subdirectory, and initialize the git infrastructure with `git-init-db`:
------------------------------------------------
-mkdir git-tutorial
-cd git-tutorial
-git-init-db
+$ mkdir git-tutorial
+$ cd git-tutorial
+$ git-init-db
------------------------------------------------
to which git will reply
- defaulting to local storage area
+----------------
+defaulting to local storage area
+----------------
which is just git's way of saying that you haven't been doing anything
strange, and that it will have created a local `.git` directory setup for
get a feel for how this works:
------------------------------------------------
-echo "Hello World" >hello
-echo "Silly example" >example
+$ echo "Hello World" >hello
+$ echo "Silly example" >example
------------------------------------------------
you have now created two files in your working tree (aka 'working directory'), but to
The first step is trivial: when you want to tell git about any changes
to your working tree, you use the `git-update-index` program. That
program normally just takes a list of filenames you want to update, but
-to avoid trivial mistakes, it refuses to add new entries to the cache
+to avoid trivial mistakes, it refuses to add new entries to the index
(or remove existing ones) unless you explicitly tell it that you're
adding a new entry with the `\--add` flag (or removing an entry with the
`\--remove`) flag.
So to populate the index with the two files you just created, you can do
------------------------------------------------
-git-update-index --add hello example
+$ git-update-index --add hello example
------------------------------------------------
and you have now told git to track those two files.
you'll notice that git will have added two new objects to the object
database. If you did exactly the steps above, you should now be able to do
- ls .git/objects/??/*
+
+----------------
+$ ls .git/objects/??/*
+----------------
and see two files:
- .git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
- .git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
+----------------
+.git/objects/55/7db03de997c86a4a028e1ebd3a1ceb225be238
+.git/objects/f2/4c74a2e500f5ee1332c86b94199f52b1d1d962
+----------------
which correspond with the objects with names of 557db... and f24c7..
respectively.
If you want to, you can use `git-cat-file` to look at those objects, but
you'll have to use the object name, not the filename of the object:
- git-cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
+----------------
+$ git-cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
+----------------
where the `-t` tells `git-cat-file` to tell you what the "type" of the
object is. git will tell you that you have a "blob" object (ie just a
regular file), and you can see the contents with
- git-cat-file "blob" 557db03
+----------------
+$ git-cat-file "blob" 557db03
+----------------
which will print out "Hello World". The object 557db03 is nothing
more than the contents of your file `hello`.
actually saved away the contents of your files into the git object
database.
-Updating the cache did something else too: it created a `.git/index`
+Updating the index did something else too: it created a `.git/index`
file. This is the index that describes your current working tree, and
something you should be very aware of. Again, you normally never worry
about the index file itself, but you should be aware of the fact that
start off by adding another line to `hello` first:
------------------------------------------------
-echo "It's a new day for git" >>hello
+$ echo "It's a new day for git" >>hello
------------------------------------------------
and you can now, since you told git about the previous state of `hello`, ask
`git-diff-files` command:
------------
-git-diff-files
+$ git-diff-files
------------
Oops. That wasn't very readable. It just spit out its own internal
differences as a patch, using the `-p` flag:
------------
-git-diff-files -p
-------------
-
-which will spit out
-
-------------
+$ git-diff-files -p
diff --git a/hello b/hello
index 557db03..263414f 100644
--- a/hello
creating the equivalent of a git "directory" object:
------------------------------------------------
-git-write-tree
+$ git-write-tree
------------------------------------------------
and this will just output the name of the resulting tree, in this case
(if you have done exactly as I've described) it should be
- 8988da15d077d4829fc51d8544c097def6644dbb
+----------------
+8988da15d077d4829fc51d8544c097def6644dbb
+----------------
which is another incomprehensible object name. Again, if you want to,
you can use `git-cat-file -t 8988d\...` to see that this time the object
all with a sequence of simple shell commands:
------------------------------------------------
-tree=$(git-write-tree)
-commit=$(echo 'Initial commit' | git-commit-tree $tree)
-git-update-ref HEAD $(commit)
+$ tree=$(git-write-tree)
+$ commit=$(echo 'Initial commit' | git-commit-tree $tree)
+$ git-update-ref HEAD $commit
------------------------------------------------
which will say:
- Committing initial tree 8988da15d077d4829fc51d8544c097def6644dbb
+----------------
+Committing initial tree 8988da15d077d4829fc51d8544c097def6644dbb
+----------------
just to warn you about the fact that it created a totally new commit
that is not related to anything else. Normally you do this only *once*
But now we can do
- git-diff-index -p HEAD
+----------------
+$ git-diff-index -p HEAD
+----------------
(where `-p` has the same meaning as it did in `git-diff-files`), and it
will show us the same difference, but for a totally different reason.
