35 +0200704up to date (so that you don't have to refresh it afterward), and the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500705`-a` flag means "check out all files" (if you have a stale copy or an
706older version of a checked out tree you may also need to add the `-f`
Thomas Rast0b444cd2010-01-10 00:33:00 +0100707flag first, to tell 'git checkout-index' to *force* overwriting of any old
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700708files).
J. Bruce Fields927a5032006-01-22 23:57:25 -0500709
710Again, this can all be simplified with
711
712----------------
Jeff King0d0bac62016-01-30 02:21:26 -0500713$ git clone git://git.kernel.org/pub/scm/git/git.git/ my-git
J. Bruce Fields927a5032006-01-22 23:57:25 -0500714$ cd my-git
715$ git checkout
716----------------
717
718which will end up doing all of the above for you.
719
720You have now successfully copied somebody else's (mine) remote
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700721repository, and checked it out.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500722
723
724Creating a new branch
725---------------------
726
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100727Branches in Git are really nothing more than pointers into the Git
J. Bruce Fields927a5032006-01-22 23:57:25 -0500728object database from within the `.git/refs/` subdirectory, and as we
729already discussed, the `HEAD` branch is nothing but a symlink to one of
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700730these object pointers.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500731
732You can at any time create a new branch by just picking an arbitrary
Thomas Ackermannd5fa1f12013-04-15 19:49:04 +0200733point in the project history, and just writing the SHA-1 name of that
J. Bruce Fields927a5032006-01-22 23:57:25 -0500734object into a file under `.git/refs/heads/`. You can use any filename you
735want (and indeed, subdirectories), but the convention is that the
736"normal" branch is called `master`. That's just a convention, though,
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700737and nothing enforces it.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500738
739To show that as an example, let's go back to the git-tutorial repository we
740used earlier, and create a branch in it. You do that by simply just
741saying that you want to check out a new branch:
742
743------------
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +0700744$ git switch -c mybranch
J. Bruce Fields927a5032006-01-22 23:57:25 -0500745------------
746
747will create a new branch based at the current `HEAD` position, and switch
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700748to it.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500749
750[NOTE]
751================================================
752If you make the decision to start your new branch at some
753other point in the history than the current `HEAD`, you can do so by
Heba Waly1a7e4542020-01-08 00:31:36 +0000754just telling 'git switch' what the base of the checkout would be.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500755In other words, if you have an earlier tag or branch, you'd just do
756
757------------
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +0700758$ git switch -c mybranch earlier-commit
J. Bruce Fields927a5032006-01-22 23:57:25 -0500759------------
760
761and it would create the new branch `mybranch` at the earlier commit,
762and check out the state at that time.
763================================================
764
765You can always just jump back to your original `master` branch by doing
766
767------------
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +0700768$ git switch master
J. Bruce Fields927a5032006-01-22 23:57:25 -0500769------------
770
771(or any other branch-name, for that matter) and if you forget which
772branch you happen to be on, a simple
773
774------------
J. Bruce Fields927a5032006-01-22 23:57:25 -0500775$ cat .git/HEAD
776------------
777
Junio C Hamano960c7022006-02-06 12:27:33 -0800778will tell you where it's pointing. To get the list of branches
779you have, you can say
J. Bruce Fields927a5032006-01-22 23:57:25 -0500780
781------------
782$ git branch
783------------
784
Benoit Sigoure3b274282007-10-29 08:00:32 +0100785which used to be nothing more than a simple script around `ls .git/refs/heads`.
786There will be an asterisk in front of the branch you are currently on.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500787
788Sometimes you may wish to create a new branch _without_ actually
789checking it out and switching to it. If so, just use the command
790
791------------
792$ git branch <branchname> [startingpoint]
793------------
794
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700795which will simply _create_ the branch, but will not do anything further.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500796You can then later -- once you decide that you want to actually develop
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +0700797on that branch -- switch to that branch with a regular 'git switch'
J. Bruce Fields927a5032006-01-22 23:57:25 -0500798with the branchname as the argument.
799
800
801Merging two branches
802--------------------
803
804One of the ideas of having a branch is that you do some (possibly
805experimental) work in it, and eventually merge it back to the main
806branch. So assuming you created the above `mybranch` that started out
807being the same as the original `master` branch, let's make sure we're in
808that branch, and do some work there.
809
810------------------------------------------------
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +0700811$ git switch mybranch
J. Bruce Fields927a5032006-01-22 23:57:25 -0500812$ echo "Work, work, work" >>hello
Sergei Organovd336fc02007-11-02 20:12:57 +0300813$ git commit -m "Some work." -i hello
J. Bruce Fields927a5032006-01-22 23:57:25 -0500814------------------------------------------------
815
816Here, we just added another line to `hello`, and we used a shorthand for
Jonathan Niederb1889c32008-06-30 01:09:04 -0500817doing both `git update-index hello` and `git commit` by just giving the
Junio C Hamano960c7022006-02-06 12:27:33 -0800818filename directly to `git commit`, with an `-i` flag (it tells
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100819Git to 'include' that file in addition to what you have done to
Junio C Hamano960c7022006-02-06 12:27:33 -0800820the index file so far when making the commit). The `-m` flag is to give the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500821commit log message from the command line.
822
823Now, to make it a bit more interesting, let's assume that somebody else
824does some work in the original branch, and simulate that by going back
825to the master branch, and editing the same file differently there:
826
827------------
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +0700828$ git switch master
J. Bruce Fields927a5032006-01-22 23:57:25 -0500829------------
830
831Here, take a moment to look at the contents of `hello`, and notice how they
832don't contain the work we just did in `mybranch` -- because that work
833hasn't happened in the `master` branch at all. Then do
834
835------------
836$ echo "Play, play, play" >>hello
837$ echo "Lots of fun" >>example
Sergei Organovd336fc02007-11-02 20:12:57 +0300838$ git commit -m "Some fun." -i hello example
J. Bruce Fields927a5032006-01-22 23:57:25 -0500839------------
840
841since the master branch is obviously in a much better mood.
