in your git archive. We'll start off with a few bad examples, just to
get a feel for how this works:
- echo "Hello World" > a
- echo "Silly example" > b
+ echo "Hello World" >hello
+ echo "Silly example" >example
you have now created two files in your working directory, but to
actually check in your hard work, you will have to go through two steps:
So to populate the index with the two files you just created, you can do
- git-update-cache --add a b
+ git-update-cache --add hello example
and you have now told git to track those two files.
git-cat-file "blob" 557db03de997c86a4a028e1ebd3a1ceb225be238
which will print out "Hello World". The object 557db... is nothing
-more than the contents of your file "a".
+more than the contents of your file "hello".
-[ Digression: don't confuse that object with the file "a" itself. The
+[ Digression: don't confuse that object with the file "hello" itself. The
object is literally just those specific _contents_ of the file, and
- however much you later change the contents in file "a", the object we
+ however much you later change the contents in file "hello", the object we
just looked at will never change. Objects are immutable. ]
Anyway, as we mentioned previously, you normally never actually take a
most basic git commands to manipulate the files or look at their status.
In particular, let's not even check in the two files into git yet, we'll
-start off by adding another line to "a" first:
+start off by adding another line to "hello" first:
- echo "It's a new day for git" >> a
+ echo "It's a new day for git" >>hello
-and you can now, since you told git about the previous state of "a", ask
+and you can now, since you told git about the previous state of "hello", ask
git what has changed in the tree compared to your old index, using the
"git-diff-files" command:
oops. That wasn't very readable. It just spit out its own internal
version of a "diff", but that internal version really just tells you
-that it has noticed that "a" has been modified, and that the old object
+that it has noticed that "hello" has been modified, and that the old object
contents it had have been replaced with something else.
To make it readable, we can tell git-diff-files to output the
which will spit out
- diff --git a/a b/a
- --- a/a
- +++ b/a
+ diff --git a/hello b/hello
+ --- a/hello
+ +++ b/hello
@@ -1 +1,2 @@
Hello World
+It's a new day for git
-ie the diff of the change we caused by adding another line to "a".
+ie the diff of the change we caused by adding another line to "hello".
In other words, git-diff-files always shows us the difference between
what is recorded in the index, and what is currently in the working
and this will just output the name of the resulting tree, in this case
(if you have does exactly as I've described) it should be
- 3ede4ed7e895432c0a247f09d71a76db53bd0fa4
+ 8988da15d077d4829fc51d8544c097def6644dbb
which is another incomprehensible object name. Again, if you want to,
-you can use "git-cat-file -t 3ede4.." to see that this time the object
+you can use "git-cat-file -t 8988d.." to see that this time the object
is not a "blob" object, but a "tree" object (you can also use
git-cat-file to actually output the raw object contents, but you'll see
mainly a binary mess, so that's less interesting).
which will say:
- Committing initial tree 3ede4ed7e895432c0a247f09d71a76db53bd0fa4
+ 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_
Making a change
---------------
-Remember how we did the "git-update-cache" on file "a" and then we
-changed "a" afterward, and could compare the new state of "a" with the
+Remember how we did the "git-update-cache" on file "hello" and then we
+changed "hello" afterward, and could compare the new state of "hello" with the
state we saved in the index file?
Further, remember how I said that "git-write-tree" writes the contents
of the _index_ file to the tree, and thus what we just committed was in
-fact the _original_ contents of the file "a", not the new ones. We did
+fact the _original_ contents of the file "hello", not the new ones. We did
that on purpose, to show the difference between the index state, and the
state in the working directory, and how they don't have to match, even
when we commit things.
work through the index file, so the first thing we need to do is to
update the index cache:
- git-update-cache a
+ git-update-cache hello
(note how we didn't need the "--add" flag this time, since git knew
about the file already).
Note what happens to the different git-diff-xxx versions here. After
-we've updated "a" in the index, "git-diff-files -p" now shows no
+we've updated "hello" in the index, "git-diff-files -p" now shows no
differences, but "git-diff-cache -p HEAD" still _does_ show that the
current state is different from the state we committed. In fact, now
"git-diff-cache" shows the same difference whether we use the "--cached"
flag or not, since now the index is coherent with the working directory.
