show-branch: make the current branch and merge commits stand out.
[git/git.git] / Documentation / tutorial.txt
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1A short git tutorial
2====================
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3
4Introduction
5------------
6
7This is trying to be a short tutorial on setting up and using a git
2a29da7c 8repository, mainly because being hands-on and using explicit examples is
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9often the best way of explaining what is going on.
10
11In normal life, most people wouldn't use the "core" git programs
12directly, but rather script around them to make them more palatable.
13Understanding the core git stuff may help some people get those scripts
14done, though, and it may also be instructive in helping people
15understand what it is that the higher-level helper scripts are actually
16doing.
17
18The core git is often called "plumbing", with the prettier user
2a29da7c 19interfaces on top of it called "porcelain". You may not want to use the
f35ca9ed 20plumbing directly very often, but it can be good to know what the
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21plumbing does for when the porcelain isn't flushing.
22
23The material presented here often goes deep describing how things
24work internally. If you are mostly interested in using git as a
25SCM, you can skip them during your first pass.
26
27[NOTE]
28And those "too deep" descriptions are often marked as Note.
8c7fa247 29
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30[NOTE]
31If you are already familiar with another version control system,
32like CVS, you may want to take a look at
33link:everyday.html[Everyday GIT in 20 commands or so] first
34before reading this.
35
8c7fa247 36
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37Creating a git repository
38-------------------------
8c7fa247 39
2a29da7c 40Creating a new git repository couldn't be easier: all git repositories start
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41out empty, and the only thing you need to do is find yourself a
42subdirectory that you want to use as a working tree - either an empty
43one for a totally new project, or an existing working tree that you want
44to import into git.
45
2a29da7c 46For our first example, we're going to start a totally new repository from
8db9307c 47scratch, with no pre-existing files, and we'll call it `git-tutorial`.
8c7fa247 48To start up, create a subdirectory for it, change into that
8db9307c 49subdirectory, and initialize the git infrastructure with `git-init-db`:
8c7fa247 50
8db9307c 51------------------------------------------------
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52$ mkdir git-tutorial
53$ cd git-tutorial
54$ git-init-db
8db9307c 55------------------------------------------------
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56
57to which git will reply
58
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59----------------
60defaulting to local storage area
61----------------
8c7fa247 62
837eedf4 63which is just git's way of saying that you haven't been doing anything
914328ac 64strange, and that it will have created a local `.git` directory setup for
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65your new project. You will now have a `.git` directory, and you can
66inspect that with `ls`. For your new empty project, it should show you
2a29da7c 67three entries, among other things:
8c7fa247 68
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69 - a symlink called `HEAD`, pointing to `refs/heads/master` (if your
70 platform does not have native symlinks, it is a file containing the
71 line "ref: refs/heads/master")
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72+
73Don't worry about the fact that the file that the `HEAD` link points to
914328ac 74doesn't even exist yet -- you haven't created the commit that will
8db9307c 75start your `HEAD` development branch yet.
8c7fa247 76
8db9307c 77 - a subdirectory called `objects`, which will contain all the
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78 objects of your project. You should never have any real reason to
79 look at the objects directly, but you might want to know that these
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80 objects are what contains all the real 'data' in your repository.
81
82 - a subdirectory called `refs`, which contains references to objects.
83
84In particular, the `refs` subdirectory will contain two other
85subdirectories, named `heads` and `tags` respectively. They do
86exactly what their names imply: they contain references to any number
87of different 'heads' of development (aka 'branches'), and to any
88'tags' that you have created to name specific versions in your
89repository.
90
91One note: the special `master` head is the default branch, which is
92why the `.git/HEAD` file was created as a symlink to it even if it
93doesn't yet exist. Basically, the `HEAD` link is supposed to always
94point to the branch you are working on right now, and you always
95start out expecting to work on the `master` branch.
96
97However, this is only a convention, and you can name your branches
98anything you want, and don't have to ever even 'have' a `master`
99branch. A number of the git tools will assume that `.git/HEAD` is
100valid, though.
101
102[NOTE]
914328ac 103An 'object' is identified by its 160-bit SHA1 hash, aka 'object name',
8db9307c 104and a reference to an object is always the 40-byte hex
914328ac 105representation of that SHA1 name. The files in the `refs`
8db9307c 106subdirectory are expected to contain these hex references
914328ac 107(usually with a final `\'\n\'` at the end), and you should thus
8db9307c 108expect to see a number of 41-byte files containing these
914328ac 109references in these `refs` subdirectories when you actually start
8db9307c 110populating your tree.
8c7fa247 111
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112[NOTE]
113An advanced user may want to take a look at the
114link:repository-layout.html[repository layout] document
115after finishing this tutorial.
116
2a29da7c 117You have now created your first git repository. Of course, since it's
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118empty, that's not very useful, so let's start populating it with data.
119
120
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121Populating a git repository
122---------------------------
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123
124We'll keep this simple and stupid, so we'll start off with populating a
125few trivial files just to get a feel for it.
126
127Start off with just creating any random files that you want to maintain
2a29da7c 128in your git repository. We'll start off with a few bad examples, just to
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129get a feel for how this works:
130
8db9307c 131------------------------------------------------
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132$ echo "Hello World" >hello
133$ echo "Silly example" >example
8db9307c 134------------------------------------------------
8c7fa247 135
914328ac 136you have now created two files in your working tree (aka 'working directory'), but to
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137actually check in your hard work, you will have to go through two steps:
138
914328ac 139 - fill in the 'index' file (aka 'cache') with the information about your
2a29da7c 140 working tree state.
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141
142 - commit that index file as an object.
143
144The first step is trivial: when you want to tell git about any changes
215a7ad1 145to your working tree, you use the `git-update-index` program. That
8c7fa247 146program normally just takes a list of filenames you want to update, but
5f3aa197 147to avoid trivial mistakes, it refuses to add new entries to the index
8c7fa247 148(or remove existing ones) unless you explicitly tell it that you're
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149adding a new entry with the `\--add` flag (or removing an entry with the
150`\--remove`) flag.
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151
152So to populate the index with the two files you just created, you can do
153
8db9307c 154------------------------------------------------
f2416c27 155$ git-update-index --add hello example
8db9307c 156------------------------------------------------
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157
158and you have now told git to track those two files.
159
160In fact, as you did that, if you now look into your object directory,
837eedf4 161you'll notice that git will have added two new objects to the object
2a29da7c 162database. If you did exactly the steps above, you should now be able to do
8c7fa247 163
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164
165----------------
166$ ls .git/objects/??/*
167----------------
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168
169and see two files:
170
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171----------------
172.git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
173.git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
174----------------
8c7fa247 175
2a29da7c 176which correspond with the objects with names of 557db... and f24c7..
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177respectively.
178
914328ac 179If you want to, you can use `git-cat-file` to look at those objects, but
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180you'll have to use the object name, not the filename of the object:
181
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182----------------
183$ git-cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
184----------------
8c7fa247 185
914328ac 186where the `-t` tells `git-cat-file` to tell you what the "type" of the
72e9340c 187object is. git will tell you that you have a "blob" object (ie just a
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188regular file), and you can see the contents with
189
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190----------------
191$ git-cat-file "blob" 557db03
192----------------
8c7fa247 193
2a29da7c 194which will print out "Hello World". The object 557db03 is nothing
914328ac 195more than the contents of your file `hello`.
8c7fa247 196
8db9307c 197[NOTE]
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198Don't confuse that object with the file `hello` itself. The
199object is literally just those specific *contents* of the file, and
200however much you later change the contents in file `hello`, the object
201we just looked at will never change. Objects are immutable.
2a29da7c 202
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203[NOTE]
204The second example demonstrates that you can
205abbreviate the object name to only the first several
206hexadecimal digits in most places.
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207
208Anyway, as we mentioned previously, you normally never actually take a
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209look at the objects themselves, and typing long 40-character hex
210names is not something you'd normally want to do. The above digression
215a7ad1 211was just to show that `git-update-index` did something magical, and
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212actually saved away the contents of your files into the git object
213database.
8c7fa247 214
5f3aa197 215Updating the index did something else too: it created a `.git/index`
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216file. This is the index that describes your current working tree, and
217something you should be very aware of. Again, you normally never worry
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218about the index file itself, but you should be aware of the fact that
219you have not actually really "checked in" your files into git so far,
914328ac 220you've only *told* git about them.
8c7fa247 221
f35ca9ed 222However, since git knows about them, you can now start using some of the
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223most basic git commands to manipulate the files or look at their status.
