-A short git tutorial
-====================
+A tutorial introduction to git
+==============================
-Introduction
-------------
+This tutorial explains how to import a new project into git, make
+changes to it, and share changes with other developers.
-This is trying to be a short tutorial on setting up and using a git
-repository, mainly because being hands-on and using explicit examples is
-often the best way of explaining what is going on.
-
-In normal life, most people wouldn't use the "core" git programs
-directly, but rather script around them to make them more palatable.
-Understanding the core git stuff may help some people get those scripts
-done, though, and it may also be instructive in helping people
-understand what it is that the higher-level helper scripts are actually
-doing.
-
-The core git is often called "plumbing", with the prettier user
-interfaces on top of it called "porcelain". You may not want to use the
-plumbing directly very often, but it can be good to know what the
-plumbing does for when the porcelain isn't flushing...
-
-
-Creating a git repository
--------------------------
-
-Creating a new git repository couldn't be easier: all git repositories start
-out empty, and the only thing you need to do is find yourself a
-subdirectory that you want to use as a working tree - either an empty
-one for a totally new project, or an existing working tree that you want
-to import into git.
-
-For our first example, we're going to start a totally new repository from
-scratch, with no pre-existing files, and we'll call it `git-tutorial`.
-To start up, create a subdirectory for it, change into that
-subdirectory, and initialize the git infrastructure with `git-init-db`:
+First, note that you can get documentation for a command such as "git
+diff" with:
------------------------------------------------
-mkdir git-tutorial
-cd git-tutorial
-git-init-db
+$ man git-diff
------------------------------------------------
-to which git will reply
-
- 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
-your new project. You will now have a `.git` directory, and you can
-inspect that with `ls`. For your new empty project, it should show you
-three entries, among other things:
-
- - a symlink called `HEAD`, pointing to `refs/heads/master` (if your
- platform does not have native symlinks, it is a file containing the
- line "ref: refs/heads/master")
-+
-Don't worry about the fact that the file that the `HEAD` link points to
-doesn't even exist yet -- you haven't created the commit that will
-start your `HEAD` development branch yet.
-
- - a subdirectory called `objects`, which will contain all the
- objects of your project. You should never have any real reason to
- look at the objects directly, but you might want to know that these
- objects are what contains all the real 'data' in your repository.
-
- - a subdirectory called `refs`, which contains references to objects.
-
-In particular, the `refs` subdirectory will contain two other
-subdirectories, named `heads` and `tags` respectively. They do
-exactly what their names imply: they contain references to any number
-of different 'heads' of development (aka 'branches'), and to any
-'tags' that you have created to name specific versions in your
-repository.
-
-One note: the special `master` head is the default branch, which is
-why the `.git/HEAD` file was created as a symlink to it even if it
-doesn't yet exist. Basically, the `HEAD` link is supposed to always
-point to the branch you are working on right now, and you always
-start out expecting to work on the `master` branch.
-
-However, this is only a convention, and you can name your branches
-anything you want, and don't have to ever even 'have' a `master`
-branch. A number of the git tools will assume that `.git/HEAD` is
-valid, though.
-
-[NOTE]
-An 'object' is identified by its 160-bit SHA1 hash, aka 'object name',
-and a reference to an object is always the 40-byte hex
-representation of that SHA1 name. The files in the `refs`
-subdirectory are expected to contain these hex references
-(usually with a final `\'\n\'` at the end), and you should thus
-expect to see a number of 41-byte files containing these
-references in these `refs` subdirectories when you actually start
-populating your tree.
-
-[NOTE]
-An advanced user may want to take a look at the
-link:repository-layout.html[repository layout] document
-after finishing this tutorial.
-
-You have now created your first git repository. Of course, since it's
-empty, that's not very useful, so let's start populating it with data.
-
-
-Populating a git repository
----------------------------
-
-We'll keep this simple and stupid, so we'll start off with populating a
-few trivial files just to get a feel for it.
-
-Start off with just creating any random files that you want to maintain
-in your git repository. We'll start off with a few bad examples, just to
-get a feel for how this works:
+It is a good idea to introduce yourself to git before doing any
+operation. The easiest way to do so is:
------------------------------------------------
-echo "Hello World" >hello
-echo "Silly example" >example
+$ cat >~/.gitconfig <<\EOF
+[user]
+ name = Your Name Comes Here
+ email = you@yourdomain.example.com
+EOF
------------------------------------------------
-you have now created two files in your working tree (aka 'working directory'), but to
-actually check in your hard work, you will have to go through two steps:
-
- - fill in the 'index' file (aka 'cache') with the information about your
- working tree state.
- - commit that index file as an object.
-
-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
-(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.
+Importing a new project
+-----------------------
-So to populate the index with the two files you just created, you can do
+Assume you have a tarball project.tar.gz with your initial work. You
+can place it under git revision control as follows.
------------------------------------------------
-git-update-index --add hello example
+$ tar xzf project.tar.gz
+$ cd project
+$ git init-db
------------------------------------------------
-and you have now told git to track those two files.
-
-In fact, as you did that, if you now look into your object directory,
-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/??/*
-
-and see two files:
+Git will reply
- .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:
+------------------------------------------------
+Initialized empty Git repository in .git/
+------------------------------------------------
- git-cat-file -t 557db03de997c86a4a028e1ebd3a1ceb225be238
+You've now initialized the working directory--you may notice a new
+directory created, named ".git". Tell git that you want it to track
+every file under the current directory with (notice the dot '.'
+that means the current directory):
-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 add .
+------------------------------------------------
- git-cat-file "blob" 557db03
+Finally,
-which will print out "Hello World". The object 557db03 is nothing
-more than the contents of your file `hello`.
+------------------------------------------------
+$ git commit
+------------------------------------------------
-[NOTE]
-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 `hello`, the object
-we just looked at will never change. Objects are immutable.
