-A tutorial introduction to git
-==============================
+A tutorial introduction to git (for version 1.5.1 or newer)
+===========================================================
This tutorial explains how to import a new project into git, make
changes to it, and share changes with other developers.
+If you are instead primarily interested in using git to fetch a project,
+for example, to test the latest version, you may prefer to start with
+the first two chapters of link:user-manual.html[The Git User's Manual].
+
First, note that you can get documentation for a command such as "git
diff" with:
$ man git-diff
------------------------------------------------
+It is a good idea to introduce yourself to git with your name and
+public email address before doing any operation. The easiest
+way to do so is:
+
+------------------------------------------------
+$ git config --global user.name "Your Name Comes Here"
+$ git config --global user.email you@yourdomain.example.com
+------------------------------------------------
+
+
Importing a new project
-----------------------
------------------------------------------------
$ tar xzf project.tar.gz
$ cd project
-$ git init-db
+$ git init
------------------------------------------------
Git will reply
------------------------------------------------
-defaulting to local storage area
+Initialized empty Git repository in .git/
------------------------------------------------
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
+directory created, named ".git".
+
+Next, tell git to take a snapshot of the contents of all files under the
+current directory (note the '.'), with gitlink:git-add[1]:
------------------------------------------------
$ git add .
------------------------------------------------
-Finally,
+This snapshot is now stored in a temporary staging area which git calls
+the "index". You can permanently store the contents of the index in the
+repository with gitlink:git-commit[1]:
------------------------------------------------
-$ git commit -a
+$ git commit
------------------------------------------------
-will prompt you for a commit message, then record the current state
-of all the files to the repository.
+This will prompt you for a commit message. You've now stored the first
+version of your project in git.
-Try modifying some files, then run
+Making changes
+--------------
+
+Modify some files, then add their updated contents to the index:
------------------------------------------------
-$ git diff
+$ git add file1 file2 file3
+------------------------------------------------
+
+You are now ready to commit. You can see what is about to be committed
+using gitlink:git-diff[1] with the --cached option:
+
+------------------------------------------------
+$ git diff --cached
+------------------------------------------------
+
+(Without --cached, gitlink:git-diff[1] will show you any changes that
+you've made but not yet added to the index.) You can also get a brief
+summary of the situation with gitlink:git-status[1]:
+
+------------------------------------------------
+$ git status
+# On branch master
+# Changes to be committed:
+# (use "git reset HEAD <file>..." to unstage)
+#
+# modified: file1
+# modified: file2
+# modified: file3
+#
+------------------------------------------------
+
+If you need to make any further adjustments, do so now, and then add any
+newly modified content to the index. Finally, commit your changes with:
+
------------------------------------------------
+$ git commit
+------------------------------------------------
+
+This will again prompt your for a message describing the change, and then
+record a new version of the project.
-to review your changes. When you're done,
+Alternatively, instead of running `git add` beforehand, you can use
------------------------------------------------
$ git commit -a
------------------------------------------------
-will again prompt your for a message describing the change, and then
-record the new versions of the modified files.
+which will automatically notice any modified (but not new) files, add
+them to the index, and commit, all in one step.
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
+example, use the first line on the Subject: line and the rest of the
commit in the body.
-To add a new file, first create the file, then
+Git tracks content not files
+----------------------------
-------------------------------------------------
-$ git add path/to/new/file
-------------------------------------------------
+Many revision control systems provide an "add" command that tells the
+system to start tracking changes to a new file. Git's "add" command
+does something simpler and more powerful: `git add` is used both for new
+and newly modified files, and in both cases it takes a snapshot of the
+given files and stages that content in the index, ready for inclusion in
+the next commit.
-then commit as usual. No special command is required when removing a
-file; just remove it, then commit.
+Viewing project history
+-----------------------
At any point you can view the history of your changes using
$ git log -p
------------------------------------------------
+Often the overview of the change is useful to get a feel of
+each step
+
+------------------------------------------------
+$ git log --stat --summary
+------------------------------------------------
+
Managing branches
-----------------
------------------------------------------------
at this point the two branches have diverged, with different changes
-made in each. To merge the changes made in the two branches, run
+made in each. To merge the changes made in experimental into master, run
------------------------------------------------
-$ git pull . experimental
+$ git merge experimental
------------------------------------------------
If the changes don't conflict, you're done. If there are conflicts,
will show a nice graphical representation of the resulting history.
+At this point you could delete the experimental branch with
+
+------------------------------------------------
+$ git branch -d experimental
+------------------------------------------------
+
+This command ensures that the changes in the experimental branch are
+already in the current branch.
+
If you develop on a branch crazy-idea, then regret it, you can always
delete the branch with
This creates a new directory "myrepo" containing a clone of Alice's
repository. The clone is on an equal footing with the original
-project, posessing its own copy of the original project's history.
+project, possessing its own copy of the original project's history.
Bob then makes some changes and commits them:
------------------------------------------------
$ cd /home/alice/project
-$ git pull /home/bob/myrepo
+$ git pull /home/bob/myrepo master
------------------------------------------------
-This actually pulls changes from the branch in Bob's repository named
-"master". Alice could request a different branch by adding the name
-of the branch to the end of the git pull command line.
+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.)
+
+The "pull" command thus performs two operations: it fetches changes
+from a remote branch, then merges them into the current branch.