842
843Now, you've got two branches, and you decide that you want to merge the
844work done. Before we do that, let's introduce a cool graphical tool that
845helps you view what's going on:
846
847----------------
848$ gitk --all
849----------------
850
Jeff King6cf378f2012-04-26 04:51:57 -0400851will show you graphically both of your branches (that's what the `--all`
J. Bruce Fields927a5032006-01-22 23:57:25 -0500852means: normally it will just show you your current `HEAD`) and their
853histories. You can also see exactly how they came to be from a common
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700854source.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500855
Jonathan Nieder42d36bb2008-07-03 00:49:55 -0500856Anyway, let's exit 'gitk' (`^Q` or the File menu), and decide that we want
J. Bruce Fields927a5032006-01-22 23:57:25 -0500857to merge the work we did on the `mybranch` branch into the `master`
858branch (which is currently our `HEAD` too). To do that, there's a nice
Thomas Rast0b444cd2010-01-10 00:33:00 +0100859script called 'git merge', which wants to know which branches you want
J. Bruce Fields927a5032006-01-22 23:57:25 -0500860to resolve and what the merge is all about:
861
862------------
Sergei Organovba178922007-10-30 22:54:02 +0300863$ git merge -m "Merge work in mybranch" mybranch
J. Bruce Fields927a5032006-01-22 23:57:25 -0500864------------
865
866where the first argument is going to be used as the commit message if
867the merge can be resolved automatically.
868
869Now, in this case we've intentionally created a situation where the
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100870merge will need to be fixed up by hand, though, so Git will do as much
J. Bruce Fields927a5032006-01-22 23:57:25 -0500871of it as it can automatically (which in this case is just merge the `example`
872file, which had no differences in the `mybranch` branch), and say:
873
874----------------
Junio C Hamanoa6080a02007-06-07 00:04:01 -0700875 Auto-merging hello
876 CONFLICT (content): Merge conflict in hello
Markus Heidelbergec9f0ea2008-12-19 13:14:52 +0100877 Automatic merge failed; fix conflicts and then commit the result.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500878----------------
879
Junio C Hamano5fe3acc2007-01-14 21:31:30 -0800880It tells you that it did an "Automatic merge", which
881failed due to conflicts in `hello`.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500882
883Not to worry. It left the (trivial) conflict in `hello` in the same form you
884should already be well used to if you've ever used CVS, so let's just
885open `hello` in our editor (whatever that may be), and fix it up somehow.
886I'd suggest just making it so that `hello` contains all four lines:
887
888------------
889Hello World
890It's a new day for git
891Play, play, play
892Work, work, work
893------------
894
895and once you're happy with your manual merge, just do a
896
897------------
Junio C Hamano130fcca2006-02-05 00:07:44 -0800898$ git commit -i hello
J. Bruce Fields927a5032006-01-22 23:57:25 -0500899------------
900
901which will very loudly warn you that you're now committing a merge
902(which is correct, so never mind), and you can write a small merge
Thomas Rast0b444cd2010-01-10 00:33:00 +0100903message about your adventures in 'git merge'-land.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500904
Jeff King6cf378f2012-04-26 04:51:57 -0400905After you're done, start up `gitk --all` to see graphically what the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500906history looks like. Notice that `mybranch` still exists, and you can
907switch to it, and continue to work with it if you want to. The
908`mybranch` branch will not contain the merge, but next time you merge it
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100909from the `master` branch, Git will know how you merged it, so you'll not
J. Bruce Fields927a5032006-01-22 23:57:25 -0500910have to do _that_ merge again.
911
912Another useful tool, especially if you do not always work in X-Window
913environment, is `git show-branch`.
914
915------------------------------------------------
Jonathan Niederb1889c32008-06-30 01:09:04 -0500916$ git show-branch --topo-order --more=1 master mybranch
J. Bruce Fields927a5032006-01-22 23:57:25 -0500917* [master] Merge work in mybranch
918 ! [mybranch] Some work.
919--
920- [master] Merge work in mybranch
921*+ [mybranch] Some work.
Sergei Organov2782c932007-11-08 18:10:28 +0300922* [master^] Some fun.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500923------------------------------------------------
924
925The first two lines indicate that it is showing the two branches
Jeremy White52ffe992012-09-13 17:27:09 -0500926with the titles of their top-of-the-tree commits, you are currently on
927`master` branch (notice the asterisk `*` character), and the first
928column for the later output lines is used to show commits contained in the
J. Bruce Fields927a5032006-01-22 23:57:25 -0500929`master` branch, and the second column for the `mybranch`
Jeremy White52ffe992012-09-13 17:27:09 -0500930branch. Three commits are shown along with their titles.
Jeff King6cf378f2012-04-26 04:51:57 -0400931All of them have non blank characters in the first column (`*`
Benoit Sigoure3b274282007-10-29 08:00:32 +0100932shows an ordinary commit on the current branch, `-` is a merge commit), which
J. Bruce Fields927a5032006-01-22 23:57:25 -0500933means they are now part of the `master` branch. Only the "Some
934work" commit has the plus `+` character in the second column,
935because `mybranch` has not been merged to incorporate these
936commits from the master branch. The string inside brackets
937before the commit log message is a short name you can use to
938name the commit. In the above example, 'master' and 'mybranch'
Sergei Organov2782c932007-11-08 18:10:28 +0300939are branch heads. 'master^' is the first parent of 'master'
Jonathan Nieder9d83e382010-10-11 11:03:32 -0500940branch head. Please see linkgit:gitrevisions[7] if you want to
J. Bruce Fields927a5032006-01-22 23:57:25 -0500941see more complex cases.
942
Sergei Organov2782c932007-11-08 18:10:28 +0300943[NOTE]
Thomas Rast0b444cd2010-01-10 00:33:00 +0100944Without the '--more=1' option, 'git show-branch' would not output the
Sergei Organov2782c932007-11-08 18:10:28 +0300945'[master^]' commit, as '[mybranch]' commit is a common ancestor of
Jonathan Nieder483bc4f2008-06-30 13:56:34 -0500946both 'master' and 'mybranch' tips. Please see linkgit:git-show-branch[1]
947for details.
Sergei Organov2782c932007-11-08 18:10:28 +0300948
949[NOTE]
950If there were more commits on the 'master' branch after the merge, the
Thomas Rast0b444cd2010-01-10 00:33:00 +0100951merge commit itself would not be shown by 'git show-branch' by
Matthieu Moybcf96262016-06-28 13:40:11 +0200952default. You would need to provide `--sparse` option to make the
Sergei Organov2782c932007-11-08 18:10:28 +0300953merge commit visible in this case.