224
225In particular, let's not even check in the two files into git yet, we'll
914328ac 226start off by adding another line to `hello` first:
8c7fa247 227
8db9307c 228------------------------------------------------
f2416c27 229$ echo "It's a new day for git" >>hello
8db9307c 230------------------------------------------------
8c7fa247 231
914328ac 232and you can now, since you told git about the previous state of `hello`, ask
8c7fa247 233git what has changed in the tree compared to your old index, using the
914328ac 234`git-diff-files` command:
8c7fa247 235
914328ac 236------------
f2416c27 237$ git-diff-files
914328ac 238------------
8c7fa247 239
2a29da7c 240Oops. That wasn't very readable. It just spit out its own internal
914328ac 241version of a `diff`, but that internal version really just tells you
a05ed8cb 242that it has noticed that "hello" has been modified, and that the old object
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243contents it had have been replaced with something else.
244
245To make it readable, we can tell git-diff-files to output the
914328ac 246differences as a patch, using the `-p` flag:
8c7fa247 247
914328ac 248------------
f2416c27 249$ git-diff-files -p
914328ac 250diff --git a/hello b/hello
2ae6c706 251index 557db03..263414f 100644
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252--- a/hello
253+++ b/hello
254@@ -1 +1,2 @@
255 Hello World
256+It's a new day for git
257----
8c7fa247 258
914328ac 259i.e. the diff of the change we caused by adding another line to `hello`.
8c7fa247 260
914328ac 261In other words, `git-diff-files` always shows us the difference between
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262what is recorded in the index, and what is currently in the working
263tree. That's very useful.
264
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265A common shorthand for `git-diff-files -p` is to just write `git
266diff`, which will do the same thing.
ed616049 267
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268------------
269$ git diff
270diff --git a/hello b/hello
271index 557db03..263414f 100644
272--- a/hello
273+++ b/hello
274@@ -1 +1,2 @@
275 Hello World
276+It's a new day for git
277------------
278
8c7fa247 279
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280Committing git state
281--------------------
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282
283Now, we want to go to the next stage in git, which is to take the files
284that git knows about in the index, and commit them as a real tree. We do
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285that in two phases: creating a 'tree' object, and committing that 'tree'
286object as a 'commit' object together with an explanation of what the
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287tree was all about, along with information of how we came to that state.
288
914328ac 289Creating a tree object is trivial, and is done with `git-write-tree`.
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290There are no options or other input: git-write-tree will take the
291current index state, and write an object that describes that whole
2a29da7c 292index. In other words, we're now tying together all the different
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293filenames with their contents (and their permissions), and we're
294creating the equivalent of a git "directory" object:
295
8db9307c 296------------------------------------------------
f2416c27 297$ git-write-tree
8db9307c 298------------------------------------------------
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299
300and this will just output the name of the resulting tree, in this case
ade75a59 301(if you have done exactly as I've described) it should be
8c7fa247 302
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303----------------
3048988da15d077d4829fc51d8544c097def6644dbb
305----------------
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306
307which is another incomprehensible object name. Again, if you want to,
914328ac 308you can use `git-cat-file -t 8988d\...` to see that this time the object
8c7fa247 309is not a "blob" object, but a "tree" object (you can also use
914328ac 310`git-cat-file` to actually output the raw object contents, but you'll see
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311mainly a binary mess, so that's less interesting).
312
914328ac 313However -- normally you'd never use `git-write-tree` on its own, because
8c7fa247 314normally you always commit a tree into a commit object using the
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315`git-commit-tree` command. In fact, it's easier to not actually use
316`git-write-tree` on its own at all, but to just pass its result in as an
317argument to `git-commit-tree`.
8c7fa247 318
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319`git-commit-tree` normally takes several arguments -- it wants to know
320what the 'parent' of a commit was, but since this is the first commit
2a29da7c 321ever in this new repository, and it has no parents, we only need to pass in
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322the object name of the tree. However, `git-commit-tree`
323also wants to get a commit message
2a29da7c 324on its standard input, and it will write out the resulting object name for the
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325commit to its standard output.
326
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327And this is where we create the `.git/refs/heads/master` file
328which is pointed at by `HEAD`. This file is supposed to contain
329the reference to the top-of-tree of the master branch, and since
330that's exactly what `git-commit-tree` spits out, we can do this
331all with a sequence of simple shell commands:
8c7fa247 332
8db9307c 333------------------------------------------------
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334$ tree=$(git-write-tree)
335$ commit=$(echo 'Initial commit' | git-commit-tree $tree)
336$ git-update-ref HEAD $commit
8db9307c 337------------------------------------------------
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338
339which will say:
340
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341----------------
342Committing initial tree 8988da15d077d4829fc51d8544c097def6644dbb
343----------------
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344
345just to warn you about the fact that it created a totally new commit
914328ac 346that is not related to anything else. Normally you do this only *once*
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347for a project ever, and all later commits will be parented on top of an
348earlier commit, and you'll never see this "Committing initial tree"
349message ever again.
350
2a29da7c 351Again, normally you'd never actually do this by hand. There is a
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352helpful script called `git commit` that will do all of this for you. So
353you could have just written `git commit`
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354instead, and it would have done the above magic scripting for you.
355
8c7fa247 356
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357Making a change
358---------------
8c7fa247 359
215a7ad1 360Remember how we did the `git-update-index` on file `hello` and then we
914328ac 361changed `hello` afterward, and could compare the new state of `hello` with the
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362state we saved in the index file?
363
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364Further, remember how I said that `git-write-tree` writes the contents
365of the *index* file to the tree, and thus what we just committed was in
366fact the *original* contents of the file `hello`, not the new ones. We did
8c7fa247 367that on purpose, to show the difference between the index state, and the
2a29da7c 368state in the working tree, and how they don't have to match, even
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369when we commit things.
370
914328ac 371As before, if we do `git-diff-files -p` in our git-tutorial project,
8c7fa247 372we'll still see the same difference we saw last time: the index file
2a29da7c 373hasn't changed by the act of committing anything. However, now that we
8c7fa247 374have committed something, we can also learn to use a new command:
215a7ad1 375`git-diff-index`.
8c7fa247 376
914328ac 377Unlike `git-diff-files`, which showed the difference between the index
215a7ad1 378file and the working tree, `git-diff-index` shows the differences
914328ac 379between a committed *tree* and either the index file or the working
215a7ad1 380tree. In other words, `git-diff-index` wants a tree to be diffed
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381against, and before we did the commit, we couldn't do that, because we
382didn't have anything to diff against.
8c7fa247 383
914328ac 384But now we can do
8c7fa247 385
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386----------------
387$ git-diff-index -p HEAD
388----------------
8c7fa247 389
914328ac 390(where `-p` has the same meaning as it did in `git-diff-files`), and it
8c7fa247 391will show us the same difference, but for a totally different reason.
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392Now we're comparing the working tree not against the index file,
393but against the tree we just wrote. It just so happens that those two
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394are obviously the same, so we get the same result.
395
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396Again, because this is a common operation, you can also just shorthand
397it with
398
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399----------------
400$ git diff HEAD
401----------------
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402
403which ends up doing the above for you.
404
215a7ad1 405In other words, `git-diff-index` normally compares a tree against the
914328ac 406working tree, but when given the `\--cached` flag, it is told to
a7b20909 407instead compare against just the index cache contents, and ignore the
2a29da7c 408current working tree state entirely. Since we just wrote the index
215a7ad1 409file to HEAD, doing `git-diff-index \--cached -p HEAD` should thus return
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410an empty set of differences, and that's exactly what it does.
411
8db9307c 412[NOTE]
914328ac 413================
215a7ad1 414`git-diff-index` really always uses the index for its
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415comparisons, and saying that it compares a tree against the working
416tree is thus not strictly accurate. In particular, the list of
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417files to compare (the "meta-data") *always* comes from the index file,
418regardless of whether the `\--cached` flag is used or not. The `\--cached`
419flag really only determines whether the file *contents* to be compared
8db9307c 420come from the working tree or not.
914328ac 421
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422This is not hard to understand, as soon as you realize that git simply
423never knows (or cares) about files that it is not told about
72e9340c 424explicitly. git will never go *looking* for files to compare, it
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425expects you to tell it what the files are, and that's what the index
426is there for.
914328ac 427================
8c7fa247 428
914328ac 429However, our next step is to commit the *change* we did, and again, to
837eedf4 430understand what's going on, keep in mind the difference between "working
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431tree contents", "index file" and "committed tree". We have changes
432in the working tree that we want to commit, and we always have to
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433work through the index file, so the first thing we need to do is to
434update the index cache:
435
8db9307c 436------------------------------------------------
f2416c27 437$ git-update-index hello
8db9307c 438------------------------------------------------
8c7fa247 439
914328ac 440(note how we didn't need the `\--add` flag this time, since git knew
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441about the file already).
442
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443Note what happens to the different `git-diff-\*` versions here. After
444we've updated `hello` in the index, `git-diff-files -p` now shows no
215a7ad1 445differences, but `git-diff-index -p HEAD` still *does* show that the
2a29da7c 446current state is different from the state we committed. In fact, now
215a7ad1 447`git-diff-index` shows the same difference whether we use the `--cached`
2a29da7c 448flag or not, since now the index is coherent with the working tree.