+will prompt you for a commit message, then record the current state
+of all the files to the repository.
-[NOTE]
-The second example demonstrates that you can
-abbreviate the object name to only the first several
-hexadecimal digits in most places.
+Try modifying some files, then run
-Anyway, as we mentioned previously, you normally never actually take a
-look at the objects themselves, and typing long 40-character hex
-names is not something you'd normally want to do. The above digression
-was just to show that `git-update-index` did something magical, and
-actually saved away the contents of your files into the git object
-database.
+------------------------------------------------
+$ git diff
+------------------------------------------------
-Updating the cache 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
-you have not actually really "checked in" your files into git so far,
-you've only *told* git about them.
+to review your changes. When you're done,
-However, since git knows about them, you can now start using some of the
-most basic git commands to manipulate the files or look at their status.
+------------------------------------------------
+$ git commit file1 file2...
+------------------------------------------------
-In particular, let's not even check in the two files into git yet, we'll
-start off by adding another line to `hello` first:
+will again prompt your for a message describing the change, and then
+record the new versions of the files you listed. It is cumbersome
+to list all files and you can say `-a` (which stands for 'all')
+instead.
------------------------------------------------
-echo "It's a new day for git" >>hello
+$ git commit -a
------------------------------------------------
-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:
+A note on commit messages: Though not required, it's a good idea to
+begin the commit message with a single short (less than 50 character)
+line summarizing the change, followed by a blank line and then a more
+thorough description. Tools that turn commits into email, for
+example, use the first line on the Subject line and the rest of the
+commit in the body.
-------------
-git-diff-files
-------------
-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 "hello" has been modified, and that the old object
-contents it had have been replaced with something else.
+Git tracks content not files
+----------------------------
-To make it readable, we can tell git-diff-files to output the
-differences as a patch, using the `-p` flag:
+With git you have to explicitly "add" all the changed _content_ you
+want to commit together. This can be done in a few different ways:
-------------
-git-diff-files -p
-------------
+1) By using 'git add <file_spec>...'
-which will spit out
+ This can be performed multiple times before a commit. Note that this
+ is not only for adding new files. Even modified files must be
+ added to the set of changes about to be committed. The "git status"
+ command gives you a summary of what is included so far for the
+ next commit. When done you should use the 'git commit' command to
+ make it real.
-------------
-diff --git a/hello b/hello
-index 557db03..263414f 100644
---- a/hello
-+++ b/hello
-@@ -1 +1,2 @@
- Hello World
-+It's a new day for git
-----
+ Note: don't forget to 'add' a file again if you modified it after the
+ first 'add' and before 'commit'. Otherwise only the previous added
+ state of that file will be committed. This is because git tracks
+ content, so what you're really 'add'ing to the commit is the *content*
+ of the file in the state it is in when you 'add' it.
-i.e. the diff of the change we caused by adding another line to `hello`.
+2) By using 'git commit -a' directly
-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
-tree. That's very useful.
+ This is a quick way to automatically 'add' the content from all files
+ that were modified since the previous commit, and perform the actual
+ commit without having to separately 'add' them beforehand. This will
+ not add content from new files i.e. files that were never added before.
+ Those files still have to be added explicitly before performing a
+ commit.
-A common shorthand for `git-diff-files -p` is to just write `git
-diff`, which will do the same thing.
+But here's a twist. If you do 'git commit <file1> <file2> ...' then only
+the changes belonging to those explicitly specified files will be
+committed, entirely bypassing the current "added" changes. Those "added"
+changes will still remain available for a subsequent commit though.
+However, for normal usage you only have to remember 'git add' + 'git commit'
+and/or 'git commit -a'.
-Committing git state
---------------------
-Now, we want to go to the next stage in git, which is to take the files
-that git knows about in the index, and commit them as a real tree. We do
-that in two phases: creating a 'tree' object, and committing that 'tree'
-object as a 'commit' object together with an explanation of what the
-tree was all about, along with information of how we came to that state.
+Viewing the changelog
+---------------------
-Creating a tree object is trivial, and is done with `git-write-tree`.
-There are no options or other input: git-write-tree will take the
-current index state, and write an object that describes that whole
-index. In other words, we're now tying together all the different
-filenames with their contents (and their permissions), and we're
-creating the equivalent of a git "directory" object:
+At any point you can view the history of your changes using
------------------------------------------------
-git-write-tree
+$ git log
------------------------------------------------
-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
-
-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
-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).
-
-However -- normally you'd never use `git-write-tree` on its own, because
-normally you always commit a tree into a commit object using the
-`git-commit-tree` command. In fact, it's easier to not actually use
-`git-write-tree` on its own at all, but to just pass its result in as an
-argument to `git-commit-tree`.
-
-`git-commit-tree` normally takes several arguments -- it wants to know
-what the 'parent' of a commit was, but since this is the first commit
-ever in this new repository, and it has no parents, we only need to pass in
-the object name of the tree. However, `git-commit-tree`
-also wants to get a commit message
-on its standard input, and it will write out the resulting object name for the
-commit to its standard output.
-
-And this is where we create the `.git/refs/heads/master` file
-which is pointed at by `HEAD`. This file is supposed to contain
-the reference to the top-of-tree of the master branch, and since
-that's exactly what `git-commit-tree` spits out, we can do this
-all with a sequence of simple shell commands:
+If you also want to see complete diffs at each step, use
------------------------------------------------
-tree=$(git-write-tree)
-commit=$(echo 'Initial commit' | git-commit-tree $tree)
-git-update-ref HEAD $(commit)
+$ git log -p
------------------------------------------------
-which will say:
-
- 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*
-for a project ever, and all later commits will be parented on top of an
-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 written `git commit`
-instead, and it would have done the above magic scripting for you.