-This merges Bob's changes into her repository; "git log" will
-now show the new commits. If Alice has made her own changes in the
-meantime, then Bob's changes will be merged in, and she will need to
-manually fix any conflicts.
+When you are working in a small closely knit group, it is not
+unusual to interact with the same repository over and over
+again. By defining 'remote' repository shorthand, you can make
+it easier:
-A more cautious Alice might wish to examine Bob's changes before
-pulling them. She can do this by creating a temporary branch just
-for the purpose of studying Bob's changes:
+------------------------------------------------
+$ git remote add bob /home/bob/myrepo
+------------------------------------------------
+
+With this, you can perform the first operation alone using the
+"git fetch" command without merging them with her own branch,
+using:
-------------------------------------
-$ git fetch /home/bob/myrepo master:bob-incoming
+$ git fetch bob
-------------------------------------
-which fetches the changes from Bob's master branch into a new branch
-named bob-incoming. (Unlike git pull, git fetch just fetches a copy
-of Bob's line of development without doing any merging). Then
+Unlike the longhand form, when Alice fetches from Bob using a
+remote repository shorthand set up with `git remote`, what was
+fetched is stored in a remote tracking branch, in this case
+`bob/master`. So after this:
-------------------------------------
-$ git log -p master..bob-incoming
+$ git log -p master..bob/master
-------------------------------------
shows a list of all the changes that Bob made since he branched from
Alice's master branch.
-After examing those changes, and possibly fixing things, Alice can
-pull the changes into her master branch:
+After examining those changes, Alice
+could merge the changes into her master branch:
-------------------------------------
-$ git checkout master
-$ git pull . bob-incoming
+$ git merge bob/master
-------------------------------------
-The last command is a pull from the "bob-incoming" branch in Alice's
-own repository.
+This `merge` can also be done by 'pulling from her own remote
+tracking branch', like this:
+
+-------------------------------------
+$ git pull . remotes/bob/master
+-------------------------------------
+
+Note that git pull always merges into the current branch,
+regardless of what else is given on the commandline.
Later, Bob can update his repo with Alice's latest changes using
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.
-
-Bob may also notice a branch in his repository that he didn't create:
+repository in the repository configuration, and that location is
+used for pulls:
-------------------------------------
-$ git branch
-* master
- origin
+$ git config --get remote.origin.url
+/home/bob/myrepo
-------------------------------------
-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.
+(The complete configuration created by git-clone is visible using
+"git config -l", and the gitlink:git-config[1] man page
+explains the meaning of each option.)
+
+Git also keeps a pristine copy of Alice's master branch under the
+name "origin/master":
+
+-------------------------------------
+$ git branch -r
+ origin/master
+-------------------------------------
If Bob later decides to work from a different host, he can still
perform clones and pulls using the ssh protocol:
$ git show c82a22c39cbc32576f64f5c6b3f24b99ea8149c7
-------------------------------------
-But there other ways to refer to commits. You can use any initial
+But there are other ways to refer to commits. You can use any initial
part of the name that is long enough to uniquely identify the commit:
-------------------------------------
$ 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:
+Every commit usually has one "parent" commit
+which points to the previous state of the project:
-------------------------------------
$ git show HEAD^ # to see the parent of HEAD
$ 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 its state at HEAD^
+ # directory to its state at HEAD^
-------------------------------------
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.)
+commits, they will be lost. Also, don't use "git reset" on a
+publicly-visible branch that other developers pull from, as it will
+force needless merges on other developers to clean up the history.
+If you need to undo changes that you have pushed, use gitlink:git-revert[1]
+instead.
The git grep command can search for strings in any version of your
project, so
$ git grep "hello" v2.5
-------------------------------------
-searches for all occurences of "hello" in v2.5.
+searches for all occurrences of "hello" in v2.5.
If you leave out the commit name, git grep will search any of the
files it manages in your current directory. So
-------------------------------------
allows you to browse any commits from the last 2 weeks of commits
-that modified files under the "drivers" directory.
+that modified files under the "drivers" directory. (Note: you can
+adjust gitk's fonts by holding down the control key while pressing
+"-" or "+".)
Finally, most commands that take filenames will optionally allow you
to precede any filename by a commit, to specify a particular version
-fo the file:
+of the file:
-------------------------------------
$ git diff v2.5:Makefile HEAD:Makefile.in
-------------------------------------
+You can also use "git show" to see any such file:
+
+-------------------------------------
+$ git show v2.5:Makefile
+-------------------------------------
+
Next Steps
----------
-Some good commands to explore next:
+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:
+
+ * The object database is the rather elegant system used to
+ store the history of your project--files, directories, and
+ commits.
+
+ * 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.
+
+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.
+
+If you don't want to continue with that right away, a few other
+digressions that may be interesting at this point are:
* gitlink:git-format-patch[1], gitlink:git-am[1]: These convert
series of git commits into emailed patches, and vice versa,
smart enough to perform a close-to-optimal search even in the
case of complex non-linear history with lots of merged branches.
-Other good starting points include link:everyday.html[Everday GIT
-with 20 Commands Or So] and link:cvs-migration.html[git for CVS
-users]. Also, link:core-tutorial.html[A short git tutorial] gives an
-introduction to lower-level git commands for advanced users and
-developers.
+ * link:everyday.html[Everyday GIT with 20 Commands Or So]
+
+ * link:cvs-migration.html[git for CVS users].