Again, because this is a common operation, you can also just shorthand
it with
- git diff HEAD
+----------------
+$ git diff HEAD
+----------------
which ends up doing the above for you.
update the index cache:
------------------------------------------------
-git-update-index hello
+$ git-update-index hello
------------------------------------------------
(note how we didn't need the `\--add` flag this time, since git knew
already, so let's just use the helpful script this time:
------------------------------------------------
-git commit
+$ git commit
------------------------------------------------
which starts an editor for you to write the commit message and tells you
Write whatever message you want, and all the lines that start with '#'
will be pruned out, and the rest will be used as the commit message for
the change. If you decide you don't want to commit anything after all at
-this point (you can continue to edit things and update the cache), you
+this point (you can continue to edit things and update the index), you
can just leave an empty message. Otherwise `git commit` will commit
the change for you.
of that commit itself, and show the difference directly. Thus, to get
the same diff that we've already seen several times, we can now do
- git-diff-tree -p HEAD
+----------------
+$ git-diff-tree -p HEAD
+----------------
(again, `-p` means to show the difference as a human-readable patch),
and it will show what the last commit (in `HEAD`) actually changed.
+[NOTE]
+============
+Here is an ASCII art by Jon Loeliger that illustrates how
+various diff-\* commands compare things.
+
+ diff-tree
+ +----+
+ | |
+ | |
+ V V
+ +-----------+
+ | Object DB |
+ | Backing |
+ | Store |
+ +-----------+
+ ^ ^
+ | |
+ | | diff-index --cached
+ | |
+ diff-index | V
+ | +-----------+
+ | | Index |
+ | | "cache" |
+ | +-----------+
+ | ^
+ | |
+ | | diff-files
+ | |
+ V V
+ +-----------+
+ | Working |
+ | Directory |
+ +-----------+
+============
+
More interestingly, you can also give `git-diff-tree` the `-v` flag, which
tells it to also show the commit message and author and date of the
commit, and you can tell it to show a whole series of diffs.
To see the whole history of our pitiful little git-tutorial project, you
can do
- git log
+----------------
+$ git log
+----------------
which shows just the log messages, or if we want to see the log together
with the associated patches use the more complex (and much more
powerful)
- git-whatchanged -p --root
+----------------
+$ git-whatchanged -p --root
+----------------
and you will see exactly what has changed in the repository over its
short history.
So the simplest form of tag involves nothing more than
------------------------------------------------
-git tag my-first-tag
+$ git tag my-first-tag
------------------------------------------------
which just writes the current `HEAD` into the `.git/refs/tags/my-first-tag`
file, after which point you can then use this symbolic name for that
particular state. You can, for example, do
- git diff my-first-tag
+----------------
+$ git diff my-first-tag
+----------------
to diff your current state against that tag (which at this point will
obviously be an empty diff, but if you continue to develop and commit
that tag. You create these annotated tags with either the `-a` or
`-s` flag to `git tag`:
- git tag -s <tagname>
+----------------
+$ git tag -s <tagname>
+----------------
which will sign the current `HEAD` (but you can also give it another
argument that specifies the thing to tag, ie you could have tagged the
Copying repositories
--------------------
-git repositories are normally totally self-sufficient, and it's worth noting
-that unlike CVS, for example, there is no separate notion of
+git repositories are normally totally self-sufficient and relocatable
+Unlike CVS, for example, there is no separate notion of
"repository" and "working tree". A git repository normally *is* the
working tree, with the local git information hidden in the `.git`
subdirectory. There is nothing else. What you see is what you got.