-
-
-Making a change
----------------
-
-Remember how we did the `git-update-index` 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 `hello`, not the new ones. We did
-that on purpose, to show the difference between the index state, and the
-state in the working tree, and how they don't have to match, even
-when we commit things.
-
-As before, if we do `git-diff-files -p` in our git-tutorial project,
-we'll still see the same difference we saw last time: the index file
-hasn't changed by the act of committing anything. However, now that we
-have committed something, we can also learn to use a new command:
-`git-diff-index`.
-
-Unlike `git-diff-files`, which showed the difference between the index
-file and the working tree, `git-diff-index` shows the differences
-between a committed *tree* and either the index file or the working
-tree. In other words, `git-diff-index` wants a tree to be diffed
-against, and before we did the commit, we couldn't do that, because we
-didn't have anything to diff against.
-
-But now we can do
-
- 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.
-Now we're comparing the working tree not against the index file,
-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-index` normally compares a tree against the
-working tree, but when given the `\--cached` flag, it is told to
-instead compare against just the index cache contents, and ignore the
-current working tree state entirely. Since we just wrote the index
-file to HEAD, doing `git-diff-index \--cached -p HEAD` should thus return
-an empty set of differences, and that's exactly what it does.
-
-[NOTE]
-================
-`git-diff-index` really always uses the index for its
-comparisons, and saying that it compares a tree against the working
-tree is thus not strictly accurate. In particular, the list of
-files to compare (the "meta-data") *always* comes from the index file,
-regardless of whether the `\--cached` flag is used or not. The `\--cached`
-flag really only determines whether the file *contents* to be compared
-come from the working tree or not.
-
-This is not hard to understand, as soon as you realize that git simply
-never knows (or cares) about files that it is not told about
-explicitly. git will never go *looking* for files to compare, it
-expects you to tell it what the files are, and that's what the index
-is there for.
-================
-
-However, our next step is to commit the *change* we did, and again, to
-understand what's going on, keep in mind the difference between "working
-tree contents", "index file" and "committed tree". We have changes
-in the working tree that we want to commit, and we always have to
-work through the index file, so the first thing we need to do is to
-update the index cache:
+Managing branches
+-----------------
+
+A single git repository can maintain multiple branches of
+development. To create a new branch named "experimental", use
------------------------------------------------
-git-update-index hello
+$ git branch experimental
------------------------------------------------
-(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-\*` versions here. After
-we've updated `hello` in the index, `git-diff-files -p` now shows no
-differences, but `git-diff-index -p HEAD` still *does* show that the
-current state is different from the state we committed. In fact, now
-`git-diff-index` shows the same difference whether we use the `--cached`
-flag or not, since now the index is coherent with the working tree.
-
-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
-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:
+If you now run
------------------------------------------------
-git commit
+$ git branch
------------------------------------------------
-which starts an editor for you to write the commit message and tells you
-a bit about what you have done.
-
-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
-can just leave an empty message. Otherwise `git commit` will commit
-the change for you.
-
-You've now made your first real git commit. And if you're interested in
-looking at what `git commit` really does, feel free to investigate:
-it's a few very simple shell scripts to generate the helpful (?) commit
-message headers, and a few one-liners that actually do the
-commit itself (`git-commit`).
-
-
-Inspecting Changes
-------------------
-
-While creating changes is useful, it's even more useful if you can tell
-later what changed. The most useful command for this is another of the
-`diff` family, namely `git-diff-tree`.
-
-`git-diff-tree` can be given two arbitrary trees, and it will tell you the
-differences between them. Perhaps even more commonly, though, you can
-give it just a single commit object, and it will figure out the parent
-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
-
-(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.
-Alternatively, you can tell it to be "silent", and not show the diffs at
-all, but just show the actual commit message.
-
-In fact, together with the `git-rev-list` program (which generates a
-list of revisions), `git-diff-tree` ends up being a veritable fount of
-changes. A trivial (but very useful) script called `git-whatchanged` is
-included with git which does exactly this, and shows a log of recent
-activities.
-
-To see the whole history of our pitiful little git-tutorial project, you
-can do
-
- 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
-
-and you will see exactly what has changed in the repository over its
-short history.
-
-[NOTE]
-The `\--root` flag is a flag to `git-diff-tree` to tell it to
-show the initial aka 'root' commit too. Normally you'd probably not
-want to see the initial import diff, but since the tutorial project
-was started from scratch and is so small, we use it to make the result
-a bit more interesting.
-
-With that, you should now be having some inkling of what git does, and
-can explore on your own.
-
-[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-index` 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-index` on them for you.
-
-
-Tagging a version
------------------
-
-In git, there are two kinds of tags, a "light" one, and an "annotated 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
+you'll get a list of all existing branches:
------------------------------------------------
-git tag my-first-tag
+ experimental
+* master
------------------------------------------------
-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 an "anchor-point" to see what has changed
-since you tagged it.
-
-An "annotated 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 optionally a PGP signature that says that yes,
-you really did
-that tag. You create these annotated tags with either the `-a` or
-`-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 repositories
---------------------
-
-git repositories are normally totally self-sufficient, and it's worth noting
-that 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.
-
-[NOTE]
-You can tell git to split the git internal information from
-the directory that it tracks, but we'll ignore that for now: it's not
-how normal projects work, and it's really only meant for special uses.
-So the mental model of "the git information is always tied directly to
-the working tree that it describes" may not be technically 100%
-accurate, but it's a good model for all normal use.
-
-This has two implications:
-
- - 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
+The "experimental" branch is the one you just created, and the
+"master" branch is a default branch that was created for you
+automatically. The asterisk marks the branch you are currently on;
+type
- rm -rf git-tutorial
-+
-and it will be gone. There's no external repository, and there's no
-history outside the project you created.