-Now, since we've updated "a" in the index, we can commit the new
+Now, since we've updated "hello" in the index, we can commit the new
version. We could do it by writing the tree by hand again, and
committing the tree (this time we'd have to use the "-p HEAD" flag to
tell commit that the HEAD was the _parent_ of the new commit, and that
can explore on your own.
+[ Side note: most likely, you are not directly using the core
+ git Plumbing commands, but using Porcelain like Cogito on top
+ of it. Cogito works a bit differently and you usually do not
+ have to run "git-update-cache" yourself for changed files (you
+ do tell underlying git about additions and removals via
+ "cg-add" and "cg-rm" commands). Just before you make a commit
+ with "cg-commit", Cogito figures out which files you modified,
+ and runs "git-update-cache" on them for you. ]
+
+
+ Tagging a version
+ -----------------
+
+In git, there's two kinds of tags, a "light" one, and a "signed tag".
+
+A "light" tag is technically nothing more than a branch, except we put
+it in the ".git/refs/tags/" subdirectory instead of calling it a "head".
+So the simplest form of tag involves nothing more than
+
+ 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
+
+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
+stuff, you can use your tag as a "anchor-point" to see what has changed
+since you tagged it.
+
+A "signed tag" is actually a real git object, and contains not only a
+pointer to the state you want to tag, but also a small tag name and
+message, along with a PGP signature that says that yes, you really did
+that tag. You create these signed tags with the "-s" flag to "git tag":
+
+ 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
+current "mybranch" point by using "git tag <tagname> mybranch").
+
+You normally only do signed tags for major releases or things
+like that, while the light-weight tags are useful for any marking you
+want to do - any time you decide that you want to remember a certain
+point, just create a private tag for it, and you have a nice symbolic
+name for the state at that point.
+
+
Copying archives
-----------------
history outside of the project you created.
- if you want to move or duplicate a git archive, you can do so. There
- is no "git clone" command: if you want to create a copy of your
- archive (with all the full history that went along with it), you can
- do so with a regular "cp -a git-tutorial new-git-tutorial".
+ is "git clone" command, but if all you want to do is just to
+ create a copy of your archive (with all the full history that
+ went along with it), you can do so with a regular
+ "cp -a git-tutorial new-git-tutorial".
Note that when you've moved or copied a git archive, your git index
file (which caches various information, notably some of the "stat"
mkdir my-git
cd my-git
- rsync -rL rsync://rsync.kernel.org/pub/scm/linux/kernel/git/torvalds/git.git/ .git
+ rsync -rL rsync://rsync.kernel.org/pub/scm/git/git.git/ .git
followed by
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
-"-a" file means "check out all files" (if you have a stale copy or an
+"-a" flag means "check out all files" (if you have a stale copy or an
older version of a checked out tree you may also need to add the "-f"
-file first, to tell git-checkout-cache to _force_ overwriting of any old
+flag first, to tell git-checkout-cache to _force_ overwriting of any old
files).
Again, this can all be simplified with
- git clone rsync://rsync.kernel.org/pub/scm/linux/kernel/git/torvalds/git.git/ my-git
+ git clone rsync://rsync.kernel.org/pub/scm/git/git.git/ my-git
cd my-git
git checkout
---------------------
Branches in git are really nothing more than pointers into the git
-object space from within the ",git/refs/" subdirectory, and as we
+object space from within the ".git/refs/" subdirectory, and as we
already discussed, the HEAD branch is nothing but a symlink to one of
these object pointers.
and nothing enforces it.
To show that as an example, let's go back to the git-tutorial archive we
-used earlier, and create a branch in it. You literally do that by just
-creating a new SHA1 reference file, and switch to it by just making the
-HEAD pointer point to it:
+used earlier, and create a branch in it. You do that by simply just
+saying that you want to check out a new branch:
- cat .git/HEAD > .git/refs/heads/mybranch
- ln -sf refs/heads/mybranch .git/HEAD
+ git checkout -b mybranch
-and you're done.