8c7fa247 449
914328ac 450Now, since we've updated `hello` in the index, we can commit the new
2a29da7c 451version. We could do it by writing the tree by hand again, and
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452committing the tree (this time we'd have to use the `-p HEAD` flag to
453tell commit that the HEAD was the *parent* of the new commit, and that
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454this wasn't an initial commit any more), but you've done that once
455already, so let's just use the helpful script this time:
8c7fa247 456
8db9307c 457------------------------------------------------
f2416c27 458$ git commit
8db9307c 459------------------------------------------------
8c7fa247 460
ed616049 461which starts an editor for you to write the commit message and tells you
2a29da7c 462a bit about what you have done.
ed616049 463
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464Write whatever message you want, and all the lines that start with '#'
465will be pruned out, and the rest will be used as the commit message for
466the change. If you decide you don't want to commit anything after all at
5f3aa197 467this point (you can continue to edit things and update the index), you
914328ac 468can just leave an empty message. Otherwise `git commit` will commit
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469the change for you.
470
8c7fa247 471You've now made your first real git commit. And if you're interested in
914328ac 472looking at what `git commit` really does, feel free to investigate:
8c7fa247 473it's a few very simple shell scripts to generate the helpful (?) commit
914328ac 474message headers, and a few one-liners that actually do the
215a7ad1 475commit itself (`git-commit`).
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476
477
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478Inspecting Changes
479------------------
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480
481While creating changes is useful, it's even more useful if you can tell
2a29da7c 482later what changed. The most useful command for this is another of the
914328ac 483`diff` family, namely `git-diff-tree`.
8c7fa247 484
914328ac 485`git-diff-tree` can be given two arbitrary trees, and it will tell you the
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486differences between them. Perhaps even more commonly, though, you can
487give it just a single commit object, and it will figure out the parent
488of that commit itself, and show the difference directly. Thus, to get
489the same diff that we've already seen several times, we can now do
490
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491----------------
492$ git-diff-tree -p HEAD
493----------------
8c7fa247 494
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495(again, `-p` means to show the difference as a human-readable patch),
496and it will show what the last commit (in `HEAD`) actually changed.
8c7fa247 497
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498[NOTE]
499============
500Here is an ASCII art by Jon Loeliger that illustrates how
501various diff-\* commands compare things.
502
503 diff-tree
504 +----+
505 | |
506 | |
507 V V
508 +-----------+
509 | Object DB |
510 | Backing |
511 | Store |
512 +-----------+
513 ^ ^
514 | |
515 | | diff-index --cached
516 | |
517 diff-index | V
518 | +-----------+
519 | | Index |
520 | | "cache" |
521 | +-----------+
522 | ^
523 | |
524 | | diff-files
525 | |
526 V V
527 +-----------+
528 | Working |
529 | Directory |
530 +-----------+
531============
532
914328ac 533More interestingly, you can also give `git-diff-tree` the `-v` flag, which
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534tells it to also show the commit message and author and date of the
535commit, and you can tell it to show a whole series of diffs.
536Alternatively, you can tell it to be "silent", and not show the diffs at
537all, but just show the actual commit message.
538
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539In fact, together with the `git-rev-list` program (which generates a
540list of revisions), `git-diff-tree` ends up being a veritable fount of
541changes. A trivial (but very useful) script called `git-whatchanged` is
8c7fa247 542included with git which does exactly this, and shows a log of recent
2a29da7c 543activities.
8c7fa247 544
81bb573e 545To see the whole history of our pitiful little git-tutorial project, you
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546can do
547
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548----------------
549$ git log
550----------------
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551
552which shows just the log messages, or if we want to see the log together
cc29f732 553with the associated patches use the more complex (and much more
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554powerful)
555
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556----------------
557$ git-whatchanged -p --root
558----------------
8c7fa247 559
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560and you will see exactly what has changed in the repository over its
561short history.
562
8db9307c 563[NOTE]
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564The `\--root` flag is a flag to `git-diff-tree` to tell it to
565show the initial aka 'root' commit too. Normally you'd probably not
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566want to see the initial import diff, but since the tutorial project
567was started from scratch and is so small, we use it to make the result
568a bit more interesting.
8c7fa247 569
837eedf4 570With that, you should now be having some inkling of what git does, and
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571can explore on your own.
572
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573[NOTE]
574Most likely, you are not directly using the core
575git Plumbing commands, but using Porcelain like Cogito on top
576of it. Cogito works a bit differently and you usually do not
215a7ad1 577have to run `git-update-index` yourself for changed files (you
8db9307c 578do tell underlying git about additions and removals via
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579`cg-add` and `cg-rm` commands). Just before you make a commit
580with `cg-commit`, Cogito figures out which files you modified,
215a7ad1 581and runs `git-update-index` on them for you.
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582
583
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584Tagging a version
585-----------------
3eb5128a 586
2a29da7c 587In git, there are two kinds of tags, a "light" one, and an "annotated tag".
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588
589A "light" tag is technically nothing more than a branch, except we put
914328ac 590it in the `.git/refs/tags/` subdirectory instead of calling it a `head`.
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591So the simplest form of tag involves nothing more than
592
8db9307c 593------------------------------------------------
f2416c27 594$ git tag my-first-tag
8db9307c 595------------------------------------------------
3eb5128a 596
914328ac 597which just writes the current `HEAD` into the `.git/refs/tags/my-first-tag`
a7333f9e 598file, after which point you can then use this symbolic name for that
2a29da7c 599particular state. You can, for example, do
3eb5128a 600
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601----------------
602$ git diff my-first-tag
603----------------
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604
605to diff your current state against that tag (which at this point will
606obviously be an empty diff, but if you continue to develop and commit
ade75a59 607stuff, you can use your tag as an "anchor-point" to see what has changed
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608since you tagged it.
609
2a29da7c 610An "annotated tag" is actually a real git object, and contains not only a
3eb5128a 611pointer to the state you want to tag, but also a small tag name and
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612message, along with optionally a PGP signature that says that yes,
613you really did
614that tag. You create these annotated tags with either the `-a` or
615`-s` flag to `git tag`:
3eb5128a 616
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617----------------
618$ git tag -s <tagname>
619----------------
3eb5128a 620
914328ac 621which will sign the current `HEAD` (but you can also give it another
3eb5128a 622argument that specifies the thing to tag, ie you could have tagged the
914328ac 623current `mybranch` point by using `git tag <tagname> mybranch`).
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624
625You normally only do signed tags for major releases or things
626like that, while the light-weight tags are useful for any marking you
914328ac 627want to do -- any time you decide that you want to remember a certain
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628point, just create a private tag for it, and you have a nice symbolic
629name for the state at that point.
630
631
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632Copying repositories
633--------------------
f35ca9ed 634
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635git repositories are normally totally self-sufficient and relocatable
636Unlike CVS, for example, there is no separate notion of
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637"repository" and "working tree". A git repository normally *is* the
638working tree, with the local git information hidden in the `.git`
2a29da7c 639subdirectory. There is nothing else. What you see is what you got.
f35ca9ed 640
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641[NOTE]
642You can tell git to split the git internal information from
643the directory that it tracks, but we'll ignore that for now: it's not
644how normal projects work, and it's really only meant for special uses.
645So the mental model of "the git information is always tied directly to
646the working tree that it describes" may not be technically 100%
647accurate, but it's a good model for all normal use.
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648
649This has two implications:
650
2a29da7c 651 - if you grow bored with the tutorial repository you created (or you've
f35ca9ed 652 made a mistake and want to start all over), you can just do simple
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653+
654----------------
655$ rm -rf git-tutorial
656----------------
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657+
658and it will be gone. There's no external repository, and there's no
659history outside the project you created.
f35ca9ed 660
2a29da7c 661 - if you want to move or duplicate a git repository, you can do so. There
914328ac 662 is `git clone` command, but if all you want to do is just to
2a29da7c 663 create a copy of your repository (with all the full history that
e7c1ca42 664 went along with it), you can do so with a regular
914328ac 665 `cp -a git-tutorial new-git-tutorial`.
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666+
667Note that when you've moved or copied a git repository, your git index
668file (which caches various information, notably some of the "stat"
669information for the files involved) will likely need to be refreshed.
914328ac 670So after you do a `cp -a` to create a new copy, you'll want to do
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671+
672----------------
673$ git-update-index --refresh
674----------------
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675+
676in the new repository to make sure that the index file is up-to-date.
f35ca9ed 677
2a29da7c 678Note that the second point is true even across machines. You can
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679duplicate a remote git repository with *any* regular copy mechanism, be it
680`scp`, `rsync` or `wget`.