954
J. Bruce Fields927a5032006-01-22 23:57:25 -0500955Now, let's pretend you are the one who did all the work in
956`mybranch`, and the fruit of your hard work has finally been merged
957to the `master` branch. Let's go back to `mybranch`, and run
Thomas Rast0b444cd2010-01-10 00:33:00 +0100958'git merge' to get the "upstream changes" back to your branch.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500959
960------------
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +0700961$ git switch mybranch
Sergei Organovba178922007-10-30 22:54:02 +0300962$ git merge -m "Merge upstream changes." master
J. Bruce Fields927a5032006-01-22 23:57:25 -0500963------------
964
965This outputs something like this (the actual commit object names
966would be different)
967
968----------------
969Updating from ae3a2da... to a80b4aa....
Felipe Contrerasa75d7b52009-10-24 11:31:32 +0300970Fast-forward (no commit created; -m option ignored)
Zbigniew Jędrzejewski-Szmekdc801e72012-04-30 22:38:58 +0200971 example | 1 +
972 hello | 1 +
Nguyễn Thái Ngọc Duy7f814632012-02-01 19:55:07 +0700973 2 files changed, 2 insertions(+)
J. Bruce Fields927a5032006-01-22 23:57:25 -0500974----------------
975
Markus Heidelberg04c8ce92008-12-19 13:14:18 +0100976Because your branch did not contain anything more than what had
977already been merged into the `master` branch, the merge operation did
J. Bruce Fields927a5032006-01-22 23:57:25 -0500978not actually do a merge. Instead, it just updated the top of
979the tree of your branch to that of the `master` branch. This is
Felipe Contrerasa75d7b52009-10-24 11:31:32 +0300980often called 'fast-forward' merge.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500981
Jeff King6cf378f2012-04-26 04:51:57 -0400982You can run `gitk --all` again to see how the commit ancestry
Jonathan Nieder5833d732008-07-03 00:59:09 -0500983looks like, or run 'show-branch', which tells you this.
J. Bruce Fields927a5032006-01-22 23:57:25 -0500984
985------------------------------------------------
986$ git show-branch master mybranch
987! [master] Merge work in mybranch
988 * [mybranch] Merge work in mybranch
989--
990-- [master] Merge work in mybranch
991------------------------------------------------
992
993
994Merging external work
995---------------------
996
997It's usually much more common that you merge with somebody else than
Thomas Ackermann2de9b712013-01-21 20:17:53 +0100998merging with your own branches, so it's worth pointing out that Git
J. Bruce Fields927a5032006-01-22 23:57:25 -0500999makes that very easy too, and in fact, it's not that different from
Thomas Rast0b444cd2010-01-10 00:33:00 +01001000doing a 'git merge'. In fact, a remote merge ends up being nothing
J. Bruce Fields927a5032006-01-22 23:57:25 -05001001more than "fetch the work from a remote repository into a temporary tag"
Thomas Rast0b444cd2010-01-10 00:33:00 +01001002followed by a 'git merge'.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001003
1004Fetching from a remote repository is done by, unsurprisingly,
Thomas Rast0b444cd2010-01-10 00:33:00 +01001005'git fetch':
J. Bruce Fields927a5032006-01-22 23:57:25 -05001006
1007----------------
1008$ git fetch <remote-repository>
1009----------------
1010
1011One of the following transports can be used to name the
1012repository to download from:
1013
J. Bruce Fields927a5032006-01-22 23:57:25 -05001014SSH::
1015 `remote.machine:/path/to/repo.git/` or
1016+
1017`ssh://remote.machine/path/to/repo.git/`
1018+
1019This transport can be used for both uploading and downloading,
1020and requires you to have a log-in privilege over `ssh` to the
1021remote machine. It finds out the set of objects the other side
1022lacks by exchanging the head commits both ends have and
1023transfers (close to) minimum set of objects. It is by far the
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001024most efficient way to exchange Git objects between repositories.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001025
1026Local directory::
1027 `/path/to/repo.git/`
1028+
Jonathan Nieder2fd02c92008-07-03 00:55:07 -05001029This transport is the same as SSH transport but uses 'sh' to run
J. Bruce Fields927a5032006-01-22 23:57:25 -05001030both ends on the local machine instead of running other end on
Jonathan Nieder2fd02c92008-07-03 00:55:07 -05001031the remote machine via 'ssh'.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001032
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001033Git Native::
J. Bruce Fields927a5032006-01-22 23:57:25 -05001034 `git://remote.machine/path/to/repo.git/`
1035+
1036This transport was designed for anonymous downloading. Like SSH
1037transport, it finds out the set of objects the downstream side
1038lacks and transfers (close to) minimum set of objects.
1039
1040HTTP(S)::
1041 `http://remote.machine/path/to/repo.git/`
1042+
1043Downloader from http and https URL
1044first obtains the topmost commit object name from the remote site
1045by looking at the specified refname under `repo.git/refs/` directory,
1046and then tries to obtain the
Jonathan Nieder70676e62010-08-20 05:37:51 -05001047commit object by downloading from `repo.git/objects/xx/xxx...`
J. Bruce Fields927a5032006-01-22 23:57:25 -05001048using the object name of that commit object. Then it reads the
1049commit object to find out its parent commits and the associate
1050tree object; it repeats this process until it gets all the
Horst H. von Brandabda1ef2006-06-03 16:27:26 -04001051necessary objects. Because of this behavior, they are
J. Bruce Fields927a5032006-01-22 23:57:25 -05001052sometimes also called 'commit walkers'.
1053+
1054The 'commit walkers' are sometimes also called 'dumb
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001055transports', because they do not require any Git aware smart
1056server like Git Native transport does. Any stock HTTP server
J. Bruce Fields927a5032006-01-22 23:57:25 -05001057that does not even support directory index would suffice. But
Thomas Rast0b444cd2010-01-10 00:33:00 +01001058you must prepare your repository with 'git update-server-info'
J. Bruce Fields927a5032006-01-22 23:57:25 -05001059to help dumb transport downloaders.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001060
Junio C Hamano207dfa02007-02-07 10:37:03 -08001061Once you fetch from the remote repository, you `merge` that
J. Bruce Fields927a5032006-01-22 23:57:25 -05001062with your current branch.
1063
1064However -- it's such a common thing to `fetch` and then
Junio C Hamano207dfa02007-02-07 10:37:03 -08001065immediately `merge`, that it's called `git pull`, and you can
J. Bruce Fields927a5032006-01-22 23:57:25 -05001066simply do
1067
1068----------------
1069$ git pull <remote-repository>
1070----------------
1071
1072and optionally give a branch-name for the remote end as a second
1073argument.