-
- - if you want to move or duplicate a git repository, you can do so. There
- is `git clone` command, but if all you want to do is just to
- create a copy of your repository (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 repository, your git index
-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
-+
-in the new repository to make sure that the index file is up-to-date.
-
-Note that the second point is true even across machines. You can
-duplicate a remote git repository with *any* regular copy mechanism, be it
-`scp`, `rsync` or `wget`.
+------------------------------------------------
+$ git checkout experimental
+------------------------------------------------
-When copying a remote repository, you'll want to at a minimum update the
-index cache when you do this, and especially with other peoples'
-repositories you often want to make sure that the index cache is in some
-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
+to switch to the experimental branch. Now edit a file, commit the
+change, and switch back to the master branch:
- git-read-tree --reset HEAD
- git-update-index --refresh
+------------------------------------------------
+(edit file)
+$ git commit -a
+$ git checkout master
+------------------------------------------------
-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`
-makes sure to match up all index entries with the checked-out files.
-If the original repository had uncommitted changes in its
-working tree, `git-update-index --refresh` notices them and
-tells you they need to be updated.
+Check that the change you made is no longer visible, since it was
+made on the experimental branch and you're back on the master branch.
-The above can also be written as simply
+You can make a different change on the master branch:
- git reset
+------------------------------------------------
+(edit file)
+$ git commit -a
+------------------------------------------------
-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
-at what the various git scripts do. For example, `git reset` is the
-above two lines implemented in `git-reset`, but some things like
-`git status` and `git commit` are slightly more complex scripts around
-the basic git commands.
+at this point the two branches have diverged, with different changes
+made in each. To merge the changes made in experimental into master, run
-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.
-
-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
-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
-
-followed by
-
- 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 pull . experimental
+------------------------------------------------
- git-checkout-index -u -a
+If the changes don't conflict, you're done. If there are conflicts,
+markers will be left in the problematic files showing the conflict;
-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` 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`
-flag first, to tell git-checkout-index 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.
+------------------------------------------------
+$ git diff
+------------------------------------------------
-You have now successfully copied somebody else's (mine) remote
-repository, and checked it out.
+will show this. Once you've edited the files to resolve the
+conflicts,
+------------------------------------------------
+$ git commit -a
+------------------------------------------------
-Creating a new branch
----------------------
+will commit the result of the merge. Finally,
-Branches in git are really nothing more than pointers into the git
-object database 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.
+------------------------------------------------
+$ gitk
+------------------------------------------------
-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.
+will show a nice graphical representation of the resulting history.
-To show that as an example, let's go back to the git-tutorial repository we
-used earlier, and create a branch in it. You do that by simply just
-saying that you want to check out a new branch:
+If you develop on a branch crazy-idea, then regret it, you can always
+delete the branch with
-------------
-git checkout -b mybranch
-------------
+-------------------------------------
+$ git branch -D crazy-idea
+-------------------------------------
-will create a new branch based at the current `HEAD` position, and switch
-to it.
+Branches are cheap and easy, so this is a good way to try something
+out.
-[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
+Using git for collaboration
+---------------------------
-------------
-git checkout -b mybranch earlier-commit
-------------
+Suppose that Alice has started a new project with a git repository in
+/home/alice/project, and that Bob, who has a home directory on the
+same machine, wants to contribute.
-and it would create the new branch `mybranch` at the earlier commit,
-and check out the state at that time.
-================================================
+Bob begins with:
-You can always just jump back to your original `master` branch by doing
+------------------------------------------------
+$ git clone /home/alice/project myrepo
+------------------------------------------------
-------------
-git checkout master
-------------
+This creates a new directory "myrepo" containing a clone of Alice's
+repository. The clone is on an equal footing with the original
+project, possessing its own copy of the original project's history.
-(or any other branch-name, for that matter) and if you forget which
-branch you happen to be on, a simple
+Bob then makes some changes and commits them:
-------------
-ls -l .git/HEAD
-------------
+------------------------------------------------
+(edit files)
+$ git commit -a
+(repeat as necessary)
+------------------------------------------------
-will tell you where it's pointing (Note that on platforms with bad or no
-symlink support, you have to execute
+When he's ready, he tells Alice to pull changes from the repository
+at /home/bob/myrepo. She does this with:
-------------
-cat .git/HEAD
-------------
+------------------------------------------------
+$ cd /home/alice/project
+$ git pull /home/bob/myrepo master
+------------------------------------------------
-instead). To get the list of branches you have, you can say
+This merges the changes from Bob's "master" branch into Alice's
+current branch. If Alice has made her own changes in the meantime,
+then she may need to manually fix any conflicts. (Note that the
+"master" argument in the above command is actually unnecessary, as it
+is the default.)
-------------
-git branch
-------------
+The "pull" command thus performs two operations: it fetches changes
+from a remote branch, then merges them into the current branch.
-which is nothing more than a simple script around `ls .git/refs/heads`.
-There will be asterisk in front of the branch you are currently on.
+You can perform the first operation alone using the "git fetch"
+command. For example, Alice could create a temporary branch just to
+track Bob's changes, without merging them with her own, using:
-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 fetch /home/bob/myrepo master:bob-incoming
+-------------------------------------
-------------
-git branch <branchname> [startingpoint]
-------------
+which fetches the changes from Bob's master branch into a new branch
+named bob-incoming. Then
-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.
+-------------------------------------
+$ git log -p master..bob-incoming
+-------------------------------------
+shows a list of all the changes that Bob made since he branched from
+Alice's master branch.
-Merging two branches
---------------------
+After examining those changes, and possibly fixing things, Alice
+could pull the changes into her master branch:
-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 master
+$ git pull . bob-incoming
+-------------------------------------
-------------------------------------------------
-git checkout mybranch
-echo "Work, work, work" >>hello
-git commit -m 'Some work.' hello
-------------------------------------------------
+The last command is a pull from the "bob-incoming" branch in Alice's
+own repository.