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681
682When copying a remote repository, you'll want to at a minimum update the
2a29da7c 683index cache when you do this, and especially with other peoples'
f35ca9ed 684repositories you often want to make sure that the index cache is in some
914328ac 685known state (you don't know *what* they've done and not yet checked in),
215a7ad1 686so usually you'll precede the `git-update-index` with a
f35ca9ed 687
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688----------------
689$ git-read-tree --reset HEAD
690$ git-update-index --refresh
691----------------
f35ca9ed 692
914328ac 693which will force a total index re-build from the tree pointed to by `HEAD`.
215a7ad1 694It resets the index contents to `HEAD`, and then the `git-update-index`
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695makes sure to match up all index entries with the checked-out files.
696If the original repository had uncommitted changes in its
215a7ad1 697working tree, `git-update-index --refresh` notices them and
2a29da7c 698tells you they need to be updated.
f35ca9ed 699
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700The above can also be written as simply
701
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702----------------
703$ git reset
704----------------
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705
706and in fact a lot of the common git command combinations can be scripted
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707with the `git xyz` interfaces. You can learn things by just looking
708at what the various git scripts do. For example, `git reset` is the
709above two lines implemented in `git-reset`, but some things like
710`git status` and `git commit` are slightly more complex scripts around
711the basic git commands.
ce30a4b6 712
2a29da7c 713Many (most?) public remote repositories will not contain any of
914328ac 714the checked out files or even an index file, and will *only* contain the
2a29da7c 715actual core git files. Such a repository usually doesn't even have the
8db9307c 716`.git` subdirectory, but has all the git files directly in the
ce30a4b6 717repository.
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718
719To create your own local live copy of such a "raw" git repository, you'd
cc29f732 720first create your own subdirectory for the project, and then copy the
914328ac 721raw repository contents into the `.git` directory. For example, to
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722create your own copy of the git repository, you'd do the following
723
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724----------------
725$ mkdir my-git
726$ cd my-git
727$ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
728----------------
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729
730followed by
731
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732----------------
733$ git-read-tree HEAD
734----------------
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735
736to populate the index. However, now you have populated the index, and
737you have all the git internal files, but you will notice that you don't
2a29da7c 738actually have any of the working tree files to work on. To get
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739those, you'd check them out with
740
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741----------------
742$ git-checkout-index -u -a
743----------------
f35ca9ed 744
914328ac 745where the `-u` flag means that you want the checkout to keep the index
cc29f732 746up-to-date (so that you don't have to refresh it afterward), and the
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747`-a` flag means "check out all files" (if you have a stale copy or an
748older version of a checked out tree you may also need to add the `-f`
215a7ad1 749flag first, to tell git-checkout-index to *force* overwriting of any old
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750files).
751
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752Again, this can all be simplified with
753
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754----------------
755$ git clone rsync://rsync.kernel.org/pub/scm/git/git.git/ my-git
756$ cd my-git
757$ git checkout
758----------------
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759
760which will end up doing all of the above for you.
761
cc29f732 762You have now successfully copied somebody else's (mine) remote
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763repository, and checked it out.
764
ed616049 765
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766Creating a new branch
767---------------------
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768
769Branches in git are really nothing more than pointers into the git
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770object database from within the `.git/refs/` subdirectory, and as we
771already discussed, the `HEAD` branch is nothing but a symlink to one of
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772these object pointers.
773
774You can at any time create a new branch by just picking an arbitrary
775point in the project history, and just writing the SHA1 name of that
914328ac 776object into a file under `.git/refs/heads/`. You can use any filename you
ed616049 777want (and indeed, subdirectories), but the convention is that the
914328ac 778"normal" branch is called `master`. That's just a convention, though,
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779and nothing enforces it.
780
2a29da7c 781To show that as an example, let's go back to the git-tutorial repository we
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782used earlier, and create a branch in it. You do that by simply just
783saying that you want to check out a new branch:
ed616049 784
8db9307c 785------------
f2416c27 786$ git checkout -b mybranch
8db9307c 787------------
ed616049 788
914328ac 789will create a new branch based at the current `HEAD` position, and switch
a7333f9e 790to it.
ed616049 791
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792[NOTE]
793================================================
794If you make the decision to start your new branch at some
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795other point in the history than the current `HEAD`, you can do so by
796just telling `git checkout` what the base of the checkout would be.
8db9307c 797In other words, if you have an earlier tag or branch, you'd just do
ed616049 798
2ae6c706 799------------
f2416c27 800$ git checkout -b mybranch earlier-commit
2ae6c706 801------------
ed616049 802
914328ac 803and it would create the new branch `mybranch` at the earlier commit,
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804and check out the state at that time.
805================================================
ed616049 806
914328ac 807You can always just jump back to your original `master` branch by doing
ed616049 808
2ae6c706 809------------
f2416c27 810$ git checkout master
2ae6c706 811------------
ed616049 812
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813(or any other branch-name, for that matter) and if you forget which
814branch you happen to be on, a simple
ed616049 815
2ae6c706 816------------
f2416c27 817$ ls -l .git/HEAD
2ae6c706 818------------
ed616049 819
2ae6c706
JS
820will tell you where it's pointing (Note that on platforms with bad or no
821symlink support, you have to execute
ed616049 822
2ae6c706 823------------
f2416c27 824$ cat .git/HEAD
2ae6c706
JS
825------------
826
827instead). To get the list of branches you have, you can say
828
829------------
f2416c27 830$ git branch
2ae6c706 831------------
2a29da7c 832
8db9307c 833which is nothing more than a simple script around `ls .git/refs/heads`.
928f74de 834There will be asterisk in front of the branch you are currently on.
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835
836Sometimes you may wish to create a new branch _without_ actually
a7333f9e
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837checking it out and switching to it. If so, just use the command
838
2ae6c706 839------------
f2416c27 840$ git branch <branchname> [startingpoint]
2ae6c706 841------------
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842
843which will simply _create_ the branch, but will not do anything further.
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844You can then later -- once you decide that you want to actually develop
845on that branch -- switch to that branch with a regular `git checkout`
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846with the branchname as the argument.
847
ed616049 848
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849Merging two branches
850--------------------
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851
852One of the ideas of having a branch is that you do some (possibly
853experimental) work in it, and eventually merge it back to the main
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854branch. So assuming you created the above `mybranch` that started out
855being the same as the original `master` branch, let's make sure we're in
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856that branch, and do some work there.
857
914328ac 858------------------------------------------------
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859$ git checkout mybranch
860$ echo "Work, work, work" >>hello
861$ git commit -m 'Some work.' hello
914328ac 862------------------------------------------------
ed616049 863
914328ac 864Here, we just added another line to `hello`, and we used a shorthand for
96768e31 865doing both `git-update-index hello` and `git commit` by just giving the
914328ac 866filename directly to `git commit`. The `-m` flag is to give the
2a29da7c 867commit log message from the command line.
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868
869Now, to make it a bit more interesting, let's assume that somebody else
870does some work in the original branch, and simulate that by going back
871to the master branch, and editing the same file differently there:
872
8db9307c 873------------
f2416c27 874$ git checkout master
8db9307c 875------------
ed616049 876
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877Here, take a moment to look at the contents of `hello`, and notice how they
878don't contain the work we just did in `mybranch` -- because that work
879hasn't happened in the `master` branch at all. Then do
ed616049 880
8db9307c 881------------
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882$ echo "Play, play, play" >>hello
883$ echo "Lots of fun" >>example
884$ git commit -m 'Some fun.' hello example
8db9307c 885------------
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886
887since the master branch is obviously in a much better mood.
888
889Now, you've got two branches, and you decide that you want to merge the
890work done. Before we do that, let's introduce a cool graphical tool that
891helps you view what's going on:
892
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893----------------
894$ gitk --all
895----------------
ed616049 896
914328ac
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897will show you graphically both of your branches (that's what the `\--all`
898means: normally it will just show you your current `HEAD`) and their
2a29da7c 899histories. You can also see exactly how they came to be from a common
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900source.
901
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902Anyway, let's exit `gitk` (`^Q` or the File menu), and decide that we want
903to merge the work we did on the `mybranch` branch into the `master`
904branch (which is currently our `HEAD` too). To do that, there's a nice
44760f1d 905script called `git merge`, which wants to know which branches you want
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906to resolve and what the merge is all about:
907
8db9307c 908------------
f2416c27 909$ git merge "Merge work in mybranch" HEAD mybranch
8db9307c 910------------
ed616049 911
44760f1d 912where the first argument is going to be used as the commit message if
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913the merge can be resolved automatically.
914
915Now, in this case we've intentionally created a situation where the
916merge will need to be fixed up by hand, though, so git will do as much
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917of it as it can automatically (which in this case is just merge the `example`
918file, which had no differences in the `mybranch` branch), and say:
ed616049 919
f2416c27 920----------------
44760f1d
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921 Trying really trivial in-index merge...
922 fatal: Merge requires file-level merging
923 Nope.
924 ...