1074
1075[NOTE]
1076You could do without using any branches at all, by
1077keeping as many local repositories as you would like to have
Thomas Rast0b444cd2010-01-10 00:33:00 +01001078branches, and merging between them with 'git pull', just like
J. Bruce Fields927a5032006-01-22 23:57:25 -05001079you merge between branches. The advantage of this approach is
Mike Colemanaacd4042007-02-02 00:25:30 -06001080that it lets you keep a set of files for each `branch` checked
J. Bruce Fields927a5032006-01-22 23:57:25 -05001081out and you may find it easier to switch back and forth if you
1082juggle multiple lines of development simultaneously. Of
1083course, you will pay the price of more disk usage to hold
1084multiple working trees, but disk space is cheap these days.
1085
J. Bruce Fields927a5032006-01-22 23:57:25 -05001086It is likely that you will be pulling from the same remote
1087repository from time to time. As a short hand, you can store
Nicolas Pitrec14261e2007-01-14 22:44:18 -05001088the remote repository URL in the local repository's config file
1089like this:
J. Bruce Fields927a5032006-01-22 23:57:25 -05001090
1091------------------------------------------------
Tom Princee0d10e12007-01-28 16:16:53 -08001092$ git config remote.linus.url http://www.kernel.org/pub/scm/git/git.git/
J. Bruce Fields927a5032006-01-22 23:57:25 -05001093------------------------------------------------
1094
Thomas Rast0b444cd2010-01-10 00:33:00 +01001095and use the "linus" keyword with 'git pull' instead of the full URL.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001096
1097Examples.
1098
1099. `git pull linus`
1100. `git pull linus tag v0.99.1`
J. Bruce Fields927a5032006-01-22 23:57:25 -05001101
1102the above are equivalent to:
1103
1104. `git pull http://www.kernel.org/pub/scm/git/git.git/ HEAD`
1105. `git pull http://www.kernel.org/pub/scm/git/git.git/ tag v0.99.1`
J. Bruce Fields927a5032006-01-22 23:57:25 -05001106
1107
1108How does the merge work?
1109------------------------
1110
1111We said this tutorial shows what plumbing does to help you cope
1112with the porcelain that isn't flushing, but we so far did not
1113talk about how the merge really works. If you are following
1114this tutorial the first time, I'd suggest to skip to "Publishing
1115your work" section and come back here later.
1116
1117OK, still with me? To give us an example to look at, let's go
1118back to the earlier repository with "hello" and "example" file,
1119and bring ourselves back to the pre-merge state:
1120
1121------------
Sergei Organov065c5ac2007-11-10 16:17:33 +03001122$ git show-branch --more=2 master mybranch
J. Bruce Fields927a5032006-01-22 23:57:25 -05001123! [master] Merge work in mybranch
1124 * [mybranch] Merge work in mybranch
1125--
1126-- [master] Merge work in mybranch
1127+* [master^2] Some work.
1128+* [master^] Some fun.
1129------------
1130
Thomas Rast0b444cd2010-01-10 00:33:00 +01001131Remember, before running 'git merge', our `master` head was at
J. Bruce Fields927a5032006-01-22 23:57:25 -05001132"Some fun." commit, while our `mybranch` head was at "Some
1133work." commit.
1134
1135------------
Nguyễn Thái Ngọc Duy328c6cb2019-03-29 17:39:19 +07001136$ git switch -C mybranch master^2
1137$ git switch master
J. Bruce Fields927a5032006-01-22 23:57:25 -05001138$ git reset --hard master^
1139------------
1140
1141After rewinding, the commit structure should look like this:
1142
1143------------
1144$ git show-branch
1145* [master] Some fun.
1146 ! [mybranch] Some work.
1147--
J. Bruce Fields927a5032006-01-22 23:57:25 -05001148* [master] Some fun.
Nanako Shiraishi5d166cc2009-11-25 08:08:08 +09001149 + [mybranch] Some work.
1150*+ [master^] Initial commit
J. Bruce Fields927a5032006-01-22 23:57:25 -05001151------------
1152
1153Now we are ready to experiment with the merge by hand.
1154
1155`git merge` command, when merging two branches, uses 3-way merge
1156algorithm. First, it finds the common ancestor between them.
Thomas Rast0b444cd2010-01-10 00:33:00 +01001157The command it uses is 'git merge-base':
J. Bruce Fields927a5032006-01-22 23:57:25 -05001158
1159------------
Jonathan Niederb1889c32008-06-30 01:09:04 -05001160$ mb=$(git merge-base HEAD mybranch)
J. Bruce Fields927a5032006-01-22 23:57:25 -05001161------------
1162
1163The command writes the commit object name of the common ancestor
1164to the standard output, so we captured its output to a variable,
Benoit Sigoure3b274282007-10-29 08:00:32 +01001165because we will be using it in the next step. By the way, the common
Stephen Boyd7c5858a2009-11-04 22:33:53 -08001166ancestor commit is the "Initial commit" commit in this case. You can
J. Bruce Fields927a5032006-01-22 23:57:25 -05001167tell it by:
1168
1169------------
Stephen Boyd7c5858a2009-11-04 22:33:53 -08001170$ git name-rev --name-only --tags $mb
J. Bruce Fields927a5032006-01-22 23:57:25 -05001171my-first-tag
1172------------
1173
1174After finding out a common ancestor commit, the second step is
1175this:
1176
1177------------
Jonathan Niederb1889c32008-06-30 01:09:04 -05001178$ git read-tree -m -u $mb HEAD mybranch
J. Bruce Fields927a5032006-01-22 23:57:25 -05001179------------
1180
Thomas Rast0b444cd2010-01-10 00:33:00 +01001181This is the same 'git read-tree' command we have already seen,
J. Bruce Fields927a5032006-01-22 23:57:25 -05001182but it takes three trees, unlike previous examples. This reads
1183the contents of each tree into different 'stage' in the index
Sergei Organov065c5ac2007-11-10 16:17:33 +03001184file (the first tree goes to stage 1, the second to stage 2,
J. Bruce Fields927a5032006-01-22 23:57:25 -05001185etc.). After reading three trees into three stages, the paths
1186that are the same in all three stages are 'collapsed' into stage
11870. Also paths that are the same in two of three stages are
Thomas Ackermannd5fa1f12013-04-15 19:49:04 +02001188collapsed into stage 0, taking the SHA-1 from either stage 2 or
J. Bruce Fields927a5032006-01-22 23:57:25 -05001189stage 3, whichever is different from stage 1 (i.e. only one side
1190changed from the common ancestor).