+will create a new branch based at the current HEAD position, and switch
+to it.
-Now, if you make the decision to start your new branch at some other
-point in the history than the current HEAD, you usually also want to
-actually switch the contents of your working directory to that point
-when you switch the head, and "git checkout" will do that for you:
-instead of switching the branch by hand with "ln -sf", you can just do
+[ Side note: if you make the decision to start your new branch at some
+ other point in the history than the current HEAD, you can do so by
+ just telling "git checkout" what the base of the checkout would be.
+ In other words, if you have an earlier tag or branch, you'd just do
- git checkout mybranch
+ git checkout -b mybranch earlier-branch
-which will basically "jump" to the branch specified, update your working
-directory to that state, and also make it become the new default HEAD.
+ and it would create the new branch "mybranch" at the earlier point,
+ and check out the state at that time. ]
You can always just jump back to your original "master" branch by doing
git checkout master
-and if you forget which branch you happen to be on, a simple
+(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
will tell you where it's pointing.
+NOTE! Sometimes you may wish to create a new branch _without_ actually
+checking it out and switching to it. If so, just use the command
+
+ git branch <branchname> [startingpoint]
+
+which will simply _create_ the branch, but will not do anything further.
+You can then later - once you decide that you want to actually develop
+on that branch - switch to that branch with a regular "git checkout"
+with the branchname as the argument.
+
Merging two branches
--------------------
that branch, and do some work there.
git checkout mybranch
- echo "Work, work, work" >> a
- git commit a
+ echo "Work, work, work" >>hello
+ git commit hello
-Here, we just added another line to "a", and we used a shorthand for
-both going a "git-update-cache a" and "git commit" by just giving the
-filename directly to "git commit".
+Here, we just added another line to "hello", and we used a shorthand for
+both going a "git-update-cache hello" and "git commit" by just giving the
+filename directly to "git commit".
Now, to make it a bit more interesting, let's assume that somebody else
does some work in the original branch, and simulate that by going back
git checkout master
-Here, take a moment to look at the contents of "a", and notice how they
+Here, take a moment to look at the contents of "hello", and notice how they
don't contain the work we just did in "mybranch" - because that work
hasn't happened in the "master" branch at all. Then do
- echo "Play, play, play" >> a
- echo "Lots of fun" >> b
- git commit a b
+ echo "Play, play, play" >>hello
+ echo "Lots of fun" >>example
+ git commit hello example
since the master branch is obviously in a much better mood.
file, which had no differences in the "mybranch" branch), and say:
Simple merge failed, trying Automatic merge
- Auto-merging a.
+ Auto-merging hello.
merge: warning: conflicts during merge
- ERROR: Merge conflict in a.
+ ERROR: Merge conflict in hello.
fatal: merge program failed
Automatic merge failed, 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"
-instead, but that too failed due to conflicts in "a".
+instead, but that too failed due to conflicts in "hello".
-Not to worry. It left the (trivial) conflict in "a" in the same form you
+Not to worry. It left the (trivial) conflict in "hello" in the same form you
should already be well used to if you've ever used CVS, so let's just
-open "a" in our editor (whatever that may be), and fix it up somehow.
-I'd suggest just making it so that "a" contains all four lines:
+open "hello" in our editor (whatever that may be), and fix it up somehow.
+I'd suggest just making it so that "hello" contains all four lines:
Hello World
It's a new day for git
and once you're happy with your manual merge, just do a
- git commit a
+ git commit hello
which will very loudly warn you that you're now committing a merge
(which is correct, so never mind), and you can write a small merge
message about your adventures in git-merge-land.
After you're done, start up "gitk --all" to see graphically what the
-history looks like. Notive that "mybranch" still exists, and you can
+history looks like. Notice that "mybranch" still exists, and you can
switch to it, and continue to work with it if you want to. The
"mybranch" branch will not contain the merge, but next time you merge it
from the "master" branch, git will know how you merged it, so you'll not
and optionally give a branch-name for the remote end as a second
argument.