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925 Auto-merging hello
926 CONFLICT (content): Merge conflict in hello
44760f1d 927 Automatic merge failed/prevented; fix up by hand
f2416c27 928----------------
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929
930which is way too verbose, but it basically tells you that it failed the
931really trivial merge ("Simple merge") and did an "Automatic merge"
914328ac 932instead, but that too failed due to conflicts in `hello`.
ed616049 933
914328ac 934Not to worry. It left the (trivial) conflict in `hello` in the same form you
ed616049 935should already be well used to if you've ever used CVS, so let's just
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936open `hello` in our editor (whatever that may be), and fix it up somehow.
937I'd suggest just making it so that `hello` contains all four lines:
ed616049 938
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939------------
940Hello World
941It's a new day for git
942Play, play, play
943Work, work, work
944------------
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945
946and once you're happy with your manual merge, just do a
947
8db9307c 948------------
f2416c27 949$ git commit hello
8db9307c 950------------
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951
952which will very loudly warn you that you're now committing a merge
953(which is correct, so never mind), and you can write a small merge
914328ac 954message about your adventures in git-merge-land.
ed616049 955
e1ccf53a 956After you're done, start up `gitk \--all` to see graphically what the
914328ac 957history looks like. Notice that `mybranch` still exists, and you can
2a29da7c 958switch to it, and continue to work with it if you want to. The
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959`mybranch` branch will not contain the merge, but next time you merge it
960from the `master` branch, git will know how you merged it, so you'll not
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961have to do _that_ merge again.
962
8db9307c 963Another useful tool, especially if you do not always work in X-Window
914328ac 964environment, is `git show-branch`.
2a29da7c
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965
966------------------------------------------------
967$ git show-branch master mybranch
0501c240 968* [master] Merge work in mybranch
2a29da7c
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969 ! [mybranch] Some work.
970--
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971- [master] Merge work in mybranch
972*+ [mybranch] Some work.
2a29da7c
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973------------------------------------------------
974
975The first two lines indicate that it is showing the two branches
976and the first line of the commit log message from their
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977top-of-the-tree commits, you are currently on `master` branch
978(notice the asterisk `*` character), and the first column for
2a29da7c 979the later output lines is used to show commits contained in the
914328ac 980`master` branch, and the second column for the `mybranch`
2a29da7c 981branch. Three commits are shown along with their log messages.
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982All of them have non blank characters in the first column (`*`
983shows an ordinary commit on the current branch, `.` is a merge commit), which
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984means they are now part of the `master` branch. Only the "Some
985work" commit has the plus `+` character in the second column,
986because `mybranch` has not been merged to incorporate these
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987commits from the master branch. The string inside brackets
988before the commit log message is a short name you can use to
989name the commit. In the above example, 'master' and 'mybranch'
990are branch heads. 'master~1' is the first parent of 'master'
991branch head. Please see 'git-rev-parse' documentation if you
992see more complex cases.
2a29da7c
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993
994Now, let's pretend you are the one who did all the work in
914328ac
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995`mybranch`, and the fruit of your hard work has finally been merged
996to the `master` branch. Let's go back to `mybranch`, and run
2a29da7c
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997resolve to get the "upstream changes" back to your branch.
998
2ae6c706 999------------
f2416c27
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1000$ git checkout mybranch
1001$ git merge "Merge upstream changes." HEAD master
2ae6c706 1002------------
2a29da7c
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1003
1004This outputs something like this (the actual commit object names
1005would be different)
1006
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1007----------------
1008Updating from ae3a2da... to a80b4aa....
1009 example | 1 +
1010 hello | 1 +
1011 2 files changed, 2 insertions(+), 0 deletions(-)
1012----------------
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1013
1014Because your branch did not contain anything more than what are
914328ac 1015already merged into the `master` branch, the resolve operation did
2a29da7c 1016not actually do a merge. Instead, it just updated the top of
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1017the tree of your branch to that of the `master` branch. This is
1018often called 'fast forward' merge.
ed616049 1019
e1ccf53a 1020You can run `gitk \--all` again to see how the commit ancestry
914328ac 1021looks like, or run `show-branch`, which tells you this.
2a29da7c
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1022
1023------------------------------------------------
1024$ git show-branch master mybranch
0501c240
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1025! [master] Merge work in mybranch
1026 * [mybranch] Merge work in mybranch
2a29da7c 1027--
ebedc319 1028-- [master] Merge work in mybranch
2a29da7c
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1029------------------------------------------------
1030
1031
1032Merging external work
1033---------------------
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1034
1035It's usually much more common that you merge with somebody else than
1036merging with your own branches, so it's worth pointing out that git
1037makes that very easy too, and in fact, it's not that different from
067744bd 1038doing a `git merge`. In fact, a remote merge ends up being nothing
ed616049 1039more than "fetch the work from a remote repository into a temporary tag"
067744bd 1040followed by a `git merge`.
ed616049 1041
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1042Fetching from a remote repository is done by, unsurprisingly,
1043`git fetch`:
ed616049 1044
f2416c27
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1045----------------
1046$ git fetch <remote-repository>
1047----------------
ed616049 1048
914328ac
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1049One of the following transports can be used to name the
1050repository to download from:
ed616049 1051
914328ac
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1052Rsync::
1053 `rsync://remote.machine/path/to/repo.git/`
1054+
1055Rsync transport is usable for both uploading and downloading,
1056but is completely unaware of what git does, and can produce
1057unexpected results when you download from the public repository
1058while the repository owner is uploading into it via `rsync`
1059transport. Most notably, it could update the files under
1060`refs/` which holds the object name of the topmost commits
1061before uploading the files in `objects/` -- the downloader would
1062obtain head commit object name while that object itself is still
1063not available in the repository. For this reason, it is
1064considered deprecated.
1065
1066SSH::
1067 `remote.machine:/path/to/repo.git/` or
1068+
1069`ssh://remote.machine/path/to/repo.git/`
1070+
1071This transport can be used for both uploading and downloading,
1072and requires you to have a log-in privilege over `ssh` to the
1073remote machine. It finds out the set of objects the other side
1074lacks by exchanging the head commits both ends have and
1075transfers (close to) minimum set of objects. It is by far the
1076most efficient way to exchange git objects between repositories.
1077
1078Local directory::
1079 `/path/to/repo.git/`
1080+
1081This transport is the same as SSH transport but uses `sh` to run
1082both ends on the local machine instead of running other end on
1083the remote machine via `ssh`.
ed616049 1084
72e9340c 1085git Native::
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1086 `git://remote.machine/path/to/repo.git/`
1087+
1088This transport was designed for anonymous downloading. Like SSH
1089transport, it finds out the set of objects the downstream side
1090lacks and transfers (close to) minimum set of objects.
ed616049 1091
f2416c27 1092HTTP(S)::
914328ac
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1093 `http://remote.machine/path/to/repo.git/`
1094+
80248b2e
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1095Downloader from http and https URL
1096first obtains the topmost commit object name from the remote site
1097by looking at the specified refname under `repo.git/refs/` directory,
1098and then tries to obtain the
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1099commit object by downloading from `repo.git/objects/xx/xxx\...`
1100using the object name of that commit object. Then it reads the
1101commit object to find out its parent commits and the associate
1102tree object; it repeats this process until it gets all the
1103necessary objects. Because of this behaviour, they are
1104sometimes also called 'commit walkers'.
1105+
1106The 'commit walkers' are sometimes also called 'dumb
72e9340c
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1107transports', because they do not require any git aware smart
1108server like git Native transport does. Any stock HTTP server
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1109that does not even support directory index would suffice. But
1110you must prepare your repository with `git-update-server-info`
1111to help dumb transport downloaders.
914328ac 1112+
215a7ad1 1113There are (confusingly enough) `git-ssh-fetch` and `git-ssh-upload`
914328ac 1114programs, which are 'commit walkers'; they outlived their
72e9340c 1115usefulness when git Native and SSH transports were introduced,
914328ac 1116and not used by `git pull` or `git push` scripts.
ed616049 1117
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1118Once you fetch from the remote repository, you `resolve` that
1119with your current branch.
ade75a59 1120
914328ac
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1121However -- it's such a common thing to `fetch` and then
1122immediately `resolve`, that it's called `git pull`, and you can
1123simply do
ed616049 1124
f2416c27
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1125----------------
1126$ git pull <remote-repository>
1127----------------
914328ac
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1128
1129and optionally give a branch-name for the remote end as a second
1130argument.
ed616049 1131
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1132[NOTE]
1133You could do without using any branches at all, by
1134keeping as many local repositories as you would like to have
914328ac 1135branches, and merging between them with `git pull`, just like
8db9307c 1136you merge between branches. The advantage of this approach is
914328ac 1137that it lets you keep set of files for each `branch` checked
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1138out and you may find it easier to switch back and forth if you
1139juggle multiple lines of development simultaneously. Of
1140course, you will pay the price of more disk usage to hold
1141multiple working trees, but disk space is cheap these days.