- if you grow bored with the tutorial repository you created (or you've
made a mistake and want to start all over), you can just do simple
-
- rm -rf git-tutorial
++
+----------------
+$ rm -rf git-tutorial
+----------------
+
and it will be gone. There's no external repository, and there's no
history outside the project you created.
file (which caches various information, notably some of the "stat"
information for the files involved) will likely need to be refreshed.
So after you do a `cp -a` to create a new copy, you'll want to do
-
- git-update-index --refresh
++
+----------------
+$ git-update-index --refresh
+----------------
+
in the new repository to make sure that the index file is up-to-date.
known state (you don't know *what* they've done and not yet checked in),
so usually you'll precede the `git-update-index` with a
- git-read-tree --reset HEAD
- git-update-index --refresh
+----------------
+$ git-read-tree --reset HEAD
+$ git-update-index --refresh
+----------------
which will force a total index re-build from the tree pointed to by `HEAD`.
It resets the index contents to `HEAD`, and then the `git-update-index`
The above can also be written as simply
- git reset
+----------------
+$ git reset
+----------------
and in fact a lot of the common git command combinations can be scripted
with the `git xyz` interfaces. You can learn things by just looking
raw repository contents into the `.git` directory. For example, to
create your own copy of the git repository, you'd do the following
- mkdir my-git
- cd my-git
- rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
+----------------
+$ mkdir my-git
+$ cd my-git
+$ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
+----------------
followed by
- git-read-tree HEAD
+----------------
+$ git-read-tree HEAD
+----------------
to populate the index. However, now you have populated the index, and
you have all the git internal files, but you will notice that you don't
actually have any of the working tree files to work on. To get
those, you'd check them out with
- git-checkout-index -u -a
+----------------
+$ git-checkout-index -u -a
+----------------
where the `-u` flag means that you want the checkout to keep the index
up-to-date (so that you don't have to refresh it afterward), and the
Again, this can all be simplified with
- git clone rsync://rsync.kernel.org/pub/scm/git/git.git/ my-git
- cd my-git
- git checkout
+----------------
+$ git clone rsync://rsync.kernel.org/pub/scm/git/git.git/ my-git
+$ cd my-git
+$ git checkout
+----------------
which will end up doing all of the above for you.
saying that you want to check out a new branch:
------------
-git checkout -b mybranch
+$ git checkout -b mybranch
------------
will create a new branch based at the current `HEAD` position, and switch
In other words, if you have an earlier tag or branch, you'd just do
------------
-git checkout -b mybranch earlier-commit
+$ git checkout -b mybranch earlier-commit
------------
and it would create the new branch `mybranch` at the earlier commit,
You can always just jump back to your original `master` branch by doing
------------
-git checkout master
+$ git checkout master
------------
(or any other branch-name, for that matter) and if you forget which
branch you happen to be on, a simple
------------
-ls -l .git/HEAD
+$ ls -l .git/HEAD
------------
will tell you where it's pointing (Note that on platforms with bad or no
symlink support, you have to execute
------------
-cat .git/HEAD
+$ cat .git/HEAD
------------
instead). To get the list of branches you have, you can say
------------
-git branch
+$ git branch
------------
which is nothing more than a simple script around `ls .git/refs/heads`.
checking it out and switching to it. If so, just use the command
------------
-git branch <branchname> [startingpoint]
+$ git branch <branchname> [startingpoint]
------------
which will simply _create_ the branch, but will not do anything further.
that branch, and do some work there.