-[ Todo: fill in real examples ]
+The "remote" repository can even be on the same machine. One of
+the following notations can be used to name the repository to
+pull from:
+ Rsync URL
+ rsync://remote.machine/path/to/repo.git/
- Tagging a version
- -----------------
+ HTTP(s) URL
+ http://remote.machine/path/to/repo.git/
-In git, there's two kinds of tags, a "light" one, and a "signed tag".
+ GIT URL
+ git://remote.machine/path/to/repo.git/
+ remote.machine:/path/to/repo.git/
-A "light" tag is technically nothing more than a branch, except we put
-it in the ".git/refs/tags/" subdirectory instead of calling it a "head".
-So the simplest form of tag involves nothing more than
+ Local directory
+ /path/to/repo.git/
- cat .git/HEAD > .git/refs/tags/my-first-tag
+[ Side Note: currently, HTTP transport is slightly broken in
+ that when the remote repository is "packed" they do not always
+ work. But we have not talked about packing repository yet, so
+ let's not worry too much about it for now. ]
-after which point you can use this symbolic name for that particular
-state. You can, for example, do
+[ Digression: you could do without using any branches at all, by
+ keeping as many local repositories as you would like to have
+ branches, and merging between them with "git pull", just like
+ you merge between branches. The advantage of this approach is
+ that it lets you keep set of files for each "branch" checked
+ out and you may find it easier to switch back and forth if you
+ juggle multiple lines of development simultaneously. Of
+ course, you will pay the price of more disk usage to hold
+ multiple working trees, but disk space is cheap these days. ]
- git diff my-first-tag
+It is likely that you will be pulling from the same remote
+repository from time to time. As a short hand, you can store
+the remote repository URL in a file under .git/branches/
+directory, like this:
-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
-stuff, you can use your tag as a "anchor-point" to see what has changed
-since you tagged it.
+ mkdir -p .git/branches
+ echo rsync://kernel.org/pub/scm/git/git.git/ \
+ >.git/branches/linus
-A "signed tag" is actually a real git object, and contains not only a
-pointer to the state you want to tag, but also a small tag name and
-message, along with a PGP signature that says that yes, you really did
-that tag. You create these signed tags with
+and use the filenae to "git pull" instead of the full URL.
+The contents of a file under .git/branches can even be a prefix
+of a full URL, like this:
- git tag <tagname>
+ echo rsync://kernel.org/pub/.../jgarzik/
+ >.git/branches/jgarzik
-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
-current "mybranch" point by using "git tag <tagname> mybranch").
+Examples.
+
+ (1) git pull linus
+ (2) git pull linus tag v0.99.1
+ (3) git pull jgarzik/netdev-2.6.git/ e100
+
+the above are equivalent to:
+
+ (1) git pull rsync://kernel.org/pub/scm/git/git.git/ HEAD
+ (2) git pull rsync://kernel.org/pub/scm/git/git.git/ tag v0.99.1
+ (3) git pull rsync://kernel.org/pub/.../jgarzik/netdev-2.6.git e100
+
+
+ Publishing your work
+ --------------------
+
+So we can use somebody else's work from a remote repository; but
+how can _you_ prepare a repository to let other people pull from
+it?
+
+Your do your real work in your working directory that has your
+primary repository hanging under it as its ".git" subdirectory.
+You _could_ make that repository accessible remotely and ask
+people to pull from it, but in practice that is not the way
+things are usually done. A recommended way is to have a public
+repository, make it reachable by other people, and when the
+changes you made in your primary working directory are in good
+shape, update the public repository from it. This is often
+called "pushing".
+
+[ Side note: this public repository could further be mirrored,
+ and that is how kernel.org git repositories are done. ]
+
+Publishing the changes from your local (private) repository to
+your remote (public) repository requires a write privilege on
+the remote machine. You need to have an SSH account there to
+run a single command, "git-receive-pack".
+
+First, you need to create an empty repository on the remote
+machine that will house your public repository. This empty
+repository will be populated and be kept up-to-date by pushing
+into it later. Obviously, this repository creation needs to be
+done only once.