1142
1143[NOTE]
1144You could even pull from your own repository by
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1145giving '.' as <remote-repository> parameter to `git pull`. This
1146is useful when you want to merge a local branch (or more, if you
1147are making an Octopus) into the current branch.
ed616049 1148
0c04094b 1149It is likely that you will be pulling from the same remote
2a29da7c 1150repository from time to time. As a short hand, you can store
c9517341 1151the remote repository URL in a file under .git/remotes/
0c04094b
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1152directory, like this:
1153
c9517341 1154------------------------------------------------
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1155$ mkdir -p .git/remotes/
1156$ cat >.git/remotes/linus <<\EOF
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1157URL: http://www.kernel.org/pub/scm/git/git.git/
1158EOF
1159------------------------------------------------
0c04094b 1160
914328ac 1161and use the filename to `git pull` instead of the full URL.
c9517341 1162The URL specified in such file can even be a prefix
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1163of a full URL, like this:
1164
c9517341 1165------------------------------------------------
f2416c27 1166$ cat >.git/remotes/jgarzik <<\EOF
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1167URL: http://www.kernel.org/pub/scm/linux/git/jgarzik/
1168EOF
1169------------------------------------------------
1170
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1171
1172Examples.
1173
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1174. `git pull linus`
1175. `git pull linus tag v0.99.1`
1176. `git pull jgarzik/netdev-2.6.git/ e100`
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1177
1178the above are equivalent to:
1179
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1180. `git pull http://www.kernel.org/pub/scm/git/git.git/ HEAD`
1181. `git pull http://www.kernel.org/pub/scm/git/git.git/ tag v0.99.1`
1182. `git pull http://www.kernel.org/pub/.../jgarzik/netdev-2.6.git e100`
0c04094b 1183
e7c1ca42 1184
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1185How does the merge work?
1186------------------------
1187
1188We said this tutorial shows what plumbing does to help you cope
1189with the porcelain that isn't flushing, but we so far did not
1190talk about how the merge really works. If you are following
1191this tutorial the first time, I'd suggest to skip to "Publishing
1192your work" section and come back here later.
1193
1194OK, still with me? To give us an example to look at, let's go
1195back to the earlier repository with "hello" and "example" file,
1196and bring ourselves back to the pre-merge state:
1197
1198------------
1199$ git show-branch --more=3 master mybranch
1200! [master] Merge work in mybranch
1201 * [mybranch] Merge work in mybranch
1202--
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1203-- [master] Merge work in mybranch
1204+* [master^2] Some work.
1205+* [master^] Some fun.
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1206------------
1207
1208Remember, before running `git merge`, our `master` head was at
1209"Some fun." commit, while our `mybranch` head was at "Some
1210work." commit.
1211
1212------------
1213$ git checkout mybranch
1214$ git reset --hard master^2
1215$ git checkout master
1216$ git reset --hard master^
1217------------
1218
1219After rewinding, the commit structure should look like this:
1220
1221------------
1222$ git show-branch
1223* [master] Some fun.
1224 ! [mybranch] Some work.
1225--
1226 + [mybranch] Some work.
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1227* [master] Some fun.
1228*+ [mybranch^] New day.
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1229------------
1230
1231Now we are ready to experiment with the merge by hand.
1232
1233`git merge` command, when merging two branches, uses 3-way merge
1234algorithm. First, it finds the common ancestor between them.
1235The command it uses is `git-merge-base`:
1236
1237------------
1238$ mb=$(git-merge-base HEAD mybranch)
1239------------
1240
1241The command writes the commit object name of the common ancestor
1242to the standard output, so we captured its output to a variable,
1243because we will be using it in the next step. BTW, the common
1244ancestor commit is the "New day." commit in this case. You can
1245tell it by:
1246
1247------------
1248$ git-name-rev $mb
1249my-first-tag
1250------------
1251
1252After finding out a common ancestor commit, the second step is
1253this:
1254
1255------------
1256$ git-read-tree -m -u $mb HEAD mybranch
1257------------
1258
1259This is the same `git-read-tree` command we have already seen,
1260but it takes three trees, unlike previous examples. This reads
1261the contents of each tree into different 'stage' in the index
1262file (the first tree goes to stage 1, the second stage 2,
1263etc.). After reading three trees into three stages, the paths
1264that are the same in all three stages are 'collapsed' into stage
12650. Also paths that are the same in two of three stages are
1266collapsed into stage 0, taking the SHA1 from either stage 2 or
1267stage 3, whichever is different from stage 1 (i.e. only one side
1268changed from the common ancestor).
1269
1270After 'collapsing' operation, paths that are different in three
1271trees are left in non-zero stages. At this point, you can
1272inspect the index file with this command:
1273
1274------------
1275$ git-ls-files --stage
1276100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
1277100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1278100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1279100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1280------------
1281
1282In our example of only two files, we did not have unchanged
1283files so only 'example' resulted in collapsing, but in real-life
1284large projects, only small number of files change in one commit,
1285and this 'collapsing' tends to trivially merge most of the paths
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1286fairly quickly, leaving only a handful the real changes in non-zero
1287stages.
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1288
1289To look at only non-zero stages, use `\--unmerged` flag:
1290
1291------------
1292$ git-ls-files --unmerged
1293100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1294100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1295100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
1296------------
1297
1298The next step of merging is to merge these three versions of the
1299file, using 3-way merge. This is done by giving
1300`git-merge-one-file` command as one of the arguments to
1301`git-merge-index` command:
1302
1303------------
1304$ git-merge-index git-merge-one-file hello
1305Auto-merging hello.
1306merge: warning: conflicts during merge
1307ERROR: Merge conflict in hello.
1308fatal: merge program failed
1309------------
1310
1311`git-merge-one-file` script is called with parameters to
1312describe those three versions, and is responsible to leave the
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1313merge results in the working tree.
1314It is a fairly straightforward shell script, and
1315eventually calls `merge` program from RCS suite to perform a
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1316file-level 3-way merge. In this case, `merge` detects
1317conflicts, and the merge result with conflict marks is left in
361c06d8 1318the working tree.. This can be seen if you run `ls-files
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1319--stage` again at this point:
1320
1321------------
1322$ git-ls-files --stage
1323100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
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1324100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
1325100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
1326100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
44760f1d
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1327------------
1328
44760f1d
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1329This is the state of the index file and the working file after
1330`git merge` returns control back to you, leaving the conflicting
361c06d8
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1331merge for you to resolve. Notice that the path `hello` is still
1332unmerged, and what you see with `git diff` at this point is
1333differences since stage 2 (i.e. your version).
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1334
1335
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1336Publishing your work
1337--------------------
e7c1ca42 1338
3eb5128a 1339So we can use somebody else's work from a remote repository; but
914328ac 1340how can *you* prepare a repository to let other people pull from
3eb5128a 1341it?
e7c1ca42 1342
2a29da7c 1343Your do your real work in your working tree that has your
914328ac
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1344primary repository hanging under it as its `.git` subdirectory.
1345You *could* make that repository accessible remotely and ask
3eb5128a 1346people to pull from it, but in practice that is not the way
2a29da7c 1347things are usually done. A recommended way is to have a public
3eb5128a 1348repository, make it reachable by other people, and when the
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1349changes you made in your primary working tree are in good shape,
1350update the public repository from it. This is often called
914328ac 1351'pushing'.
e7c1ca42 1352
8db9307c 1353[NOTE]
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1354This public repository could further be mirrored, and that is
1355how git repositories at `kernel.org` are managed.
e7c1ca42 1356
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1357Publishing the changes from your local (private) repository to
1358your remote (public) repository requires a write privilege on
2a29da7c 1359the remote machine. You need to have an SSH account there to
914328ac 1360run a single command, `git-receive-pack`.
e7c1ca42 1361
3eb5128a 1362First, you need to create an empty repository on the remote
2a29da7c 1363machine that will house your public repository. This empty
3eb5128a 1364repository will be populated and be kept up-to-date by pushing
2a29da7c 1365into it later. Obviously, this repository creation needs to be
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1366done only once.
1367
8db9307c 1368[NOTE]
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1369`git push` uses a pair of programs,
1370`git-send-pack` on your local machine, and `git-receive-pack`
8db9307c
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1371on the remote machine. The communication between the two over
1372the network internally uses an SSH connection.
3eb5128a 1373
72e9340c 1374Your private repository's git directory is usually `.git`, but
3eb5128a 1375your public repository is often named after the project name,
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1376i.e. `<project>.git`. Let's create such a public repository for
1377project `my-git`. After logging into the remote machine, create
3eb5128a 1378an empty directory:
e7c1ca42 1379
2ae6c706 1380------------
f2416c27 1381$ mkdir my-git.git
2ae6c706 1382------------
e7c1ca42 1383
72e9340c 1384Then, make that directory into a git repository by running
914328ac
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1385`git init-db`, but this time, since its name is not the usual
1386`.git`, we do things slightly differently:
e7c1ca42 1387
2ae6c706 1388------------
f2416c27 1389$ GIT_DIR=my-git.git git-init-db
2ae6c706 1390------------
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1391
1392Make sure this directory is available for others you want your
2a29da7c 1393changes to be pulled by via the transport of your choice. Also
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1394you need to make sure that you have the `git-receive-pack`
1395program on the `$PATH`.