------------------------------------------------
-git checkout mybranch
-echo "Work, work, work" >>hello
-git commit -m 'Some work.' hello
+$ git checkout mybranch
+$ echo "Work, work, work" >>hello
+$ git commit -m 'Some work.' hello
------------------------------------------------
Here, we just added another line to `hello`, and we used a shorthand for
to the master branch, and editing the same file differently there:
------------
-git checkout master
+$ git checkout master
------------
Here, take a moment to look at the contents of `hello`, and notice how they
hasn't happened in the `master` branch at all. Then do
------------
-echo "Play, play, play" >>hello
-echo "Lots of fun" >>example
-git commit -m 'Some fun.' hello example
+$ echo "Play, play, play" >>hello
+$ echo "Lots of fun" >>example
+$ git commit -m 'Some fun.' hello example
------------
since the master branch is obviously in a much better mood.
work done. Before we do that, let's introduce a cool graphical tool that
helps you view what's going on:
- gitk --all
+----------------
+$ gitk --all
+----------------
will show you graphically both of your branches (that's what the `\--all`
means: normally it will just show you your current `HEAD`) and their
Anyway, let's exit `gitk` (`^Q` or the File menu), and decide that we want
to merge the work we did on the `mybranch` branch into the `master`
branch (which is currently our `HEAD` too). To do that, there's a nice
-script called `git resolve`, which wants to know which branches you want
+script called `git merge`, which wants to know which branches you want
to resolve and what the merge is all about:
------------
-git resolve HEAD mybranch "Merge work in mybranch"
+$ git merge "Merge work in mybranch" HEAD mybranch
------------
-where the third argument is going to be used as the commit message if
+where the first argument is going to be used as the commit message if
the merge can be resolved automatically.
Now, in this case we've intentionally created a situation where the
of it as it can automatically (which in this case is just merge the `example`
file, which had no differences in the `mybranch` branch), and say:
- Simple merge failed, trying Automatic merge
- Auto-merging hello.
+----------------
+ Trying really trivial in-index merge...
+ fatal: Merge requires file-level merging
+ Nope.
+ ...
merge: warning: conflicts during merge
ERROR: Merge conflict in hello.
fatal: merge program failed
- Automatic merge failed, fix up by hand
+ Automatic merge failed/prevented; fix up by hand
+----------------
which is way too verbose, but it basically tells you that it failed the
really trivial merge ("Simple merge") and did an "Automatic merge"
and once you're happy with your manual merge, just do a
------------
-git commit hello
+$ git commit hello
------------
which will very loudly warn you that you're now committing a merge
resolve to get the "upstream changes" back to your branch.
------------
-git checkout mybranch
-git resolve HEAD master "Merge upstream changes."
+$ git checkout mybranch
+$ git merge "Merge upstream changes." HEAD master
------------
This outputs something like this (the actual commit object names
would be different)
- Updating from ae3a2da... to a80b4aa....
- example | 1 +
- hello | 1 +
- 2 files changed, 2 insertions(+), 0 deletions(-)
+----------------
+Updating from ae3a2da... to a80b4aa....
+ example | 1 +
+ hello | 1 +
+ 2 files changed, 2 insertions(+), 0 deletions(-)
+----------------
Because your branch did not contain anything more than what are
already merged into the `master` branch, the resolve operation did
It's usually much more common that you merge with somebody else than
merging with your own branches, so it's worth pointing out that git
makes that very easy too, and in fact, it's not that different from
-doing a `git resolve`. In fact, a remote merge ends up being nothing
+doing a `git merge`. In fact, a remote merge ends up being nothing
more than "fetch the work from a remote repository into a temporary tag"
-followed by a `git resolve`.
+followed by a `git merge`.
Fetching from a remote repository is done by, unsurprisingly,
`git fetch`:
- git fetch <remote-repository>
+----------------
+$ git fetch <remote-repository>
+----------------
One of the following transports can be used to name the
repository to download from:
transport, it finds out the set of objects the downstream side
lacks and transfers (close to) minimum set of objects.