+
+[ Digression: "git push" uses a pair of programs,
+ "git-send-pack" on your local machine, and "git-receive-pack"
+ on the remote machine. The communication between the two over
+ the network internally uses an SSH connection. ]
+
+Your private repository's GIT directory is usually .git, but
+your public repository is often named after the project name,
+i.e. "<project>.git". Let's create such a public repository for
+project "my-git". After logging into the remote machine, create
+an empty directory:
+
+ mkdir my-git.git
+
+Then, make that directory into a GIT repository by running
+git-init-db, but this time, since it's name is not the usual
+".git", we do things slightly differently:
+
+ GIT_DIR=my-git.git git-init-db
+
+Make sure this directory is available for others you want your
+changes to be pulled by via the transport of your choice. Also
+you need to make sure that you have the "git-receive-pack"
+program on the $PATH.
+
+[ Side note: many installations of sshd do not invoke your shell
+ as the login shell when you directly run programs; what this
+ means is that if your login shell is bash, only .bashrc is
+ read and not .bash_profile. As a workaround, make sure
+ .bashrc sets up $PATH so that you can run 'git-receive-pack'
+ program. ]
+
+Your "public repository" is now ready to accept your changes.
+Come back to the machine you have your private repository. From
+there, run this command:
+
+ git push <public-host>:/path/to/my-git.git master
+
+This synchronizes your public repository to match the named
+branch head (i.e. "master" in this case) and objects reachable
+from them in your current repository.
+
+As a real example, this is how I update my public git
+repository. Kernel.org mirror network takes care of the
+propagation to other publicly visible machines:
+
+ git push master.kernel.org:/pub/scm/git/git.git/
+
+
+[ Digression: your GIT "public" repository people can pull from
+ is different from a public CVS repository that lets read-write
+ access to multiple developers. It is a copy of _your_ primary
+ repository published for others to use, and you should not
+ push into it from more than one repository (this means, not
+ just disallowing other developers to push into it, but also
+ you should push into it from a single repository of yours).
+ Sharing the result of work done by multiple people are always
+ done by pulling (i.e. fetching and merging) from public
+ repositories of those people. Typically this is done by the
+ "project lead" person, and the resulting repository is
+ published as the public repository of the "project lead" for
+ everybody to base further changes on. ]
+
+
+ Packing your repository
+ -----------------------
+
+Earlier, we saw that one file under .git/objects/??/ directory
+is stored for each git object you create. This representation
+is convenient and efficient to create atomically and safely, but
+not so to transport over the network. Since git objects are
+immutable once they are created, there is a way to optimize the
+storage by "packing them together". The command
+
+ git repack
+
+will do it for you. If you followed the tutorial examples, you
+would have accumulated about 17 objects in .git/objects/??/
+directories by now. "git repack" tells you how many objects it
+packed, and stores the packed file in .git/objects/pack
+directory.
+
+[ Side Note: you will see two files, pack-*.pack and pack-*.idx,
+ in .git/objects/pack directory. They are closely related to
+ each other, and if you ever copy them by hand to a different
+ repository for whatever reason, you should make sure you copy
+ them together. The former holds all the data from the objects
+ in the pack, and the latter holds the index for random
+ access. ]
+
+If you are paranoid, running "git-verify-pack" command would
+detect if you have a corrupt pack, but do not worry too much.
+Our programs are always perfect ;-).
+
+Once you have packed objects, you do not need to leave the
+unpacked objects that are contained in the pack file anymore.
+
+ git prune-packed
+
+would remove them for you.
+
+You can try running "find .git/objects -type f" before and after
+you run "git prune-packed" if you are curious.
+
+[ Side Note: as we already mentioned, "git pull" is broken for
+ some transports dealing with packed repositories right now, so
+ do not run "git prune-packed" if you plan to give "git pull"
+ access via HTTP transport for now. ]
+
+If you run "git repack" again at this point, it will say
+"Nothing to pack". Once you continue your development and
+accumulate the changes, running "git repack" again will create a
+new pack, that contains objects created since you packed your
+archive the last time. We recommend that you pack your project
+soon after the initial import (unless you are starting your
+project from scratch), and then run "git repack" every once in a
+while, depending on how active your project is.