1191
1192After 'collapsing' operation, paths that are different in three
1193trees are left in non-zero stages. At this point, you can
1194inspect the index file with this command:
1195
1196------------
Jonathan Niederb1889c32008-06-30 01:09:04 -05001197$ git ls-files --stage
J. Bruce Fields927a5032006-01-22 23:57:25 -05001198100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
Stephen Boyd7c5858a2009-11-04 22:33:53 -08001199100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1 hello
1200100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2 hello
J. Bruce Fields927a5032006-01-22 23:57:25 -05001201100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1202------------
1203
1204In our example of only two files, we did not have unchanged
Jon Loeliger323b9db2009-01-12 14:02:07 -06001205files so only 'example' resulted in collapsing. But in real-life
1206large projects, when only a small number of files change in one commit,
1207this 'collapsing' tends to trivially merge most of the paths
1208fairly quickly, leaving only a handful of real changes in non-zero
J. Bruce Fields927a5032006-01-22 23:57:25 -05001209stages.
1210
Jeff King6cf378f2012-04-26 04:51:57 -04001211To look at only non-zero stages, use `--unmerged` flag:
J. Bruce Fields927a5032006-01-22 23:57:25 -05001212
1213------------
Jonathan Niederb1889c32008-06-30 01:09:04 -05001214$ git ls-files --unmerged
Stephen Boyd7c5858a2009-11-04 22:33:53 -08001215100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1 hello
1216100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2 hello
J. Bruce Fields927a5032006-01-22 23:57:25 -05001217100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1218------------
1219
1220The next step of merging is to merge these three versions of the
1221file, using 3-way merge. This is done by giving
Thomas Rast0b444cd2010-01-10 00:33:00 +01001222'git merge-one-file' command as one of the arguments to
1223'git merge-index' command:
J. Bruce Fields927a5032006-01-22 23:57:25 -05001224
1225------------
Jonathan Niederb1889c32008-06-30 01:09:04 -05001226$ git merge-index git-merge-one-file hello
Markus Heidelbergec9f0ea2008-12-19 13:14:52 +01001227Auto-merging hello
1228ERROR: Merge conflict in hello
J. Bruce Fields927a5032006-01-22 23:57:25 -05001229fatal: merge program failed
1230------------
1231
Thomas Rast0b444cd2010-01-10 00:33:00 +01001232'git merge-one-file' script is called with parameters to
J. Bruce Fields927a5032006-01-22 23:57:25 -05001233describe those three versions, and is responsible to leave the
1234merge results in the working tree.
1235It is a fairly straightforward shell script, and
Jonathan Nieder2fd02c92008-07-03 00:55:07 -05001236eventually calls 'merge' program from RCS suite to perform a
1237file-level 3-way merge. In this case, 'merge' detects
J. Bruce Fields927a5032006-01-22 23:57:25 -05001238conflicts, and the merge result with conflict marks is left in
1239the working tree.. This can be seen if you run `ls-files
1240--stage` again at this point:
1241
1242------------
Jonathan Niederb1889c32008-06-30 01:09:04 -05001243$ git ls-files --stage
J. Bruce Fields927a5032006-01-22 23:57:25 -05001244100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
Stephen Boyd7c5858a2009-11-04 22:33:53 -08001245100644 557db03de997c86a4a028e1ebd3a1ceb225be238 1 hello
1246100644 ba42a2a96e3027f3333e13ede4ccf4498c3ae942 2 hello
J. Bruce Fields927a5032006-01-22 23:57:25 -05001247100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1248------------
1249
1250This is the state of the index file and the working file after
Thomas Rast0b444cd2010-01-10 00:33:00 +01001251'git merge' returns control back to you, leaving the conflicting
J. Bruce Fields927a5032006-01-22 23:57:25 -05001252merge for you to resolve. Notice that the path `hello` is still
Thomas Rast0b444cd2010-01-10 00:33:00 +01001253unmerged, and what you see with 'git diff' at this point is
J. Bruce Fields927a5032006-01-22 23:57:25 -05001254differences since stage 2 (i.e. your version).
1255
1256
1257Publishing your work
1258--------------------
1259
Mike Colemanaacd4042007-02-02 00:25:30 -06001260So, we can use somebody else's work from a remote repository, but
J. Bruce Fields927a5032006-01-22 23:57:25 -05001261how can *you* prepare a repository to let other people pull from
1262it?
1263
Luiz Fernando N. Capitulino79dbbed2007-04-25 11:18:28 -03001264You do your real work in your working tree that has your
J. Bruce Fields927a5032006-01-22 23:57:25 -05001265primary repository hanging under it as its `.git` subdirectory.
1266You *could* make that repository accessible remotely and ask
1267people to pull from it, but in practice that is not the way
1268things are usually done. A recommended way is to have a public
1269repository, make it reachable by other people, and when the
1270changes you made in your primary working tree are in good shape,
1271update the public repository from it. This is often called
1272'pushing'.
1273
1274[NOTE]
1275This public repository could further be mirrored, and that is
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001276how Git repositories at `kernel.org` are managed.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001277
1278Publishing the changes from your local (private) repository to
1279your remote (public) repository requires a write privilege on
1280the remote machine. You need to have an SSH account there to
Jonathan Niederba020ef2008-07-03 00:41:41 -05001281run a single command, 'git-receive-pack'.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001282
1283First, you need to create an empty repository on the remote
1284machine that will house your public repository. This empty
Martin Ågren7560f542017-08-23 19:49:35 +02001285repository will be populated and be kept up to date by pushing
J. Bruce Fields927a5032006-01-22 23:57:25 -05001286into it later. Obviously, this repository creation needs to be
1287done only once.