-HTTP(s)::
+HTTP(S)::
`http://remote.machine/path/to/repo.git/`
+
HTTP and HTTPS transport are used only for downloading. They
immediately `resolve`, that it's called `git pull`, and you can
simply do
- git pull <remote-repository>
+----------------
+$ git pull <remote-repository>
+----------------
and optionally give a branch-name for the remote end as a second
argument.
[NOTE]
You could even pull from your own repository by
-giving '.' as <remote-repository> parameter to `git pull`.
+giving '.' as <remote-repository> parameter to `git pull`. This
+is useful when you want to merge a local branch (or more, if you
+are making an Octopus) into the current branch.
It is likely that you will be pulling from the same remote
repository from time to time. As a short hand, you can store
directory, like this:
------------------------------------------------
-mkdir -p .git/remotes/
-cat >.git/remotes/linus <<\EOF
+$ mkdir -p .git/remotes/
+$ cat >.git/remotes/linus <<\EOF
URL: http://www.kernel.org/pub/scm/git/git.git/
EOF
------------------------------------------------
of a full URL, like this:
------------------------------------------------
-cat >.git/remotes/jgarzik <<\EOF
+$ cat >.git/remotes/jgarzik <<\EOF
URL: http://www.kernel.org/pub/scm/linux/git/jgarzik/
EOF
------------------------------------------------
. `git pull http://www.kernel.org/pub/.../jgarzik/netdev-2.6.git e100`
+How does the merge work?
+------------------------
+
+We said this tutorial shows what plumbing does to help you cope
+with the porcelain that isn't flushing, but we so far did not
+talk about how the merge really works. If you are following
+this tutorial the first time, I'd suggest to skip to "Publishing
+your work" section and come back here later.
+
+OK, still with me? To give us an example to look at, let's go
+back to the earlier repository with "hello" and "example" file,
+and bring ourselves back to the pre-merge state:
+
+------------
+$ git show-branch --more=3 master mybranch
+! [master] Merge work in mybranch
+ * [mybranch] Merge work in mybranch
+--
+++ [master] Merge work in mybranch
+++ [master^2] Some work.
+++ [master^] Some fun.
+------------
+
+Remember, before running `git merge`, our `master` head was at
+"Some fun." commit, while our `mybranch` head was at "Some
+work." commit.
+
+------------
+$ git checkout mybranch
+$ git reset --hard master^2
+$ git checkout master
+$ git reset --hard master^
+------------
+
+After rewinding, the commit structure should look like this:
+
+------------
+$ git show-branch
+* [master] Some fun.
+ ! [mybranch] Some work.
+--
+ + [mybranch] Some work.
++ [master] Some fun.
+++ [mybranch^] New day.
+------------
+
+Now we are ready to experiment with the merge by hand.
+
+`git merge` command, when merging two branches, uses 3-way merge
+algorithm. First, it finds the common ancestor between them.
+The command it uses is `git-merge-base`:
+
+------------
+$ mb=$(git-merge-base HEAD mybranch)
+------------
+
+The command writes the commit object name of the common ancestor
+to the standard output, so we captured its output to a variable,
+because we will be using it in the next step. BTW, the common
+ancestor commit is the "New day." commit in this case. You can
+tell it by:
+
+------------
+$ git-name-rev $mb
+my-first-tag
+------------
+
+After finding out a common ancestor commit, the second step is
+this:
+
+------------
+$ git-read-tree -m -u $mb HEAD mybranch
+------------
+
+This is the same `git-read-tree` command we have already seen,
+but it takes three trees, unlike previous examples. This reads
+the contents of each tree into different 'stage' in the index
+file (the first tree goes to stage 1, the second stage 2,
+etc.). After reading three trees into three stages, the paths
+that are the same in all three stages are 'collapsed' into stage
+0. Also paths that are the same in two of three stages are
+collapsed into stage 0, taking the SHA1 from either stage 2 or
+stage 3, whichever is different from stage 1 (i.e. only one side
+changed from the common ancestor).
