-- linux爱好者,业余时间热衷于分析linux内核源码 -- 目前主要研究云计算和虚拟化相关的技术,主要包括libvirt/qemu,openstack,opennebula架构和源码分析。 -- 第五届云计算大会演讲嘉宾 微博:@Marshal-Liu
分类: LINUX
2009-10-31 09:49:01
If you are just after tracking someone else's project, this get you started quickly:
git clone url git pull |
svn checkout url svn update |
In those small tables, at the left we always list the Git commands for the task, while at the right the corresponding Subversion commands you would use for the job are listed. If you are in hurry, just skimming over them should give you a good idea about the Git usage basics.
Before running any command the first time, it's recommended that you
at least quickly skim through its manual page. Many of the commands have
very useful and interesting features (that we won't list here) and sometimes
there are some extra notes you might want to know. There's a quick usage
help available for the Git commands if you pass them the -h
switch.
There are couple important concepts it is good to know when starting with Git. If you are in hurry though, you can skip this section and only get back to it when you get seriously confused; it should be possible to pick up with just using your intuition.
.git
subdirectory in the project tree root).
So you can have local and remote branches.
You can also have a so-called bare repository which is not
attached to a working copy; that is useful especially when you want
to publish your repository. We will get to that.
trunk/
,
branches/
and tags/
directories. In Git
the URL is just the location of the repository, and it always
contains branches and tags. One of the branches is the default (normally named
master).
HEAD
,
its parent as HEAD^
and its parent as HEAD^^ = HEAD~2
(you can go on adding carrets),
cut'n'paste helps a lot and you can write only the few leading digits
of a revision - as long as it is unique, Git will guess the rest.
(You can do even more advanced stuff with revision specifiers, see the
for details.)
git config -l
and set them with:
git config --global user.name "Your Name Comes Here"
git config --global user.email you@yourdomain.example.com
git command
.
You can interchangeably use the git-command
form as well.
git config --global color.diff auto
git config --global color.status auto
git config --global color.branch auto
gitk
repository as you go.
For the first introduction, let's make your project tracked by Git
and see how we get around to do daily development in it. Let's
cd
to the directory with your project and initialize
a brand new Git repository with it:
git init git add . git commit |
svnadmin create repo svn import file://repo |
git init
will initialize the repository,
git add .
will add all the files under the current directory
and git commit
will create the
initial import, given that repositories are coupled with working copies.
Now your tree is officially tracked by Git. You can explore the
.git
subdirectory a bit if you want, or don't if you
don't care. Do some random changes to your tree now - poke into few
files or such. Let's check what we've done:
git diff | svn diff | less |
That's it. This is one of the more powerful commands. To get a diff with an specific revision and path do:
git diff rev path | svn diff -rrev path |
Git embeds special information in the diffs about adds, removals and mode changes:
git apply | patch -p0 |
That will apply the patch while telling Git about and performing those "meta-changes".
There is a more concise representation of changes available:
git status | svn status |
This will show the concise changes summary as well as list any files that you haven't either ignored or told Git about. In addition, it will also show at the top which branch you are in.
While we are at the status command, over time plenty of the
"Untracked files" will get in there, denoting files not tracked by Git.
Wait a moment if you want to add them, run git clean
if you want to get rid of all of them, or add them to the .gitignore
file if you want to keep them around untracked (works the same as the svn:ignore
property in SVN).
To restore a file from the last revision:
git checkout path | svn revert path |
You can restore everything or just specified files.
So, just like in SVN, you need to tell Git when you add, move or remove any files:
git add file
git rm file git mv file |
svn add file svn rm file svn mv file |
You can also recursively add/remove whole directories and so on; Git's cool!
So, it's about time we commit our changes. Big surprise about the command:
git commit -a | svn commit |
to commit all the changes or, as with Subversion,
you can limit the commit only to specified files
and so on. A few words on the commit message: it is customary
to have a short commit summary as the first line of the message,
because various tools listing commits frequently show only the
first line of the message. You can specify the commit message
using the -m
parameter as you are used, but
you can pass several -m
arguments and they will create
separate paragraphs in the commit message:
If you don't pass any -m
parameter or pass
the -e
parameter, your favorite $EDITOR
will get run and you can compose your commit message there,
just as with Subversion. In addition, the list of files to be committed
is shown.
And as a bonus, if you pass it the -v
parameter
it will show the whole patch being committed in the editor
so that you can do a quick last-time review.
By the way, if you screwed up committing, there's not much you
can do with Subversion, except using some enigmatic svnadmin
subcommands. Git does it better - you can amend your latest commit
(re-edit the metadata as well as update the tree) using
git commit --amend
, or toss your latest
commit away completely using git reset HEAD^
,
this will not change the working tree.
Now that we have committed some stuff, you might want to review your history:
git log git blame file |
svn log | less svn blame file |
The log command works quite similar in SVN and Git; again,
git log
is quite powerful, please look through
its options to see some of the stuff it can do.
The blame command is more powerful as it can detect the movement of lines,
even with file copies and renames. But there is a
big chance that you probably want to do something different! Usually,
when using annotate you are looking for the origin of some piece of
code, and the so-called pickaxe of Git is much more comfortable
tool for that job (git log -Sstring
shows the
commits which add or remove any file data matching string).
