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diff --git a/Documentation/tutorial.txt b/Documentation/tutorial.txt new file mode 100644 index 0000000000..e2bbda53f0 --- /dev/null +++ b/Documentation/tutorial.txt @@ -0,0 +1,584 @@ +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 +----------------------- + +Assume you have a tarball project.tar.gz with your initial work. You +can place it under git revision control as follows. + +------------------------------------------------ +$ tar xzf project.tar.gz +$ cd project +$ git init +------------------------------------------------ + +Git will reply + +------------------------------------------------ +Initialized empty Git repository in .git/ +------------------------------------------------ + +You've now initialized the working directory--you may notice a new +directory created, named ".git". + +Next, tell git to take a snapshot of the contents of all files under the +current directory (note the '.'), with linkgit:git-add[1]: + +------------------------------------------------ +$ git add . +------------------------------------------------ + +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 linkgit:git-commit[1]: + +------------------------------------------------ +$ git commit +------------------------------------------------ + +This will prompt you for a commit message. You've now stored the first +version of your project in git. + +Making changes +-------------- + +Modify some files, then add their updated contents to the index: + +------------------------------------------------ +$ git add file1 file2 file3 +------------------------------------------------ + +You are now ready to commit. You can see what is about to be committed +using linkgit:git-diff[1] with the --cached option: + +------------------------------------------------ +$ git diff --cached +------------------------------------------------ + +(Without --cached, linkgit: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 linkgit: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. + +Alternatively, instead of running `git add` beforehand, you can use + +------------------------------------------------ +$ git commit -a +------------------------------------------------ + +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 +commit in the body. + +Git tracks content not files +---------------------------- + +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. + +Viewing project history +----------------------- + +At any point you can view the history of your changes using + +------------------------------------------------ +$ git log +------------------------------------------------ + +If you also want to see complete diffs at each step, use + +------------------------------------------------ +$ git log -p +------------------------------------------------ + +Often the overview of the change is useful to get a feel of +each step + +------------------------------------------------ +$ git log --stat --summary +------------------------------------------------ + +Managing branches +----------------- + +A single git repository can maintain multiple branches of +development. To create a new branch named "experimental", use + +------------------------------------------------ +$ git branch experimental +------------------------------------------------ + +If you now run + +------------------------------------------------ +$ git branch +------------------------------------------------ + +you'll get a list of all existing branches: + +------------------------------------------------ + experimental +* master +------------------------------------------------ + +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 + +------------------------------------------------ +$ git checkout experimental +------------------------------------------------ + +to switch to the experimental branch. Now edit a file, commit the +change, and switch back to the master branch: + +------------------------------------------------ +(edit file) +$ git commit -a +$ git checkout master +------------------------------------------------ + +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. + +You can make a different change on the master branch: + +------------------------------------------------ +(edit file) +$ git commit -a +------------------------------------------------ + +at this point the two branches have diverged, with different changes +made in each. To merge the changes made in experimental into master, run + +------------------------------------------------ +$ git merge experimental +------------------------------------------------ + +If the changes don't conflict, you're done. If there are conflicts, +markers will be left in the problematic files showing the conflict; + +------------------------------------------------ +$ git diff +------------------------------------------------ + +will show this. Once you've edited the files to resolve the +conflicts, + +------------------------------------------------ +$ git commit -a +------------------------------------------------ + +will commit the result of the merge. Finally, + +------------------------------------------------ +$ gitk +------------------------------------------------ + +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 + +------------------------------------- +$ git branch -D crazy-idea +------------------------------------- + +Branches are cheap and easy, so this is a good way to try something +out. + +Using git for collaboration +--------------------------- + +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. + +Bob begins with: + +------------------------------------------------ +$ git clone /home/alice/project myrepo +------------------------------------------------ + +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. + +Bob then makes some changes and commits them: + +------------------------------------------------ +(edit files) +$ git commit -a +(repeat as necessary) +------------------------------------------------ + +When he's ready, he tells Alice to pull changes from the repository +at /home/bob/myrepo. She does this with: + +------------------------------------------------ +$ cd /home/alice/project +$ git pull /home/bob/myrepo master +------------------------------------------------ + +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. + +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: + +------------------------------------------------ +$ git remote add bob /home/bob/myrepo +------------------------------------------------ + +With this, Alice can perform the first operation alone using the +"git fetch" command without merging them with her own branch, +using: + +------------------------------------- +$ git fetch bob +------------------------------------- + +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/master +------------------------------------- + +shows a list of all the changes that Bob made since he branched from +Alice's master branch. + +After examining those changes, Alice +could merge the changes into her master branch: + +------------------------------------- +$ git merge bob/master +------------------------------------- + +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 command line. + +Later, Bob can update his repo with Alice's latest changes using + +------------------------------------- +$ git pull +------------------------------------- + +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 repository configuration, and that location is +used for pulls: + +------------------------------------- +$ git config --get remote.origin.url +/home/alice/project +------------------------------------- + +(The complete configuration created by git-clone is visible using +"git config -l", and the linkgit: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 clone alice.org:/home/alice/project myrepo +------------------------------------- + +Alternatively, git has a native protocol, or can use rsync or http; +see linkgit:git-pull[1] for details. + +Git can also be used in a CVS-like mode, with a central repository +that various users push changes to; see linkgit:git-push[1] and +link:cvs-migration.html[git for CVS users]. + +Exploring history +----------------- + +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: + +------------------------------------- +$ 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. +------------------------------------- + +We can give this name to git show to see the details about this +commit. + +------------------------------------- +$ git show c82a22c39cbc32576f64f5c6b3f24b99ea8149c7 +------------------------------------- + +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 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 usually has one "parent" commit +which points to the previous state of the project: + +------------------------------------- +$ 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: + +------------------------------------- +$ 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 +------------------------------------- + +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 +linkgit:git-tag[1] for details. + +Any git command that needs to know a commit can take any of these +names. For example: + +------------------------------------- +$ 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^ +------------------------------------- + +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 it will +force needless merges on other developers to clean up the history. +If you need to undo changes that you have pushed, use linkgit: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 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 + +------------------------------------- +$ git grep "hello" +------------------------------------- + +is a quick way to search just the files that are tracked by git. + +Many git commands also take sets of commits, which can be specified +in a number of ways. Here are some examples with git log: + +------------------------------------- +$ 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 +------------------------------------- + +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 + +------------------------------------- +$ git log stable..experimental +------------------------------------- + +will list commits made in the experimental branch but not in the +stable branch, while + +------------------------------------- +$ git log experimental..stable +------------------------------------- + +will show the list of commits made on the stable branch but not +the experimental branch. + +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. + +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, + +------------------------------------- +$ gitk --since="2 weeks ago" drivers/ +------------------------------------- + +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 "+".) + +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: + +------------------------------------- +$ 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 +---------- + +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: + + * linkgit:git-format-patch[1], linkgit: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. + + * linkgit: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. + + * link:everyday.html[Everyday GIT with 20 Commands Or So] + + * link:cvs-migration.html[git for CVS users]. |