3eb5128a 1396
8db9307c 1397[NOTE]
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1398Many installations of sshd do not invoke your shell as the login
1399shell when you directly run programs; what this means is that if
1400your login shell is `bash`, only `.bashrc` is read and not
1401`.bash_profile`. As a workaround, make sure `.bashrc` sets up
1402`$PATH` so that you can run `git-receive-pack` program.
3eb5128a 1403
953e5842
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1404[NOTE]
1405If you plan to publish this repository to be accessed over http,
1406you should do `chmod +x my-git.git/hooks/post-update` at this
1407point. This makes sure that every time you push into this
1408repository, `git-update-server-info` is run.
1409
3eb5128a 1410Your "public repository" is now ready to accept your changes.
2a29da7c 1411Come back to the machine you have your private repository. From
e7c1ca42
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1412there, run this command:
1413
2ae6c706 1414------------
f2416c27 1415$ git push <public-host>:/path/to/my-git.git master
2ae6c706 1416------------
e7c1ca42
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1417
1418This synchronizes your public repository to match the named
914328ac 1419branch head (i.e. `master` in this case) and objects reachable
3eb5128a 1420from them in your current repository.
e7c1ca42
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1421
1422As a real example, this is how I update my public git
2a29da7c 1423repository. Kernel.org mirror network takes care of the
3eb5128a 1424propagation to other publicly visible machines:
e7c1ca42 1425
2ae6c706 1426------------
f2416c27 1427$ git push master.kernel.org:/pub/scm/git/git.git/
2ae6c706 1428------------
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1429
1430
2a29da7c
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1431Packing your repository
1432-----------------------
3eb5128a 1433
914328ac 1434Earlier, we saw that one file under `.git/objects/??/` directory
2a29da7c 1435is stored for each git object you create. This representation
914328ac 1436is efficient to create atomically and safely, but
2a29da7c 1437not so convenient to transport over the network. Since git objects are
3eb5128a 1438immutable once they are created, there is a way to optimize the
2a29da7c 1439storage by "packing them together". The command
3eb5128a 1440
2ae6c706 1441------------
f2416c27 1442$ git repack
2ae6c706 1443------------
3eb5128a 1444
2a29da7c 1445will do it for you. If you followed the tutorial examples, you
914328ac
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1446would have accumulated about 17 objects in `.git/objects/??/`
1447directories by now. `git repack` tells you how many objects it
1448packed, and stores the packed file in `.git/objects/pack`
3eb5128a
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1449directory.
1450
8db9307c 1451[NOTE]
914328ac
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1452You will see two files, `pack-\*.pack` and `pack-\*.idx`,
1453in `.git/objects/pack` directory. They are closely related to
8db9307c
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1454each other, and if you ever copy them by hand to a different
1455repository for whatever reason, you should make sure you copy
1456them together. The former holds all the data from the objects
1457in the pack, and the latter holds the index for random
1458access.
3eb5128a 1459
914328ac 1460If you are paranoid, running `git-verify-pack` command would
3eb5128a
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1461detect if you have a corrupt pack, but do not worry too much.
1462Our programs are always perfect ;-).
1463
1464Once you have packed objects, you do not need to leave the
1465unpacked objects that are contained in the pack file anymore.
1466
2ae6c706 1467------------
f2416c27 1468$ git prune-packed
2ae6c706 1469------------
3eb5128a
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1470
1471would remove them for you.
1472
914328ac
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1473You can try running `find .git/objects -type f` before and after
1474you run `git prune-packed` if you are curious. Also `git
1475count-objects` would tell you how many unpacked objects are in
1476your repository and how much space they are consuming.
3eb5128a 1477
8db9307c 1478[NOTE]
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1479`git pull` is slightly cumbersome for HTTP transport, as a
1480packed repository may contain relatively few objects in a
8db9307c
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1481relatively large pack. If you expect many HTTP pulls from your
1482public repository you might want to repack & prune often, or
1483never.
3eb5128a 1484
914328ac 1485If you run `git repack` again at this point, it will say
2a29da7c 1486"Nothing to pack". Once you continue your development and
914328ac 1487accumulate the changes, running `git repack` again will create a
3eb5128a 1488new pack, that contains objects created since you packed your
2a29da7c 1489repository the last time. We recommend that you pack your project
3eb5128a 1490soon after the initial import (unless you are starting your
914328ac 1491project from scratch), and then run `git repack` every once in a
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1492while, depending on how active your project is.
1493
914328ac 1494When a repository is synchronized via `git push` and `git pull`
ade75a59 1495objects packed in the source repository are usually stored
3eb5128a 1496unpacked in the destination, unless rsync transport is used.
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1497While this allows you to use different packing strategies on
1498both ends, it also means you may need to repack both
1499repositories every once in a while.
3eb5128a
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1500
1501
2a29da7c
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1502Working with Others
1503-------------------
3eb5128a 1504
a232a132
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1505Although git is a truly distributed system, it is often
1506convenient to organize your project with an informal hierarchy
2a29da7c 1507of developers. Linux kernel development is run this way. There
a232a132 1508is a nice illustration (page 17, "Merges to Mainline") in Randy
914328ac 1509Dunlap's presentation (`http://tinyurl.com/a2jdg`).
a232a132 1510
914328ac 1511It should be stressed that this hierarchy is purely *informal*.
a232a132 1512There is nothing fundamental in git that enforces the "chain of
2a29da7c 1513patch flow" this hierarchy implies. You do not have to pull
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1514from only one remote repository.
1515
a232a132 1516A recommended workflow for a "project lead" goes like this:
3eb5128a 1517
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15181. Prepare your primary repository on your local machine. Your
1519 work is done there.
3eb5128a 1520
8db9307c 15212. Prepare a public repository accessible to others.
914328ac
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1522+
1523If other people are pulling from your repository over dumb
80248b2e
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1524transport protocols (HTTP), you need to keep this repository
1525'dumb transport friendly'. After `git init-db`,
914328ac
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1526`$GIT_DIR/hooks/post-update` copied from the standard templates
1527would contain a call to `git-update-server-info` but the
1528`post-update` hook itself is disabled by default -- enable it
80248b2e
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1529with `chmod +x post-update`. This makes sure `git-update-server-info`
1530keeps the necessary files up-to-date.
3eb5128a 1531
8db9307c
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15323. Push into the public repository from your primary
1533 repository.
3eb5128a 1534
914328ac 15354. `git repack` the public repository. This establishes a big
8db9307c 1536 pack that contains the initial set of objects as the
914328ac 1537 baseline, and possibly `git prune` if the transport
8db9307c
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1538 used for pulling from your repository supports packed
1539 repositories.
3eb5128a 1540
8db9307c
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15415. Keep working in your primary repository. Your changes
1542 include modifications of your own, patches you receive via
1543 e-mails, and merges resulting from pulling the "public"
1544 repositories of your "subsystem maintainers".
1545+
1546You can repack this private repository whenever you feel like.
3eb5128a 1547
8db9307c
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15486. Push your changes to the public repository, and announce it
1549 to the public.
3eb5128a 1550
8db9307c
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15517. Every once in a while, "git repack" the public repository.
1552 Go back to step 5. and continue working.
3eb5128a 1553
a232a132 1554
ade75a59
JS
1555A recommended work cycle for a "subsystem maintainer" who works
1556on that project and has an own "public repository" goes like this:
3eb5128a 1557
914328ac 15581. Prepare your work repository, by `git clone` the public
8db9307c 1559 repository of the "project lead". The URL used for the
914328ac 1560 initial cloning is stored in `.git/remotes/origin`.
3eb5128a 1561
914328ac
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15622. Prepare a public repository accessible to others, just like
1563 the "project lead" person does.
3eb5128a 1564
8db9307c 15653. Copy over the packed files from "project lead" public
aa7f412a
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1566 repository to your public repository, unless the "project
1567 lead" repository lives on the same machine as yours. In the
1568 latter case, you can use `objects/info/alternates` file to
1569 point at the repository you are borrowing from.
3eb5128a 1570
8db9307c 15714. Push into the public repository from your primary
914328ac
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1572 repository. Run `git repack`, and possibly `git prune` if the
1573 transport used for pulling from your repository supports
1574 packed repositories.
3eb5128a 1575
8db9307c
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15765. Keep working in your primary repository. Your changes
1577 include modifications of your own, patches you receive via
1578 e-mails, and merges resulting from pulling the "public"
1579 repositories of your "project lead" and possibly your
1580 "sub-subsystem maintainers".
1581+
1582You can repack this private repository whenever you feel
1583like.