-Here, we just added another line to `hello`, and we used a shorthand for
-doing both `git-update-index hello` and `git commit` by just giving the
-filename directly to `git commit`. The `-m` flag is to give the
-commit log message from the command line.
-
-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 `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" >>hello
-echo "Lots of fun" >>example
-git commit -m 'Some fun.' hello example
-------------
-
-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 `example`
-file, which had no differences in the `mybranch` branch), and say:
-
- Simple merge failed, trying Automatic merge
- Auto-merging hello.
- merge: warning: conflicts during merge
- 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 `hello`.
-
-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 `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
-Play, play, play
-Work, work, work
-------------
-
-and once you're happy with your manual merge, just do 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. 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
-have to do _that_ merge again.
-
-Another useful tool, especially if you do not always work in X-Window
-environment, is `git show-branch`.
+Alice could also perform both steps at once with:
-------------------------------------------------
-$ git show-branch master mybranch
-* [master] Merged "mybranch" changes.
- ! [mybranch] Some work.
---
-+ [master] Merged "mybranch" changes.
-++ [mybranch] Some work.
-------------------------------------------------
+-------------------------------------
+$ git pull /home/bob/myrepo master:bob-incoming
+-------------------------------------
-The first two lines indicate that it is showing the two branches
-and the first line of the commit log message from their
-top-of-the-tree commits, you are currently on `master` branch
-(notice the asterisk `*` character), and the first column for
-the later output lines is used to show commits contained in the
-`master` branch, and the second column for the `mybranch`
-branch. Three commits are shown along with their log messages.
-All of them have plus `+` characters in the first column, which
-means they are now part of the `master` branch. Only the "Some
-work" commit has the plus `+` character in the second column,
-because `mybranch` has not been merged to incorporate these
-commits from the master branch. The string inside brackets
-before the commit log message is a short name you can use to
-name the commit. In the above example, 'master' and 'mybranch'
-are branch heads. 'master~1' is the first parent of 'master'
-branch head. Please see 'git-rev-parse' documentation if you
-see more complex cases.
-
-Now, let's pretend you are the one who did all the work in
-`mybranch`, and the fruit of your hard work has finally been merged
-to the `master` branch. Let's go back to `mybranch`, and run
-resolve to get the "upstream changes" back to your branch.
-
-------------
-git checkout mybranch
-git resolve HEAD master "Merge upstream changes."
-------------
-
-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(-)
-
-Because your branch did not contain anything more than what are
-already merged into the `master` branch, the resolve operation did
-not actually do a merge. Instead, it just updated the top of
-the tree of your branch to that of the `master` branch. This is
-often called 'fast forward' merge.
-
-You can run `gitk \--all` again to see how the commit ancestry
-looks like, or run `show-branch`, which tells you this.
+This is just like the "git pull /home/bob/myrepo master" that we saw
+before, except that it also stores the unmerged changes from bob's
+master branch in bob-incoming before merging them into Alice's
+current branch. Note that git pull always merges into the current
+branch, regardless of what else is given on the commandline.
-------------------------------------------------
-$ git show-branch master mybranch
-! [master] Merged "mybranch" changes.
- * [mybranch] Merged "mybranch" changes.
---
-++ [master] Merged "mybranch" changes.
-------------------------------------------------
+Later, Bob can update his repo with Alice's latest changes using
+-------------------------------------
+$ git pull
+-------------------------------------
-Merging external work
----------------------
+Note that he doesn't need to give the path to Alice's repository;
+when Bob cloned Alice's repository, git stored the location of her
+repository in the file .git/remotes/origin, and that location is used
+as the default for pulls.
-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`.
-
-Fetching from a remote repository is done by, unsurprisingly,
-`git fetch`:
-
- git fetch <remote-repository>
-
-One of the following transports can be used to name the
-repository to download from:
-
-Rsync::
- `rsync://remote.machine/path/to/repo.git/`
-+
-Rsync transport is usable for both uploading and downloading,
-but is completely unaware of what git does, and can produce
-unexpected results when you download from the public repository
-while the repository owner is uploading into it via `rsync`
-transport. Most notably, it could update the files under
-`refs/` which holds the object name of the topmost commits
-before uploading the files in `objects/` -- the downloader would
-obtain head commit object name while that object itself is still
-not available in the repository. For this reason, it is
-considered deprecated.
-
-SSH::
- `remote.machine:/path/to/repo.git/` or
-+
-`ssh://remote.machine/path/to/repo.git/`
-+
-This transport can be used for both uploading and downloading,
-and requires you to have a log-in privilege over `ssh` to the
-remote machine. It finds out the set of objects the other side
-lacks by exchanging the head commits both ends have and
-transfers (close to) minimum set of objects. It is by far the
-most efficient way to exchange git objects between repositories.
-
-Local directory::
- `/path/to/repo.git/`
-+
-This transport is the same as SSH transport but uses `sh` to run
-both ends on the local machine instead of running other end on
-the remote machine via `ssh`.
-
-git Native::
- `git://remote.machine/path/to/repo.git/`
-+
-This transport was designed for anonymous downloading. Like SSH
-transport, it finds out the set of objects the downstream side
-lacks and transfers (close to) minimum set of objects.
-
-HTTP(s)::
- `http://remote.machine/path/to/repo.git/`
-+
-HTTP and HTTPS transport are used only for downloading. They
-first obtain the topmost commit object name from the remote site
-by looking at `repo.git/info/refs` file, tries to obtain the
-commit object by downloading from `repo.git/objects/xx/xxx\...`
-using the object name of that commit object. Then it reads the
-commit object to find out its parent commits and the associate
-tree object; it repeats this process until it gets all the
-necessary objects. Because of this behaviour, they are
-sometimes also called 'commit walkers'.