1288
1289[NOTE]
Thomas Rast0b444cd2010-01-10 00:33:00 +01001290'git push' uses a pair of commands,
1291'git send-pack' on your local machine, and 'git-receive-pack'
J. Bruce Fields927a5032006-01-22 23:57:25 -05001292on the remote machine. The communication between the two over
1293the network internally uses an SSH connection.
1294
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001295Your private repository's Git directory is usually `.git`, but
J. Bruce Fields927a5032006-01-22 23:57:25 -05001296your public repository is often named after the project name,
1297i.e. `<project>.git`. Let's create such a public repository for
1298project `my-git`. After logging into the remote machine, create
1299an empty directory:
1300
1301------------
1302$ mkdir my-git.git
1303------------
1304
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001305Then, make that directory into a Git repository by running
Thomas Rast0b444cd2010-01-10 00:33:00 +01001306'git init', but this time, since its name is not the usual
J. Bruce Fields927a5032006-01-22 23:57:25 -05001307`.git`, we do things slightly differently:
1308
1309------------
Jonathan Niederb1889c32008-06-30 01:09:04 -05001310$ GIT_DIR=my-git.git git init
J. Bruce Fields927a5032006-01-22 23:57:25 -05001311------------
1312
1313Make sure this directory is available for others you want your
Markus Heidelberg04c8ce92008-12-19 13:14:18 +01001314changes to be pulled via the transport of your choice. Also
Jonathan Niederba020ef2008-07-03 00:41:41 -05001315you need to make sure that you have the 'git-receive-pack'
J. Bruce Fields927a5032006-01-22 23:57:25 -05001316program on the `$PATH`.
1317
1318[NOTE]
1319Many installations of sshd do not invoke your shell as the login
1320shell when you directly run programs; what this means is that if
Jonathan Nieder2fd02c92008-07-03 00:55:07 -05001321your login shell is 'bash', only `.bashrc` is read and not
J. Bruce Fields927a5032006-01-22 23:57:25 -05001322`.bash_profile`. As a workaround, make sure `.bashrc` sets up
Jonathan Niederba020ef2008-07-03 00:41:41 -05001323`$PATH` so that you can run 'git-receive-pack' program.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001324
1325[NOTE]
1326If you plan to publish this repository to be accessed over http,
Petr Baudis7dce9912008-08-12 00:34:46 +02001327you should do `mv my-git.git/hooks/post-update.sample
1328my-git.git/hooks/post-update` at this point.
1329This makes sure that every time you push into this
Jonathan Niederb1889c32008-06-30 01:09:04 -05001330repository, `git update-server-info` is run.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001331
1332Your "public repository" is now ready to accept your changes.
1333Come back to the machine you have your private repository. From
1334there, run this command:
1335
1336------------
1337$ git push <public-host>:/path/to/my-git.git master
1338------------
1339
1340This synchronizes your public repository to match the named
1341branch head (i.e. `master` in this case) and objects reachable
1342from them in your current repository.
1343
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001344As a real example, this is how I update my public Git
J. Bruce Fields927a5032006-01-22 23:57:25 -05001345repository. Kernel.org mirror network takes care of the
1346propagation to other publicly visible machines:
1347
1348------------
Junio C Hamanoa6080a02007-06-07 00:04:01 -07001349$ git push master.kernel.org:/pub/scm/git/git.git/
J. Bruce Fields927a5032006-01-22 23:57:25 -05001350------------
1351
1352
1353Packing your repository
1354-----------------------
1355
1356Earlier, we saw that one file under `.git/objects/??/` directory
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001357is stored for each Git object you create. This representation
J. Bruce Fields927a5032006-01-22 23:57:25 -05001358is efficient to create atomically and safely, but
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001359not so convenient to transport over the network. Since Git objects are
J. Bruce Fields927a5032006-01-22 23:57:25 -05001360immutable once they are created, there is a way to optimize the
1361storage by "packing them together". The command
1362
1363------------
1364$ git repack
1365------------
1366
1367will do it for you. If you followed the tutorial examples, you
1368would have accumulated about 17 objects in `.git/objects/??/`
Thomas Rast0b444cd2010-01-10 00:33:00 +01001369directories by now. 'git repack' tells you how many objects it
Kristoffer Haugsbakk8b9bb332016-12-09 16:51:09 +01001370packed, and stores the packed file in the `.git/objects/pack`
J. Bruce Fields927a5032006-01-22 23:57:25 -05001371directory.
1372
1373[NOTE]
Jeff King6cf378f2012-04-26 04:51:57 -04001374You will see two files, `pack-*.pack` and `pack-*.idx`,
J. Bruce Fields927a5032006-01-22 23:57:25 -05001375in `.git/objects/pack` directory. They are closely related to
1376each other, and if you ever copy them by hand to a different
1377repository for whatever reason, you should make sure you copy
1378them together. The former holds all the data from the objects
1379in the pack, and the latter holds the index for random
1380access.
1381
Thomas Rast0b444cd2010-01-10 00:33:00 +01001382If you are paranoid, running 'git verify-pack' command would
J. Bruce Fields927a5032006-01-22 23:57:25 -05001383detect if you have a corrupt pack, but do not worry too much.
1384Our programs are always perfect ;-).
1385
1386Once you have packed objects, you do not need to leave the
1387unpacked objects that are contained in the pack file anymore.
1388
1389------------
1390$ git prune-packed
1391------------
1392
1393would remove them for you.
1394
1395You can try running `find .git/objects -type f` before and after
1396you run `git prune-packed` if you are curious. Also `git
1397count-objects` would tell you how many unpacked objects are in
1398your repository and how much space they are consuming.
1399
1400[NOTE]
1401`git pull` is slightly cumbersome for HTTP transport, as a
1402packed repository may contain relatively few objects in a
1403relatively large pack. If you expect many HTTP pulls from your
1404public repository you might want to repack & prune often, or
1405never.
1406
1407If you run `git repack` again at this point, it will say
Markus Heidelbergec9f0ea2008-12-19 13:14:52 +01001408"Nothing new to pack.". Once you continue your development and
J. Bruce Fields927a5032006-01-22 23:57:25 -05001409accumulate the changes, running `git repack` again will create a
1410new pack, that contains objects created since you packed your
1411repository the last time. We recommend that you pack your project
1412soon after the initial import (unless you are starting your
1413project from scratch), and then run `git repack` every once in a
1414while, depending on how active your project is.