3eb5128a 1584
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15856. Push your changes to your public repository, and ask your
1586 "project lead" and possibly your "sub-subsystem
1587 maintainers" to pull from it.
a232a132 1588
914328ac 15897. Every once in a while, `git repack` the public repository.
8db9307c 1590 Go back to step 5. and continue working.
3eb5128a 1591
a232a132 1592
3eb5128a 1593A recommended work cycle for an "individual developer" who does
2a29da7c 1594not have a "public" repository is somewhat different. It goes
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1595like this:
1596
914328ac 15971. Prepare your work repository, by `git clone` the public
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1598 repository of the "project lead" (or a "subsystem
1599 maintainer", if you work on a subsystem). The URL used for
914328ac 1600 the initial cloning is stored in `.git/remotes/origin`.
3eb5128a 1601
914328ac 16022. Do your work in your repository on 'master' branch.
3eb5128a 1603
914328ac 16043. Run `git fetch origin` from the public repository of your
8db9307c 1605 upstream every once in a while. This does only the first
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1606 half of `git pull` but does not merge. The head of the
1607 public repository is stored in `.git/refs/heads/origin`.
3eb5128a 1608
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16094. Use `git cherry origin` to see which ones of your patches
1610 were accepted, and/or use `git rebase origin` to port your
8db9307c 1611 unmerged changes forward to the updated upstream.
3eb5128a 1612
914328ac 16135. Use `git format-patch origin` to prepare patches for e-mail
8db9307c 1614 submission to your upstream and send it out. Go back to
914328ac 1615 step 2. and continue.
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1616
1617
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1618Working with Others, Shared Repository Style
1619--------------------------------------------
1620
1621If you are coming from CVS background, the style of cooperation
1622suggested in the previous section may be new to you. You do not
1623have to worry. git supports "shared public repository" style of
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1624cooperation you are probably more familiar with as well.
1625
1626For this, set up a public repository on a machine that is
1627reachable via SSH by people with "commit privileges". Put the
1628committers in the same user group and make the repository
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1629writable by that group. Make sure their umasks are set up to
1630allow group members to write into directories other members
1631have created.
c9517341 1632
914328ac 1633You, as an individual committer, then:
c9517341 1634
914328ac 1635- First clone the shared repository to a local repository:
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1636------------------------------------------------
1637$ git clone repo.shared.xz:/pub/scm/project.git/ my-project
1638$ cd my-project
1639$ hack away
1640------------------------------------------------
1641
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1642- Merge the work others might have done while you were hacking
1643 away:
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1644------------------------------------------------
1645$ git pull origin
1646$ test the merge result
1647------------------------------------------------
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1648[NOTE]
1649================================
1650The first `git clone` would have placed the following in
1651`my-project/.git/remotes/origin` file, and that's why this and
1652the next step work.
1653------------
1654URL: repo.shared.xz:/pub/scm/project.git/ my-project
1655Pull: master:origin
1656------------
1657================================
c9517341 1658
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1659- push your work as the new head of the shared
1660 repository.
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1661------------------------------------------------
1662$ git push origin master
1663------------------------------------------------
c9517341 1664If somebody else pushed into the same shared repository while
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1665you were working locally, `git push` in the last step would
1666complain, telling you that the remote `master` head does not
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1667fast forward. You need to pull and merge those other changes
1668back before you push your work when it happens.
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1669
1670
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1671Advanced Shared Repository Management
1672-------------------------------------
1673
1674Being able to push into a shared repository means being able to
1675write into it. If your developers are coming over the network,
1676this means you, as the repository administrator, need to give
1677each of them an SSH access to the shared repository machine.
1678
1679In some cases, though, you may not want to give a normal shell
1680account to them, but want to restrict them to be able to only
1681do `git push` into the repository and nothing else.
1682
1683You can achieve this by setting the login shell of your
1684developers on the shared repository host to `git-shell` program.
1685
1686[NOTE]
1687Most likely you would also need to list `git-shell` program in
1688`/etc/shells` file.
1689
1690This restricts the set of commands that can be run from incoming
1691SSH connection for these users to only `receive-pack` and
1692`upload-pack`, so the only thing they can do are `git fetch` and
1693`git push`.
1694
1695You still need to create UNIX user accounts for each developer,
1696and put them in the same group. Make sure that the repository
1697shared among these developers is writable by that group.
1698
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1699. Initializing the shared repository with `git-init-db --shared`
1700helps somewhat.
1701
1702. Run the following in the shared repository:
1703+
1704------------
1705$ chgrp -R $group repo.git
1706$ find repo.git -type d -print | xargs chmod ug+rwx,g+s
1707$ GIT_DIR=repo.git git repo-config core.sharedrepository true
1708------------
1709
1710The above measures make sure that directories lazily created in
1711`$GIT_DIR` are writable by group members. You, as the
1712repository administrator, are still responsible to make sure
1713your developers belong to that shared repository group and set
1714their umask to a value no stricter than 027 (i.e. at least allow
1715reading and searching by group members).
1716
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1717You can implement finer grained branch policies using update
1718hooks. There is a document ("control access to branches") in
1719Documentation/howto by Carl Baldwin and JC outlining how to (1)
1720limit access to branch per user, (2) forbid overwriting existing
1721tags.
1722
1723
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1724Bundling your work together
1725---------------------------
1726
1727It is likely that you will be working on more than one thing at
361c06d8 1728a time. It is easy to manage those more-or-less independent tasks
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1729using branches with git.
1730
361c06d8 1731We have already seen how branches work previously,
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1732with "fun and work" example using two branches. The idea is the
1733same if there are more than two branches. Let's say you started
1734out from "master" head, and have some new code in the "master"
1735branch, and two independent fixes in the "commit-fix" and
1736"diff-fix" branches:
1737
1738------------
1739$ git show-branch
1740! [commit-fix] Fix commit message normalization.
1741 ! [diff-fix] Fix rename detection.
1742 * [master] Release candidate #1
1743---
1744 + [diff-fix] Fix rename detection.
1745 + [diff-fix~1] Better common substring algorithm.
1746+ [commit-fix] Fix commit message normalization.
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1747 * [master] Release candidate #1
1748++* [diff-fix~2] Pretty-print messages.
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1749------------
1750
1751Both fixes are tested well, and at this point, you want to merge
1752in both of them. You could merge in 'diff-fix' first and then
1753'commit-fix' next, like this:
1754
1755------------
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1756$ git merge 'Merge fix in diff-fix' master diff-fix
1757$ git merge 'Merge fix in commit-fix' master commit-fix
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1758------------
1759
1760Which would result in:
1761
1762------------
1763$ git show-branch
1764! [commit-fix] Fix commit message normalization.
1765 ! [diff-fix] Fix rename detection.
1766 * [master] Merge fix in commit-fix
1767---
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1768 - [master] Merge fix in commit-fix
1769+ * [commit-fix] Fix commit message normalization.
1770 - [master~1] Merge fix in diff-fix
1771 +* [diff-fix] Fix rename detection.
1772 +* [diff-fix~1] Better common substring algorithm.
1773 * [master~2] Release candidate #1
1774++* [master~3] Pretty-print messages.
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1775------------
1776
1777However, there is no particular reason to merge in one branch
1778first and the other next, when what you have are a set of truly
1779independent changes (if the order mattered, then they are not
1780independent by definition). You could instead merge those two
1781branches into the current branch at once. First let's undo what
1782we just did and start over. We would want to get the master
1783branch before these two merges by resetting it to 'master~2':
1784
1785------------
1786$ git reset --hard master~2
1787------------
1788
1789You can make sure 'git show-branch' matches the state before
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1790those two 'git merge' you just did. Then, instead of running
1791two 'git merge' commands in a row, you would pull these two
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1792branch heads (this is known as 'making an Octopus'):
1793
1794------------
1795$ git pull . commit-fix diff-fix
1796$ git show-branch
1797! [commit-fix] Fix commit message normalization.
1798 ! [diff-fix] Fix rename detection.
1799 * [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1800---
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1801 - [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
1802+ * [commit-fix] Fix commit message normalization.
1803 +* [diff-fix] Fix rename detection.
1804 +* [diff-fix~1] Better common substring algorithm.
1805 * [master~1] Release candidate #1
1806++* [master~2] Pretty-print messages.
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1807------------
1808
1809Note that you should not do Octopus because you can. An octopus
1810is a valid thing to do and often makes it easier to view the
1811commit history if you are pulling more than two independent
1812changes at the same time. However, if you have merge conflicts
1813with any of the branches you are merging in and need to hand
1814resolve, that is an indication that the development happened in
1815those branches were not independent after all, and you should
1816merge two at a time, documenting how you resolved the conflicts,
1817and the reason why you preferred changes made in one side over
1818the other. Otherwise it would make the project history harder
1819to follow, not easier.
1820
3eb5128a 1821[ to be continued.. cvsimports ]