+
+After 'collapsing' operation, paths that are different in three
+trees are left in non-zero stages. At this point, you can
+inspect the index file with this command:
+
+------------
+$ git-ls-files --stage
+100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
+100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
+100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
+100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
+------------
+
+In our example of only two files, we did not have unchanged
+files so only 'example' resulted in collapsing, but in real-life
+large projects, only small number of files change in one commit,
+and this 'collapsing' tends to trivially merge most of the paths
+fairly quickly, leaving only a handful the real changes in non-zero
+stages.
+
+To look at only non-zero stages, use `\--unmerged` flag:
+
+------------
+$ git-ls-files --unmerged
+100644 263414f423d0e4d70dae8fe53fa34614ff3e2860 1 hello
+100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 2 hello
+100644 cc44c73eb783565da5831b4d820c962954019b69 3 hello
+------------
+
+The next step of merging is to merge these three versions of the
+file, using 3-way merge. This is done by giving
+`git-merge-one-file` command as one of the arguments to
+`git-merge-index` command:
+
+------------
+$ git-merge-index git-merge-one-file hello
+Auto-merging hello.
+merge: warning: conflicts during merge
+ERROR: Merge conflict in hello.
+fatal: merge program failed
+------------
+
+`git-merge-one-file` script is called with parameters to
+describe those three versions, and is responsible to leave the
+merge results in the working tree and register it in the index
+file. It is a fairly straightforward shell script, and
+eventually calls `merge` program from RCS suite to perform the
+file-level 3-way merge. In this case, `merge` detects
+conflicts, and the merge result with conflict marks is left in
+the working tree, while the index file is updated with the
+version from the current branch (this is to make `git diff`
+useful after this step). This can be seen if you run `ls-files
+--stage` again at this point:
+
+------------
+$ git-ls-files --stage
+100644 7f8b141b65fdcee47321e399a2598a235a032422 0 example
+100644 06fa6a24256dc7e560efa5687fa84b51f0263c3a 0 hello
+------------
+
+As you can see, there is no unmerged paths in the index file.
+This is the state of the index file and the working file after
+`git merge` returns control back to you, leaving the conflicting
+merge for you to resolve.
+
+
Publishing your work
--------------------
an empty directory:
------------
-mkdir my-git.git
+$ mkdir my-git.git
------------
Then, make that directory into a git repository by running
`.git`, we do things slightly differently:
------------
-GIT_DIR=my-git.git git-init-db
+$ GIT_DIR=my-git.git git-init-db
------------
Make sure this directory is available for others you want your
there, run this command:
------------
-git push <public-host>:/path/to/my-git.git master
+
$ git push <public-host>:/path/to/my-git.git master
------------
This synchronizes your public repository to match the named
propagation to other publicly visible machines:
------------
-git push master.kernel.org:/pub/scm/git/git.git/
+$ git push master.kernel.org:/pub/scm/git/git.git/
------------
storage by "packing them together". The command
------------
-git repack
+$ git repack
------------
will do it for you. If you followed the tutorial examples, you
unpacked objects that are contained in the pack file anymore.
------------
-git prune-packed
+$ git prune-packed
------------
would remove them for you.
'commit-fix' next, like this:
------------
-$ git resolve master diff-fix 'Merge fix in diff-fix'
-$ git resolve master commit-fix 'Merge fix in commit-fix'
+$ git merge 'Merge fix in diff-fix' master diff-fix
+$ git merge 'Merge fix in commit-fix' master commit-fix
------------
Which would result in:
------------
You can make sure 'git show-branch' matches the state before
-those two 'git resolve' you just did. Then, instead of running
-two 'git resolve' commands in a row, you would pull these two
+those two 'git merge' you just did. Then, instead of running
+two 'git merge' commands in a row, you would pull these two
branch heads (this is known as 'making an Octopus'):
------------