1415
1416When a repository is synchronized via `git push` and `git pull`
1417objects packed in the source repository are usually stored
Jeff King0d0bac62016-01-30 02:21:26 -05001418unpacked in the destination.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001419While this allows you to use different packing strategies on
1420both ends, it also means you may need to repack both
1421repositories every once in a while.
1422
1423
1424Working with Others
1425-------------------
1426
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001427Although Git is a truly distributed system, it is often
J. Bruce Fields927a5032006-01-22 23:57:25 -05001428convenient to organize your project with an informal hierarchy
1429of developers. Linux kernel development is run this way. There
Junio C Hamano505739f2007-02-02 23:17:34 -08001430is a nice illustration (page 17, "Merges to Mainline") in
Jeff Kingf991c622017-04-20 16:33:49 -04001431https://web.archive.org/web/20120915203609/http://www.xenotime.net/linux/mentor/linux-mentoring-2006.pdf[Randy Dunlap's presentation].
J. Bruce Fields927a5032006-01-22 23:57:25 -05001432
1433It should be stressed that this hierarchy is purely *informal*.
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001434There is nothing fundamental in Git that enforces the "chain of
J. Bruce Fields927a5032006-01-22 23:57:25 -05001435patch flow" this hierarchy implies. You do not have to pull
1436from only one remote repository.
1437
1438A recommended workflow for a "project lead" goes like this:
1439
14401. Prepare your primary repository on your local machine. Your
1441 work is done there.
1442
14432. Prepare a public repository accessible to others.
1444+
1445If other people are pulling from your repository over dumb
1446transport protocols (HTTP), you need to keep this repository
Nicolas Pitre5c94f872007-01-12 16:01:46 -05001447'dumb transport friendly'. After `git init`,
Petr Baudis7dce9912008-08-12 00:34:46 +02001448`$GIT_DIR/hooks/post-update.sample` copied from the standard templates
Thomas Rast0b444cd2010-01-10 00:33:00 +01001449would contain a call to 'git update-server-info'
Petr Baudis7dce9912008-08-12 00:34:46 +02001450but you need to manually enable the hook with
1451`mv post-update.sample post-update`. This makes sure
Martin Ågren7560f542017-08-23 19:49:35 +02001452'git update-server-info' keeps the necessary files up to date.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001453
14543. Push into the public repository from your primary
1455 repository.
1456
Thomas Rast0b444cd2010-01-10 00:33:00 +010014574. 'git repack' the public repository. This establishes a big
J. Bruce Fields927a5032006-01-22 23:57:25 -05001458 pack that contains the initial set of objects as the
Thomas Rast0b444cd2010-01-10 00:33:00 +01001459 baseline, and possibly 'git prune' if the transport
J. Bruce Fields927a5032006-01-22 23:57:25 -05001460 used for pulling from your repository supports packed
1461 repositories.
1462
14635. Keep working in your primary repository. Your changes
1464 include modifications of your own, patches you receive via
1465 e-mails, and merges resulting from pulling the "public"
1466 repositories of your "subsystem maintainers".
1467+
1468You can repack this private repository whenever you feel like.
1469
14706. Push your changes to the public repository, and announce it
1471 to the public.
1472
Thomas Rast0b444cd2010-01-10 00:33:00 +010014737. Every once in a while, 'git repack' the public repository.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001474 Go back to step 5. and continue working.
1475
1476
1477A recommended work cycle for a "subsystem maintainer" who works
1478on that project and has an own "public repository" goes like this:
1479
Kristoffer Haugsbakkf383e4e2016-12-09 16:51:10 +010014801. Prepare your work repository, by running 'git clone' on the public
J. Bruce Fields927a5032006-01-22 23:57:25 -05001481 repository of the "project lead". The URL used for the
Nicolas Pitrec14261e2007-01-14 22:44:18 -05001482 initial cloning is stored in the remote.origin.url
1483 configuration variable.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001484
14852. Prepare a public repository accessible to others, just like
1486 the "project lead" person does.
1487
14883. Copy over the packed files from "project lead" public
1489 repository to your public repository, unless the "project
1490 lead" repository lives on the same machine as yours. In the
1491 latter case, you can use `objects/info/alternates` file to
1492 point at the repository you are borrowing from.
1493
14944. Push into the public repository from your primary
Thomas Rast0b444cd2010-01-10 00:33:00 +01001495 repository. Run 'git repack', and possibly 'git prune' if the
J. Bruce Fields927a5032006-01-22 23:57:25 -05001496 transport used for pulling from your repository supports
1497 packed repositories.
1498
14995. Keep working in your primary repository. Your changes
1500 include modifications of your own, patches you receive via
1501 e-mails, and merges resulting from pulling the "public"
1502 repositories of your "project lead" and possibly your
1503 "sub-subsystem maintainers".
1504+
1505You can repack this private repository whenever you feel
1506like.
1507
15086. Push your changes to your public repository, and ask your
1509 "project lead" and possibly your "sub-subsystem
1510 maintainers" to pull from it.
1511
Thomas Rast0b444cd2010-01-10 00:33:00 +010015127. Every once in a while, 'git repack' the public repository.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001513 Go back to step 5. and continue working.
1514
1515
1516A recommended work cycle for an "individual developer" who does
1517not have a "public" repository is somewhat different. It goes
1518like this:
1519
Thomas Rast0b444cd2010-01-10 00:33:00 +010015201. Prepare your work repository, by 'git clone' the public
J. Bruce Fields927a5032006-01-22 23:57:25 -05001521 repository of the "project lead" (or a "subsystem
1522 maintainer", if you work on a subsystem). The URL used for
Nicolas Pitrec14261e2007-01-14 22:44:18 -05001523 the initial cloning is stored in the remote.origin.url
1524 configuration variable.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001525
15262. Do your work in your repository on 'master' branch.
1527
15283. Run `git fetch origin` from the public repository of your
1529 upstream every once in a while. This does only the first
1530 half of `git pull` but does not merge. The head of the
Nicolas Pitrec14261e2007-01-14 22:44:18 -05001531 public repository is stored in `.git/refs/remotes/origin/master`.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001532
15334. Use `git cherry origin` to see which ones of your patches
1534 were accepted, and/or use `git rebase origin` to port your
1535 unmerged changes forward to the updated upstream.