-+
-The 'commit walkers' are sometimes also called 'dumb
-transports', because they do not require any git aware smart
-server like git Native transport does. Any stock HTTP server
-would suffice.
-+
-There are (confusingly enough) `git-ssh-fetch` and `git-ssh-upload`
-programs, which are 'commit walkers'; they outlived their
-usefulness when git Native and SSH transports were introduced,
-and not used by `git pull` or `git push` scripts.
-
-Once you fetch from the remote repository, you `resolve` that
-with your current branch.
-
-However -- it's such a common thing to `fetch` and then
-immediately `resolve`, 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.
-
-[NOTE]
-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.
-
-[NOTE]
-You could even pull from your own repository by
-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
-the remote repository URL in a file under .git/remotes/
-directory, like this:
+Bob may also notice a branch in his repository that he didn't create:
-------------------------------------------------
-mkdir -p .git/remotes/
-cat >.git/remotes/linus <<\EOF
-URL: http://www.kernel.org/pub/scm/git/git.git/
-EOF
-------------------------------------------------
+-------------------------------------
+$ git branch
+* master
+ origin
+-------------------------------------
-and use the filename to `git pull` instead of the full URL.
-The URL specified in such file can even be a prefix
-of a full URL, like this:
+The "origin" branch, which was created automatically by "git clone",
+is a pristine copy of Alice's master branch; Bob should never commit
+to it.
-------------------------------------------------
-cat >.git/remotes/jgarzik <<\EOF
-URL: http://www.kernel.org/pub/scm/linux/git/jgarzik/
-EOF
-------------------------------------------------
+If Bob later decides to work from a different host, he can still
+perform clones and pulls using the ssh protocol:
+-------------------------------------
+$ git clone alice.org:/home/alice/project myrepo
+-------------------------------------
-Examples.
-
-. `git pull linus`
-. `git pull linus tag v0.99.1`
-. `git pull jgarzik/netdev-2.6.git/ e100`
-
-the above are equivalent to:
+Alternatively, git has a native protocol, or can use rsync or http;
+see gitlink:git-pull[1] for details.
-. `git pull http://www.kernel.org/pub/scm/git/git.git/ HEAD`
-. `git pull http://www.kernel.org/pub/scm/git/git.git/ tag v0.99.1`
-. `git pull http://www.kernel.org/pub/.../jgarzik/netdev-2.6.git e100`
+Git can also be used in a CVS-like mode, with a central repository
+that various users push changes to; see gitlink:git-push[1] and
+link:cvs-migration.html[git for CVS users].
+Exploring history
+-----------------
-Publishing your work
---------------------
+Git history is represented as a series of interrelated commits. We
+have already seen that the git log command can list those commits.
+Note that first line of each git log entry also gives a name for the
+commit:
-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?
+-------------------------------------
+$ git log
+commit c82a22c39cbc32576f64f5c6b3f24b99ea8149c7
+Author: Junio C Hamano <junkio@cox.net>
+Date: Tue May 16 17:18:22 2006 -0700
+
+ merge-base: Clarify the comments on post processing.
+-------------------------------------
-Your do your real work in your working tree 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 tree are in good shape,
-update the public repository from it. This is often called
-'pushing'.
+We can give this name to git show to see the details about this
+commit.
-[NOTE]
-This public repository could further be mirrored, and that is
-how git repositories at `kernel.org` are managed.
+-------------------------------------
+$ git show c82a22c39cbc32576f64f5c6b3f24b99ea8149c7
+-------------------------------------
-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`.
+But there other ways to refer to commits. You can use any initial
+part of the name that is long enough to uniquely identify the commit:
-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.
+-------------------------------------
+$ git show c82a22c39c # the first few characters of the name are
+ # usually enough
+$ git show HEAD # the tip of the current branch
+$ git show experimental # the tip of the "experimental" branch
+-------------------------------------
+
+Every commit has at least one "parent" commit, which points to the
+previous state of the project:
-[NOTE]
-`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.
+-------------------------------------
+$ git show HEAD^ # to see the parent of HEAD
+$ git show HEAD^^ # to see the grandparent of HEAD
+$ git show HEAD~4 # to see the great-great grandparent of HEAD
+-------------------------------------
+
+Note that merge commits may have more than one parent:
-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:
+-------------------------------------
+$ git show HEAD^1 # show the first parent of HEAD (same as HEAD^)
+$ git show HEAD^2 # show the second parent of HEAD
+-------------------------------------
+
+You can also give commits names of your own; after running
+
+-------------------------------------
+$ git-tag v2.5 1b2e1d63ff
+-------------------------------------
-------------
-mkdir my-git.git
-------------
+you can refer to 1b2e1d63ff by the name "v2.5". If you intend to
+share this name with other people (for example, to identify a release
+version), you should create a "tag" object, and perhaps sign it; see
+gitlink:git-tag[1] for details.
-Then, make that directory into a git repository by running
-`git init-db`, but this time, since its name is not the usual
-`.git`, we do things slightly differently:
+Any git command that needs to know a commit can take any of these
+names. For example:
-------------
-GIT_DIR=my-git.git git-init-db
-------------
+-------------------------------------
+$ git diff v2.5 HEAD # compare the current HEAD to v2.5
+$ git branch stable v2.5 # start a new branch named "stable" based
+ # at v2.5
+$ git reset --hard HEAD^ # reset your current branch and working
+ # directory to its state at HEAD^
+-------------------------------------
-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 `$PATH`.
+Be careful with that last command: in addition to losing any changes
+in the working directory, it will also remove all later commits from
+this branch. If this branch is the only branch containing those
+commits, they will be lost. (Also, don't use "git reset" on a
+publicly-visible branch that other developers pull from, as git will
+be confused by history that disappears in this way.)
