You can not select more than 25 topics
Topics must start with a letter or number, can include dashes ('-') and can be up to 35 characters long.
487 lines
16 KiB
487 lines
16 KiB
A tutorial introduction to git |
|
============================== |
|
|
|
This tutorial explains how to import a new project into git, make |
|
changes to it, and share changes with other developers. |
|
|
|
First, note that you can get documentation for a command such as "git |
|
diff" with: |
|
|
|
------------------------------------------------ |
|
$ man git-diff |
|
------------------------------------------------ |
|
|
|
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-db |
|
------------------------------------------------ |
|
|
|
Git will reply |
|
|
|
------------------------------------------------ |
|
defaulting to local storage area |
|
------------------------------------------------ |
|
|
|
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 |
|
|
|
------------------------------------------------ |
|
$ git add . |
|
------------------------------------------------ |
|
|
|
Finally, |
|
|
|
------------------------------------------------ |
|
$ git commit -a |
|
------------------------------------------------ |
|
|
|
will prompt you for a commit message, then record the current state |
|
of all the files to the repository. |
|
|
|
Try modifying some files, then run |
|
|
|
------------------------------------------------ |
|
$ git diff |
|
------------------------------------------------ |
|
|
|
to review your changes. When you're done, |
|
|
|
------------------------------------------------ |
|
$ git commit -a |
|
------------------------------------------------ |
|
|
|
will again prompt your for a message describing the change, and then |
|
record the new versions of the modified files. |
|
|
|
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. |
|
|
|
To add a new file, first create the file, then |
|
|
|
------------------------------------------------ |
|
$ git add path/to/new/file |
|
------------------------------------------------ |
|
|
|
then commit as usual. No special command is required when removing a |
|
file; just remove it, then commit. |
|
|
|
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 |
|
------------------------------------------------ |
|
|
|
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 the two branches, run |
|
|
|
------------------------------------------------ |
|
$ git pull . 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. |
|
|
|
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 |
|
------------------------------------------------ |
|
|
|
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 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. |
|
|
|
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 fetch /home/bob/myrepo master:bob-incoming |
|
------------------------------------- |
|
|
|
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 |
|
|
|
------------------------------------- |
|
$ git log -p master..bob-incoming |
|
------------------------------------- |
|
|
|
shows a list of all the changes that Bob made since he branched from |
|
Alice's master branch. |
|
|
|
After examining those changes, and possibly fixing things, Alice can |
|
pull the changes into her master branch: |
|
|
|
------------------------------------- |
|
$ git checkout master |
|
$ git pull . bob-incoming |
|
------------------------------------- |
|
|
|
The last command is a pull from the "bob-incoming" branch in Alice's |
|
own repository. |
|
|
|
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 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: |
|
|
|
------------------------------------- |
|
$ git branch |
|
* master |
|
origin |
|
------------------------------------- |
|
|
|
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. |
|
|
|
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 gitlink: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 gitlink: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 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 has at least 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 |
|
gitlink: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 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.) |
|
|
|
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 cat-file -p" to see any such file: |
|
|
|
------------------------------------- |
|
$ git cat-file -p 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 consider 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, |
|
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. |
|
|
|
* link:everyday.html[Everyday GIT with 20 Commands Or So] |
|
|
|
* link:cvs-migration.html[git for CVS users].
|
|
|