what is recorded in the index, and what is currently in the working
tree. That's very useful.
+A common shorthand for "git-diff-files -p" is to just write
+
+ git diff
+
+which will do the same thing.
+
Committing git state
--------------------
earlier commit, and you'll never see this "Committing initial tree"
message ever again.
+Again, normally you'd never actually do this by hand. There is a
+helpful script called "git commit" that will do all of this for you. So
+you could have just writtten
+
+ git commit
+
+instead, and it would have done the above magic scripting for you.
+
Making a change
---------------
but against the tree we just wrote. It just so happens that those two
are obviously the same, so we get the same result.
+Again, because this is a common operation, you can also just shorthand
+it with
+
+ git diff HEAD
+
+which ends up doing the above for you.
+
In other words, "git-diff-cache" normally compares a tree against the
working directory, but when given the "--cached" flag, it is told to
instead compare against just the index cache contents, and ignore the
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
-version. We could do it by writing the tree by hand, 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 this wasn't an
-initial commit any more), but the fact is, git has a simple helper
-script for doing all of the non-initial commits that does all of this
-for you, and starts up an editor to let you write your commit message
-yourself, so let's just use that:
+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
+this wasn't an initial commit any more), but you've done that once
+already, so let's just use the helpful script this time:
git commit
+which starts an editor for you to write the commit message and tells you
+a bit about what you're doing.
+
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
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
+
+ cat .git/HEAD > .git/refs/tags/my-first-tag
+
+after which point you can 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
+
+ git tag <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"
known state (you don't know _what_ they've done and not yet checked in),
so usually you'll precede the "git-update-cache" with a
- git-read-tree HEAD
+ git-read-tree --reset HEAD
git-update-cache --refresh
-which will force a total index re-build from the tree pointed to by
-HEAD.
+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-cache
+makes sure to match up all index entries with the checked-out files).
+
+The above can also be written as simply
+
+ git reset
-In fact, many public remote repositories will not contain any of the
-checked out files or even an index file, and will _only_ contain the
-actual core git files. Such a repository usually doesn't even have the
+and in fact a lot of the common git command combinations can be scripted
+with the "git xyz" interfaces, and you can learn things by just looking
+at what the git-*-script scripts do ("git reset" is the above two lines
+implemented in "git-reset-script", but some things like "git status" and
+"git commit" are slightly more complex scripts around the basic git
+commands).
+
+NOTE! Many (most?) public remote repositories will not contain any of
+the checked out files or even an index file, and will _only_ contain the
+actual core git files. Such a repository usually doesn't even have the
".git" subdirectory, but has all the git files directly in the
-repository.
+repository.
To create your own local live copy of such a "raw" git repository, you'd
first create your own subdirectory for the project, and then copy the
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/ my-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/git/git.git/ my-git
+ cd my-git
+ git checkout
+
+which will end up doing all of the above for you.
+
You have now successfully copied somebody else's (mine) remote
repository, and checked it out.
-[ to be continued.. cvs2git, tagging versions, branches, merging.. ]
+
+ Creating a new branch
+ ---------------------
+
+Branches in git are really nothing more than pointers into the git
+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.
+
+You can at any time create a new branch by just picking an arbitrary
+point in the project history, and just writing the SHA1 name of that
+object into a file under .git/refs/heads/. You can use any filename you
+want (and indeed, subdirectories), but the convention is that the
+"normal" branch is called "master". That's just a convention, though,
+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:
+
+ cat .git/HEAD > .git/refs/heads/mybranch
+ ln -sf refs/heads/mybranch .git/HEAD
+
+and you're done.
+
+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
+
+ git checkout mybranch
+
+which will basically "jump" to the branch specified, update your working
+directory to that state, and also make it become the new default HEAD.
+
+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
+
+ ls -l .git/HEAD
+
+will tell you where it's pointing.
+
+
+ Merging two branches
+ --------------------
+
+One of the ideas of having a branch is that you do some (possibly
+experimental) work in it, and eventually merge it back to the main
+branch. So assuming you created the above "mybranch" that started out
+being the same as the original "master" branch, let's make sure we're in
+that branch, and do some work there.
+
+ git checkout mybranch
+ echo "Work, work, work" >> a
+ git commit a
+
+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".
+
+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
+to the master branch, and editing the same file differently there:
+
+ git checkout master
+
+Here, take a moment to look at the contents of "a", 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
+
+since the master branch is obviously in a much better mood.
+
+Now, you've got two branches, and you decide that you want to merge the
+work done. Before we do that, let's introduce a cool graphical tool that
+helps you view what's going on:
+
+ 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
+histories. You can also see exactly how they came to be from a common
+source.
+
+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
+to resolve and what the merge is all about:
+
+ git resolve HEAD mybranch "Merge work in mybranch"
+
+where the third 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
+merge will need to be fixed up by hand, though, so git will do as much
+of it as it can automatically (which in this case is just merge the "b"
+file, which had no differences in the "mybranch" branch), and say:
+
+ Simple merge failed, trying Automatic merge
+ Auto-merging a.
+ merge: warning: conflicts during merge
+ ERROR: Merge conflict in a.
+ 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".
+
+Not to worry. It left the (trivial) conflict in "a" 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:
+
+ Hello World
+ It's a new day for git
+ Play, play, play
+ Work, work, work
+
+and once you're happy with your manual merge, just do a
+
+ git commit a
+
+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
+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
+have to do _that_ merge again.
+
+
+ Merging external work
+ ---------------------
+
+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
+more than "fetch the work from a remote repository into a temporary tag"
+followed by a "git resolve".
+
+It's such a common thing to do that it's called "git pull", and you can
+simply do
+
+ git pull <remote-repository>
+
+and optionally give a branch-name for the remote end as a second
+argument.
+
+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/
+
+ HTTP(s) URL
+ http://remote.machine/path/to/repo.git/
+
+ GIT URL
+ git://remote.machine/path/to/repo.git/
+ remote.machine:/path/to/repo.git/
+
+ Local directory
+ /path/to/repo.git/
+
+[ 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. ]
+
+[ 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. ]
+
+
+ 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
+ -------------------
+
+A recommended work cycle for a "project lead" is 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.
+
+ (5) Keep working in your primary repository, and push your
+ changes to the public repository. Your changes include
+ your own, patches you receive via e-mail, and merge resulting
+ from pulling the "public" repositories of your "subsystem
+ maintainers".
+
+ You can repack this private repository whenever you feel
+ like.
+
+ (6) 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" is like
+this:
+
+ (1) Prepare your work repository, by "git clone" the public
+ repository of the "project lead".
+
+ (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.
+
+ (5) Keep working in your primary repository, and push your
+ changes to your public repository, and ask your "project
+ lead" to pull from it. Your changes include your own,
+ patches you receive via e-mail, and merge 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) 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 repositories, by "git clone" the public
+ repository of the "project lead" (or "subsystem
+ maintainer", if you work on a subsystem).
+
+ (2) Copy .git/refs/master to .git/refs/upstream.
+
+ (3) Do your work there. Make commits.
+
+ (4) Run "git fetch" 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/FETCH_HEAD. Copy it in
+ .git/refs/heads/upstream.
+
+ (5) Use "git cherry" to see which ones of your patches were
+ accepted, and/or use "git rebase" to port your unmerged
+ changes forward to the updated upstream.
+
+ (6) Use "git format-patch upstream" to prepare patches for
+ e-mail submission to your upstream and send it out.
+ Go back to step (3) and continue.
+
+[Side Note: I think Cogito calls this upstream "origin".
+ Somebody care to confirm or deny? ]
+
+
+[ to be continued.. cvsimports ]