-[NOTE]
-Many installations of sshd do not invoke your shell as the login
-shell when you directly run programs; what this means is that if
-your login shell is `bash`, only `.bashrc` is read and not
-`.bash_profile`. As a workaround, make sure `.bashrc` sets up
-`$PATH` so that you can run `git-receive-pack` program.
+The git grep command can search for strings in any version of your
+project, so
-[NOTE]
-If you plan to publish this repository to be accessed over http,
-you should do `chmod +x my-git.git/hooks/post-update` at this
-point. This makes sure that every time you push into this
-repository, `git-update-server-info` is run.
+-------------------------------------
+$ git grep "hello" v2.5
+-------------------------------------
+
+searches for all occurrences of "hello" in v2.5.
-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:
+If you leave out the commit name, git grep will search any of the
+files it manages in your current directory. So
+
+-------------------------------------
+$ git grep "hello"
+-------------------------------------
+
+is a quick way to search just the files that are tracked by git.
-------------
-git push <public-host>:/path/to/my-git.git master
-------------
+Many git commands also take sets of commits, which can be specified
+in a number of ways. Here are some examples with git log:
-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.
+-------------------------------------
+$ git log v2.5..v2.6 # commits between v2.5 and v2.6
+$ git log v2.5.. # commits since v2.5
+$ git log --since="2 weeks ago" # commits from the last 2 weeks
+$ git log v2.5.. Makefile # commits since v2.5 which modify
+ # Makefile
+-------------------------------------
-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/
-------------
-
-
-Packing your repository
------------------------
+You can also give git log a "range" of commits where the first is not
+necessarily an ancestor of the second; for example, if the tips of
+the branches "stable-release" and "master" diverged from a common
+commit some time ago, then
-Earlier, we saw that one file under `.git/objects/??/` directory
-is stored for each git object you create. This representation
-is efficient to create atomically and safely, but
-not so convenient 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.
-
-[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. Also `git
-count-objects` would tell you how many unpacked objects are in
-your repository and how much space they are consuming.
-
-[NOTE]
-`git pull` is slightly cumbersome for HTTP transport, as a
-packed repository may contain relatively few objects in a
-relatively large pack. If you expect many HTTP pulls from your
-public repository you might want to repack & prune often, or
-never.
-
-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
-repository 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 are usually stored
-unpacked in the destination, unless rsync transport is used.
-While this allows you to use different packing strategies on
-both ends, it also means you may need to repack both
-repositories every once in a while.
-
-
-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.
-+
-If other people are pulling from your repository over dumb
-transport protocols, you need to keep this repository 'dumb
-transport friendly'. After `git init-db`,
-`$GIT_DIR/hooks/post-update` copied from the standard templates
-would contain a call to `git-update-server-info` but the
-`post-update` hook itself is disabled by default -- enable it
-with `chmod +x post-update`.
-
-3. Push into the public repository from your primary
- repository.
-
-4. `git repack` the public repository. This establishes a big
- pack that contains the initial set of objects as the
- baseline, and possibly `git prune` if the transport
- used for pulling from your repository supports packed
- repositories.
-
-5. Keep working in your primary repository. Your changes
- include modifications of your own, patches you receive via
- e-mails, and merges resulting from pulling the "public"
- repositories of your "subsystem maintainers".
-+
-You can repack this private repository whenever you feel like.
-
-6. Push your changes to the public repository, and announce it
- to the public.
-
-7. Every once in a while, "git repack" the public repository.
- Go back to step 5. and continue working.
-
-
-A recommended work cycle for a "subsystem maintainer" who works
-on that project and has an own "public repository" goes like this:
-
-1. Prepare your work repository, by `git clone` the public
- repository of the "project lead". The URL used for the
- initial cloning is stored in `.git/remotes/origin`.
-
-2. Prepare a public repository accessible to others, just like
- the "project lead" person does.
+-------------------------------------
+$ git log stable..experimental
+-------------------------------------
-3. Copy over the packed files from "project lead" public
- repository to your public repository.
-
-4. Push into the public repository from your primary
- repository. Run `git repack`, and possibly `git prune` 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.
+will list commits made in the experimental branch but not in the
+stable branch, while
-7. Every once in a while, `git repack` the public repository.
- Go back to step 5. and continue working.
+-------------------------------------
+$ git log experimental..stable
+-------------------------------------
+will show the list of commits made on the stable branch but not
+the experimental branch.
-A recommended work cycle for an "individual developer" who does
-not have a "public" repository is somewhat different. It goes
-like this:
+The "git log" command has a weakness: it must present commits in a
+list. When the history has lines of development that diverged and
+then merged back together, the order in which "git log" presents
+those commits is meaningless.
-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/remotes/origin`.
+Most projects with multiple contributors (such as the linux kernel,
+or git itself) have frequent merges, and gitk does a better job of
+visualizing their history. For example,
-2. Do your work in your repository on 'master' branch.
+-------------------------------------
+$ gitk --since="2 weeks ago" drivers/
+-------------------------------------
-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`.
+allows you to browse any commits from the last 2 weeks of commits
+that modified files under the "drivers" directory. (Note: you can
+adjust gitk's fonts by holding down the control key while pressing
+"-" or "+".)
-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.
+Finally, most commands that take filenames will optionally allow you
+to precede any filename by a commit, to specify a particular version
+of the file:
-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.