You can see the contents of a file, the listing of a directory or a commit with:
git show rev:path/to/file
git show rev:path/to/directory git show rev |
svn cat url
svn list url svn log -rrev url svn diff -crev url |
Subversion marks certain checkpoints in history through copies, the copy is usually placed in a directory named tags. Git tags are much more powerful. The Git tag can have an arbitrary description attached (the first line is special as in the commit case), some people actually store the whole release announcements in the tag descriptions. The identity of the person who tagged is stored (again following the same rules as identity of the committer). You can tag other objects than commits (but that is conceptually rather low-level operation). And the tag can be cryptographically PGP signed to verify the identity (by Git's nature of working, that signature also confirms the validity of the associated revision, its history and tree). So, let's do it:
git tag -a name | svn copy name |
To list tags and to show the tag message:
git tag -l git show tag |
svn list tags/
svn log --limit 1 tag |
Like Subversion, Git can do branches (surprise surprise!). In Subversion, you basically copy your project to a subdirectory. In Git, you tell it, well, to create a branch.
git branch branch
git checkout branch |
svn copy
branches/branch
svn switch branches/branch |
The first command creates a branch, the second command switches
your tree to a certain branch. You can pass an extra argument to
git branch
to base your new branch on a different
revision than the latest one.
You can list your branches conveniently using the aforementioned
git-branch
command without arguments the listing of branches.
The current one is denoted by an "*".
git branch | svn list branches/ |
To move your tree to some older revision, use:
git checkout rev
git checkout prevbranch |
svn update -r rev svn update |
or you could create a temporary branch. In Git you can make commits on top of the older revision and use it as another branch.
Git supports merging between branches much better than Subversion - history of both branches is preserved over the merges and repeated merges of the same branches are supported out-of-the-box. Make sure you are on one of the to-be-merged branches and merge the other one now:
git merge branch |
svn merge -r 20:HEAD
branches/branch
(assuming the branch was created in revision 20 and you are inside a working copy of trunk) |
If changes were made on only one of the branches since the last merge,
they are simply replayed on your other branch (so-called fast-forward merge).
If changes were made on both branches, they are merged intelligently
(so-called three-way merge): if any changes conflicted, git merge
will report them and let you resolve them, updating the rest of the tree
already to the result state; you can git commit
when you resolve
the conflicts. If no changes conflicted, a commit is made automatically with
a convenient log message (or you can do
git merge --no-commit branch
to review the merge
result and then do the commit yourself).
Aside from merging, sometimes you want to just pick one commit from a different branch. To apply the changes in revision rev and commit them to the current branch use:
git cherry-pick rev | svn merge -c rev url |
So far, we have neglected that Git is a distributed version control system. It is time for us to set the record straight - let's grab some stuff from remote sites.
If you are working on someone else's project, you usually want to clone its repository instead of starting your own. We've already mentioned that at the top of this document:
git clone url | svn checkout url |
Now you have the default branch (normally master
),
but in addition you got all the remote branches and tags.
In clone's default setup, the default local branch tracks
the origin remote, which represents the default branch in the
remote repository.
Remote branch, you ask? Well, so far we have worked only with local branches. Remote branches are a mirror image of branches in remote repositories and you don't ever switch to them directly or write to them. Let me repeat - you never mess with remote branches. If you want to switch to a remote branch, you need to create a corresponding local branch which will "track" the remote branch:
git checkout -b branch origin/branch | svn switch url |
You can add more remote branches to a cloned repository, as well as just
an initialized one, using git remote add remote url
.
The command git remote
lists all the remotes
repositories and git remote show remote
shows
the branches in a remote repository.
Now, how do you get any new changes from a remote repository?
You fetch them: git fetch
.
At this point they are in your repository and you can examine them using
git log origin
(git log HEAD..origin
to see just the changes you don't have in your branch), diff them, and obviously, merge them - just do
git merge origin
. Note that if you don't specify a branch
to fetch, it will conveniently default to the tracking remote.
Since you frequently just fetch + merge the tracking remote branch, there is a command to automate that:
git pull | svn update |
Your local repository can be used by others to pull changes, but
normally you would have a private repository and a public repository.
The public repository is where everybody pulls and you... do the
opposite? Push your changes? Yes!
We do git push remote
which will push
all the local branches with a corresponding remote branch - note that this works
generally only over SSH (or HTTP but with special webserver setup).
It is highly recommended to setup a SSH key and an SSH agent mechanism
so that you don't have to type in a password all the time.
One important thing is that you should push only to remote branches that are not currently checked out on the other side (for the same reasons you never switch to a remote branch locally)! Otherwise the working copy at the remote branch will get out of date and confusion will ensue. The best way to avoid that is to push only to remote repositories with no working copy at all - so called bare repositories which are commonly used for public access or developers' meeting point - just for exchange of history where a checked out copy would be a waste of space anyway. You can create such a repository. See for details.
Git can work with the same workflow as Subversion, with a group of developers
using a single repository for exchange of their work. The only change
is that their changes aren't submitted automatically but they have
to push (however, you can setup a post-commit hook that will push for you
every time you commit; that loses the flexibility to fix up a screwed
commit, though). The developers must have either an entry in htaccess
(for HTTP DAV) or a UNIX account (for SSH). You can restrict their
shell account only to Git pushing/fetching by using the
git-shell
login shell.
You can also exchange patches by mail. Git has very good support
for patches incoming by mail. You can apply them by feeding mailboxes
with patch mails to git am
. If you
want to send patches use git format-patch
and
possibly git send-email
.
To maintain a set of patches it is best to use
the StGIT tool (see
the ).
If you have any questions or problems which are not obvious from the documentation, please contact us at the Git mailing list at . We hope you enjoy using Git!