+
+When a repository is synchronized via "git push" and "git pull",
+objects packed in the source repository is usually stored
+unpacked in the destination, unless rsync transport is used.
+
+
+ Working with Others
+ -------------------
+
+Although git is a truly distributed system, it is often
+convenient to organize your project with an informal hierarchy
+of developers. Linux kernel development is run this way. There
+is a nice illustration (page 17, "Merges to Mainline") in Randy
+Dunlap's presentation (http://tinyurl.com/a2jdg).
+
+It should be stressed that this hierarchy is purely "informal".
+There is nothing fundamental in git that enforces the "chain of
+patch flow" this hierarchy implies. You do not have to pull
+from only one remote repository.
+
+
+A recommended workflow for a "project lead" goes like this:
+
+ (1) Prepare your primary repository on your local machine. Your
+ work is done there.
+
+ (2) Prepare a public repository accessible to others.
+
+ (3) Push into the public repository from your primary
+ repository.
+
+ (4) "git repack" the public repository. This establishes a big
+ pack that contains the initial set of objects as the
+ baseline, and possibly "git prune-packed" if the transport
+ used for pulling from your repository supports packed
+ repositories.
+
+ (5) Keep working in your primary repository. Your changes
+ include modifications of your own, patches you receive via
+ e-mails, and merges resulting from pulling the "public"
+ repositories of your "subsystem maintainers".
+
+ You can repack this private repository whenever you feel
+ like.
+
+ (6) Push your changes to the public repository, and announce it
+ to the public.
+
+ (7) Every once in a while, "git repack" the public repository.
+ Go back to step (5) and continue working.
+
+
+A recommended work cycle for a "subsystem maintainer" that works
+on that project and has own "public repository" goes like this:
+
+ (1) Prepare your work repository, by "git clone" the public
+ repository of the "project lead". The URL used for the
+ initial cloning is stored in .git/branches/origin.
+
+ (2) Prepare a public repository accessible to others.
+
+ (3) Copy over the packed files from "project lead" public
+ repository to your public repository by hand; this part is
+ currently not automated.
+
+ (4) Push into the public repository from your primary
+ repository. Run "git repack", and possibly "git
+ prune-packed" if the transport used for pulling from your
+ repository supports packed repositories.
+
+ (5) Keep working in your primary repository. Your changes
+ include modifications of your own, patches you receive via
+ e-mails, and merges resulting from pulling the "public"
+ repositories of your "project lead" and possibly your
+ "sub-subsystem maintainers".
+
+ You can repack this private repository whenever you feel
+ like.
+
+ (6) Push your changes to your public repository, and ask your
+ "project lead" and possibly your "sub-subsystem
+ maintainers" to pull from it.
+
+ (7) Every once in a while, "git repack" the public repository.
+ Go back to step (5) and continue working.
+
+
+A recommended work cycle for an "individual developer" who does
+not have a "public" repository is somewhat different. It goes
+like this:
+
+ (1) Prepare your work repository, by "git clone" the public
+ repository of the "project lead" (or a "subsystem
+ maintainer", if you work on a subsystem). The URL used for
+ the initial cloning is stored in .git/branches/origin.
+
+ (2) Do your work there. Make commits.
+
+ (3) Run "git fetch origin" from the public repository of your
+ upstream every once in a while. This does only the first
+ half of "git pull" but does not merge. The head of the
+ public repository is stored in .git/refs/heads/origin.
+
+ (4) Use "git cherry origin" to see which ones of your patches
+ were accepted, and/or use "git rebase origin" to port your
+ unmerged changes forward to the updated upstream.
+
+ (5) Use "git format-patch origin" to prepare patches for e-mail
+ submission to your upstream and send it out. Go back to
+ step (2) and continue.
-You normally only do signed tags for major releases or things
-like that, while the light-weight tags are useful for any marking you
-want to do - any time you decide that you want to remember a certain
-point, just create a private tag for it, and you have a nice symbolic
-name for the state at that point.
-[ to be continued.. cvsimports, pushing and pulling ]
+[ to be continued.. cvsimports ]
projects / git.git / blobdiff