+-------------------------------------
+$ git diff v2.5:Makefile HEAD:Makefile.in
+-------------------------------------
+
+You can also use "git cat-file -p" to see any such file:
+-------------------------------------
+$ git cat-file -p v2.5:Makefile
+-------------------------------------
-Working with Others, Shared Repository Style
---------------------------------------------
+Next Steps
+----------
+
+This tutorial should be enough to perform basic distributed revision
+control for your projects. However, to fully understand the depth
+and power of git you need to understand two simple ideas on which it
+is based:
-If you are coming from CVS background, the style of cooperation
-suggested in the previous section may be new to you. You do not
-have to worry. git supports "shared public repository" style of
-cooperation you are probably more familiar with as well.
+ * The object database is the rather elegant system used to
+ store the history of your project--files, directories, and
+ commits.
-For this, set up a public repository on a machine that is
-reachable via SSH by people with "commit privileges". Put the
-committers in the same user group and make the repository
-writable by that group.
+ * The index file is a cache of the state of a directory tree,
+ used to create commits, check out working directories, and
+ hold the various trees involved in a merge.
-You, as an individual committer, then:
+link:tutorial-2.html[Part two of this tutorial] explains the object
+database, the index file, and a few other odds and ends that you'll
+need to make the most of git.
-- First clone the shared repository to a local repository:
-------------------------------------------------
-$ git clone repo.shared.xz:/pub/scm/project.git/ my-project
-$ cd my-project
-$ hack away
-------------------------------------------------
+If you don't want to consider with that right away, a few other
+digressions that may be interesting at this point are:
-- Merge the work others might have done while you were hacking
- away:
-------------------------------------------------
-$ git pull origin
-$ test the merge result
-------------------------------------------------
-[NOTE]
-================================
-The first `git clone` would have placed the following in
-`my-project/.git/remotes/origin` file, and that's why this and
-the next step work.
-------------
-URL: repo.shared.xz:/pub/scm/project.git/ my-project
-Pull: master:origin
-------------
-================================
-
-- push your work as the new head of the shared
- repository.
-------------------------------------------------
-$ git push origin master
-------------------------------------------------
-If somebody else pushed into the same shared repository while
-you were working locally, `git push` in the last step would
-complain, telling you that the remote `master` head does not
-fast forward. You need to pull and merge those other changes
-back before you push your work when it happens.
+ * gitlink:git-format-patch[1], gitlink:git-am[1]: These convert
+ series of git commits into emailed patches, and vice versa,
+ useful for projects such as the linux kernel which rely heavily
+ on emailed patches.
+ * gitlink:git-bisect[1]: When there is a regression in your
+ project, one way to track down the bug is by searching through
+ the history to find the exact commit that's to blame. Git bisect
+ can help you perform a binary search for that commit. It is
+ smart enough to perform a close-to-optimal search even in the
+ case of complex non-linear history with lots of merged branches.
-Bundling your work together
----------------------------
+ * link:everyday.html[Everyday GIT with 20 Commands Or So]
-It is likely that you will be working on more than one thing at
-a time. It is easy to use those more-or-less independent tasks
-using branches with git.
-
-We have already seen how branches work in a previous example,
-with "fun and work" example using two branches. The idea is the
-same if there are more than two branches. Let's say you started
-out from "master" head, and have some new code in the "master"
-branch, and two independent fixes in the "commit-fix" and
-"diff-fix" branches:
-
-------------
-$ git show-branch
-! [commit-fix] Fix commit message normalization.
- ! [diff-fix] Fix rename detection.
- * [master] Release candidate #1
----
- + [diff-fix] Fix rename detection.
- + [diff-fix~1] Better common substring algorithm.
-+ [commit-fix] Fix commit message normalization.
- + [master] Release candidate #1
-+++ [diff-fix~2] Pretty-print messages.
-------------
-
-Both fixes are tested well, and at this point, you want to merge
-in both of them. You could merge in 'diff-fix' first and then
-'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'
-------------
-
-Which would result in:
-
-------------
-$ git show-branch
-! [commit-fix] Fix commit message normalization.
- ! [diff-fix] Fix rename detection.
- * [master] Merge fix in commit-fix
----
- + [master] Merge fix in commit-fix
-+ + [commit-fix] Fix commit message normalization.
- + [master~1] Merge fix in diff-fix
- ++ [diff-fix] Fix rename detection.
- ++ [diff-fix~1] Better common substring algorithm.
- + [master~2] Release candidate #1
-+++ [master~3] Pretty-print messages.
-------------
-
-However, there is no particular reason to merge in one branch
-first and the other next, when what you have are a set of truly
-independent changes (if the order mattered, then they are not
-independent by definition). You could instead merge those two
-branches into the current branch at once. First let's undo what
-we just did and start over. We would want to get the master
-branch before these two merges by resetting it to 'master~2':
-
-------------
-$ git reset --hard master~2
-------------
-
-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
-branch heads (this is known as 'making an Octopus'):
-
-------------
-$ git pull . commit-fix diff-fix
-$ git show-branch
-! [commit-fix] Fix commit message normalization.
- ! [diff-fix] Fix rename detection.
- * [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
----
- + [master] Octopus merge of branches 'diff-fix' and 'commit-fix'
-+ + [commit-fix] Fix commit message normalization.
- ++ [diff-fix] Fix rename detection.
- ++ [diff-fix~1] Better common substring algorithm.
- + [master~1] Release candidate #1
-+++ [master~2] Pretty-print messages.
-------------
-
-Note that you should not do Octopus because you can. An octopus
-is a valid thing to do and often makes it easier to view the
-commit history if you are pulling more than two independent
-changes at the same time. However, if you have merge conflicts
-with any of the branches you are merging in and need to hand
-resolve, that is an indication that the development happened in
-those branches were not independent after all, and you should
-merge two at a time, documenting how you resolved the conflicts,
-and the reason why you preferred changes made in one side over
-the other. Otherwise it would make the project history harder
-to follow, not easier.
-
-[ to be continued.. cvsimports ]
+ * link:cvs-migration.html[git for CVS users].