1536
15375. Use `git format-patch origin` to prepare patches for e-mail
1538 submission to your upstream and send it out. Go back to
1539 step 2. and continue.
1540
1541
1542Working with Others, Shared Repository Style
1543--------------------------------------------
1544
Kristoffer Haugsbakk8b9bb332016-12-09 16:51:09 +01001545If you are coming from a CVS background, the style of cooperation
J. Bruce Fields927a5032006-01-22 23:57:25 -05001546suggested in the previous section may be new to you. You do not
Kristoffer Haugsbakk8b9bb332016-12-09 16:51:09 +01001547have to worry. Git supports the "shared public repository" style of
J. Bruce Fields927a5032006-01-22 23:57:25 -05001548cooperation you are probably more familiar with as well.
1549
Jonathan Nieder6998e4d2008-06-30 17:01:21 -05001550See linkgit:gitcvs-migration[7] for the details.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001551
1552Bundling your work together
1553---------------------------
1554
1555It is likely that you will be working on more than one thing at
1556a time. It is easy to manage those more-or-less independent tasks
Thomas Ackermann2de9b712013-01-21 20:17:53 +01001557using branches with Git.
J. Bruce Fields927a5032006-01-22 23:57:25 -05001558
1559We have already seen how branches work previously,
1560with "fun and work" example using two branches. The idea is the
1561same if there are more than two branches. Let's say you started
1562out from "master" head, and have some new code in the "master"
1563branch, and two independent fixes in the "commit-fix" and
1564"diff-fix" branches:
1565
1566------------
1567$ git show-branch
1568! [commit-fix] Fix commit message normalization.
1569 ! [diff-fix] Fix rename detection.
1570 * [master] Release candidate #1
1571---
1572 + [diff-fix] Fix rename detection.
1573 + [diff-fix~1] Better common substring algorithm.
1574+ [commit-fix] Fix commit message normalization.
1575 * [master] Release candidate #1
1576++* [diff-fix~2] Pretty-print messages.
1577------------
1578
1579Both fixes are tested well, and at this point, you want to merge
1580in both of them. You could merge in 'diff-fix' first and then
1581'commit-fix' next, like this:
1582
1583------------
Sergei Organovd336fc02007-11-02 20:12:57 +03001584$ git merge -m "Merge fix in diff-fix" diff-fix
1585$ git merge -m "Merge fix in commit-fix" commit-fix
J. Bruce Fields927a5032006-01-22 23:57:25 -05001586------------
1587
1588Which would result in:
1589
1590------------
1591$ git show-branch
1592! [commit-fix] Fix commit message normalization.
1593 ! [diff-fix] Fix rename detection.
1594 * [master] Merge fix in commit-fix
1595---
1596 - [master] Merge fix in commit-fix
1597+ * [commit-fix] Fix commit message normalization.
1598 - [master~1] Merge fix in diff-fix
1599 +* [diff-fix] Fix rename detection.
1600 +* [diff-fix~1] Better common substring algorithm.
1601 * [master~2] Release candidate #1
1602++* [master~3] Pretty-print messages.
1603------------
1604
1605However, there is no particular reason to merge in one branch
1606first and the other next, when what you have are a set of truly
1607independent changes (if the order mattered, then they are not
1608independent by definition). You could instead merge those two
1609branches into the current branch at once. First let's undo what
1610we just did and start over. We would want to get the master
1611branch before these two merges by resetting it to 'master~2':
1612
1613------------
1614$ git reset --hard master~2
1615------------
1616
Jonathan Niederdb5d6662008-07-03 01:06:23 -05001617You can make sure `git show-branch` matches the state before
Thomas Rast0b444cd2010-01-10 00:33:00 +01001618those two 'git merge' you just did. Then, instead of running
1619two 'git merge' commands in a row, you would merge these two
J. Bruce Fields927a5032006-01-22 23:57:25 -05001620branch heads (this is known as 'making an Octopus'):
1621
1622------------
Nicolas Pitrec14261e2007-01-14 22:44:18 -05001623$ git merge commit-fix diff-fix
J. Bruce Fields927a5032006-01-22 23:57:25 -05001624$ git show-branch
1625! [commit-fix] Fix commit message normalization.
1626 ! [diff-fix] Fix rename detection.
1627 * [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1628---
1629 - [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1630+ * [commit-fix] Fix commit message normalization.
1631 +* [diff-fix] Fix rename detection.
1632 +* [diff-fix~1] Better common substring algorithm.
1633 * [master~1] Release candidate #1
1634++* [master~2] Pretty-print messages.
1635------------
1636
Kristoffer Haugsbakkc857c3a2016-12-09 16:51:11 +01001637Note that you should not do Octopus just because you can. An octopus
J. Bruce Fields927a5032006-01-22 23:57:25 -05001638is a valid thing to do and often makes it easier to view the
Nicolas Pitrec14261e2007-01-14 22:44:18 -05001639commit history if you are merging more than two independent
J. Bruce Fields927a5032006-01-22 23:57:25 -05001640changes at the same time. However, if you have merge conflicts
1641with any of the branches you are merging in and need to hand
1642resolve, that is an indication that the development happened in
1643those branches were not independent after all, and you should
1644merge two at a time, documenting how you resolved the conflicts,
1645and the reason why you preferred changes made in one side over
1646the other. Otherwise it would make the project history harder
1647to follow, not easier.
Christian Couder497c8332008-05-29 19:21:46 +02001648
1649SEE ALSO
1650--------
Christian Couderde077672008-11-14 13:26:47 +01001651linkgit:gittutorial[7],
1652linkgit:gittutorial-2[7],
1653linkgit:gitcvs-migration[7],
Christian Couder6e702c22008-11-17 16:43:04 +01001654linkgit:git-help[1],
Philip Oakley673151a2014-10-10 22:25:37 +01001655linkgit:giteveryday[7],
Christian Couder497c8332008-05-29 19:21:46 +02001656link:user-manual.html[The Git User's Manual]
1657
1658GIT
1659---
Stefan Beller941b9c52017-02-08 17:29:30 -08001660Part of the linkgit:git[1] suite